JPH0580635B2 - - Google Patents

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, a control rod for a nuclear reactor that is hybridized with a neutron absorbing material and has 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]

Inside the control rod used in a nuclear reactor, four stainless steel wings are joined together through a joint, and boron carbide, a boron compound, is inserted into a large number of accommodation holes formed in the width direction of the wing. A product filled with powder of (B ₄ C) 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 B ₄ C powder filled in the wing tip and blade tip deteriorates more quickly than in 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 B ₄ C 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 end portions of the wings, which are exposed to strong neutron irradiation, are filled with 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 three to six times longer than 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, B ₄ C, which is a normal neutron absorbing material,
The powder is formed by boron-10 ( ¹⁰ B) reacting with neutrons to form Li.
-7 and He-4 are generated. The generated helium gas gradually accumulates as the neutron irradiation time passes, and as the helium gas accumulates, the B ₄ C powder causes swelling and expands each accommodation hole in the wing.
Further, since a part of the helium gas is released from the B ₄ C powder, gas pressure is generated inside the accommodation hole, which acts in the direction of expanding 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 rise abnormally.

However, the swelling phenomenon of B ₄ C powder is noticeable in a limited area that is exposed to strong neutron irradiation, and the amount of swelling in that area becomes large. Furthermore, in the reactor control rods 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, designed to be about 1 mm thick. . 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 around each accommodation hole, at the end of the control rod's life, due to local expansion due to swelling of B ₄ C, the thickness between each accommodation hole and There is a possibility that cracks may occur between the receiving hole and the surface. In addition, while stainless steel itself becomes brittle when exposed to large amounts of neutron irradiation, the hardness of B ₄ C grains is larger than that of stainless steel, so when some stress occurs due to the swelling phenomenon of B ₄ C powder grains, the wing There was a risk of damage and 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 all the neutron absorbing materials filled in each wing by almost simultaneously reaching the end of their life _. 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 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 has inner ends of a plurality of rectangular wings integrally connected to each other via a connecting part, and a hole is bored in the wing in the width direction thereof. In a control rod for a nuclear reactor, in which accommodation holes 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, a plurality of accommodation holes are located at the tip of the wing in the insertion direction. A long-life neutron absorbing material is filled near the outer ends of the holes and wings to form a long-life neutron absorbing region, and an intermediate neutron absorbing region is formed adjacent to this neutron absorbing region. Each accommodation hole arranged has a tapered shape on the inner side of the wing, and each accommodation hole in the intermediate neutron absorption region is filled with a neutron absorbing material that reacts with neutrons and causes swelling. .

[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, basically 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,
This operating handle 13 is integrally or integrally connected to the tip of each wing 11.

Each wing 11 of the control rod 10 is formed of a flat metal material such as stainless steel, and has a large number of accommodation holes 14a, 14b, 14c extending in the width direction inside.
is formed. Each housing hole 14 is arranged in a row in the vertical direction of the wing 11, and has a diameter of about several mm (for example, 6 mm).
Each hole has a diameter of mm). Each of the above accommodation holes 14
a, 14b, 14c are communication grooves 15 extending in the vertical direction.
are communicated with each other. 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 _B4 is inserted into the remaining many accommodation holes 14b, 14c.
Neutron absorbing material 1 made of C powder or pellets
7 is filled. Further, in the communication groove 15 formed near the outer end of the wing 11, a long-life neutron absorbing material 16c such as hafnium is interposed at least half the total length from the tip of the wing. In addition to hafnium, the long-life neutron absorbing materials 16a to 16c include Hf-Zr alloy, Ag-In-Cd alloy, _{Eu2O3 - HfO2} sintered material, _{Dy2O3 - HfO2} sintered material, etc. is used.

In this way, the reactor control rods 10 are exposed to strong neutron irradiation at the tip of each wing 11 (region with length l ₁ = 5 to 15 cm from the tip) and near the wing tip (width
l ₂ =1.0 to 1.5 cm) is filled with long-life neutron absorbing materials 16a to 16c, thereby forming a long-life neutron absorbing region 18. Long-life neutron absorber 1
6a to 16c are formed in a rod shape or 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. The length toward the wing 11 is shortened, and the end is closer to the outer end of the wing 11 than the adjacent accommodation hole 14b. That is, the tip of the wing 11 has a housing hole 14 at its inner end.
A solid portion in which no a is present is formed to prevent the wing 11 from weakening against strong neutron irradiation. Generally, all of the nuclear reactor control rods 10 are fully inserted into the reactor core during reactor shutdown. Therefore, the insertion tip of the control rod 10 is generally located at the end of the reactor core, and as taught by reactor physics theory, it contributes reactivity to reactor shutdown (reactivity effect).
is small. Furthermore, the central axis side of the nuclear reactor control rod 10, which has a cross-shaped cross section, that is, the wing 1
The reactivity effect on the inner end side of wing 1 is smaller than that on the other parts, especially on the outer end side of wing 11.
Therefore, the reactivity effect on the inner end side of the wing 11 is extremely small during the reactor shutdown, and the decrease in the reactivity effect on the reactor control rod 10 on the inner end side is small.

Additionally, during reactor operation, most of the reactor control rods 10 are generally completely withdrawn from the core, and some control rods 10 are controlled to be moved in and out of the reactor core in order to control the reactivity and power distribution of the reactor. Ru. latter control rod 10
is inserted into the reactor core in a partially withdrawn state during high-power operation of the reactor, so it is irradiated with a high neutron flux. In particular, it is known that the amount of neutron irradiation at the insertion tip of the control rod 10 and the outer end of the wing 11 becomes significantly high (the inventors of the present application et al.
(Disclosed in Publication No. 74697).

If a solid part of the wing 11 is formed on the central axis side of the wing 11 at the insertion tip of the control rod 10, that is, a part where no neutron absorbing material is placed without drilling a hole in the structural member of the wing 11, it is possible to In the mid-insertion control rod 10 inserted into the reactor core in a partially withdrawn state, the wing inner end side is the wing 11.
The neutron absorption effect is reduced compared to the outer end side. As a result, the drop in temperature of the output from the control rod at the corner of the fuel assembly adjacent to the wing inner part on the insertion tip side of the mid-inserted control rod 10 is alleviated, and the decrease in the temperature of the output due to the control rod movement during reactor operation is reduced. The output impact at the corners of the assembly is reduced.

Further, 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. Accommodation hole 14b
By tapering the tip of the wing 11, the wall thickness of the wing 11 is increased and its mechanical strength is improved.

An intermediate neutron absorption region 19 is formed in the upper part of the control rod 10 adjacent to the long-life neutron absorption region 18 . This intermediate neutron absorption region 19 is 15 cm to 50 cm
It has a length l ₄ of the order of cm. Intermediate neutron absorption region 1
The plurality of accommodation holes 14b formed in the wing 9 are tapered toward the inner end of the wing as shown in FIG. 4, thereby improving the mechanical strength of the inner end of the wing 11. Each of the accommodation holes 14b contains boron carbide (B ₄
C) The powder grains are packed to improve the packing density of the B ₄ C powder grains. The open end of the filled B ₄ C powder end is closed with a long-life neutron absorbing material 16c housed in the communication groove 15. At that time, each accommodation hole 1
4b and 14c are communicated with each other through a communication hole 20 so that 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 slate hole shape as shown in FIG. Each accommodation hole 14c contains a neutron absorbing material with different particle sizes.
B ₄ C powder particles 17 are filled. The accommodation hole 14c in this area may be formed by considering machinability, and there is no need for complicated machining such that the hole diameters are different. That is,
When the control rod 10 moves away from the tip to a certain extent, for example, about 30 cm, the amount of neutron irradiation decreases, and each accommodation hole 1
4c does not necessarily have to be the diameter of the small hole. Since the amount of neutron irradiation decreases, B ₄ C due to neutron irradiation
The amount of swelling of powder grains is also small, and each wing 11
Since the expansion stress acting on the inner edge of B ₄ is small,
The problem of wing breakage due to expansion of C powder grains does not need to be considered.

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

When manufacturing the control rod 10 for a nuclear reactor, each inner end of the four wings 11 each having a large number of accommodation holes 14a, 14b, and 14c formed in a row is attached to the connecting member 12.
are connected together to form an integral structure. After each wing 11 is integrated, a large number of accommodation holes 14a, 14b, 14c are formed in each wing 11.
Long-life neutron absorbing materials 16a, 16b and B ₄ C
Each is filled with a neutron absorbing material consisting of powder grains 17.

After each accommodation hole 14a, 14b, 14c is filled with a neutron absorbing material, a communication groove 15 extending in the vertical direction
A long-life neutron absorbing material 16c is filled inside. 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 strong neutron irradiation, are configured as long-life neutron absorption regions 18, and long-life neutron absorption materials 16a, 16b, and 16c are loaded. Therefore, even if exposed to large amounts of neutron irradiation,
Its lifespan can be maintained at or above the same level as other areas. 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.

Moreover, this control rod 10 for a nuclear reactor does not require a tie rod, and when inserted into the core of a nuclear reactor,
Since reactor water exists in the area of the central axis of the control rod 10 (particularly l ₁ and l ₄ ), it is exposed to high neutron irradiation during reactor operation when it is used in the mid-insertion state. Since it has a solid structure or a thick wall structure, the mechanical strength is improved and it is possible to effectively cope with weakening of the wing 11 due to strong neutron irradiation.

In addition, since 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, the wing 11 in that part has a thick structure, and its mechanical strength is reduced. improves. Therefore, even if the B ₄ C powder particles accommodated in each accommodation hole 14b swell due to relatively strong neutron irradiation, 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 are explained as shown in FIGS. 2 to 5. but not limited to. For example, the accommodation holes 21a and 21b formed in the intermediate neutron absorption region 19 may have the hole shapes shown in FIGS. 6A, B, and C. At that time, as shown in FIGS. 6B and 6C, pellet-shaped long-life neutron absorbing materials 22a and 22 are placed at the tips of the accommodation holes 21a and 21b.
b may be filled.

〔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 B ₄ C undergoes swelling under neutron irradiation,
Mechanical strength can be maintained sufficiently, and wing weakness can be effectively prevented.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of a nuclear reactor control rod according to the present invention, and FIG. 2 is a plane view of a wing obtained by cutting the nuclear reactor control rod shown in FIG. 1 along line A-A. 3 is a plan sectional view along line B-B in FIG. 1, FIG. 4 is a plan sectional view taken along line C-C in FIG. 1, and FIG. 5 is a plan sectional view taken along line C-C in FIG. Planar sectional view along the line,
FIGS. 6A, 6B, and 6C are views showing modified examples of each accommodation hole formed in the intermediate neutron absorption region of the wing of the control rod for a nuclear reactor according to the present invention. 10...Reactor control rod, 11...Wing,
14a, 14b, 14c, 21a, 21b...Accommodation hole, 15...Communication groove, 16a, 16b, 16
c, 22a, 22b...Long-life neutron absorber,
17... Neutron absorbing material (B ₄ C), 18... Long-life neutron absorption region, 19... Intermediate neutron absorption region.

Claims (1)

[Scope of Claims] 1. The inner ends of a plurality of rectangular wings are integrally connected to each other via a connecting portion, and a plurality of accommodation holes are formed in the width direction of the wing in the longitudinal direction of the wing. In a nuclear reactor control rod arranged in a row and having the accommodation holes filled with a neutron absorbing material, a long-life type is provided in the plurality of accommodation holes located at the tips in the insertion direction of the wings and near the outer ends of the wings. A long-life neutron absorption region is formed by filling with a neutron absorption material, an intermediate neutron absorption region is formed adjacent to this neutron absorption region, and each accommodation hole arranged in this intermediate neutron absorption region has a wing inner end side. A control rod for a nuclear reactor, characterized in that it has a tapered shape and that each accommodation hole in the intermediate neutron absorption region is filled with a neutron absorbing material that reacts with neutrons and causes swelling. 2. The nuclear reactor according to claim 1, wherein the long-life neutron absorption region is comprised of the tip of the wing and a portion near the outer edge of the wing that is at least 1/2 of the total length of the wing from the tip of the wing to the end. control rod. 3. A patent in which the accommodation hole at the tip of the wing that accommodates the long-life neutron absorbing material is shortened in length toward the inner end of the wing, and terminates closer to the outer end 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 absorbing material is hafnium, Hf-
The patent claim is made of Zr alloy, Ag-In-Cd alloy, Eu ₂ O ₃ -HfO ₂ sintered product or Dy ₂ O ₃ -HfO ₂ sintered product and configured in the shape of the receiving hole or an approximate shape thereof. A control rod for a nuclear reactor according to scope 1. 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.