DESCRIPTION

METHOD OF SEARCHING FOR UNSTEADY DUST SOURCE POSITION OF DUSTFALL

TECHNICAL FIELD

[0001]
The present invention relates to a technique for searching for a source of atmospheric dustfall.

Priority is claimed on Japanese Patent Application No. 2011-108105, filed on May 13,2011, and Japanese Patent Application No. 2012-057297, filed on March 14, 2012, the contents of which are incorporated herein by reference.

BACKGROUND ART

[0002]
When a nuclear power station is damaged or destroyed in an accident, it is important to be able to keep track of radioactive dustfall diffused to the surroundings from radioactive dust generation facilities. In addition, dustfall generated from various industries, including agriculture and forestry, and from the environment, such as sand dunes, also needs to be monitored. When there are a large number of dust sources, a technique that can analyze the degree of contribution of the dust source as an influence on the "measured value of the amount of dustfall" at the evaluation point of the dustfall is important in measuring and managing such dustfall.

From this viewpoint, Patent Documents 1 to 4 disclose a technique which evaluates the amount of dust generated from a plurality of generation sources from the amount of dustfall measured at an evaluation point; that is, a technique which searches for the main source of the dustfall.

[0003]
Patent Document 1 discloses the following technique. That is, a model suitable for simulations is selected from input conditions, such as atmospheric conditions, meteorological data, and topographical data on the evaluation range of the diffusion of air pollutants. In addition, adjustment input parameters are selected from the measured values corresponding to the input conditions. Then, input data is created from the analysis conditions by the selected model and the selected adjustment input parameters and simulations are performed. The deviation between the simulation result and data for the measured value of a discharge source is calculated and the discharge source corresponding to the data in which the deviation is the minimum is estimated.

[0004]
In addition, Patent Document 2 discloses the following technique. That is, a normal emission amount which is discharged from an emission source for the period for which the concentration of a chemical substance in the atmosphere preliminarily measured by an atmosphere observation station is not abnormally high and the abnormal emission amount of chemical substance from the emission source for the period for which the concentration of the chemical substance in the atmosphere is abnormally high are obtained. Then, a solution which minimizes the sum of the square of (the normal emission amount-the abnormal emission amount) in the emission source is found to specify the emission source which causes the abnormally high concentration of the chemical substance in the atmosphere.

[0005]
Patent Document 3 discloses the following technique. That is, the amount of scattered dust and the wind direction are measured at predetermined time intervals for an appropriate period of time at a plurality of arbitrary measurement points A, B, and C in the vicinity of a plurality of dust generating points. Then, the average amount of scattered dust in each wind direction is calculated at each measurement point from the obtained amount of scattered dust and the obtained wind. Then, a plurality of wind directions in which the average amount of scattered dust is large is plotted, centering on each measurement point, on a map including the plurality of dust generating points and the plurality of measurement points. Then, the dust-generating point disposed at the intersection of the wind directions from the created measurement points, or the dust-generating point in the wind direction on the map when the wind directions from each measurement point are substantially aligned with each other is specified as the source of the scattered dust.

[0006]
Patent Document 4 discloses the following technique. That is, one or more independent-type portable multi-sensing terminal units which measure multiple items of atmospheric pollution conditions are remotely controlled through a wireless or wired network to measure the multiple items of atmospheric pollution conditions, and the measured data is collected and displayed.

[0007]
When the concentration of dustfall at the evaluation point is evaluated from the amount of dust generated from the generation source, a plume equation is generally used. The plume equation (plume model) is one type of diffusion formula and represents advection and diffusion with smoke. For example, when the wind, a diffusion coefficient, and the amount of emission are constant, a steady solution of a concentration distribution is found. The diffusion formula is a theoretical calculation formula that estimates the advection and diffusion of containments which are discharged from the generation source to the atmosphere under constant weather conditions and predicts the concentration of the containments in the environment (extracted from p. 196 of Suspended Particulate Matter Pollution Forecast Manual edited by Pollution Control Division, Nature Conservation Bureau, Ministry of the Environment, Toyokan Publishing Co., Ltd. (Tokyo), 1997). Patent Document 5 discloses a standard plume equation (1) as the atmosphere diffusion model of gas from a point generation source which is not absorbed from the surface of the ground: (Expression (1))

[0008]
Here, the meaning of symbols in Expression (1) is as follows. The meaning of the symbols holds for the following description. The following symbols are all based on the SI unit system:

x, y, z: three-dimensional rectangular coordinates of an evaluation point (a gas source is the origin)

x: a coordinate value corresponding to a direction in which the central axis of a plume extends on the horizontal plane

y: a coordinate value in a direction (in the following description, this direction is referred to as a "horizontal direction", when necessary) perpendicular to the direction in which the central axis of the plume extends on the horizontal plane

z: a coordinate value in the vertical direction

C: gas concentration at an evaluation point (x, y, z) [kg/m3 or m3/L]

QP: the amount of gas generated [kg/s or m3/s]

WS: a wind speed [m/s]

He: the height of a gas source from the surface of the ground [m] σ y, σ z: a plume diffusion width [m] (a standard deviation of a gas concentration distribution in a direction perpendicular to the flow of gas and there are a plume diffusion width in the horizontal direction and a plume diffusion width in the vertical direction).

[0009]
Non-patent Document 1 and Non-patent Document 2 disclose a plume equation (2) related to gas which is absorbed by the surface of the ground and a suspended particulate matter (SPM) with a low fall velocity: (Expression (2))

In Expression (2), a is represented by the following Expression (3): (Expression (3))

The meaning of the symbols in Expression (3) is as follows. The meaning of the symbols holds for the following description:
Vd: a deposition velocity [m/s]
Vs: a fall velocity [m/s] (in the case of SPM. In the case of gas, the fall velocity is 0).

[0010]
Here, σ y and σ z are characteristic values for representing a "plume diffusion width" in the direction perpendicular to the central axis of the plume and are the distance between the central axis of the plume and the point at which the concentration is a standard deviation when the concentration distribution of the Gaussian distribution is assumed in the direction perpendicular to the central axis of the plume.

The plume equation is not limited to Expression (1). For example, Non-patent Document 3 discloses a plume equation when the double Gaussian distribution of concentration is assumed and a curve is used as the central axis of a plume.

A first common characteristic of the plume equations is that the concentration value of a specific concentration evaluation point is represented by a functional formula of, for example, the coordinate values of the evaluation point and the generation source, a generation speed from the generation source, and weather conditions, such as the wind direction and the wind speed, and the result is uniquely given. A second common characteristic of the plume equations is that, in the calculation of concentration, a central axis is assumed and a "plume" in which a high-concentration region characterized by "plume diffusion widths" σ y and σ z is formed around the central axis is set. When the plume equation is compared with other methods, a numerical analysis method which numerically solves a plurality of simultaneous physical equations to calculate the concentration value of a specific concentration evaluation point differs from the plume equation in that it calculates concentration without assuming the plume and the calculation result is not unique. In addition, a multi-regression equation which calculates the concentration value of a specific concentration evaluation point using the coordinate values of the evaluation point and the generation source, the generation speed from the generation source, and weather conditions, such as the wind direction and the wind speed, as variables does not assume the plume. Therefore, the multi-regression equation is not the plume equation.

[0011]
In Expression (2), the "term multiplied by a" represents the effect of gas or SPM remaining above the surface of the ground, without being absorbed, when the shape of the distribution of gas or SPM in the vertical direction is symmetrically inverted on the surface of the ground. The absorption effect of gas or SPM to the surface of the ground is adjusted by the magnitude of a. However, in the following description, the "term multiplied by a" in Expression (2) is referred to as a "surface reflection term", if necessary.

[0012]
In addition, Patent Document 6 discloses the following technique as a technique which measures the amount of dustfall at an evaluation point in a short cycle of about 10 minutes. That is, each of the mass of a coarse particle and the mass of a fine particle is continuously measured using a funnel-shaped particle collection port, an airflow path which circulates through a measurement device, and an inertial classifier which is provided in the airflow path. Then, a change in the fall velocity of dustfall in the atmosphere is calculated from the measured value of the mass of the coarse particle.

[0013]
However, the above-mentioned techniques according to the related art have the following problems.

That is, the first problem is that a generated material, which is a search target from the generation source, is not dustfall.

For example, in the techniques disclosed in Patent Documents 1 to 4, the search target from the generation source is gas. In the technique disclosed in Patent Document 3, SPM is included in the search target from the generation source. SPM is a particle which is significantly smaller than dustfall (by definition, SPM is a particle with a diameter of 10 um or less) and the diffusion behavior of SPM in the atmosphere is substantially the same as that of gas except that fine particles are precipitated. [0014]

The dustfall is a dust particle which is significantly larger than SPM (a particle with a diameter of about 10 |am or more) and the fall velocity thereof is very high. Therefore, the diffusion behavior of the dustfall in the atmosphere is greatly affected by the fall velocity of particles. Therefore, the diffusion behavior of the dustfall is greatly different from that of gas.

The amount of dustfall to be observed and managed is the deposition amount of dustfall on the surface of the ground. In the techniques disclosed in Patent Documents 1 to 4, since the concentration of gas and SPM at the evaluation point is observed and managed, it is difficult to directly know the deposition velocity of gas and SPM to the surface of the ground. The deposition velocity Va is reliably described in the above-mentioned Expression (2). Therefore, when the deposition velocity Va can be accurately given, it is possible to convert the concentration of gas and SPM at the evaluation point into the deposition amount of gas and SPM on the surface of the ground.

[0015]
However, as disclosed in Non-patent Document 1, the deposition velocity Va of SPM is affected by the state of the surface of the ground or air turbulence and varies greatly due to the state of the surface of the ground or air turbulence. In addition, a method of generally giving the deposition velocity of gas has not been developed. Therefore, it is very difficult to accurately give the value of the deposition velocity Vd in practice and it is difficult to at least quantitatively treat dustfall in the techniques disclosed in Patent Documents 1 to 4.

[0016]
The second problem is that a dust source search method for dustfall has not been disclosed in the related art. As represented by Patent Document 3, the generation source search method according to the related art premised the search of a generation source in the horizontal plane (the surface of the ground). Therefore, in the generation source search method according to the related art, it is difficult to three-dimensionally treat the source of the dustfall which has a high particle fall velocity Vs and the problem of the deposition amount on the surface of the ground. In particular, in the method disclosed in Patent Document 3 in which a generation source search line extends from the evaluation point in the wind direction, it is difficult to quantitatively and generally treat the influence of the surface reflection term (aexp[-(He+z-Vsx/WS)2/2az2]) in Expression (2). Therefore, in the related art, an effective method has not been proposed which associates the generation source search line with the plume equation.

[0017]
The third problem is that it is indispensable to assume the position of the generation source and the rough amount of particles generated from the generation source in advance when the generation source is searched in the above-mentioned techniques according to the related art.

For example, in the techniques disclosed in Patent Documents 1 and 2, first, for all of the assumed generation sources and all evaluation points, the relationship between the amount of particles generated from an arbitrary generation source and concentration at an arbitrary evaluation point is predicted as a weather condition function such as the above-mentioned plume equation. Then, the parameters (for example, γy or QP) of the function are adjusted by an optimization method such that the difference between the measured value of concentration at all evaluation points and the predicted value of concentration is the minimum. Therefore, it is necessary to give at least the position of all generation sources in advance. In addition, in order to ensure the validity of a calculation process of the optimization method, it is generally desirable to give the rough amount of particles generated from each generation source as initial conditions in advance. The reason is as follows. In the optimization problem, when the initial conditions are very different from the actual conditions, a solution is likely to converge on a local stabilization point which is very different from the actual stabilization point.

[0018]
In the technique disclosed in Patent Document 3, a plurality of dust (SPM) generation points are assumed in advance and the concentration of SPM is measured at a plurality of evaluation points around the dust generation points for a long period. Then, the average value of concentration of SPM in each wind direction is calculated at each evaluation point for the period and generation source search lines extend from a plurality of evaluation points in the horizontal plane (the surface of the ground) in the upwind direction of the wind direction in which the average value of concentration of SPM is the maximum. Among the intersections of the generation source search lines, an intersection corresponding to any one of the dust (SPM) generation points is determined to be a generation point where a particularly large amount of dust (SPM) is generated.

In the technique disclosed in Patent Document 4, it is premised that a measurement device is provided in the vicinity of the assumed generation source. Therefore, the generation source needs to be known in advance.

However, when there are a large number of generation sources, in practice, it is difficult to check the position of all of the generation sources and the rough amount of dust generated from the generation sources. If possible, a large amount of resources is needed, which is not preferable. In addition, in some cases, it is difficult to approach the dust source such as an accident spot of the nuclear power station. Therefore, the techniques disclosed in Patent Documents 1 to 4 can be effectively applied only in an environment in which the number of generation sources is very small or it is possible to sufficiently accurately check the amount of dust generated from the generation source.

[0019]
The fourth problem is that the generation source, which is a search target, is basically a steady generation source whose generation amount does not vary over time or a quasi-steady dust source whose generation amount varies slightly over time in the vicinity of the average value of time.

For example, in the techniques disclosed in Patent Documents 1 and 2, since the optimization method is applied, in general, the number of evaluation points needs to be more than the number of parameters which can be adjusted in the function such as the applied plume equation. When the number of adjustable parameters is substantially more than the number of evaluation points, in general, the found solution is not uniquely determined and the method fails.

[0020]
In addition, where there are a large number of generation sources, in many cases, the number of evaluation points is set to be less than the number of generation sources in terms of economic efficiency. In this case, when the generation source is limited to a steady generation source (that is, when the amount of dust Qp generated is an adjustable parameter), it is possible to ensure the measured value equal to or larger than the number of generation sources by using the measured values at the evaluation points at a plurality of different times and the optimization method can be applied. On the other hand, when the techniques disclosed in Patent Documents 1 and 2 are applied to the unsteady generation source whose generation amount QP is unsteadily greatly changed, the amount of dust Qp generated needs to be an adjustable parameter. Therefore, when a large number of generation sources are search targets, it is necessary to provide a much larger number of evaluation points than the number of generation sources, which is not practical in terms of economic efficiency.

[0021]
In the technique disclosed in Patent Document 3, data for the concentration of SPM which is discretely collected at the evaluation point for a period of two months or more is averaged to search for the generation source. Therefore, the generation source is limited to a steady generation source.

In the technique disclosed in Patent Document 4, since the evaluation point is arranged in the vicinity of the assumed generation source, it is possible, in principle, to search for an unsteady generation source. However, in this technique, when the gases generated from a plurality of generation sources reach a specific evaluation point at the same time, a method of determining a prominent generation source of the plurality of generation sources is not disclosed and a method of arranging the evaluation points in the vicinity of all of the assumed generation sources is not disclosed. Therefore, in this technique, it is possible to search for the unsteady dust source only when the distance between the generation sources is so long that the generation sources have no influence on each other. That is, this technique can be applied only when the generation sources are substantially in one-to-one correspondence with the evaluation point.

However, in practice, the amount of dust generated from the generation source is generally large and varies over time. Therefore, the technique according to the related art in which only the steady generation source or only the generation source which is in one-to-one correspondence with the evaluation point is a search target cannot be sufficiently applied to the actual search of the generation source.

[0022]
When dust is exposed to radiation, it is possible to measure the amount of radiation, such as a-rays, P-rays, or y-rays, present in dust using, for example, the methods disclosed in Patent Documents 7 to 9.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0023]
(Patent Document 1) Japanese Unexamined Patent Application, First Publication No. 2003-255055
(Patent Document 2) Japanese Unexamined Patent Application, First Publication No. 2005-292041
(Patent Document 3) Japanese Unexamined Patent Application, First Publication No. 2004-170112
(Patent Document 4) Japanese Unexamined Patent Application, First Publication No. 2003-281671
(Patent Document 5) Japanese Unexamined Patent Application, First Publication No. 2007-122365
(Patent Document 6) Japanese Unexamined Patent Application, First Publication No. 2008-224332
(Patent Document 7) Japanese Unexamined Patent Application, First Publication No. H8-327741
(Patent Document 8) Japanese Unexamined Patent Application, First Publication No. H7-35900
(Patent Document 9) Japanese Unexamined Patent Application, First Publication No. 2009-63510

NON-PATENT DOCUMENETS

[0024]
(Non-patent Document 1) Suspended Particulate Matter Measure Conference (Reviewed by Pollution Control Division, Nature Conservation Bureau, Ministry of the Environment): Suspended Particulate Matter Pollution Forecast Manual, Toyokan Publishing Co., Ltd., 1997 (Non-patent Document 2) Shinichi Okamoto: Air Quality Forecast Lecture, Gyosei, 2001 (Non-patent Document 3) United States Environment Protection Agency: EPA-454/R- 03-004,2004

DISCLOSURE OF INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0025]
The present invention has been made in view of the above-mentioned problems and an object of the present invention is to effectively search for a dustfall source that generates dust, the amount of which is unsteadily changed (the dustfall generation speed of the dust source), with high accuracy.

MEANS FOR SOLVING THE PROBLEMS

[0026]
The inventors conducted a study in order to solve the problems and conceived the following solution.

(1) A method of searching for an unsteady dust source position of dustfall in accordance with a first aspect of the present invention includes:

a dust amount-setting step of collecting the dustfall for a period Td(it) from a time td(it-l) to a time td(it), which is an irth time in each cycle Atd, at at least two different evaluation points and obtaining a measured value of the amount of dustfall M per unit time;

a representative wind direction derivation step of continuously measuring a wind direction in a cycle Atwjnt shorter than the cycle Atd for the period Td(it) in the vicinity of each of the evaluation points and deriving a representative wind direction WD for the period Td(it);

a representative wind speed derivation step of continuously measuring a wind speed in the cycle Atwint for the period Td(it) in the vicinity of each of the evaluation points and deriving a representative wind speed WS for the period Td(it);

a representative fall velocity derivation step of continuously measuring a fall velocity of the dustfall in the cycle AW for the period Td(it) in the vicinity of each of the evaluation points and deriving a representative fall velocity Vs for the period Td(it);

a dustfall source search region-setting step of setting a first dustfall source search region Γ(IM) that has a central axis which extends from a first evaluation point im as a starting point in an upwind direction of the representative wind direction WD and has a dustfall source search region width around the central axis and a distance range from the central axis to the dustfall source search region width in a vertical direction and a second dustfall source search region y(i>j) that has a central axis which extends from a second evaluation point i^ different from the first evaluation point \M as a starting point in the upwind direction of the representative wind direction WD and has the dustfall source search region width around the central axis and a distance range from the central axis to the dustfall source search region width in the vertical direction;

a distance calculation step of calculating a first distance Ld(iM) between the first evaluation point iM and a coordinate point p which is included in both the first dustfall source search region YOM) and the second dustfall source search region YON) and a second distance Ld(iN) between the coordinate point p and the second evaluation point IN;

a cross-sectional area calculation step of calculating a first dust source search region central axis vertical cross-sectional area Spi, which is a cross-sectional area of the first dustfall source search region in a vertical plane of the central axis of the first dustfall source search region including the coordinate point p, and a second dust source search region central axis vertical cross-sectional area SP2, which is a cross-sectional area of the second dustfall source search region in a vertical plane of the central axis of the second dustfall source search region including the coordinate point p, using the dustfall source search region width;

a dust amount calculation step of calculating a first assumed amount of dust E1 which is proportional to the first dust source search region central axis vertical cross-sectional area Sp1 and a second assumed amount of dust E2 which is proportional to the second dust source search region central axis vertical cross-sectional area SP2; and

a dust source determination step of determining that the coordinate point p is an unsteady dust source of the dustfall when all of the ratios of the first assumed amount of dust Ei and the second assumed amount of dust E2 which are calculated for all combinations of all dustfall source search regions including the coordinate point p in the dust amount calculation step is within a range of predetermined upper and lower limit threshold values, determining that the coordinate point p is not the unsteady dust source of the dustfall when any one of the ratios of the first assumed amount of dust Ei and the second assumed amount of dust E2 which are calculated in the dust amount calculation step is beyond the range of the predetermined upper and lower limit threshold values, and not determining the unsteady dust source of the dustfall at the coordinate point p when the coordinate point p is included in neither the first dustfall source search region nor the second dustfall source search region, wherein, in a plume equation, the central axis of the dustfall source search region is a central axis of a plume, a plume diffusion width is calculated at the second distance Ld(iN) on the central axis of the plume, and the calculated plume diffusion width is used as the dustfall source search region width.

In the representative wind direction derivation step, the representative wind direction WD may be derived as an average value of a measured value of the wind direction for the period Td(it).

In the representative wind speed derivation step, the representative wind speed WS may be derived as an average value of a measured value of the wind speed for the period Td(it).

In the representative fall velocity derivation step, the representative fall velocity Vs may be derived as an average value of a measured value of the fall velocity of the dustfall for the period Td(it).

(2) As a second aspect of the present invention, in the method of searching for an unsteady dust source position of dustfall according to the first aspect, the central axis of the dustfall source search region may have the upwind direction of the wind direction as a horizontal component and has a value VS/WS obtained by dividing the representative fall velocity Vs of the dustfall by the representative wind speed WS as a vertical gradient, and in the plume equation, the central axis of the dustfall source search region may be the central axis of the plume, a horizontal-direction plume diffusion width σ y at the second distance Ld(iN) on the central axis of the plume may be used as a horizontal component of the dustfall source search region width, and a vertical-direction plume diffusion width az at the second distance Ld(iN) on the central axis of the plume may be used as a vertical component of the dustfall source search region width.

(3) As a third aspect of the present invention, the method of searching for an unsteady dust source position of dustfall according to the first or second aspect, as the plume equation, the following Expressions (1) and (2) may be used which represent dust concentration C(x) at a distance x on the central axis using a horizontal-direction plume diffusion width σ y, a vertical-direction plume diffusion width σ z, the distance x from a generation source on the central axis of the plume, an amount of dust QP generated, the representative speed WS, a constant B, and a plume range defined by the horizontal-direction plume diffusion width σ y and the vertical-direction plume diffusion width σ 2 (units are all SI units): (Expression (1)) C(x) = B(Qp/27tσ yσ zWS) (inside the plume range); and (Expression (2)) C(x) = 0 (outside the plume range).

(4) As a fourth aspect of the present invention, in the method of searching for an unsteady dust source position of dustfall according to the third aspect, an ellipse in which the length of a major axis is two times larger than the horizontal-direction plume diffusion widthσ y and the vertical-direction plume diffusion width σ z and the length of a minor axis may be two times smaller than the horizontal-direction plume diffusion widthσ y and the vertical-direction plume diffusion width Σ Z may be the cross-sectional shape of the plume which is vertical to the central axis of the plume, and the inside of the ellipse may be the inside of the plume range.

(5) As a fifth aspect of the present invention, the method of searching for an unsteady dust source position of dustfall according to any one of the first to fourth aspect may further include: a dust species classification step of measuring the radiation of dustfall samples which are collected at the evaluation point for the period Td(it) and classifying the dustfall by a dust species on the basis of the intensity of the measured radiation, wherein, among the collected dustfall samples, the mass of the dustfall samples corresponding to any one of the dust species classified in the dust species classification step may be the amount of dustfall M.

EFFECTS OF THE INVENTION

[0027]
According to each of the above-mentioned aspects, it is possible to effectively search for a dustfall source that generates dust, the amount of which is unsteadily changed, with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]
FIG. 1 is a diagram illustrating an example of a plume which is projected onto a horizontal plane according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a plume which is projected onto a vertical plane according to the embodiment of the present invention.

FIG 3 is a flowchart illustrating an example of the process of a dust source search device according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a dust source search region according to the embodiment of the present invention.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION [0029] (Characteristics of Embodiment of the Present Invention)

First, the characteristics of an embodiment of the present invention will be described.

A first characteristic of the embodiment of the present invention is that dustfall is directly measured at an evaluation point to search for the source of the dustfall. [0030]

A second characteristic of the embodiment of the present invention is that, in the search of the source of the dustfall, a dust source search region which extends from the evaluation point in an upwind direction is associated with a plume equation to obtain information about the amount of dust generated from dust source candidates.

Specifically, as described above, in the related art, it is difficult to treat the ground reflection term (aexp[-(He+z-Vsx/WS)2/2crz2]) in Expression (2). Therefore, it is difficult to associate a dust source search line which extends from the evaluation point in the upwind direction with the plume equation. However, the examination result of the inventors proved that the problem of the ground surface reflection term was caused since the main target of the technique according to the related art was gas or SPM. In the case of dustfall, since the falling velocity of particles is high, a deposition velocity Vd is substantially equal to a falling velocity Vs. Therefore, the influence of the reflection of particles from the surface of the ground is small and a = 0 is regarded to be established. Thus, an atmosphere diffusion formula (plume equation) for the dustfall is the following Expression (4) obtained by substituting a = 0 into Expression (2): (Expression (4))

[0031]
When coordinates are converted by the following Expression (5), Expression (4) becomes the following Expression (6):

(Expression (5))
Z = z+Vsx/WS-He; and (Expression (6))

Here, the coordinate conversion of z into Z by Expression (5) corresponds to the definition of concentration when the generation source (dust source) is the origin, the central axis of a dust plume is set in the vertical plane at a depression angle of tan" 1(VS (particle fall velocity)/WS (wind speed)) in a downwind direction, and the central axis is the Z-axis.

[0032]
The plume diffusion width σ y is the standard deviation of the concentration distribution in the y direction. The plume diffusion width σ z is the standard deviation of the concentration distribution in the z direction. In general, Vs« WS is satisfied and the z direction is regarded to be substantially equal to the Z direction under the condition that Vs« WS is satisfied. In many cases, when there is no influence of reflection from the surface of the ground, the concentration distribution in the y direction and the z direction is regarded as a normal distribution. In this case, while a concentration value at y =σ y and Z = σ z is 60%) of the maximum concentration value, a concentration value at y = 2σ y and Z = 2az is 13% of the maximum concentration value. That is, in the region in which y >σ y and Z > σ z are satisfied, concentration is rapidly reduced. Therefore, in the embodiment of the present invention, the following Expressions (7a) and (7b) are premised as the plume equation.

[0033] (Expression (7a))

C(x) = B(Qp/2σx,σzWS) (inside the plume range) (Expression (7b))
C(x) = 0 (outside the plume range)

[0034]
Here, the meaning of symbols in Expression (7a) is as follows:
B: a proportional constant.

In this method, since the only problem of Expression (7a) is a relative value, an arbitrary value (for example, 1) may be given to the proportional constant B.

The inside of the plume range means a region in which, assuming that the concentration distribution in the vertical direction of the plume is a Gaussian distribution as represented by Expression (4), the concentration is closer to the central axis than to the position indicating the value of the standard deviation of the concentration distribution. Alternatively, simply, when the cross-section of the plume is an ellipse in which the length of a major axis is two times larger than ay and a7 and the length of a minor axis is two times smaller than σy and <σz, the inside of the ellipse may be the inside of the plume range. In addition, more simply, the inside of the plume range may be the range represented by the following Expression (8). On the other hand, the outside of the plume range is a range other than the inside of the plume range.

(Expression (8))
ay > y > -σy and ΣZ > Z > -<σz
Here, ay and ΣZ are a function of a distance Lo from the dust source and a period ∆td (ay[L0, ∆td] and az[L0, ∆td]). In addition, ay and oz are the tabulated or diagrammatized values which are calculated by fixing ∆td (using ∆td as a reference period) and are calculated by empirically correcting the influence of Atd using the Pasquill-Gifford formula or the Briggs formula disclosed in Non-patent Document 1. As disclosed in Non-patent Document 2, a method of empirically correcting the influence of Atd multiplies ([Atd which is actually used]/[ Atd of a reference pure time])p by σy.

[0035]
When a dust species and a dust particle are given, the particle fall velocity Vs is determined as a terminal velocity. Therefore, the amount of dustfall M(x) can be represented by the following Expressions (9a) and (9b) in which concentration C(x) is multiplied by the particle fall velocity Vs: (Expression (9a))
M(x) = VsB(Qp/27tσyvzWS) (inside the plume range); and (Expression (9b))
M(x) = 0 (outside the plume range).

[0036]
In Expression (9a), under the condition of a constant wind speed, the amount of dustfall M(x) in a limited part of the plume range is determined only by the amount of dust Qp and the plume diffusion widths σy and σz. In addition, the values of the plume diffusion widths σy and vz are a function of x and weather conditions and can be represented by, for example, the Pasquill-Gifford equation disclosed in Non-patent Document 1. Therefore, under constant dust source conditions and constant weather conditions, the amount of dustfall M(x) at a specific evaluation point can be represented only by the distance x from a specific dust source.

Next, the range of the dust source at a specific evaluation point will be described using Expression (9).

FIG. 1 is a diagram in which plumes a(i01) and a(i02) which are generated on the same horizontal plane as that including an evaluation point iM are projected from two dust sources i01 and io2 disposed at a position x'=Lo onto the entire coordinate system x' and y' (the surface of the ground) in the horizontal plane having the specific evaluation point iM as the origin O. In this case, a wind direction WD is the negative direction of x'. The plumes a(i01) and a(i02) are arranged such that the central axes 10a and 10b thereof are aligned with the surface of the ground at x-0 and pass through the origin O at the ends of the plumes in the horizontal direction (the end of the plume a(io1) in the -y' direction and the end of the plume a(i02) in the +y' direction). The arrangement positions of the plumes oc(i01) and a(i02) are limit positions where the plumes oc(io1) and a(i02) can reach an evaluation point iM from the dust sources i01 and i02 which are set at x=Lo. That is, the position of the dust source i01 is a limit position in the +y' direction and the position of the dust source io2 is a limit position in the -y' direction.

[0037]
The diffusion width oy of the plumes a(i01) and a(i02) at x'=0 is ay(Lo). Therefore, the half-width of the distance between the dust sources i01 and i02 at x'=Lo is equal to ay(Lo), that is, the diffusion width ay of the plumes a(i0i) and a(i02) at x-0. When the positions of the dust sources i01 and i02 are estimated during the measurement of dustfall at the evaluation point iM, the dust sources i0i and i02 are present in a region Y(IM) (a hatched region) interposed between a line which passes through the origin O and the point of the dust source i01 and a line which passes through the origin O and the point of the dust source i02 in the horizontal plane. The regionα (iM) is the dust source search region.

[0038]
However, the value of x'=Lo where the dust sources i01 and i02 are arranged is arbitrary. Therefore, at the arbitrary position of x', the half-width of the range of the dust sources i01and i02 which can reach the evaluation point iM in the y' direction is constantly ay(x'). That is, the half-width of the dust source search region y(iu) in the y' direction is equal to ay on the same horizontal plane as that including the dust source in, for example, the plume equation of Expression (6). Therefore, the dust source search region y(iM) in the horizontal plane can be set by the width of the search region which is represented by a function of only the distance from the evaluation point iM on a central axis 11 which extends from the evaluation point iM in the upwind direction of the representative wind direction.

[0039]
FIG. 2 is a diagram in which plumes ct(i03) and ct(io4) which are generated on the same vertical plane as that including the evaluation point iM are projected from two dust sources i03 and io4 which are disposed at a position x'=L0 onto all coordinate systems x' and y' in the vertical plane having the specific evaluation point iM as the origin O.

Specifically, the dust source search range Γ (M) is set by the same method as that described with reference to FIG. 1. At that time, the width of the dust source search range Γ (1M) is represented by a diffusion width z(x').

However, since dust falls, the central axes 10a and 10b of the plumes α (i03) and a(i04) and the central axis 11 of the dust source search region Γ (IM) are inclined at an angle 8 (= tan'-1(V/WS)) in the vertical cross-section. Therefore, only the dustfall which is generated in a portion of the region extending from the evaluation point iM in the upwind direction can reach the evaluation point iM from the dust sources i03 and i04 among points in the upwind direction of the evaluation point iM. As such, in the dust source search method in which the generation source search region γ (iM) extends from the evaluation point iM in the upwind direction, the range of the distance in the upwind direction is limited, which is not disclosed in the method according to the related art. This method has the advantage over the method according to the related art in that it is possible to limit the dust source search region Γ (IM).

[0040]
A simple and quantitative expression of the dust source search region γ (iM), which is a modification of the plume equation for the amount of dustfall, has not been achieved by the plume equation according to the related art based on gas or SPM. The inventors paid attention to the fact that the falling velocity Vs of dust was relatively high and first achieved a simple and quantitative expression through a series of studies.

The present invention is not limited to the use of the plume equation of Expression (9). For example, when precise measurement is performed in advance to accurately express the influence of the ground surface reflection term, the term az in Expression (9) may be appropriately corrected on the basis of the plume equation while leaving the ground surface reflection term.

[0041]
A third characteristic of the embodiment of the present invention is that the dust source or the amount of dust generated is not necessarily assumed in advance. In practice, in many cases, since the position of the dust source or the amount of dust generated therefrom is not known, the method according to the embodiment of the present invention is advantageous since it practically searches for the dust source.

[0042]
A fourth characteristic of the embodiment of the present invention is that an unsteady dust source is specified. The method according to the embodiment of the present invention can specify the main dust source for each acquisition cycle of the measured value of the amount of dustfall or for the time corresponding to several successive acquisition cycles of the measured value of the amount of dustfall. Therefore, it is possible to check the unsteady dust source which varies in a time-scale equal to or more than several acquisition cycles of the measured value of the amount of dustfall. In addition, the number of evaluation points required to specify the unsteady dust source may be sufficiently less than the number of latent dust sources.

[0043]
A fifth characteristic of the embodiment of the present invention is that dustfall collected at the evaluation point is classified into radioactive dustfall or non-radioactive dustfall and it is possible to specify the unsteady source of the radioactive dustfall using dustfall measurement data at a long distance, without approaching the radioactive dust source.

[0044]
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, in the specification and the drawings, components having substantially the same functional structures are denoted by the same reference numerals and the description thereof will not be repeated.

(First Embodiment)

First, a first embodiment will be described.

Dustfall amount measurement means (device) measures the amount of dustfall (the mass of dustfall) in each cycle ∆ ta and the measured value of the amount of dustfall is output in each cycle ∆ td. It is assumed that the time when the amount of dustfall is output from the dustfall amount measurement means is ta(it). The time (period) from a time ta(it-l) to the time td(it) is defined as a "period Td(it)". Here, it is an integer which is increased by 1 from 0 which is the time when dustfall starts to be measured. In this embodiment, a dustfall source is specified for each "period Td(it)" and a dust source which has a time-scale (that is, the time when dust is continuously generated) equal to or more than the cycle ∆ td is a search target.

[0045]
In addition, a rectangular coordinate system including x, y, and z is set in a three-dimensional region in which the dust source can be searched, nx coordinate components, ny coordinate components, and n2 coordinate components are provided on each coordinate axis, and the three-dimensional space is represented by nxxnyxnz coordinate points p. Here, the coordinate point p indicates a coordinate point with an ix-th coordinate component, an iy-th coordinate component, and an iz-th coordinate component. The position of each coordinate point is represented using the orders ix, iy, and iz of the coordinate components on each coordinate axis and Sc(ix, iy, iz) is represented as a position vector from the origin. At each coordinate point p, any one of three dust source determination modes "dust source", "no dust source", and "undetermined" is set.

[0046]
An example of the process (dust source search process) of the dust source search device searching for a dust source will be described with reference to the flowchart of FIG. 3. The dust source search device is implemented by an information-processing apparatus (for example, a commercial personal computer (PC)) including, for example, an arithmetic device, such as a CPU, a memory, a hard disc drive (HDD), and various interfaces. For example, the flowchart shown in FIG. 3 is translated into an executable computer program by a programming language, such as the C language, and is stored in the HDD in advance. When the information-processing apparatus performs the dust source search process, the arithmetic device, such as a CPU, reads the executable computer program stored in, for example, the HDD, starts the executable computer program, and the arithmetic device, such as a CPU, sequentially performs the operations based on the commands of the executable computer program. The executable computer program may be started manually, or periodically and automatically to start the dust source search process. As described above, the dust source search device according to this embodiment searches for a dustfall source for the "period Td(it)" at a given time.

Position information, such as an evaluation point and a coordinate point, and necessary input information, such as the measured values of the amount of dustfall, the wind direction, and the wind speed, or an analysis value related to a dust species, can be manually input to the dust source search device through a keyboard or a console screen connected to the information-processing apparatus in advance. The input information is stored in, for example, the HDD and is appropriately read with the progress of the dust source search process.

In the dust source search device, for example, the determination result of the unsteady dust source or the calculation result, such as the amount of dust, at the calculated specific coordinate point can be stored in the HDD and displayed on the console screen.

A portion of or the entire process of the dust source search device may be replaced with other means such as manual calculation.

[0047]
First, a first process will be described.
In Step S101, the dust source search device initializes the dust source determination mode to "undetermined" at all coordinate points p.

Then, in Step S102, the dust source search device sets (inputs) "a representative wind speed WS, a representative wind direction WD, the amount of dustfall M(i) at all evaluation points (the evaluation points are distinguished by a number i and nM > i > 1 is satisfied), the "representative fall velocity Vs of dustfall particles" for the "period Td(it)". In this embodiment, for example, in Step S102, a dust amount-setting process, a representative wind direction derivation process, a representative wind speed derivation process, and a representative fall velocity derivation process are performed.

[0048]
The amount of dustfall M(i) can be measured by, for example, the continuous dustfall monitor disclosed in Patent Document 6 in a cycle ∆ td of 10 minutes. The values of the wind direction and the wind speed can be measured by, for example, a commercial propeller anemometer in a cycle AtWint (for example, 1 second) shorter than the cycle ∆ td. The spatial resolution of the wind direction is, for example, an interval of 1°. For example, the average value of the "measured values of the wind direction and the wind speed" for the "period Td" may be used as the representative wind direction WD and the representative wind speed WS. Alternatively, the instantaneous measured value of the wind direction or the wind speed may be stratified and a stratified value causing a mode for the "period Ta" may be used as the representative wind direction WD and the representative wind speed WS.

[0049]
An anemoscope and an anemometer are provided in the vicinity of a dustfall management point i. Here, the "vicinity of the dustfall management point i" may be the range in which the wind direction and the wind speed have high correlation with the wind direction and the wind speed above the dustfall management point i and may be, for example, within a horizontal distance of 1 km from the dustfall management point i. In a region in which the land is monotonous and the distribution of the wind direction and the wind speed is small, the vicinity of the dustfall management point i may be a horizontal distance equal to or more than 1 km. In addition, the height of the measurement point of the wind direction and the wind speed may be, for example, a measurement height of 10 m from the surface of the ground, which is recommended by the meteorological office. When the assumed height of the dust source is sufficiently larger than 10 m, for example, an intermediate value between the surface of the ground and the height of the dust source may be used as the height of the measurement point.

[0050]
In addition, the average fall velocity of a dustfall sample which is captured at the evaluation point can be measured for the "period Td(it)" and can be used as the representative fall velocity Vs of the dustfall particles. For example, there is the following method as a method of measuring the fall velocity of the dustfall sample. That is, the dustfall sample is discharged from the upper part of an airtight container, the time required for each dustfall particle to reach the bottom of the container is measured, and the falling distance is divided by the falling time to calculate the representative fall velocity Vs of the dustfall particles. In order to detect the arrival of each dustfall particle to the bottom of the container, for example, a method can be used which continuously radiates a sheet-shaped laser beam in the horizontal direction on the bottom of the container and detects scattered light which is generated when dustfall passes through the laser beam using a photodetector.

[0051]
As a method of calculating the representative fall velocity Vs from the fall velocity of each dustfall particle, a method can be adopted which uses the falling time corresponding to the time required for 50% of all dustfall particles to reach the bottom of the container as the fall velocity of the dustfall particles related to the representative fall velocity Vs of the dustfall particles. Alternatively, when the density and shape of dustfall are roughly determined, simply, the particle diameter distribution of the dustfall sample can be measured to calculate the representative fall velocity Vs of the dustfall particles. As a method of calculating the representative fall velocity Vs of the dustfall particles from the diameter of the dustfall particles, for example, the following Stokes terminal velocity Expression (10) can be used:

(Expression (10))

Here, the meaning of the symbols in Expression (10) is as follows (units are all SI units):
g: gravity acceleration [m/s2]
Dp: a particle diameter [m]
PP, pr1: the density of particles and the density of a fluid [kg/m3]
CR: a resistance coefficient [-] (various number tables are disclosed depending on the shape of particles).

[0052]
Then, in Step S103, the dust source search device calculates the positions of all evaluation points i in the horizontal plane (for example, a ground height of 1.5 m) as a position vector P(i) indicating the position from the origin of the coordinate system.

In Step S104, the dust source search device sets the dust source search region γ(i) related to each evaluation point i at all evaluation points i. FIG. 4 is a diagram illustrating an example of the dust source search region γ(i). An example of a method of setting the dust source search region γ(i) will be described with reference to FIG. 4. In this embodiment, for example, in Step S104, a dustfall source search region-setting process is performed.

[0053]
In FIG. 4, Γ (IMI is another expression of the dust source search region Y(IM), which is decomposed for each coordinate component and shown in FIGS. 2 and 3, in one diagram by isomeric projection. In FIG. 4, two evaluation points iM and iN are arranged on the absolute coordinates (x', y', z) and the central axes of dust source search regions Γ (IM) and γ (iN) are set at an elevation angle 9 (= tan-1(Vs/WS)) in the upwind direction of the representative wind direction WD, using the evaluation points iM and in as starting points. The dust source search region is set such that the cross-section of an ellipse with a width 2σy in the horizontal direction and a width 2ΣZ in the vertical direction is formed around the central axis.

[0054]
Next, a second process and a third process will be described. The second process and the third process determine the dust source for a specific coordinate point p at a specific evaluation point i (=1M) (sets any one of the dust source determination modes). If necessary, the evaluation point i and the coordinate point p are changed and the same determination process as described above is performed.

[0055]
In the second process, first, in Step S105, the dust source search device selects a non-selected evaluation point i as a first evaluation point iM.

Then, in Step S106, the dust source search device selects a non-selected coordinate point p among the coordinate points p.

Then, in Step S107, the dust source search device sets the position vector Sc(ix, iy, iz) of the coordinate point p. The position vector Sc of the coordinate point p is set such that the origin of the coordinate axis is a starting point and the point (that is, the point p) at which coordinate components are an ix-th coordinate axis division point, an iy-th coordinate axis division point, and an iz-th coordinate axis division point is an end point. Here, a first dust source search region γ (iM) related to the first evaluation point iM is referred to as a first dust source search region Γ (IM) and a second dust source search region γ (iN) related to the second evaluation point is is referred to as a second dust source search region γ (iN).

[0056]
Then, in Step S108, the dust source search device selects a non-selected evaluation point i as the second evaluation point in.

Then, in Step S109, the dust source search device determines whether the first evaluation point 1M selected in Step S105 and the second evaluation point in selected in Step S108 are disposed at the same position. When it is determined that the first evaluation point iM and the second evaluation point IN are disposed at different positions, the process proceeds to Step S110. On the other hand, when it is determined that the first evaluation point im and the second evaluation point is are disposed at the same position, Steps S110 to S118 are omitted and the process proceeds to Step S1 19 which will be described below.

[0057]
When the process proceeds to Step S110, the dust source search device determines whether the dust source determination conditions in which the coordinate point p selected in Step S106 is included in both the first dust source search region y(im) and the second dust source search region Γ (IN) and the dust source determination mode of the coordinate point p selected in Step S106 is in the mode other than "no dust source" are satisfied.

When it is determined that all the dust source determination conditions are satisfied, the coordinate point p selected in Step S106 is likely to be a dust source. The state in which the dust source determination conditions are satisfied corresponds to the state in which the coordinate point p is in a common region 41 (a hatched region) between the first dust source search region y(iu) and the second dust source search region γ (in) in FIG. 4. As such, when the dust source determination conditions are satisfied, the process proceeds to Step S1ll. On the other hand, when the dust source determination conditions are not satisfied, Steps S111 to S118 are omitted and the process proceeds to Step S119 which will be described below.

[0058]
When the process proceeds to Step S1ll, the dust source search device calculates a first (shortest) distance Ld(iM) between the coordinate point p selected in Step S106 and the first evaluation point iM selected in Step S105 and a second (shortest) distance Ld(iN) between the coordinate point p selected in Step S106 and the second evaluation point iN selected in Step S108. In this embodiment, for example, in Step S108, a distance calculation process is performed.

The first distance Ld(im) between the coordinate point p and the first evaluation point iM is calculated, for example, as the norm of a vector connecting the end point of the vector P(IM) of the first evaluation point iM and the end point of the position vector Sc of the coordinate point p. The second distance Ld(iN) between the coordinate point p and the second evaluation point iN is calculated by the same method as described above.

[0059]
Then, in Step S112, the dust source search device calculates the first central axis vertical cross-sectional area Sp1 of the first dust source search region γ(im) related to the first evaluation point iM at the coordinate point p and the second central axis vertical cross-sectional area SP2 of the second dust source search region Γ(IN) related to the second evaluation point iN at the coordinate point p. As a method of calculating the first central axis vertical cross-sectional area Sp1 of the first dust source search region Γ(IM) and the second central axis vertical cross-sectional area SP2 of the second dust source search region Y(IN), for example, the area of an ellipse in which the length of a major axis is two times larger than the diffusion widths cry[Ld] and az[Ld] and the length of a minor axis is two times smaller than the diffusion widths σy[Ld] and az[Ld] can be calculated as the cross-sectional area. In this embodiment, for example, in Step S112, the cross-sectional area calculation process is implemented.

[0060]
Then, in Step S113, the dust source search device calculates the "first assumed amount of dust Ei at the coordinate point p selected in Step S106" which is estimated from the first evaluation point iM and the "second assumed amount of dust E2 at the coordinate point p selected in Step S106" which is estimated from the second evaluation point iN. In this embodiment, for example, in Step S113, the dust amount calculation process is performed. The first assumed amount of dust Ei is calculated by, for example, Expression (11a) and the second assumed amount of dust E2 is calculated by, for example, Expression (11b): (Expression (11a))
E1 = BiSpiM(iM); and (Expression (11b))
E2 = B1Sp2M(iN).

[0061]
In Expression (11a) and Expression (11b), Bi is a coefficient. Expression (11a) and Expression (11b) correspond to the concentration at a limited part being proportional to the amount of dust generated by the generation source and being inversely proportional to the cross-sectional area of the plume at a limited part in the general plume equation. That is, when the coordinate point p selected in Step S106 is the dust source, a concentration which is inversely proportional to the cross-sectional area of the plume at the first evaluation point iM and the second evaluation point iN is detected. Therefore, the amount of dust generated by the dust source is supposed to be inversely proportional to the cross-sectional area of the plume at the first evaluation point iM and the second evaluation point iN.

[0062]
In Expression (11a) and Expression (11b), B1 is a coefficient which will be changed by a large number of parameters such as weather conditions in the related art. However, in this embodiment, only the ratio of the first assumed amount of dust Ei and the second assumed amount of dust E2 is used to determine the dust source, as will be described below. In addition, since the first assumed amount of dust Ei and the second assumed amount of dust E2 are calculated on the basis of data at the same time, the common weather conditions are premised. Therefore, in this embodiment, it is possible to set Bi to a constant using a simple method.

[0063]
In the third process, first, in Step S114, the dust source search device calculates the ratio R of the first assumed amount of dust Ei and the second assumed amount of dust E2. The ratio R of the first assumed amount of dust Ei and the second assumed amount of dust E2 may be Ei/E2 or E2/Ei.

Then, in Step SI 15, the dust source search device determines whether the coordinate point p selected in Step S106 is the dust source. Specifically, the dust source search device determines whether the ratio R of the first assumed amount of dust Ei and the second assumed amount of dust E2 is in the range (Rmax > R > Rm;n) of predetermined upper and lower limit threshold values. In this embodiment, for example, in Steps S110 and S115, a dust source determination process is performed. When it is determined that the ratio R of the first assumed amount of dust Ei and the second assumed amount of dust E2 is in the range of the predetermined upper and lower limit threshold values, it is determined that the coordinate point p selected in Step S106 is the "dust source". On the other hand, when it is determined that the ratio R of the first assumed amount of dust Ei and the second assumed amount of dust E2 is beyond the range of the predetermined upper and lower limit threshold values, it is determined that the coordinate point p selected in Step S106 is "no dust source".

[0064]
The range of the upper and lower limit threshold values of the ratio R of the first assumed amount of dust E1 and the second assumed amount of dust E2 needs to include 1. A method of setting the upper and lower limit threshold values may be appropriately set depending on the accuracy required for determining the unsteady dust source. That is, the upper and lower limit threshold values may be set to a wide range, considering all possible unsteady dust sources (for example, the lower limit threshold value is set to 0.1 and the upper limit threshold value is set to 10). Alternatively, when only the point which is more likely to be the unsteady dust source is extracted, the upper and lower limit threshold values may be set to a narrow range (for example, the lower limit threshold value is set to 0.8 and the upper limit threshold value is set to 1.2).

[0065]
The determination method is based on the following. A variation in the amount of dust generated by the unsteady dust source with a time-scale equal to or more than the cycle Atd is sufficiently small in the "period Td(it)" by definition. Therefore, it is considered that, when a dust source which generates a larger amount of dust than other dust sources, that is, a main dust source is searched, dustfall generated from the main dust source is dominant at all evaluation points i which dust can reach for the "period Td(it)". In this case, when there are a plurality of evaluation points i which dust can reach for the "period Td(it)", the amounts of dustfall observed at the evaluation points i have a constant ratio therebetween according to a function (that is, the plume equation) of the distance between the dust source (coordinate point p) and each evaluation point i. Therefore, the coordinate point p which satisfies this condition is more likely to be the main dust source. Thus, when the ratio R of the first assumed amount of dust E1 and the second assumed amount of dust E2 is within the range of the predetermined upper and lower limit threshold values, the coordinate point p selected in Step S106 is determined to be the "dust source".

[0066]
On the other hand, when the ratio of the amounts of dustfall observed at the evaluation points i is greatly different from the value which is calculated from the plume equation, the coordinate point p selected in Step S106 is likely to be a false dust source even though it is disposed at the position where dustfall can reach a plurality of evaluation points i during the "period Td(it)". Therefore, when the ratio R of the first assumed amount of dust E1 and the second assumed amount of dust E2 is beyond the range of the predetermined upper and lower limit threshold values, the coordinate point p selected in Step S106 is determined not to be the "dust source".

[0067]
When it is determined that the coordinate point p selected in Step S106 is not the dust source, the process proceeds to Step S116. On the other hand, when it is determined that the coordinate point p selected in Step S106 is the dust source, the process proceeds to Step S117, which will be described below.

When the process proceeds to Step S116, the dust source search device sets the dust source determination mode of the coordinate point p selected in Step S106 to "no dust source". Then, the process proceeds to Step S119, which will be described below.

On the other hand, when the process proceeds to Step S117, the dust source search device sets the dust source determination mode of the coordinate point p selected in Step S106 to the "dust source". In this embodiment, for example, in Step S117, a dust source-setting process is performed.

Then, in Step S1 18, the dust source search device calculates the estimated amount of dust at the coordinate point p which is determined to be the "dust source". For example, the estimated amount of dust can be the average value of all of the assumed amounts of dust E which are used in the determination of the dust source (Step S115) at the coordinate point p which is determined to be the "dust source". Then, the process proceeds to Step S119.

[0068]
When the process proceeds to Step S1 19, the dust source search device determines whether all evaluation points i have been selected. When it is determined that all evaluation points i have not been selected, the process returns to Step S108. On the other hand, when it is determined that all evaluation points i have been selected, the process proceeds to Step S120.

When the process proceeds to Step S120, the dust source search device determines whether all coordinate points p have been selected. When it is determined that all coordinate points p have not been selected, the process proceeds to Step S106. On the other hand, when it is determined that all coordinate points p have been selected, the process proceeds to Step S121.

[0069]
When the process proceeds to Step S121, the dust source search device determines whether all evaluation points i have been selected. When it is determined that all evaluation points i have not been selected, the process returns to Step S105. On the other hand, when it is determined that all evaluation points i have been selected, the process proceeds to Step S122.

When the process proceeds to Step S122, the dust source search device displays the position of the dust source and the estimated amount of dust from the dust source. Then, the process of the flowchart shown in FIG. 3 ends. However, all coordinate points p may not be determined to be the dust source. In this case, in Step S122, the dust source search device displays information indicating that all coordinate points p may not be determined to be the dust source. In this embodiment, all coordinate points p and all evaluation points iM and IN are selected. However, all coordinate points p and all evaluation points iM and iN are not necessarily selected, but some of the coordinate points p and the evaluation points iM and in may be selected. In this case, the initial value "undetermined" remains as the dust source determination mode at the coordinate point p which has not been the dust source determination target (determination target in Step SI 15). In addition, the process may end at the time when the dust source is obtained.

[0070]
As such, in this embodiment, since the concept of the plume equation is applied to the generation source search region which extends from the evaluation point p in the upwind direction, it is possible to accurately specify the position of the dustfall source with a time-scale equal to or more than the cycle Atd and the amount of dust generated by the generation source. Therefore, dustfall is measured at a small number of evaluation points and it is possible to effectively search for the dust sources including an unsteady dust source with high accuracy.

[0071] (Second Embodiment)
Next, a second embodiment of the present invention will be described.

When it is determined that the height of the dust source is limited to a value in the vicinity of the surface of the ground, a dust source search region is not a three-dimensional region unlike the first embodiment, but is set in the horizontal plane (in a two-dimensional region). Therefore, it is possible to simplify a process of searching for the dust source.

[0072]
Specifically, in Step S104 of FIG. 3, a dust source search device omits the inclination of the central axes of a first dust source search region γ(iM) and a second dust source search regionγ(itN) with respect to the vertical direction (the above-mentioned elevation angle 6 is 0°) and forms a two-dimensional first dust source search region γ(iM) and a two-dimensional second dust source search region γ(iN).

In addition, position vectors P and Sc in Steps S103 and S107 are two-dimensional vectors without a vertical component.

[0073]
However, as such, even when the first dust source search region y(iM) and the second dust source search region y(iN) are two-dimensionally formed, it is necessary to consider the influence of the diffusion of a dust plume in the vertical direction in the calculation of the amount of dust at a coordinate point p. Therefore, in Step S112, it is necessary to calculate the first central axis vertical cross-sectional area Sp1 of the first dust source search region and the second central axis vertical cross-sectional area SP2 of the second dust source search region. The first central axis vertical cross-sectional area Sp1 of the first dust source search region and the second central axis vertical cross-sectional area SP2 of the second dust source search region can be the cross-sectional area of a circle having, as its radius, the "diffusion width y[La] of dustfall particles in the horizontal direction" at the calculated "first and second distances Ld(iM) and Ld(iN)". Alternatively, the "diffusion width γ 2[Ld] of dustfall particles in the vertical direction" at the "first and second distances Ld(im) and Ld(iN)" corresponding to the "diffusion width ay[Ld] of dustfall particles in the horizontal direction" at the "first and second distances Ld(iM) and Ld(iN)" may be used and the cross-sectional area of an ellipse having 2xσ y or 2xγ z as the major axis and the minor axis may be the first central axis vertical cross-sectional area Sp1 and the second central axis vertical cross-sectional area

This treatment makes it possible to reduce a calculation load required to search for the dust source.

[0074] (Third Embodiment)
Next, a third embodiment of the present invention will be described.
The radiation of dustfall collected at an evaluation point can be measured, (the sample of) each dustfall particle or (the sample of) all dustfall particles can be classified into radioactive dustfall or non-radioactive dustfall on the basis of the intensity of the radiation, and a process of searching for the unsteady dust source of the radioactive dustfall (or the non-radioactive dustfall) can be performed for only the radioactive dustfall (or only the non-radioactive dustfall).

A known method can be used to measure the radiation intensity of the dustfall. For example, the methods disclosed in Patent Documents 7 to 9 can be used.

As a method of classifying dustfall samples on the basis of the intensity of the radiation, for example, the following method can be used: the dustfall particles in the samples which are collected at each evaluation point for the period Td(it) (the time (period) from a time td(it-1) to a time td(it)) are separated one by one; the radiation intensity of each dustfall particle is measured; when the radiation intensity is equal to or greater than a predetermined threshold value, the dustfall particle with the radiation intensity is classified as the radioactive dustfall and the other dustfall particles are classified as the non-radioactive dustfall. Since the mass of all samples is measured as the amount of dustfall, a value obtained by multiplying the ratio of the number of radioactive dustfall particles (= [the number of radioactive dustfall particles (the number of radioactive dustfall particles + the number of non-radioactive dustfall particles)]) by the mass of all samples can be the mass of the radioactive dustfall in the samples. Alternatively, the radiation intensity of the captured specific dustfall particles in all samples may be measured. When the radiation intensity is equal to or greater than a predetermined threshold value, the mass of all samples may be the mass of the radioactive dustfall. When the radiation intensity is less than the predetermined threshold value, the mass of all samples may be the mass of the non-radioactive dustfall. In Step S102 of FIG. 3, the obtained mass of the radioactive dustfall (or the mass of the non-radioactive dustfall) is set as the amount of dustfall M(i). Then, the radioactive dustfall (or the non-radioactive dustfall) is set to any one of "dust source", "no dust source", and "undetermined".

This treatment makes it possible to specify the unsteady dust source of the radioactive dustfall at a long distance using dustfall measurement data, without approaching the radioactive dust source. However, the user can set (input) one of the radioactive dustfall and the non-radioactive dustfall as a dust source search target through, for example, a keyboard or a console screen connected to an information-processing apparatus before the flowchart shown in FIG. 3 starts.

[0075]
However, a computer can execute a program to implement the above-described embodiments of the present invention. In addition, the embodiments of the present invention can be applied to a computer-readable recording medium having the program recorded thereon and a computer program product such as the program. Examples of the recording medium may include a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a non-volatile memory card, and a ROM.

[0076]
While the preferred embodiments of the present invention have been described and illustrated above, it should be understood that these are exemplary of the present invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. That is, the present invention is not limited only by the above-described embodiments.

INDUSTRIAL APPLICABILITY

[0077]
The present invention can be widely applied to a method of searching for a dustfall source, such as a nuclear power station, in which the amount of dust (the generation speed of dustfall from the dust source) is unsteadily changed and can effectively search for a dustfall source with high accuracy.

DESCRIPTION OF THE REFERENCE SYMBOLS

i: EVALUATION POINT
p: DUST SOURCE (COORDINATE POINT)
WD: WIND DIRECTION
a: DUSTFALL PLUME
y: DUST SOURCE SEARCH RANGE
10: CENTRAL AXIS OF PLUME
11: CENTRAL AXIS OF DUST SOURCE SEARCH REGION
41: COMMON REGION BETWEEN DUST SOURCE SEARCH REGIONS

What is claimed is:

1. A method of searching for an unsteady dust source position of dustfall, comprising:

a dust amount-setting step of collecting the dustfall for a period Ta(it) from a time td(it-l) to a time ta(it), which is an it-th time in each cycle ∆td, at at least two different evaluation points and obtaining a measured value of the amount of dustfall M per unit time;

a representative wind direction derivation step of continuously measuring a wind direction in a cycle twnt shorter than the cycle Atd for the period Ta(it) in the vicinity of each of the evaluation points and deriving a representative wind direction WD for the period Td(it);

a representative wind speed derivation step of continuously measuring a wind speed in the cycle ∆twjnt for the period Td(it) in the vicinity of each of the evaluation points and deriving a representative wind speed WS for the period Td(it);

a representative fall velocity derivation step of continuously measuring a fall velocity of the dustfall in the cycle ∆tvvint for the period Td(it) in the vicinity of each of the evaluation points and deriving a representative fall velocity Vs for the period Td(it);

a dustfall source search region-setting step of setting a first dustfall source search region Γ IM) that has a central axis which extends from a first evaluation point iM as a starting point in an upwind direction of the representative wind direction WD and has a dustfall source search region width around the central axis and a distance range from the central axis to the dustfall source search region width in a vertical direction and a second dustfall source search region y(iN) that has a central axis which extends from a second evaluation point iN different from the first evaluation point i\i as a starting point in the upwind direction of the representative wind direction WD and has the dustfall source search region width around the central axis and a distance range from the central axis to the dustfall source search region width in the vertical direction;

a distance calculation step of calculating a first distance Ld(iM) between the first evaluation point iM and a coordinate point p which is included in both the first dustfall source search region Y(IM) and the second dustfall source search region YON) and a second distance Ld(iN) between the coordinate point p and the second evaluation point iN;

a cross-sectional area calculation step of calculating a first dust source search region central axis vertical cross-sectional area Sp1, which is a cross-sectional area of the first dustfall source search region in a vertical plane of the central axis of the first dustfall source search region including the coordinate point p, and a second dust source search region central axis vertical cross-sectional area SP2, which is a cross-sectional area of the second dustfall source search region in a vertical plane of the central axis of the second dustfall source search region including the coordinate point p, using the dustfall source search region width;

a dust amount calculation step of calculating a first assumed amount of dust E1 which is proportional to the first dust source search region central axis vertical cross-sectional area Sp1 and a second assumed amount of dust E2 which is proportional to the second dust source search region central axis vertical cross-sectional area Sp2; and

a dust source determination step of determining that the coordinate point p is an unsteady dust source of the dustfall when all of the ratios of the first assumed amount of dust E1 and the second assumed amount of dust E2 which are calculated for all combinations of all dustfall source search regions including the coordinate point p in the dust amount calculation step is within a range of predetermined upper and lower limit threshold values, determining that the coordinate point p is not the unsteady dust source of the dustfall when any one of the ratios of the first assumed amount of dust Ej and the second assumed amount of dust E2 which are calculated in the dust amount calculation step is beyond the range of the predetermined upper and lower limit threshold values, and not determining the unsteady dust source of the dustfall at the coordinate point p when the coordinate point p is included in neither the first dustfall source search region nor the second dustfall source search region, wherein, in a plume equation, the central axis of the dustfall source search region is a central axis of a plume, a plume diffusion width is calculated at the second distance La(iN) on the central axis of the plume, and the calculated plume diffusion width is used as the dustfall source search region width.

2. The method of searching for an unsteady dust source position of dustfall according to Claim 1, wherein, in the representative wind direction derivation step, the representative wind direction WD is derived as an average value of a measured value of the wind direction for the period Td(it).

3. The method of searching for an unsteady dust source position of dustfall according to Claim 1, wherein, in the representative wind speed derivation step, the representative wind speed WS is derived as an average value of a measured value of the wind speed for the period Td(it).

4. The method of searching for an unsteady dust source position of dustfall according to Claim 1, wherein, in the representative fall velocity derivation step, the representative fall velocity Vs is derived as an average value of a measured value of the fall velocity of the dustfall for the period Td(it).

5. The method of searching for an unsteady dust source position of dustfall according to Claim 1, wherein the central axis of the dustfall source search region has the upwind direction of the wind direction as a horizontal component and has a value V./WS obtained by dividing the representative fall velocity Vs of the dustfall by the representative wind speed WS as a vertical gradient, and in the plume equation, the central axis of the dustfall source search region is the central axis of the plume, a horizontal-direction plume diffusion width σ y at the second distance Ld(in) on the central axis of the plume is used as a horizontal component of the dustfall source search region width, and a vertical-direction plume diffusion width σ z at the second distance Ld(in) on the central axis of the plume is used as a vertical component of the dustfall source search region width.

6. The method of searching for an unsteady dust source position of dustfall according to Claim 1, wherein, as the plume equation, the following Expressions (1) and (2) are used which represent dust concentration C(x) at a distance x on the central axis using a horizontal-direction plume diffusion width σy, a vertical-direction plume diffusion width σz, the distance x from a generation source on the central axis of the plume, an amount of dust Qp generated, the representative speed WS, a constant B, and a plume range defined by the horizontal-direction plume diffusion width σy and the vertical-direction plume diffusion width σz (units are all SI units): (Expression (1)) C(x) = B(Qp/27πσ yσ zWS) (inside the plume range); and (Expression (2)) C(x) = 0 (outside the plume range).

7. The method of searching for an unsteady dust source position of dustfall according to Claim 6, wherein an ellipse in which the length of a major axis is two times larger than the horizontal-direction plume diffusion width σ y and the vertical-direction plume diffusion width σ z and the length of a minor axis is two times smaller than the horizontal-direction plume diffusion width σ y and the vertical-direction plume diffusion width Σ Z is the cross-sectional shape of the plume which is vertical to the central axis of the plume, and the inside of the ellipse is the inside of the plume range.

8. The method of searching for an unsteady dust source position of dustfall according to Claim 5, wherein, as the plume equation, the following Expressions (1) and (2) are used which represent dust concentration C(x) at a distance x on the central axis using the horizontal-direction plume diffusion width σy, the vertical-direction plume diffusion width ΣZ, the distance x from a generation source on the central axis of the plume, an amount of dust Qp generated, the representative speed WS, a constant B, and a plume range defined by the horizontal-direction plume diffusion width σy and the vertical-direction plume diffusion width vz (units are all SI units): (Expression (1)) C(x) = B(Qp/27π-σyσzWS) (inside the plume range); and (Expression (2)) C(x) = 0 (outside the plume range).

9. The method of searching for an unsteady dust source position of dustfall according to Claim 8, wherein an ellipse in which the length of a major axis is two times larger than the horizontal-direction plume diffusion width σy and the vertical-direction plume diffusion width σz and the length of a minor axis is two times smaller than the horizontal-direction plume diffusion width σy and the vertical-direction plume diffusion width Σ2 is the cross-sectional shape of the plume which is vertical to the central axis of the plume, and the inside of the ellipse is the inside of the plume range.

10. The method of searching for an unsteady dust source position of dustfall according to any one of Claims 1 to 9, further comprising:
a dust species classification step of measuring the radiation of dustfall samples which are collected at the evaluation point for the period Td(it) and classifying the dustfall by a dust species on the basis of the intensity of the measured radiation, wherein, among the collected dustfall samples, the mass of the dustfall samples corresponding to any one of the dust species classified in the dust species classification step is the amount of dustfall M.