JP6468931B2 - Apparatus and method for measuring the amount of nuclear material in a damaged / molten fuel-containing material - Google Patents

Description

  The present invention relates to a measuring device and a measuring method for the amount of nuclear material in a damaged / molten fuel-containing material.

  The amount of nuclear material contained in spent fuel generated from a nuclear power plant is ascertained by analysis or the like in units of fuel assemblies. In addition, based on the amount of nuclear material obtained as a result of analysis, appropriate management such as temporary storage in the power plant, intermediate storage, transportation, and reprocessing facilities is performed.

  On the other hand, at the Fukushima Daiichi Nuclear Power Station, it is assumed that the nuclear material in the fuel assembly is in a molten state and the shape of the assembly cannot be maintained, and it is considered impossible to take out fuel assemblies. In the future, materials containing damaged or molten fuel (hereinafter referred to as fuel debris) will be removed from the furnace and properly managed (selection of long-term storage method, selection of storage method, safety analysis of transportation between facilities, stabilization of fuel debris, or In order to select a reprocessing method, direct disposal, etc.), it is necessary to accurately measure the amount of nuclear material in units of containers containing fuel debris, but this is high due to the effects of impurities such as a large amount of core structure materials. Accurate non-destructive measurement is a difficult situation.

  In this regard, there is currently no specific proposal for an apparatus and method for measuring the amount of nuclear material in fuel debris for fuel debris.

  In general, a technique using a high-energy X-ray CT apparatus as a non-destructive inspection technique for an object is known, for example, from Patent Document 1 instead of fuel debris. In patent document 1, the presence or absence of the internal space | gap of the radioactive waste solidified body obtained by solidifying the radioactive waste generated from a nuclear power plant etc. with a solidification material is test | inspected with a X-ray CT apparatus.

Japanese Patent Laid-Open No. 05-302997

  According to Patent Document 1, although there is a concept of using an X-ray CT apparatus for measurement of radioactive waste from a nuclear power plant, it does not assume that fuel debris is targeted. Moreover, it is only what measures an internal space | gap, and does not have a viewpoint of measurement of the amount of nuclear materials.

  In view of the above, in the present invention, an apparatus and a method for measuring the amount of nuclear material in a damaged / molten fuel-containing material that can measure the amount of nuclear material by using an X-ray CT apparatus for fuel debris Is to provide.

  From the above, in the present invention, an X-ray generator that irradiates a fuel debris storage container storing fuel debris with X-rays, a radiation detector that detects X-rays transmitted through the fuel debris storage container, and a fuel debris storage A rotation drive mechanism for rotating and scanning the X-ray generator and the radiation detector with respect to the container 3 and a signal processing device for obtaining a detection signal detected by the radiation detector are provided. Using the density at each point of the debris and the known density of the nuclear material and the structural material constituting the fuel debris, the amount of nuclear material of the fuel debris is obtained.

  Further, the present invention detects X-rays transmitted through the fuel debris storage container by irradiating the fuel debris storage container storing the fuel debris while rotating and scanning the X-rays, and each point of the fuel debris obtained from the detection signal. The amount of the nuclear material of the fuel debris is obtained using the density in the above and the known density of the nuclear material and the structural material constituting the fuel debris.

  According to the present invention, since the composition of each part in the fuel debris is clarified, the eutectic, the raw material and the structural material in the phase-separated state can be identified together with their masses, and the nuclear debris is stored in units of 3 fuel debris storage containers The amount of substance can be grasped. As a result, appropriate processing such as selection of long-term storage method, selection of storage method, safety analysis of transportation between facilities, stabilization of debris or reprocessing method, direct disposal, etc. can be made depending on the amount of nuclear material.

Flow diagram showing an outline of a method for measuring the amount of nuclear material in fuel debris according to the present invention. The figure which shows the state which the nuclear material and the structural material mixed and formed the eutectic. The figure which shows a nuclear substance and a structural material in a phase-separated state. The figure which shows schematic structure of the high energy X-ray CT apparatus used by this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present invention described below, attention is paid to obtaining information on the density of fuel debris to be inspected by using an X-ray CT apparatus. This density is different from the density of the nuclear material, which is the raw material, and the density of the structural material, and the fuel debris exists either in the eutectic by mixing the raw material and the structural material, or in the phase separation state thereof. It is a thing that paid attention to.

  First, according to the X-ray CT apparatus, the density distribution and volume inside the subject can be obtained.

  On the other hand, as for the fuel debris, which is the specimen, the fuel debris collected from the Three Mile Island nuclear power plant in the United States showed that the fuel debris was a eutectic or a phase-separated state of the raw material and structural material. It is known to exist. FIG. 2 is a diagram showing a state in which a nuclear material and a structural material are mixed to form a eutectic, and FIG. 3 is a diagram showing a phase separated state of the nuclear material and the structural material. 2 and 3 show a state in which the fuel debris FD is stored in the fuel debris storage container 3.

In this case, the densities of the raw material and the structural material are known in advance. The density ρu of the nuclear material as a raw material is relatively high, and 11 g / cm ³ for uranium oxide UO ₂ . Density ρz structural member is lower than the density of nuclear matter Rou, the zirconium Zr 6.5g / cm ^3, zirconium oxide ZrO ₂ in 5.6 g / cm ^3, a 7.9 g / cm ³ in a stainless steel SUS. Also, for the eutectic portion of FIG. 2, the density here should show an intermediate density value between the density of the raw material and the density of the structural material.

  In the present invention, by utilizing this difference, the amount of nuclear material is obtained from the density distribution measured non-destructively with a high energy X-ray CT apparatus and its volume.

  FIG. 4 shows a schematic configuration of a high energy X-ray CT apparatus used in the present invention. The X-ray CT apparatus in the embodiment of FIG. 1 includes an X-ray generator 1 that generates X-rays with a fan-shaped beam, a radiation detector 2 (consisting of a number of radiation sensors arranged side by side), and a fuel debris that is a subject. A turntable 4 for rotating and scanning the X-ray generator 1 and the radiation detector 2 with respect to the storage container 3 and its rotational drive mechanism 6, and the X-ray generator 1 and the radiation detector 2 with respect to the fuel debris storage container 3 are translated. Data from scanning translation scanner 5 and its translation drive mechanism 7, scanner controller 8 for controlling rotation drive mechanism 6 and translation drive mechanism 7, signal processor 9 for processing signals from radiation detector 2, and signal processing circuit 9 The image processing apparatus 10 that creates an image based on the image and the CRT 11 that displays the image are provided. X-rays emitted from the X-ray generator 1 enter the radiation detector 2, and a signal proportional to the incident intensity is sent to the signal processor 9. An image is created based on the collected data and displayed on the CRT 11. To do.

  The X-ray generator 1 includes an electron beam accelerator for accelerating electrons to, for example, 12 MeV and a metal target with which the electron beam collides in order to generate high energy X-rays of 1 MeV or higher. The metal target may be anything as long as it has a high density. For example, tungsten is preferable. High energy X-rays radiated from the metal target pass through the fuel debris storage container 3 and then enter the radiation detector 2. The translation scanner 5 housing the X-ray generator 1 and the radiation detector 2 can be translated on the turntable 4 by a translation drive mechanism 7, and the turntable 4 is around the fuel debris storage container 3. The X-ray generator 1 and the radiation detector 2 are translated and rotated with respect to the fuel debris storage container 3. The high-energy X-rays radiated from the metal target of the X-ray generator 1 pass through the inside of the fuel debris storage container 3 as the subject at all angles in the horizontal direction, and the data from the radiation detector 2 is signal processed. The image is sent to the device 9 and is displayed on the CRT 11 by the image processing device 10.

  According to the above apparatus, density information (including density distribution) at each point of the fuel debris is obtained for the fuel debris in the fuel debris storage container 3. In addition, information on the volume of fuel debris is known. 2 and 3 described above can be referred to as a cross-sectional imaging screen of the fuel debris FD in the fuel debris storage container 3 obtained as described above. The cross-sectional imaging screen of the fuel debris FD is displayed on the CRT 11 that displays an image, and the internal state can be grasped.

The cross-sectional imaging screen of the fuel debris FD displayed on the CRT 11 can identify and display the eutectic or the phase separation state from the viewpoint of the density of each point in the fuel debris FD. Specifically, in the signal processing device 9 that processes a signal from the radiation detector 2, information on the density ρ at the point is evaluated.
[Equation 1]
ρ = yρu + (1−y) ρz (1)
This equation (1) is an equation showing the relationship between the measured density ρ, the known nuclear material density ρu, and the structural material density ρz, using the nuclear material ratio y. For example, when the density ρu of the nuclear material is 11 g / cm ³ of uranium oxide UO ₂ and the density ρz of the structural material is 6.5 g / cm ³ of zirconium Zr, the density ρ of the nuclear material as a measured value of the point Is 11 g / cm ³ , the nuclear material ratio y is 1, and this point is found to be a nuclear material.

Similarly, if the density ρ of the nuclear material as a measured value at this point is 6.5 g / cm ³ , the nuclear material ratio y is 0, and this point is found to be a structural material. Moreover, when it is this intermediate value, it can be estimated that the eutectic body defined by the numerical value of the nuclear material ratio y is formed. The density ρ is a value obtained as a signal incident on the radiation detector 2 and proportional to the incident intensity.

Thus, when the nuclear material in the fuel debris forms a eutectic with the structural material, the density of the eutectic is ρu having a high density and ρz having a low density (UO2: 11 g / cm3) (Zr / ZrO2: 6.5 / 5.6, SUS: 7.9), and can be measured with a high energy X-ray CT apparatus. In that case, the composition of the eutectic (Zr composition or Zr (ZrO2) / SUS ratio) is predicted from the composition of fuel debris around the eutectic, and the nuclear material ratio y is calculated from the measured density. Further, from the calculated nuclear material ratio y and the volume of the eutectic Vx, the nuclear material amount Mu1 is obtained by the equation (2).
[Equation 2]
Mu1 = yρu × Vx (2)
When the nuclear material in the fuel debris is phase-separated, the nuclear material weight is obtained from the volume Vu of the high density (nuclear material density ρu) region using the equation (3). In Equation (3), Mu2 is the amount of nuclear material during phase separation, ρu is the density of high-density nuclear material, and Vu is the volume of the high-density region.
[Equation 3]
Mu2 = ρu × Vu (3)
FIG. 1 is a flowchart showing an outline of the series of processes. According to this figure, in the first processing step S1, the fuel debris storage container 3 is placed on the turntable 4 of FIG. In the process step S2, the process of irradiating the X-ray from the X-ray generator 1 and detecting the transmitted X-ray with the radiation detector 2 is executed at least one turn with the rotation of the turntable 4. In processing step S3, density information of each point in the fuel debris FD is obtained by processing in the signal processing device 9.

  In the processing step S4, it is identified from the density of each point whether the point is a eutectic or a phase separation state, and when it is a eutectic, each substance ratio y is obtained by the equation (1), The nuclear material amount Mu1 is calculated from the equation (2). These processes correspond to process steps S5 and S6. When in the phase separation state, in processing step S7, the amount of nuclear material Mu2 during phase separation is calculated using the density ρu of the high-density nuclear material and the volume Vu of the high-density region. In the processing step S8, the nuclear material amount Mu1 in the eutectic and the nuclear material amount Mu2 in the phase separation state are added together to obtain a total nuclear material amount Mu.

  The series of processing from the above processing steps S4 to S8 is performed on the entire fuel debris FD based on the density information of each point in the fuel debris FD, so that the volume and the total nuclear material amount Mu are determined. Can be obtained. These processing results are configured as a cross-sectional imaging screen of the fuel debris FD, displayed on the CRT 11, and used for grasping the internal state and for external provision.

  According to the present invention, since the composition of each part in the fuel debris is clarified, the eutectic, the raw material and the structural material in the phase-separated state can be identified together with their masses, and the nuclear debris is stored in units of 3 fuel debris storage containers. The amount of substance can be grasped. As a result, appropriate processing such as selection of long-term storage method, selection of storage method, safety analysis of transportation between facilities, stabilization of debris or reprocessing method, direct disposal, etc. can be made depending on the amount of nuclear material. Also, derived from this, it is possible to select a fuel debris criticality management method. Moreover, in the method of the present invention, a method for measuring the amount of nuclear material in fuel debris can be easily performed.

1: X-ray generator 2: Radiation detector 3: Fuel debris storage container 4: Turntable 5: Translation scanner 6: Rotation drive mechanism 7: Translation drive mechanism 8: Scanner 9: Signal processing device 10: Image processing device 11: CRT display

Claims (6)

An X-ray generator for irradiating a fuel debris storage container containing X-rays, a radiation detector for detecting X-rays transmitted through the fuel debris storage container, and an X-ray generator for the fuel debris storage container A rotational drive mechanism that rotationally scans the radiation detector, and a signal processing device that processes a signal from the radiation detector,
The signal processing device uses the density at each point of the fuel debris obtained from the signal from the radiation detector and the known density of the nuclear material and the structural material constituting the fuel debris. The amount of nuclear material in
The signal processing device uses the density at each point of the fuel debris obtained from the signal from the radiation detector and the known density of the nuclear material and the structural material constituting the fuel debris. A device for measuring the amount of nuclear material in a damaged / molten fuel-containing material, wherein the state at each point is identified as nuclear material, structural material, or eutectic thereof . A device for measuring the amount of nuclear material in a damaged / molten fuel-containing material according to claim 1 ,
When the state of each point of the fuel debris is a eutectic that is a mixture of a nuclear material and a structural material, the signal processing device obtains each material ratio that is a ratio of the nuclear material and the structural material, An apparatus for measuring the amount of nuclear material in a damaged / molten fuel-containing material, wherein the amount of nuclear material in the fuel debris is determined from density and volume. A device for measuring the amount of nuclear material in a damaged / molten fuel-containing material according to claim 1 ,
The signal processing device obtains the nuclear material amount of the fuel debris from the density and volume of the nuclear material when the state at each point of the fuel debris is a phase separation state by the nuclear material and the structural material. A device for measuring the amount of nuclear material in damaged / molten fuel-containing materials. At each point of the fuel debris obtained from the detected X-ray, the X-ray transmitted through the fuel debris storage container is detected by irradiating the fuel debris storage container storing the fuel debris while rotating and scanning with X-rays . Using the density and the known density of the nuclear material and structural material constituting the fuel debris, the amount of the nuclear material of the fuel debris is obtained ,
Using the density at each point of the fuel debris determined from the detected X-rays and the known density of the nuclear material and structural material constituting the fuel debris, the state at each point of the fuel debris is A method for measuring the amount of nuclear material in a damaged / molten fuel-containing material characterized by identifying the material, structural material, or eutectic thereof . A method for measuring the amount of nuclear material in a damaged / molten fuel-containing material according to claim 4 ,
When the state at each point of the fuel debris is a eutectic in which a nuclear material and a structural material are mixed, a ratio of each material, which is a ratio of the nuclear material and the structural material, is obtained, and the fuel is obtained from the average density and volume of the eutectic. A method for measuring the amount of nuclear material in a damaged / molten fuel-containing material, characterized in that the amount of debris is determined. A method for measuring the amount of nuclear material in a damaged / molten fuel-containing material according to claim 4 ,
A damaged / molten fuel-containing material characterized in that when the state at each point of the fuel debris is a phase separation state by a nuclear material and a structural material, the nuclear material amount of the fuel debris is obtained from the density and volume of the nuclear material. Method for measuring the amount of nuclear material in the inside.

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