JP6502759B2 - Neutron detector and reactor power detection system - Google Patents

Description

  Embodiments of the present invention relate to a neutron detector for detecting neutrons in a nuclear reactor and a reactor power detection system using the same.

  As a neutron detector for measuring the neutron flux in the reactor, the neutron detector installed in the reactor piping inserted separately from the reactor water in the reactor, the reaction inside the neutron detector by neutron irradiation The substance is consumed and the sensitivity decreases, and the life is reached at a stage below the lowest counting rate.

  As a condition required for a system in which the above-described neutron detector is mounted on the in-reactor piping, firstly, it is required to electrically insulate the in-reactor piping and the neutron detector. This is because in this neutron detector, it is necessary to minimize signal noise (noise) generated due to electrical contact between the furnace piping and the neutron detector in order to pulse-detect minute signals. is there.

  Second, the furnace piping is filled with helium gas to remove the heat generated by gamma irradiation, but the insulator covering the neutron detector and other components also dissipate heat from the neutron detector. It is necessary to select a material that can effectively transfer heat.

  In such a neutron detector, in order to achieve a long life, for example, as in Patent Document 1, it is conceivable to install a shielding material which is a neutron absorber and reduce the amount of neutrons reaching the reaction material. .

  FIG. 11 is an elevation sectional view showing a conventional neutron detector and the periphery thereof, and FIG. 12 is a plan sectional view taken along line XII-XII in FIG.

  In FIG. 11 and FIG. 12, the in-reactor piping 4 is inserted into the core of the reactor. The furnace pipe 4 has a cylindrical shape extending at the upper end and extending downward, and is made of metal. The neutron detector 1 is inserted into the furnace pipe 4 from below. The neutron detector 1 is a fission type ionization chamber. The neutron detector 1 includes a detector container 1d which is a substantially cylindrical metal airtight container, a cylindrical cathode 1c accommodated in the detector container 1d, and a cylindrical member disposed inside the cathode 1c. And an anode 1a. A cylindrical reactant 1b is sandwiched between the cathode 1c and the anode 1a. An ionized gas is enclosed in the detector container 1d.

  A cylindrical insulator 13 is disposed so as to cover the outer side surface of the detector container 1 d, and a cylindrical neutron absorber 14 is disposed outside the insulator 13 and inside the in-furnace pipe 4. The neutron absorber 14 is made of hafnium.

  At the center of each of the upper and lower end portions of the detector container 1d, an upper protrusion 20 and a lower protrusion 21 are respectively formed outward. An annular upper insulator 9 and a lower insulator 10 are disposed so as to surround the radial outer sides of the upper protrusion 20 and the lower protrusion 21 respectively.

  The collision of neutrons with the reactant 1b causes the reactant 1b to undergo fission and produce fission fragments. The fission fragments ionize the ionized gas to produce electron-ion pairs. This electron-ion pair is collected by the anode 1a and the cathode 1c.

  By providing the neutron absorber 14 around the neutron detector 1, consumption of the reactant 1b is alleviated.

Japanese Patent Publication No. 62-61906

  In the prior art, since the insulator was necessary in addition to the neutron absorber, if the thickness of each of the neutron absorber and the insulator is sufficiently thick, the combined thickness becomes large, and the piping in the furnace is designed to be compact. It was difficult to do. On the contrary, when the furnace piping is designed compactly, there is a problem that the thickness of the neutron absorber can not be sufficiently obtained, the consumption of the reactant is severe, and the life of the neutron detector becomes short.

  In order to solve the above problems, the embodiment of the present invention enhances the neutron absorption performance of the neutron absorber while maintaining the electrical insulation with the piping in the reactor, and further enables a compact design and a neutron detector and a nuclear reactor It aims to provide an output detection system.

  In order to solve the above problems, a neutron detector according to an embodiment of the present invention is a neutron detector installed in in-reactor piping in a nuclear reactor, which is a reactant that causes fission by neutrons to generate fission fragments. And an ionized gas ionized by the fission fragments to generate electron-ion pairs, an anode and a cathode for collecting the electron-ion pairs, the reactant, the ionized gas, the anode, and the cathode. A detector container, and an electrically insulating neutron absorber disposed in an air gap between the outside of the detector container and the furnace inner pipe.

  In addition, a reactor power detection system according to an embodiment of the present invention includes in-reactor piping in the reactor, a neutron detector installed in the in-reactor piping, and the neutron detection disposed outside the reactor. A preamplifier for amplifying a signal obtained from the reactor, a computing unit for calculating the output of the reactor based on the signal obtained from the preamplifier, and a cable for connecting the neutron detector and the preamplifier A reactor power detection system comprising: a reactor power detection system, wherein the neutron detector is a reaction material which is fissioned by neutrons to produce fission fragments, and ionized gas which is ionized by the fission fragments to produce electron-ion pairs An anode and a cathode for collecting the electron-ion pair, a detector container for containing the reactant, the ionized gas, the anode and the cathode, an outer side of the detector container, and a piping in the furnace Wherein by having the neutron absorber with a positioned electrical insulation in the gap, the.

  According to an embodiment of the present invention, a neutron detector and a reactor power detection system capable of enhancing the neutron absorption performance of the neutron absorber while maintaining the electrical insulation with the piping in the reactor and capable of compact design are provided. can do.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows the structure of the neutron detector which concerns on the 1st Embodiment of this invention, and a reactor power detection system using the same. It is an elevation sectional view showing the details of the neutron detector concerning the 1st embodiment of Drawing 1, and its circumference. FIG. 3 is an enlarged partial sectional view showing a part III of FIG. 2; It is a plane sectional view in alignment with the IV-IV line of FIG. FIG. 3 is an elevational view showing a neutron detector as seen through the furnace piping of FIG. 2; It is a table | surface which shows the thermal neutron macro absorption cross section and insulation of various substance. It is a graph which shows the relative sensitivity of the neutron detector in the neutron detector concerning a 1st embodiment of the present invention, and the time course of the amount of neutron incidence to the neutron detector. FIG. 5 is an elevation view showing a neutron detector according to a second embodiment of the present invention and the periphery thereof, as seen through a furnace internal piping. It is a plane sectional view in alignment with the IX-IX line of FIG. FIG. 10 is an elevation view showing a neutron detector according to a third embodiment of the present invention and the periphery thereof, as seen through a furnace internal piping. It is an elevation sectional view showing the conventional neutron detector and its circumference. It is a plane sectional view in alignment with the XII-XII line of FIG.

  Hereinafter, an embodiment of a neutron detector according to the present invention will be described with reference to the drawings. Here, the same reference numerals as in the above-described prior art, or the same or similar parts are given the same reference numerals, and redundant description will be omitted.

First Embodiment
(Constitution)
FIG. 1 is a schematic configuration view showing a neutron detector and a reactor power detection system using the same according to a first embodiment of the present invention. FIG. 2 is an elevation cross-sectional view showing details of the neutron detector and its periphery according to the first embodiment of FIG. FIG. 3 is an enlarged partial sectional view showing a part III of FIG. FIG. 4 is a plan sectional view taken along the line IV-IV of FIG. FIG. 5 is an elevational view showing the neutron detector through the in-furnace piping of FIG.

  As shown in FIG. 1, in the first embodiment, a core 3 is disposed in a nuclear reactor (for example, a boiling water reactor) 2. In-reactor piping 4 is inserted from the bottom of the reactor 2. The upper end of the in-reactor pipe 4 is closed and located in the core 3, and the lower end of the in-core pipe 4 is opened below the reactor 2. A neutron detector 1 is disposed in the reactor core 3 in the in-reactor piping 4.

  A preamplifier 6 and an operation unit 7 are disposed outside the reactor piping 2 and outside the reactor piping 4. A cable 5 is connected between the neutron detector 1 and the preamplifier 6 and between the preamplifier 6 and the operation unit 7. The cable 5 connected to the neutron detector 1 passes through the in-reactor pipe 4 and exits from the lower end thereof, and is connected to the preamplifier 6.

  In the first embodiment, the detector container 1d and the internal structure thereof are the same as those of the above-described conventional neutron detector (FIGS. 11 and 12).

  In this embodiment, a neutron absorber 8 is disposed instead of the combination of the insulator 13 and the neutron absorber 14 (FIGS. 11 and 12) in the above-mentioned prior art. The neutron absorber 8 is in the in-reactor piping 4 and is cylindrical and covers the outer surface of the detector container 1d. The neutron absorber 8 is made of, for example, hafnium oxide (hafnia), and has the functions of both the insulator 13 and the neutron absorber 14 of the prior art.

  The signal sent from the neutron detector 1 to the preamplifier 6 by the cable 5 is amplified by the preamplifier 6 and then the neutron flux value and the sensitivity deterioration function of the neutron detector 1 and the reactor in the operation unit 7 (2) Converted to an output% value which is multiplied by an output conversion constant specific to the characteristic, etc., and is output as an indicated value.

  Here, since the signal obtained from the neutron detector 1 is a minute signal, it is necessary to suppress the signal noise (noise) generated when the in-reactor pipe 4 and the neutron detector 1 contact with each other. The neutron detectors 1 are electrically isolated. In order to remove heat generated by gamma ray irradiation, the furnace pipe 4 is filled with helium gas, and the components of the neutron detector 1 are heated so as to effectively dissipate heat from the neutron detector 1 A high conductivity material is selected.

  Since the neutron detector 1 remains loaded in the reactor piping 4 during operation of the reactor 2, the irradiation of neutrons consumes the reactant 1b and the sensitivity of the neutron detector 1 gradually decreases. . Then, when the indicated value of the neutron detector 1 falls below the preset minimum counting rate, the lifetime is reached.

In this embodiment, a hafnia (hafnium oxide, HfO ₂₎ that as a material of the neutron absorber 8 with insulation in the voids in between the neutron detector 1 and the furnace pipe 4 of the outer. By using the insulating hafnia, the insulation between the neutron detector 1 and the furnace pipe 4 can be maintained.

  The Hafnia neutron absorber 8 is cylindrical in shape. The thickness of the neutron absorber 8 is determined from the neutron absorptivity of the neutron absorber 8 and the size of the air gap between the neutron detector 1 and the furnace pipe 4. The neutron absorber 8 is fixed by the upper insulator 9 and the lower insulator 10, as shown in FIG. The upper insulator 9 and the lower insulator 10 are the same as those provided for fixing the insulator 13 (FIGS. 11 and 12), which was conventionally required.

  The material of the neutron absorber 8 may use, besides hafnia, an insulating compound containing an element having a large neutron absorption cross section. Here, as elements having a large neutron absorption cross section, iridium, rhodium, dysprosium, thulium, boron, lutetium, uranium, silver, gold, lithium, cadmium, indium, samarium, europium, gadolinium, erbium, mercury, hafnium and the like Insulating compounds having isotopes and containing these include, in addition to hafnia, rhodium oxide and the like. The neutron absorber 8 may be made of an insulating material provided by oxidizing the surface of the aforementioned material containing an element having a large neutron absorption cross section. FIG. 6 shows thermal neutron macro absorption cross sections of hafnium, hafnia and rhodium oxide and the presence or absence of insulation.

(effect)
In this embodiment, a neutron absorber 8 made of hafnia is used instead of the neutron absorber made of hafnium according to the prior art. Thereby, since the neutron absorber 8 made of hafnia has insulation, the insulator becomes unnecessary, and the neutron absorber 8 with a sufficient thickness can be installed. Furthermore, since the hafnia has the same heat conductivity as the insulator of the prior example, the neutron detector 1 is cooled via the heat transfer by the helium gas filled in the furnace piping 4 and the contact portion with the furnace piping 4 Be done.

  Also, by coating the neutron detector with the neutron absorber according to the prior art, the amount of neutrons incident on the detector is reduced, so if the sensitivity of the neutron detector decreases with long-term use, the minimum counting rate There is a problem that it can not be maintained and the life becomes short. On the other hand, in the present embodiment, by using hafnia as the material of the neutron absorber, it is possible to obtain the property that the electrical insulation property is high and the neutron absorption rate decreases with the passage of time.

  FIG. 7 is a graph showing the relative sensitivity of the neutron detector in the neutron detector according to the first embodiment of the present invention and the time course of the neutron incident amount on the neutron detector. As indicated by the solid line A in FIG. 7, the relative sensitivity of the neutron detector generally decreases with the passage of time due to the deterioration of the reactant inside the neutron detector. When hafnia is used as the material of the neutron absorber 8, the neutron absorptivity of the neutron absorber also decreases with time. Thereby, as shown to the dotted line B of FIG. 7, the neutron incident amount to a neutron detector increases with time progress. Therefore, when hafnia is used as the material of the neutron absorber 8, even if the sensitivity of the neutron detector 1 is reduced due to long-term use, the neutron absorptivity of the neutron absorber 8 is simultaneously reduced and the neutron detector 1 is made incident. As the amount of neutrons increases, the minimum count rate can be maintained longer. This makes it possible to further extend the life.

Second Embodiment
Next, with reference to FIGS. 8 and 9, a neutron detector according to a second embodiment of the present invention will be described. Here, the same or similar configuration as that of the first embodiment is denoted by the same reference numeral, and the overlapping description is omitted.

  FIG. 8 is an elevation view showing a neutron detector according to a second embodiment of the present invention and the periphery thereof, as seen through a furnace pipe. FIG. 9 is a plan sectional view taken along the line IX-IX in FIG. However, in FIG. 8, the illustration of the cross section in the detector container 1d is omitted.

  The second embodiment is different from the first embodiment only in the structure of the neutron absorber 8 and the other parts are the same as the first embodiment. The neutron absorber 8 of the second embodiment is configured by arranging a plurality of elongated flat plate-like neutron absorber pieces 30 extending in the vertical direction in the circumferential direction. Each neutron absorber piece 30 is made of a material that is capable of absorbing neutrons and is electrically insulating, such as hafnia. Neutron absorber pieces 30 adjacent to each other in the circumferential direction are welded at a welding point 11. In the example shown in FIG. 8, the welding points 11 are two in the vertical direction, but may be any places. By combining the plurality of neutron absorber pieces 30, a cylindrical neutron absorber 8 can be obtained.

  According to this embodiment, by combining a plurality of simple flat plate-like neutron absorber pieces 30, a cylindrical neutron absorber 8 can be obtained, and the manufacture becomes easy. In addition, the same effects as those of the first embodiment described above can be obtained.

Third Embodiment
Next, a neutron detector according to a third embodiment of the present invention will be described with reference to FIG. Here, the same or similar configuration as that of the second embodiment is denoted by the same reference numeral, and the overlapping description is omitted.

  FIG. 10 is an elevation view showing a neutron detector according to a third embodiment of the present invention and the periphery thereof, as seen through a furnace pipe.

  The third embodiment is a modification of the second embodiment, and upper and lower end portions of a plurality of elongated flat plate-like neutron absorber pieces 30 extending in the vertical direction are joined by two annular outer frames 12. The neutron absorber 8 is constructed. The outer frame 12 is disposed below the upper insulator 9 adjacent to the upper insulator 9 and above the lower insulator 10 adjacent to the lower insulator 10. The neutron absorber pieces 30 are not joined by welding.

  According to this embodiment, by combining a plurality of simple flat plate-like neutron absorber pieces 30, a cylindrical neutron absorber 8 can be obtained, and the manufacture becomes easy. In addition, the same effects as those of the first embodiment described above can be obtained.

[Other embodiments]
While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and the equivalents thereof as well as included in the scope and the gist of the invention.

DESCRIPTION OF SYMBOLS 1 ... Neutron detector 1a ... Anode 1b ... Reactant 1c ... Cathode 1d ... Detector container 2 ... Reactor 3 ... Core 4 ... In-reactor piping 5 ... Cable 6 ... Preamplifier 7 ... Arithmetic part 8 ... Neutron absorber 9 ... upper insulator 10 ... lower insulator 11 ... weld point 12 ... outer frame 13 ... insulator 14 ... neutron absorber 20 ... upper protrusion 21 ... lower end protrusion 30 ... neutron absorber piece

Claims (6)

A neutron detector installed in piping in a reactor in a reactor,
Reactants that are fissioned by neutrons to produce fission fragments;
An ionized gas which is ionized by the fission fragments to generate electron-ion pairs;
An anode and a cathode for collecting the electron-ion pairs;
A detector vessel containing the reactant, the ionizing gas, the anode and the cathode;
An electrically insulating neutron absorber disposed in the air gap between the outside of the detector container and the furnace piping;
A neutron detector characterized by having.   The neutron absorber is at least one of hafnia or at least one of iridium, rhodium, dysprosium, thulium, boron, lutetium, uranium, silver, gold, lithium, cadmium, indium, samarium, europium, gadolinium, erbium, mercury and hafnium. The neutron detector according to claim 1, wherein the neutron detector comprises a compound containing one. The detector container and the neutron absorber are cylindrical,
The neutron detector according to claim 1 or 2, wherein the neutron absorber is disposed so as to surround the radially outer side of the detector container.   The neutron detector according to claim 3, wherein the neutron absorber includes a plurality of neutron absorber pieces extending in the axial direction and arranged in the circumferential direction.   The neutron detector according to any one of claims 1 to 4, wherein the neutron absorber has a characteristic that a neutron absorption rate decreases with the passage of time. In-reactor piping in the reactor,
A neutron detector installed in the furnace piping;
A preamplifier disposed outside the reactor for amplifying a signal obtained from the neutron detector;
An arithmetic unit that calculates the output of the nuclear reactor based on the signal obtained from the preamplifier;
A cable connecting the neutron detector and the preamplifier;
Reactor power detection system comprising:
The neutron detector
Reactants that are fissioned by neutrons to produce fission fragments;
An ionized gas which is ionized by the fission fragments to generate electron-ion pairs;
An anode and a cathode for collecting the electron-ion pairs;
A detector vessel containing the reactant, the ionizing gas, the anode and the cathode;
An electrically insulating neutron absorber disposed in the air gap between the outside of the detector container and the furnace piping;
Reactor power detection system characterized by having.

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