JPS63259494A - 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] [Object of the Invention] (Industrial Application Field) The present invention relates to a control rod for a nuclear reactor that adjusts and controls the reactor output, and particularly relates to a control rod for a nuclear reactor that has a long life with a high reactor shutdown margin. Concerning control rods for type nuclear reactors.

(Prior art) As a control rod for a nuclear reactor that controls the output of a nuclear reactor, for example, four stainless steel wings are integrally connected to a central tie rod, and a large number of accommodation holes are formed inside the wings in the width direction. A new type of control rod has been developed that is filled with powder of a neutron absorbing material such as boron carbide (84C) at a uniform density.

When this nuclear reactor control rod is inserted into the core of a boiling water reactor, etc., the neutron absorbing material filled in the accommodation hole is irradiated with neutrons and gradually loses its neutron absorption ability, so it is not suitable for operation for a predetermined period of time. It will then be replaced periodically.

(Problem to be Solved by the Invention) By the way, control rods used in the core of a nuclear reactor are not irradiated with neutrons uniformly over the entire surface of each wing. and the lateral edge regions are subjected to intense neutron irradiation. Therefore, the neutron absorbing material filled in the gA castle absorbs a large amount of neutrons and is consumed faster than other areas, ending its nuclear life in 9 days. Therefore, even though the neutron absorbing material filled in other areas still has sufficient nuclear life remaining, there is an uneconomical and uneconomical situation in which the entire reactor control rod must be disposed of as radioactive waste. If the frequency of replacement is high, there may be a problem that the radiation dose of the workers who perform the replacement RF work will also increase.

In addition, in conventional control rods for nuclear reactors, the entire wing area is filled with neutron absorbing material at a uniform density, and the neutron absorption capacity, or reactivity, in the axial direction is adjusted to be equal. As such, the non-uniformity of the neutral dried fish tJ4ffi causes variations in reactivity over time, which may partially reduce the reactor shutdown margin at the end of the reactor operating cycle.

In other words, when the reactor is operated for a predetermined period using the above-mentioned reactor control rods, the distribution of the reactor shutdown margin (subcriticality) in the core axis direction depends on the design specifications of the fuel assembly or the operation of the reactor. Although there are some differences depending on the method, the distribution basically becomes as shown in FIG. 3(A). In other words, the reactor shutdown margin is large at the upper and lower ends of the core, while taking a minimum value at a position slightly below the upper end.

Possible causes of this are as follows.

If the axial length of the reactor core is L, then 3/3 from the bottom end.
In the upper end region from the 4L position to the upper end, the bubble rate (void rate) during operation is high and the power density of the reactor decreases slightly. The residual amount is relatively large, and the generated bubbles (voids) cause a phenomenon of hardening of the neutron spectrum.

As a result, the plutonium production reaction (neutron absorption reaction) is promoted, so the concentration of fissile material in the upper part of the reactor core becomes high after the reactor is in operation, reducing the margin for reactor shutdown in that region.

On the other hand, it is inevitable that future nuclear reactors will shift to higher burn-up of nuclear fuel and longer operating cycles due to the demand for improved operating economy. As a concrete response to this, the adoption of highly enriched nuclear fuel is progressing, and as a result, there is a strong demand for flilJ rods for nuclear reactors that have a long life and have a large margin for reactor shutdown.

However, when conventional INI control rods for nuclear reactors are employed in nuclear reactors loaded with A12100 nuclear fuel, the reactor control rods must be frequently replaced every short operating cycle.

Replacing nuclear reactor control rods requires the complicated work of shutting down the reactor and removing from the reactor core a large number of fuel assemblies arranged around the control rods to be replaced. Therefore, reactor shutdowns occur frequently to replace control rods, and the shutdown period becomes long, which can significantly reduce the operating efficiency and economic efficiency of the reactor, while also significantly increasing management effort. .

The present invention was made in order to solve the above problems, and it increases the reactivity value of the entire control rod for a nuclear reactor, and also provides a control rod with particularly high reactivity in a region where reactor shutdown margin tends to decrease. Alternatively, by partially installing long-life neutron absorbing materials, it is possible to inexpensively and effectively increase the margin for reactor shutdown, and eliminate nuclear damage! The purpose of this invention is to provide a long-life reactor control rod that can prolong 9QI.

[Structure of the invention]

(Means for Solving the Problems) A nuclear reactor control rod according to the present invention includes a plurality of connecting members arranged at predetermined intervals in the axial direction, and a plurality of rectangular wings connected via the connecting members. The inner ends are joined to each other, and accommodation holes bored in the width direction of the wing are arranged in multiple rows from the insertion tip of the wing in the vertical direction over a length L corresponding to the entire axial length of the reactor core. In the reactor control unit 11 in which the accommodation hole is filled with a neutron absorbing material, the plurality of accommodation holes located at the insertion tip, inner edge, and outer edge of the wing are filled with a long-life neutron absorbing material. a first region is formed, a second region is formed in the longitudinal direction adjacent to the first region, and the length from the lower end of the second region to the insertion tip is set to 1/4L to 1/2L. , the accommodation hole located in the second region is filled with a highly reactive neutron absorbing material having a large neutron absorption capacity, while the accommodation hole located in the second region is filled in the second region in the axial direction from the lower end of the inner edge filled with the long-life neutron absorbing material. It is characterized in that a neutron absorber is interposed between the coupling members disposed within the range up to the lower end.

(Function) The control rod for a nuclear reactor according to the present invention has accommodation holes drilled in the width direction of each wing arranged in multiple rows in the longitudinal direction of the wing, and the tip of the wing in the insertion direction. Since the first region filled with a long-life neutron absorbing material is formed in the accommodation holes located in the inner edge and outer edge regions, the first region of the insertion tip receives a particularly high amount of neutron irradiation during operation. The neutron absorption capacity does not decline for a long time and the nuclear lifetime is long. Therefore, the life of the entire nuclear reactor control rod can be significantly extended.

In addition, when the reactor control rod is used with the reactor control rod fully inserted into the reactor core, the core inside the fuel assembly corresponding to the second region provided vertically adjacent to the first region of the reactor control rod is Since the reaction is suppressed by the void phenomenon, there is a large amount of nuclear fuel remaining in that area. Moreover, the reactions that produce plutonium increase the concentration of fissile material. However, since the second region is filled with a highly reactive neutron absorber, even after the reactor has been operated for a long period of time, the neutron absorber in the second region.

The reactivity value of is retained. Therefore, a sufficient margin for reactor shutdown can be ensured when all reactor control rods are fully inserted.

Furthermore, when the reactor control rods are inserted into the reactor core, a second region is defined in the axial direction from the lower end of the inner edge of the wing filled with long-life neutron absorbing material, which is the range where the reactor shutdown margin is reduced. Since the neutron absorber is interposed between the coupling members disposed within the range up to the lower end, the neutron absorption effect in that range increases, and the reactor shutdown margin can be significantly improved.

On the other hand, no neutron absorber is interposed between the connecting members in the lower region where the reactor shutdown margin is less reduced even in the inserted state, and the space between the connecting members is sufficiently filled with reactor water, which is a moderator. Therefore, a decrease in output at the corner of the fuel assembly facing the filled portion is suppressed, and on the other hand, a sudden increase in output is alleviated when the fuel assembly is withdrawn.

In addition, the minimum required amount of expensive neutron absorbing material with long life or high reactivity is provided in the first and second regions, thereby reducing the manufacturing cost of the entire reactor control rod. Can be done.

(Example) Hereinafter, an example of a control rod for a nuclear reactor according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a partially cutaway front view showing a wing of a control rod for a nuclear reactor according to the present invention.

The nuclear reactor control rod A of this embodiment is constructed by arranging a plurality of coupling members 1 at predetermined intervals in the axial direction and fixing a plurality of wings 2 via the coupling members 1. Specifically, the inner ends of four rectangular wings 2 made of stainless steel plates are connected to each other via a connecting member 1 to form a cross-shaped cross section, and a handle 3 for operation is provided at the insertion tip. It is fixed. On the other hand, an end structure member is attached to the insertion end portion (not shown). Accommodation holes 4 are bored in the width direction of each wing 2, and the accommodation holes 4 are arranged in multiple rows in the longitudinal direction of each wing 2 with a length corresponding to the entire axial length of the core. The holes 4 are filled with neutron absorbing materials having various properties.

In addition, the accommodation holes 4 located in the insertion tip, inner edge, and outer edge regions of each wing 2 are filled with a long-life neutron absorbing material α to form a first region X. Here, the length Jl of the insertion tip of the first region X is about 5 to 15 cIR from the insertion tip.

Furthermore, at the outer edge of the first region X of the wing 2, the width W of the region filled with the long-life neutron absorber α is 1 to 2O
In a nuclear reactor control rod that is always used in an inserted state, the length A4 is at least 1/2 or more of the total axial length of the reactor core.

On the other hand, at the inner edge of the first region from 15 to 301f'1 degree.

Here, the long-life neutron absorber α is one selected from hafnium metal, hafnium-zirconium alloy, silver-indium-cadmium alloy, hafnium oxide, or rare earth oxide such as europium oxide or dysprosium oxide. Powdered or solid neutron absorbing materials containing one or more types of substances are employed, and the optimal combination is determined in consideration of neutron irradiation intensity, operating period, etc.

According to the above configuration, even in the first region X of the insertion tip where neutron irradiation m is particularly high during reactor operation, the neutron absorption ability continues for a long period of time, and the nuclear lifetime is long. Therefore, it becomes possible to significantly extend the life of the reactor control rod A as a whole.

Further, the long-life neutron absorbing material α may be a powdered raw material, but for example, it may be a solid sintered body prepared by sintering a powdered raw material, and the sintered body is inserted into the accommodation hole 4. When it is molded into a shape that can be used, the operability when filling or extracting the neutron absorbing material is performed is excellent.

Next, the configuration of the second region Y portion will be explained.

The second region Y is formed in the vertical direction adjacent to the first region X, and has a length j! from the lower end of the second region Y to the insertion tip. 2 is about 1/4 to 1/2 of the total axial length of the core. The accommodation hole 4 located in the second region Y is filled with a highly reactive neutron absorbing material β having a large neutron absorption capacity, as a preferable example.
is filled.

As the highly reactive neutron absorbing material β, a powdery boron carbide obtained by concentrating boron having a mass number of 10 or a sintered body mainly composed of europium oxide is employed.

When using the Ill all rod A for a nuclear reactor in a state where it is fully inserted into the reactor core, the fuel corresponding to the second #4 region Y provided vertically adjacent to the first region X of the control rod A for the reactor. Nuclear reactions inside the assembly are suppressed by the void phenomenon, so there is a large amount of nuclear fuel remaining in that area.

Furthermore, the concentration of fissile material increases due to the plutonium production reaction, resulting in an area where the margin for reactor shutdown inevitably decreases.

However, due to the action of the highly reactive neutron absorber β such as boron carbide or europium oxide filled in the accommodation hole 4 of the second region Y, a high reactivity value is maintained for a long period of time. Therefore, even after the reactor has been operated for a long period of time, a sufficient margin for reactor shutdown can be ensured for the reactor control rod as a whole.

In addition, the accommodation hole 4 located in the third region Z formed in the range from the lower end of the second region [Y to the terminal structural member of each wing 2]
is filled with an inexpensive and lightweight neutron absorbing material such as natural boron gamma. The length l of this third region Z varies depending on the length 12 to the second region Y, but is approximately 1/2 to 3/4 of the total length in the core axis direction.

Furthermore, in the nuclear reactor control rod of this embodiment, a neutron absorber is also disposed at the control rod shaft center in a range where the reactor shutdown margin decreases after a long period of reactor operation. That is,
A neutron absorber 5 is interposed between coupling members disposed within a range from the lower end of the inner edge of the wing filled with the long-life neutron absorber α to the lower end of the second region Y in the axial direction. .

The neutron absorber 5 is made of hafnium metal or an alloy material mainly composed of hafnium and zirconium and has a cross-shaped cross section, and is held by the inner edge of each wing 2 and the upper and lower connecting members 1 as shown in FIG. be done. Since hafnium or a hafnium alloy can be used without a covering material, processing and preparation of the neutron absorber 5 is easy.

Generally, the wings 2 made of stainless steel are difficult to weld with hafnium material. On the other hand, if the side edges of the neutron absorber 5 are fixed to the side edges of each wing 2 along the entire line by welding, etc., atoms There is a risk that the rigidity of the reactor control rod will become excessive.

Therefore, as shown in FIG. 2, by forming a concave groove 6 on the side edge of the wing 2, and forming a convex part 7 on the protrusion of the neutron absorber 5, and fitting the convex part 7 into the concave groove 6, A structure in which the neutron absorber 5 is sandwiched between the wings 2 is preferable.

Further, the neutron absorber 5 may be divided into a plurality of pieces between the coupling members 1, 1 to facilitate assembly work. Further, in FIG. 2, the neutron absorber 5 is made of a solid hafnium material, but it can also be configured to have a moderator flow path formed therein to obtain a neutron moderating effect.

According to the reactor control rod of this embodiment, since the neutron absorber 5 is interposed between the connecting members 1 in the upper region of the control rod where the reactor shutdown margin is reduced, the reduction in the reactor shutdown margin in that area is reduced. be fully compensated.

On the other hand, between the coupling members 1 located at the lower part of the second region Y,
It is preferable for operation to secure a space occupied by reactor water, which is a moderator, in the axial center of the Hil control rod without intervening the neutron absorber 5.

In other words, when transitioning to high-power operation, before and after withdrawing the control rod,! The increase in fuel output at the corner of the fuel assembly that was facing the 11111 rod axis is reduced, resulting in less thermal shock. That is, when the amount of reactor water at the axial center of the control rod increases, the thermal neutron flux increases, and as a result, the output of the fuel at the corner of the fuel assembly adjacent to the axial center improves. That is, even when the υ control rods are inserted, the combustion delay at the corners is reduced, so the concentration of fissile material is also reduced. Therefore, even during high-power operation after control rod withdrawal, the power at the corners of the fuel assembly will not increase in a short period of time.
The health of the fuel can also be improved.

Next, the effects etc. when using the above-mentioned &IJIIl rod A for nuclear reactors will be explained with reference to FIG. 3.

FIG. 3(B) is a graph showing the axial distribution of neutron absorption characteristics in the reactor control rod A according to this example, and shows each of the reactor control rods A corresponding to the total axial length of the reactor core. The relative values of reactivity in regions X, Y, and Z are shown. The first region ing.

Generally, near the upper end of a nuclear reactor control rod, the degree of subcriticality suddenly increases as shown in FIG. 3(A). One of the causes of this is a decrease in the multiplication factor due to leakage of neutron beams from the core end, and another reason is that the core fuel is increased by placing natural uranium or low-enrichment nuclear fuel at the core end. This is due to core design policy aimed at improving economic efficiency. In accordance with this policy, in this example,
As shown in Figure 3 (B), the first region ing.

A nuclear reactor control rod with a distribution of neutron absorption characteristics in the axial direction as shown in Figure 3 (B) is attached to the reactor, and after operation for a predetermined period, subcriticality in the axial direction of the core, that is, reactor shutdown. The distribution of margin is shown in No. 31i4(C). Figure 3 (A)
The subcriticality distribution in the lower half of the reactor core has been improved compared to the conventional example shown in Figure 2, and an almost uniform subcriticality curve can be obtained over the entire axial direction of the reactor control rods. It can be seen that sufficient stop margin is secured.

In addition, between the region filled with the high-reactivity neutron absorber β and the region filled with natural boron γ, a neutron absorber having a reactivity intermediate between the two, such as low enrichment boron carbide or low concentration of europium oxide (Eu2
By intervening a region filled with O3>, etc., it is possible to further flatten the subcriticality curve. Alternatively, it is also possible to adjust the neutron absorption capacity and flatten the neutron absorber 5 inserted between the coupling members by reducing its thickness or perforating it, and in addition, it is possible to use an expensive neutron absorber. It is also possible to reduce grinding and production costs.

As explained above, according to the 1IIIIII rod for nuclear reactors of this embodiment, it is possible to sufficiently maintain the reactivity value and to achieve a long life at the same time.

Therefore, even when operating a nuclear reactor for a long period of time, the reactivity value of the entire 1m rod for the reactor is maintained,
Sufficient margin for reactor shutdown can also be secured.

〔Effect of the invention〕

According to the control rod for a nuclear reactor according to the present invention, each wing is divided into each area in the vertical direction from the insertion tip, and 1ffi of neutral dried fish is
The accommodation hole in the first region, which consists of the insertion tip, inner edge, and outer edge of the wing, which has a large be. In addition, the second region of the reactor control rod, which corresponds to the part where the concentration of fissile material increases due to void phenomena and plutonium production reactions, is filled with highly reactive neutron absorbing material, so even after long-term operation, 2nd g
The reactivity value of the neutron absorber in region A is maintained.

Therefore, it is possible to secure a sufficient margin for reactor shutdown when all reactor control rods are fully inserted.

In addition, expensive long-life neutron absorbers and highly reactive neutron absorbers are locally filled in the minimum necessary amount, so
Control rods for nuclear reactors can be manufactured at low cost.

In addition, there is a second region in the axial direction from the lower end of the inner edge of the wing filled with long-life neutron absorbing material, which is the region where the reactor shutdown margin is particularly reduced when the Ill lft rod for the reactor is inserted into the reactor core. Since the neutron absorber is interposed between the connecting members arranged within the range up to the lower end of the
The neutron absorption effect within that range increases.

Therefore, according to the present invention, the reactor shutdown margin is effectively improved and the manufacturing cost is also low. In particular, the problem of insufficient reactor shutdown margin due to F increase in enrichment corresponding to higher burnup of reactor fuel is resolved, and safe shutdown capability of 8N of the reactor is guaranteed.

On the other hand, since the nuclear lifetime can be significantly extended, it can be actively adopted in nuclear reactors with long operating cycles, and the cost efficiency of nuclear couplant operation can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view of Embodiment 4 of a control rod for a nuclear reactor according to the present invention, and FIG.
■A sectional view in the direction of arrows, Figure 3 (A) is a graph showing the axial distribution of the reactor shutdown margin when the reactor is operated for a predetermined period using conventional reactor control rods, Figure 3 (B) ) is a graph showing the axial distribution of neutron absorption characteristics in the control rod for a nuclear reactor according to the present invention, and FIG. 12 is a graph showing the axial distribution of the reactor shutdown margin in comparison with a conventional example. DESCRIPTION OF SYMBOLS 1... Coupling member, 2... Wing, 3... Handle, 4... Accommodation hole, 5... Neutron absorber, 6...
Concave groove, 7...Protrusion, A...Reactor control rod, H.
...Insertion tip, L...Total length in the axial direction of the reactor core, α...Long-life neutron absorber, β...Highly reactive neutron absorber,
γ...Natural boron, X...First region, Y...Second
Area, Z... Third area, 11... Length of the upper end of 1st fI4t4, 12... Length from the lower end of the second area to the insertion tip, 3rd... Length of the third area , 4th... Length of the outer edge of the wing filled with long-life neutron absorbing material,
15...Length of the inner edge of the wing filled with long-life neutron absorber. Applicant's agent Hisashi Hatano Figure 1

Claims (1)

[Claims] 1. A plurality of coupling members are arranged at predetermined intervals in the axial direction, and the inner ends of the plurality of rectangular wings are coupled to each other via the coupling members, and the inner ends of the wings are connected in the width direction of the wings. A number of accommodation holes are arranged in a row from the insertion tip of the wing in the vertical direction over a length L corresponding to the entire axial length of the core, and the accommodation holes are filled with a neutron absorbing material. In the reactor control rod, a plurality of accommodation holes located at the insertion tip, inner edge, and outer edge of the wing are filled with a long-life neutron absorbing material to form a first region, and the first region is filled with a long-life neutron absorbing material. A second region is formed adjacently in the longitudinal direction, the length from the lower end of the second region to the insertion tip is set to 1/4L to 1/2L, and a neutron absorbing material is placed in the accommodation hole located in the second region. and a neutron absorber is interposed between the coupling members disposed in the range from the lower end of the inner edge filled with the long-life neutron absorber to the lower end of the second region in the axial direction. A nuclear reactor control rod featuring: 2. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorber interposed between the connecting members is made of hafnium or a hafnium alloy. 3. Long-life neutron absorbers include hafnium (Hf) metal, hafnium-zirconium (Hf-Zr) alloy, silver-
Indium-cadmium (Ag-In-Cd) alloy, hafnium oxide (HfO_2), europium oxide (
Eu_2O_3), dysprosium oxide (Dy_2O
_3) A solid absorbent material containing one or more kinds of substances selected from control rod. 4. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorbing material filled in the storage hole located in the second region is boron carbide enriched with boron (B-10) having a mass number of 10. 5. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorbing material filled in the storage hole located in the second region is a sintered body containing europium oxide (Eu_2O_3) as a main component.