JPS6340244A - Neutron detector for atomic reactor - Google Patents

Abstract

PURPOSE:To enable to confirm, with an ordinary measuring board, activation amount after the use of a detector by providing a neutron sensitive substance in such a way as to generate inside the detector a neutron source corresponding to the neutron amount received by the detector itself. CONSTITUTION:If a mixture 22 of antimony and berylium arranged inside a detector is irradiated with neutron, <123>SB(n, r) and <124>Sb are subjected to bets decay into <124>T(e) for emitting <124>T(e), and gamma rays emitted from the <124>T(e) cause <9>B(e) to generate neutrons with photonuclear reaction of <9>B(e)(r, n) <3>B(e). An amount of neutron generated by this nuclear reaction forms a formula, closely relating to the amount of neutron the mixture 22 received. In the formula, A is the amount of generated neutron, B is the amount of neutron irradiated, T<1> is irradiation period, T2 is time after an atomic reactor shutdown, and alphaand beta are constants determined depending upon decayed nucleides. Normally, alphaand beta are known values while T1 and T2 are also known values. And, A can be obtained by measuring while B becomes computable. In other words, if an amount of neutron is obtained, the activation amount can be computed from components of detector constituting members.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a neutron detector for a nuclear reactor.

[Conventional technology]

FIG. 2 is a cross-sectional view showing a conventional neutron detector for nuclear reactors (11 is a high voltage electrode, (2) is a signal electrode, (31 is arranged to cover the high voltage electrode Il+ and signal electrode (21). The shield cylinder 14) is a vacuum airtight envelope disposed to cover the outer periphery of the shield cylinder (3), 15) to (9).
) is a ceramic for insulating each electrode from the shield cylinder, tto+ is a bolt for fixing the internal electrode, (11) is an oak +
-1U is the signal, high-voltage lead wire, the seal is the seal h, the ceramic that insulates the internal electrode assembly from the airtight envelope 14), +l[l-171id neutron sensitive material, 9~ is the M electrode for daytime voltage. Cable, decoy is M ecaple for signal, (A) is t release gas, 2υ is the high voltage electrode Il+ and signal electrode (
2) is the space between.

Next, the operation will be explained. Neutrons generated in a nuclear reactor pass through an airtight envelope (41) and a shield (31), causing a nuclear reaction with a neutron-sensitive substance, and the resulting ions form an electric layer on the ionized gas.Ionization generated at that time The particles are measured as an ionization current by applying a high voltage between electrodes 111 and +21.

[Problem that the invention seeks to solve]

Conventional neutron detectors for nuclear reactors are configured as described above, so it is important to know how much total neutron radiation (amount of activation of the detector) the detector has received after being used in a nuclear reactor. I couldn't.

For this reason, safety checks during bare radiation work during the maintenance of the detector involved bringing a survey meter onto the surface of the detector to measure the amount of radiation in the detector, which resulted in a problem of increased radiation exposure during maintenance.

This invention was made in order to solve the above-mentioned problems, and the object is to obtain a neutron detector for a nuclear reactor that allows the amount of activation after use of the detector to be confirmed from the outside using a normal measurement panel. With the goal.

[Means for solving problems]

The neutron detector for a nuclear reactor according to the present invention generates a neutron source inside the detector according to the amount of neutrons received by the detector itself, so that counts according to the intensity of the neutron source can be calculated by an external circuit system. This allows for monitoring.

[Effect]

The neutron detector for a nuclear reactor according to the present invention has a mixture of antimony and beryllium inside the detector, and when the substance receives a neutron amount of 1 t', a nuclear reaction of 123Sb (CnJ) 81) occurs, and sb becomes β. The gamma rays emitted by - decay to become T8) causes photoneutrons to be emitted by the neutrons, and by counting these neutrons, the amount of neutrons received by the detector itself can be determined, that is, the amount of activation of the detector itself can be determined.

〔Example〕

FIG. 1 is a cross-sectional view showing a neutron detector for nuclear reactors according to the present invention, in which a high voltage electrode is shown at Ill, (21 is a signal electrode,
i The high-voltage electrode +11 and the signal electrode (shield tube disposed so as to cover 21, 14) are connected to the shield tube (vacuum airtight outer shell disposed so as to cover the outer periphery of 31, Otori 6) ~
t91 Ceramic for insulating the entire Vi valley electrode from the shield cylinder, 101 is the internal electrode fixing bolt, (12+ is the signal, high voltage lead wire, (131 is the shield lead wire, 114+, aFA is the internal electrode assembly Ceramic, αtg, insulating from the hermetic envelope (4)
, L171 is a neutron-sensitive substance, 181 i is an M cable for A voltage, 4 is a M cable for a signal, 4 is a 1 release gas, 29 is a space between the high voltage electrode Il+ and the signal electrode (2), It is a mixture of antimony and beryllium.

Next, the operation will be explained.

When the mixture of antimony and beryllium placed inside the detector is irradiated with neutrons, it becomes 5b(n・γ)81)8
1) undergoes β-decay and becomes T13. Due to the gamma rays emitted by the gloss, 9Be generates neutrons by the photonuclear reaction of 's(r, nAe.The amount of neutrons generated by this nuclear reaction is the same as the amount received by the above mixture. It is related to the amount of neutrons and the can opener, and is AOCB (1-6'') 6-βT''.

A: Amount of neutrons generated B: Amount of neutrons irradiated TI = Irradiation period (Hr) Time after the two Tt reactors were shut down (Hr) α, β: Constants determined by decay nuclides Normally α and β are F5 ．． 'r, 'r, and 'r are already available for plant monitoring. Then, A can be determined by measurement, and the time around B can be calculated. B, that is, when the amount of irradiated neutrons is yK', the amount of activation can be calculated from the components of the detector constituent materials. Here, the neutron absorption Fi 5b(n,
γ) About 8 burns in sb. On the other hand, since the neutron absorption cross section of the sensitive material (n, γlLi) considered as a neutron detector is about 4000 burns, the neutron absorption cross section of The decrease in sensitivity is negligible, and there is no problem with the effect on neutron counting in the original neutron measurement.

[Effects of the Invention] As described above, according to the VC of the present invention, the detector activation t can be calculated in advance by measuring neutrons from the mixture of antimony and beryllium disposed inside the detector, and maintenance of the detector can be simplified. This enables safe work at times.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a neutron detector for a nuclear reactor according to an embodiment of the present invention. The $2 diagram shows a conventional neutron detector for nuclear reactors! Il? A picture of a mask. In the figure, 111 is a high-voltage electrode, +21V'i old name pole, (31 is a shield tube, 14) is an airtight envelope, -51~
(91 is ceramic, 101 is bolt, Ill is nut, (+27 is signal, high voltage lead ring, AA shield lead bare, H. a51 is ceramic, llυ, 171 is neutron sensitive material, a■ is 1 M for depressed pressure Ecaple and outlet are signal MI cables, 211 is space, and a mixture of antimony and beryllium. In the figures, the same reference numerals indicate the same or removed parts.

Claims (1)

[Claims] A neutron detector for a nuclear reactor, characterized in that the detector is equipped with a neutron-sensitive substance inside the detector so that a neutron source corresponding to the amount of neutrons received by the detector is generated. .