CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of priority to U.S. Provisional Application No.
62/061,089 filed October 7, 2014, the entirety of which is incorporated herein by reference.
BACKGROUND
[0002] The present invention generally relates to storage of nuclear fuel assemblies, and more
particularly to an improved spent fuel pool for wet storage of such fuel assemblies.
[0003] A spent fuel pool (sometimes, two or more) is an integral part of every nuclear power
plant. At certain sites, standalone wet storage facilities have also been built to provide additional
storage capacity for the excess fuel discharged by the reactors. An autonomous wet storage
facility that serves one or more reactor units is sometimes referred to by the acronym AFR
meaning "Away-from-Reactor." While most countries have added to their in-plant used fuel
storage capacity by building dry storage facilities, the French nuclear program has been the most
notable user of AFR storage.
[0004] As its name implies, the spent fuel pool (SFP) stores the fuel irradiated in the plant's
reactor in a deep pool of water. The pool is typically 40 feet deep with upright Fuel Racks
positioned on its bottom slab. Under normal storage conditions, there is at least 25 feet of water
cover on top of the fuel to ensure that the dose at the pool deck level is acceptably low for the
plant workers. Fuel pools at most (but not all) nuclear plants are at grade level, which is
desirable from the standpoint of structural capacity of the reinforced concrete structure that
forms the deep pond of water. To ensure that the pool's water does not seep out through the
voids and discontinuities in the pool slab or walls, fuel pools in nuclear plants built since the
1970s have always been lined with a thin single-layer stainless steel liner (typically in the range
of 3/16 inch to 5/16 inch thick). The liner is made up of sheets of stainless steel (typically
ASTM 240 - 304 or 304L) seam welded along their contiguous edges to form an impervious
barrier between the pool's water and the undergirding concrete. In most cases, the welded liner
seams are monitored for their integrity by locating a leak chase channel underneath them (see,
e.g. FIG. 1). The leak chase channels' detection ability, however, is limited to welded regions
only; the base metal area of the liner beyond the seams remains un-surveilled.
[0005] The liners have generally served reliably at most nuclear plants, but isolated cases of
water seepage of pool water have been reported. Because the pool's water bears radioactive
contaminants (most of it carried by the crud deposited on the fuel during its "burn" in the
reactor), leaching out of the pool water to the plant's substrate, and possibly to the underground
water, is evidently inimical to public health and safety. To reduce the probability of pool water
reaching the ground water, the local environment and hence some AFR pools have adopted the
pool-in-pool design wherein the fuel pool is enclosed by a secondary outer pool filled with clean
water. In the dual-pool design, any leakage of water from the contaminated pool will occur into
the outer pool, which serves as the barrier against ground water contamination. The dual pool
design, however, has several unattractive aspects, viz.: (1) the structural capacity of the storage
system is adversely affected by two reinforced concrete containers separated from each other
except for springs and dampers that secure their spacing; (2) there is a possibility that the outer
pool may leak along with the inner pool, defeating both barriers and allowing for contaminated
water to reach the external environment; and (3) the dual-pool design significantly increases the
cost of the storage system.
[0006] Prompted by the deficiencies in the present designs, a novel design of a spent nuclear fuel
pool that would guarantee complete confinement of pool's water and monitoring of the entire
liner structure including seams and base metal areas is desirable.
SUMMARY
[0007] The present invention provides an environmentally sequestered spent fuel pool system
having a dual impervious liner system and leak detection/evacuation system configured to collect
and identify leakage in the interstitial space formed between the liners. The internal cavity of the
pool has not one but two liners layered on top of each other, each providing an independent
barrier to the out-migration (emigration) of pool water. Each liner encompasses the entire extent
of the water occupied space and further extends above the pool's "high water level." The top of
the pool may be equipped with a thick embedment plate (preferably 2 inches thick minimum in
one non-limiting embodiment) that circumscribes the perimeter of the pool cavity at its top
extremity along the operating deck of the pool. Each liner may be independently welded to the
top embedment plate. The top embedment plate features at least one telltale hole, which
provides direct communication with the interstitial space between the two liner layers. In one
implementation, a vapor extraction system comprising a vacuum pump downstream of a oneway
valve is used to draw down the pressure in the inter-liner space through the telltale hole to a
relatively high state of vacuum. The absolute pressure in the inter-liner space ("set pressure")
preferably should be such that the pool's bulk water temperature is above the boiling temperature
of water at the set pressure as further described herein.
[0008] In one embodiment, an environmentally sequestered nuclear spent fuel pool system
includes: a base slab; a plurality of vertical sidewalls extending upwards from and adjoining the
base slab, the sidewalls forming a perimeter; a cavity collectively defined by the sidewalls and
base slab that holds pool water; a pool liner system comprising an outer liner adjacent the
sidewalls, an inner liner adjacent the outer liner and wetted by the pool water, and an interstitial
space formed between the liners; a top embedment plate circumscribing the perimeter of the pool
at a top surface of the sidewalls adjoining the cavity; and the inner and outer sidewalls having
top terminal ends sealably attached to the embedment plate.
[0009] In another embodiment, an environmentally sequestered nuclear spent fuel pool with
leakage detection system includes: a base slab; a plurality of vertical sidewalls extending
upwards from and adjoining the base slab, the sidewalls forming a perimeter; a cavity
collectively defined by the sidewalls and base slab that holds pool water; at least one fuel storage
rack disposed in the cavity that holds a nuclear spent fuel assembly containing nuclear fuel rods
that heat the pool water; a pool liner system comprising an outer liner adjacent the sidewalls and
base slab, an inner liner adjacent the outer liner and wetted by the pool water, and an interstitial
space formed between the liners; a top embedment plate circumscribing the perimeter of the
pool, the embedment plate embedded in the sidewalls adjoining the cavity; the inner and outer
liners attached to the top embedment plate; a flow plenum formed along the sidewalls that is in
fluid communication with the interstitial space; and a vacuum pump fluidly coupled to the flow
plenum, the vacuum pump operable to evacuate the interstitial space to a negative set pressure
below atmospheric pressure.
[0010] A method for detecting leakage from a nuclear spent fuel pool is provided. The method
includes: providing a spent fuel pool comprising a plurality of sidewalls, a base slab, a cavity
containing cooling water, and a liner system disposed in the cavity including an outer liner, an
inner liner, and an interstitial space between the liner; placing a fuel storage rack in the pool;
inserting at least one nuclear fuel assembly into the storage rack, the fuel assembly including a
plurality of spent nuclear fuel rods; heating the cooling water in the pool to a first temperature
from decay heat generated by the spent nuclear fuel rods; drawing a vacuum in the interstitial
space with a vacuum pump to a negative pressure having a corresponding boiling point
temperature less than the first temperature; collecting cooling water leaking from the pool
through the liner system in the interstitial space; converting the leaking cooling water into vapor
via boiling; and extracting the vapor from the interstitial space using the vacuum pump; wherein
the presence of vapor in the interstitial space allows detection of a liner breach. The method may
further include discharging the vapor extracted by the vacuum pump through a charcoal filter to
remove contaminants. The method may further include: monitoring a pressure in the interstitial
space; detecting a first pressure in the interstitial space prior to collecting cooling water leaking
from the pool through the liner system in the interstitial space; and detecting a second pressure
higher than the first pressure after collecting cooling water leaking from the pool through the
liner system in the interstitial space; wherein the second pressure is associated with a cooling
water leakage condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The features of the exemplary embodiments will be described with reference to the
following drawings where like elements are labeled similarly, and in which:
[0012] FIG. 1 is a cross sectional diagram of a known approach used to monitor the integrity of
weld seams for leakage in a single spent fuel pool liner system;
[0013] FIG. 2 is a side cross-sectional view of an environmentally sequestered nuclear spent fuel
pool having a dual liner and leakage collection and monitoring system according to the present
disclosure;
[0014] FIG. 3 is a top plan view of the fuel pool with liner and leakage collection/monitoring
system of FIG. 2;
[0015] FIG. 4 is a detail taken from FIG. 2 showing a bottom joint of the liner system at the
intersection of liners from the sidewalls and base slab of the fuel pool;
[0016] FIG. 5 is a detail taken from FIG. 2 showing a top joint of the liner system at the terminal
top ends of the sidewall liners;
[0017] FIG. 6 is a perspective view of an example nuclear fuel assembly containing spent
nuclear fuel rods; and
[0018] FIG. 7 is a schematic diagram of a vacuum leakage collection and monitoring system
according to the present disclosure.
[0019] All drawings are schematic and not necessarily to scale. Parts shown and/or given a
reference numerical designation in one figure may be considered to be the same parts where they
appear in other figures without a numerical designation for brevity unless specifically labeled
with a different part number and described herein. References herein to a figure number (e.g.
FIG. 1) shall be construed to be a reference to all subpart figures in the group (e.g. FIGS. 1A, IB,
etc.) unless otherwise indicated.
DETAILED DESCRIPTION
[0020] The features and benefits of the invention are illustrated and described herein by
reference to exemplary embodiments. This description of exemplary embodiments is intended to
be read in connection with the accompanying drawings, which are to be considered part of the
entire written description. Accordingly, the disclosure expressly should not be limited to such
exemplary embodiments illustrating some possible non-limiting combination of features that
may exist alone or in other combinations of features.
[0021] In the description of embodiments disclosed herein, any reference to direction or
orientation is merely intended for convenience of description and is not intended in any way to
limit the scope of the present invention. Relative terms such as "lower," "upper," "horizontal,"
"vertical,", "above," "below," "up," "down," "top" and "bottom" as well as derivative thereof
(e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the
orientation as then described or as shown in the drawing under discussion. These relative terms
are for convenience of description only and do not require that the apparatus be constructed or
operated in a particular orientation. Terms such as "attached," "affixed," "connected,"
"coupled," "interconnected," and similar refer to a relationship wherein structures are secured or
attached to one another either directly or indirectly through intervening structures, as well as
both movable or rigid attachments or relationships, unless expressly described otherwise.
[0022] Referring to FIGS. 2-6, an environmentally sequestered spent fuel pool system includes a
spent fuel pool 40 comprising a plurality of vertical sidewalls 4 1 rising upwards from an
adjoining substantially horizontal base wall or slab 42 (recognizing that some slope may
intentionally be provided in the upper surface of the bottom wall for drainage toward a low point
if the pool is to be emptied and rinsed/decontaminated at some time and due to installation
tolerances). The base slab 42 and sidewalls 4 1 may be formed of reinforced concrete in one nonlimiting
embodiment. The fuel pool base slab 42 may be formed in and rest on the soil subgrade
26 the top surface of which defines grade G. In this embodiment illustrated in the present
application, the sidewalls are elevated above grade. In other possible embodiments
contemplated, the base slab 42 and sidewalls 4 1 may alternatively be buried in sub-grade 26
which surrounds the outer surfaces of the sidewalls. Either arrangement may be used and does
not limit of the invention.
[0023] In one embodiment, the spent fuel pool 40 may have a rectilinear shape in top plan view.
Four sidewalls 4 1 may be provided in which the pool has an elongated rectangular shape (in top
plan view) with two longer opposing sidewalls and two shorter opposing sidewalls (e.g. end
walls). Other configurations of the fuel pool 40 are possible such as square shapes, other
polygonal shapes, and non-polygonal shapes.
[0024] The sidewalls 4 1 and base slab 42 of the spent fuel pool 40 define a cavity 43 configured
to hold cooling pool water W and a plurality of submerged nuclear spent fuel assembly storage
racks 27 holding fuel bundles or assemblies 28 each containing multiple individual nuclear spent
fuel rods. The storage racks 27 are disposed on the base slab 42 in typical fashion. With
continuing reference to FIGS. 1-6, the spent fuel pool 40 extends from an operating deck 22
surrounding the spent fuel pool 40 downwards to a sufficient depth Dl to submerge the fuel
assemblies 28 (see, e.g. FIG. 6) beneath the surface level S of the pool water W for proper
radiation shielding purposes. In one implementation, the fuel pool may have a depth such that at
least 10 feet of water is present above the top of the fuel assembly.
[0025] A nuclear fuel assembly storage rack 27 is shown in FIGS. 2 and 3, and further described
in commonly assigned U.S. Patent Application No. 14/367,705 filed June 20, 1014, which is
incorporated herein by reference in its entirety. The storage rack 27 contains a plurality of
vertically elongated individual cells as shown each configured for holding a fuel assembly 28
comprising a plurality of individual nuclear fuel rods. An elongated fuel assembly 28 is shown
in FIG. 6 holding multiple fuel rods 28a and further described in commonly assigned U.S. Patent
Application No. 14/413,807 filed July 9, 2013, which is incorporated herein by reference in its
entirety. Typical fuel assemblies 28 for a pressurized water reactor (PWR) may each hold over
150 fuel rods in 10x10 to 17x17 fuel rod grid arrays per assembly. The assemblies may typically
be on the order of approximately 14 feet high weighing about 1400-1500 pounds each.
[0026] The substantially horizontal operating deck 22 that circumscribes the sidewalls 4 1 and
pool 40 on all sides in one embodiment may be formed of steel and/or reinforced concrete. The
surface level of pool water W (i.e. liquid coolant) in the pool 40 may be spaced below the
operating deck 22 by a sufficient amount to prevent spillage onto the deck during fuel assembly
loading or unloading operations and to account to seismic event. In one non-limiting
embodiment, for example, the surface of the operating deck 22 may be at least 5 feet above the
maximum 100 year flood level for the site in one embodiment. The spent fuel pool 40 extending
below the operating deck level may be approximately 40 feet or more deep (e.g. 42 feet in one
embodiment). The fuel pool is long enough to accommodate as many spent fuel assemblies as
required. In one embodiment, the fuel pool 40 may be about 60 feet wide. There is sufficient
operating deck space around the pool to provide space for the work crew and for staging
necessary tools and equipment for the facility's maintenance. There may be no penetrations in
the spent fuel pool 40 within the bottom 30 feet of depth to prevent accidental draining of water
and uncovering of the spent fuel.
[0027] According to one aspect of the invention, a spent fuel pool liner system comprising a
double liner is provided to minimize the risk of pool water leakage to the environment. The liner
system is further designed to accommodate cooling water leakage collection and
detection/monitoring to indicate a leakage condition caused by a breach in the integrity of the
liner system.
[0028] The liner system comprises a first outer liner 60 separated from a second inner liner 6 1 by
an interstitial space 62 formed between the liners. An outside surface of liner 60 is disposed
against or at least proximate to the inner surface 63 of the fuel pool sidewalls 4 1 and opposing
inside surface is disposed proximate to the interstitial space 62 and outside surface of liner 61.
The inside surface of liner 6 1 is contacted and wetted by the fuel pool water W. It bears noting
that placement of liner 60 against liner 6 1 without spacers therebetween provides a natural
interstitial space of sufficient width to allow the space and any pool leakage there-into to be
evacuated by a vacuum system, as further described herein. The natural surface roughness of the
materials used to construct the liners and slight variations in flatness provides the needed space
or gap between the liners. In other embodiments contemplated, however, metallic or nonmetallic
spacers may be provided which are distributed in the interstitial space 62 between the
liners if desired.
[0029] The liners 60, 6 1 may be made of any suitable metal which is preferably resistant to
corrosion, including without limitation stainless steel, aluminum, or other. In some
embodiments, each liner may be comprised of multiple substantially flat metal plates which are
seal welded together along their peripheral edges to form a continuous liner system
encapsulating the sidewalls 4 1 and base slab 42 of the spent fuel pool 40.
[0030] The inner and outer liners 61, 60 may have the same or different thicknesses (measured
horizontally or vertically between major opposing surfaces of the liners depending on the
position of the liners). In one embodiment, the thicknesses may be the same. In some instances,
however, it may be preferable that the inner liner 6 1 be thicker than the outer liner 60 for
potential impact resistant when initially loading empty fuel storage racks 27 into the spent fuel
pool 40.
[0031] The outer and inner liners 60, 6 1 (with interstitial space therebetween) extend along the
vertical sidewalls 4 1 of the spent fuel pool 40 and completely across the horizontal base slab 42
in one embodiment to completely cover the wetted surface area of the pool. This forms
horizontal sections 60b, 61b and vertical sections 60a, 61a of the liners 60, 6 1 to provide an
impervious barrier to out-leakage of pool water W from spent fuel pool 40. The horizontal
sections of liners 60b, 61b on the base slab 42 may be joined to the vertical sections 60a, 61a
along the sidewalls 4 1 of the pool 40 by welding. The detail in FIG. 4 shows one or many
possible constructions of the bottom liner joint 64 comprising the use of seal welds 65 (e.g.
illustrated fillet welds or other) to seal sections 60a to 60b along their respective terminal edges
and sections 61a to 61b along their respective terminal edges as shown. Preferably, the joint 64
is configured and arranged to fluidly connect the horizontal interstitial space 64 between
horizontal liner sections 60b, 61b to the vertical interstitial space 64 between vertical liner
sections 60a, 61a for reasons explained elsewhere herein.
[0032] The top liner joint 65 in one non-limiting embodiment between the top terminal edges
60c, 61c of the vertical liner sections 60a, 61a is shown in the detail of FIG. 5. The top of the
spent fuel pool 40 is equipped with a substantially thick metal embedment plate 70 which
circumscribes the entire perimeter of the fuel pool. The embedment plate 70 may be continuous
in one embodiment and extends horizontally along the entire inner surface 63 of the sidewalls 4 1
at the top portion of the sidewalls. The embedment plate 70 has an exposed portion of the inner
vertical side facing the pool which extends above the top terminal ends 60c, 61c of the inner and
outer liners 60, 61. The opposing outer vertical side of the plate 70 is embedded entirely into the
sidewalls 41. A top surface 7 1 of the embedment plate 70 that faces upwards may be
substantially flush with the top surface 44 of the sidewalls 4 1 to form a smooth transition
therebetween. In other possible implementations, the top surface 7 1 may extend above the top
surface 44 of the sidewalls. The embedment plate 70 extends horizontal outward from the fuel
pool 40 for a distance into and less than the lateral width of the sidewalls 4 1 as shown.
[0033] The embedment plate 70 has a horizontal thickness greater than the horizontal thickness
of the inner liner 61, outer liner 60, and in some embodiments both the inner and outer liners
combined.
[0034] The top embedment plate 70 is embedded into the top surface 44 of the concrete
sidewalls 4 1 has a sufficient vertical depth or height to allow the top terminal edges 60c, 61c of
liners 60, 6 1 (i.e. sections 60a and 61a respectively) to be permanently joined to the plate. The
top terminal edges of liners 60, 6 1 terminate at distances D2 and Dl respectively below a top
surface 7 1 of the embedment plate 70 (which in one embodiment may be flush with the top
surface of the pool sidewalls 4 1 as shown). Distance Dl is less than D2 such that the outer liner
60 is vertical shorter in height than the inner liner 61. In one embodiment, the embedment plate
70 has a bottom end which terminates below the top terminal edges 60c, 61c of the liners 60, 6 1
to facilitate for welding the liners to the plate.
[0035] In various embodiments, the embedment plate 70 may be formed of a suitable corrosion
resistant metal such as stainless steel, aluminum, or another metal which preferably is compatible
for welding to the metal used to construct the outer and inner pool liners 60, 6 1 without requiring
dissimilar metal welding.
[0036] As best shown in FIG. 5, the top terminal edges 60c, 61c of inner and outer liners 60, 6 1
may have a vertically staggered arranged and be separately seal welded to the top embedment
plate 70 independently of each other. A seal weld 66 couples the top terminal edge 61c of liner
6 1 to the exposed portion of the inner vertical side of the embedment plate 70. A second seal
weld 67 couples the top terminal edge 60c of liner 60 also to the exposed portion of the inner
vertical side of the embedment plate 70 at a location below and spaced vertical apart from seal
weld 66. This defines a completely and hermetically sealed enclosed flow plenum 68 that
horizontal circumscribes the entire perimeter of the spent fuel pool 40 in one embodiment. The
flow plenum 68 is in fluid communication with the interstitial space 62 as shown. One vertical
side of the flow plenum is bounded by a portion of inner liner 6 1 and the opposing vertical side
of the plenum is bounded by the inner vertical side of the top embedment plate 70.
[0037] The top flow plenum 68 may be continuous or discontinuous in some embodiments.
Where discontinuous, it is preferable that a flow passageway 105 in the top embedment plate 70
be provided for each section of the separate passageways.
[0038] Seal welds 66 and 67 may be any type of suitable weld needed to seal the liners 60, 6 1 to
the top embedment plate 70. Backer plates, bars, or other similar welding accessories may be
used to make the welds as needed depending on the configuration and dimensions of the welds
used. The invention is not limited by the type of weld.
[0039] In one embodiment, the outer and inner liners 60, 6 1 are sealably attached to the spent
fuel pool 40 only at top embedment plate 70. The remaining portions of the liners below the
embedment plate may be in abutting contact with the sidewalls 4 1 and base slab 42 without
means for fixing the liners to these portions.
[0040] It bears noting that at least the inner liner 6 1 has a height which preferably is higher than
the anticipated highest water level (surface S) of the pool water W in one embodiment. If the
water level happens to exceed that for some reason, the top embedment plate 70 will be wetted
directly by the pool water and contain the fluid to prevent overflowing the pool onto the
operating deck 22.
[0041] According to another aspect of the invention, a vapor extraction or vacuum system 100 is
provided that is used to draw down the air pressure in the interstitial space between the outer and
inner liners 60, 6 1 to a relatively high state of vacuum for leakage control and/or detection. FIG.
7 is a schematic diagram of one embodiment of a vacuum system 100.
[0042] Referring to FIGS. 5 and 7, vacuum system 100 generally includes a vacuum pump 101
and a charcoal filter 102. Vacuum pump 101 may be any suitable commercially-available
electric -driven vacuum pump capable of creating a vacuum or negative pressure within the
interstitial space 62 between the pool liners 60 and 61. The vacuum pump 101 is fluidly
connected to the interstitial space 68 via a suitable flow conduit 103 which is fluidly coupled to a
telltale or flow passageway 105 extending from the top surface 7 1 of the top embedment plate 70
to the top flow plenum 68 formed between the pool liners 60 and 61. Flow conduit 103 may be
formed of any suitable metallic or non-metallic tubing or piping capable of withstanding a
vacuum. A suitably-configured fluid coupling 104 may be provided and sealed to the outlet end
of the flow passageway 105 for connecting the flow conduit 103. The inlet end of the flow
passageway penetrates the inner vertical side of top embedment plate 70 within the flow plenum
68. The flow passageway 105 and external flow conduit 103 provides a contiguous flow conduit
that fluidly couples the flow plenum 68 to the vacuum pump 101. A one-way check valve is
disposed between the flow plenum 105 and the suction inlet of the vacuum pump 101 to permit
air and/or vapor to flow in a single direction from the liner system to the pump.
[0043] The absolute pressure maintained by the vacuum system 100 in the interstitial space 62
between the liners 60, 6 1 (i.e. "set pressure") preferably should be such that the bulk water
temperature of the spent fuel pool 40 which is heated by waste decay heat generated from the
fuel rods/assemblies is above the boiling temperature of water at the set pressure. The table
below provides the boiling temperature of water at the level of vacuum in inches of mercury
(Hg) which represent some examples of set pressures that may be used. .
Pressure in inch, HgA Boiling Temp, deg F
1 79
2 101
3 115
4 125
5 133
[0044] Any significant rise in pressure would indicate potential leakage of water in the
interstitial space 62 between the liners 60, 61. Because of sub-atmospheric conditions
maintained by the vacuum pump 101 in the interstitial space, any water that may leak from the
pool into this space through the inner liner 6 1 would evaporate, causing the pressure to rise
which may be monitored and detected by a pressure sensor 104. The vacuum pump 101
preferably should be set to run and drive down the pressure in the interstitial space 62 to the "set
pressure."
[0045] In operation as one non-limiting example, if the vacuum pump 101 is operated to create a
negative pressure (vacuum) in the interstitial space 62 of 2 inches of Hg, the corresponding
boiling point of water at that negative pressure is 101 degrees Fahrenheit (degrees F) from the
above Table. If the bulk water temperature of pool water W in the spent fuel pool 40 were at any
temperature above 101 degrees F and leakage occurred through the inner pool liner 6 1 into the
interstitial space 62, the liquid leakage would immediately evaporate therein creating steam or
vapor. The vacuum pump 101 withdraws the vapor through the flow plenum 68, flow
passageway 105 in the top embedment plate 70, and flow conduit 103 (see, e.g. directional flow
arrows of the water vapor in FIGS. 5 and 7). Pressure sensor 104 disposed on the suction side of
the pump 101 would detect a corresponding rise in pressure indicative of a potential leak in the
liner system. In some embodiments, the pressure sensor 104 may be operably linked to a control
panel of a properly configured computer processor based plant monitoring system 107 which
monitors and detects the pressure measured in the interstitial space 62 between the liners on a
continuous or intermittent basis to alert operators of a potential pool leakage condition. Such
plant monitoring systems are well known in the art without further elaboration.
[0046] The extracted vapor in the exhaust or discharge from the vacuum pump 101 is routed
through a suitable filtration device 102 such as a charcoal filter or other type of filter media
before discharge to the atmosphere, thereby preventing release of any particulate contaminants to
the environment.
[0047] Advantageously, it bears noting that if leakage is detected from the spent fuel pool 40 via
the vacuum system 100, the second outer liner 60 encapsulating the fuel pool provides a
secondary barrier and line of defense to prevent direct leaking of pool water W into the
environment.
[0048] It bears noting that there is no limit to the number of vapor extraction systems including a
telltale passageway, vacuum pump, and filter combination with leakage monitoring/detection
capabilities that may be provided. In some instances, four independent systems may provide
adequate redundancy. In addition, it is also recognized that a third or even fourth layer of liner
may be added to increase the number of barriers against leakage of pool water to the
environment. A third layer in some instances may be used as a palliative measure if the leak
tightness of the first inter-liner space could not, for whatever reason, be demonstrated by a high
fidelity examination in the field such as helium spectroscopy.
[0049] While the foregoing description and drawings represent exemplary embodiments of the
present disclosure, it will be understood that various additions, modifications and substitutions
may be made therein without departing from the spirit and scope and range of equivalents of the
accompanying claims. In particular, it will be clear to those skilled in the art that the present
invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with
other elements, materials, and components, without departing from the spirit or essential
characteristics thereof. In addition, numerous variations in the methods/processes described
herein may be made within the scope of the present disclosure. One skilled in the art will further
appreciate that the embodiments may be used with many modifications of structure,
arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of
the disclosure, which are particularly adapted to specific environments and operative
requirements without departing from the principles described herein. The presently disclosed
embodiments are therefore to be considered in all respects as illustrative and not restrictive. The
appended claims should be construed broadly, to include other variants and embodiments of the
disclosure, which may be made by those skilled in the art without departing from the scope and
range of equivalents.

CLAIMS
What is claimed is:
1. An environmentally sequestered nuclear spent fuel pool system comprising:
a base slab;
a plurality of vertical sidewalls extending upwards from and adjoining the base slab, the
sidewalls forming a perimeter;
a cavity collectively defined by the sidewalls and base slab that holds pool water;
a pool liner system comprising an outer liner adjacent the sidewalls, an inner liner
adjacent the outer liner and wetted by the pool water, and an interstitial space formed between
the liners;
a top embedment plate circumscribing the perimeter of the pool at a top surface of the
sidewalls adjoining the cavity; and
the inner and outer sidewalls having top terminal ends sealably attached to the
embedment plate.
2. The spent fuel pool system according to claim 1, wherein a horizontal portion of the inner
and outer liners extend across and covers the base slab between opposing sidewalls, the
horizontal portions of the inner and outer liners and portions covering the sidewalls forming a
continuous barrier encapsulating the pool water.
3. The spent fuel pool system according to claim 1, further comprising a top flow plenum
formed at the top terminal edges of the inner and outer liners along the sidewalls, the flow
plenum in fluid communication with the interstitial space.
4. The spent fuel pool system according to claim 3, wherein the top flow plenum extends
around the entire perimeter of the spent fuel pool.
5. The spent fuel pool system according to claim 3, further comprising a flow passageway
formed through the top embedment plate that is in fluid communication with the top flow
plenum, the flow passageway having an outlet end penetrating a top surface of the top
embedment plate.
6. The spent fuel pool system according to claim 1, wherein the top embedment plate has a
horizontal thickness greater than a thickness of the inner and outer liners combined.
7. The spent fuel pool system according to claim 1, wherein the top terminal ends of the
inner and outer liners are welded separately and directly to the top embedment plate.
8. The spent fuel pool system according to claim 1, wherein the inner liner, outer liner, and
top embedment plate are made of the same metallic material.
9. The spent fuel pool system according to claim 1, further comprising at least one fuel
storage rack disposed on the base slab, the storage rack having a plurality of cells each
configured for holding a spent nuclear fuel assembly containing nuclear fuel rods.
10. An environmentally sequestered nuclear spent fuel pool with leakage detection system
comprising:
a base slab;
a plurality of vertical sidewalls extending upwards from and adjoining the base slab, the
sidewalls forming a perimeter;
a cavity collectively defined by the sidewalls and base slab that holds pool water;
at least one fuel storage rack disposed in the cavity that holds a nuclear spent fuel
assembly containing nuclear fuel rods that heat the pool water;
a pool liner system comprising an outer liner adjacent the sidewalls and base slab, an
inner liner adjacent the outer liner and wetted by the pool water, and an interstitial space formed
between the liners;
a flow plenum formed along the sidewalls that is in fluid communication with the
interstitial space; and
a vacuum pump fluidly coupled to the flow plenum, the vacuum pump operable to
evacuate the interstitial space to a negative set pressure below atmospheric pressure.
11. The spent fuel pool according to claim 10, further comprising:
a top embedment plate circumscribing the perimeter of the pool, the embedment plate
embedded in the sidewalls adjoining the cavity;
the inner and outer liners attached to the top embedment plate in staggered relationship to
form the flow plenum; and
the vacuum pump fluidly coupled to the flow plenum through the top embedment plate.
12. The spent fuel pool according to claim 11, further comprising a telltale passageway
which fluidly couples the vacuum pump to the interstitial space.
13. The spent fuel pool according to claim 12, further comprising a pressure sensor disposed
in a flow conduit fluidly coupling a suction inlet of the vacuum pump to the telltale passageway.
14. The spent fuel pool system according to claim 11, wherein top terminal ends of the inner
and outer liners are welded separately to the top embedment plate for forming the flow plenum.
15. The spent fuel pool according to claim 10, further comprising a computer processor based
plant monitoring system which monitors and detects a pressure measured in the interstitial space
between the inner and outer liners.
16. The spent fuel pool system according to claim 10, further comprising a charcoal filter
fluidly coupled to a discharge from the vacuum pump and operable to remove contaminants from
vapor collected from the interstitial space between the inner and outer liners.
17. The spent fuel pool according to claim 10, wherein top terminal ends of the inner and
outer liners terminate at a point below a top surface of the top embedment plate within the cavity.
18. A method for detecting leakage from a nuclear spent fuel pool, the method comprising:
providing a spent fuel pool comprising a plurality of sidewalls, a base slab, a cavity
containing cooling water, and a liner system disposed in the cavity including an outer liner, an
inner liner, and an interstitial space between the liner;
placing a fuel storage rack in the pool;
inserting at least one nuclear fuel assembly into the storage rack, the fuel assembly
including a plurality of spent nuclear fuel rods;
heating the cooling water in the pool to a first temperature from decay heat generated by
the spent nuclear fuel rods;
drawing a vacuum in the interstitial space with a vacuum pump to a negative pressure
having a corresponding boiling point temperature less than the first temperature;
collecting cooling water leaking from the pool through the liner system in the interstitial
space;
converting the leaking cooling water into vapor via boiling; and
extracting the vapor from the interstitial space using the vacuum pump;
wherein the presence of vapor in the interstitial space allows detection of a liner breach.
19. The method according to claim 18, further comprising discharging the vapor extracted by
the vacuum pump through a charcoal filter to remove contaminants.
20. The method according to claim 18, further comprising:
monitoring a pressure in the interstitial space;
detecting a first pressure in the interstitial space prior to collecting cooling water leaking
from the pool through the liner system in the interstitial space;
detecting a second pressure higher than the first pressure after collecting cooling water
leaking from the pool through the liner system in the interstitial space;
wherein the second pressure is associated with a cooling water leakage condition.