JPS63215992A - Control-rod for nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) 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. This invention relates to a control rod for a nuclear reactor that has a high reactor shutdown margin.

(Prior art) As a nuclear reactor control rod 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 control rod for a nuclear reactor 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. After that, it is exchanged regularly.

(Problem to be solved by the invention) By the way, the control rods used in the core of a nuclear reactor are not irradiated with neutrons uniformly over the entire surface of each wing. The region and the lateral edge regions receive intense neutron irradiation. Therefore,
The neutron absorbing material filled in that area absorbs a large amount of neutrons and is consumed more than other areas, ending its nuclear lifespan earlier. Therefore, even though the neutron absorbing materials filled in other regions still have sufficient nuclear life remaining,
There is an uneconomical problem in that the entire I tit rod must be disposed of as radioactive waste, and on the other hand, there is also the problem that if it is replaced less frequently, the radiation exposure of the workers who perform the replacement work will increase.

In addition, conventional illumination rods for nuclear reactors uniformly distribute the neutron absorbing material over the entire area of the wing! It is filled with
The neutron absorption capacity, that is, the reactivity in the axial direction, is adjusted to be equal, but as mentioned above, the reactivity varies over time due to the non-uniformity of neutron irradiation ω, and at the end of the reactor operation cycle, some atoms The margin for reactor shutdown may decrease.

In other words, when the reactor is operated for a predetermined period using the above-mentioned υ control rod for a nuclear reactor, the distribution of the reactor shutdown margin (subcriticality) in the core axis direction is determined by the design specifications of the fuel assembly or the operation of the reactor. Although there are some differences depending on the method, basically the indicated size distribution is shown in FIG. 2(A). In other words, the reactor shutdown margin is large at the -L end and bottom end of the core,
On the other hand, the minimum value is taken at a position slightly below the upper D'J. 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 4L to the upper end, the bubble generation rate (void rate) during operation is high, and the power density of the reactor decreases slightly, so the remaining uranium (jJ-235) with a mass number of 235, which is a fissile material, ω 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, which increases the concentration of fissile material in the upper part of the core after the reactor is in operation, reducing the margin for reactor shutdown in these seven regions.

On the other hand, it is inevitable that future nuclear reactors will shift to higher burn-up of nuclear fuel and longer operating cycle due to the demand for improved light-flow operation. 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 control rods for nuclear reactors that have a long life and a large margin for reactor shutdown.

However, if conventional nuclear reactor control rods are used in a nuclear reactor loaded with high desert nuclear fuel, the reactor control rods must be replaced frequently every short operating cycle. Furthermore, when replacing control rods for a nuclear reactor, it is necessary to shut down the reactor and remove from the reactor a large number of fuel assemblies arranged around the control rods to be replaced, which is a complicated process.

Therefore, as nuclear reactor shutdowns occur frequently and the shutdown period becomes long, the operational efficiency and R uniformity of the reactor are significantly reduced, and the management effort may significantly increase.

The present invention has been 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 improves the reactivity value of the control rod, especially in areas where the reactor shutdown margin tends to decrease. Alternatively, we provide a control rod for a nuclear reactor that can inexpensively and effectively increase the reactor shutdown margin and prolong the nuclear life by partially disposing a neutron absorbing material with a long V life. The purpose is to

[Structure of the invention]

(Means for solving the problem) For nuclear reactors according to the present invention! The III-shaped wing integrally connects the inner ends of a plurality of rectangular wings to each other via a connecting member, and also has a housing hole bored in the width direction of the wing extending vertically from the insertion tip of the wing. In U control rods for nuclear reactors, which are arranged in multiple rows across the length and the accommodation holes are filled with neutron absorbing material, long-life neutron absorbing material is placed in the plurality of accommodation holes located at the insertion tip of the wing. 12 regions are formed in the vertical direction adjacent to the first region, and the length from the lower end of the second region to the insertion tip is at least b1/411/4. A highly reactive neutron absorbing material having a large neutron absorption capacity is filled into the accommodation hole located in the second region, and a third region is formed in PR contact with the second region to the end in the insertion direction. The receiving hole located in the region is filled with natural neutrons, and a long-life neutron is filled in the region of the outer edge of the wing with a length of at least 1/2 [longitudinal] from the insertion tip. It is characterized by being filled with an absorbent material.

(Function) The υ1m 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 area at the tip of the wing in the insertion direction. Since the first region filled with long-life neutron absorbing material is formed in the accommodation hole located at It does not decline and has a long nuclear lifespan. 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 inside of the fuel assembly corresponding to the second region provided vertically adjacent to the first region of the reactor U control rod is Because nuclear reactions are suppressed by void phenomena,
There is a large amount of nuclear fuel remaining in that area. Moreover, the Il signature of fissile material is increasing due to the plutonium production reaction. However, since the second region is filled with a highly reactive neutron absorber, the reactivity value of the neutron absorber in the second region is maintained even after the reactor is operated for a long period of time. Therefore, a sufficient margin for reactor shutdown can be ensured when all reactor control rods are fully inserted.

Furthermore, a third region of each wing from the lower end of the second region to the terminal structure is filled with natural boron, and this third region is filled with natural boron.
The area of the area is 1/2 to 3/4 of the total area of each wing.
Since this region is filled with light-chain natural boron, an increase in the weight of the entire reactor control rod is hardly a problem.

In addition, an octavalent neutron absorbing material with a long life or high reactivity is provided in the first and second regions in a limited amount, while the third region is made of inexpensive natural boron. The manufacturing cost of i+11 illll metal rods for nuclear reactors can be reduced.

Furthermore, since the outer edge area of the wing is filled with long-life neutron absorbing material in an area having a length of at least 1/2 L or more in the longitudinal direction from the insertion tip, the outer edge area of the wing receives a large amount of neutron irradiation. can extend the nuclear lifespan of

(Example) Hereinafter, an example of the 1111II 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 υI control rod wing for a nuclear reactor according to the present invention.

The reactor control rod A of this embodiment is constructed by integrally connecting the inner ends of four rectangular wings 1 made of, for example, stainless steel plates to each other in a cross shape via a connecting member 2. A handle 3 for operation is fixed to the tip. On the other hand, an end structure material is attached to the insertion end (not shown).
j is being kicked.

Accommodation holes 4 are bored in the width direction of each wing 1, and the accommodation holes 4 are arranged in multiple rows in the longitudinal direction of each wing 1,
The accommodation hole 4 is filled with neutron absorbing materials having various properties.

That is, the accommodation hole 4 located in the region of the insertion tip of each wing 1 is filled with the long-life type neutron absorbing material α to form the first region bIir. Here, the length Jl of the first region I is about 5 to 15 cm from the insertion tip 1''.

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. A powdered or solid neutron absorbing material containing a substance of 2fl or more is used, and the optimal combination is determined by taking into consideration the neutron irradiation intensity, operating period, etc.

According to the above configuration, even in the first region 1 of the insertion tip where neutral dried fish O4m is particularly abundant during reactor operation, the neutron absorption ability continues for a long period of time, and the nuclear life 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. If it is molded into a shape that can be used, the operability when filling or extracting neutron absorbing material is performed is excellent.

Next, the configuration of the second area (3) will be explained.

The second region (2) is formed vertically adjacent to the first region (2), and the length O from the lower end of the second region (2) to the insertion tip (1) is 1/1/2 of the total axial length of the core. It is about 4 to 1/2. The accommodation hole 4 located in the second region (3) is filled with a highly reactive neutron absorbing material β having a large neutron absorption capacity.

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 the reactor control rod A is used with the reactor control rod A fully inserted into the reactor core, the inside of the fuel assembly corresponding to the second region (2) provided vertically adjacent to the first region work of the reactor control rod A. Since the nuclear reaction in is suppressed by the void phenomenon,
1) There is a large amount of nuclear fuel remaining in that area. Moreover,
The plutonium production reaction increases the concentration of fissile material, resulting in an area where the margin for reactor shutdown inevitably decreases.

However, due to the action of the highly reactive neutron absorbing material β such as boron carbide or europium oxide filled in the accommodation hole 4 of the second region (2), the 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.

Next, the third region (2) is formed in the range from the lower end of the second region (2) of each wing 1 to the terminal structural member, and the length 13 of this region is 1/2 to 3 of the total length in the core axial direction. It is about /4. The accommodation hole 4 located in the third region (2) is filled with natural boron γ.

Further, in the outer edge region of the wing 1, a region having a length of at least 1/2 L or more in the longitudinal direction from the insertion tip is filled with a long-life neutron absorbing material α, as in the first region (2). Here, the width W1 of the long-life neutron absorbing material α disposed on the outer edge of the wing 1 is about 1 to 2C11, and the length 4th of the long-life neutron absorbing material α disposed including the first region It is at least 1/2 or more of the total axial length of.

Next, the effects of using the above-mentioned nuclear reactor control rod A will be explained with reference to FIG. 2.

FIG. 2(B) is a graph showing the axial distribution of the neutron absorption characteristics of the reactor control rod A according to this example, and shows the axial distribution of the reactor control rod A corresponding to the changes in the axial direction of the reactor core. The relative values of reactivity in each region I, II, and III are shown. The first region ■ is filled with a long-life neutron absorber α, the second region ■ is filled with a highly reactive neutron absorber β, and the third region ■ is filled with natural boron γ. ing.

Generally speaking, near the upper end of a nuclear reactor control rod, the degree of subcriticality suddenly increases as shown in Figure 2 (A>. One of the reasons for this is that the neutron beam from the end of the core This is due to a decrease in the multiplication factor due to leakage, and another cause is due to the core design policy, which attempts to improve the economic efficiency of the reactor fuel by placing natural uranium or low-enrichment nuclear fuel at the end of the reactor core. Corresponding to that policy, in this example as well, as shown in Fig. 2 (B), the highly reactive neutron absorbing material β is not placed in the first region including the upper end, and a long-life neutron absorbing material is used. The only attempt is to extend the service life by filling with material α.

A nuclear reactor control rod with a distribution of neutron absorption characteristics in the axial direction as shown in Figure 2 (B) is installed in a nuclear reactor, and after operating for a predetermined period, subcriticality in the axial direction of the reactor core, that is, reactor shutdown. The distribution of margins is shown in FIG. 2(C). Compared to the conventional example shown in Figure 2 (A>), the subcriticality curve in the upper half of the reactor core has been improved, and the subcriticality curve is almost uniform throughout the axial direction of the reactor control rod. It can be seen that sufficient margin for reactor shutdown is obtained.

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 somewhere between the two, such as boron carbide with a low concentration, is added. Or, low concentration of 1-Robium oxide (Eu2
By interposing a region filled with O3) etc.,
It is possible to further flatten the subcriticality curve, and at the same time, it is possible to reduce the amount of expensive neutron absorbing material used, thereby reducing manufacturing costs.

Furthermore, as shown in FIG. 1, the upper end region of the inner edge of each wing 1 is partially filled with long-life neutron absorbing material α, similar to the first region I, to further improve the characteristics of the control rod. be able to. The width W2 of the long-life neutron absorbing material α disposed in this upper end region is appropriately about 0.5 to 1.51, and the disposed length 15 is about 15 to 30 aa from the insertion tip.

According to this embodiment, it is possible to effectively extend the nuclear lifetime at the inner edge of the insertion tip which receives a large amount of neutron irradiation. In other words, the reactor control rod A of this example is
Because it has a tie rod in the center and has a structure in which that part is filled with reactor water, which is a neutron moderator,
The inner edge of the upper end of each wing 1 is also exposed to intense neutron irradiation and may be worn away. However, the service life can be maintained over a long period of time due to the action of the long-life neutron absorbing material α filled over the width W and the length 15 at the inner edge.

As explained above, the reactor a, II 1il of this example
According to the L rod, it is possible to sufficiently maintain the reactivity value and to extend the service life at the same time.

Therefore, the reactivity value of the entire reactor control rod is maintained even during long-term operation of the reactor, and a sufficient margin for reactor shutdown can 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 first to third regions in the vertical direction from the insertion tip, and a long-life neutron absorber is placed in the accommodation hole of the first region where the neutron irradiation amount is high. Since the core is filled with 100% of the nuclear power, it is possible to extend the nuclear life of that part. 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, The reactivity value of the neutron absorber in the second region is maintained. Therefore, it is possible to secure a sufficient margin for reactor shutdown when all reactor control rods are fully inserted.

Moreover, since the third region is filled with natural boron, which is inexpensive and lightweight, the control rod for a nuclear reactor can be manufactured at low cost and with a light weight ω.

In addition, since the outer edge region of the wing, where the amount of neutron irradiation is especially high, is filled with a long-life neutron absorbing material, the nuclear lifetime in the outer edge portion can be extended.

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 the increase in enrichment corresponding to the high burnup of nuclear reactor fuel is resolved, and the safe shutdown function of the nuclear reactor is guaranteed.

On the other hand, since the nuclear power life can be significantly extended, it can be widely used in nuclear reactors with long operating cycles, and the economic efficiency of nuclear couplant operation can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view of one embodiment of the nuclear reactor control rod according to the present invention, and FIG. A graph showing the axial distribution of the reactor shutdown margin during period operation, Figure 2 (F3
) 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. It is a graph showing the axial distribution of reactor shutdown margin when operated for a period of time in comparison with a conventional example. DESCRIPTION OF SYMBOLS 1...Wing, 2...Connecting member, 3...Handle, 4...Accommodation hole, A...Reactor control rod, H.
...Insertion tip, ...Total length in the radial direction of the core, α...Long-life neutron absorption port, β...Highly reactive neutron absorption material,
γ...Natural boron, ■...First region, ■...Second
Area, ■...Third area, 1...Length of the first area,
A2... Length from the lower end of the second region to the insertion tip, (3
... Length of the third region, 14 ... Length of the outer edge of the wing that fills the long-life neutron absorption material, i5 ... Length of the inner edge of the wing that fills the long-life neutron absorption port difference. Applicant's agent Hata Kugami Hata
Upper end (shoulder, side door stop margin) (A) (B) Upper end in Figure 2 (C)

Claims (1)

[Claims] 1. The inner ends of a plurality of rectangular wings are integrally connected to each other via a connecting member, and an accommodation hole bored in the width direction of the wing is inserted from the insertion tip of the wing. In a control rod for a nuclear reactor, which is arranged in multiple rows over a length L in the longitudinal direction, and in which the accommodation holes are filled with a neutron absorbing material, the plurality of accommodation holes located at the insertion tips of the wings are provided with long-life type rods. A first region is formed by filling a neutron absorbing material, a second region is formed in the vertical direction adjacent to the first region, and the length from the lower end of the second region to the insertion tip is at least 1/4 L or more. , filling the accommodation hole located in the second region with a highly reactive neutron absorbing material having a large neutron absorption capacity, and forming a third region adjacent to the second region to the end in the insertion direction,
The accommodation hole located in the third region is filled with natural boron, and a long-life neutron absorber is filled in the region of the outer edge of the wing, which is at least 1/2L in length from the insertion tip in the longitudinal direction. A control rod for a nuclear reactor, characterized in that it is filled with. 2. The control rod for a nuclear reactor according to claim 1, wherein the wing has a region filled with a long-life neutron absorbing material near the upper end of the inner edge. 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 rare earth oxides such as The described control rod for a nuclear reactor. 4. The highly reactive neutron absorber is made of boron (B) with a mass number of 10.
The control rod for a nuclear reactor according to claim 1, which is boron carbide enriched with -10). 5. Highly reactive neutron absorbing material is europium oxide (E
The control rod for a nuclear reactor according to claim 1, which is a sintered body containing u_2O_3) as a main component.