JP2017173003A - Fuel debris measurement system and fuel debris measurement method - Google Patents

Abstract

A system and method for measuring the average burnup of fuel debris contained in a container from the outside of the container with higher accuracy. A fuel debris measurement system (1) has a substantially cylindrical shape and a metal container (5) that contains fuel debris therein, and is disposed radially outside the container (5) and discharged from the fuel debris. Gamma ray detectors 21 to 24 that can detect gamma rays that have passed through the light source, and a shielding body that causes gamma rays from a predetermined portion having a circular shape centered on the axis A to enter the corresponding gamma ray detectors in the accommodation region. 31-34. The number of gamma rays from the entire storage area and the number of gamma rays from the predetermined portions 51 to 54 detected by the gamma ray detector while the container 5 is relatively rotating around the axis A at a predetermined angular velocity, respectively. Counting and weighting the number of gamma rays from the predetermined portions 51 to 54, the average burnup of the fuel debris contained in the container 5 is calculated. [Selection] Figure 2

Description

  Embodiments of the present invention relate to a system and method for measuring the average burnup of fuel debris contained in a container.

  When an accident such as loss of coolant occurs in a nuclear power plant and the core is melted, the nuclear fuel in the core is melted and solidified together with the cladding tube and the internal structure of the reactor, so-called fuel debris. Such fuel debris is usually taken out from a nuclear pressure vessel or the like and stored in a metal vessel. The shape and size of the container are determined so that the nuclear fuel constituting the fuel debris does not become critical. The container generally has an elongated cylindrical shape.

  Fuel debris is usually transported, stored and disposed in a state of being accommodated in the container described above, and in addition, it is required to manage the remaining amount of nuclear fuel material (radioactive material). In the technique for evaluating the remaining amount of nuclear fuel material contained in the fuel debris contained in the container, a radiation detector is arranged on the outer side in the radial direction of the container, and the container is fixed to the radiation detector. A device has been proposed in which radiation from fuel debris is detected by the radiation detector while rotating relatively at an angular velocity.

Japanese Patent Laying-Open No. 2015-227817

  The fuel debris is solidified in a state where the metal constituting the reactor internals and the nuclear fuel material are melted together. When the fuel debris is taken out from the nuclear reactor, it is difficult to disassemble the fuel debris finely with a manipulator or the like and store it in the container described above.

  When the fuel debris taken out from the nuclear reactor is accommodated in the container without being disassembled finely, it is conceivable that the fuel debris and the nuclear fuel material contained therein are unevenly distributed in the container. For example, in the cross section perpendicular to the axial center of the container, there may be a case where nuclear fuel material is non-uniformly present in the vicinity of the axial center in the region where the fuel debris is accommodated and on the radially outer side (that is, in the vicinity of the peripheral wall). is there.

  In such a case, when a gamma ray emitted from the fuel debris is detected by a gamma ray detector located radially outside the container while rotating the container containing the fuel debris around its axis, Some of the gamma rays emitted from the nuclear fuel material in the vicinity of the heart may be absorbed by the nuclear fuel material located radially outside, and may not reach the gamma ray detector.

  Therefore, when measuring the burnup of fuel debris in the vessel based on the gamma ray count incident on the gamma ray detector located radially outside the vessel, the gamma rays emitted from the nuclear fuel material near the axis are It is necessary to eliminate as much as possible the so-called self-absorption effect absorbed by the nuclear fuel material outside the direction.

  Embodiments of the present invention have been made in view of the above circumstances, and provide a system and method capable of measuring the average burnup of fuel debris contained in a container from the outside of the container with higher accuracy. The purpose is to do.

  In order to achieve the above-described object, a fuel debris measurement system according to an embodiment of the present invention has a substantially cylindrical shape, and is disposed inside a metal container that accommodates fuel debris and radially outside the container. At least one gamma ray detector capable of detecting gamma rays emitted from the fuel debris and transmitted through the container, and a crossing perpendicular to the axis of the container. A gamma ray from a predetermined portion having a circular shape centered on the axis of the containing region where the fuel debris can be received, and at least one shield that makes the corresponding gamma ray detector incident on the surface. The container is configured to be rotatable relative to the gamma ray detector about its axis, and the gamma ray detector is rotated while the container is relatively rotated at a predetermined angular velocity. The number of gamma rays from the entire containing area detected and the number of gamma rays from the predetermined portion are respectively counted, and the number of gamma rays from the predetermined portion is weighted to be contained in the container. And a data processing device for calculating an average burnup of the fuel debris.

  Further, the fuel debris measuring method of the embodiment of the present invention has a substantially cylindrical shape, and is disposed inside a metal container for containing the fuel debris and radially outside the container, At least one gamma ray detector capable of detecting gamma rays that have been emitted and transmitted through the container, and corresponding to the gamma ray detector are provided, and contains fuel debris in a cross section perpendicular to the axis of the container. Gamma rays from a predetermined portion having a circular shape centered on the axis of the possible accommodation area are incident on a corresponding gamma ray detector and detected by the gamma ray detector. A fuel debris measuring method for measuring an average burnup of fuel debris contained in the container using a data processing device for acquiring data relating to gamma rays, A number of gamma rays from the entire containing area detected by the gamma ray detector while the container is rotating relative to the gamma ray detector at a predetermined angular velocity about the axis; A step of counting the number of gamma rays from each of the predetermined portions, and the data processing device weights the number of gamma rays from the predetermined portions to average fuel debris contained in the container. And calculating the burnup.

  According to the embodiment of the present invention, the effect of so-called self-absorption, in which gamma rays emitted from the vicinity of the shaft center in the accommodation region are absorbed by the fuel debris (nuclear fuel material) on the radially outer side, is suppressed. This makes it possible to estimate the average burnup of the fuel debris contained in the container with high accuracy.

It is a schematic diagram which shows the structure of the fuel debris measurement system of 1st Embodiment. It is a figure explaining the arrangement | positioning relationship of a gamma ray detector and a shield with respect to a container among the fuel debris measurement systems of 1st Embodiment, and has shown the cross section by the II-II line of FIG. It is a schematic diagram which shows the structure of the fuel debris measurement system of 2nd Embodiment. It is a figure explaining the arrangement | positioning relationship of a gamma ray detector and a shield with respect to a container among the fuel debris measurement systems of 2nd Embodiment, and has shown the cross section by the IV-IV line of FIG.

  Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the embodiments described below, and various modifications can be made without departing from the scope of the invention.

[First Embodiment]
First, the configuration of the fuel debris measurement system for measuring the average combustion rate of the fuel debris of this embodiment and the fuel debris contained in the container will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing the overall configuration of the fuel debris measurement system of the present embodiment. FIG. 2 is a view for explaining the positional relationship between the gamma ray detector and the shield with respect to the container in the fuel debris measurement system of the embodiment, and shows a cross section taken along the line II-II in FIG.

  The fuel debris of the present embodiment is a so-called core melt produced by melting the core of a nuclear reactor (not shown), and more specifically, nuclear fuel together with a cladding tube and a reactor internal structure (not shown). It has melted, cooled and solidified. Fuel debris is mainly composed of oxidized nuclear fuel and contains a relatively high concentration of radioactive material (nuclear fuel material). The fuel debris is removed from the nuclear reactor and accommodated in the vessel 5.

  The container 5 for storing fuel debris is made of metal, and specifically, is made of a metal material that can transmit at least part of gamma rays. The container 5 has a substantially cylindrical shape, and an inner space for accommodating fuel debris is formed inside the peripheral wall 5c. That is, the internal space has a substantially cylindrical shape. The container 5 contains fuel debris in the internal space, and the ends 5a and 5e on both sides thereof are closed to seal the internal space.

  In each figure, the axis of the container 5 is indicated by a one-dot chain line A or point A. A direction along the axis A is referred to as an “axial direction”. The space for housing the fuel debris and the axis of the peripheral wall 5c coincide with the axis A. That is, the internal space and the peripheral wall 5 c of the container 5 extend in the axial direction along the axis A.

  A direction orthogonal to the axial direction is referred to as a “radial direction”. The radially inner side is indicated by an arrow R1, and the radially outer side is indicated by an arrow R2. Further, the circumferential direction around the axis A is indicated by an arrow C in FIG.

  The fuel debris measurement system 1 of the present embodiment is configured so that the axial direction of the container 5 coincides with the vertical direction. In each figure, the upper side in the vertical direction, that is, the drawing side in the axial direction is indicated by an arrow U in the figure, and the lower side in the vertical direction, that is, the insertion side in the axial direction is indicated by an arrow D in the figure.

  The shape and size of the container 5 are determined so that the nuclear fuel material contained in the fuel debris in the internal space does not become critical. The diameter of the internal space of the container 5, that is, the inner diameter of the peripheral wall 5c can be set to 200 mm, for example. The container 5 has an elongated shape in the axial direction. The fuel debris is transferred and stored in a state of being accommodated in the container 5.

  The fuel debris accommodated in the container 5 in the radial position shown in FIG. 1 contains a radioactive substance at a relatively high concentration, and radiation containing gamma rays is emitted from the fuel debris (radioactive substance). . Most of the gamma rays pass through the container 5 and are released to the outside of the container 5.

  The fuel debris measurement system 1 has a container 5 and a device (hereinafter referred to as a handling device) 6 for driving the container 5. In the present embodiment, the handling device 6 holds a vertical upper end 5 a of the container 5. In the figure, only the portion of the handling device 6 that holds the container 5 is shown. The handling device 6 holds the container 5 so that the axial direction of the container 5 coincides with the vertical direction.

  The handling device 6 is configured to be capable of rotationally driving the container 5 at a predetermined angular velocity around the axis A of the container 5. In addition, the handling device 6 is configured to be able to drive the container 5 at a predetermined speed in the axial direction. In the present embodiment, the handling device 6 can drive the container 5 in the axial direction at a constant speed while rotating the container 5 in the circumferential direction at a constant angular speed. In the present embodiment, the container 5 is driven to rotate by the handling device 6 and rotates about the axis A.

  The fuel debris measurement system 1 has a main body 10 that can accommodate at least a part of the container 5. Gamma ray detectors 21, 22, 23, and 24 and shields 31, 32, 33, and 34, which will be described later, are coupled to the main body 10. In the present embodiment, the main body 10 is disposed in water, and more specifically, is disposed on the vertical upper side of the bottom 3 of the spent fuel pool.

  The main body 10 includes a portion (hereinafter, referred to as an axially extending portion) 11 that extends in the axial direction (that is, the vertical direction) on the radially outer side of the container 5 and a vertical lower side. It has a portion (hereinafter referred to as a bottom portion) 13 in contact with the bottom 3 and a portion (hereinafter referred to as an opening edge portion) 15 that constitutes an upper side and defines an opening 16 that receives the container 5. The main body 10 also has a portion 12 (hereinafter referred to as an outer protrusion) that protrudes radially outward from the axially extending portion 11.

  The axially extending portion 11 is configured to surround the radially outer side of the container 5. In the present embodiment, the axially extending portion 11 has a substantially cylindrical shape in which the container 5 and the axis A match.

  The bottom 13 is installed vertically above the bottom 3 of the spent fuel pool and has a substantially disc shape. A support member 14 is provided on the radially inner side of the axially extending portion 11 and on the vertical upper side of the bottom portion 13 to receive the vertically lower end 5e of the container 5 and support the container 5.

  The opening edge 15 is a portion that extends radially inward from the vertical upper end of the axially extending portion 11, and is a portion that defines an opening 16 through which the container 5 passes. The container 5 is inserted into or extracted from the main body 10 through the opening 16. The container 5 is driven in the axial direction by the handling device 6 described above.

  A guide mechanism 18 for positioning the container 5 in the radial direction of the axis A is provided in the main body 10 on the vertical upper side of the opening edge 15. The guide mechanism 18 guides the container 5 to a predetermined radial position by contacting the container 5. The guide mechanism 18 is disposed on the radially outer side of the opening 16 that receives the container 5. In the present embodiment, a plurality of guide mechanisms 18 are arranged in the circumferential direction along the opening 16. As shown in FIG. 1, the plurality of guide mechanisms 18 are arranged such that gaps are formed between the container 5 and the peripheral wall 5 c of the container 5 when the container 5 is at a predetermined radial position.

  The guide mechanism 18 is configured to allow the axial movement of the container 5 in the radial position relative to the main body 10 and the rotation of the container 5 about the axis A. In addition, the guide mechanism 18 limits the movement of the container 5 from the predetermined radial position to the radially outer side by contacting the peripheral wall 5c of the container 5. The guide mechanism 18 can guide the container 5 to a predetermined radial position by contacting the peripheral wall 5c when the container 5 is inserted into the main body 10 from the opening 16.

  The fuel debris measurement system 1 includes radiation detectors 21, 22, 23, and 24 that can detect gamma rays emitted from the container 5 (hereinafter, referred to as gamma ray detectors). The gamma ray detectors 21, 22, 23, and 24 are arranged on the outer side in the radial direction of the container 5, and more specifically, arranged on the outer side in the radial direction from the peripheral wall 5 c of the container 5. . Each of the gamma ray detectors 21, 22, 23, 24 detects radiation transmitted through the peripheral wall 5 c, mainly gamma rays, of the radiation emitted from the nuclear fuel material contained in the fuel debris in the container 5.

  In the present embodiment, each of the gamma ray detectors 21, 22, 23, and 24 includes a semiconductor detector using a germanium single crystal, a so-called germanium detector. The gamma ray detectors 21, 22, 23, and 24 are respectively installed on the upper side of the outer protrusion 12 in the main body 10.

  The fuel debris measurement system 1 includes a plurality of shields 31, 32, 33, and 34 that correspond one-to-one with the plurality of gamma ray detectors 21, 22, 23, and 24 described above. Each shield 31, 32, 33, 34 is made of a material that can shield gamma rays, such as lead, and can shield a part of the gamma rays toward the corresponding gamma ray detectors 21, 22, 23, 24. It is. That is, each shield 31, 32, 33, 34 can limit the gamma rays incident on the corresponding gamma ray detectors 21, 22, 23, 24.

  As shown in FIG. 1, the shields 31, 32, 33, and 34 are arranged on the radially outer side of the container 5, and in the present embodiment, are vertically above the outer protrusion 12 in the main body 10. The main body 10 is disposed radially outside the axially extending portion 11.

  As shown in FIG. 2, the shields 31, 32, 33, 34 and the corresponding gamma ray detectors 21, 22, 23, 24 are arranged on the radially outer side of the container 5, and the peripheral wall of the container 5 Opposing 5c. Each shield 31, 32, 33, 34 is released from the nuclear fuel material of the fuel debris in the container 5 and passes through the peripheral wall 5 c on the radially inner side of the corresponding gamma ray detectors 21, 22, 23, 24. Shield part of gamma rays.

  As shown in FIG. 2, in the cross section perpendicular to the axis A of the container 5, one of the plurality of shields 31, 32, 33, 34 is on the radially inner side of the peripheral wall 5 c of the container 5. The gamma rays emitted from the entire area where the fuel debris can be accommodated (hereinafter referred to as the accommodation area) are made incident on the corresponding gamma ray detector 21. The gamma ray detector 21 corresponding to such a shield 31 can detect gamma rays from the entire storage area in the container 5 and is hereinafter referred to as “total measurement gamma ray detector 21”.

  Further, the shield 31 corresponding to the whole measurement gamma ray detector 21 is referred to as a “first shield 31” below. The first shield 31 is configured such that gamma rays emitted from the accommodation region in the container 5 enter the gamma ray detector 21 for overall measurement. The first shield 31 restricts the gamma rays emitted from the outer side in the radial direction from the container 5 from entering the gamma ray detector 21 for whole measurement.

  The accommodation region on the radially inner side of the peripheral wall 5c has a concentric shape centered on the axis A of the container 5, and can be divided into a plurality of portions 51, 52, 53, 54 having different outer diameters. .

  Among the plurality of gamma ray detectors 21, 22, 23, 24, the gamma ray detectors 22, 23, 24 other than the overall measurement gamma ray detector 21 are limited in gamma rays incident by the corresponding shields 32, 33, 34, respectively. This is a so-called “partial measurement gamma ray detector” that detects gamma rays from a predetermined portion of the accommodation area (51, 52, 53, 54), in particular, “second gamma ray detector 22”. , “Third gamma ray detector 23” and “fourth gamma ray detector 24”.

  Of the shields 31, 32, 33, and 34 described above, those provided corresponding to the second gamma ray detector 22 are referred to as “second shield 32” and correspond to the third gamma ray detector 23. What is provided in this manner is referred to as “third shield 33”, and what is provided corresponding to the fourth gamma ray detector 24 is referred to as “fourth shield 34”.

  The second shield 32 is configured such that gamma rays emitted from predetermined portions 52, 53, and 54 of the accommodation area are incident on the corresponding second gamma ray detector 22. The second shield 32 restricts the gamma rays emitted from the portion 51 and the outside in the radial direction from entering the second gamma ray detector 22. The second gamma ray detector 22 including the second shield 32 detects gamma rays from predetermined portions 52, 53, and 54 centered on the axis A in the storage area in the container 5. It becomes possible.

  Similarly, the 3rd shielding body 33 is comprised so that the gamma ray emitted from the predetermined parts 53 and 54 of the accommodating area | region may inject into the 3rd gamma ray detector 23 corresponding to this. The third shield 33 restricts the gamma rays emitted from the portions 51 and 52 and the outside in the radial direction from entering the third gamma ray detector 23. The third gamma ray detector 23 having such a third shield 33 can detect gamma rays from predetermined portions 53 and 54 centering on the axis A in the accommodation region.

  The fourth shield 34 is configured such that gamma rays emitted from the predetermined portion 54 of the accommodation region enter the corresponding fourth gamma ray detector 24. The fourth shield 34 restricts the portions 51, 52, 53 and the gamma rays from the outside in the radial direction from entering the fourth gamma ray detector 24. The fourth gamma ray detector 24 provided with such a fourth shield 34 can detect gamma rays from the most radially inner portion 54 centering on the axis A in the accommodation region. .

  In the present embodiment, the shields 31, 32, 33, and 34 and the gamma ray detectors 21, 22, 23, and 24 are arranged in the circumferential direction (arrows in the figure) in a cross section perpendicular to the axis A of the container 5 shown in FIG. (Shown as C). More specifically, the shields 31, 32, 33, and 34 are arranged in the circumferential direction with an angle of about 90 degrees around the axis A of the container 5.

  In the cross section perpendicular to the axis A of the container 5 shown in FIG. 2, each shield 31, 32, 33, 34 detects the gamma ray that can enter the corresponding gamma ray detectors 21, 22, 23, 24. The angles with respect to the vessels 21, 22, 23, and 24 (hereinafter referred to as incident angles) are different from each other. In FIG. 2, the incident angle of the whole measurement gamma ray detector 21 restricted by the first shield 31 is denoted by E1, and the incident angle of the second gamma ray detector 22 restricted by the second shield 32 is denoted by E2. The incident angle of the third gamma ray detector 23 restricted by the third shield 33 is indicated by E3, and the incident angle of the fourth gamma ray detector 24 restricted by the fourth shield 34 is indicated by E4.

  The incident angle E <b> 1 is set so that gamma rays emitted from the entire storage area in the container 5 can reach the gamma ray detector 21 for whole measurement. The incident angle E <b> 2 is set so that gamma rays emitted from predetermined portions 52, 53, and 54 excluding the outermost portion 51 in the radial direction can reach the second gamma ray detector 22. Similarly, the incident angle E3 is set so that the gamma rays emitted from the predetermined portions 53 and 54 in the accommodation area can reach the third gamma ray detector 23, and the incident angle E4 is a predetermined value in the accommodation area. The gamma rays emitted only from the portion 54 are set so as to reach the fourth gamma ray detector 24. As described above, the shields 31, 32, 33, and 34 are configured to have different incident angles E1, E2, E3, and E4, respectively.

  In this embodiment, the gamma ray detectors 21, 22, 23, and 24 can be detected in the accommodation region in the container 5 by varying the incident angle of the gamma rays limited by the shields 31, 32, 33, and 34. The different parts are different. In the present embodiment, the storage region in which the fuel debris is stored in the container 5 is divided into four portions 51, 52, 53, and 54 that are concentric with the axis A as the center. The weighted average is calculated by assigning different weights to the portions 51, 52, 53, and 54, and the details will be described below.

  Further, as shown in FIG. 1, the fuel debris measurement system 1 is a device capable of acquiring various data relating to gamma rays detected by the gamma ray detectors 21, 22, 23, and 24 and performing various arithmetic processes. (Hereinafter referred to as a data processing device) 7. The data processing device 7 includes a processor (not shown) that can execute various operations and a memory (not shown) that can store various constants and mathematical expressions. Hereinafter, the data processing content of the data processing device 7 will be described later.

  The relative movement of the container 5 with respect to the gamma ray detectors 21, 22, 23, 24 and the shields 31, 32, 33, 34 in the fuel debris measurement system 1 described above will be described with reference to FIGS.

  The fuel debris measurement system 1 of the present embodiment drives the container 5 by the handling device 6, thereby causing the container 5 to move relative to the gamma ray detectors 21, 22, 23, 24 and the shields 31, 32, 33, 34. The gamma rays transmitted through the peripheral wall 5c of the container 5 are detected by the gamma ray detectors 21, 22, 23, and 24, respectively, while relatively rotating around the axis A at a constant angular velocity.

  In the cross section perpendicular to the axis A of the container 5 shown in FIG. 2, the entire measurement gamma ray detector 21 emits from the entire storage area (51, 52, 53, 54) in which fuel debris can be stored. Gamma rays are incident.

  At this time, the gamma rays emitted from the portions 52, 53, and 53 except the outermost portion 51 in the radial direction in the accommodation region are incident on the second gamma ray detector 22. Similarly, the gamma rays emitted from the portions 53 and 54 of the accommodation area are incident on the third gamma ray detector 23, and the fourth gamma ray detector 24 is the most radially including the axis A in the accommodation area. Gamma rays emitted from the inner portion 54 are incident.

  In addition, the container 5 has an axial center A with respect to the gamma ray detectors 21, 22, 23, 24 so that almost all of the peripheral wall 5c faces the gamma ray detectors 21, 22, 23, 24. The relative movement in the axial direction at a constant speed while rotating relative to the center. In the present embodiment, the container 5 is driven in a spiral shape around the axis A by the handling device 6.

  As a result, each of the gamma ray detectors 21, 22, 23, and 24 detects the gamma rays that are emitted from all the fuel debris accommodated in the container 5 so as to face all of the peripheral wall 5c of the container 5 and are transmitted through the peripheral wall 5c. can do. In this way, the number of gamma rays detected by each gamma ray detector 21, 22, 23, 24 is counted (counted) by the data processing device 7.

  The data processing device 7 determines the fuel debris contained in the container 5 based on the weighted average of the number of gamma rays detected by the gamma ray detectors 21, 22, 23, and 24 by the relative movement of the container 5 described above. The average burnup is calculated, and the calculation method will be described below.

  The “burning degree” is the amount of heat generated until the nuclear fuel is loaded into the nuclear reactor and taken out from the nuclear reactor, and expressed as the amount of heat per ton of nuclear fuel. On the other hand, the “average burnup” is the burnup when the fuel debris contained in the container 5 is regarded as nuclear fuel.

  First, the data processing device 7 is emitted from the entire storage area (51, 52, 53, 54) in the container 5 and enters the gamma ray detector 21 for total measurement, that is, the gamma ray detector 21 for total measurement. Based on the number of gamma rays detected by the above, a temporary value (hereinafter referred to as an average burnup before correction) C ′ of the average burnup of the fuel debris is calculated.

  Methods for calculating the average burnup C ′ before correction are disclosed in JP-A-2015-227817, JP-A-2014-185993, and the like, and description thereof is omitted in this specification.

  The average burnup C ′ before correction is that the gamma rays emitted from the nuclear fuel material in the vicinity of the axis A in the cross section perpendicular to the axis A of the container 5 are absorbed by the nuclear fuel material located radially outside. In particular, the gamma rays emitted from the portion 54 including the axial center A in the accommodation region (51, 52, 53, 54) are in the vicinity of the peripheral wall 5c on the radially outer side. As compared with the gamma rays emitted from the portion 51, there is a problem that it is difficult to enter the gamma ray detector 21 for whole measurement due to self absorption or the like.

  Therefore, the data processing device 7 according to the present embodiment counts the number of gamma rays emitted from the predetermined portions 51, 52, 53, and 54 in the accommodation area in addition to the entire accommodation area, respectively. Based on the weighted average of the number of gamma rays emitted from 52, 53, and 54, the average burnup C of the fuel debris contained in the container 5 is calculated. In the present embodiment, the average burnup C can be expressed using the following mathematical formula.

In the above formula,
C: Average burnup of fuel debris contained in container 5 (average burnup after correction)
C ′: Average burnup calculated based on the number of gamma rays detected by an overall measurement gamma ray detector capable of entering gamma rays from the entire containing region in the container 5 that can contain combustion debris (before correction) Average burnup)
α: Correction factor (variable) of average burnup calculated based on the weighted average of the number of gamma rays detected by all gamma ray detectors
n (i): the number (constant) of portions (divided in the radial direction) constituting the accommodating region in which the fuel debris is accommodated in the cross section perpendicular to the axis A of the container
m (j): number of rotations relative to the gamma ray detector and the shield of the container, that is, the number of parts divided in the axial direction along the axis A of the container (constant)
R: constant (weighting coefficient) preset for each part of the accommodation area
A: Number of gamma rays emitted from each part of the accommodation area and incident on any gamma ray detector (variable)

  The mathematical formulas described above and various constants constituting the mathematical formulas are stored in advance in a memory (not shown) of the data processing device 7. In the present embodiment, the accommodation region is composed of four concentric portions 51, 52, 53, 54 centered on the axis A, and n = 4 in the above formula.

Each time the container 5 rotates one rotation relative to the gamma ray detectors 21, 22, 23, 24 and the shields 31, 32, 33, 34, the data processing device 7 configures each of the storage areas The numbers A ₁ , A ₂ , A ₃ , A ₄ of the gamma rays emitted from the portions 51, 52, 53, 54 and detected by the gamma ray detector are calculated.

Specifically, the number A ₁ of the emitted gamma rays from the portion 51, the gamma rays from all namely portions 51, 52, 53 and 54 of the housing area is detected by the entire measuring gamma ray detector 21 that is incident gamma rays It is obtained from the difference between the number and the number of gamma rays detected by the second gamma ray detector 22 on which gamma rays from the portions 52, 53 and 54 excluding the portion 51 are incident.

Similarly, the number A _{2 of} gamma rays emitted from the portion 52 is obtained from the difference between the number of gamma rays detected by the second gamma ray detector 22 and the number of gamma rays detected by the third gamma ray detector 23. It is done. The number A _{3 of} gamma rays emitted from the portion 53 is obtained from the difference between the number of gamma rays detected by the third gamma ray detector 23 and the number of gamma rays detected by the fourth gamma ray detector 24. Note that the number A _{4 of} gamma rays emitted from the portion 54 is the number of gamma rays detected by the fourth gamma ray detector 24.

In this manner, the data processing device 7 sets the storage area each time the container 5 rotates once relative to the gamma ray detectors 21, 22, 23, 24 and the shields 31, 32, 33, 34. The numbers (so-called counts) A ₁ , A ₂ , A ₃ , A ₄ of the gamma rays respectively corresponding to the constituent parts 51, 52, 53, 54 are calculated.

The data processing device 7 multiplies the numbers A ₁ , A ₂ , A ₃ , A ₄ of these gamma rays by the corresponding constants R ₁ , R ₂ , R ₃ , R ₄ , respectively, thereby obtaining the respective parts 51, 52, 53. , 54 is weighted. The constants R ₁ , R ₂ , R ₃ , and R ₄ are arbitrary values that consider the attenuation of gamma rays due to the distance between each part constituting the accommodation region and the corresponding gamma ray detector, transmission through the peripheral wall 5c of the container 5, and the like. Is set in advance.

These constants R ₁ , R ₂ , R ₃ , and R ₄ are set to larger values as they correspond to portions near the axis A in the accommodation region. Specifically, the constant R ₄ corresponding to the most radially inner portion 54 of the accommodation region is set to the largest value among the constants R ₁ , R ₂ , R ₃ , R ₄ , and the largest diameter The constant R ₁ corresponding to the portion 51 on the outer side in the direction is set to the smallest value among the constants R ₁ , R ₂ , R ₃ , R ₄ . In the present embodiment, the constant R ₁ is set to 1.0, and the constant R ₂ is set to a value greater than 1.0 and less than 2.0. These constants R ₁ , R ₂ , R ₃ and R ₄ can be obtained in advance by performing a simulation or the like.

  In the present embodiment, the gamma ray detectors 21, 22, 23, 24 rotate the container 5 around the axis A one time and make a relative rotation so as to face almost the entire surface of the peripheral wall 5 c. One, 21, 22, 23, and 24 are moved in the axial direction. That is, as shown in the above formula, the gamma ray detectors 21, 22, 23, and 24 are moved in the axial direction by m pieces of the gamma ray detectors while rotating and relatively rotating the container 5. The container 5 is driven so as to face the entire surface of the peripheral wall 5c.

In this way, the gamma ray detectors 21, 22, 23, and 24 scan almost the entire surface of the peripheral wall 5 c of the container 5. Different numbers of gamma rays A ₁ , A ₂ , A ₃ , and A ₄ corresponding to the portions 51, 52, 53, and 54 constituting the accommodation area are assigned different weights, that is, different constants R ₁ , R ₂ , and R ₃ , respectively. , multiplied by R _4, repeatedly integrating m times this in the axial direction. By dividing this integrated value by the total number of gamma rays detected by each of the gamma ray detectors 21, 22, 23, and 24, as shown in the above formula, the correction coefficient (non-dimensional number) α for the average burnup is obtained. calculate.

  The data processing device 7 calculates the average of the correction coefficient α calculated as described above based on the number of gamma rays detected only by the overall measurement gamma ray detector 21 capable of entering gamma rays from the entire accommodation area. The average burnup C of the fuel debris contained in the container 5 is calculated by multiplying the burnup, that is, the “average burnup C ′ before correction”.

  According to this embodiment, compared with the case where the average burnup C ′ is calculated based on the number of gamma rays detected only by the total measurement gamma ray detector 21 capable of receiving gamma rays from the entire accommodation region, The gamma rays emitted from the portion in the vicinity of the shaft center A can be suppressed by the so-called self-absorption, which is absorbed by the fuel debris (nuclear fuel material) located outside in the radial direction. The average burnup of the fuel debris contained in the fuel can be estimated and evaluated.

  The fuel debris measurement system 1 according to the present embodiment is configured so that the axial direction, which is the direction along the axis of the container 5, coincides with the vertical direction, but the fuel debris measurement according to the present invention is performed. The system is not limited to this aspect. For example, the axial direction in which the axial center of the container 5 extends may extend in a predetermined direction in the horizontal direction.

  In the present embodiment, the gamma ray detectors 21, 22, 23, and 24 are arranged at predetermined intervals in the circumferential direction of the axis A of the container 5 as shown in FIG. The arrangement of the gamma ray detectors according to the present invention is not limited to this mode. The gamma ray detector is disposed so as to face the peripheral wall 5c of the container 5, and the shield may be any one that can limit the incidence of gamma rays to the corresponding gamma ray detector.

[Second Embodiment]
The fuel debris measurement system of this embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic diagram showing the configuration of the fuel debris measurement system of the present embodiment. FIG. 4 is a diagram for explaining the arrangement relationship of the gamma ray detector and the shield with respect to the container in the fuel debris measurement system of the present embodiment, and shows a cross section taken along line IV-IV in FIG. In addition, about the structure substantially common to 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIGS. 3 and 4, the fuel debris measurement system 1 </ b> C of the present embodiment detects gamma rays from the entire containing region in a cross section perpendicular to the axis A of the container 5, as in the first embodiment. It has a possible gamma ray detector 21 for total measurement and a first shield 31 provided corresponding to the gamma ray detector 21 for total measurement. The first shield 31 allows gamma rays emitted from the fuel debris storage area of the container 5 to enter the gamma ray detector 21 for overall measurement, and gamma rays from the radial outside of the container 5 are for overall measurement. The incident to the gamma ray detector 21 is restricted.

  In addition, the fuel debris measurement system 1C includes a single gamma ray detector 26 as a partial measurement gamma ray detector for detecting gamma rays from a predetermined portion of the accommodation region.

  The fuel debris measurement system 1 </ b> C includes a shielding device 40 provided corresponding to the gamma ray detector 26 in addition to the gamma ray detector 26. The shielding device 40 includes shielding bodies 44 and 45 configured to be movable with respect to the gamma ray detector 26 (hereinafter referred to as movable shielding bodies) 44 and 45, and respond by moving the movable shielding bodies 44 and 45. A predetermined portion from which gamma rays incident on the gamma ray detector 26 are emitted can be changed.

  The movable shields 44 and 45 are disposed between the corresponding gamma ray detector 26 and the container 5 in the cross section perpendicular to the axis A of the container 5 shown in FIG. It is configured to be movable in a predetermined direction. The movable shields 44 and 45 are configured to be close to each other or separated from each other in a direction perpendicular to a straight line connecting the gamma ray detector 26 and the axis A (indicated by an arrow M in the drawing). ing.

  The shielding device 40 is configured to be able to change an interval between the movable shields 44 and 45 (hereinafter referred to as an opening degree) by bringing the two movable shields 44 and 45 close to or away from each other. In the present embodiment, the shielding device 40 is configured to be able to change three opening degrees.

  Specifically, the shielding device 40 shields gamma rays from the portion 51 in the accommodation area and makes the gamma rays from the portions 52, 53, and 54 enter the gamma ray detector 26 (hereinafter referred to as a first opening). An opening (hereinafter referred to as a second opening) that shields gamma rays from the portions 51 and 52 and makes the gamma rays from the portions 53 and 54 enter the gamma ray detector 26, and The gamma rays from the portions 51, 52, and 53 in the region are shielded, and the opening (hereinafter referred to as the third opening) at which the gamma rays from the portion 54 enter the gamma ray detector 26 can be changed. .

  The fuel debris measurement system 1 </ b> C includes a device (hereinafter simply referred to as “controller”) 9 that can control driving of the movable shields 44 and 45 in the shielding device 40, that is, switching of the opening degree. The controller 9 is electrically connected to the shielding device 40 and the data processing device 7 that acquires data relating to the gamma rays detected by the gamma ray detector 21 for whole measurement and the gamma ray detector 26. The controller 9 can receive the signal from the data processing device 7 and control the opening degree of the shielding device 40.

  In the present embodiment, the controller 9 may be a programmable logic controller (PLC) that can perform timing, counting, and calculation for controlling the shielding device 40.

  In the present embodiment, the container 5 is placed against the gamma ray detector 26 and the shields 44 and 45 in a state where the shield device 40 is controlled to the first opening in the cross section perpendicular to the axis A of the container 5. The gamma rays from the portions 52, 53, and 54 are incident on the gamma ray detector 26 after being rotated once and relatively rotated. During this time, the data processing device 7 counts the gamma rays from the portions 52, 53 and 54 detected by the gamma ray detector 26.

  In addition, while the shielding device 40 is controlled to the second opening, the data processing device 7 is emitted from the portions 53 and 54 and detected by the gamma ray detector 26 while the container 5 is rotated once and relatively rotated. Count the gamma rays. Similarly, while the shielding device 40 is controlled to the third opening, the data processing device 7 is discharged from the portion 54 and detected by the gamma ray detector 26 while the container 5 is rotated once and relatively rotated. Count gamma rays.

  Thus, during relative rotation of the container 5 by three rotations (that is, one rotation at the first opening, one rotation at the second opening, and one rotation at the third opening), the data processing device 7 The gamma rays emitted from the entire accommodation area (51, 52, 53, 54) detected by the gamma ray detector 21 are counted.

From the difference between the number of gamma rays detected by the gamma ray detector for overall measurement 21 and the number of gamma rays detected by the gamma ray detector 26 when the shielding device 40 is at the first opening, the data processing device 7 calculates the number a ₁ of the emitted gamma rays from the portion 51 of the receiving area. Further, the data processing device 7 determines that the difference between the number of gamma rays detected by the gamma ray detector 26 when the shielding device 40 is at the first opening and the number of gamma rays detected when the shielding device 40 is at the second opening. From this, the number A _{2 of} gamma rays emitted from the portion 52 of the accommodation area is calculated.

Similarly, the data processing device 7 determines the number of gamma rays detected by the gamma ray detector 26 when the shielding device 40 is at the second opening, and the number of gamma rays detected when the shielding device 40 is at the third opening. from the difference, calculates the number a ₃ of the emitted gamma rays from the portion 53 of the receiving area. Note that the number A _{4 of} gamma rays emitted from the portion 54 in the accommodation area is the number of gamma rays detected by the gamma ray detector 26 when the shielding device 40 is at the third opening.

In this way, the data processing device 7 is configured so that each of the portions 51 constituting the accommodation region is provided each time the container 5 rotates three times relative to the whole measurement gamma ray detector 21 and the partial measurement gamma ray detector 26. , 52, 53, and 54, the numbers of gamma rays A ₁ , A ₂ , A ₃ , and A ₄ respectively can be calculated.

The data processing device 7 multiplies the numbers A ₁ , A ₂ , A ₃ , A ₄ of these gamma rays by the corresponding constants R ₁ , R ₂ , R ₃ , R ₄ , respectively, thereby obtaining the respective parts 51, 52, 53. , 54 is weighted to calculate a weighted average, and an average burnup C of fuel debris contained in the container 5 is calculated based on the weighted average as shown in the above formula.

  According to the present embodiment, in addition to the entire measurement gamma ray detector 21 and the shield 31, in addition to the single partial measurement gamma ray detector 26 and the shielding device 40 whose opening degree can be changed, the accommodation area can be increased. The average burnup C of the fuel debris accommodated in the container 5 can be calculated by weighting each of the four portions 51, 52, 53, and 54 constituting the same.

  In the present embodiment, the gamma rays emitted from the fuel debris accommodated in the container 5 are detected using two gamma ray detectors, ie, the whole measurement gamma ray detector 21 and the partial measurement gamma ray detector 26. Although detected, the fuel debris measurement system according to the present invention is not limited to this mode. The fuel debris measurement system is disposed outside the container 5 in the radial direction, and includes a gamma ray detector that can detect gamma rays emitted from the fuel debris accommodated in the container 5 and transmitted through the peripheral wall 5c of the container 5. It is sufficient to have at least one.

  For example, the gamma ray detector 26 can be used as a gamma ray detector for overall measurement by configuring the shielding device 40 so that gamma rays from the entire accommodation area can enter the gamma ray detector 26 described above. In the case of this aspect, the data processing device 7 can count gamma rays from the four portions constituting the storage area while rotating the container 5 four times and relatively rotating.

  In the present embodiment, the receiving area is divided into four parts, and the shielding device 40 that restricts the incidence of gamma rays to the partial measurement gamma ray detector 26 can change three opening degrees. However, the division | segmentation aspect of the accommodating area | region which concerns on this invention, and the opening degree switching of a shielding apparatus are not limited to this aspect. If the opening degree of the shielding device can be changed more, it is possible to divide the containing region into a larger number of parts and calculate the average burnup of the fuel debris with higher accuracy.

[Other Embodiments]
In each of the above-described embodiments, the whole measurement gamma ray detector 21 and the partial measurement gamma ray detectors 22, 23, 24, and 26 that detect gamma rays from the fuel debris accommodated in the container 5 include a germanium detector. Although the semiconductor detector is used, the gamma ray detector according to the present invention is not limited to this. The gamma ray detector may be disposed outside the container 5 in the radial direction and can detect gamma rays mainly from the radiation transmitted through the container 5.

  For example, a scintillation detector can be used as such a gamma ray detector. For example, it is also preferable to use a radiation detector having a light detection device (for example, a photodiode) optically coupled to the scintillator, that is, a so-called NaI scintillation detector, using a NaI single crystal as a scintillator.

  In each embodiment, the container 5 has an axis A relative to the gamma ray detectors 21, 22, 23, 24 (see FIGS. 1 and 2) and the gamma ray detector 26 (see FIGS. 3 and 4). In the present invention, the relative rotation of the container with respect to the gamma ray detector is performed by the relative rotation at a constant angular speed while rotating relative to the gamma ray detector. It is not limited to the embodiment. The container only needs to be able to rotate relative to the gamma ray detector at a constant angular velocity about its axis A.

  For example, the container 5 moves relative to the gamma ray detectors 21, 22, 23, and 24 and the shields 31, 32, 33, and 34 by a predetermined distance in the axial direction every time the container 5 rotates and makes a relative rotation. It may be driven. Also according to this aspect, it is possible to detect gamma rays from all fuel debris accommodated in the container 5 by making the respective gamma ray detectors 21, 22, 23, and 24 face all the peripheral walls 5 c of the container 5. It is.

  Further, in each embodiment, the fuel debris measurement systems 1 and 1C can rotate and drive the container 5 in which the fuel debris is stored around the axis A, and the container 5 is aligned along the axis A. Although the handling device 6 that can be driven in the axial direction is provided, the fuel debris measurement system according to the present invention is not limited to this mode. In the fuel debris measurement system, the container 5 only needs to be configured to be rotatable relative to each gamma ray detector and each shield around the axis A thereof.

  For example, the fuel debris measurement system may be configured such that each gamma ray detector and each shield are rotationally driven about the axis A of the stationary container 5. Also in this aspect, each gamma-ray detector and each shield are driven in the axial direction so that the entire surface of the peripheral wall 5c of the container 5 and the gamma-ray detectors 21, 22, 23, and 24 are opposed to each other. The average burnup of the fuel debris can be measured with the same accuracy as the embodiment.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1,1C Fuel debris measurement system 3 Spent fuel pool bottom 5 Container 5a End 5c Peripheral wall 5e End 6 Handling device 7 Data processing device 9 Controller 10 Main body 11 Axial extension 12 Outer protrusion 13 Bottom 14 Support member 15 Opening edge 16 Opening 18 Guide mechanism 21 Gamma ray detector (gamma ray detector for whole measurement)
22 Gamma ray detector (gamma ray detector for partial measurement, second gamma ray detector)
23 Gamma ray detector (Gamma ray detector for partial measurement, 3rd gamma ray detector)
24 Gamma ray detector (Gamma ray detector for partial measurement, 4th gamma ray detector)
26 Gamma ray detector (gamma ray detector for partial measurement)
31 Shield (first shield)
32 Shield (second shield)
33 Shield (Third Shield)
34 Shield (4th shield)
40 Shielding device 44 Shielding body (movable shielding body)
45 Shield (movable shield)
51, 52, 53, 54 Predetermined part of the storage area

Claims (12)

A metal container that has a substantially cylindrical shape and contains fuel debris inside,
At least one gamma ray detector disposed on the radially outer side of the container and capable of detecting gamma rays emitted from the fuel debris and transmitted through the container;
A predetermined portion provided corresponding to the gamma ray detector and having a circular shape centering on the axis of the storage area capable of storing fuel debris in a cross section perpendicular to the axis of the container At least one shield that impinges gamma rays from a corresponding gamma ray detector;
With
The container is configured to be rotatable relative to the gamma ray detector about its axis.
While the container is relatively rotating at a predetermined angular velocity, the number of gamma rays detected from the entire containing area detected by the gamma ray detector and the number of gamma rays from the predetermined portion are counted, respectively. A data processing device that weights the number of gamma rays from a portion and calculates an average burnup of fuel debris contained in the container,
A fuel debris measurement system further comprising: One of the plurality of shields is configured such that gamma rays from the entire containing area can enter a corresponding gamma ray detector,
The fuel debris measurement system according to claim 1, wherein at least one of the shields is configured such that gamma rays from the predetermined portion can enter a corresponding gamma ray detector. The gamma ray detector is
A corresponding shield is configured so that gamma rays from the entire containing area are incident, and a gamma ray detector for whole measurement for detecting gamma rays from the whole containing area,
A corresponding shield is configured so that gamma rays from the predetermined portion are incident, and a gamma ray detector for partial measurement that detects gamma rays from the predetermined portion;
The fuel debris measurement system according to claim 1 or 2, characterized by comprising: The plurality of gamma ray detectors and the plurality of shields respectively corresponding to the gamma ray detectors are arranged in the circumferential direction around the axis.
Each of the shields is configured such that, in a cross section perpendicular to the axis, the incident angles of the gamma rays that can enter the corresponding gamma ray detectors with respect to the gamma ray detectors are different from each other. The fuel debris measurement system according to any one of claims 1 to 3. A movable shield that is the shield configured to be movable with respect to a corresponding gamma ray detector, and by moving the movable shield, a gamma ray incident on the corresponding gamma ray detector is emitted. A shielding device that can change the part,
The fuel debris measurement system according to any one of claims 1 to 3, further comprising: The plurality of movable shields are arranged between a corresponding gamma ray detector and the container in a cross section perpendicular to the axis, and each movable shield is configured to be movable in a predetermined direction. It is configured to be able to approach or separate,
6. The fuel debris measurement system according to claim 5, wherein the shielding device changes the predetermined portion by moving the movable shields close to or away from each other. A handling device that holds the container and is capable of rotationally driving the container at a predetermined angular velocity about the axis;
The fuel debris measurement system according to any one of claims 1 to 6, wherein the container is driven to rotate by the handling device and rotates around the axis. The gamma ray detector and the shield are combined, and a main body capable of accommodating at least a part of the container;
A guide mechanism that is provided in the main body and guides the container to a predetermined radial position by contacting the container;
The fuel debris measurement system according to claim 7, further comprising: The container has a constant speed in the axial direction along the axis while relatively rotating around the axis with respect to the gamma ray detector so that almost all of the peripheral wall faces the gamma ray detector. The fuel debris measurement system according to any one of claims 1 to 8, wherein the fuel debris measurement system moves relative to each other. The data processing device multiplies the average burnup calculated based on the number of gamma rays from the entire containing area by a correction coefficient calculated based on a weighted average of the number of gamma rays from the plurality of predetermined portions. The fuel debris measurement system according to any one of claims 1 to 8, wherein an average burnup of the fuel debris contained in the container is calculated. It has a substantially cylindrical shape, and is disposed in a metal container that contains fuel debris inside, and radially outward of the container, and can detect gamma rays that have been emitted from the fuel debris and transmitted through the container. At least one gamma ray detector and a circular shape centered on the axis of the storage region that is provided corresponding to the gamma ray detector and can store fuel debris in a cross section perpendicular to the axis of the container Using at least one shield that causes gamma rays from a predetermined portion forming the light to enter a corresponding gamma ray detector, and a data processing device that acquires data on gamma rays detected by the gamma ray detector, A fuel debris measuring method for measuring an average burnup of fuel debris contained in the container,
The number of gamma rays from the entire containing area detected by the gamma ray detector while the data processing device is rotating relative to the gamma ray detector at a predetermined angular velocity about the axis of the container. Counting the number of gamma rays from each of the predetermined portions,
The data processor weights the number of gamma rays from the predetermined portion to calculate an average burnup of fuel debris contained in the container;
A fuel debris measuring method comprising: The step of calculating the average burnup includes
The data processor calculates an average burnup based on the number of gamma rays from the entire containment area;
The data processing device calculating a correction coefficient for multiplying the average burnup based on a weighted average of the number of gamma rays from the plurality of the predetermined portions;
The fuel debris measuring method according to claim 11, comprising:

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