JPS61194391A - 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 hybridizes a neutron absorbing material to achieve a long life. This invention relates to control rods for nuclear reactors that are designed to improve

[Technical background of the invention and its problems]

In the control rod used in a nuclear reactor, four stainless steel wings are joined together via a joint, and boron carbide (84C) is inserted into a large number of accommodation holes formed in the width direction of the wing. A powder-filled version has been developed.

When this nuclear reactor control rod is used in a thermal neutron reactor such as a boiling water reactor and inserted into the reactor core, the control rod is irradiated with neutrons. At this time, the amount of neutron irradiation is not uniform over the entire surface of each wing of the control rod, and the tip of each wing and the tip of the wing receive strong neutron irradiation. For this reason, the 84C powder filled in the wing tip and blade tip deteriorates more quickly than other parts, and its neutron absorption capacity decreases, reaching the end of its nuclear lifetime. Therefore, the control rods had to be disposed of before the remaining B4C powder, which was present in large quantities, reached its nuclear lifetime.

From this point of view, the present applicant proposed a control rod for a nuclear reactor in which the tip and tip portions of the wings, which are exposed to strong neutron irradiation, are filled with a long-life neutron absorbing material such as hafnium (Japanese Patent Application No. 17355/1982). reference). Hafnium is a metal material with excellent neutron absorption ability, has a lifespan 3 to 6 times that of boron carbide, and does not generate He gas or the like even when irradiated with neutrons. In this way, the life of the part that receives strong neutron irradiation is extended, so it is possible to extend the life of the control rod.

By the way, in B4C powder, which is a normal neutron absorbing material, boron-10 ("B) reacts with neutrons to form Li-7 and He.
-4 is generated. The generated helium gas gradually accumulates as the neutron irradiation time passes, and as the helium gas accumulates, the B4C powder causes swelling and expands each accommodation hole in the wing. Further, since a part of the helium gas is released from the B4C powder, gas pressure is generated inside the accommodation hole, which acts in a direction to expand the accommodation hole. Since the accommodation holes are connected to each other via the communication hole formed on the outer end side of the wing, the gas pressure in only some of the accommodation holes does not increase abnormally.

However, the swelling phenomenon of B4C powder is noticeable in a limited area that is exposed to strong neutron irradiation, and the amount of swelling in that area becomes large. In addition, in the control rods for nuclear reactors currently in use, the thickness of the stainless steel material between each accommodation hole and the thickness of the stainless steel material between the accommodation hole and the outer surface are thin, for example, 1.
It is designed to have a thickness of about M. Furthermore, each receiving hole formed in the wing may be partially thinner due to tolerances in the drilling operation.

When the stainless steel that makes up each wing of a nuclear reactor control rod is thinned at the same time as each accommodation hole, at the end of the control rod's life, due to the local expansion effect caused by the swelling of B4C, the walls between each accommodation hole and the accommodation hole become thinner. There is a risk of cracks forming between the surface and the surface. In addition, while stainless steel itself becomes brittle when exposed to large amounts of neutron irradiation, the hardness of 84C grains is greater than that of stainless steel, so when some stress is generated due to the swelling phenomenon of B4C powder grains, the wings may break.
There was a risk of mechanical damage.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned points, and aims to extend the life of B4 by making all the neutron absorbing materials filled in each wing reach the end of their life at almost the same time.
The object of the present invention is to provide a long-life nuclear reactor control rod that can maintain sufficient mechanical strength even when subjected to weakening effects due to local swelling of C powder or localized strong neutron irradiation.

[Summary of the Invention] In order to achieve the above-mentioned object, the control rod for a nuclear reactor according to the present invention integrally connects the inner ends of a plurality of rectangular wings to each other via a connecting portion, and also provides a control rod for a nuclear reactor according to the present invention. In a control rod for a nuclear reactor, in which accommodation holes bored in the wing are arranged in a plurality of rows in the longitudinal direction of the wing, and the accommodation holes are filled with a neutron absorbing material, the control rod is located at the tip of the wing in the insertion direction. A long-life neutron absorbing region is formed by filling the plurality of accommodation holes and the vicinity of the outer end of the wing with a long-life neutron absorbing material, and an intermediate neutron region is formed adjacent to this neutron absorbing region. Each accommodation hole arranged in the neutron region is characterized by having a tapered shape on the inner side of the wing.

[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.

A nuclear reactor control rod 10 according to the present invention is used in a thermal neutron reactor such as a boiling water reactor, and has a plurality of rectangular wings 11, preferably four rectangular wings 11. Each wing 11 is integrally connected at its inner end to a connecting member 12 with a cross-shaped connecting portion, essentially forming a control rod 10 having a cross-shaped cross section. An operating handle 13 is provided at the tip of the control rod 10, and the operating handle 13 is integrally or integrally connected to the tip of each wing 11.

Each wing 11 of the control rod 10 is made of a flat metal material such as stainless steel, and has a large number of accommodation holes 14a, 14b, and 14c extending in the width direction formed therein. Each accommodation hole 14 is arranged in a row in the longitudinal direction of the wing 11, and the number M
(e.g. 6 rm).

Each of the accommodation holes 14a.

14b and 14C communicate with each other through a communication groove 15 extending in the vertical direction. The communication groove 15 is formed near the outer end of the wing 11 so as to extend in the longitudinal direction thereof.

Thus, long-life neutron absorbing materials 16a, 16b such as hafnium are inserted into the plurality of accommodation holes 14a, 14b formed at the tip of the wing 11, and B4C powder is inserted into the remaining many accommodation holes 14b, 14C. Alternatively, the neutron absorbing material 17 made of pellets is filled. Also, Wing 11
In the communication groove 15 formed near the outer end of the wing, a long-life neutron absorbing material 16C such as hafnium is interposed at least 1/2 of the total length from the tip of the wing. In addition to hafnium, long-life neutron absorbers 16a to 16G include:
Hf-Zn alloy, Aa-1n-Cd alloy or Eu2O
3HfO2 sintered material, DV2O3 HfO7 sintered material, etc. are used.

In this way, the reactor control rod 10 is exposed to strong neutron irradiation at the tip of each wing 11 (the length from the tip is 11=5~
15cjI area) and near the wing tip (width J!2 = 1
．． Long-life neutron absorber 16a in the region of 0 to 1.5
~16c is filled to form a long-life neutron absorption region 18. The long-life neutron absorbing materials 168 to 16C are formed into a rond shape or a pellet shape corresponding to the shape of each accommodation hole 14a, 14b and communication groove 15.

Furthermore, among the accommodation holes for accommodating the long-life neutron absorption rods 16a and 16b, the plurality of accommodation holes 14a formed at the tip of the wing are located at the inner end of the wing 11, as shown in FIGS. 1 and 2. The length toward the wing 11 is shortened, and ends at the outer end side of the wing 11 from the adjacent accommodation hole 14t). That is, a solid portion in which the accommodation hole 14a does not exist is formed at the tip end of the wing 11 on its inner end side, thereby preventing the wing 11 from weakening against strong neutron irradiation. Since the reactivity effect is small on the central axis side of the control rod 10, that is, on the inner end side of the wing 11, the decrease in reactivity is small. In addition, by forming a solid part of the wing 11 on the control rod center axis side at the tip of the wing, the neutron absorption effect is reduced, and as a result, this part is used to output power from the control rod at the corner part of the adjacent fuel assembly. The excessive decline in
The output impact at the corner portion due to movement of the control rod is reduced.

Furthermore, the plurality of accommodation holes 14b for accommodating the remaining long-life neutron absorption rods 16b are configured such that their tips are tapered toward the inner end of the wing 11, as shown in FIG. By tapering the tip of the accommodation hole 14b, the wall thickness of the wing 11 is increased and its mechanical strength is improved.

A control rod 10 is provided adjacent to the long-life neutron absorption region 18.
An intermediate neutron absorption region 19 is formed above the neutron absorbing region 19 . This intermediate neutron absorption region 19 has a length j of about 15 cIR to 50 cIR! It has 4. The plurality of accommodation holes 14b formed in the intermediate neutron absorption region 19 are formed in a tapered shape toward the inner end of the wing, as shown in FIG. 4, to improve the mechanical strength of the inner end of the wing 11. Each accommodation hole 1 above
4b is filled with boron carbide (B C) powder grains as a neutron absorbing material having different particle sizes to improve the packing density of the 84C powder grains. The open end of the filled 84C powder end is closed with the long-life neutron absorbing material 16C housed in the communication groove 15. At that time, each accommodation hole 14b, 14C
are communicated through the communication hole 2O, and the pressure is equalized.

Further, most of the accommodation holes 14C adjacent to the intermediate neutron absorption region 19 on the wing end side are configured in a straight hole shape as shown in FIG. Each accommodation hole 14C is filled with B4C powder particles 17 having different particle sizes as a neutron absorbing material. The accommodation holes 14G in this area only need to be formed with consideration to machinability, and there is no need for complicated machining such that the hole diameters are different. That is, the control rod 10 has a certain degree of pressure, for example, 30 cI, from the tip.
When separated by about R, the amount of neutron irradiation also decreases, and it is not necessarily necessary to make each accommodation hole 14G a small hole diameter. Since the amount of neutron irradiation is reduced, the amount of swelling of the B4C powder grains due to neutron irradiation is also small, and the expansion stress acting on the inner edge of each wing 11 is small, so the problem of wing breakage due to expansion of the B4C powder grains does not need to be considered. Good too.

Next, the function of the nuclear reactor control rod will be explained.

When manufacturing a control rod 10 for a nuclear reactor, the inner ends of four wings 11 each having a large number of accommodation holes 14a, 14b, and 14c formed in a row are joined together via a joining member 12, and then A structure. After integrating each wing 11, a large number of accommodation holes 14a, 1 formed in each wing 11
4b and 14C are respectively filled with a neutron absorbing substance consisting of long-life neutron absorbing materials 16a and 16b and B4C powder particles 17.

After each of the accommodation holes 14a, 14b, and 14c is filled with a neutron absorbing material, a long-life neutron absorbing material 16c is filled into the communication W415 extending in the vertical direction. After this filling, the outer end side of each wing 11 is caulked so as to be wrapped inward, and the outer end is shielded by welding or the like, thereby constructing the nuclear reactor control rod 10.

In this nuclear reactor control rod 10, the tips and outer ends of each wing 11, which are exposed to intense neutron irradiation, are configured as long-life neutron absorbing regions 18, and long-life neutron absorbing materials 16
Since the regions a, 16b, and 16c are loaded, even if it receives a large amount of neutron irradiation, its lifespan can be maintained at least equal to that of other regions. In this way, by arranging the long-life neutron absorbers 16a to 16C in the parts that receive strong neutron irradiation, the life of each region of the control rod 10 can be averaged and the life of the control rod 10 can be extended as a whole. can.

Furthermore, this reactor control rod 10 does not require tie rods, and when inserted into the reactor core, reactor water is present in the area on the central axis side (length 11 and width 13) of the control rod 10. Therefore, the amount of neutron irradiation is high, but since that part is constructed with a solid structure or a thick structure, the mechanical strength is improved and it is possible to effectively cope with weakening of the wing 11 due to strong neutron irradiation. can.

In addition, the inner end of the wing of each accommodation hole 14b of the intermediate neutron absorption region 19, which is subjected to relatively strong neutron irradiation, is configured in a tapered shape, so the wing 11 in that part has a thick structure and its mechanical strength is reduced. improves. Therefore, even if the B4C powder particles accommodated in each accommodation hole 14b undergo relatively strong neutron irradiation and swell, their mechanical strength can be effectively maintained.

In addition, in one embodiment of the present invention, the hole shapes of the accommodation holes formed in each wing of the nuclear reactor control rod have been described as shown in FIGS. 2 to 5. but not limited to. For example, each accommodation hole 218.21b formed in the intermediate neutron absorption region 19 is as shown in FIG.
The hole shapes shown in (B) and (C) may also be used. At that time, as shown in FIGS. 6(B) and (C), the accommodation hole 21
Pellet-shaped long-life neutron absorbing materials 22a and 22b may be filled at the tips of the tubes a and 21b.

〔Effect of the invention〕

As described above, the nuclear reactor control rod according to the present invention has a long life by filling a plurality of accommodation holes located at the tip of the wing in the insertion direction and near the outer end of the wing with a long-life neutron absorbing material. Since a type neutron absorption region is formed, a long-life neutron absorption material is placed in a portion that receives strong neutron irradiation, which averages out the life of each region of the control rod and extends the life of the control rod as a whole.

In addition, the multiple accommodation holes in the intermediate neutron absorption region adjacent to the long-life neutron absorption region are configured in a tapered shape toward the inner end of the wing, and the wing in that part has a thick structure, making it relatively strong. Even if B4C undergoes swelling due to neutron irradiation, sufficient mechanical strength can be maintained, and wing brittleness can be effectively prevented.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a nuclear reactor control rod according to the present invention, and FIG.
- A plan sectional view of the wing cut along line A, Figure 3 is a plane sectional view taken along line B-B in Figure 1, and Figure 4 is a plane sectional view taken along line C in Figure 1.
5 is a plan sectional view taken along the line D-D in FIG. FIG. 6 is a diagram illustrating a modification of each accommodation hole formed in the intermediate neutron absorption region of the wing. 10... Nuclear reactor control rod, 11... Wing, 14
a, 14b, 14c, 21a, 21b--Accommodation hole, 1
5-...Communication grooves, 16a, 16b, 16c, 22a. 22b... Long-life neutron absorbing material, 17... Neutron absorbing material (84C), 18... Long-life neutron absorbing region, 19... Intermediate neutron absorbing region. Figure 1 Figure 4 Figure 5

Claims (1)

[Claims] 1. The inner ends of a plurality of rectangular wings are integrally connected to each other via a connecting portion, and a housing hole formed in the width direction of the wing is formed in the longitudinal direction of the wing. In a nuclear reactor control rod which is arranged in multiple rows and whose accommodation holes are filled with neutron absorbing material, a long life is provided in the plurality of accommodation holes located at the tips of the wings in the insertion direction and near the outer ends of the wings. A long-life neutron absorption region is formed by filling a type neutron absorption material, and an intermediate neutron absorption region is formed adjacent to this neutron absorption region, and each accommodation hole arranged in this intermediate neutron absorption region is located at the inner edge of the wing. A nuclear reactor control rod characterized by having a tapered side. 2. The long-life neutron absorption region is located at the tip of the wing and at least part of the entire length of the wing from the tip of the wing to the end.
2. The control rod for a nuclear reactor according to claim 1, wherein the control rod is comprised of a wing outer end portion of 1/2. 3. The accommodation hole at the tip of the wing that accommodates the long-life neutron absorbing material is shortened in length toward the inner edge of the wing, and terminates closer to the outer edge of the wing than the accommodation hole in the adjacent intermediate neutron absorption region. A control rod for a nuclear reactor according to claim 1. 4. The control rod for a nuclear reactor according to claim 1, wherein the accommodation hole at the tip of the wing that accommodates the long-life neutron absorbing material is tapered toward the inner end of the wing. 5. Long-life neutron absorbers include hafnium, Hf-Zn alloy, Ag-In-Cd alloy, Eu_2O_3-HfO_
2. The control rod for a nuclear reactor according to claim 1, which is formed of a Dy_2O_3-HfO_2 sintered product and configured in the shape of a receiving hole or an approximate shape thereof. 6. The control rod for a nuclear reactor according to claim 1, wherein the large number of accommodation holes adjacent to the intermediate neutron absorption region in the withdrawal direction are configured to have a uniform size and shape over the entire length.