WATER INTAKE INSTALLATION FOR COOLING A NUCLEAR POWER
PLANT, AND NUCLEAR POWER PLANT COMPRISING
SUCH AN INSTALLATION
The invention relates to a water intake installation for at least one heat
exchanger-based cooling circuit, comprising a suction basin supplied with water and
from which at least one pumping station of the plant draws water in order to circulate it
within one said cooling circuit, and further comprising at least one suction tunnel
connected to at least one main water intake submerged in a body of water such as a sea5 ,
lake, or river, said suction tunnel supplying the suction basin with water so as to maintain
a water level in the suction basin that is sufficient for the operation of the pumping
station.
The heat exchanger-based cooling circuit is typically designed to cool the
10 steam exiting a turbine-generator in a secondary circuit of a reactor of the nuclear plant,
in order to condense this steam so that water returned to the liquid state is fed back to the
steam generators of the secondary circuit. The steam generators draw heat from a
pressurized primary circuit to cool the reactor, by heat exchange between the primary
circuit and the secondary circuit. The primary and secondary circuits are closed systems
15 fluid-wise, while the heat exchanger-based cooling circuit is open and completely
isolated from the secondary circuit which in turn is completely isolated from the primary
circuit. The water exiting a heat exchanger is therefore not radioactive, and can be
drained away for example to be returned to the body of water supplying the circuit.
A water intake installation as defined above is known, particularly the
20 Seabrook nuclear power plant, constructed near the coastline in southern New Hampshire
(USA) and commissioned in 1990. The installation comprises a single suction tunnel
several kilometers long, connected to three vertical suction shafts. Each suction shaft
opens just above the seabed about fifteen meters below the average water level, and
comprises an upper portion forming one of said submerged water intakes.
25 Also known, from Japanese patent application no. JP60111089A published on
17 June 1985, is a water intake installation comprising a suction basin supplied with
water by an underground suction tunnel, the tunnel being connected to a water intake
submerged at a relatively shallow depth in the sea. The water intake could be left exposed
before a tsunami wave.
2
These water intake installations are not designed to handle the admittedly
unlikely situation of a critical collapse in the suction tunnel, which would result in almost
complete obstruction of the tunnel, the consequence being the almost complete
interruption in the supply of water to the suction basin and the risk of insufficient water
supplied to the backup pumps of the plant's pumping station. The backup pumps a5 re
typically auxiliary pumps to supplement the pumps of a pumping station that are used
during electricity production ("production pumps"), and are provided to supply a reduced
flow to the heat-exchanger based cooling circuit when the production pumps are shut
down. These backup pumps are intended for cooling the nuclear reactor or reactors when
10 they are shut down for a long or extended period.
Even if there are two suction tunnels, one cannot ignore the possibility of a
critical collapse in both suction tunnels almost completely cutting off the supply of water
to the suction basin and therefore to the pumping station, particularly in areas of
relatively high seismic risk. Furthermore, supplying water to the suction basin by a tunnel
15 connected to a water intake submerged in the sea can have the advantage of significantly
lowering the maximum temperature of the water in the suction basin compared to the
maximum temperature of the water at the surface of the sea, this lower temperature being
related primarily to the depth at which the water intake is placed below the mean sea
level. The addition of a second suction tunnel to supplement a first suction tunnel, in
20 order to limit the risk of an interruption in the supply of water to the suction basin in case
of a critical collapse in the first tunnel, involves placing the new water intakes at least at
substantially the same depth as the first water intakes, to avoid significantly heating the
water in the suction basin.
Warming the water in the suction basin does indeed result in a decrease in the
25 efficiency η of a secondary circuit of the plant. The efficiency depends on the
temperature Tf of the cold source, meaning the temperature of the water at the inlet to the
heat exchangers, and is defined as follows:
η = (Tc – Tf)/Tc
Tc being the temperature of the heat source, meaning the temperature of the water exiting
30 the heat exchangers. The efficiency η therefore increases as the temperature Tf of the
cold source decreases.
Depending on the underwater topology, the necessary length of a suction
tunnel generally increases with the depth at which the water intakes are arranged. In
3
addition, besides the cost of constructing an additional tunnel, the risk of a critical
collapse in the tunnel also generally increases with the tunnel length, especially in areas
at risk for major seismic events. The solution of an additional suction tunnel to provide a
more secure supply of water to the suction basin is therefore not entirely satisfactory,
either because of the lower efficiency of the plant's secondary circuits when 5 n the
additional water intakes are not as deep, or in terms of cost and/or safety when the
additional water intakes are deeper.
The present invention aims to provide a water intake installation in which,
when there is a critical collapse in the suction tunnel or tunnels supplying the suction
10 basin, water continues to be supplied to the suction basin for at least the backup pumps of
the plant's pumping station; this installation does not affect the efficiency of a secondary
circuit of the plant during normal operation of the plant, meaning when water is supplied
in the normal manner to the suction basin by the suction tunnel or tunnels.
To this end, the invention relates to a water intake installation as defined in
15 the preamble above, characterized in that it further comprises a system for supplying
additional water distinct from said at least one suction tunnel and capable of supplying
water to the suction basin from at least one emergency water reserve, said system for
supplying additional water comprising at least one water duct connecting the suction
basin to said emergency water reserve and an obstructing device closing off said water
20 duct, the obstructing device being able to open said water duct at least partially if the
water level in the suction basin drops in a manner defined beforehand as abnormal, so
that the suction basin is supplied with water by said system for supplying additional
water if the water supplied by said at least one suction tunnel becomes insufficient.
With these arrangements, the water of the suction basin generally does not
25 mix with the water from an emergency water reserve during normal plant operation, and
therefore the efficiency of a secondary circuit of the plant is not impacted by the presence
of an emergency water reserve. The use of an emergency water reserve is only triggered
if the water level in the suction basin drops in a manner defined beforehand as abnormal.
A drop in water level defined beforehand as abnormal generally corresponds to a critical
30 collapse in one or more suction tunnels, resulting in a lasting interruption or at least a
major decrease in the supply of water to the suction basin. Such a drop in water level may
also correspond to an exceptional drop in the body of water for a relatively short period,
as may occur for example along the coastline in areas prone to tsunamis. The invention
therefore also can be applied to water intake installations for nuclear power plants on the
4
coastline where on rare occasions the sea may drop below the level of the lowest tide, as
is sometimes the case before the first wave of a tsunami.
According to an advantageous embodiment of a water intake installation
according to the invention, said body of water constitutes one said emergency water
reserve. In this manner, the supplying of water to the suction basin by said system 5 stem for
supplying additional water can continue for an unlimited period and with no need for
pumping means to maintain the water level in the emergency water reserve.
In other preferred embodiments of a water intake installation according to the
invention, use is made of one or more of the following arrangements:
10 said body of water is a sea, and said system for supplying additional water is
arranged between the suction basin and a portion of a channel which communicates with
the sea;
said system for supplying additional water comprises a backup tunnel
connected to at least one backup water intake submerged in said body of water, said
15 backup water intake being placed at a height at least ten meters above one said main
water intake;
one said at least one emergency water reserve comprises a reserve basin
containing a volume of water which remains substantially unchanged when water is
being supplied normally to the suction basin by said at least one suction tunnel;
20 said at least one main water intake is placed at a certain depth relative to a
mean reference level of said body of water, said depth being determined such that the
water flowing into the suction basin has, during at least one period of the year, a
maximum temperature at least 4°C less than the maximum temperature of the water at the
surface of said body of water;
25 said obstructing device comprises an obstructing member able to pivot about a
pivot shaft in order to open said water duct;
said obstructing device is adapted so that the pivoting of said obstructing
member occurs autonomously according to a drop in the water level in the suction basin;
the pivoting of said obstructing member is actuated by a trigger device
30 connected to a control system able to generate a trigger command for the trigger device,
the control system being associated with an analysis system receiving data provided by a
device for measuring the water level in the suction basin, said analysis system being able
to determine whether the water level in the suction basin is dropping in a manner defined
beforehand as abnormal;
5
said trigger device is adapted to allow the pivoting of said obstructing member
to be performed autonomously by said obstructing device if the trigger device does not
perform its function:
said obstructing member pivots to open said water duct when a height
difference between the water level in the emergency water reserve and the water level 5 l in
the suction basin exceeds a predetermined threshold;
said obstructing device comprises a counterweight means arranged on a side
opposite the obstructing member relative to said pivot shaft, said counterweight means
comprising a main counterweight member located at a fixed distance from said pivot
10 shaft, and said main counterweight member weighing between 80% and 200% of the
weight of said obstructing member;
said obstructing device comprises a float device arranged so that it is fully
submerged in water when water is being supplied normally by said at least one suction
tunnel and so that it is at least partially exposed if the water level in the suction basin falls
15 below a predetermined level of lowest tide to reach a predetermined trigger level, said
float device being adapted to cause said obstructing member to pivot when said trigger
level is reached.
The invention also relates to a nuclear power plant comprising a water intake
installation according to the invention, wherein the suction basin is covered by a device
20 forming a substantially watertight cover, and at least one calibrated opening is made in
the cover device or nearby to allow a limited flow of water to outside the suction basin if
the suction basin overflows due to an unusual rise in said body of water, the nuclear
power plant further comprising at least one discharge shaft feeding water to an outflow
tunnel, said discharge shaft also being provided with a cover device having at least one
25 calibrated opening to allow a limited flow of water to the outside in case of overflow of
the discharge shaft.
According to an advantageous embodiment of such a nuclear power plant, one
said emergency water reserve comprises a reserve basin having its top open to the outside
and containing a volume of water that remains substantially unchanged when water is
30 being supplied normally to the suction basin by said at least one suction tunnel, and said
at least one calibrated opening leads to said reserve basin to allow collecting said limited
flow of water therein.
6
Other features and advantages of the invention will be apparent from the
following description of some non-limiting exemplary embodiments, with reference to
the figures in which:
FIG. l schematically represents a top view of a nuclear power plant near the
coastline, comprising a water intake installation able to be modified to equip it with 5 a
system for supplying additional water.
FIG. 2 schematically represents a partial side view of the water intake
installation represented in FIG. 1, as well as the different tide levels to be taken into
account in the design.
10 FIG. 3 schematically represents a top view of the nuclear power plant of FIG.
1, in a situation with highly degraded operation of the suction tunnel after a collapse; this
situation does not allow the plant to continue operating normally.
FIG. 4 schematically represents a partial side view of modifications made to
the water intake installation of FIG. 1 in order to implement a system for supplying
15 additional water according to the invention, with the obstructing device of the system
represented in a position where it closes off the water duct.
FIG. 5 represents the system for supplying additional water of FIG. 4, with the
obstructing device in a position that opens the water duct, placing the suction basin in
communication with a channel.
20 FIG. 6 schematically represents a partial top view of the system for supplying
additional water of FIG. 4.
FIG. 7 schematically represents a partial top view of the system for supplying
additional water of FIG. 4, with the obstructing device in the open position of FIG. 5.
FIG. 8 schematically represents a partial side view of a portion of the
25 obstructing device of FIG. 4.
FIG. 9 schematically represents a partial side view of the obstructing device of
FIG. 8 plus a counterweight adjustment means.
FIG. 10 schematically represents a partial side view of an obstructing device
similar to the one of FIG. 9.
7
FIG. 11 schematically represents a partial side view of another embodiment of
a system for supplying additional water of the invention, which can be used as an
alternative to the system for supplying additional water of FIG. 4.
FIG. 12 represents the system for supplying additional water of FIG. 11 with
the obstructing device in a position that fully opens the water duct5 .
FIG. 13 schematically represents a partial side view of a variant of the system
for supplying additional water of FIG. 11, with the obstructing device in a position that
closes off the water duct.
FIG. 14 schematically represents the system for supplying additional water of
10 FIG. 13, with the obstructing device in a position that fully opens the water duct.
FIG. 15 schematically represents a partial side view of another variant of a
system for supplying additional water similar to that of FIG. 11, with an obstructing
device according to another embodiment.
FIG. 16 represents the system for supplying additional water of FIG. 15, with
15 the obstructing device in a position that fully opens the water duct.
FIG. 17 schematically represents a partial side view of another embodiment of
a water intake installation of the invention for a nuclear power plant that could
experience a tidal wave, the obstructing device of the water supply system being
represented in a position that closes off the water duct.
20 FIG. 18 represents the system for supplying additional water of FIG. 17, the
obstructing device being in a position that opens the water duct so that the suction basin
communicates with the sea via a backup tunnel.
FIG. 19 schematically represents a partial side view of the system for
supplying additional water of FIG. 17, equipped with an obstructing device according to
25 another embodiment.
FIG. 20 schematically represents a partial side view of another embodiment of
a water intake installation of the invention, for a nuclear power plant by the coastline that
could experience a tidal wave, with a first emergency water reserve comprising a reserve
basin particularly intended for handling a tsunami situation.
30 FIG. 21 represents the water intake installation of FIG. 20 in a situation where
the sea bordering the plant drops below the level of the lowest tide prior to the first wave
8
of a tsunami, the reserve basin allowing the supply of water to the production pumps to
continue.
FIG. 22 represents the water intake installation of FIG. 20 in a situation where
the level of the sea bordering the plant reaches its peak during a tsunami.
FIG.23 represents the water intake installation of FIG. 20 in a situation whe5 re
the supply of water through the suction tunnel to the suction basin is interrupted due to a
collapse, the suction basin being supplied with water indirectly by a backup tunnel in
order to maintain operation of the backup pumps.
FIG. 24 schematically represents a portion of the water intake installation of
10 FIG. 20, in which trigger devices are installed to control the opening of the obstructing
devices sealing off the system for supplying additional water, one of the trigger devices
being represented as actuated to allow the reserve basin to be filled.
FIG. 25 schematically represents another embodiment of the water intake
installation of FIG. 23, in the same situation where the supply of water through the
15 suction tunnel to the suction basin has been interrupted, the suction basin being supplied
with water directly by a backup tunnel.
FIG. 26 schematically represents a front view of one embodiment of an
obstructing device with exclusively controlled opening, usable in a water supply system
of the water intake installation of FIG. 25, the obstructing device being shown in a
20 position where it closes off the water duct.
FIG. 27 represents the obstructing device of FIG. 26 in an intermediate
position of unobstructing the water duct immediately after it is triggered to open.
FIG. 28 schematically represents a partial side view of the obstructing device
of FIG. 26.
25 FIG. 29 represents the obstructing device of FIG. 28 in an intermediate
position of unobstructing the water duct.
FIG. 30 schematically represents a partial side view of a modified portion of
the obstructing device of FIG. 26, in a position of closing off the water duct as well as in
an intermediate position of unobstructing the water duct.
30 FIG. 31 schematically and partially represents another embodiment of a water
intake installation similar to that of FIG. 20, where both the reserve basin and the suction
basin are covered by a cover device.
9
FIG. 32 schematically represents a partial side view of another embodiment of
a water intake installation of the invention for a nuclear power plant separated from the
water's edge by a strip of land not suitable for construction, an emergency water reserve
comprising a reserve basin which can be supplied water from an auxiliary water source
such as a rive5 r.
FIG. l, FIG. 2, and FIG. 3 represent the same water intake installation and are
discussed together in the following. The water intake installation is installed at the site of
a nuclear power plant 1 on the coastline, and comprises a suction basin 2 located in a
bottom portion 63 of a channel 6, as well as an underground suction tunnel 3 which
10 supplies the suction basin with water. A plant pumping station 10 pumps water into the
suction basin 2 for use in at least one heat exchanger-based cooling circuit. The
underground tunnel 3 is in communication with the suction basin 2 by means of two
shafts each formed by a generally vertical passage 7 which leads to the bottom 2B of the
basin, as represented in FIG. 2.
15 The underground suction tunnel 3 is visible in figures 1 and 3 for explanatory
purposes, but it is understood that this tunnel is buried below the seabed and is therefore
not visible from the sea. The tunnel 3 extends to a certain distance from the shoreline,
passing below the bed to reach a depth below sea level (MSL in France) that is defined
beforehand based on a maximum temperature that the water in the suction basin is not to
20 exceed. In the embodiment represented in FIG. l, the suction tunnel 3 lies under the
seabed at depths of about 40 meters below mean sea level, and is connected to two water
intakes 51 and 52 spaced apart from each other.
Each water intake 51 and 52 sits several meters above the seabed at a depth H
below mean sea level L0, and is located at an upper end of a substantially vertical suction
25 shaft 8 connected to the suction tunnel as represented in FIG. 2. The water gains very
little heat in an underground suction tunnel, and therefore the water arriving at the suction
basin is substantially the same temperature as the water collected at a water intake 51 or
52. Preferably, the depth H is determined so that the water reaching the suction basin 2
has a maximum temperature during at least a period of the year that is at least 4ºC lower
30 than the maximum surface temperature of the water constituting the body of water 5.
In the example represented in FIG. 1, the suction tunnel 3 forms a loop having
a curved section 3C forming at least a half-circle, and has two ends which each
communicate with the suction basin 2 by means of a generally vertical passage 7. The
water intakes 51 and 52 allow the tunnel to pull water in respective streams flowing at
10
rates I1 and I2 that are a function of the pumping rate of the pumping station 10. If a
reactor unit 1A at full power requires about 70 m3 per second of water during normal
operation for example, the flow rate of each stream I1 or I2 is about 35 m3 per second of
water. The inside diameter of the tunnel 3, as well as the inside diameter of a passage 7
and of a suction shaft 8, is chosen to be about 5 meters for example, which ensures a 5 flow
rate of 70 m3 per second of water in one arm 3B or 3D of the tunnel without substantial
head loss in an unaffected arm if the other arm is blocked by a collapse.
In a water intake installation according to the invention, it is not necessary for
the suction tunnel 3 to form a loop or for only one suction tunnel 3 to supply a suction
10 basin 2 of the plant. Any other form of suction tunnel is possible, and a suction basin 2
can be supplied with water by two or even three separate suction tunnels. In particular, if
one suction basin is allocated to pumping stations for multiple reactors of a plant, for
safety reasons or in order to maintain the necessary flow rate it may be decided to have
the suction basin supplied by two looped suction tunnels 3 arranged side by side.
15 Furthermore, in a known manner, a pumping station comprises pumps R (see FIG. 4) for
sending the water exiting the heat exchanger 13-based cooling circuit 11 to a discharge
shaft 14 leading to an outflow tunnel 4 which ends in underwater mouths 41 located at a
distance from the water intakes 51 and 52. The flow rate IR of water discharged by the
outflow tunnel 4 is normally equal to the sum of flow rates I1 and I2.
20 The channel 6 comprises an intake portion 60 which communicates with the
sea 5, and is protected from the sea by a dike 61 between the channel and the shoreline
5B. A wall 62, for example in the form of a dam wall, creates a separation between the
bottom portion 63 and the intake portion 60 of the channel, so that water from the suction
basin 2 does not mix with the water of the intake portion of the channel. In this manner,
25 water from the suction basin 2 is not heated by the generally warmer water of the channel
6. The wall 62 and the tunnel and suction shafts may be constructed as part of
modifications to a nuclear power plant already in operation where the suction basin was
originally formed by the channel 6, in order to lower the maximum temperature of the
water supplied to the plant pumping station.
30 In the unlikely event of damage to both arms of the suction tunnel 3, for
example in areas 55 of the tunnel suffering a critical collapse as schematically
represented in FIG. 3, there could be significant localized narrowing of the inside crosssectional
area of the tunnel. Studies conducted by the applicant allow one to assume that
with a tunnel containing reinforcing wall segments that can move in a direction
11
transverse to the tunnel, and in the most serious collapses considered, the inside crosssectional
area of the tunnel in the damaged areas would remain sufficient to allow a flow
rate for example of at least 5 m3 per second of water and greater than the emergency flow
rate required by the backup pumps in the pumping station 10. An emergency flow rate of
about 4 m3 per second of water is usually enough to cover the water supply require5 ments
of a pumping station of a reactor unit where the generation of electricity has been
stopped.
Nevertheless, the current state of research does not allow predicting with
certainty that the inside cross-sectional area of the tunnel would systematically remain
10 sufficient in all possible cases of collapse. One cannot completely rule out the possibility
of severe narrowing of the inside cross-sectional area of the tunnel, more or less cutting
off the water supply to the suction basin 2 which means sufficient water is prevented
from reaching the backup pumps from the suction tunnel. The case of a critical collapse
as represented in FIG. 3 could therefore lead to cooling failure of the nuclear reactor,
15 even during reactor shutdown. For these reasons, the applicant has sought to design a
system for supplying additional water that is capable of placing the suction basin in
communication with an emergency water reserve, said system being intended to ensure
that the supply of water to the suction basin from the emergency water reserve is
infallibly triggered whenever the flow of water from the suction tunnel becomes
20 insufficient to supply the backup pumps.
In the following description, it is assumed that the body of water 5 is a sea
subjected to tides. It is understood that the embodiment described is also suitable for a
body of water having no substantial variation in level. Each wall of the passage 7 ends at
the suction basin 2 at a level which is substantially below the level LL of the lowest tide
25 during the largest tidal coefficients (see FIG. 2). Indeed, the supply of water through the
suction tunnel 3 to the suction basin is effected by the equilibrium established between
levels due to atmospheric pressure. Taking into account the pumping rate of the pumping
station 10, the head losses in the suction shafts 8 and tunnel 3 may result in the water
level L2 in the suction basin being several centimeters or tens of centimeters below the
30 level L1 of the sea measured above the water intakes 51 and 52, the level L1 in question
being averaged between the peaks and troughs of the swell waves. This averaged level L1
is substantially the same above the water intakes and in the channel 6, which smooths out
the rapid variations in water level due to swells. When the level L1 of the sea reaches the
level LL of the lowest tide, the water level L2 in the suction basin reaches a level L2L
12
which must be at a certain height above the mouth 7E of the passage 7, to prevent the
suction basin from being progressively emptied by the production pumps of the pumping
station 10. The height of the suction basin is such that when the level L1 of the sea
reaches the level LH of the highest tide during the largest tidal coefficients, water does not
overflow from the suction basin5 .
In the embodiment represented in FIG. 1, where the suction basin 2 is
implemented within a channel 6, the emergency water reserve is preferably formed by the
intake portion 60 of the channel which is mostly protected from the waves and ground
swells that can be encountered outside the channel in a coastline setting. A filtration
10 system may be provided at the entrance to the channel, not shown in the figure, for
example comprising grills that can be cleaned from time to time, to keep the water in the
intake portion 60 of the channel free of contaminants such as floating objects or algae. In
fact, due to the fact that the water coming through the suction tunnel 3 does not contain
such contaminants, a filtration system 12 for the pumping station 10 (see FIG. 2) can
15 advantageously omit the filtration and cleaning means specifically handling these types
of contaminants. In an emergency situation where the suction basin 2 must quickly be
supplied with water by the intake portion 60 of the channel, we do not want to risk
fouling the filtration system 12.
As represented in FIG. 4 as well as in figures 5 to 7, in order to implement
20 the system for supplying additional water, the closed wall 62 is replaced by a partition
wall 620 having an opening 65 blocked by an obstructing device in the form of a pivoting
valve 9. The valve 9 comprises an obstructing member 90 in the form of a sealing panel
that is generally planar, for example substantially rectangular, and pivotable about a pivot
shaft 91. The valve 9 further comprises a counterweight means arranged on a side
25 opposite the sealing panel 90 relative to the pivot shaft 91. The counterweight means
comprises a main counterweight member 92 located at a fixed distance from the pivot
shaft 91. The counterweight means further comprises an adjustable auxiliary
counterweight means, which comprises for example an auxiliary counterweight 94
movably mounted on two arms 93 fixed to the valve 9. In this manner, the position of the
30 center of gravity G of the obstructing device 9 can be adjusted to some extent, as detailed
below with reference to FIG. 9. The valve 9 is designed such that the center of gravity G
is located at a certain distance from the plane of the sealing panel 90, so that the torque
exerted by the weight of the valve with respect to the pivot shaft 91 provides a force that
13
keeps the valve closed despite the level L1 of the sea being higher than the water level L2
in the suction basin.
In order to have a constant pumping rate of the pumping station 10 supplying
water to a heat exchanger 13-based cooling circuit 11, the difference in height Δh
between the level L1 of the sea and the water level L2 in the suction basin virtually doe5 s
not vary with the level of the sea. The valve 9 closing force provided by the weight of the
valve as explained above is intended to be greater than the valve opening force required
by the water pressure differential between the two faces of the sealing panel 90 due to the
difference in height Δh, this difference Δh being considered for a pumping rate of the
10 pumping station during normal operation with the corresponding reactor unit at full
power. In this manner, as long as the suction basin 2 is supplied with water by a suction
tunnel 3 as normal, the valve 9 remains closed as represented in FIG. 4 and FIG. 6, so
that there is almost no mixing of the water in the suction basin with the water of the
emergency water reserve formed by the intake portion 60 of the channel. It is not
15 necessary for the valve 9 to provide a perfect seal, as it is acceptable for water to leak
from the intake portion 60 to the suction basin 2 as long as this does not significantly
increase the water temperature in the suction basin.
The valve 9 closing force provided by the weight of the valve is intended to
correspond to a predetermined critical difference ΔhV in the water levels that unerringly
20 indicates an insufficient supply of water to the basin 2 via the suction tunnel or tunnels 3.
In other words, it is arranged that the valve opening force resulting from this critical
difference ΔhV is stronger than the valve closing force once the height difference Δh
exceeds the critical difference ΔhV, causing the valve to open once the critical difference
ΔhV is reached. In practice, the static friction of the valve's pivoting elements must also
25 be considered, for example the bearings associated with the pivot shaft 91 if the latter
pivots on bearings 95 (see FIG. 5 and FIG. 7).
A collapse in a suction tunnel 3 is unlikely to occur precisely during a period
when the level L1 of the sea is as low as the level LL of the lowest tide during the
strongest tidal coefficients. As a result, if the critical height difference ΔhV is reached
30 after a collapse in the tunnel, the valve 9 will generally open while the water level L2 in
the suction basin 2 is still above a critical level L2V corresponding to the case of the
lowest tide indicated in FIG. 5.
Furthermore, the sizing of the valve 9 may vary depending on the desired
function of the system for supplying additional water. It may be desired to allow the
14
water to travel through the valve 9, once it is open, at a rate sufficient to allow normal
operation of the pumping station 10 for a reactor unit generating electricity at full
capacity during periods where the water temperature at the surface of the sea does not
exceed a certain value, for example between 10°C and 20°C. The repair of a suction
tunnel having experienced a collapse may take months or even more than a year for 5 r a
critical collapse in several arms of the tunnel. Electricity generation by the nuclear power
plant could then be continued during some or all of the work period, particularly in the
winter, by using the channel 6 to supply water to the suction basin 2. As an alternative to
a valve 9 of large dimensions to accommodate the maximum flow rate required for
10 electricity generation, a valve 9 of smaller size can be provided, arranged in parallel with
a main gate valve such as a raising gate installed beside valve 9 within the partition wall
620. The main gate valve, not shown in the figures, would be controlled to open after
valve 9 is triggered, the opening of the gate valve being required in order to restart the
production pumps.
15 In other configurations of nuclear power plants, for example in the case of a
nuclear power plant installed near a sea that remains relatively warm year round, normal
operation of the pumping station 10 to generate electricity at full capacity may be
impossible if the water must be supplied to the suction basin through the channel 6. In
this case, valve 9 can have relatively small dimensions that allow sufficient water through
20 to achieve a minimum flow rate, for example about 5 m3 per second, for reliably
supplying the backup pumps of the pumping station 10 with the water required. It is also
conceivable for valve 9 to have sufficient dimensions for supplying the production pumps
with a reduced flow, in a context of reduced electricity production by the plant.
The dimensions of the suction basin 2 should take into account the extreme
25 case where a critical collapse in the suction tunnel 3 occurs during a period when the
level L1 of the sea has reached the level LL of lowest tide during the strongest tidal
coefficients. Just before the supply of water from the passages 7 connected to the suction
tunnel is cut off, the water level L2L in the suction basin is at a height below level LL.
Once the water supply is cut off or is at least insufficient for the water consumed by the
30 pumping station 10, a more or less rapid drop in the water level in the suction basin
occurs, to reach the critical level L2V as shown in FIG. 5. As explained above, the valve 9
is then forced to pivot open. In addition, a system for detecting the water level and/or the
pivoting of the valve 9 may advantageously be provided, for forcing shutdown of
15
electricity production and a switch from the production pumps of the pumping station 10
to the backup pumps.
The filtration system 12 is arranged below the critical level L2V, and the water
intakes of the pumping station 10 are arranged sufficiently below this level to avoid their
exposure as the water level in the suction basin continues to drop during the shut5 down
phase of the production pumps. Depending on the flow rate of the water through the open
valve 9, the water level in the suction basin will climb back more or less quickly, and at
the latest once the production pumps have completely stopped. Thanks to the
counterweight means of the valve 9, the positioning of the center of gravity G of the
10 obstructing device above the level of the pivot shaft 91 allows the torque exerted by the
weight of the valve about the pivot shaft 91 to decrease as the valve opens. As a result,
the valve remains open in a position of dynamic equilibrium which is maintained when
the height difference Δh of the water is once again less than the critical difference ΔhV.
The valve 9 described above is an obstructing device in which the pivoting
15 occurs autonomously, meaning in a passive manner without requiring an external device
to trigger it. Optionally, the pivoting of the valve 9 can be actuated by a trigger device
connected for example to a control system associated with a water level detection system.
The trigger device may, for example, act on a cable connected to a crank attached to the
valve at the pivot shaft 91, and may advantageously be adapted to allow the valve to
20 pivot autonomously in the event that the trigger device does not function. The trigger
device may also be arranged to maintain the valve 9, after it is triggered, in a position
where it is more widely open than in the dynamic equilibrium position mentioned above
with reference to FIG. 5.
As represented in FIG. 6 and FIG. 7, the auxiliary counterweight 94 may be
25 formed by a beam structure mounted to be slidable perpendicularly to two arms 93
parallel to each other, in a manner that adjusts the distance between the beam 94 and the
pivot shaft 91 parallel to it. In addition, the opening 65 forming the water duct in the wall
620 separating the suction basin 2 from the intake portion 60 of the channel may be
provided with a filtration and/or safety grid on the intake portion 60 side.
30 Advantageously, the main counterweight member 92 weighs between 80%
and 200% of the weight of the obstructing member 90. In this manner, as represented in
FIG. 8, the center of gravity G1 of the assembly of the two members is relatively close to
the pivot shaft 91 within a height range DG1. To raise the position of the center of
gravity G1, the weight of the main counterweight 92 can be increased and/or the position
16
of its center of gravity raised. The auxiliary counterweight means attached to this
assembly is arranged such that the center of gravity G of the entire assembly is located
above the level X of the pivot shaft 91, as represented in FIG. 9. Adjusting the position of
the auxiliary counterweight 94 in a direction A1 within a certain margin DG2 moves the
center of gravity G2 of the auxiliary counterweight means, and therefore 5 moves the
center of gravity G more or less further away from the pivot shaft 91. Thus, if during
testing or normal operation the valve 9 is opened unexpectedly while the suction tunnel is
functioning, for example during a storm hitting the coastline 5B, the position of the
auxiliary counterweight 94 can be readjusted to correspond to a critical height difference
10 ΔhV that has been reevaluated upward.
The main counterweight member 92 and the device comprising the auxiliary
counterweight 94 may form an assembly that is a single piece for all intents and
purposes, which is secured to the obstructing member 90 by fitting it thereon, as
represented in FIG. 10.
15 Another embodiment of a system for supplying additional water is represented
in FIGS. 11 to 14, for a water intake installation according to the invention. In
comparison to the previous embodiment, this embodiment allows reducing the
dimensions of the obstructing device 9, and in particular the dimensions of the
obstructing member 90. As represented in FIG. 11 and FIG. 12, the opening 65 forming
20 the water duct in the wall 621 separating the suction basin 2 from the intake portion 60 of
the channel is arranged in a lower portion of the wall 621. A sealing panel that is
generally planar, for example substantially rectangular, forms the obstructing member 90
of the valve 9. The dimensions of the sealing panel 90 are somewhat larger than the
cross-sectional area of the passage of the opening 65, said cross-sectional area possibly
25 being relatively small, for example about 2 to 3 m2, to permit only the passage of enough
water to supply reliably the backup pumps of the pump station 10. As explained for the
previous embodiment, it is also possible to arrange in parallel a main gate valve such as a
sliding gate valve actuated by a control, also known as a slice valve, installed beside
valve 9 in the partition wall 621.
30 The pivot shaft 91 of the valve 9 is attached at a lower edge of the sealing
panel 90. The pivot elements of the valve comprise, for example, the bearings associated
with the pivot shaft 91 and arranged to rotate on bearing mounts on the bottom of the
suction basin. Pneumatic caissons or hollow watertight columns may be provided, each
having a wall traversed by the pivot shaft 91, in order to contain the bearings and mounts
17
and surround them with air. As an alternative to the bearings, it may be arranged that the
pivot shaft 91 is formed by a bar having a ridge for example of stainless steel along its
length, which presses against the inner surface of a half-tube or similar bearing element
having a concave face parallel to the bar and attached to the ground at the bottom of the
basin. The concave face of the bearing element will generally be oriented towards 5 rds the
intake portion 60 of the channel, to prevent movement of the pivot shaft 91 in the
direction of the suction basin including after the valve 9 has pivoted as represented in
FIG. 12. The static friction of such a device with its ridged pivot shaft can be fairly low,
and in particular can be relatively stable over time without requiring special maintenance
10 of the device.
The sealing panel 90 is installed within the opening 65 in the wall 621 so as to
seal the opening in a more or less fluidtight manner, and is mounted with a certain
inclination relative to the vertical direction. An abutment maintaining the inclined
position of the panel 90 is formed for example by a shoulder 622 of the wall 621. The
15 inclination and weight of the panel 90 are defined beforehand so that the panel remains in
position during situations of normal operation of the suction tunnel, as shown in FIG. 11.
In other words, the panel 90 must not pivot under normal conditions, despite the
differential water pressure on the face of the panel on the channel side due to the height
difference Δh between the level L1 of the sea and the water level L2 in the suction basin,
20 but must pivot to open the valve 9 if the critical height difference ΔhV is reached as
represented in FIG. 12.
The valve 9 does not require a massive counterweight member such as the
main counterweight member 92 described above. In fact, once the panel 90 begins to
pivot, the inclination of the panel relative to the vertical direction decreases, which
25 reduces the torque exerted by the weight of the panel relative to the pivot shaft 91 and
therefore decreases the resistance of the valve to the opening force caused by the critical
height difference ΔhV. The valve 9 is therefore certain to open fully when the panel 90
starts to rotate.
In FIG. 13, a variant of the system for supplying additional water of FIG. 11
30 consists of providing the valve with an adjustable counterweight means comprising, for
example, a counterweight 94 movably mounted on two parallel arms 93 fixed to the valve
9, in a manner analogous to the auxiliary counterweight means 94 described above in
reference to FIG. 4 and FIG. 6. Furthermore, in order to optimize the cross-sectional area
of the opening 65 in the partition wall 621, the floor is sunken under the counterweight
18
94, and the abutment maintaining the inclined position of the panel 90 is formed near the
pivot shaft 91. A relatively light counterweight 94, for example weighing less than 10%
of the weight of the panel 90, can be sufficient for tests adjusting the center of gravity G
of the valve.
As represented in FIG. 13, the valve 13 is subjected to two opposing torques5 ,
meaning torques in opposite directions relative to the pivot shaft 91. The torque exerted
by the weight of the valve is equal to the value F1 of the weight multiplied by the
distance D1 between the weight vector applied at the center of gravity G of the valve and
the center axis C of the pivot shaft 91. The algebraic torque exerted by the force of the
10 differential water pressure that is applied to the panel 90 is equal to the algebraic value
F2 of this force multiplied by the distance D2 between the force vector F2 and the central
axis C. The angle of the panel 90, as well as the center of gravity and the weight of the
valve, are defined beforehand so that the two opposing torques have the same absolute
value if the critical height difference ΔhV in the water levels is reached. As represented
15 in FIG. 14, when the critical height difference ΔhV is slightly exceeded this overcomes
the static friction of the device with its pivot shaft 91, causing the panel 90 to pivot which
opens the valve 9. The water level L2 in the suction basin may continue to descend as
long as the production pumps are not completely shut down, and climbs back up when
only the backup pumps are active.
20 Another embodiment of a system for supplying additional water similar to the
one of FIG. 11 for a water intake installation according to the invention is represented in
FIG. 15. The implementation of the obstructing device 9 in particular is different from
the previous embodiment, especially in that the sealing panel 90 is not the only sealing
element of the valve 9 between the suction basin 2 and the intake portion 60 of the
25 channel. Indeed, here a main counterweight member 92 as previously described forms a
sealing surface S3 on the side of the panel 90 away from the pivot shaft 91. In this
manner, torque exerted due to the force F3 of the differential water pressure which is
applied to the sealing surface S3 is added to the torque exerted by the weight F1 of the
valve, in a direction of rotation opposing the torque exerted by the force F2 of the
30 differential water pressure which is applied to the panel 90.
This implementation of the valve 9 keeps the valve closed until there is a
relatively large critical height difference ΔhV, without requiring a particularly massive
counterweight system. Indeed, the design may provide for increased dimensions of the
sealing surface S3 in order to adapt the valve for a greater critical height difference ΔhV.
19
In addition, as represented in FIG. 16, once the valve 9 is open it exposes a water duct
having a cross-sectional area virtually equal to the cross-sectional area of the opening 65.
In addition, depending on the intended position of its center of gravity G, the valve may
be arranged to close autonomously if the operation of the suction tunnel is restored.
Optionally, a filtration and/or safety grid 12' may be provided on the opening 65 on 5 the
suction basin 2 side.
A system for supplying additional water for a water intake installation
according to the invention may comprise a backup tunnel, in particular if the suction
basin is at a distance from the emergency water reserve. This may be the case, for
10 example, if the nuclear power plant is separated from the sea by a section of land where
construction is not possible, thus preventing the construction of a channel to the suction
basin but allowing the passage of a backup tunnel beneath said section of land. This may
also be the case, for example, if the power plant is located next to a body of water likely
to experience an unusual rise in water level.
15 In FIG.17, a water intake installation according to the invention can be
adapted for such a nuclear power plant located next to such a body of water. An unusual
rise in water level is understood to mean a tidal wave such as those caused for example
by a tsunami, or floodwaters swelling a river. A water intake installation such as the one
represented in FIG. 1 requires relatively few arrangements to withstand an unusual rise in
20 water level. The dike 61 must be of sufficient height to prevent flooding if the body of
water 5 reaches the height L1P of the highest estimated level. In addition, the dike 61 must
protect the plant completely, and therefore there is no longer any question of an opening
to the sea such as a channel. To simplify the description, it is considered in the following
that the body of water 5 is a sea, but it is understood that the installation described also
25 relates to any body of water suitable for cooling a plant, such as a river for example.
Advantageously, the mouth 7E of a passage 7 connecting the suction basin 2
to the suction tunnel 3 is located at a predetermined height above the bottom 2B of the
suction basin, so that in the event of an exceptional drop of the sea to below the level LL
of the lowest tide, as can occur for example along the coastline in areas prone to
30 tsunamis, a certain volume of water remains as a reserve in the suction basin. In the most
critical estimate of the drop in the sea level, the level L1 of the sea will remain below the
level of the mouth 7E of the passage 7 for a certain period of time, which means that
during this time, which may last several minutes, the water to the pumping station 10 will
only be supplied from the reserve volume of water. This volume of water must therefore
20
be arranged so that there is time to shut down the production of electricity by the nuclear
reactor and to switch from the production pumps of the pumping station 10 to the backup
pumps, and to do so with no risk of interruption of the water supply to the backup pumps.
It must be possible to supply the backup pumps from the reserve volume of water until
the sea rises sufficiently for the water in the passage 7 to return to above the level of 5 the
mouth 7E of the passage, meaning until the tunnel 3 is again supplying the suction basin.
As a first approximation, it is estimated for example that a reserve volume of water of
about 10,000 m3 for a pumping station for one nuclear unit is sufficient to offset the most
critical drop possible in the level of the sea prior to a first wave of a tsunami, lasting at
10 least fifteen minutes or so.
To avoid an uncontrolled overflow of the suction basin 2 during an unusual
rise in the sea, for example during or after a first wave of a tsunami, the basin is covered
by a device forming an essentially watertight cover 25. Calibrated openings 26 can be
made in or near the cover 25, for example in a side wall of the basin between the basin
15 and its outside environment. In this manner, if the basin 2 is completely filled, the
calibrated openings 26 allow a limited flow of water Ip from the basin to the outside
environment. The flow Ip may be channeled to a small basin 22 formed on a cover of a
compartment 21 of the suction basin 2, before being discharged for example into the sea
at low tide.
20 In addition, as explained above with reference to FIG. 1 and FIG. 4, in a
nuclear power plant 1A the water leaving the heat exchanger 13-based cooling circuit 11
is drained into a discharge shaft 14 for discharge into the sea via an outflow tunnel 4. In
the event of an unusual rise of the sea, uncontrolled overflow of the discharge shaft must
be avoided. Advantageously, the discharge shaft 14 is also provided with a cover device
25 with at least one calibrated opening to allow a limited flow of water to outside the
discharge shaft in the event of overflow. This arrangement applies to any nuclear power
plant comprising a water intake installation of the invention and likely to experience an
unusual rise in the level of the body of water 5. Furthermore, in order to counter the
possibility of a relative blockage of the outflow tunnel 4, the discharge shaft 14 may
30 advantageously be provided with a closed valve which opens to the outside only beyond
a certain water pressure in the shaft, or an obstructing device which is controlled to open
so that it is in communication with an auxiliary outflow passage leading to the sea. In the
event of blockage of the outflow tunnel 4, the water level in the discharge shaft 14 will
rise due to the water contributed by the pumps R (FIG. 4), and the valve or the
21
obstructing device is triggered to open shortly before the level reaches the top of the shaft
in order to drain the water away by the auxiliary outflow passage.
The maximum water pressure in the suction basin 2 at the cover 25 is a
function of the highest level L1P of the sea directly above the water intakes 51 and 52,
relative to the cover 25. The depressurization in the suction basin 2 will be more or 5 less
significant, depending on the flow of water Ip through the calibrated openings 26. It is
possible to dispense with the openings 26 and replace them with valves that allow air to
enter and prevent water from exiting. In this case, the structures of the basin 2, the cover
25, and the filtration system 12, must withstand the added pressure.
10 The water intake installation further comprises a system for supplying
additional water that is functionally analogous to the one described above with reference
to FIG. 4, and that includes a water duct in the form of a backup tunnel 30 connected to at
least one backup water intake 15 submerged in the sea. A backup water intake 15 must be
submerged at a depth that ensures it is never exposed except in the case of an extremely
15 exceptional drop in the sea as can occur before the arrival of the first wave of a tsunami,
and therefore is located below the level LL of the lowest tide during the strongest tidal
coefficients. It is generally not necessary for a backup water intake 15 to be arranged
more than ten meters below level LL, an arrangement of less than ten meters below this
level LL generally being sufficient to prevent contamination of the water intake by
20 floating objects or algae. A main water intake 51 or 52 is generally arranged at more than
twenty meters below the level LL of the lowest tide, so that the decrease in the maximum
temperature of the water it draws is significant. A backup water intake 15 will therefore
usually be positioned at a height HE of at least ten meters above a main water intake.
The backup tunnel 30 passes under the dike 61 and comprises a horizontal
25 passage 35 which traverses a wall of the suction basin 2 to open into the basin at an end
35B that forms a vertical planar surface. An obstructing device 9 in the form of an
autonomous pivoting valve, which may be virtually identical to the one described above
with reference to FIG. 4, is installed in the suction basin 2, for example in a compartment
2B of the basin providing maintenance access to the valve without the risk of objects or
30 workers being sucked into the main chamber 2A of the suction basin. An opening 21
provided between the compartment 2B and the chamber 2A may be equipped with a
security grid. In the closed position of the valve 9, the planar sealing panel 90 forming
the obstructing member of the valve is seated against the end 35B of the backup tunnel
30 and thus closes off the water duct.
22
As represented in FIG. 18, in the case of an insufficient supply to the pumping
station 10 of water coming from the suction tunnel, the water level L2 in the suction basin
2 drops until the predetermined critical difference ΔhV between the level L1 of the sea
and the level L2 of the basin is exceeded, which causes the valve 9 to pivot and therefore
opens the water duct. The water coming from the sea through the backup tunnel 5 30
passes into the compartment 2B of the basin and then into the main chamber 2A of the
basin through the opening 21.
It is understood that the obstructing device of the system for supplying
additional water of FIG. 17 is not limited to a valve 9 with a massive counterweight
10 means. For example, a valve device 9 as described above with reference to FIG. 11, FIG.
13, or FIG.15, may instead be provided in the compartment 2B of the suction basin, with
the passage 35 being suitably adapted.
As represented in FIG. 19, according to another embodiment of the
obstructing device, the pivoting valve device 16 comprises a float device 96, arranged so
15 as to be fully submerged in water during a normal supply of water by the suction tunnel
3. The volume of the float device 96 is defined beforehand so that the buoyancy exerted
on the fully submerged float is sufficient to keep the valve 16 closed during a normal
supply of water, by counterbalancing the opening force of the valve due to the differential
water pressure exerted on the face of the sealing panel 90 on the backup tunnel 30 side.
20 The float 96 has a structure adapted to withstand the high water pressure in the suction
basin 2 in case of tidal waves.
In a case of insufficient water supply to the pumping station 10, if the level of
water L2 in the suction tank 2 falls sufficiently below the level L2L of lowest tide to reach
the predetermined trigger level L2V, the float 96 is designed to emerge at least partially
25 from the water, so that the decrease in buoyancy exerted on the float causes the valve 16
and thus the obstructing member 90 to pivot. Advantageously, the volume and weight of
the float device 96 are defined beforehand so that if the critical difference in water level
ΔhV is exceeded, the valve opening force due to the water pressure differential is greater
than the valve closing force due to the torque of the floating device with respect to the
30 pivot shaft 91. Thus, once the level L1 of the sea is substantially above the level LL of the
lowest tide during the strongest tidal coefficients, the valve 16 begins to pivot to open the
water duct as soon as the predetermined critical difference in water level ΔhV is
exceeded.
23
A significant advantage of such a valve 16 with its float device 96 lies in that
it is virtually certain that the valve will pivot autonomously, at the very latest shortly after
the water level L2 in the suction basin drops below the trigger level L2V. Even assuming
some seizing of the pivot shaft 91 or adherence of the panel 90 to the end 35 of the
passage due to organic matter, the drop of the water level L2 to below the trigger leve5 l
L2V exposes the float 96 to the point where the valve opening force inevitably becomes
sufficiently strong to overcome the static forces preventing pivoting. For example, with a
water level L2 as indicated in FIG. 19, one can see that the valve 16 cannot remain closed
and it pivots to open as represented. It is understood that such a valve with float device
10 may also be used as an obstructing device in place of valve 9 in a system for supplying
additional water such as that of FIG. 4.
A possible disadvantage of the device lies in the limitation to how far the
valve can pivot, which may not allow sufficient flow of water through the backup tunnel
30 if the production pumps of the pumping station 10 are restarted during periods when
15 the water temperature at the sea's surface remains cold. In this case, one solution would
be to provide a sufficient cross-sectional area of the backup tunnel 30 and the passage 35,
and to have a controlled valve appropriate for a large cross-sectional area in parallel with
the valve 16 which in turn may be arranged to simply allow a water flow certain to be
sufficient to supply the backup pumps of the pumping station. In addition, the pivot shaft
20 91 may be formed by a bar having a supporting ridge along its length as explained above
in relation with the embodiment shown in FIG. 11, which should prevent significant
seizing of the shaft without requiring special maintenance.
Moreover, if the high water is due to a tsunami, and if no significant
earthquake before the tsunami is felt in the plant, it may be desirable not to shut down the
25 reactor units in the plant and therefore not to shut down the production pumps in the
pumping station during the high water. A water intake installation such as the one
described above with reference to FIG. 17 and FIG. 18 allows such operation. However,
as explained above, during this period which may last several minutes, the supply of
water to the production pumps must then be able to occur solely from the reserve of
30 water contained in the suction basin 2 below the mouth 7E of the passage 7. As a first
approximation, it is estimated for example that a reserve volume of water of up to about
100,000 m3 for a pumping station of a reactor unit would be needed to overcome the
most critical drop conceivable in the level of the sea preceding the first wave of a
tsunami, lasting at least fifteen minutes. For example, with a height of at least five meters
24
between the bottom 2B of the basin 2 and the mouth 7E of the passage 7, it would take
about two hectares of basin surface area to ensure such a reserve volume of water.
There are disadvantages to creating a suction basin such as the one in FIG. 17,
for the case of a particularly large reserve volume below the level of the mouth 7E of the
passage 7. First, since the basin has a roof that forms a cover resistant to a water pressur5 e
in the basin of for example about two bar in order to contain the water in case of tsunami
or tidal wave, the implementation of such a roof to cover an area of a hectare or more
involves significant construction costs. This is even more true if the suction basin 2 is
shared by multiple pumping stations supplying several reactor units, where the surface
10 area of the basin roof substantially increases the construction costs of the water intake
installation as a whole. Furthermore, since the pumping rate of a pumping station when
supplying a reactor unit in full production is about 70 m3 per second for example, it
would take almost an hour at a flow rate of about 140 m3 per second to refill completely
a suction basin shared by two reactor units and containing about 500,000 m3 measured as
15 the high tide average. Depending on the temperature of the outside air, especially if the
outside temperature exceeds 30°C in the shade, the water flowing into the basin could
grow warmer by about 1°C or more between when it exits the suction tunnel and enters
the pumping station. A relative decrease in efficiency of the facility may therefore occur
during certain times of the year, in comparison to a suction basin of much smaller
20 volume.
To overcome these potential disadvantages, an embodiment of a water intake
installation of the invention proposes establishing an emergency water reserve in a
reserve basin containing a volume of water which remains substantially unchanged while
water is being supplied normally to the suction basin by the suction tunnel or tunnels.
25 An example of such an embodiment is represented in FIG. 20. A reserve tank
20 is separated from the suction basin 2 by a dam wall 80 in which is provided with an
opening 85 forming a water duct for the system for supplying additional water. The water
duct 85 opens into the suction basin 2 in a curved side of the wall 80 forming a circular
arc or some other continuous curve in a vertical plane corresponding to the plane of the
30 figure. An obstructing device 17, shown in its closed position in the figure, comprises an
obstructing member in the form of a sealing panel 90' associated with a supporting
structure, the panel having an outer surface of a shape substantially complementary to the
curved side of the wall 80. The panel 90' with its supporting structure is connected to a
horizontal pivot shaft 91' on which it pivots to bring the obstructing device 17 to a
25
position which opens the water duct 85 as shown in FIG. 21. The pivot shaft 91' may
substantially be coincident with a straight line forming the central axis of curvature of the
curved side of the wall 80. Since the widest pivot angle of the obstructing device 17 is
less than 90°, and here is even less than 45°, it may be arranged that the pivot shaft 91 is
formed by a bar having ridges along its length that are in alignment with a same straig5 ht
line and that face towards opposite sides and press against concave mount surfaces, thus
providing a submerged pivot shaft that does not require lubrication.
The outer surface of the sealing panel 90' is arranged to be flush with the
surface of the curved side of the wall 80 when the obstructing device 17 is in the closed
10 position, leaving only a small gap allowing a limited flow of water to escape from the
reserve basin 20 to the suction basin 2 when the water duct 85 is closed off. However, the
gap between the sealing panel 90' and the curved side of the wall 80 is sufficient to
prevent any risk of the panel catching on the wall, the thickness of the gap being able to
fluctuate for example with the thermal expansion of the supporting structure of the panel.
15 Too thin of a gap could allow contact where the panel and the wall become jammed,
preventing the obstructing device 17 from opening.
The obstructing device 17 comprises a counterweight means arranged on the
side opposite to the obstructing member 90' relative to the pivot shaft 91'. The
counterweight means comprises a main counterweight member 97 including a supporting
20 structure rigidly connected to the supporting structure of the panel 90'. The obstructing
device 17 is designed to begin pivoting from its closed position as soon as the water level
in the basin reaches a predetermined trigger level L2V at which a substantial portion of the
main counterweight member 97 emerges from the water. The main counterweight
member 97 preferably weighs between 80% and 200% of the weight of the obstructing
25 member 90'. For example, a weight approaching 200% of the weight of the obstructing
member allows placing the pivot shaft 91' and main counterweight member 97 closer
together, thereby reducing the overall size of the obstructing device 17 and in addition
allowing a wider pivot angle and thus a wider opening of the device for a given decrease
of the water level in the suction basin. In addition, the counterweight means may
30 comprise an auxiliary counterweight movably mounted on the supporting structure of the
main counterweight. In addition, in order to reduce the surface area of the suction basin
floor, thereby reducing the surface area of the roof forming the cover device 25 of the
basin, it is possible to install at least one obstructing device 17 between two mouths 7E of
two passages 7 connecting the tunnel 3 to the suction basin 2.
26
The floor of the reserve basin 20 extends over a much greater surface area
than the suction basin 2, and its top is open to the outside. The reserve basin 20 does not
require a waterproof roof, although a system of protection against the sun's rays, for
example a tarpaulin, remains possible. The water level L3 in the reserve basin 20 is kept
relatively constant, below the cover device 25 of the suction basin. For example, pump5 s
to circulate water in both directions between the suction basin and the reserve basin may
be provided, to compensate for the continuous leakage of water into the suction basin
through the obstructing device 17 or conversely to discharge water into the suction basin
during heavy rains. The volume of water in the reserve basin 20 remains substantially
10 unchanged as long as the suction basin is being supplied with water normally by the
suction tunnel or tunnels. For a nuclear power plant where the suction basin supplies
water to two reactor units, a reserve basin 20 containing for example about 100,000 m3
of water seems sufficient to overcome the most critical drops conceivable in the level of
the sea.
15 The difference in height between the water level L3 in the reserve basin 20
and the water level L2 in the suction basin 2 can be significant, particularly at low tide,
and for example can reach about ten meters at the lowest tide of the year for an ocean. As
a result, a differential water pressure on the order of a bar at its peak is applied to the
sealing panel forming the obstructing member 90' between the reserve basin 20 and the
20 suction basin 2. In addition, the water duct 85 closed off by the sealing panel 90' must
have a sufficient cross-sectional area to allow a flow of water enabling the production
pumps of a pumping station to continue to operate, for example about 70 m3 per second,
which implies a relatively large surface area for the sealing panel 90'. The forces
generated by the differential water pressure on the sealing panel 90' result in a force
25 represented in FIG. 20 by a vector F2 which is applied at or near the geometric center of
the surface of the sealing panel blocking the water duct 85. This force vector F2 is
directed perpendicularly to the central axis of curvature of the curved side of the wall 80,
which may be designed to be coincident with the pivot shaft 91', such that the force
vector generates no torque on the sealing device 17. Advantageously, the central axis of
30 curvature of the curved side of the wall 80 may be located somewhat above the pivot
shaft 91', such that the force vector F2 directed perpendicularly to this central axis
generates a torque on the obstructing device 17 that helps the device to pivot open. This
latter arrangement may be of interest for reducing the weight necessary for the main
27
counterweight member 97, as long as the volume of this member remains sufficient for
the buoyancy required when the obstructing device 17 is in the closed position.
In the embodiment represented in FIG. 20, the system for supplying additional
water can provide indirect communication between the suction basin 2 and a second
emergency water reserve consisting of the body of water 5, which is the sea in 5 this
example. In the case where the supply of water to the suction basin by the suction tunnel
or tunnels becomes insufficient for a lasting period, and in particular in the case of a
critical collapse in the suction tunnel or tunnels, a lasting solution must be implemented
for supplying water to the suction basin once the volume of water in the reserve basin 20
10 has severely decreased. Given the proximity of the sea, it is advantageous to provide a
water duct in the form of a backup tunnel 30 connected to at least one backup water
intake 15 submerged in the sea, as described above in reference to FIG. 17. It is
understood that if the plant is located near a water source such as a river or lake providing
the possibility of a reliable and sustainable source for the second emergency water
15 reserve, a link for supplying water between such a water source and the reserve basin 20
may possibly be preferred over the solution of a backup tunnel 30. For example, a small
artificial lake of seawater maintained at a certain level by pumping water from the sea
could be provided at or near the site of the nuclear power plant, at a height slightly above
the reserve basin 20 and connected to the reserve basin or directly to the suction basin
20 through a pipe closed off by a valve.
Given that the reserve basin 20 is not closed off by a cover device, the
obstructing device sealing the water duct created by the backup tunnel 30 must not allow
seawater to enter the reserve basin in case of a tidal wave, because the reserve basin
could then overflow and risk flooding the plant. Therefore, a sealing device such as the
25 device 9 referenced in FIG. 17 is not appropriate for the reserve basin 20. In addition,
when the water level in the suction basin 2 drops in a manner defined beforehand as
abnormal, it may be advantageous to detect the state of the sea's level to determine
whether the decreased level in the suction basin is caused by the sea abnormally
retreating. If the level of the sea has not changed significantly, leading to the conclusion
30 that a critical collapse has occurred in the suction tunnel or tunnels, the production pumps
of the pumping station can be shut down and switched over to the backup pumps. The
volume of water in the reserve basin 20 is usually enough to supply water to the backup
pumps for at least two hours. As this provides the time to open the obstructing device
blocking the backup tunnel 30, an obstructing device in the form of a non-autonomous
28
controlled valve, for instance a gate valve, is possible. Unlike an autonomous valve, such
an obstructing device does not provide a passive safety mechanism, and once the valve is
open it must be possible to ensure its closure in the event of a tidal wave.
An autonomous obstructing device similar to device 17 may be used to close
off the backup tunnel 30. Alternatively, a pivoting float device 18 may be employed 5 that
does not require a counterweight. The obstructing device 18 represented in FIG. 20
comprises a curved sealing panel 90' pivoting about a pivot shaft 91' which can be
arranged to coincide with the straight line forming the central axis of curvature of the
curved face of the panel. A float 98 is attached to the supporting structure of the sealing
10 panel and is adapted to push the structure upward as long as the float is completely
submerged. A small adjusting counterweight can be added to the device, in order to
adjust the pivoting that is triggered when the float rises above the water surface.
As represented in FIG. 21, during a critical drop in the level of the sea
preceding the first wave of a tsunami, the sea withdraws to below the level LL of the
15 lowest tide for a period of several minutes. The level L2 of the water in the suction basin
2 first drops very quickly because the water flows back toward the passages 7 where the
water level is attempting to establish an equilibrium with the level L1 of the sea. The
rapid exposure of a large portion of the main counterweight member 97 of the obstructing
device 17 greatly decreases the buoyancy exerted on this member and causes an almost
20 complete opening of the closing device, allowing the reserve basin 20 to supply water to
the suction basin 2 in a limited flow but designed to be sufficient for the production
pumps if these have not been shut down. The obstructing device 17 is arranged such that
level L2 stabilizes at a height slightly below the mouths 7E of the passages 7, so that as
little water as possible is lost from the reserve basin through the passages 7. One will note
25 that if level L2 climbs back up slightly, the obstructing device 17 pivots and somewhat
obstructs the water duct 85, which reduces the flow so that level L2 can stabilize as
represented in FIG. 21. Furthermore, it may be advantageous to detect the state of the
sea's level in order to check whether the decreased level in the suction basin is caused by
an abnormal withdrawal of the sea. In this case, and if no significant earthquake
30 preceding the tsunami was felt in the plant, it is not necessary to shut down the
production pumps which can continue to be supplied with water by the reserve basin until
the water returns to the suction basin via the suction tunnel or tunnels. Even so, it may be
decided when designing the plant that the production pumps will be shut down
systematically in the event of an abnormally low water level in the suction basin, thus
29
limiting the volume required in the reserve basin and therefore the construction cost of
the basin.
When the first wave of the tsunami arrives, as represented in FIG. 22, the sea
can reach a level L1P located several meters above the cover device 25 of the suction
basin. The water in the suction basin rises, which causes the obstructing device 17 5 to
close. Once the water in the suction basin has reached the cover 25, a limited flow of
water Ip is allowed to exit to the outside environment through the calibrated openings 26.
This flow Ip can be channeled to the reserve basin 20, where the water level L3 is still far
below the maximum capacity of the basin. The obstructing device 18 which blocks the
10 backup tunnel 30 is not triggered to pivot by the differential water pressure applied to its
obstructing member 90', since the pressures result in a force vector F2 directed toward the
pivot shaft 91'. The operation of the nuclear power plant can be continued in this tidal
wave situation during the period required for the sea to return to its normal level, for
example about half an hour.
15 In FIG. 23, one can see that a critical collapse has occurred in the suction
tunnel or tunnels in at least one collapse area 55. The water level L2 in the suction basin 2
has dropped which has caused the obstructing device 17 to open, significantly draining
the reserve basin 20 into the suction basin to achieve substantially the same level L2.
During this water transfer period, the production pumps of the pumping station were shut
20 down and switched over to the backup pumps. The float of the obstructing device 18 has
been partially exposed above the surface of the water, causing the partial opening of the
obstructing device and thus supplying the reserve basin 20 via the backup tunnel 30. The
partial opening of the obstructing device 18 adjusts automatically to the water
consumption of the pumping station, because if the level L2 drops too much the
25 obstructing device 18 opens further until equilibrium is restored.
As represented in FIG. 24, the pivoting of an obstructing device 17 or 18 to
open it, and possibly also to close it, may optionally be actuated by a trigger device 70
connected for example to a control system associated with at least one water level
detection system. The trigger device 70 may, for example, comprise a winch possibly on
30 a crane, acting on a cable 71 connected to the structure of the obstructing device. Such a
trigger device has the advantage of allowing the obstructing device to pivot automatically
if the winch is not activated. In the example shown in FIG. 24, once the suction tunnel 3
is repaired and the suction basin 2 is being supplied with water normally, the trigger
device is actuated to force open the obstructing device 18 in order to fill the reserve basin
30
via the backup tunnel 30 while the sea is at high tide. Considering the situation of a
critical collapse of the suction tunnel 3 in reference to FIG. 23, one will note that the
installation of trigger devices 70 as represented in FIG. 24 would allow keeping the
obstructing devices 17 and 18 completely open if it is desired to increase the flow of
water between the backup tunnel 30 and the suction basin 2, making it possible to restar5 t
the production pumps.
In addition, during the design phase one could provide means for securing the
obstructing device 18 in its closed position, or for removing the obstructing device 18 and
sealing the water duct formed by the backup tunnel 30. Once sufficient experience has
10 been obtained with the operation of nuclear power plants supplied with water through
reinforced suction tunnels, it is found out that a critical collapse in a suction tunnel
cannot reduce the flow of water to the point that it impacts the water supply to the backup
pumps, it could be decided to temporarily or definitively block off the water duct
provided by the backup tunnel. In such a scenario, it might even be possible to do without
15 a backup tunnel in the construction of new water intake installations of the invention
similar to the installation of FIG. 20. The proximity of the sea in this case allows
providing emergency solutions for supplying water to the reserve basin 20 if so needed.
In FIG. 25, another embodiment of a water intake installation according to the
invention is represented that is similar to the embodiment described above with reference
20 to FIG. 23. These essentially differ in that the suction basin 2 is directly supplied with
water by a backup tunnel 31 connected to at least one backup water intake 15 submerged
in the sea. For the purposes of the diagrammatic representation in FIG. 25, the backup
tunnel 31 is represented as passing through the reserve basin 20 to end in a horizontal
pipe 36 traversing a face of the dam wall 80 separating the reserve basin 20 from the
25 suction basin 2. The horizontal pipe 36 forms a water duct 86 distanced to a greater or
lesser extent from the water duct 85 associated with the obstructing device 17. It may be
preferred to have a backup tunnel 31 which does not traverse the reserve basin 20.
Furthermore, as explained above with reference to FIG. 24, the obstructing device 17
may be associated with a trigger device 70 comprising, for example, a winch acting on a
30 cable 71. The trigger device 70 is connected here to a control system 50 associated with
multiple water level detection systems using water sensors 28 to detect primarily whether
the water level in the suction basin 2 has dropped in a manner defined beforehand as
abnormal, the measurement of the rate of change of the water level possibly being a
parameter for determining an abnormal drop.
31
In order to close off the water duct 86 formed by the backup tunnel 31, an
autonomous closing device such as one or the other of the obstructing devices 9 and 16
described above with reference to FIG. 17 and FIG. 19 may be used, as this is the same
configuration of a closed suction basin that one must be able to place in communication
with the sea via a backup tunnel. With such an obstructing device 9 or 16, the opening 5 of
the device will be arranged to trigger for a level L2 higher than the predetermined level
L2V for triggering the opening of the closing device 17 which blocks the water duct 85
between the suction basin and the reserve basin, so that practically none of the water in
the reserve basin is used except when there is an abnormal withdrawal of the sea.
10 An autonomous obstructing device such as device 9 or 16 is not essential,
however, and in particular it is conceivable to use an obstructing device 19 which is only
opened by a trigger device. The lack of autonomy of such an obstructing device 19 does
not necessarily compromise the safety of the installation, and in particular there can be
redundancy in the trigger device assigned to the obstructing device. In addition, the
15 obstructing device 19 in the installation of FIG. 25 is preferably designed to open only
when a critical collapse in the suction tunnel or tunnels 3 has occurred, and is intended to
open before the water level L2 in the suction basin reaches the predetermined level L2V
for triggering the opening of the obstructing device 17. As a result, if there is a
malfunction in opening obstructing device 19, the water level L2 in the suction basin
20 continues to drop to the predetermined level L2V, which triggers the opening of
obstructing device 17 automatically or by the associated trigger device 70, thus supplying
the suction basin from the reserve basin. The volume of water in the reserve basin 20 is
usually enough to supply the pumps for backup operation for at least two hours, which
provides time to restore control to the opening of obstructing device 19.
25 To ensure that obstructing device 19 is only opened in cases of critical
collapse in the suction tunnel or tunnels 3, we need to be able to determine with certainty
that a rapid drop in the water level L2 of the suction basin is not due to a withdrawal of
the sea. To achieve this, the control system 50 may be associated not only with a system
for detecting a decrease in the suction tank water level, but also a system for detecting a
30 decrease in the level of the sea. Each detection system, comprising for example water
sensors 28 at different heights for measuring the water level, sends data 29 to an analysis
system associated with the control system 50. The analysis system is intended to
determine if the water level in the suction tank 2 is dropping in a manner defined
beforehand as abnormal and if the level of the sea has not dropped abnormally. If both
32
conditions are true, it is almost certain that the suction tunnel or tunnels have suffered a
critical collapse. The control system 50 then sends a trigger command 59 to a trigger
device 70 to actuate opening obstructing device 19, for example by pulling a cable 71 to
unlock a locking system that keeps obstructing device 19 closed. The trigger command
59 may also initiate switching from the production pumps of the pumping station to 5 the
backup pumps. As represented in FIG. 25, once the obstructing device 19 is open, the
backup tunnel 31 supplies water to the suction basin 2 and the water level L2 rises to
stabilize at more or less the level L1 of the sea. One will note that the water duct 86
formed by the backup tunnel 31 may be lower than the representation shown in FIG. 25,
10 and may for example be located at the bottom of the reserve basin in the same manner as
water duct 85.
FIG. 26, as well as FIG. 27, FIG. 28, and FIG. 29, represent different
positions of a same obstructing device 19 and are discussed together. The obstructing
device 19 shown is an example embodiment of a non-autonomous closing device which
15 can be used in the water supply system of the water intake installation of FIG. 25. In FIG.
26 and FIG. 28, the obstructing device 19 is represented in its closed position. The device
comprises an obstructing member 90 in the form of a generally planar sealing panel that
is pivotable about a pivot shaft 91. The panel 90 closes off the water duct 86 formed in a
face of the dam wall 80. The closed position is maintained by a locking system
20 comprising brackets 82 attached to the wall 80 and a locking bar 72 inserted between the
brackets 82 and a free end portion of the panel 90. The locking bar 72 is connected to at
least one cable 71 which can be pulled by a trigger device 70 as described above. Rollers
73 may be provided on either side of the locking bar 72 to facilitate displacement of the
bar when unlocking the device.
25 As represented in FIG. 27 and FIG. 29, actuation of a cable 71 pulls the
locking bar 72 upward so that it no longer prevents the sealing panel 90 from pivoting
under the effect of the differential water pressure applied on the face of the panel on the
reserve basin 20 side. The panel 90 is designed to pivot at least 90° in order to completely
unobstruct the water duct 86 formed by the backup tunnel. As represented in FIG. 30, it
30 may be arranged that the pivot shaft 91 of the sealing panel 90 is formed by a bar 99
having a ridge along its length, for example a ridge having an oval profile, the bar 99
pressing against a concave surface of a mounting member 81 parallel to the bar 99 and
fixed to the wall 80. The contours of said ridge of the bar 99 and of the concave surface
33
of the mounting member 81 are shaped to allow the panel to pivot at least 90° without
excessive jamming or friction.
In FIG. 31, another embodiment of a water intake installation similar to that of
FIG. 20 exclusively uses non-autonomous obstructing devices 19, meaning devices
which are only opened by a trigger device. The control system 50 is adapted to 5 control
the opening of each obstructing device 19 individually, and is associated with systems for
detecting a water level decrease in the suction basin 2 and in the reserve basin 20 using
sensors 28 that detect the presence of water. An obstructing device 19 may open
irreversibly, meaning as was the case for the device 19 described above that it is not
10 possible to close the obstructing member 90 without performing a specific operation once
open. It is also possible for an obstructing device 19 to open reversibly, as is the case for
example for a butterfly valve or a gate valve.
If there is an abnormal drop in the water level L2 in the suction basin, the first
obstructing device 19, located between the suction basin 2 and the reserve basin 20, is
15 triggered open while the second obstructing device 19 which blocks the backup tunnel 30
remains closed. The trigger command 59 also causes a switch from the production pumps
of the pumping station to the backup pumps. The cross-sectional area of the water duct
opened by the first obstructing device 19 is intended to be small enough that the water
level L3 in the reserve basin 20 does not drop too quickly, but must allow sufficient flow,
20 for example between 5 m3 and 15 m3 per second, so that while the production pumps are
shut down the water level L2 in the suction basin 2 remains only slightly below the mouth
E7 of a passage 7 connecting the suction basin to the suction tunnel 3. The volume of
water in the storage basin 20 is intended to be enough so that, if the abnormal drop in
level L2 is due to a withdrawal of the sea, the supply of water to the backup pumps is
25 ensured until the sea returns to above its lowest tide level LL, and the water level in the
reserve basin 20 remains above the level L4 that triggers the second obstructing device
19. The reserve basin 20 is covered by a cover device 25' provided with at least one
calibrated opening 27, in particular in the case of an obstructing device 19 that opens
non-reversibly, to prevent the reserve basin from overflowing and flooding the plant in
30 case of a tsunami.
If the abnormal drop in level L2 is due to a critical collapse in the suction
tunnel or tunnels 3, the water level in the reserve basin 20 falls relatively slowly until it
reaches the level L4 that triggers the second obstructing device 19, and the system for
detecting a dropping water level in the reserve basin 20 issues a trigger command 59 to
34
open the second obstructing device. As a precaution, it is possible to order the second
obstructing device to open before level L4 is reached, once it is certain that there has been
a critical collapse in a tunnel 3. The reserve basin is then supplied with water by the
backup tunnel 30. The water level L2 in the suction basin 2 and the water level L3 in the
reserve basin 20 climb back up to substantially the level L1 of the sea. The operation 5 on of
the pumping station of the nuclear power plant in safe mode is thus ensured, even in the
case of another tsunami event.
As an alternative to the above embodiment, it is also possible to connect the
backup tunnel 30 to the suction basin 2 directly. The opening of the second obstructing
10 device 19 associated with the backup tunnel 30 would then be ordered once it is certain
that the suction tunnel or tunnels 3 are more or less blocked. In addition, a nonautonomous
obstructing device such as the obstructing device 19 described above with
reference to figures 26-30 may be used in place of an autonomous obstructing device in a
water supply system with no reserve basin, for example the water supply system
15 described above in reference to FIG. 17, instead of the valve device 9. In this case, if the
obstructing device 19 must be opened at some point, the device must be returned to the
closed position before the production pumps are restarted once the suction tunnel or
tunnels 3 are operational, to avoid the water coming from a suction tunnel being heated
by the water coming from a backup tunnel 30.
20 A water intake installation according to the invention can be intended for
equipping a nuclear power plant separated from the sea by land unsuitable for
construction or by a wide strip of dunes or other irregularities that descend in the inland
direction, to mean sea level or below. It is understood that a suction basin of the
installation must be shaped so that the basin floor is below mean sea level and at least
25 several meters below the lowest tides for bodies of water having tides. Depending on the
suitability for construction and/or the topology of the land along the coast, it is possible
to construct the nuclear power plant at a site some distance from the shore, for example
up to about five kilometers away, taking into consideration the increased construction
costs of a suction tunnel for an installation with a tunnel of such length.
30 If the coastline may experience exceptional tidal waves such as tsunamis, a
nuclear power plant having a water intake installation such as one of the installations
described above with reference to figures 17 to 31 can be installed away from the
shoreline, lengthening each suction tunnel and each backup tunnel accordingly. In other
cases, where there is no such risk of tidal waves, a water intake installation as described
35
above with reference to FIG. 17 but without the cover device for the suction basin may be
used.
For reasons concerning the construction costs and maintenance of the water
intake installation, or for safety reasons in areas of seismic activity, it may be
advantageous to dispense with a backup tunnel for such a plant established at a distanc5 e
from the shoreline, as long as there is an auxiliary source of water such as a river or lake
for example. In such cases, an emergency water reserve may be provided, comprising a
reserve basin which can supply water to the suction basin of the installation by a system
for supplying additional water as described above.
10 As represented in FIG. 32, such an embodiment of a water intake installation
according to the invention, intended for a nuclear power plant separated from the
shoreline by a strip of land Z unsuitable for construction, comprises a reserve basin 20
which can be placed in communication with the suction basin 2 via a water duct 86
formed in a wall 80 separating the two basins. The water duct 86 here is closed off by a
15 non-autonomous obstructing device 19, controlled by a control system 50 associated with
a system for detecting a decrease in the suction basin water level. Alternatively, an
autonomous obstructing device may be used such as one of the passively activated
obstructing devices 9, 16, 17, and 18 described above. Regardless of the type of
obstructing device, the device must open when there is an abnormal drop in the water
20 level L2 in the suction basin, and at the latest when the water level L2 has dropped below
the lowest tide level L2L down to the predetermined trigger level L2V.
In the embodiment represented, water sensors 28 measure the rate of change
of the water level. If the level is dropping at a rate exceeding a predetermined threshold
greater than the highest known normal rate of change in the tide level, this event is
25 characteristic of an abnormal condition indicating either an obstruction or blocking of the
suction tunnel or tunnels 3 or an abnormal withdrawal of the sea. Once the abnormal
condition is detected, the control system 50 sends a trigger command 59 to a trigger
device, not shown in the figure, to actuate the opening of the obstructing device 19. The
control system 50 also controls the shutdown of electricity production by the reactor unit
30 or units associated with the suction basin 2, and the switch from the normal production
pumps of the pumping station 10 to the backup pumps.
In a situation of normal production of electricity by the plant as represented in
FIG. 32, the obstructing device 19 closes off the water duct 86 and thus prevents the
water in the suction basin from being heated by the water in the reserve basin when the
36
latter is warmer, especially in summer. The water level L3 in the storage basin 20 is kept
relatively constant and close to completely filling the basin, for example at a height
exceeding the highest tide level LH, so that in case of heavy rainfall the surplus water in
the reserve basin overflows to the suction basin 2 where the level L2 is lower. The
volume of water in the reserve basin is intended to be sufficient to supply the bac5 kup
pumps for a predetermined emergency period after the production pumps have been shut
down, for example at least four hours.
During the predefined emergency period, and according to a set procedure,
arrangements are quickly made to supply water to the reserve basin, or to the suction
10 basin directly, by an auxiliary water source such as a river 5'. The average flow of water
that can be drawn from the auxiliary source must be greater than or equal to the pumping
rate of the backup pumps. For example, taking enough water to ensure an average flow
rate of at least 5 m3 per second of water is usually sufficient in most nuclear power plants
to meet the needs of a pumping station of a reactor unit which has stopped producing
15 electricity.
The water can be drawn from the river 5' for example using an auxiliary
pumping station 10' located at the edge of the reserve basin 20 and connected to the river
5' by underground piping. The pumps of the auxiliary pumping station 10 are
advantageously started up shortly after the obstructing device 19 is opened, in order to
20 maintain in the reserve basin 20 a level L3 that is close to the fill level of the basin. In this
manner, even if a long term problem arises with drawing water from the river 5', for
example a failure in the auxiliary pumping station 10', the plant personnel has a period of
several hours to take appropriate measures to restore an adequate water supply for the
backup pumps.

Claims
1/ Water intake installation for at least one heat exchanger (13)-based cooling
circuit (11) of a nuclear power plant (1), comprising:
a suction basin (2) from which at least one pumping station (10) of the plant
draws water in order to circulate it within one said cooling circuit (11); a5 nd
at least one suction tunnel (3) connected to at least one main water intake (51,
52) submerged in a body of water (5), said suction tunnel (3) supplying the suction basin
(2) with water so as to maintain a water level (L2) in the suction basin (2) that is
sufficient for the operation of said at least one pumping station (10);
10 characterized in that it further comprises a system for supplying additional
water distinct from said at least one suction tunnel (3) and capable of supplying water to
the suction basin (2) from at least one emergency water reserve (60, 5, 20), said system
for supplying additional water comprising at least one water duct (65, 30, 31, 85, 86)
connecting the suction basin (2) to said emergency water reserve (60, 5, 20) and an
15 obstructing device (9, 16, 17, 18, 19) closing off said water duct, the obstructing device
being able to open said water duct at least partially if the water level in the suction basin
(2) drops in a manner defined beforehand as abnormal, so that the suction basin (2) is
supplied with water by said system for supplying additional water if the water supplied
by said at least one suction tunnel (3) becomes insufficient.
20 2/ Water intake installation according to claim 1, wherein said body of water
(5) constitutes one said emergency water reserve.
3/ Water intake installation according to claim 2, wherein said body of water
(5) is a sea, and said system for supplying additional water (620, 65, 9) is arranged
between the suction basin (2) and a portion (60) of a channel (6) which communicates
25 with the sea (5).
4/ Water intake installation according to claim 2, wherein said system for
supplying additional water comprises a backup tunnel (30) connected to at least one
backup water intake (15) submerged in said body of water (5), said backup water intake
(15) being placed at a height (HE) at least ten meters above one said main water intake
30 (51).
5/ Water intake installation according to claim 1 or claim 4, wherein one said
at least one emergency water reserve comprises a reserve basin (20) containing a volume
38
of water which remains substantially unchanged when water is being supplied normally
to the suction basin (2) by said at least one suction tunnel (3).
6/ Water intake installation according to any one of claims 1 to 5, wherein
said at least one main water intake (51, 52) is placed at a certain depth (H) relative to a
mean reference level (L0) of said body of water (5), said depth (H) being determined 5 d such
that the water flowing into the suction basin (2) has, during at least one period of the
year, a maximum temperature at least 4ºC lower than the maximum temperature of the
water at the surface of said body of water (5).
7/ Water intake installation according to any one of claims 1 to 6, wherein
10 said obstructing device (9, 16, 17, 18, 19) comprises an obstructing member (90, 90') able
to pivot about a pivot shaft (91, 91', 98) in order to open said water duct (65, 30, 31, 85,
86).
8/ Water intake installation according to claim 7, wherein said obstructing
device (9, 16, 17, 18) is adapted so that the pivoting of said obstructing member (90, 90')
15 occurs autonomously according to a drop in the water level (L2) in the suction basin (2).
9/ Water intake installation according to claim 7 or 8, wherein the pivoting of
said obstructing member (90, 90') is actuated by a trigger device (70, 71) connected to a
control system (50) able to generate a trigger command (59) for the trigger device, the
control system (50) being associated with an analysis system receiving data (29) provided
20 by a device (28) for measuring the water level (L2) in the suction basin (2), said analysis
system being able to determine whether the water level (L2) in the suction basin (2) is
dropping in a manner defined beforehand as abnormal.
10/ Water intake installation according to claim 9 in combination with claim
8, wherein said trigger device (70, 71) is adapted to allow the pivoting of said obstructing
25 member (90, 90') to be performed autonomously by said obstructing device (9, 16, 17,
18) if the trigger device (70, 71) does not perform its function.
11/ Water intake installation according to claim 8 or 10, wherein said
obstructing member (90) pivots to open said water duct (65, 30, 31, 85) when a height
difference (Δh) between the water level (L1, L3) in the emergency water reserve (60, 5,
30 20) and the water level (L2) in the suction basin (2) exceeds a predetermined threshold
(ΔhV).
12/ Water intake installation according to any one of claims 8 to 11, wherein
said obstructing device (9, 17, 18) comprises a counterweight means (92, 93, 94, 97)
39
arranged on a side opposite the obstructing member (90, 90') relative to said pivot shaft
(91, 91'), said counterweight means comprising a main counterweight member (92, 97)
located at a fixed distanced from said pivot shaft (91, 91'), and said main counterweight
member (92, 97) weighing between 80% and 200% of the weight of said obstructing
member (90, 90')5 .
13/ Water intake installation according to any one of claims 8 to 12, wherein
said obstructing member (16, 17, 18) comprises a float device (96, 97, 98) arranged so
that it is fully submerged in water when water is being supplied normally by said at least
one suction tunnel (3) and so that it is at least partially exposed if the water level (L2) in
10 the suction basin (2) falls below a predetermined level (L2L) of lowest tide to reach a
predetermined trigger level (L2V), said float device (96, 97, 98) being adapted to cause
said obstructing member (90, 90') to pivot when said trigger level (L2V) is reached.
14/ Nuclear power plant comprising a water intake installation according to
claim 1, wherein the suction basin (2) is covered by a device forming a substantially
15 watertight cover (25), and at least one calibrated opening (26) is made in the cover device
or nearby to allow a limited flow of water (Ip) to outside the suction basin (2) if the
suction basin (2) overflows due to an unusual rise in said body of water (5), the nuclear
power plant further comprising at least one discharge shaft (14) feeding water to an
outflow tunnel (4), said discharge shaft (14) also being provided with a cover device
20 having at least one calibrated opening to allow a limited flow of water to the outside in
case of overflow of the discharge shaft (14).
15/ Nuclear power plant according to claim 14, wherein one said emergency
water reserve comprises a reserve basin (20) having its top open to the outside and
containing a volume of water that remains substantially unchanged when water is being
25 supplied normally to the suction basin (2) by said at least one suction tunnel (3), and
wherein said at least one calibrated opening (26) leads to said reserve basin (20) to allow
collecting said limited flow of water (Ip) therein.