JPS6010596B2 - Neutron detection device mounting structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a neutron detection device mounting structure having a local power range neutron detection assembly (hereinafter abbreviated as LPRM) for a commercial reactor, particularly a boiling water reactor.

As is well known, IPRM is a monitor that instantly and continuously transmits neutron information inside the reactor to the outside of the reactor to ensure safer operation of the reactor and more efficient combustion of nuclear fuel, that is, fuel economy. Although large numbers of LPRMs are used at various locations within the reactor core, the reality is that radiation exposure is unavoidable as the LPRM replacement work that is carried out at every regular inspection is carried out under a special environment.
Therefore, there is a strong desire to reduce the amount of radiation exposure during replacement work, and regulation of work time, that is, short-time work is most commonly sought. However, although this method can reduce individual radiation exposure, it reduces work efficiency and requires a large number of personnel, which poses a major problem in terms of securing personnel for the work performed at each periodic inspection. According to general work records, LPRM replacement work is carried out simultaneously at two locations, on the 6th floor of the reactor building and in the vedestal located directly below the reactor pressure vessel, using dedicated telephones, etc. The radiation dose is approximately 150 to 20 hR/hr (actual results in the 5th year after the reactor started operation), and considering the permissible exposure amount stipulated by law, the actual operation time is 30 minutes/day, and approximately 30 people work. Personnel are needed.

It is clear that if nuclear reactors start operating in various places in the future and periodic inspections begin to overlap, it will be extremely difficult to secure personnel if we assume zero. After being linked to a nuclear reactor, activation of the reactor body structure progresses due to the influence of neutron irradiation as the operating time progresses, and it is inevitable that the radiation dose in the surrounding area will increase. (abbreviated as clad)
There is a desire to reduce the amount of radiation exposure during replacement work.

The locations where crud is expected to accumulate on LPR ships will be explained in detail based on drawings.

In Figure 1 a and b, 0 11' reactor pressure vessel, 1
2 is a nuclear fuel assembly, 13 is an in-core guide tube, 14 is an LP
RM body, 45 is a mating flange, 16 is packing, 17
The flange fixing bolt "18' is a special nut for fixing and holding the LPRM main body. As shown in the figure, there is a clad 19 in the gap between the incoater guide tube 13 and the LPRM main body 14, and a cladding 19 inside the LPRM main body 14. A guide tube 14a for shark adjustment and a detector 14b necessary for detector sensitivity adjustment are housed, and cladding 20 is accumulated between them.
It is known that these cruds 19 and 20 float inside the reactor, that is, in the reactor water, during steady operation of the nuclear reactor and eventually accumulate in the lower part, and the amount of sedimentation increases with operating time.

The place where cruds 19 and 20 are accumulated during replacement work,
The location near the worker's head makes the work difficult. The present invention was developed in view of the above circumstances, and since the occurrence and accumulation of crud is an unavoidable fact, the present invention is designed to have a structure that allows the location where crud accumulates to be separated to the extent that it does not affect the work. This ensures a reduction in radiation exposure.

The present invention will be explained in detail below based on the drawings.

Note that the same parts are represented by the same symbols. In FIGS. 2a, b and 3 a, b, a partition plate 21 for accumulating crud is provided halfway inside the LPRM body 11, and pins 22 are used to securely hold this partition plate 21. . After this pin 22 is inserted into a predetermined position, the tip end is welded, for example, by welding, etc., and serves to completely fix the partition plate 21 while maintaining a fine cage on the circumferential surface. The position of this partition plate 21 is selected to be approximately 6 to 7 meters away from the operator when it is assumed to be replaced, thereby preventing direct exposure to radiation from the crud 20 that accumulates on the upper part of the partition plate 21.

The crud that accumulates on the outer periphery of the LPRM, that is, between the LPRM main body 4 and the inner core guide tube 13, is accumulated above. That is, the LPRM main body 14 has a guide ring 24 that is pressed downward by a spring 23, and the spring 23 and guide ring 24 are connected to upper and lower stoppers 25, 2.
It is held between 6 and 6. When the LPRM main body 14 is installed, the guide ring 24 is fixed in surface contact with the tapered part 27 on the inner surface of the in-core guide tube 13, catches the crud 19 floating in the reactor water as shown in the figure, and prevents the crud from moving to the lower end of the LPRM. It is prevented. To further note about one embodiment of the present invention, the main constituent material of the LPRM is stainless steel (S
The sling 23 is preferably made of Inconel X-750.

The features of the present invention detailed above are enumerated as follows. {1} The partition plate provided as a countermeasure against internal cladding is relatively easy to machine and easy to install.

In addition, it greatly contributes to reducing radiation exposure. [
2} The spring-type guide ring, which was explored as a countermeasure for external cladding, is similar to '1} in that it has a large radiation exposure reduction effect, but also serves to reduce vibrations of the LPRM during reactor operation.

'3' Material costs are negligible despite the large effect of reducing radiation exposure.

[Brief explanation of the drawing]

Figure 1a is a cross-sectional view of the main part of the attachment part of the secondary LPRM, Figure b is an enlarged cross-sectional view of part A, Figure 2a is a cross-sectional view of the main part showing the embodiment of the present invention, Figure b 3 is a sectional view taken along line B-B, FIG. 3a is a partially cutaway view, and FIG. 3b is an enlarged view of section C. 11... Reactor pressure vessel, 13... In-core guide pipe, 1
4... LPRM body, 21... Partition plate, 23...
Spring, 24...Guide ring, 27...Taper part. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 Local power range neutron detector assembly main body 14 is installed inside the in-core guide pipe 13 provided in the reactor pressure vessel 11.
In the neutron detection device mounting structure, a partition plate 21 is provided halfway inside the assembly body 14, and a guide ring 24 pressed by a spring is provided on the outer periphery of the assembly body 14. At the same time, the guide ring 24 is connected to the inner surface tapered portion 2 of the in-core guide tube 13.
7. A neutron detection device mounting structure, characterized in that the neutron detection device mounting structure is in contact with and locked by 7.