JPH01202693A - Nuclear reactor control rod - Google Patents

Abstract

PURPOSE:To plan long term of nuclear lifetime by arranging a long-lived neutron absorber in housing holes of the insert edge area of a wing contributing to reactivity value, and enlarging the hole volume of the housing holes in the area where subcritical degree is shallow during reactor stop. CONSTITUTION:A wing 11 is partitioned into an insert edge area X contributing to reactivity value, an high-reactivity area Y where subcritical degree is shallow during reactor stop and an area X in the neighborhood of the area Y. Next, each housing hole 17 of the area X and the housing channel of a wing outside are filled with long-lived neutron absorbers 20, 21 such as hafnium. Further, each hole 18 of the area Y, for example, is made as a long hole and the filling quantity of an absorber 23 is enlarged while the housing holes 19 of the area Z are filled with an absorber 25. The neutron absorbing capacity of the area X is maintained for a long time while the reactivity value of the area Y is held. Therefore, the long term of nuclear lifetime can be planned.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear reactor control rod that adjusts and controls nuclear reactor output, and particularly relates to a long-life type control rod that has a high reactor shutdown margin. Regarding control rods for 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 by placing a connecting member in the center, and formed inside the wing in the width direction. A new type of control rod has been developed in which a large number of accommodation holes are filled with powder of a neutron absorbing material such as boron carbide (84G) 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.

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. For example, the insertion tip region and blade tip (outer edge) region of each wing are Subject to intense neutron irradiation. Therefore, the neutron absorbing material filled in that area absorbs a large amount of neutrons and is consumed faster than other areas, ending its nuclear life earlier. Therefore, even though the neutron absorbing material filled in other areas still has sufficient nuclear life left, it is uneconomical to discard the entire reactor control rod as radioactive waste. On the other hand, if the control rods for a nuclear reactor are replaced frequently, the replacement work takes a long time, which reduces the operating rate of the reactor and causes a major economic disadvantage.

In addition, there may be cases where there is a risk that the radiation dose of workers 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, non-uniformity in the amount of neutron irradiation causes variations in reactivity over time, and there is a possibility that the reactor shutdown margin may partially decrease at the end of the reactor operating cycle.

°In other words, when the reactor is operated for a predetermined WJ using the above-mentioned reactor control rods, 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 reactor Although there are some differences depending on the driving method, basically the distribution is as shown in FIG. 3(A). In other words, the reactor shutdown margin is large at the upper and lower ends of the core,
On the other hand, the minimum value is taken 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 increases after the reactor is in operation, and the margin for reactor shutdown in that region decreases.

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 control rods for nuclear reactors that have a long life and a large margin for reactor shutdown.

(Problems to be Solved by the Invention) When conventional nuclear reactor control rods are employed in a nuclear reactor loaded with highly enriched nuclear fuel, the reactor control rods must be frequently replaced every short operating cycle. When replacing reactor control rods, the reactor must be shut down and the time required for replacement
A complicated work is required to remove in advance from the core a large number of fuel assemblies arranged around the JI ill rod. Therefore, reactor shutdowns occur frequently to replace control rods, and the extended shutdown period reduces the operating efficiency of the reactor.
Management effort may increase significantly while economics will be significantly reduced.

The present invention has been made 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, especially in the area where the reactor shutdown margin tends to decrease. Control for a long-life nuclear reactor that can inexpensively and effectively increase reactor shutdown margin and prolong the nuclear life by partially disposing neutron absorbing material with high or long life. The purpose is to provide sticks.

[Structure of the invention]

(Means for Solving the Problems) A control rod for a nuclear reactor according to the present invention connects the inner ends of a plurality of rectangular wings with a plurality of connecting members spaced apart in the longitudinal direction of the wings, and In a control rod for a nuclear reactor, accommodation holes drilled in the direction are arranged in a row from the insertion tip to the insertion end of the wing, and the accommodation holes are filled with a neutron absorbing material. A long-life neutron absorber is arranged in the accommodation hole at least in the insertion tip region, and the hole volume per unit length in the longitudinal direction of each accommodation hole is arranged in the region where subcriticality becomes shallow during reactor shutdown. is larger than the pore volume in other regions.

The present invention also includes connecting the inner ends of the plurality of rectangular wings with a plurality of connecting members at intervals in the wing longitudinal direction,
In the control rod for a nuclear reactor, accommodation holes bored in the width direction of the wing are arranged in a row from the insertion tip to the insertion end of the wing, and the accommodation hole is filled with a neutron absorbing material. The first ff on the insertion tip side where the amount of neutron irradiation is extremely high! 11, and the second f! which is adjacent to this first region and whose subcriticality becomes shallow during reactor shutdown! divided into four regions and a third region adjacent to the second region on the insertion end side,
A long-life neutron absorbing material is placed in the accommodation hole in the first region, and a second
The accommodation hole in the third region is filled with a neutron absorbing material such as boron carbide, and a part of the accommodation hole formed in the third region is a control rod for a nuclear reactor formed as a gas plenum.

(Function) The MH rod for a nuclear reactor according to the present invention has a large number of accommodation holes drilled in the width direction of each wing arranged in the longitudinal direction of the wing, and the reactivity value of at least the insertion tip of the wing is increased. Since a long-life neutron absorbing material is placed in the contributing accommodation hole, the insertion tip, which is exposed to neutron irradiation even if it is inserted into the reactor core during reactor operation or withdrawn, has a long neutron absorption capacity. It has a long nuclear lifespan and does not deteriorate over time.

In addition, when the reactor control rod is used with the reactor control rod fully inserted into the reactor core, the subcriticality corresponds to the second flj region provided vertically adjacent to the first region of the reactor control rod, where the degree of subcriticality becomes shallower. Since the nuclear reaction inside the fuel assembly is suppressed by the void phenomenon, there is a large amount of nuclear fuel remaining in that area. Moreover, the concentration of fissile material is decreasing due to plutonium production reactions. However, by changing the pitch, shape, etc. between accommodation holes in the second region, the hole volume per unit length in the longitudinal direction of the wing was increased compared to the hole volume of other its, so the filling amount of the neutron absorbing material was able to increase. Therefore, even after the reactor is operated for a long JI period, the reactivity value of the neutron absorbing material in the second region is maintained. Therefore, a sufficient margin for reactor shutdown can be ensured when all reactor control rods are fully inserted.

Further, since the expensive neutron absorbing material having a long life or high reactivity is provided in a limited amount to the minimum required amount, the manufacturing cost of the entire control rod for a nuclear reactor can be reduced.

(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 shows a nuclear reactor control rod 10 according to the present invention, and this nuclear reactor control rod 10 has a plurality of rectangular wings 11 made of, for example, a stainless steel plate. The nuclear reactor control rod 10 has a plurality of coupling members 12 spaced apart from each other in the axial direction, and the inner ends of the plurality of wings 11 are coupled via the coupling members 12 to form a cross-shaped cross section. Ru.

An operating handle 13 is fixed to the insertion tip of the wing 11. The wing 11 may be made of a long-life neutron absorber diluted alloy containing hafnium, such as a hafnium-zirconium alloy or a hafnium-titanium alloy, instead of the stainless steel plate.

In this case, the effect of absorbing phi trons due to hafnium is added, and the life of the control rod 10 can be extended and the reactivity can be increased.

A terminal structural member 15 is provided on the insertion end side of the nuclear reactor control rod 10, and a connecting portion to a speed limiter and a control rod drive mechanism (not shown) is provided at the lower part of the terminal structural member 15.

The wing 11 of the reactor control rod 10 receives strong neutron irradiation on the insertion tip side and the outer edge side (11 end side), and has a first region including an insertion tip region 111x that contributes to reactivity value, and this first region. It is divided into a high reactivity region Y, which is a second region adjacent to the reactor and whose subcriticality becomes shallow during reactor shutdown, and a third region Z adjacent to this reactivity region Y on the insertion end side.
In each wing 11 of the nuclear reactor control rod 10, a large number of accommodation holes 17, 18, and 19 are bored as horizontal holes extending in the width direction of the wing from the insertion tip to the insertion end of the wing.

On the other hand, the insertion tip region formed in the first region of the wing 11! 4! x is formed to have a length of about 5 cm or more and about 321 cm or less from the insertion tip to the insertion end side of the axial effective length of the reactor control rod, and preferably the insertion tip region X is about 5 rJ or more from the insertion tip It is said to be approximately 161 or less. Each accommodation hole 17 formed in the insertion tip region X and the longitudinal accommodation groove located in the area of the outer edge of the wing are filled with a long-life neutron absorbing material 20, 21 such as hafnium. In this nuclear reactor control rod 10, water is filled in the void formed on the inner end side of the wing 11, but if this void is wide, the thermal neutron flux increases significantly. The end side has a width of about 0.5 to 1°5C11 from the inner edge and a constant length from the insertion tip to the insertion end, for example, 15 to 1.
A long-life neutron absorbing material of about 40α may be arranged.

Further, on the outer edge side of the wing in the first region, the width 15 of the region filled with the long-life neutron absorbing material 21 is, for example, about 1 to
However, in the control rod 10 for atomic bombs whose main purpose is to increase the reactivity, the long-life neutron absorber 21 often has a reactivity value inferior to that of 84G, so the region width 15 should be set to 0. It may be about .5 cm. The length 11 of this region width 15 portion may be short in the case of a control rod whose main purpose is to increase the reactivity, but the main purpose is to insert it into the reactor core during reactor operation and control the reactor operation. In this case, the length must be at least 1/4 of the effective length in the axial direction. If the control rod usage method cannot be specified, set the area width 15 to 0.5~
About 11, if (j!4-1.) is about 1/2L,
It is not detrimental to the purpose of achieving high reactivity without causing a decrease in reactivity value. The outer edge of the wing 11 is welded, etc. to the opening side of each accommodation hole with a long-life neutron absorbing material 21.
etc. to be closed so as to be closed.

By the way, as long-life neutron absorbing material 20.21,
One or more substances selected from rare earth oxides such as hafnium metal, hafnium-zirconium alloy, hafnium-titanium alloy, silver-indium cadmium alloy, europium oxide, dysprosium oxide, samarium oxide, etc. A solid or powdered neutron absorbing material is used, and the optimal combination is determined by considering neutron irradiation intensity, operation period, etc.

In addition, the second region Y of the wing 11 is the reactor control rod 10
In order to achieve high reactivity value, the hole volume per unit length in the wing longitudinal direction of each accommodation hole 18 is made larger than the hole volumes of the insertion tip region X and the third region Z. Specifically, by making each accommodation hole 18 in the second region Y long, the filling amount of the neutron absorbing material 23 such as 84C is increased, and the subcriticality becomes shallow during reactor shutdown. Increases reactivity,
High reactivity.

The region where subcriticality becomes shallow during reactor shutdown is shown in Figure 3 (A>
As shown in the figure, the neutron irradiation amount in this region Y is relatively high, but it is considerably lower than that in the insertion tip region B4C can be used as a neutron absorbing material suitable for. If a boron compound such as B4C enriched with boron-10, boron nitride, or europium hexapolide (EuB6) is used, the reaction degree can be further increased. By using europium oxide as the main neutron absorbing material and using a neutron absorbing material that does not contain boron, it is possible to achieve a high reactivity and a long life at the same time. However, eurobium oxide is expensive and is not suitable for achieving high reactivity compared to enriched boron, so eurobium oxide is used in the region adjacent to the insertion tip region X in the high reactivity region (second region) Y. Most suitable for use alone.

In this reactor control rod, by making the accommodation hole in the second region Y longer, it is possible to fill a larger amount of high-reactivity neutron absorbing material (a typical example is B4C).

Moreover, the accommodation hole 18 formed in the second region Y is shown in FIG.
As shown in A), when the diameter of the accommodation hole 18 is constant, if the distance between hole centers (pitch between holes) is changed, the amount of filling wA and the reactivity value (relative value) of the neutron absorbing material 23 change to the second level. Figure (B
) can be changed as shown. - In a typical design example of this type of Ill Ill bar, the plate thickness t is 8 m, the hole diameter d is 6 tuts, and the distance between hole centers (pitch: p) is 8 m. Therefore, when the pitch p is changed under these conditions, the amount of neutron absorbing material and the resulting change in the reactivity value are shown in FIG. 2(B). When the diameter and pitch of the accommodation holes are the same, the amount of neutron absorbing material is approximately 1.3 times that of the conventional one, and when the accommodation holes almost overlap, the plate has a thickness (t-d)/2.
When the absorbent material is divided into two sheets and filled with absorbent material in the form of a plate (at its limit), it becomes approximately 1.7 times as large. Relative changes in reactivity values cannot be uniformly discussed because they are affected by core configuration, fuel enrichment, water gap width, burnable poison, etc.; however, as an example, the It looks like a two-dot chain line. In this example, the accommodation holes are adjacent to each other without overlapping (
4% at p=d), approximately 7.5 when fully overlapped
% increase.

In the actual design of the control rod 10 for a nuclear reactor, the plates of the wing 11 cannot be completely divided, and some kind of partition (bonding) material is required between the plates, so the hole pitch p= Although a state of 0 is impossible, the idea of reducing this pitch p is to group several adjacent accommodation holes, reduce the inter-hole pitch p between them, and make the distance between other groups within the base material. If the configuration is as shown in FIG. 1 where the (wing) is left, it can effectively be made into a p-4 to 5 shoe (d-6M), which is fully achievable. FIG. 2(B) shows that the reactivity value can be improved by about 5% in this case.

The above is the principle of improving reactivity value in the present invention. Assuming that the region Y where the reactivity value becomes large has a longitudinal length O, the axial neutron absorption characteristic distribution will be as shown in FIG. 3(B). Therefore, the axial distribution of subcriticality during reactor shutdown is improved as shown in Figure 3 (A) to Figure 3 (C), and there is no part where the subcriticality is extremely shallow, and it is almost uniform in the axial direction. be converted into

By the way, each accommodation hole 19 in the third region Z of the wing 11 is filled with a neutron absorbing material 25 such as 84C, but each accommodation hole formed within L/2 from the insertion end side in the third region Z Since there is no need to increase the reactivity value in a part of 19, a gas plenum may be used instead of being filled with a neutron absorbing material. In this case, it is desirable that the gas plenums be provided so as to avoid the accommodation holes 19 that are adjacent to each other.

In addition, each accommodation hole formed in the second region Y of the wing 11 can be modified in various ways as shown in FIGS. It is designed to be filled with

Among these, each accommodation hole 1 formed in the second region Y, which is a high reactivity region of the wing 11A shown in FIG.
8a is a region in which the pitch between holes is arranged more densely (smaller) than in other regions.

The wing 11B shown in FIG. 4(8) has a second region (
Of each accommodation hole 18b formed in the high reactivity region) Y,
A plurality of mutually adjacent holes are grouped, and the pitch between the holes in each group (h1 to ho) is made small. In FIG. 4(C), the accommodation holes 18C of the wing 11C are connected to each other in each group to form elongated holes.

Furthermore, as shown in the wing 11D in FIG. 4(D),
Small diameter accommodation hole 17d1 normal accommodation hole 19d and long hole 1
Even if 8d is combined, the wing I in Fig. 4(E)
As shown in IE, a small-diameter accommodation hole 18e2 may be bored between the long holes 18e1, which are high reactivity regions, and the accommodation hole 18e2 in the high reactivity region may be formed in the wing 11F in FIG. 8(F). As shown, it may be a rectangular hole 18f. Furthermore, like the wing 11G in FIG. 4(G), the modified rectangular hole 18
g1 and the triangular hole 18g2 may be combined, or may have various other shapes.

Further, the filling density of B4C filled in each accommodation hole of the wing 11 can be set to 30 to 65% of the theoretical filling density on the insertion tip side where the amount of neutron irradiation is particularly high. In existing control rods, B4C powder is 70% TD (theoretical density) ± 5% T.
Although it is filled with O, the filling amount of 84C powder is about 5% T.
It is conceivable that the amount of neutron irradiation at which the swelling stress remains the same changes by about 20% due to a change in D. This change in swelling stress depends on the particle size of the B4C powder, so it is not necessarily unambiguous, but by reducing the density, the time until swelling stress occurs can be delayed.

As shown in FIGS. 4(A)-(G), wings 11A-
If an accommodation hole is drilled in 11G, the problem of B4C powder deposition is virtually eliminated, so it is possible to achieve a somewhat lower density. , it is necessary to use a mixture of B4C powders with different particle sizes, but at around 60% TO or less, only one type of B4C powder is sufficient, which has a cost reduction effect and eliminates the need for particle size control. Become.

On the other hand, if the particle size of the B4C powder is set to 30% TO or less, 8-10 is quickly consumed due to neutron reaction, which is inappropriate for extending the service life. Furthermore, although it is difficult to achieve low density packing without sedimentation, this can be easily overcome by reducing the particle size of the B4C powder up to 30% TD.

〔Effect of the invention〕

As described above, in the nuclear reactor control rod according to the present invention, the accommodation holes bored in the width direction of each wing are arranged in a row in the longitudinal direction of the wing, and the reactivity value of the wing is Since a long-life neutron absorbing material is disposed in at least the accommodation hole in the insertion tip region, which contributes to the insertion tip region, the insertion tip portion, which is exposed to strong neutron irradiation, does not lose its neutron absorption ability over a long period of time and has a long nuclear life.

In addition, the wing used for the 8a rod for nuclear reactors has a hole volume per unit length in the longitudinal direction of the wing of each accommodation hole formed in the region where the degree of subcriticality is shallow compared to other regions, and neutrons are Since the absorber is filled, the reactivity value of the neutron absorber in the second region is maintained even after long-term operation of the reactor, and the reactor shutdown margin is reduced when all the reactor υ control rods are fully inserted. can also be secured in sufficient quantities.

Further, since the expensive neutron absorbing material having a long life and high reactivity is provided in a limited amount to the minimum necessary amount, the manufacturing cost of the entire control rod can be reduced.

[Brief explanation of the drawing]

FIG. 1(A) is a diagram showing the pitch relationship between the accommodation holes formed in the wings of the nuclear reactor control rod according to the present invention, and FIG. 2(B) is Pitch between accommodation holes, filling amount of neutron absorbing material, and reactivity value (relative value)
3(A) is a diagram showing the axial subcriticality of a conventional nuclear reactor control rod, and FIG. 3(B) is a diagram showing the axial direction of a nuclear reactor control rod according to the present invention. Diagram showing neutron absorption characteristics,
FIG. 3(C) is a diagram comparing the subcriticality of the present invention and the conventional control rod for nuclear reactors, and FIG. It is a figure which shows each modification of the wing. 1.Im child 1flllltllll rod, 11.11A~1
1G...wing, 12...coupling member, 15...
Terminal structural material, 17, 18.19...accommodating hole, 18a,
18b, 18c, 18d, 18e, 18e2.18
f, 18a, 18a2... accommodation hole, 20.21.
...Long-life neutron absorber, 23.25...Neutron absorber. Applicant's agent Hisashi Hatano 1st (,'l) 0 2 466 (mm) Hole pitch! (B) Atsushi 2 Figure Yo Ko Kaminagi Shufusa (Hara JP stoppage allowance) (A) ?Naru Idate] (C-n

Claims (1)

[Claims] 1. The inner ends of a plurality of rectangular wings are connected by a plurality of connecting members spaced apart in the longitudinal direction of the wings, and accommodation holes bored in the wings in the width direction are connected to the inner ends of the wings. In a nuclear reactor control rod, which is arranged in a row from the insertion tip to the insertion end, and in which the accommodation hole is filled with a neutron absorbing material, long-life neutrons are provided in at least the accommodation hole in the insertion tip region of the wing that contributes to the reactivity value. In addition to arranging absorbing material, the hole volume per unit length in the longitudinal direction of the wing of each accommodation hole installed in the region where subcriticality becomes shallow during reactor shutdown was increased compared to the hole volume in other regions. A nuclear reactor control rod characterized by: 2. Connect the inner ends of a plurality of rectangular wings with a plurality of connecting members at intervals in the wing longitudinal direction, and connect the accommodation hole bored in the wing in the width direction from the insertion tip of the wing to the insertion end. In the control rods for a nuclear reactor, the control rods are arranged in a row across the range, and the accommodation holes are filled with a neutron absorbing material,
The wing is divided into a first region on the insertion tip side where the neutron irradiation dose is extremely high, a second region adjacent to this first region where the degree of subcriticality becomes shallow during reactor shutdown, and a second region on the insertion end side in this second region. and an adjacent third region, filling the accommodation holes in the first region with a long-life neutron absorbing material and filling the accommodation holes in the second and third regions with a neutron absorbing material such as boron curd, A control rod for a nuclear reactor, characterized in that a part of the accommodation hole formed in the third region is formed as a gas plenum.