JPS62187284A - 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 in particular, 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. Control 211 rod hybrid M4 construction l3II.

[Technical background of the invention and its problems]

A control rod used in a boiling water reactor, etc. is constructed as shown in FIGS. 4 and 5, with a tie rod 1 having a cross-shaped cross section, and a tip structure member 2 J3 and a terminal structure member attached to the tip and end of the tie rod 1. When 3 and 6 are connected to each other, 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. Neutron absorption rod 6
In this case, a neutron-absorbing substance such as boron carbide (B4C'') is filled into the metal clad tube.

When a nuclear reactor control rod is inserted into a reactor core and is irradiated with neutrons, the neutron-absorbing material inside the neutron-absorbing rod absorbs the neutrons and undergoes wear due to combustion, etc. Gas such as helium gas ('He), which is a substance, is generated. Therefore, the neutron absorption capacity of the control rod decreases as the neutron irradiation period 11'5 passes, and the gas pressure within the metal cladding tube increases.

The neutron irradiation time 11i 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 11' life.

By the way, when focusing on a single control rod, there are many long rods housed within the control rod! Neutron absorption (not all objects receive neutron irradiation equally). For example, when a control rod is partially inserted into the core of a nuclear reactor, the side edge J3 and the tip of each wing receive particularly strong neutron radiation DJ.
The deterioration of the neutron absorption capacity of this part is disturbing.

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 8Il) of the neutron absorption rod or the wing side edges are The neutron-absorbing rods lose their neutron-absorbing ability before the neutron-absorbing rods, and the neutron-absorbing rods on the side edges of the wings lose their lifespan 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 atomic 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, B4C powder is used as a control rod for a nuclear reactor, the bottom of the powder becomes clogged during use, and a void where no powder exists near the upper end of the rod. Occur. Generally, in a conventional neutron absorption rod filled with B4C powder, the tip of the SUS metal clad tube is closed with an SUS plug, and a few threads of ridged wool are inserted into the metal clad tube adjacent to the plug. I am wearing it.

Furthermore, since the iron wool and the plug have a considerably 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 iron C cool.

Figure 6 (△) shows a long-life medium bamboo absorber (hafnium plate or hafnium rod) 7 and a conventional B
, and a long neutron absorbing rod 8 filled with C, the boundaries between the two are aligned in a straight line through the gap 1, and the top of the neutron absorbing rod 8 is formed by the presence of the plug 9a and the iron wool 9b. An example is shown in which the control rod is a non-absorbing material for neutrons, and the neutron flux distribution of the reactor control rod in this case is estimated from the critical experiment data as shown by the solid line in FIG. 6(B).

Broken FJB shows the neutron distribution curve when B4C or hafnium (Hf) is present, and dashed line C shows the neutron distribution curve when gap O does not exist. The code 9G indicates a void formed in the iron wool part, and the gap l
When the control rod is used in a nuclear reactor for a long period of time, the neutron absorbing materials 7 and 8 are exposed to neutron irradiation, which is a protection against the so-called irradiation growth.

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 difference between the non-absorbing material part and the B4C The neutron flux at the boundary is 1.5 to 2 times higher than in the case where there is no non-absorbing U 7Js D, and this increase in neutron flux is likely to occur only in the very vicinity of the boundary. confirmed.

Then, boron-1 was added to the 12II rod used in such a nuclear reactor.
When 0 (10B) is irradiated with a large amount of neutrons until it is significantly depleted, B4C in the area adjacent to the non-absorbing material part is locally irradiated with 1.5 to 2-8 neutrons, and this neutron 4 1 is a nuclear reaction product upon irradiation.

t-Ie, LIW are generated, and B4C powder grains (
Swelling occurs due to the expansion of J:. Therefore, due to the expansion of B and C in a limited area near the boundary of the non-absorbing material part, the metal cladding tube 88 is subject to local stress and may bulge and break. .

In the critical experiment, the length of the non-absorbing material portion of the neutron absorption rod 8 was varied between 1 cm and 5α, and the neutron flux distribution on the surface of the control rod was measured. The size of the neutron flux at the center of the non-absorbing material changes depending on the length of the non-absorbing material, but the neutron flux that falls at the boundary between the non-absorbing material and B4C is The length of the absorbent portion is 1°5 cm or more, and the length is 1.5 to 2 times that of the case where the non-absorbent portion is not present. Furthermore, it was confirmed that this neutron flux surge occurs only in the IZ 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 receives 5 to 2 times more neutron irradiation, and this neutron irradiation produces nuclear reaction products 'l]e! , Ll, etc. occur, and B4
C Swelling of powder grains or pellets occurs. Therefore, B in a limited area near the boundary with the non-absorbent part
Due to the expansion of the metal cladding tube 4C, the metal cladding tube 8a may swell due to local stress and may be damaged.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned circumstances, and involves locally increasing the neutron flux based on the gap by bringing a long-life neutron absorbing material made of short, lightweight fiber into contact with the top of a long neutron absorbing material. It is an object of the present invention to provide a control rod for a nuclear reactor, which suppresses the rise of neutrons, improves the soundness and reliability of a long neutron absorber, and makes it possible to prevent Nagano whitening of the control rod.

[Summary of the invention]

The control rod for a nuclear reactor according to the present invention has a U-shaped cross-section sheath attached to each protruding leg of a 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 tip structure material is attached to the insertion end of the tie rod. Atoms in which a short long-life neutron absorbing material adjacent to the tip structural material and a long neutron absorbing material adjacent to this neutron absorbing material are arranged in parallel in the axial direction within the sheath. In a reactor control rod, the short long-life neutron absorbing material is divided in the axial direction of the control rod, and the long-life neutron absorbing material at the end of the division is made short and lightweight to absorb the long neutrons. It is characterized by being placed in contact with the material.

[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. In the figure, the left half shows the experimentally determined neutron flux distribution on the control rod surface using iso-zero lines. From this neutron flux distribution map, it can be determined at which position on the control rod 10 the neutron absorbing material is high. It's a monkey. The control rod 10 has a tie rod 11 having a cross-shaped cross section, 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 is provided with guide rollers 14 that guide insertion of the reactor control rod 10.

fJ number 15 is a handle 15 for operating the control rod 10.

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

A flat internal space is formed within the sheath 16 of the wing 17. Long-life neutron absorbing materials 18a and 18b are divided in the axial direction of the wing 17 and arranged in the internal space adjacent to the tip IM material 12. This neutron absorbing material 18a
, 18b is hafnium (I-1f) or Hf'-Z
It is made of r-alloy or the like and is shaped like a rod or a plate. Hafnium is a metal material with a neutron absorption capacity of 1.5 mm, and has a lifespan 3 to 6 times that of 84C.

Further, the long-life neutron absorbers 18a and 18b are short neutron absorbing plates (which may be neutron absorbing rods) with a total length (length in the insertion direction) of about 5 to 30 cm, and the wing 17, VI) A plurality of long-life neutron absorption rods (neutron absorption plates) 18C each having an axial length of 1.5 m or more are arranged. These long-life neutron absorbers 18a to 18c are disposed at the tip J3 and the blade tip of each wing 17, which are exposed to strong neutron irradiation. Among these, the short neutron absorption plate 18a is arranged closely to the tip structure member 12, and the tie "1"
It is engaged with the tip projection of the tube 11. On the other hand, a long neutron absorption rod 18C is disposed near the tip of each wing 17 and at the outer end of the sheath 16 as necessary.

The long-life neutron absorber 18b disposed on the distal end side of the long-life neutron absorber 18a at the tip is t + 1 in the insertion direction.
It is considered to be a short and light tH object of about 3 cm.

A long neutron absorbing rod 19 is disposed in contact with 1 lAi on the pulling side of the neutron absorbing material 18b. Neutron absorption rod 19
A plurality of these are closely arranged in the width direction of the wing 17,
As shown in FIG. 2, the metal cladding tube 20 is filled with a neutron absorbing material 21 such as boron carbide (B4C) powder or a pellet cap. A metal wool 22 such as iron wool is interposed at the tip of the neutron absorption rod 19, and a plug 2 is inserted at the tip.
3. It is hermetically sealed. This metal wool 22J3
The plug 23 has significantly inferior neutron absorption ability compared to the neutron absorbing material, and a neutron non-absorbing material portion D1 is formed.

On the other hand, between the long-life neutron absorbing material 18a at the tip and the next short neutron absorbing material 18b, each neutron absorption u'+aa accompanying neutron irradiation in the reactor core is present.

Gap 25 for absorbing irradiation particles 18b and 19
is formed, and in this gap 25, hafnium (Hf)
A neutron absorbing metal wool 24 such as wool is inserted.

By inserting the metal wool 24, the rise of the neutron flux due to the gap 25 is suppressed, while the rapid insertion of the control rod
During extraction, the displacement movement of the short neutron absorber U18b is suppressed.

Since metal wool such as Hf' 1 Cool has a low density packing as a whole, each metal wool is crushed and narrowed during neutron irradiation growth of the neutron absorber.

In addition, as the metal wool filled in the gap 25, 11 f
Instead of wool, it is possible to use something like an SO3 pipe, and when this SO3 pipe or the like is inserted, a non-absorbing material portion D2 is formed in this part. However, the length and width of the gap 25 in the insertion direction are approximately several meters, and in the case of this length, the increase in neutron flux due to the non-absorbing material portion D2 is small, but the neutron absorption A long-life neutron absorbing material 18b is placed between the tip of the rod 19 and the non-absorbing material portion D1.
is interposed, so that [34C of the long neutron absorption rod 19
At the top, the rise in the neutron flux in the gap 25 is certainly negligible, and has a neutron distribution curve shown by the solid line C1 in FIG. 3(B). The symbols Δ and B are the neutron distribution curves A33 and σB shown in FIG. 6 by solid lines and broken lines, respectively.

By the way, the long-life type short neutron absorbing material 18a at the tip usually has an insertion direction of 10 cm or more, and is considerably heavier than the short neutron absorbing material 18b adjacent to the neutron absorbing material 18 Fl with a gap 25 therebetween. . For this reason,
The neutron absorbing material 18a at the tip engages with the tip protrusion 11a of the tie rod 11 or the tip structural member 12 and is fixed so that no shock is applied to the long neutron absorbing rod 19 due to sudden withdrawal of the control rod.

Furthermore, since the long-life neutron absorbing material 18b is short, light and heavy, there is a risk of shock to the top of the long neutron absorbing rod 19 even if the control rod is suddenly inserted or there is a movement change in the intake port or Y. do not have. Therefore, there is no need to actively fix the short neutron absorbing material 18b within the wing 17, and
It can be brought into contact with the top of the neutron absorption rod 19 of the length. Therefore, the non-absorbing material portion D1 at the top of the neutron absorbing rod 19
The neutron flux force a curve C1 is J of the conventional neutron distribution curve Δ
: The sea urchin doesn't get excited and has a subdued shape.

As a result, the increase in neutron flux at the end portions of the neutron absorbing material 21 is suppressed so as to increase from e to fF, and local neutron irradiation ifl at the end portions is suppressed. Therefore, local swelling of B4C at the end of the neutron absorbing material 21 is suppressed, and the generation of local stress on the metal clad tube 20 is suppressed. Therefore, the durability of the elongated neutron absorption rod 19 is improved, and a long life can be achieved.

Next, the effect will be explained.

When the long-life neutron absorbing materials 18a to 18C and the elongated neutron absorbing material 19 are combined and the '/ζ hybrid reactor control rod 10 is inserted into the core of the reactor, the control rod 10 will not be irradiated with neutrons. receive. According to experiments, the two-dimensional distribution of neutron flux on the surface of a nuclear reactor control rod subjected to neutron irradiation is
It is represented by a contour diagram showing relative values in the left half of the figure. From this contour map, it is understood that the reactor control rod 10 receives particularly strong neutron radiation at the tips and wing tips of each wing 17. However, in this case, the reactor control rod 10 is provided with long-life bamboo shoot absorbing material 18 at the tips and blade tips of each wing 17, which are exposed to strong neutron irradiation, so that the neutron absorption capacity can be made almost uniform during the neutron irradiation time. , the length of the control rod can be improved.

In general, if the interface between the long-life neutron absorber and the long neutron absorber is straight rather than diagonal, the sixth
A bulge in the neutron flux as shown by the solid line A in Figure (B) occurs, and the fission reaction of boron-10 proceeds in a very limited area of B4C adjacent to the neutron non-absorbing material part, and as a result,
B4C causes swelling and locally bulges the metal cladding tube 8a, which may cause damage. However, in this embodiment, the long-life neutron absorbing material 18b contacts the long neutron absorbing rods 19, and each neutron absorbing rod 19
The gap O shown in FIG. 6 is not formed because it is housed so that it can be moved and displaced in accordance with the growth of neutron irradiation. As a result, in the neutron flux distribution curve 01, a large increase in the neutron flux as indicated by the symbol A is suppressed. Therefore, the bulge of the neutron flux at the top of the B4C filled in the long neutron absorption rod 19 is suppressed as shown by f, and the B
The amount of neutron irradiation to the top of 4C is reduced. therefore,
Local swelling of B4C is suppressed, local stress generation in the metal clad tube 20 is alleviated, and the metal clad '? '!
20's maneuverability is improved, and the life of the control rods is increased.

〔Effect of the invention〕

As described above, in the nuclear reactor control rod according to the present invention, the short long-life neutron absorber is divided in the axial direction of the control rod, and the long-life neutron absorber on the divided end side is Since it is placed as a short and lightweight object in contact with the long neutron absorbing material, it is formed between the long neutron absorbing material and the long-life neutron absorbing material to absorb changes in quality due to irradiation growth. The gap can be removed, and as a result, the swelling of the neutron absorbing substance filled in the long neutron absorbing material can be effectively suppressed, and the possibility of damage to the cladding tube due to As caused by this swelling can be reduced and avoided. Therefore, the performance and reliability of long neutron absorbing materials can be improved.
It is possible to reliably extend the life of the restraining rod 11.

[Brief explanation of drawings]

FIG. 1 is a partial longitudinal sectional view showing an embodiment of a nuclear reactor control rod according to the present invention, and FIG. 2 shows a long neutron absorption rod and a long life that are incorporated into the wing of the nuclear reactor control rod. Figure 3 is a partial view (not shown in an enlarged manner) of the arrangement relationship with the type neutron absorber (
A> and (B) respectively show the arrangement relationship of each neutron absorbing material and the relationship of neutron flux distribution in the nuclear reactor control rod according to the present invention. Figure 5 is a cross-sectional view along the v-v line in Figure 4, and Figures (A) and (B) are each neutron absorption diagram incorporated into a conventional control rod for a nuclear reactor. Material placement relationship J3
, and neutron flux distribution, respectively. 10... Nuclear reactor control rod, 11... Tie rod, 1
2... Tip structure material, 16... Sheath, 17... Wing, 18a, 18b, 18c... Long 17Q type neutron absorption material, 19... Long neutron absorption rod, 19a...
19f...neutron absorption rod, 20...metal clad tube, 2
1... Neutron absorbing substance, 22... Metal wool, 23
... Plug, Dl, D2... Non-absorbing material part. Applicant's agent Hisatsuri Hatano 1 Figure 2 Figure 11- CB> Name 3 Figure 4 I21 Certain 5 Figure 511 CB) Figure 6

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 short long-life neutron absorbing material is divided in the axial direction of the control rod, and the long-life neutron absorbing material at the end of the division is made short and lightweight and corresponds to the long neutron absorbing material. A control rod for a nuclear reactor characterized by being arranged in contact with each other. 2. The long-life neutron absorber is divided into two parts with a small gap in the axial direction of the control rod, and the long-life neutron absorber at the tip of the divided part is engaged with the tie rod and the tip structure member. The control rod for a nuclear reactor according to item 1. 3. The control rod for a nuclear reactor according to claim 1, wherein the minute gap has a width of about several mm in order to absorb the neutron irradiation growth length of the long neutron absorbing material. 4. The control rod for a nuclear reactor according to claim 1, wherein a metal wool such as hafnium wool is interposed in the minute gap. 5. The control rod for a nuclear reactor according to claim 1, wherein the long-life neutron absorber on the divided end side has a length of about 1 to 3 cm in the insertion direction.