JPS61189488A - Control rod for nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a control rod for a nuclear reactor inserted into the core of a nuclear reactor such as a boiling water reactor, and particularly to a control rod for a long-life nuclear reactor. Regarding the hybrid structure of.

[Technical background of the invention and its problems]

A control rod used in a boiling water reactor etc. is constructed as shown in FIGS. 3 and 4, and has a tip structure member 2 and a terminal structure member 3 at the tip and end of a tie rod 1 having a cross-shaped cross section, respectively. At the same time, a sheath 4 having an elongated U-shaped cross section is attached to each protruding leg of the tie rod 1 to form four wings 5 having a cross-shaped cross section.

A large number of long neutron absorption rods 6 are interposed and arranged in the flat space within each wing 5. The neutron absorption rod 6 is a metal clad tube filled with a neutron absorption material such as boron carbide (84C).

When a control rod for a nuclear reactor is inserted into a reactor core and is irradiated with neutrons, the neutron-absorbing material inside the neutron-absorbing rod absorbs the neutrons and is subject to wear and tear due to combustion, etc., and becomes a nuclear reaction product. Gas such as helium gas ('He) is generated. For this reason, the control rod's neutron absorption capacity decreases as the neutron irradiation time passes, and the gas pressure within the metal cladding tube increases.

The neutron irradiation time required for the neutron absorption capacity to decrease to a predetermined value is called the nuclear lifetime, and the neutron irradiation time required for the gas pressure to rise to an allowable value is called the mechanical lifetime.

By the way, when focusing on a single control rod, not all of the many long neutron absorption rods housed within the control rod receive neutron irradiation equally. For example, when a control rod is partially inserted into the core of a nuclear reactor, the vicinity of the side edges and the tip of each wing are particularly exposed to strong neutron irradiation, and the neutron absorption capacity of these parts is significantly deteriorated.

Therefore, in conventional nuclear reactor control rods in which all neutron absorption rods are made uniformly, the neutron absorption rods located at the upper end (tip) or wing side edges of the neutron absorption rods are different from other parts or other control rods. It loses its neutron absorption ability before the neutron absorption rod,
The neutron absorbing rods on the side edges of the wings lose mechanical life before the other absorbing rods. As a result, in conventional nuclear reactor control rods, even though most of the neutron absorption rods are usable, the reactor control rods must be replaced, making effective use of the control rods. I couldn't.

From this point of view, the applicant proposed a control rod in which a long-life neutron absorbing rod made of hafnium or the like, which does not generate gas even when absorbed by neutrons, is installed at the tip of the rod, which is exposed to strong neutron irradiation (Japanese Patent Laid-Open No. 53 -74697 and JP-A No. 5
7-173788). In this way, the life of the part that receives strong neutron irradiation is extended, so that the life of the reactor control rod as a whole can be extended.

However, when a conventional neutron absorption rod filled with B4C powder is used as a control rod for a nuclear reactor, the bottom of the rod becomes clogged with powder during use, and a void is created near the upper end where no powder exists. . Generally, in a conventional neutron absorption rod filled with B4C powder, the tip of the SUS metal cladding tube is closed with an SUS plug, and several layers of iron wool are interposed in the metal cladding tube adjacent to the plug. are doing.

Since the wool and plug have a significantly lower neutron absorption capacity than neutron absorbing substances such as B4C and hafnium, they constitute a non-absorbing material portion, and voids are generated under the wool.

Figure 5 (A) shows a long-life neutron absorber (hafnium plate or hafnium rod) 7 and a conventional neutron absorber 8 in the reactor control rod.
A long neutron absorption rod 8 filled with 4C is used, and the boundaries between the two are aligned in a straight line, and the neutron absorption rod 8
Figure 5 (B
) is estimated as shown by the solid line. The broken line shows the neutron flux distribution in the presence of 84C neutron absorbing material.

According to criticality experiments, the magnitude of the increase in neutron flux at the center of the non-absorbing material part of the neutron absorbing rod 8 changes depending on the length of the non-absorbing material part, but the neutron flux at the boundary between the non-absorbing material part and B4C The bundle is 1. compared to the case where the non-absorbent part is not present.
It was confirmed that the neutron flux increased by 5 to 2 times, and that this increase in neutron flux occurred only in the region extremely close to the boundary.

Boron-10 (1
0B) is irradiated with a large amount of neutrons until it is significantly depleted, B4C in the area adjacent to the non-absorbing material locally decreases to 1
．． It is irradiated with 5 to 2 times more neutrons, and this neutron irradiation generates nuclear reaction products such as 4He, 7L', etc.
Swelling occurs due to expansion of the 4C powder grains (bellets). Therefore, due to the expansion of B4C in a very limited area near the boundary with the non-absorbing material part, the metal cladding tube 8a receives local stress and bulges, and there is a possibility that it may be damaged.

[Purpose of the invention]

The present invention was made in consideration of the above-mentioned circumstances, and alleviates the stress locally generated in the region adjacent to the non-absorbing material portion of the neutron absorption rod, thereby effectively preventing local damage of the neutron absorption rod. It is an object of the present invention to provide a control rod for a nuclear reactor that can reliably prevent such problems and extend the life of the control rod.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention attaches a sheath with a U-shaped cross section to a tie rod that connects a tip structure member and a terminal structure member to form a plurality of wings, and a neutron absorbing material is placed in the wing. In a nuclear reactor control rod in which filled long neutron absorbing rods are arranged, a short long-life neutron absorber is disposed in the wing adjacent to the tip structure member, and the long-life neutron absorber is arranged in the wing. The invention is characterized in that a reinforcing sleeve is inserted into a part of the metal cladding tube of the elongated neutron absorption rod adjacent to the rod.

[Embodiments of the invention]

Hereinafter, preferred embodiments of a control rod for a nuclear reactor according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a nuclear reactor control rod 10 of the present invention used in a boiling water reactor. The control rod 10 has a tie rod 11 having a cross-shaped cross section.
A tip structural member 12 and a terminal structural member 13 are coupled to the distal end and distal side of the holder and are integrated. The tip structure member 12 is provided with a guide roller 14 for guiding the insertion of the reactor control rod 10, and is also provided with an operating handle 15.

On the other hand, a sheath 16 having a deep U-shaped cross section is attached to each protruding leg of the tie rod 11, forming four wings 17 having a cross-shaped cross section.

A flat internal space is formed within the sheath 16 of the wing 17. A long-life neutron absorber 18 is disposed in the internal space adjacent to the tip structure member 12 .

This neutron absorbing material 18 is made of hafnium (Hf) or H
It is made of f-Zn alloy or the like and is shaped like a rod or plate. Hafnium is a metal material with excellent neutron absorption ability, and B4
It has a lifespan 3 to 6 times that of C.

Further, the long-life neutron absorbing material 18 includes a long neutron absorbing rod (which may be a neutron absorbing plate) 18b having an axial length of 3 m or more and a short neutron absorbing plate (about 5 to 151 mm). These long-life neutron absorbers 18 are disposed at the tips and blade tips of each wing 17, which are exposed to strong neutron irradiation.

Among these, the short neutron absorption plate 18a is attached to the tip structure material 12.
A long neutron absorbing rod 18t) is disposed in close proximity to the wing 17 near the tip of each wing 17, that is, at the outer end of the sheath 16, as necessary.

Further, in the flat space of the reactor control rod 10, a conventional elongated neutron absorber 19 is disposed adjacent to the long-life neutron absorber 18. The neutron absorbing material 19 includes a large number of neutron absorbing rods arranged closely in rows. As shown in FIG.
1 is filled, a reinforcing sleeve 22 made of, for example, SUS is inserted into the tip thereof, and a neutron absorbing material 21 is also interposed within this sleeve 22. Various metal sheets can be considered as the sleeve material, but the same material as the metal cladding tube 20 may be used. A metal wool 23 such as iron wool is interposed at the tip of the metal cladding tube 20 filled with the neutron absorbing substance 21 and hermetically sealed with a plug 24 . The metal wool 23 and the plug 24 have significantly inferior neutron absorption ability compared to the neutron absorbing material 21, and the neutron non-absorbing material portion 2
5 is composed. Therefore, the non-absorbing material portion 25 is formed at the tip of each neutron absorbing rod 19.

By the way, the metal cladding tube 20 is a cladding tube made of, for example, SUS and has a wall thickness of about 0.5 to 1 foot, and a reinforcing sleeve 22 is locally interposed adjacent to the non-absorbent portion 25. The reinforcing sleeve 22 has a wall thickness of about 0.05 to 0.2j+s+, and its sleeve length l is 1C1cm to several cm, preferably about 21 cm, to the void length 11 that may occur due to the deposition of B4C powder. 2 (see FIG. 5(B)).

The reinforcing sleeve 22 may actually have a length of about 3a+ to 5c11.

Therefore, when the nuclear reactor control rod 1o, which is configured by arranging the long-life neutron absorbing material 18 and the neutron absorbing rod 19 filled with a neutron absorbing material such as 84c, is inserted into the core of the reactor, the control rod 1o is irradiated with neutrons. At this time, it is assumed that the II culm of the neutron absorption rods 19 and the short long-life neutron absorption plates 18a arranged in the wing 17 of the reactor control rod 1o is formed in a straight line. It is also applicable when the boundary is formed non-linearly.

When the reactor control rod 10 is irradiated with neutrons, since the non-absorbing material portion 25 exists at the tip of the neutron #1m rod 19, the neutron absorbing material 21 such as the non-absorbing material portion 25 and 84c
In a critical experiment, the neutron flux at the boundary with the non-absorbing material M2
It is predicted that the number will be about 1.5 to 2 times that of the case where No. 5 does not exist. When the length of the non-absorbing material portion 25 becomes about 11, it is expected that the increase in neutron flux will decrease, but it cannot be ignored. Moreover, the neutron flux build-up occurs only in the region extremely close to the boundary, and that region receives strong neutron irradiation.

When the reactor control rod 1o receives a large amount of neutron irradiation and the boron-10 neutron absorbing material is significantly depleted, the local area adjacent to the non-absorbing material portion 25 of the neutron absorbing rod 19 is When exposed to strong neutron irradiation of approximately 1.5 to 2 times the amount of B4, nuclear reaction products such as 'He and 7Li are generated.
The C powder particles expand as a whole due to swelling. B4
Since the hardness of the C powder grains is greater than the hardness of the metal cladding tube 20, the metal cladding tube 2o is locally affected by the expansion of the 84G grains in an extremely limited area adjacent to the non-absorbing material portion 25 due to the expansion of the B4C powder grains. There is a risk of stress. However, in this case, since the reinforcing spacer 22 is interposed in the elongated neutron absorbing rod 19 adjacent to the non-absorbing material portion 25, a small gap is created between the reinforcing spacer 22 and the metal cladding tube 20. , this void absorbs the stress generated by local swelling of the B4C powder. For this reason, metal clad tube 2
0 integrity is maintained, and its damage can be effectively prevented.

In the description of one embodiment of the present invention, an example has been described in which a cylindrical reinforcing sleeve is inserted into the top of a metal cladding tube, but this reinforcing sleeve is not necessarily limited to a cylindrical shape. B4C inside the metal cladding tube like a pressurized water reactor
If a pellet of sintered powder is inserted, the reinforcing sleeve may have a corrugated shape.

〔Effect of the invention〕

As described above, the IIJ control rod for a nuclear reactor according to the present invention has a short long-life neutron absorbing material disposed in the wing adjacent to the tip structural member, and a long long-life neutron absorbing material adjacent to the neutron absorbing material. Because a reinforcing sleeve is inserted into a part of the metal cladding tube of a long neutron absorption rod, there is a non-absorbing material region where no neutron absorption material exists at the top of the long neutron absorption rod, resulting in a localized neutron flux distribution. Even if swelling occurs in the neutron absorbing material (84G) in the vicinity thereof, the stress caused by the swelling can be sufficiently and effectively absorbed by the small gap existing between the reinforcing sleeve and the metal cladding tube. Therefore, damage to the metal clad tube can be reliably prevented.
The soundness and reliability of nuclear reactor control rods can be improved, and their lifespan can be extended.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical cross-sectional view showing an embodiment of a nuclear reactor control rod according to the present invention, and FIG. 2 is a cross-sectional view showing the internal structure of a long neutron absorption rod to be incorporated into the nuclear reactor control rod. Figure 3 is a perspective view showing a conventional nuclear reactor control rod, Figure 4 is a plan cross-sectional view taken along line IV-IV in Figure 3, and Figures 5 (A) and (B) are conventional nuclear reactor control rods. FIG. 3 is a diagram showing the relationship between the arrangement of each neutron absorber incorporated in a reactor control rod and the relationship between neutron flux distribution. 10... Nuclear reactor control rod, 11... Tie rod, 1
2... Tip structure material, 13... End structure material, 16...
・Sheath, 17... Wing, 18... Long-life neutron absorbing material, 19... Neutron absorbing rod, 2o... Metal cladding tube, 21... Neutron absorbing material, 22... Reinforcement sleeve , 23... Metal wool, 24... Plug, 2
5...Non-absorbent part. Applicant's agent Hisashi Hatano Location to Figure 5

Claims (1)

[Claims] 1. A tie rod that combines a tip structure member and an end structure member,
A control rod for a nuclear reactor in which a sheath with a U-shaped cross section is attached to form a plurality of wings, and long neutron absorption rods filled with a neutron absorption material are arranged in the wings, adjacent to the tip structure member. A short long-life neutron absorbing material is arranged in the wing, and a reinforcing sleeve is inserted into a part of the metal cladding tube of the long neutron absorbing rod adjacent to the long-life neutron absorbing material. Characteristic control rods for nuclear reactors. 2. The reinforcing sleeve is interposed at the tip of a long neutron absorbing rod, and the metal covering tube and reinforcing sleeve of the neutron absorbing rod are filled with a neutron absorbing substance such as boron carbide. Control rods for nuclear reactors as described in Section 1. 3. The reinforcing sleeve has a wall thickness of about 0.05 to 0.2 mm, and the length of the sleeve is 1 cm to the length of voids that may occur due to the deposition of neutron absorbing material during use in the reactor.
The control rod for a nuclear reactor according to claim 1, which has a length including a length of about m to several cm.