JP6640617B2 - Apparatus and method for measuring heavy element content - Google Patents

Description

  The embodiment of the present invention relates to a heavy element-containing measurement technique for measuring heavy element-containing substances such as nuclear fuel and nuclear fuel debris using a muon flight trajectory.

  In the event of a nuclear power plant loss of cooling function, nuclear fuel in the nuclear reactor melts, penetrates the pressure vessel, reaches the containment vessel, etc., and re-solidifies the molten nuclear fuel (hereinafter simply referred to as “fuel debris”). May also occur). When such a situation occurs, it is necessary to remove the fuel debris from the reactor building and store and manage it safely.

  However, it is difficult to directly grasp the material composition of the fuel debris generated by melting and mixing the nuclear fuel and the structural material constituting the pressure vessel and the like due to a problem such as a high radiation dose. If the material composition of the fuel debris cannot be determined, the total amount of nuclear fuel contained in the fuel debris cannot be determined even if the fuel debris is taken out of the reactor building, and the fuel debris will not remain in the reactor building. It is not possible to determine the total amount of recovered nuclear fuel.

Various types of non-destructive inspection techniques have been studied as methods for obtaining information on substances retained inside shielding containers and structures. Generally, radiation transmission tests and ultrasonic flaw detection tests have been considered. And eddy current testing are widely known. Further, as a method for analyzing the composition of the nuclear fuel in a non-destructive, such as the generated gas analyzer and fluorescence X-ray analysis equipment it is known.

  2. Description of the Related Art In recent years, muon fluoroscopy technology using the trajectory of a cosmic ray muon has attracted attention as a kind of radiation fluoroscopy technology. This technology measures the flight trajectory of muons, which are a type of cosmic rays entering the earth from space, without using artificial radiation, to image the inside of structures. It is used for permeation tests of objects and measurement of density distribution of volcanoes.

  In the muon fluoroscopy technology, a muon trajectory detector is provided externally to a structure to be fluoroscopy. The locus detector detects the muon's flight locus and analyzes the locus to determine the location and the material of the substance inside the structure, thereby performing imaging inside the structure.

JP 2012-501450 A

  By the way, in a general muon fluoroscopy technique, the scattering angle of a muon at a position where a heavy element (for example, uranium or plutonium) is present inside a structure is smaller than that at a position where a light element (for example, iron) is present. Utilizing the fact that it becomes larger than the corner, the location of the nuclear material and the material thereof are measured.

  However, the scattering angle of the muon is not always constant but varies even at the same scattering position, and the scattering of the muon particularly in fuel debris in which a plurality of materials are mixed is caused by the mixture. For this reason, the scattering of the scattering angle is more complicated than that of a single element, and it has been difficult to specify the composition of the fuel debris based on only the measured scattering angle.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a heavy element-containing measurement technique capable of specifying the composition of heavy element-containing substances such as nuclear fuel and nuclear fuel debris.

The heavy element-containing substance measuring apparatus according to the embodiment of the present invention is configured to receive a muon incident trajectory incident on the storage container from a first trajectory detector externally provided in the storage container holding the heavy element-containing substance. 1 receiving unit, and a second trajectory that is provided outside the storage container and that is opposed to the first trajectory detector and that receives the emission trajectory of the muon after passing through the storage container. 2 a receiving unit, a scattering angle calculating unit that calculates a scattering angle and a scattering position of the muon based on the received incident trajectory and the emitting trajectory of the muon, and the scattering position is set inside the storage container. A scattering distribution measuring unit that collects the scattering angles belonging to the measurement area and measures the count distribution of the scattering angles in the measurement area, and a substance assumed as the heavy element-containing substance is provided inside the storage container. If it is assumed to have been held, the expected count distribution of the scattering angle expected in the measuring area, is assumed and expected scatter distribution storage unit for storing for each of the substances envisioned, as the heavy-element-containing substance A mixed expected count distribution creating unit that creates a mixed expected count distribution by adding the expected count distributions stored for each of the substances, and changing the ratio of the expected count distributions that constitute the mixed expected count distribution, A composition specifying unit that specifies the composition of the heavy element-containing substance by comparing the measured count distribution with the expected mixed count distribution by waveform fitting .

In the method for measuring a heavy element-containing substance according to the embodiment of the present invention, a step of receiving an incident trajectory of a muon incident on the storage container from a first trajectory detector externally provided to the storage container holding the heavy element-containing substance Receiving the emission trajectory of the muon after passing through the storage container from a second trajectory detector provided outside the storage container and opposed to the first trajectory detector; Calculating a scattering angle and a scattering position of the muon based on the incident trajectory and the emission trajectory of the muon, and collecting the scattering angle belonging to a measurement region where the scattering position is set inside the storage container. Measuring the scattering distribution of the scattering angle in the measurement region, and that the substance assumed as the heavy element-containing substance is held inside the storage container. If was boss, the expected count distribution of the scattering angle which is expected in the measuring area, are stored for the step of storing for each of the substances envisioned, each of the substances envisioned as the heavy-element-containing substance Creating a mixed expected count distribution by adding the expected count distributions, and changing the ratio of the expected count distributions that constitute the mixed expected count distribution to obtain the measured count distribution and the mixed expected count distribution. And collating with a waveform fitting to specify the composition of the heavy element-containing substance.

  According to the embodiments of the present invention, a technique for measuring heavy element-containing substances that can specify the composition of heavy element-containing substances such as nuclear fuel and nuclear fuel debris is provided.

The block diagram of the measuring device of the heavy element containing thing concerning 1st Embodiment. (A) is a sectional view of a storage container in which a measurement region is set, and (B) is an explanatory diagram showing an example of a trajectory of a muon passing through the measurement region. The figure which shows an example of the count distribution of the muon scattering angle in a measurement area. 7 is a calculation example of a predicted count distribution of muon scattering angles in a measurement region when uranium dioxide, stainless steel, or a mixture thereof is assumed as a substance held in the storage container. 5 is a flowchart showing a procedure for measuring a heavy element-containing substance according to the first embodiment. The block diagram of the measuring device of the heavy element containing substance which concerns on 2nd Embodiment. The figure which shows an example of the mixture distribution function of the scattering angle in the mixture of a light element and a heavy element. 9 is a flowchart showing a procedure for measuring a heavy element-containing substance according to the second embodiment.

(1st Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the heavy element-containing substance measuring device 10 (hereinafter, abbreviated as the measuring device 10) according to the first embodiment is a storage container that holds the heavy element-containing substance 23 (see FIG. 2A). A first receiving unit 14 for receiving an incident trajectory of the muon incident on the storage container 11 from a first trajectory detector 12 provided outside the storage container 11, and facing the first trajectory detector 12 externally provided to the storage container 11. Receiving unit 15 for receiving the emission trajectory of the muon after passing through the storage container 11 from the second trajectory detector 13 provided as described above, and the scattering angle of the muon based on the received trajectory and the emission trajectory of the muon. And a scattering angle calculation unit 17 for calculating the scattering position and a scattering angle belonging to the measurement region 22 where the scattering position is set inside the storage container 11, and count distribution of the scattering angle in the measurement region 22 is measured. scattering Assuming that the cloth measurement unit 18 and substances such as nuclear fuel and fuel debris assumed as the heavy element-containing substance 23 are held inside the storage container 11, the expected count distribution of the scattering angle expected in the measurement area 22 A predicted scattering distribution storage unit 19 that stores each of the assumed substances, and a composition specifying unit 20 that specifies the composition of the heavy element-containing material based on the measured count distribution and the predicted count distribution. Prepare.
FIG. 1 illustrates the flight trajectory of one muon μ that passes through the storage container 11 among the muons that pour from the sky.

  The measuring device 10 according to the present embodiment measures the count distribution of the scattering angle of the muon in the set measurement region 22, and the measured count distribution corresponds to each of the substances assumed as the heavy element-containing substances 23. This is an apparatus for specifying the composition of the heavy element-containing substance 23 held in the storage container 11 by comparing the calculated scattering distribution with the expected count distribution.

  The storage container 11 is a metal storage member, in which the heavy element-containing substance 23 is held. An example of the heavy element-containing substance 23 is fuel debris generated by melting the core when a severe accident occurs in a nuclear power plant.

  Fuel debris, which is a heavy element-containing material and is generated by melting the core, is contained in iron-based materials such as pressure vessels and structures inside and outside the furnace, zirconium materials for cladding tubes and channel box materials, and nuclear fuel, which is also a heavy element-containing material. Is a mixture in which various substances such as oxide fuel (uranium oxide or plutonium oxide) and FP (fission product) oxide are mixed in a non-uniform state.

  The first trajectory detector 12 and the second trajectory detector 13 are muon trajectory detectors that detect a trajectory of a muon, which is a charged particle having a high transmission power. This muon trajectory detector has a structure in which a plurality of drift tubes (not shown) capable of detecting the passage of muons are arranged in parallel, and are arranged in a plurality of layers (at least three layers or more).

  The muon trajectory detector detects a trajectory of the muon based on a detection signal of each drift tube in which the passage of the muon is detected. Note that a scintillation detector capable of detecting the passage of muons may be used instead of the drift tube.

  The muon used for measurement may be a secondary cosmic ray generated by primary cosmic rays incident on the earth from space reacting with the atmosphere of the earth, or muons generated artificially by accelerators etc. May be used. The muon of the secondary cosmic ray has the advantage of high energy of 3 to 4 GeV and does not require a special generator, and the muon generated by the accelerator has the advantage that the energy and the incident position can be controlled.

  As the configuration of the first trajectory detector 12 and the second trajectory detector 13, the trajectory of the muon can be detected three-dimensionally. It is desirable to form a structure in which a plurality of layers are stacked alternately at right angles.

  The first trajectory detector 12 and the second trajectory detector 13 are installed at positions facing each other with the storage container 11 interposed therebetween. The two detectors may be arranged on the sides of the container with the storage container 11 interposed therebetween, or may be arranged above and below the container. In addition, the first trajectory detector 12 and the second trajectory detector 13 can detect a large flux muon when they are installed at different heights than when they are installed in parallel.

  The first trajectory detector 12 detects an incident trajectory and a transit time (incident time) of the muon incident on the storage container 11. Then, the detected incident trajectory and the transit time of the muon are transmitted to the measuring device 10.

  On the other hand, the second trajectory detector 13 detects an emission trajectory and a transit time (emission time) of the muon after passing through the storage container 11. Then, the detected emission trajectory and the transit time of the muon are transmitted to the measuring device 10.

  The measuring apparatus 10 according to the first embodiment includes a first receiving unit 14, a second receiving unit 15, a coincidence counting unit 16, a scattering angle calculating unit 17, a scattering distribution measuring unit 18, and an expected scattering distribution storing unit. 19, a composition specifying unit 20, and a weight estimating unit 21.

  The function of each unit constituting the measuring apparatus 10 is a storage medium including an external storage device such as a hard disk drive (HDD) and an optical disk device in addition to a read only memory (ROM) and a random access memory (RAM). A predetermined program code stored in a memory circuit is executed in an electronic circuit such as a processor such as a field programmable gate array (FPGA), a programmable logic device (PLD), a graphics processing unit (GPU), or a central processing unit (CPU). The present invention is not limited to such software processing, and may be realized by hardware processing using an electronic circuit such as an ASIC, or may be realized by a combination of software processing and hardware processing. You may.

  The first receiving unit 14 receives an incident trajectory and an incident time of the muon transmitted from the first trajectory detector 12. Then, the first receiving unit 14 outputs the received incident trajectory and the incident time to the coincidence unit 16.

  The second receiving unit 15 receives the emission trajectory and the transit time of the muon after passing through the storage container 11 from the second trajectory detector 13. Then, the second reception unit 15 outputs the input emission trajectory and emission time to the coincidence unit 16.

  The coincidence unit 16 uses the data of the incident time and the emission time to compare the incident trajectory and the emission trajectory detected by the first trajectory detector 12 and the second trajectory detector 13 within a certain time with the same muon. Is selected as the locus data. Note that the certain time means a time during which it can be determined that the trajectory is related to the same muon. For example, a maximum time or the like which is assumed as a time required for the muon to pass through the storage container 11 can be considered.

  The coincidence counting section 16 sorts the incident trajectory and the emission trajectory of the same muon from the trajectories of the muons detected in large quantities by the first trajectory detector 12 and the second trajectory detector 13. When the input of the trajectory is limited on the measurement device 10 side to the extent that the incident trajectory and the emission trajectory for the same muon can be sufficiently discriminated, the coincidence counting unit 16 may be omitted.

  The scattering angle calculation unit 17 calculates the scattering angle and the scattering position of the muon based on the mucus incident trajectory and the emission trajectory. The scattering angle is calculated from an angle between an expected trajectory and an emission trajectory assuming that the incident trajectory does not change due to scattering. Then, the point at which the incident trajectory changes is determined as the scattering position. Note that the scattering position may be obtained from the intersection of the muon incident trajectory and the outgoing trajectory.

For example, in the case of the muon μ shown in FIG. 1, the scattering angle θ is calculated by the angle between the expected trajectory T _in ′ and the emission trajectory T _out assuming that the incident trajectory T _in does not change due to scattering. Also, determine the point where the incident trajectory T _in is changed as a scattering position A.

  The scattering angle calculation unit 17 calculates the scattering angle and the scattering position for all the muon trajectory data input from the coincidence unit 16. Then, data of the calculated scattering angle and scattering position is output to the scattering distribution measuring unit 18.

  The scattering distribution measurement unit 18 collects scattering angles belonging to the measurement region 22 in which the calculated scattering position is set inside the storage container 11, and measures the distribution of the scattering angles in the measurement region 22.

  Here, the measurement region 22 set inside the storage container 11 will be described. FIG. 2A is a cross-sectional view of the storage container 11 in which the measurement region 22 is set, and FIG. 2B is an explanatory diagram illustrating an example of a muon trajectory passing through the measurement region 22.

  The measurement area 22 is an analytical setting surface for measuring the count distribution of the muon scattering angle in the area. The measurement region 22 is set to an arbitrary size inside the storage container 11 and at a position where the presence of the heavy element-containing substance 23 is assumed.

  It is desirable that the measurement region 22 is set in parallel with a plane defined by at least one of the first trajectory detector 12 and the second trajectory detector 13. Further, the measurement area 22 is not limited to a plane, and may be a three-dimensional area having a certain volume.

  The scattering distribution measuring unit 18 collects the scattering angles of the muons passing through the inside of the measuring region 22, in other words, the scattering positions calculated by the scattering angle calculating unit 17 belong to the measuring region 22. For example, when the scattering position A of the muon μ belongs to the measurement region 22 as shown in FIG. 2B, the scattering angle θ of the muon μ is collected.

  Then, the scattering distribution measuring unit 18 counts every collected scattering angle for each angle, and measures the counting distribution of the scattering angles in the measurement region 22. Note that the scattering distribution measuring unit 18 collects scattering angles until variations in the count distribution in the measurement region 22 can be sufficiently determined.

  FIG. 3 is a diagram showing an example of the distribution of the counting of the scattering angle in the measurement area 22 measured by the scattering distribution measuring unit 18. The horizontal axis indicates the scattering angle, and the vertical axis indicates the number of events (detection number) of the scattering angle.

  The expected scattering distribution storage unit 19 (FIG. 1) stores the expected counting distribution of the scattering angle expected in the measurement region 22 when the substance assumed as the heavy element-containing substance 23 is held inside the storage container 11. Is stored for each of the assumed substances.

  The substance assumed here means all substances assumed as the heavy element-containing substance 23, such as a compound or a mixture containing a nuclear fuel such as uranium or plutonium. When a mixture is assumed, the composition ratio of the substances to be mixed is changed in a plurality of combinations, and each changed combination is distinguished as a different substance.

  Assuming that the assumed substance is filled in the storage container 11, the scattering of the muon passing through the storage container 11 under the same conditions as the actual measurement such as the installation position of the trajectory detector is simulated, and the measurement area 22 is measured. The expected count distribution of the scattering angle at is calculated. The calculation of the expected count distribution is performed for each of the assumed substances, and is stored in the expected scattering distribution storage unit 19. The calculation of the expected count distribution is executed on the measuring device 10 or another computer.

The scattering angle due to Coulomb multiple scattering when a muon passes through a substance is represented by the following equation (1) depending on the radiation length X ₀ , density, and thickness t of the substance passing through the muon. be able to. Since v and p in the equation (1) are the speed and momentum of the muon, vp corresponds to the energy of the incident muon. Here, it is assumed that vp is the average value of the energy spectrum of the incident muon.

  When it is assumed that the substance assumed as the heavy element-containing substance 23 is filled in the storage container 11, the shape information of the storage container 11, the density of the substance, the atomic number, and the like are known. Is used, the count distribution of the scattering angle expected in the measurement region 22 can be calculated.

  Note that since the actually measured scattering angle includes muon scattering by the storage container 11, the data of the scattering angle caused by the storage container 11 is added to the calculated expected count distribution to obtain the actually measured scattering angle. Thus, an expected count distribution close to the expected count distribution is obtained.

  FIG. 4 shows an expected count distribution of the muon scattering angle in the measurement region 22 when uranium dioxide, stainless steel, or a mixture thereof is assumed as the substance held in the storage container 11. As shown in FIG. 4, it can be seen that a different count distribution is obtained for each substance.

  The composition specifying unit 20 compares (collates) the measured count distribution with the expected count distribution stored in the expected scattering distribution storage unit 19. Then, a substance (assumed substance) corresponding to the expected count distribution closest to the measured count distribution is specified (estimated) as the composition of the heavy element-containing substance 23. Note that the closest approximation includes a case where the measured count distribution matches the expected count distribution and a case where the difference between the two count distributions is the smallest. The specification of the composition of the heavy element-containing substance 23 by the composition specifying unit 20 means that the composition of the heavy element-containing substance 23 is estimated by the closest approximation, in addition to the one that clearly shows the composition of the heavy element-containing substance 23. Including.

  The weight estimating unit 21 estimates the weight of a heavy element such as nuclear fuel contained in the heavy element-containing substance 23 based on the specified composition of the heavy element-containing substance 23. Specifically, when the total weight of the storage container 11 is known, the weight of the heavy element such as nuclear fuel contained in the heavy element-containing substance 23 is calculated based on the total weight of the storage container 11 and the specified composition (composition ratio). presume. Further, since the density of the heavy element such as nuclear fuel contained in the heavy element-containing substance 23 is determined based on the specified composition of the heavy element-containing substance 23, the weight of the heavy element such as the nuclear fuel is obtained from the density and the volume of the storage container 11. May be estimated.

  FIG. 5 is a flowchart showing the measurement procedure of the heavy element-containing substance measuring device 10 according to the first embodiment (see FIG. 1 as appropriate).

  The first receiving unit 14 receives the muon incident trajectory and the incident time transmitted from the first trajectory detector 12 (S10).

  The second receiving unit 15 receives the emission trajectory and the transit time of the muon after passing through the storage container 11 from the second trajectory detector 13 (S11).

  The coincidence counting unit 16 selects an incident trajectory and an exit trajectory detected within a predetermined time as trajectories related to the same muon (S12).

  The scattering angle calculation unit 17 calculates the scattering angle and the scattering position of each muon based on the incident trajectory and the emission trajectory (S13).

  The scattering distribution measuring unit 18 collects the scattering angles in the set measurement region 22 and measures the scattering angle counting distribution (S14).

  The composition specifying unit 20 compares the measured count distribution with the expected scatter distribution stored in the expected scatter distribution storage unit 19, and determines that the substance corresponding to the expected count distribution closest to the measured count distribution contains a heavy element. The composition of the substance 23 is specified (S15).

  As described above, the scattering angle count distribution in the measurement region 22 is measured and compared with the expected counting distribution of the scattering angle of each substance assumed as the heavy element-containing substance 23, based on the data of only the scattering angle. Compared with the case where the composition of the heavy element-containing substance 23 is specified, the composition of the heavy element-containing substance 23 can be specified with high accuracy.

(2nd Embodiment)
FIG. 6 is a configuration diagram of the measuring device 10 for the heavy element-containing substance 23 according to the second embodiment. In FIG. 6, portions having the same configuration or function as those of the first embodiment (FIG. 1) are denoted by the same reference numerals, and redundant description is omitted.

  The difference between the measurement apparatus 10 according to the second embodiment and the first embodiment is that the measurement apparatus 10 further includes a mixture approximation function creation unit 24 as a mixture expected count distribution creation unit.

Mixing the approximate function creating portion 24, the expected scatter distribution is conserved storage unit 19, the expected count distributions of substances which are contemplated as heavy-element-containing substance 23, an approximate function by waveform Fi Tsu coating such as a least square method create. Then, a mixed approximation function is created by adding the approximation functions corresponding to each expected count distribution.

  Note that, in the present embodiment, an approximate function of the expected count distribution of each assumed substance is created, and a mixed approximate function is created by adding the approximate functions, but such approximate functions are added. Not limited to the mixture approximation function, by adding the expected count distribution of each assumed substance, the mixed expected count distribution when the assumed substance is a mixture of a plurality of substances may be obtained by another means. . That is, the mixture approximation function created by the mixture approximation function creation unit 24 corresponds to a mixture expected count distribution obtained by adding the estimated count distributions of the respective assumed substances.

  FIG. 7 shows an example of a mixture approximation function in a mixture of a light element and a heavy element. The mixed approximate function creating unit 24 creates a mixed approximate function by adding the approximate functions corresponding to the two expected count distributions when the expected count distributions of the light element and the heavy element are stored in the expected scattering distribution storage unit 19. I do.

  The composition specifying unit 20 changes the composition ratio of the approximation function constituting the mixture approximation function, and compares the count distribution measured by the scattering distribution measurement unit 18 with the mixture approximation function by waveform fitting. Then, the substance corresponding to the composition ratio of the approximation function in the mixed approximation function closest to the measured count distribution is specified as the composition of the heavy element-containing substance 23.

A specific example will be described.
It is assumed that the heavy element-containing substance 23 contains uranium and iron. First, the mixed approximation function creating unit 24 inputs the respective expected scattering distributions of uranium and iron from the expected scattering distribution storage unit 19, and creates an approximation function for each expected scattering distribution.

Then, as in the following equation (2), a mixed approximate function f (θ) is created by adding the approximate functions of uranium and iron. f _U (θ) and f _Fe (θ) indicate approximate functions of uranium and iron, and C ₁ and C ₂ indicate constituent ratios of each substance.

f (θ) = C ₁ × f _U (θ) + C ₂ × f _Fe (θ) Equation (2)

The composition specifying unit 20 changes the composition ratios C ₁ and C ₂ of the approximation function that forms the mixture approximation function f (θ), and changes the count distribution measured by the scattering distribution measurement unit 18 and the mixture approximation function f (θ). Is compared (matched) with.

Then, the composition of the heavy element-containing substance 23 is specified based on the constituent ratios C ₁ and C ₂ of uranium and iron in the mixed approximation function f (θ) that most closely approximates the measured count distribution. When three or more substances are contained in the heavy element-containing substance 23, the constituent ratio of each substance is derived by the same procedure.

  FIG. 8 is a flowchart showing a measurement procedure of the measurement device 10 for the heavy element-containing substance 23 according to the second embodiment (see FIG. 6 as appropriate).

  The first receiving unit 14 receives the muon incident trajectory and the incident time transmitted from the first trajectory detector 12 (S20).

  The second receiving unit 15 receives the emission trajectory and the transit time of the muon after passing through the storage container 11 from the second trajectory detector 13 (S21).

  The coincidence counting unit 16 selects an incident trajectory and an exit trajectory detected within a predetermined time as trajectories related to the same muon (S22).

  The scattering angle calculation unit 17 calculates the scattering angle and the scattering position of each muon based on the incident trajectory and the emission trajectory (S23).

  The scattering distribution measuring unit 18 collects the scattering angles in the set measurement area 22 and measures the scattering angle counting distribution (S24).

  The mixed approximation function creation unit 24 creates a mixed approximation function by adding the approximation functions of each expected scattering distribution stored in the expected scattering distribution storage unit 19 (S25).

  The composition specifying unit 20 changes the composition ratio of each approximation function in the mixture approximation function, and checks the measured count distribution with the mixture approximation function (S26).

  The composition specifying unit 20 specifies the composition of the heavy element-containing substance 23 based on the composition ratio of the approximation function in the mixed approximation function closest to the measured count distribution (S27).

  As described above, the count distribution of the muon scattering angle in the measurement region 22 is compared with the mixed approximation function created based on the expected count distribution of each of the substances assumed as the heavy element-containing substance 23, and the heavy element-containing The composition of the product 23 can be specified with higher accuracy.

  According to the heavy element-containing measurement device of each embodiment described above, the muon scattering angle count distribution is measured in a measurement region set in the storage container holding the heavy element-containing substance, and the measured count is measured. The composition of the heavy element-containing material such as nuclear fuel or fuel debris can be specified by comparing the distribution with the expected count distribution of the substance assumed as the heavy element-containing material.

  Although several embodiments of the present invention have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents. In the above-described embodiment, the storage container 11 that stores the fuel debris taken out of the reactor building is described as the measurement target. However, the first trajectory detector 12 and the second trajectory detector 12 are located outside the reactor building. By providing the two-track detector 13 outside, fuel debris held inside the containment vessel can be measured.

  DESCRIPTION OF SYMBOLS 10 ... Heavy element content measuring device, 11 ... Storage container, 12 ... 1st locus detector, 13 ... 2nd locus detector, 14 ... 1st reception part, 15 ... 2nd reception part, 16 ... Coincidence part , 17: Scattering angle calculation unit, 18: Scattering distribution measuring unit, 19: Expected scattering distribution storage unit, 20: Composition specifying unit, 21: Weight estimation unit, 22: Measurement area, 23: Heavy element content (fuel debris) , 24... A mixed approximation function creating unit, θ: scattering angle, A: scattering position.

Claims (4)

A first receiving unit that receives an incident trajectory of a muon incident on the storage container from a first trajectory detector provided outside the storage container that holds the heavy element-containing material;
A second receiving unit that is provided outside the storage container and that receives an emission trajectory of the muon after passing through the storage container, from a second trajectory detector provided to face the first trajectory detector;
A scattering angle calculation unit that calculates a scattering angle and a scattering position of the muon based on the incident trajectory and the emission trajectory of the received muon,
A scattering distribution measuring unit that collects the scattering angles belonging to a measurement region where the scattering position is set inside the storage container, and measures a count distribution of the scattering angles in the measurement region,
Assuming that the substance assumed as the heavy element-containing substance is held inside the storage container, the expected count distribution of the scattering angle expected in the measurement region is stored for each of the assumed substances. Expected scattering distribution storage unit
A mixed expected count distribution creating unit that creates a mixed expected count distribution that is the sum of the expected count distributions stored for each of the substances assumed as the heavy element-containing material,
A composition for changing the ratio of the expected count distribution that constitutes the mixed expected count distribution, and comparing the measured count distribution and the mixed expected count distribution with a waveform fitting to specify the composition of the heavy element-containing material. Specific part,
An apparatus for measuring a heavy element-containing substance, comprising:   The heavy element-containing material according to claim 1, further comprising a weight estimating unit configured to estimate a weight of the heavy element included in the heavy element-containing material based on the specified composition of the heavy element-containing material. measuring device. The estimated scatter distribution storage unit, the measuring device of the heavy-element-containing substance according to claim 1 or claim 2, characterized in that the addition of scattering of the muons caused by the said container to the expected count distribution . Receiving a muon incident trajectory incident on the storage container from a first trajectory detector provided outside the storage container holding the heavy element-containing material;
A step of receiving the emission trajectory of the muon after passing through the storage container from a second trajectory detector provided outside the storage container and opposed to the first trajectory detector;
Calculating the scattering angle and the scattering position of the muon based on the incident trajectory and the emission trajectory of the received muon,
Collecting the scattering angles belonging to a measurement region where the scattering position is set inside the storage container, and measuring a count distribution of the scattering angles in the measurement region;
Assuming that the substance assumed as the heavy element-containing substance is held inside the storage container, the expected count distribution of the scattering angle expected in the measurement region is stored for each of the assumed substances. Steps to
Creating a mixed expected count distribution by adding the expected count distribution stored for each of the substances envisioned as the heavy element-containing material,
Changing the ratio of the expected count distribution forming the mixed expected count distribution, and comparing the measured count distribution and the mixed expected count distribution by waveform fitting to specify the composition of the heavy element-containing substance. When,
A method for measuring heavy element-containing substances, comprising:

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