JPH02236198A - 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] [Objective of the Invention] [Industrial Application Field] This invention relates to a control rod for a nuclear reactor, which is constructed by disposing plate-shaped long-life neutron absorbers facing each other with a gap between them. .

<Prior Art> A conventional control rod for a boiling water reactor has a U-shaped cross-sectional sheath extending in the longitudinal direction of the central tie rod fixed to each end of the central tie rod, and a large number of neutron absorption rods are installed within this sheath. It is configured by loading.

The wings are defined by sheaths secured to each end of the central tie rod. Further, a neutron absorbing rod is prepared by filling boron carbide (B4C) powder as a neutron absorbing material into a stainless steel cladding tube, for example. The filled B4C absorbs neutrons in the nuclear reactor and gradually loses its neutron absorption ability.

By the way, the control rods inserted into or extracted from the core of a nuclear reactor are not irradiated with neutrons uniformly over their entire area; for example, the side edge area or the upper end area of the wing receives intense neutron radiation. For this reason, the neutron absorption rods arranged at the side edges and upper end regions of each wing absorb a large number of neutrons and end their nuclear life earlier than the neutron absorption rods in other regions.

Therefore, there was an uneconomical situation in that the fil+ rod had to be discarded even though the neutron absorption rods placed in other areas still had a nuclear life remaining.

In order to solve such problems, nuclear reactor control rods have been developed in which long-life neutron absorbers, such as hafnium, are partially placed in areas of the control rods that are exposed to intense neutron irradiation. Developed by the present applicant, JP-A-53
This is disclosed in Japanese Patent No.-74697. This nuclear reactor control rod has a lifespan that is approximately twice as long as that of a conventional control rod.

After that, there was a desire for a transition to high burnup operation and long continuous operation of nuclear reactors, and in response to the increasing demand for longer life of the control shaft, the present applicant filed Japanese Patent Application No. 61-7874.
As described in No. 6 Akira, we have developed a long-life reactor control rod that can dramatically extend its life.

This control rod for a nuclear reactor does not use B4C as a neutron absorbing material, but has a structure in which metal neutron absorbing plates such as hafnium metal plates having a long life are disposed facing each other in a sheath. The specific configuration is shown in FIGS. 7 and 8. That is, the end structure 1 and the tip structure 3 with the handle 2 are integrally joined in the longitudinal direction by the central tie rod 5 having a cross-shaped cross section. A stainless steel sheath 6 having a U-shaped cross section is fixed perpendicularly to the longitudinal direction of each protrusion of the central tie rod 5 to form a wing 7.

Inside the sheath 6, a plate-shaped long-life neutron absorption chamber 8 typically made of a hafnium (Hf) metal plate or the like is accommodated.

This neutron absorber 8 consists of a plurality of neutron absorbing elements 8a arranged in the axial direction of the central tie rod 5. Each neutron absorbing element 8a is composed of, for example, two neutron absorbing plates 8b, as shown in FIG.

These neutron absorption plates 8b are arranged opposite to each other in the thickness direction of the wing 7, and are integrally joined via a plurality of spacers 9.

A gap 10 is formed between the two neutron absorption plates 8b through which moderator (for example, reactor water) flows.

Further, the sheath 6 is provided with a large number of water holes 11 for allowing reactor water to flow in and out of the sheath 6 .

In this hafnium plate trap type nuclear reactor control rod, the above-mentioned gap 110 is formed for the following reason. In other words, hafnium has a slightly inferior neutron absorption ability compared to B4C and has a high specific gravity, so in order to ensure the same neutron absorption function as conventional control rods, it is necessary to install thick hafnium plates. As a result, the weight of the control rod increases significantly, requiring a change in load design. Therefore, a gap 10 is formed between the hafnium neutron absorbing plates 8b disposed facing each other in the sheath 6 to allow water, which is a moderator, to flow. This is to improve the reactivity value and reduce the thickness of the hafnium plate.

Therefore, the total weight of the hafnium plate/wrap type control rod can be suppressed, making it possible to reduce the overall weight of the control rod compared to conventional! It becomes possible to adopt it to the No. 11 drive rod drive mechanism.

By the way, as a result of confirming the reactivity value using a critical experiment device incorporating a full-scale model (mock-up) of this reactor I1 control rod, it was found that the wider the gap 10, the greater the reactivity value of the υ1 control rod. It has been proven that it increases. That is,
As the width of the gap 10 is increased, the thickness of the hafnium plate can be reduced, and the total weight 2 of the control rod can be reduced.

By the way, the hafnium plate trap type nuclear reactor control rods described above are used for in-operation control, which involves inserting most of the total length into the reactor core during reactor operation to control the power distribution and reactivity of the reactor. , has a sufficiently large reactivity value during reactor shutdown, and has the function of maintaining the reactor sufficiently subcritical. If it has a large reactivity value during reactor shutdown,
It also has a large reactivity value during reactor operation, resulting in
During reactor operation, the neutron flux of the fuel material around the control rods decreases significantly.

(Problem to be solved by the invention) As mentioned above, if the neutron flux in the fuel area around the control rods decreases significantly during reactor operation, the combustion of the fuel will be delayed compared to the fuel area away from the control rods. become. The conclusion of Song Dynasty, fJI
In the fuel part around the till rod, the concentration of residual fissile material is relatively high compared to other parts. For this reason, when the control rod is withdrawn, a large output peaking occurs in the fuel section around the control rod, which is disadvantageous in terms of the health of the fuel. This phenomenon is called "control rod history" or "blade history," and is one of the major limiting conditions for nuclear reactor operation.

This invention was made in consideration of the above-mentioned circumstances, and has a sufficiently large reactivity value during reactor shutdown to ensure subcriticality of the reactor, and a reactivity value that is maintained during reactor operation. An object of the present invention is to provide a control rod for a nuclear reactor that can reduce the fuel blade history development.

[Structure of the invention]

(Means for Solving the Problems) In the present invention, a plurality of wings are integrally connected using a tip structure material and a terminal structure material, and a plate-shaped neutron absorbing material is arranged facing each other with a gap between each wing. In the control rod for a nuclear reactor, at least a part of the neutron absorbing material is composed of a long-life neutron absorbing material, and this long-life neutron absorbing material has the ability to absorb It is characterized by having minute ventilation holes that are not large enough to sufficiently discharge air bubbles.

(Function) Therefore, according to the control rod for a nuclear reactor according to the present invention,
During reactor shutdown, the above-mentioned gap is filled with reactor water, and the reactivity value of the reactor control rods becomes sufficiently large.

On the other hand, if a reactor control rod is inserted deeply or shallowly into the reactor core during reactor operation, the long-life neutron absorber generates heat by absorbing neutrons and gamma rays, and this heat generates air bubbles in the gap. do. Since these bubbles cannot be sufficiently discharged from the microvents, a predetermined range of the gap is filled with bubbles, and most of the reactor water within the gap is removed. As a result, the reactivity value of the reactor control rod decreases within this predetermined range, and it is possible to suppress an excessive drop in neutron flux in the fuel section around this reactor control rod, and when withdrawing this reactor control rod. The blade history phenomenon can be alleviated and avoided.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1(A) shows the IA- of FIGS. 1(B) and (C) in the wing of the first embodiment of the nuclear reactor control rod according to the present invention.
A vertical cross-sectional view taken along line IA, and FIGS. 1(B) and (C) are cross-sectional views taken along line IB-IB and IC-IC in FIG. 1(A), respectively. In this first embodiment, the same parts as those in the conventional example shown in FIGS. 7 and 8 are given the same reference numerals, and a description thereof will be omitted.

Each neutron absorption plate 8b is composed of a hafnium metal plate or a hafnium alloy (an alloy of hafnium and zirconium (Zr) or an alloy of hafnium and titanium (T)). These neutron absorption plates 8b are arranged on the insertion tip side, that is, on the side of the tip structure 3, and are formed with thick walls to ensure a long life of the reactor rod and an improvement in the reactivity value. be done.

In the effective part of the control rod where the neutron absorption element 8a is arranged, a partition 12 is provided from the insertion end to about 1/4 length of the effective part.
will be installed. This partition 12 is fixed to a half area of five ties on the neutron absorbing plate 8b. Further, the partition 12 is made of hafnium or a hafnium alloy, and has a U-shaped cross section. Therefore, this partition 12 forms a substantially box-shaped space 13 on the tie rod 5 side of the insertion tip of the control rod effective section.

A micro ventilation hole 14 is formed in the upper part of the neutron absorption plate 8b corresponding to this space 13. A large number of water holes 15 are formed in the neutron absorption plate 8b at positions corresponding to the water holes 11.

This water hole 15 is connected to a neutron absorption plate 8 corresponding to the space 13.
It is also formed at the bottom of b. These water passage holes 15 have an extremely large opening area compared to the micro ventilation holes 14, and are provided so that reactor water can easily flow in and out of the gap 10 from the outside of the neutron absorption plate 8b. On the other hand, the micro ventilation hole 14 is
Bubbles generated in the space 13 during reactor operation are formed to a size that cannot be sufficiently removed.

Next, the functions of these spaces 13 and micro ventilation holes 14 will be explained.

A case will be described in which the space 13 forming portion of the reactor control rod is inserted into the core of the reactor during high power operation of the reactor.

Since the neutron absorption plate 8b and the partition 12 absorb neutrons and gamma rays and generate heat, the reactor water in the gap 10 and the space 13 is heated and bubbles are actively generated. Among these, the air bubbles generated in the space 13 cannot be sufficiently discharged due to the small opening area of the micro ventilation hole 14, so the space 13 will eventually be filled with air bubbles. When the space 13 is filled with bubbles, the neutron moderating effect in the space 13 is reduced, and neutron absorption is almost eliminated, so the reactivity value of the portion of the reactor control rod corresponding to the space 13 is reduced. As a result,
The neutron flux does not drop excessively in the fuel section surrounding the reactor control rods, and therefore the blade history phenomenon is alleviated even if the reactor is operated at high output with the reactor control rods in the reactor core. be able to.

Generally, in a nuclear reactor control rod surrounded by four fuel assemblies of a boiling water reactor, the neutron flux tends to particularly decrease near the tie rod. Therefore, by installing a partition 12 on the tie rod side of the neutron absorption plate 8b to form a space 13, the reactivity value of the portion on the tie rod 5 side at the insertion end of the reactor control rod decreases during reactor operation. However, since a decrease in neutron flux can be suppressed, blade history can be effectively alleviated.

On the other hand, when the nuclear reactor is shut down, the neutron flux level and gamma ray level are significantly lower than when the reactor is operating, so the neutron absorption plate 8b and the partition 12 only slightly generate heat due to delayed gamma rays. Therefore, no air bubbles are generated within the gap 10 and the space 13. In particular, space 13
Inside, the remaining air bubbles are discharged from the micro ventilation holes 14, and water also flows slowly within the space 13. Therefore, the space 13 is filled with water, and the water in the space 13 and the gap 10 allows the neutron absorption plate 8b and the partition 12 to absorb neutrons from the gap 10 and the space 13 side as well, increasing the reactivity value. improves.

As a result, subcriticality of the reactor can be ensured during reactor shutdown.

Here, the relationship between the reactivity value and the bubble filling rate in the space 13 is shown in FIG.

Generally, in an IJ Ill rod for a boiling water reactor, the thickness of the wing 7 is set within 10 m due to its structure.

Therefore, within this range, the relative value of the reactivity value (Δρ
/ρ) decreases linearly. In addition, ρ is the reactivity value,
Δρ indicates the amount of change in reactivity value due to a decrease in the density of hydrogen atoms.

Furthermore, as shown in Figure 3 (A), the reactivity value in the axial direction of the reactor control rods in a boiling water reactor is large when the insertion end of the effective part of the ail J control rod is do(
It is necessary to reduce blade history by ensuring subcriticality in the upper part of the reactor core (broken line) and by making the effective control rod parts uniform in the axial direction during reactor operation (solid line).

According to the first embodiment, υ on the insertion end side of the control rod effective section
At approximately 174 of the 111l rod effective section, the reactivity value becomes large when the reactor is shut down (dashed line in Figure 3 (B)), and the reactivity value decreases during reactor operation (Figure 3 (8)).
solid line). As a result, during reactor operation, the neutron flux in the fuel section around the reactor control rods is not excessively reduced, and the blade history can be alleviated. Additionally, during reactor shutdown, the reactivity value of reactor control rods increases,
Subcriticality of the reactor can be ensured.

In addition to the above effects, the first embodiment also has the following effects.

In other words, since the neutron absorption plate 8b and the partition 12 are made of hafnium or a hafnium alloy, the life of the nuclear reactor control rod can be extended. In addition, the neutron absorption plates 8b are plate-shaped, and they are arranged facing each other with a gap 10 between them, so that reactor water is guided into the gap 10, so that light solidification can be achieved while preventing a decrease in reactivity value. the result,
Conventional existing control rod drive mechanisms can be used. Figure 4 (
A) is a front view showing a second embodiment of the control rod for a nuclear reactor according to the present invention, and FIG. 4(B). (C) is IV of Figure 4 (A)
FIG. 4 is a cross-sectional view taken along the line B-IVB and the line ■C-IVC in FIG. 4(B).

In this reactor control rod, the tip structure member 2 has a cross-shaped cross section.
1 and the corresponding ends of the terminal structural member 22 are joined by two elongated neutron absorption plates 23 to form each wing 2.
4 is composed. These two neutron absorption plates 23 are arranged facing each other. Therefore, these neutron absorption plates 23 form a gap 25 extending in the longitudinal direction. Closing members 26 and 27 having the same length as the neutron absorption plate 23 are fixed to both side edges of each wing 24, respectively.

The neutron absorbing plate 23 and the blocking material 26,27 are made of hafnium or a hafnium alloy. Among these, the closing material 26 has a large cross-sectional area and is provided so as to be able to cope with a large amount of neutron irradiation.

Further, the tip structure material 21 is made of a zirconium material containing some hafnium, and the neutron absorption plate 23 is joined to this tip structure material 21 by welding.

Furthermore, a plurality of coupling members 28 are arranged in the longitudinal direction on the central side of the nuclear reactor control rod. This coupling member 28 fixes the wings to each other on the central side of the control rod. Therefore, between each coupling member 28 there is a water flow path 2.
It is considered to be 9. The reactor water in the flow path 29 also decelerates neutrons in the center of the reactor control rod to generate thermal neutrons, thereby alleviating the blade history phenomenon.

In addition, a large number of water holes 31 are opened in the neutron absorption plate 23 constituting each wing 24, except for a portion (the insertion end side portion) of about 1/3 to 1/4 of the total length of the control rod effective section 30. Ru.

This water passage hole 31 has a diameter of approximately 10M, and is used to allow reactor water to flow in and out of the gap 25. In addition, the neutron absorption plate 23
At the insertion end side where the water passage hole 31 is not formed, a minute ventilation hole 32 is bored at the top thereof. The micro vent hole 32 is set to a size that does not allow sufficient removal of air bubbles generated within the insertion tip side gap 25 during reactor operation.

Therefore, when this reactor control rod is inserted into the reactor core during reactor operation, bubbles are generated within the interval aI25. Among these, the gap 25 on the insertion end side is filled with air bubbles because most of the generated air bubbles are not discharged from the micro ventilation holes 32. Therefore, the reactivity value at the control rod insertion tip decreases, and blade history can be avoided.

On the other hand, other parts than the ta side where the reactor control rods are inserted are always filled with reactor water because reactor water and generated air bubbles flow in and out through relatively large water holes. Therefore, the reactivity value does not decrease in this part.

On the other hand, during reactor shutdown, the amount of bubbles generated within the gap 25 is extremely small, so the entire area of the gap 25 becomes reactor water, and the reactivity value of the iI11m rod for the nuclear reactor can be sufficiently increased.

For these reasons, the second embodiment also provides the same effects as the first embodiment.

FIG. 5 is a sectional view showing a modification of the first embodiment.

In this modification, the same parts as in the first embodiment are given the same reference numerals. In this modification, the neutron absorption plate 8b is suspended from the tip structure member 31.

FIG. 6 shows a modification of the second embodiment. In this modification, the same parts as in the second embodiment are given the same reference numerals.

In this modification, about 172 to 1/4 of the total length of the effective part 30 from the insertion tip side is left in the tIII III rod effective part 30, and the rest is made into a high reactivity type neutron absorber 41. This high-reactivity neutron absorber 41 is constructed by filling boron carbide 42 inside a plate-shaped long-life neutron absorbing plate (hafnium and zirconium alloy). Also in this modification, since the minute ventilation holes 32 are formed in the neutron absorption plate 23, the gap 25 is filled with bubbles during reactor operation, and the reactivity value is reduced. Furthermore, since air bubbles escape from the micro vent holes 32 during reactor shutdown, the gap 25 is filled with reactor water, increasing the reactivity value.

In addition, in this modification, the tip structure material 24 is made of zirconium, but since hafnium and zirconium have the property of forming a solid solution alloy, the neutron absorption plate 23 and this tip structure material are welded. It can be fixed by

Note that the wing 24 having the configuration shown in FIG. 6 may be covered with a sheath as it is to form a wing equipped with a sheath. Also,
In each of the embodiments and modifications described above, the nuclear reactor control rods are cross-shaped, but the present invention can also be applied to cluster-type nuclear reactor control rods.

〔Effect of the invention〕

As described above, according to the control rod for a nuclear reactor according to the present invention, at least a part of the neutron absorbers arranged facing each other with a gap formed therein is composed of a long-life neutron absorber, and the long-life neutron absorber Because micro-vents were drilled in the material that were too large to sufficiently eliminate air bubbles generated within the above-mentioned gaps during reactor operation, the material had a sufficiently large reactivity value during reactor shutdown. The subcriticality of the reactor can be ensured, and during reactor operation, the reactivity value can be reduced and the blade history phenomenon of the fuel can be alleviated.

[Brief explanation of drawings]

FIG. 1(A) shows the IA- of FIGS. 1(B) and (C) in the wing of the first embodiment of the nuclear reactor control rod according to the present invention.
Longitudinal cross-sectional view along line IA, FIG. 1(B). (C) is a cross-sectional view taken along the IB-IB line and IC-IC line in Figure 1 (A), and Figure 2 shows the relationship between the reactivity value and the bubble filling rate in the space in the first example. The graphs shown in FIG. 3 (A> and (B) are graphs showing the required reactivity value and the actual reactivity value in the axial direction of the control rod effective section, respectively, and FIG. 4 (A) is a graph according to the present invention. A front view showing the second embodiment of the control rod for a nuclear reactor, FIGS. 4(B) and (C) are similar to FIG. 4(A)
FIG. 5 is a sectional view taken along the rVB-IVB line in FIG. 4B and IVC-IVC line in FIG. FIG. 7 is a perspective view showing a conventional nuclear reactor control rod, and FIG. 8 is a cross-sectional view taken along the line ■--■ in FIG. 7. DESCRIPTION OF SYMBOLS 1... End structure material, 3... Tip structure material, 7... Wing, 8... Long-life neutron absorption material, 8a... Neutron absorption element, 8b... Neutron absorption plate, 10 ...Gap, 12...Partition, 13...Space, 14...Minute ventilation hole. Applicant's agent: Hatano Kumonsho side 9 Dan (Kiriogi Dan) (C) Figure Figure Figure Figure Figure Figure Figure

Claims (1)

[Claims] In a control rod for a nuclear reactor, in which a plurality of wings are integrally connected using a tip structural material and a terminal structural material, and a plate-shaped neutron absorbing material is arranged facing each other with a gap between each wing, the neutron absorbing material is At least a portion of the material is made up of a long-life neutron absorber, and this long-life neutron absorber has minute vent holes that are too large to sufficiently exhaust air bubbles generated within the above-mentioned gap during reactor operation. A nuclear reactor control rod characterized by: