JPS61194392A - 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 that is 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 (4He) 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 can be extended as a whole.

However, when a conventional neutron absorption rod filled with, for example, 84C powder is used as a control rod for a nuclear reactor, the bottom of the powder becomes clogged during use, and a void is created near the upper end where no powder exists. . Generally, in a conventional neutron absorption rod filled with 84C powder, the tip of the SUS metal cladding tube is closed with an SUS plug, and a length of iron wool of several meters is inserted into 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 B
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 a B4C neutron absorbing substance. Reference numeral 9C indicates a void formed in the wool portion.

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 84C 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 ("
When B) is irradiated with a large amount of neutrons until it is significantly depleted, 84C in the region adjacent to the non-absorbing material portion locally becomes 1.
It is irradiated with 5 to 2 times more neutrons, and this neutron irradiation generates nuclear reaction products such as 4H0, 71H, and swelling occurs due to the expansion of the B4C powder grains (vellets). For this reason, in a local critical experiment, the metal cladding tube 8a is caused by the expansion of B4C in a very limited area near the boundary with the non-absorbing material part. 5-5
The neutron flux distribution on the surface of the control rod was measured by changing between Q11. The size of the neutron flux at the center of the non-absorbing material is
Although it varies depending on the length of the non-absorbent part, the length of the non-absorbent part and 8
The neutron flux at the boundary with 4C is 1.5 to 2 times higher than in the case where there is no non-absorbing material portion. Moreover, it was confirmed that this neutron flux increase occurs only in the region very close to the boundary.

Boron-10 ("
When B) is irradiated with a large number of neutrons until it is significantly depleted, 84C in the area adjacent to the non-absorbing material portion locally becomes 1.
It is irradiated with 5 to 2 times more neutrons, and this neutron irradiation produces nuclear reaction products such as 7.'@e, Ll, etc., and swelling of the B4C powder grains (pellets) occurs. For this reason, due to the expansion of 84C in a very limited area near the boundary with the non-absorbent portion, the metal cladding tube 8a is subject to local stress and may bulge and be damaged.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned circumstances, and the interface between the elongated neutron absorbing material and the long-life neutron absorbing material is meshed in an uneven manner, and the non-absorbing material of the elongated neutron absorbing material is By surrounding the control rod with a neutron-absorbing material and suppressing the local increase in neutron flux, it is possible to improve the integrity and reliability of the long neutron-absorbing material and extend the life of the control rod. The purpose is to provide control rods for nuclear reactors with

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention includes a plurality of wings by attaching a sheath with a U-shaped cross section to each protruding leg of a tie rod, and a tip structure material at the insertion tip of the tie rod, and a tip structure material at the insertion tip of the tie rod. Place the terminal structural members in each section,
In a nuclear reactor control rod in which a short long-life neutron absorbing material adjacent to the tip structure member and a long neutron absorbing material adjacent to this neutron absorbing material are arranged in parallel in the axial direction within the sheath, the long-life neutron absorbing material The long neutron absorbing material is made up of a plurality of neutron absorbing rods, and each set of neutron absorbing rods engages with the recess of the long-life neutron absorbing material, and the long neutron absorbing material and the long-life neutron absorbing material are connected to each other. It is characterized in that the interface with the material is configured to mesh in an uneven manner.

[Embodiments of the invention]

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment 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 shape, and a tip structure member 12 and an end structure member (not shown) are coupled to the tip and end sides of the tie rod 11 to be integrated. The tip structure member 12 has a guide roller 1 that guides the insertion of the reactor control rod 10.
4 is provided, and an operating handle 15 is also provided.

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 @
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 may be a short neutron absorbing plate (neutron absorbing rod) of about 5 to 20 atr.

) 18a and a long neutron absorption rod (neutron absorption plate may also be used) 18b with an axial length of 3 m or more, and these long-life neutron absorption materials 18 are used for each wing 17 that receives strong neutron irradiation. Arranged at the tip and wing tip. Among these, the short neutron absorbing plate 18a is arranged closely to the tip structure member 12, and the long neutron absorbing rod 18b is arranged near the wing tip of each wing 17, that is, at the outer end of the sheath 16, as necessary. will be established.

Furthermore, a long neutron absorber 19 is disposed adjacent to the long-life neutron absorber 18 in the flat space of the reactor control rod 10 . This neutron absorbing material 19 is constructed by arranging two types of neutron absorbing rods 19a and 19b having different axial lengths in close proximity in a large number of rows. Each neutron absorption rod 19a, 19b is connected to a metal clad tube 2 as shown in FIG.
A neutron absorbing material 21 such as boron carbide (84G) powder or pellets is filled in the inside of the 0, and a metal wool 23 such as iron wool is interposed at the tip of the neutron absorbing substance 21.
is hermetically sealed. The metal wool 23 and the plug 24 have significantly inferior neutron absorption ability compared to the neutron absorbing material 21, and constitute a neutron non-absorbing material portion 25.

In this way, the non-absorbing material portion 25 includes each neutron absorbing rod 19a,
It is formed at the tip of 19b.

Among the neutron absorbing rods 19a and 19b having different axial lengths, a plurality of neutron absorbing rods of the same type having the same length form a set, for example, two neutron absorbing rods each, and each set of neutron absorbing rods has a different axial length. Arranged alternately at rough corners. Among these, the set of neutron absorption rods 19a having a longer axial length has its top inserted into and engaged with the notch recess 26 of the long-life neutron absorption plate 18a,
As a result, the interface between the elongated neutron absorbing material 19 and the long-life neutron absorbing material 18 mesh in an uneven (zikzag) shape.

Therefore, a long-life neutron absorption plate such as a hafnium plate 1
The tops of the neutron absorbing rods 19a of each set that engage with the recesses 8a are surrounded by a neutron absorbing material such as hafnium. On the other hand, a non-absorbing material portion 25 made of a plug 24, metal wool 23, etc. is provided at the top of the neutron absorbing rods 19a, 19b.
is formed, and the neutron flux tends to increase due to the presence of the non-absorbing material portion 25.
Since 5 is surrounded by a long-life neutron absorbing material such as hafnium, the tendency of the neutron flux to increase is suppressed. The tops of the remaining neutron absorption rods 19b that are not engaged with the recesses (notches) 26 of the long-life neutron absorption plate 18a are surrounded by 84C filled in the adjacent set of neutron absorption rods 19a, and the neutron flux is Excitement is suppressed. The neutron absorption rods 19b may be arranged in groups of a small number of rods or may be one rod.

Note that when the number of neutron absorption rods 19a, 19b forming each set is large, the area of their top non-absorbing material portions 25 becomes large, and the neutron absorption by other neutron absorbing materials surrounding these non-absorbing material portions 25 increases. Each set of neutron absorption rods 19a because the suppression effect is reduced.

It is desirable that the number of 19b is small.

Next, the effect will be explained.

When a hybrid reactor control rod 10, which is a combination of a long-life neutron absorber 18 and a long neutron absorber 19, is inserted into the core of a nuclear reactor, the control rod 10 is irradiated with neutrons. According to experiments, the two-dimensional distribution of neutron flux on the surface of a nuclear reactor control rod that has been irradiated with neutrons is represented by a contour map shown in relative values in the left half of FIG. As can be understood from this contour map, the reactor control rod 10 receives particularly strong neutron irradiation at the tips and blade tips of each wing 17.

However, in this case, since the reactor control rod 10 is provided with long-life neutron absorbing material 18 at the tip and tip of each wing 17 that is exposed to strong neutron irradiation, the neutron absorption capacity during the neutron irradiation time is approximately reduced. It is possible to achieve uniformity and extend the life of the control rod.

In general, when the interface between a long-life neutron absorber and a long neutron absorber is not jagged but straight, the neutron flux swells as shown in Figure 5 (B), resulting in a non-conforming The nuclear fission reaction of boron-10 proceeds in a very limited area of 84C adjacent to the absorber section 25, and as a result, B4C causes swelling, locally bulges the metal cladding tube 20, and causes damage. There is a risk of slacking off. However, in this embodiment, the long-life neutron absorbing material 18 and the long neutron absorbing rod 19 are
The boundary surfaces with a and 19b are interlocked in a zigzag shape (uneven shape), and the non-absorbing material portions 25 formed at the tops of the long neutron absorbing rods 19a and 19b are arranged alternately. Since it is surrounded by a neutron absorbing material such as 84C filled in the long-life neutron absorbing material 18 and other neutron absorbing rods, the buildup of neutron flux in that area is suppressed. As a result, the nuclear fission reaction of boron-10 near the tops of the elongated neutron absorption rods 19a and 19b is suppressed, so that the risk of damage to the metal jacketed tube 20 can be eliminated.

In the description of one embodiment of the present invention, a long-life neutron absorbing material is shown as a flat plate, but it is not necessarily limited to this, and it may also be in the shape of a rectangular bar or round bar divided into many pieces. good.

In addition, although the elongated neutron absorbing material shown in FIGS. 1 and 2 has been explained in the case where two neutron absorbing rods form a pair, the neutrons forming the pair may vary depending on the arrangement position of the neutron absorbing rods. The number of absorption rods may be varied in the width direction of the wing. In the area adjacent to the tie rod, it is preferable to have only one tie rod rather than a pair of tie rods.

〔Effect of the invention〕

As described above, in the nuclear reactor control rod according to the present invention, the long neutron absorbing material is made up of a plurality of neutron absorbing rods, and each set of neutron absorbing rods is a long-life neutron absorbing material. Since the interface between the elongated neutron absorbing material and the long-life neutron absorbing material engages with the four parts of the elongated neutron absorbing rod in an uneven manner, By surrounding the non-absorbing material portion with a neutron absorbing material, local increase in neutron flux can be suppressed. Therefore, it is possible to effectively suppress the swelling of the neutron absorbing material, reliably prevent damage due to partial expansion of the neutron absorbing rod, improve the soundness and reliability of the control rod, and extend its life. I can do it.

In addition, the long neutron absorbing material is made up of a set of multiple neutron absorbing rods, and this set of neutron absorbing rods engages with the recess of the long-life neutron absorbing material. When the recesses are formed, the number of recesses to be formed is reduced and processing is easy.

[Brief explanation of drawings]

FIG. 1 is a partial vertical view showing one embodiment of a nuclear reactor control rod according to the present invention, and FIG. 2 shows a long neutron absorption rod incorporated in the wing of the nuclear reactor control rod. Fig. 3 is a perspective view showing a conventional nuclear reactor control rod, and Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. Figure 5 (A) and (
B) is a diagram showing the arrangement relationship of each neutron absorbing material incorporated in a conventional control rod for a nuclear reactor and the relationship of neutron flux distribution. 10... Nuclear reactor control rod, 11... Tie rod, 1
2...Tip construction material, 16...Sheath, 17...Wing, 18...Long-life neutron absorbing material, 19...
Long neutron absorbing material, 19a, 19b... Neutron absorbing rod, 20... Metal clad tube, 21... Neutron absorbing material, 213... Metal wool, 24... Plug, 25...
...Non-absorbent portion, 26...Concave portion. Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Location procedure amendment (JIRI Indication of the September 22, 1985 incident 1985 patent application No. 35489 Name of the invention Correction of control rods for nuclear reactors) (and one other person) 5゜6. Contents of the amendment (1) In the 7th line of page 7 of the specification, after the word ``local'' there is a statement that ``there is a risk of swelling and damage due to stress.'' ” is inserted.

Claims (1)

[Claims] 1. A sheath with a U-shaped cross section is attached to each protruding leg of the tie rod to form a plurality of wings, and a tip structure material is attached to the insertion tip of the tie rod, and a terminal structure material is attached to the insertion end. and a short long-life neutron absorbing material adjacent to the tip structure member and a long neutron absorbing material adjacent to this neutron absorbing material are arranged in parallel in the axial direction within the sheath. In the rod, the elongated neutron absorbing material is made up of a plurality of neutron absorbing rods, each group of neutron absorbing rods is engaged with a recessed portion of the long-life neutron absorbing material, and the elongated neutron absorbing material and A control rod for a nuclear reactor, characterized in that an interface with a long-life neutron absorber is configured to mesh in an uneven manner. 2. For use in a nuclear reactor according to claim 1, the long neutron absorbing material includes a plurality of types of neutron absorbing rods having different axial lengths, and is arranged in a row in a flat space within the sheath. control rod. 3. The elongated neutron absorbing material is provided with two types of neutron absorbing rods having different axial lengths, and the neutron absorbing rods of the same type are arranged alternately in sets of two, as claimed in claim 1. A control rod for a nuclear reactor described in . 4. A neutron non-absorbing material part such as a plug or metal wool is formed at the tip of the neutron absorbing rod, and this non-absorbing material part is surrounded by a long-life neutron absorbing material or a neutron absorbing material in an adjacent neutron absorbing rod. A control rod for a nuclear reactor according to claim 2 or 3, in which: