JP6563745B2 - Debris accumulation amount estimation apparatus and estimation method - Google Patents

Description

  The present invention relates to a debris accumulation amount estimation apparatus and an estimation method for estimating a debris accumulation amount inside a nuclear reactor vessel from the outside of a nuclear reactor vessel containing a core and filled with liquid metal.

  One of the severe accidents at nuclear power plants is a core damage accident. For example, in fast breeder reactors, the power density of the core is high, and the reactivity of the core increases at the time of an accident, so it has been pointed out that the core may be damaged in a short time. For this reason, JSFR (Japan Sodium-cooled Fast Reactor) is an advanced loop-type sodium-cooled fast reactor that is under development in Japan. Various measures are taken to end the event in the furnace without occurring.

  The damaged core material is debris in which core fuel and various structures are mixed. When the event ends in the reactor, the debris is rearranged on a core catcher or the like provided at the bottom of the reactor vessel. Debris contains many isotopes that emit neutrons and gamma rays generated by nuclear reactions, and has high radioactivity.

  In the event of a severe accident, the debris relocated at each location as a means of monitoring that the measures described above to terminate the event in the furnace function as expected and avoid recriticality. It is considered effective to measure the amount.

  Conventionally, as a method for identifying the position of debris in a light water reactor power plant, a laser oscillation device, a scanning optical system for forming a laser sheet that irradiates a laser beam oscillated from the laser oscillation device in a sheet shape, and a measurement region in the laser sheet An optical cable for transmitting optical data, a camera for capturing image data by capturing the optical data transmitted by the optical cable, an image processing unit for processing the image data, a scanning optical system and an optical cable for the reactor pressure vessel or atomic And an arm that is inserted into the cooling water in the reactor containment vessel, and the position of the debris is identified by detecting convection caused by the decay heat of the debris in the surrounding cooling water by the image processing unit. (For example, see Patent Document 1 below).

  Similarly, as a method for specifying the position of debris in a light water reactor power plant, the object is irradiated with light and projected onto a screen, the light projected on the screen is photographed, and the position where there is fluctuation is determined from the photographed image, A device in which the position of debris is detected from a position where there is a fluctuation is also known (for example, see Patent Document 2 below).

JP 2013-160738 A JP 2014-215185 A

  However, the conventional debris deposition position specifying method described above is to insert a detector into the reactor containment vessel in the event of a severe accident, and it is necessary to install the detector in the environment resistance and the detector insertion opening. There are various problems such as safety and safety of workers (possibility of proximity of workers to the furnace).

  On the other hand, in recent years, as described above, since various measures have been taken to deposit debris at a specified position to some extent, if the amount of debris accumulated can be estimated, the situation inside the furnace can be grasped. It is done.

  In view of the above, an object of the present invention is to provide a debris accumulation amount estimation apparatus and an estimation method capable of safely and reliably estimating the amount of debris accumulated in a furnace.

The debris accumulation amount estimation device according to the first invention for solving the above-mentioned problems is
An apparatus for estimating the amount of debris deposited in a nuclear reactor vessel containing a core and filled with liquid metal,
A neutron detector for measuring the neutron flux in the reactor vessel from the outside of the reactor vessel;
Debris deposition amount estimation means for estimating the amount of debris deposition in the reactor vessel based on the value of the neutron flux detected by the neutron detector.

The debris accumulation amount estimation device according to the second invention for solving the above-mentioned problems is as follows.
The neutron detector is inserted into a vertically extending hole formed in a biological shielding wall covering the outer periphery of the reactor vessel,
The debris accumulation amount estimation means is
A shielding analysis unit that performs shielding analysis assuming a core damage situation and associates the deposition position and amount of debris with the vertical distribution of neutron flux,
A debris deposition amount estimation calculation unit that compares the analysis result of the shielding analysis unit with the value of the neutron flux detected by the neutron detector and estimates the amount of debris actually deposited in the reactor vessel It is characterized by that.

A debris accumulation amount estimation device according to a third invention for solving the above-described problems is
The shielding analysis unit determines a measurement position for performing measurement by the neutron detector based on the analysis result,
The debris deposition amount estimation calculation unit compares the analysis result by the shielding analysis unit with the value of the neutron flux detected by the neutron detector arranged at the measurement position, and sets the measurement position in the reactor vessel. It is characterized by estimating the amount of accumulated debris.

A debris accumulation amount estimation apparatus according to a fourth invention for solving the above-described problems is
The shielding analysis unit determines a plurality of measurement positions for actually performing measurement by the neutron detector based on the analysis result,
The debris accumulation amount estimation calculation unit compares the analysis result by the shielding analysis unit with the value of the neutron flux detected for each measurement position by the neutron detector, and each measurement position in the reactor vessel It is characterized by estimating the amount of debris deposited on the surface.

A debris accumulation amount estimation method according to a fifth aspect of the present invention for solving the above problem is as follows.
A method for estimating the amount of debris deposited in a reactor vessel containing a core and filled with liquid metal,
Measure the neutron flux from the outside of the reactor vessel,
The amount of debris deposited in the reactor vessel is estimated based on the detected neutron flux value.

A debris accumulation amount estimation method according to a sixth aspect of the present invention for solving the above problem is as follows:
Shielding analysis assuming core damage situation was performed to correlate the deposition position and amount of debris with the vertical distribution of neutron flux,
The analysis result is compared with the actually detected neutron flux value to estimate the amount of debris accumulated in the reactor vessel.

A debris accumulation amount estimation method according to a seventh aspect of the present invention for solving the above problem is as follows:
Based on the analysis results, determine the measurement position where neutron flux measurement will be performed,
The analysis result and the value of the neutron flux detected at the measurement position are compared to estimate the amount of debris accumulated in the reactor vessel.

A debris accumulation amount estimation method according to an eighth aspect of the present invention for solving the above problems is as follows.
Based on the analysis results, determine the multiple measurement positions for measuring the neutron flux,
The analysis result and the value of neutron flux detected at each measurement position are compared to estimate the amount of debris accumulated in the reactor vessel.

  According to the debris accumulation amount estimation apparatus and estimation method according to the present invention described above, the amount of debris accumulation in the furnace can be estimated safely and reliably.

It is explanatory drawing which shows the example of neutron flux measurement using the deposition amount estimation apparatus of the debris which concerns on the Example of this invention. It is a block diagram which shows the structure of the deposition amount estimation apparatus of the debris which concerns on the Example of this invention. It is a flowchart explaining the deposition amount estimation method of the debris which concerns on the Example of this invention. It is a distribution map which shows the relationship between the distance from core center height, and neutron flux distribution. It is a distribution map which shows the relationship between the distance from core center height, and a count rate. It is explanatory drawing which shows the example which debris accumulated in multiple places.

  Hereinafter, a debris accumulation amount estimation apparatus and estimation method according to the present invention will be described with reference to the drawings.

  Details of the debris accumulation amount estimation apparatus and estimation method according to an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows an example in which the debris accumulation estimation apparatus and estimation method according to this embodiment are applied to JSFR, which is a fast breeder reactor.
As shown in FIG. 1, a skirt portion 15 that separates the lower plenum 12 and the intermediate plenum 13 is provided in the internal space of the reactor vessel 10 that houses the core 11, and the core 11 includes the skirt portion 15 and the like. It is supported by the installation part.
Above the core 11, a laminated plate 16 formed in an annular shape that separates the intermediate plenum 13 and the upper plenum 14 is provided along the inner peripheral surface of the reactor vessel 10. The lower plenum 12 is provided with a core catcher 17 that serves as a tray for the molten fuel when a severe accident occurs.
The reactor vessel 10 is filled with liquid sodium 18 which is a liquid metal as a coolant. Further, the outer periphery of the nuclear reactor vessel 10 is surrounded by the biological shielding wall 20.

  FIG. 1 assumes that a severe accident has occurred, and shows a state in which debris D has accumulated on the core catcher 17.

The debris accumulation amount estimation device 30 includes a single neutron detector 31 and a debris accumulation amount estimation unit 32 as debris accumulation amount estimation means.
In the present embodiment, a measurement hole 20a is formed in the biological shielding wall 20 along the vertical direction (vertical direction in the present embodiment), and the neutron detector 31 is located in a space outside the detector 31 in the horizontal direction. The neutron flux inside the reactor vessel 10 is measured from the outside of the reactor vessel 10 through the measurement hole 20a so as to measure the existing neutron flux. The depth of the measurement hole 20 a is set to a depth at which measurement by the neutron detector 31 can be performed at least at the same height as the core catcher 17.
The result measured by the neutron detector 31 is sent to the debris accumulation amount estimation unit 32.

  As shown in FIG. 2, the debris accumulation amount estimation unit 32 includes a shielding analysis unit 321, a shielding analysis result storage unit 322, a neutron measurement result storage unit 323, and a debris accumulation amount estimation calculation unit 324.

  The shielding analysis unit 321 performs simulation analysis (hereinafter referred to as shielding analysis) assuming a situation (reactor structure, debris deposition position, debris deposition amount, measurement start timing, etc.) when a severe accident occurs in advance. The deposition position and deposition amount of debris D and the amount of neutron flux detected by the neutron detector 31 arranged at a specific position (for example, a position at the same depth as the core catcher of the measurement hole 20a) by this shielding analysis And the correlation between the deposition amount of the debris D and the vertical distribution of the neutron flux at the measurement position is performed.

The shielding analysis result storage unit 322 stores the result of the shielding analysis performed by the shielding analysis unit 321.
The neutron measurement result storage unit 323 stores the measurement result of the neutron flux detected by the neutron detector 31.

  The debris accumulation amount estimation calculation unit 324 is based on the result of the shielding analysis stored in the shielding analysis result storage unit 322 and the measurement result of the neutron flux stored in the neutron measurement result storage unit 323. The amount of debris D deposited at a specific position is estimated. That is, the deposition amount of debris D is estimated by comparing the result of measuring the neutron flux from the outside of the reactor vessel 10 with the value of the neutron flux at the measurement position with respect to the deposition amount of debris D obtained by shielding analysis. The estimation result is output to a display unit (not shown).

Hereinafter, the debris accumulation amount estimation method according to the present embodiment will be described in more detail with reference to FIGS.
In the debris deposition amount estimation apparatus according to the present embodiment, first, the shielding analysis unit 321 assumes the situation at the time of a severe accident occurrence (reactor structure, debris deposition position, debris deposition amount, measurement start timing, etc.). The shielding analysis is performed (step S1), and the vertical distribution of the neutron flux inside the reactor vessel 10 is obtained (step S2). The amount of neutron flux contained in the debris D is determined based on the composition of the debris D (ratio of fuel and structural material) obtained based on the knowledge so far. The distribution of the neutron flux obtained in step S2 is stored in the shielding analysis result storage unit 323 as an analysis result.
The example shown in FIG. 4 is an example of the distribution of neutron flux when it is assumed that the debris D is all deposited on the core catcher 17.

  Subsequently, the shielding analysis unit 321 also converts the distribution of neutron flux obtained in step S2 into the distribution of count rate measured by the neutron detector 31 (step S3). The example shown in FIG. 5 is an example in which the virtual distribution of neutron flux shown in FIG. 4 is converted into a count rate distribution. The count rate distribution obtained in step S3 is stored in the shielding analysis result storage unit 323 as an analysis result.

Subsequently, based on the following two viewpoints that characterize the accumulation of debris D from the count rate distribution obtained in step S3, the neutron detector 31 measures the neutron flux when a severe accident occurs. A position to be performed (in this embodiment, a depth at which the neutron detector 31 in the measurement hole 20a is disposed; hereinafter referred to as a measurement position) is determined (step S4).
・ There are many counting rates.
・ Vertical change in counting rate is small.

  In the example shown in FIG. 5, the position below 850 cm from the center height of the core 11 (the position where the core catcher is installed) has a high count rate and a small change in the count rate in the vertical direction. It is determined as a measurement position.

  When an accident occurs, the neutron detector 31 is placed at the measurement position determined in step S4 manually or remotely, and the neutron flux is measured at the measurement position (step S5). The measurement result is stored in the neutron measurement result storage unit 323.

  Subsequently, the debris accumulation amount estimation calculation unit 324 estimates the accumulation amount of debris D based on the result of the shielding analysis and the result measured by the neutron detector 31 (step S6). More specifically, in the debris accumulation amount estimation calculation unit 324, the debris D accumulation amount obtained in the analysis (in this embodiment, the debris D accumulation when it is assumed that all the debris D has accumulated on the core catcher 17). The ratio r when the (amount) is 1 is obtained by the following equation (1).

However, C: Count number of measured neutron flux [c]
T: Measurement time [s]
a: Count rate obtained from the analysis result [cps]

Then, the deposition amount of the debris D actually deposited in the reactor vessel 10 is estimated from the ratio r obtained by the equation (1). The estimation error in the debris accumulation amount estimation method according to the present embodiment configured as described above was about 2% (the error factor was caused by detector installation error (± 10 cm) and the fluctuation of the count number. (Considering that due to (1σ)).
In this example, the composition of the debris D (ratio of fuel and structural material) is determined based on the knowledge so far, so the amount of deposition can be estimated by measuring the neutron flux generated from it. Yes.

  As described above, the debris accumulation amount estimation method according to the present embodiment pays attention to the fact that the debris D contains an isotope element that emits neutrons, and from the outside of the reactor vessel 10, the reactor vessel 10. The amount of the debris D at the deposition position is estimated by measuring the internal neutron flux.

  Since fast breeder reactors such as JSFR use liquid metals such as sodium as coolant, neutrons are less likely to be absorbed by coolant compared to light water, and the neutron flux emitted from debris D is a reactor vessel. 10 can be measured from the outside, it is not necessary to insert the neutron detector 31 in the reactor vessel 10 and the amount of the debris D at the deposition position can be safely estimated.

  In JSFR, various measures are taken to avoid recriticality, and the position where debris accumulates can be specified to some extent. Therefore, by estimating the amount of debris, It is also possible to grasp.

  As described above, according to the debris accumulation amount estimation apparatus and the estimation method according to the present embodiment, it is possible to reliably and safely estimate the amount of debris accumulated at the specified position. Can understand the situation.

  In JSFR, in order to avoid the above-mentioned recriticality, as various measures, a duct through which the damaged core material passes is provided in the fuel assembly constituting the core, and in the event of an accident, the damaged core material is blown up through the duct and stacked on top. It accumulates on the plate, and the remaining damaged core material is configured to fall on the core catcher, which is a saucer, and accumulate (see FIG. 6). In the present embodiment, an example is shown in which the shielding analysis is performed on the assumption that all debris has accumulated on the core catcher 17. However, for example, as shown in FIG. When configured to deposit, the measurement position corresponding to each deposition position is set as the measurement position, and the debris D is deposited at each deposition position based on the analysis result and the actual measurement result for each measurement position. What is necessary is just to estimate the quantity.

  Further, in this embodiment, an example in which the neutron flux is measured by one neutron detector 31 is shown, but a plurality of measurement holes are formed in the biological shielding wall, and the neutron detector is inserted into each hole to perform atomic measurement. The neutron flux in the reactor vessel 10 may be measured, and the accumulated amount of the debris D may be estimated by comprehensively determining each measurement result.

  INDUSTRIAL APPLICABILITY The present invention can be used for a debris accumulation amount estimation apparatus and an estimation method for estimating a debris accumulation amount inside a reactor vessel from the outside of a reactor vessel that contains a core and is filled with a liquid metal.

DESCRIPTION OF SYMBOLS 10 Reactor vessel 11 Core 12 Lower plenum 13 Middle plenum 14 Upper plenum 15 Skirt part 16 Laminated board 17 Core catcher 18 Liquid sodium 20 Biological shielding wall 20a Measurement hole 30 Debris deposition amount estimation apparatus 31 Neutron detector 32 Debris deposition Quantity estimation part 321 Shielding analysis part 322 Shielding analysis result storage part 323 Neutron measurement result storage part 324 Debris deposition amount estimation calculation part D Debris

Claims (8)

An apparatus for estimating the amount of debris deposited in a nuclear reactor vessel containing a core and filled with liquid metal,
A neutron detector for measuring the neutron flux in the reactor vessel from the outside of the reactor vessel;
A debris accumulation amount estimation device, comprising: debris accumulation amount estimation means for estimating a debris accumulation amount in the reactor vessel based on a value of a neutron flux detected by the neutron detector. The neutron detector is inserted into a vertically extending hole formed in a biological shielding wall that covers the outside of the reactor vessel,
The debris accumulation amount estimation means is
A shielding analysis unit that performs shielding analysis assuming a core damage situation and associates the deposition position and amount of debris with the vertical distribution of neutron flux,
A debris deposition amount estimation calculation unit that compares the analysis result of the shielding analysis unit with the value of the neutron flux detected by the neutron detector and estimates the amount of debris actually deposited in the reactor vessel The debris accumulation amount estimation apparatus according to claim 1, wherein The shielding analysis unit determines a measurement position for performing measurement by the neutron detector based on the analysis result,
The debris deposition amount estimation calculation unit compares the analysis result by the shielding analysis unit with the value of the neutron flux detected by the neutron detector positioned at the measurement position, and deposits at the measurement position in the reactor vessel The debris accumulation amount estimation apparatus according to claim 2, wherein the debris accumulation amount is estimated. The shielding analysis unit determines a plurality of measurement positions for actually performing measurement by the neutron detector based on the analysis result,
The debris accumulation amount estimation calculation unit compares the analysis result by the shielding analysis unit with the value of the neutron flux detected for each measurement position by the neutron detector, and each measurement position in the reactor vessel The debris accumulation amount estimation device according to claim 2, wherein the amount of debris accumulated on the surface is estimated. A method for estimating the amount of debris deposited in a reactor vessel containing a core and filled with liquid metal,
Measure the neutron flux from the outside of the reactor vessel,
A debris deposition amount estimation method, comprising: estimating a debris deposition amount in the reactor vessel based on a detected neutron flux value. Shielding analysis assuming core damage situation was performed to correlate the deposition position and amount of debris with the vertical distribution of neutron flux,
6. The debris deposition amount estimation method according to claim 5, wherein the amount of debris deposited in the reactor vessel is estimated by comparing the analysis result with the actually detected neutron flux value. Based on the analysis results, determine the measurement position where neutron flux measurement will be performed,
The debris accumulation amount estimation method according to claim 6, wherein an amount of debris accumulated in the reactor vessel is estimated by comparing an analysis result with a value of a neutron flux detected at the measurement position. Based on the analysis results, determine the multiple measurement positions for measuring the neutron flux,
The amount of debris deposited in the reactor vessel is estimated by comparing an analysis result with a value of a neutron flux detected at each of the measurement positions. Method.

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