JP6021664B2 - Subcriticality measuring device and subcriticality maintenance system - Google Patents

Description

  Embodiments described herein relate generally to a subcriticality measuring apparatus and subcriticality maintenance system for a nuclear fuel material system contained in a container.

  In nuclear fuel handling technology, criticality safety management of nuclear fuel must be performed so that the criticality is not reached unintentionally under any circumstances. The criticality is a case where the effective neutron multiplication factor keff = 1, and a noncritical state when keff <1. By measuring the subcriticality indicating the tolerance up to the criticality (keff = 1), safer criticality safety management becomes possible.

  One technique for measuring subcriticality is the external neutron source multiplication method. This method is a method for obtaining the subcriticality from the count rate by utilizing the fact that the response of the neutron detector depends on the effective multiplication factor (keff) when the external neutron source intensity is constant. This external neutron source multiplication method has a very simple measurement system and excellent response.

As a prior art, a subcriticality monitoring technique in a system for handling nuclear fuel such as in a nuclear fuel transport container, a storage facility, and a processing facility has been proposed. In the case of BWR, the neutron flux at the detection position in the spent fuel storage rack to be measured is, for example, about 2.4 × 10 ⁴ (n / cm ² / s).

  This value is sufficient for measurement, but it is not applicable to systems with large neutron attenuation because neutron attenuation in the system is not taken into account.

JP 2007-121156 A

  In subcriticality measurement using an external neutron source multiplication method, it is desirable to install a neutron source and a detector outside the measurement target (tank, etc.) from the viewpoint of operability, maintainability, and maintainability.

  However, when the volume of the measurement target (tank or the like) is large, neutron absorption is large, so that the neutron flux leaking to the outer surface of the container is small, so that the counting rate necessary for measurement cannot be obtained.

  Accordingly, an object of the embodiment of the present invention is to enable subcriticality measurement even for a nuclear fuel material system contained in a container having a large volume.

  In order to achieve the above object, an embodiment of the present invention is a subcriticality measuring apparatus for measuring an effective multiplication factor of a nuclear fuel material system comprising a nuclear fuel material and a medium contained in a storage container, wherein the storage container A hollow tube that is disposed inside and excludes the medium, and is disposed outside the storage container and in the vicinity of one end of the hollow tube, and passes through the hollow tube to the nuclear fuel material system in the storage container. A neutron source for supplying neutrons, one or more radiation detectors for detecting neutrons from the nuclear fuel material system in the storage container, and an effective multiplication factor for calculating an effective multiplication factor based on the output of the radiation detectors. And a magnification calculator.

  According to the embodiment of the present invention, subcriticality can be measured even for a nuclear fuel material system contained in a container having a large volume.

1 is an elevational sectional view showing a configuration of a subcriticality measuring apparatus according to a first embodiment of the present invention. It is an elevation sectional view showing composition of a subcriticality measuring device and a subcriticality maintenance system concerning a 2nd embodiment of the present invention. It is an elevation sectional view showing composition of a subcriticality measuring device and a subcriticality maintenance system concerning a 3rd embodiment of the present invention. It is a sectional elevation showing the composition of the modification of the subcriticality measuring apparatus and subcriticality maintenance system concerning a 3rd embodiment of the present invention. It is an elevation sectional view showing composition of a subcriticality measuring device and a subcriticality maintenance system concerning a 4th embodiment of the present invention.

  Hereinafter, a subcriticality measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is an elevational sectional view showing a configuration of a subcriticality measuring apparatus according to the first embodiment of the present invention.

  The subcriticality measuring device 20 is provided for measuring an effective multiplication factor of a nuclear fuel material system composed of a nuclear fuel material contained in the storage container 1 and a medium such as water or an aqueous solution of a chemical substance. The subcriticality measuring apparatus 20 includes a hollow tube 6, a neutron source 2, a neutron detector 4, and an effective multiplication factor calculation unit 11.

  The hollow tube 6 is a circular tube extending linearly and horizontally, and is disposed in the storage container 1. The hollow tube 6 is formed so as to seal the inside thereof in order to exclude the medium in the storage container 1. In addition, the hollow tube 6 is not limited to what is sealed. As long as the medium in the storage container 1 is excluded, for example, an opening part may be provided at a position higher than the interface between the medium and the gas above it.

  The hollow tube 6 is disposed at a substantially central height of the storage container 1. One end of the hollow tube 6 is close to the inner wall of the storage container 1. The neutron source 2 is disposed outside the storage container 1 and in the vicinity of one end of the hollow tube 6. The neutron source 2 supplies neutrons into the storage container 1 through the space inside the hollow tube 6.

  The hollow tube 6 is not limited to be horizontal. The purpose is to reach the center of the distribution of nuclear fuel material in the nuclear fuel material system, that is, the part where the effect of injecting neutrons is considered to be large. Good.

  In order to suppress the attenuation of neutrons from the neutron source 2 as much as possible, it is desirable that the amount of medium existing between the inner wall of the storage container 1 and one end of the hollow tube 6 is as small as possible. The opposite end of the hollow tube 6 opposite to the one end extends to substantially the center of the horizontal cross section of the storage container 1.

  The neutron detector 4 measures neutrons generated by a reaction in the system of nuclear fuel material into which neutrons generated from the neutron source 2 are injected. The neutron detector 4 is attached to the side surface of the storage container 1 at the same height as the hollow tube 6.

  The attachment position of the neutron detector 4 is not limited to the side wall of the storage container 1, and is a position where the measurement efficiency of neutrons from the nuclear fuel material system in the storage container 1 can be secured, and the neutrons generated by the neutron source 2 If the position does not reach directly, for example, the upper surface of the storage container 1 may be used.

  Further, the installation position of the neutron detector 4 is not limited to the outside of the storage container 1. If the measurement efficiency of neutrons from the nuclear fuel material system in the storage container 1 can be ensured and there is no particular problem, for example, a well may be inserted into the storage container 1 and disposed in this well.

  However, the neutron detector 4 measures neutrons generated by reactions in the nuclear fuel material system, and is a position where the direct contribution of the neutrons generated by the neutron source 2 to the neutron detector 4 can be ignored. It is necessary.

  The condition that the position of the neutron source 2 is such that the direct contribution of the neutrons generated by the neutron source 2 to the neutron detector 4 can be ignored is the same when the neutron detector 4 is provided outside the storage container 1. . That is, the distance between the opposite end of the hollow tube 6 and the inner wall of the storage container 1 is set to have a sufficient distance so that the direct contribution of neutrons generated from the neutron source 2 to the neutron detector 4 can be ignored. Has been.

Based on the output of the neutron detector 4, the effective multiplication factor calculation unit 11 calculates the effective multiplication factor based on Expression (1) that represents the relationship between the count rate and the effective multiplication factor keff.
keff = 1−α · S / C (1)
Where α is a proportionality constant depending on the mass of the nuclear fuel material in the nuclear material system, S is the intensity of the neutron source (n / sec), and C is the neutron counting rate (count / sec).

  As shown in the equation (1), the count rate C increases as the value approaches the critical value, that is, when the keff increases from a small value and approaches 1. Regarding the proportionality constant α, the relationship with the mass of the nuclear fuel material in the nuclear fuel material system in the target storage container 1 is calculated by, for example, Monte Carlo simulation.

  In the present embodiment configured as described above, neutrons generated by the neutron source 2 pass through the hollow tube 6 and are injected into the storage container 1.

  For example, a case is considered in which nuclear fuel material is not evenly distributed in the storage container 1 and is unevenly distributed at some locations in the storage container 1 in the form of fuel debris that has solidified after the nuclear fuel has melted. .

  In this case, when there is no hollow tube 6, the neutron generated by the neutron source 2 is attenuated by the surrounding medium before reaching the location where the fuel debris exists, and a sufficient amount of neutrons reaches the fuel debris. do not do. For this reason, the reaction amount of neutrons in a system centering on fuel debris is small, and neutrons generated from this system are also small. For this reason, sufficient neutron measurement cannot be performed.

  On the other hand, in the subcriticality measuring apparatus 20 according to the present embodiment, a sufficient amount of neutrons among the neutrons generated by the neutron source 2 reach the fuel debris. As a result, the reaction amount of neutrons increases, and a sufficient amount of neutrons measured by the neutron detector 4 is ensured.

  As described above, according to the subcriticality measuring device 20 of the present embodiment, the subcriticality can be measured even for the nuclear fuel material system contained in the storage container 1 having a large volume.

[Second Embodiment]
FIG. 2 is an elevational sectional view showing the configuration of the subcriticality measuring apparatus and the subcriticality maintaining system according to the second embodiment of the present invention. The subcriticality maintenance system 30 includes the storage container 1, the subcriticality measuring device 20, and the safety device 16. The subcriticality measuring apparatus 20 is a modification of the first embodiment.

  The safety device 16 includes a neutron absorber storage container 16a and a neutron absorber supply valve 16b. The neutron absorber storage container 16 a stores a neutron absorber that is injected into the nuclear fuel material system in the storage container 1. The neutron absorber supply valve 16b is normally closed and is opened in response to an open command signal from the subcriticality measuring device 20, and the neutron absorber in the neutron absorber storage container 16a is placed in the storage container 1. Introduce.

  The subcriticality measuring device 20 further includes a set value input unit 13 and an alarm device 14. When the calculated effective multiplication factor keff exceeds the alarm set value, the effective multiplication factor calculation unit 11 issues a warning signal to the alarm device 14 that the effective multiplication factor keff has exceeded the alarm set value. The alarm device 14 receives an alarm signal and issues an alarm.

  When the value of the calculated effective multiplication factor keff exceeds the set value of the opening operation command signal, the effective multiplication factor calculation unit 11 issues an opening operation command signal to the neutron absorber supply valve 16b of the safety device 16. In response to the opening operation command signal, the neutron absorbing material supply valve 16b is opened.

  The value of keff as the set value of the opening operation command signal is set to a value with a margin with respect to 1, for example, 0.8. The keff value as the alarm setting value is the same value as the setting value of the opening operation command signal. The keff value as the alarm setting value is not limited to the same value as the setting value of the opening operation command signal. For example, the setting value of the opening operation command signal may be set to a value lower than this with a margin.

  In the subcriticality measuring apparatus and the subcriticality maintenance system according to the present embodiment configured as described above, the criticality is prevented by notifying the danger and operating the safety system before approaching the criticality, thereby It is possible to avoid human dangers such as exposure.

[Third Embodiment]
FIG. 3 is an elevational sectional view showing the configuration of the subcriticality measuring apparatus and the subcriticality maintaining system according to the third embodiment of the present invention. This embodiment is a modification of the second embodiment.

  In the storage container 1, a hollow tube 6a, a hollow tube 6b, and a hollow tube 6c are disposed. The hollow tube 6a, the hollow tube 6b, and the hollow tube 6c are disposed horizontally and parallel to each other in the height direction of the storage container 1. One end of each of the hollow tube 6a, the hollow tube 6b, and the hollow tube 6c in the vicinity of the storage container 1 is positioned in a straight line in the vertical direction.

  Further, the neutron detector 4a, the neutron detector 4b, and the neutron detector 4c are disposed at substantially the same height as the hollow tube 6a, the hollow tube 6b, and the hollow tube 6c, respectively.

  In this embodiment, it has the neutron source drive part 3a which drives the neutron source 2 up and down, and the guide part 3b which accommodates the neutron source 2 and guides it up and down. The neutron source 2 can move up and down on the outside of the storage container 1 close to one end of each of the hollow tubes 6a, 6b, and 6c. The neutron source 2 is moved up and down by a neutron source driving unit 3a, and the neutron source 2 moves in the guide unit 3b.

  In addition, although this embodiment shows the case where there are three hollow tubes and three neutron detectors, the present invention is not limited to this. The necessary number may be provided in consideration of factors such as the size of the storage container 1 and whether or not the nuclear fuel material in the nuclear fuel material system in the storage container 1 is unevenly distributed.

  Moreover, although the case where the hollow tubes 6a, 6b, and 6c are lined up and down is shown in the present embodiment, the present invention is not limited to this. For example, in the case of the storage container 1 that is wide in the horizontal direction, the hollow tubes 6a, 6b, and 6c may be arranged in the horizontal direction. Alternatively, when the storage container 1 is larger, the hollow tubes 6a, 6b, 6c may be arranged in the horizontal direction and the height direction. In this case, the neutron source 2 may be moved along such a hollow tube.

  The effective multiplication factor calculation unit 11 calculates keff by the equation (1) based on the output from the neutron detector 4a. Similarly, the effective multiplication factor calculation unit 11 calculates keff for each of the neutron detector 4b and the neutron detector 4c. The effective multiplication factor calculation unit 11 outputs the maximum value among the calculated keffs as the calculation result of the effective multiplication factor.

  When the distribution of nuclear fuel material in the container 1 is not uniform, such as when nuclear fuel material is deposited on the bottom, the attenuation of neutrons after passing through the hollow tubes 6a, 6b, 6c is different from each other. There are dependencies. Therefore, the counting rates obtained by the plurality of neutron detectors 4a, 4b, and 4c differ depending on the accumulation state of the nuclear fuel material in the storage container 1. The effective multiplication factor calculating unit 11 performs management on the safe side as an effective multiplication factor that is closest to the critical value.

  As described above, even when the distribution of nuclear fuel material in the storage container 1 is not uniform, the subcriticality of the nuclear fuel material system in the storage container 1 can be measured.

  FIG. 4 is an elevational sectional view showing a configuration of a modification of the subcriticality measuring apparatus and the subcriticality maintaining system according to the third embodiment of the present invention.

  In 3rd Embodiment, although the system which moves the neutron source 2 was shown, it is not limited to this. As shown in FIG. 4, for example, the neutron source 2a, the neutron source 2b, and the neutron source 2c may be provided individually corresponding to the hollow tubes 6a, 6b, and 6c.

  In a system in which a medium containing nuclear fuel material flows into the storage container 1 and the content of each fuel substance in the flowing medium varies greatly with time, It is conceivable that the distribution of the fuel material is biased. Even in such a case, by providing the neutron source individually, it is possible to quickly grasp the change in the effective multiplication factor of each fuel material system in the storage container 1.

[Fourth Embodiment]
FIG. 5 is an elevational sectional view showing the configuration of the subcriticality measuring apparatus and the subcriticality maintaining system according to the fourth embodiment of the present invention. This embodiment is a modification of the second embodiment. The subcriticality measuring apparatus 20 further includes a gamma ray detector 5 and a difference calculation unit 12.

  The gamma ray detector 5 is provided in the vicinity of the installation location of the neutron detector 4. The difference calculation unit 12 receives the output of the neutron detector 4 and the output of the gamma ray detector 5, subtracts the output value of the gamma ray detector 5 from the output value of the neutron detector 4, and outputs a net neutron count. Note that the neutron detector 4 and the gamma ray detector 5 are calibrated in advance so that the sensitivities of both are the same.

  The neutron detector 4 is a detector for measuring neutrons. However, since the neutron detector 4 is also sensitive to gamma rays in principle, from the viewpoint of neutron detection, the gamma ray count is a noise in neutron measurement. It becomes.

  In the present embodiment, the difference calculation unit 12 calculates the net neutron count from the neutron count obtained by the neutron detector 4 and the gamma ray count obtained by the gamma ray detector 5 to accurately obtain C in the formula (1). be able to. As a result, the effective multiplication factor keff can be calculated with high accuracy.

[Other Embodiments]
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. For example, the hollow tube may not be a tube having a constant diameter in the longitudinal direction but may have a diameter varying.

  Or even if it is not a pipe | tube, a container shape may be sufficient if a medium is excluded and the storage capacity of the storage container 1 is not impacted.

  Moreover, you may combine the characteristic of each embodiment. For example, a point in which a plurality of hollow tubes, which are features added in the third embodiment, are provided, and a point in which a neutron detector and a gamma ray detector, which are features added in the fourth embodiment, are provided may be combined. Good.

  Or you may combine the point which provides the several hollow tube which is the characteristic added in 3rd Embodiment to 1st Embodiment. Moreover, you may combine the point which provides the neutron detector and the gamma ray detector which are the features added in 4th Embodiment to 1st Embodiment.

  Furthermore, these embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Storage container, 2, 2a, 2b, 2c ... Neutron source, 3a ... Neutron source drive part, 3b ... Guide part, 4, 4a, 4b, 4c ... Neutron detector, 5 ... Gamma ray detector, 6, 6a, 6b, 6c ... hollow tube, 11 ... effective multiplication factor calculation unit, 12 ... difference calculation unit, 13 ... set value input unit, 14 ... alarm device, 16 ... safety device (safety system), 16a ... neutron absorber storage Container, 16b ... Neutron absorber supply valve, 20 ... Subcriticality measuring device, 30 ... Subcriticality maintenance system

Claims (12)

A subcriticality measuring device for measuring an effective multiplication factor of a nuclear fuel material system comprising a nuclear fuel material and a medium contained in a storage container,
A hollow tube disposed in the storage container to exclude the medium;
A neutron source that is arranged outside the storage container and near one end of the hollow tube and supplies neutrons to the nuclear fuel material system in the storage container via the hollow tube;
One or more radiation detectors for detecting neutrons from the nuclear fuel material system in the containment vessel;
An effective multiplication factor calculation unit for calculating an effective multiplication factor based on the output of the radiation detector;
A subcriticality measuring apparatus comprising: The hollow tube has one end close to the inner wall of the storage container, and the radiation detector for neutrons generated from the neutron source between the opposite end opposite to the one end and the inner wall of the storage container facing the one end. In a position that ensures a sufficient distance to ignore the direct contribution to
The subcriticality measuring apparatus according to claim 1, wherein:   The sub-criticality measuring apparatus according to claim 1 or 2, wherein the hollow tube is hermetically sealed and contains a gas.   The subcriticality measuring apparatus according to any one of claims 1 to 3, wherein a plurality of the hollow tubes are arranged at different positions.   5. The subcriticality measuring apparatus according to claim 1, wherein there are a plurality of the neutron sources, and the neutron sources are arranged at different positions.   6. The subcriticality according to claim 1, further comprising a neutron source driving unit that moves the neutron source to a plurality of positions where the neutron source is to supply neutrons. 7. Degree measuring device. The radiation detector has a first radiation detector and a second radiation detector,
A difference calculating unit that calculates a difference obtained by subtracting the output of the second radiation detector from the output of the first radiation detector;
The subcriticality measuring apparatus according to any one of claims 1 to 6, wherein the apparatus is a subcriticality measuring apparatus.   The subcriticality measuring apparatus according to claim 7, wherein the first radiation detector is a neutron detector, and the second radiation detector is a gamma ray detector. Further equipped with an alarm device for receiving an alarm signal and issuing an alarm,
The effective multiplication factor calculation unit emits the alarm signal to the alarm device when the calculated effective multiplication factor is equal to or greater than a predetermined alarm setting value.
The subcriticality measuring apparatus according to any one of claims 1 to 8, wherein the apparatus is a subcriticality measuring apparatus. The storage container is provided with a safety system for maintaining a subcritical state of the nuclear fuel material system in the storage container,
The safety system has a neutron absorber supply valve provided on a neutron absorber storage container and a flow path from the neutron absorber storage container to the storage container,
The effective multiplication factor calculation unit outputs a safe operation command signal to the safety system when the calculated effective multiplication factor is equal to or greater than a predetermined safe operation setting value.
The subcriticality measuring apparatus according to any one of claims 1 to 9, wherein   A subcriticality maintenance system comprising the subcriticality measuring apparatus according to claim 10, the storage container, and the safety system. The safety system is
A neutron absorber storage container for storing the neutron absorber, and
A neutron absorber supply valve for supplying the neutron absorber in the neutron absorber storage container into the storage container;
Have
The subcriticality maintenance system according to claim 11, wherein the neutron absorber supply valve performs an opening operation in response to the safe operation command signal.

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