JPH02176494A - Control rod for reactor - Google Patents

Abstract

PURPOSE:To increase a shutdown margin inexpensively and effectively and to make a nuclear lifetime long by a method wherein a neutron absorber having a long lifetime is disposed partially in an area wherein the shutdown margin tends to lower. CONSTITUTION:In a control rod for a reactor, the packing quantity of a neutron absorber 23 such as B4C is increased by making long each accommodation hole 18 in a second area Y, thereby the reactivity in the area wherein a subcritical degree becomes small during stoppage of the reactor is increased and a high-reaction change is caused. The area wherein the subcritical degree turns small during stoppage of the reactor is formed in the second area Y, and although a neutron exposure dose in this area Y is high relatively, it turns lower considerably than that in an insertion end area X. Therefore, B4C can be used as the neutron absorber which is nit suitable for making the lifetime long, but is suitable for a large-reactivity change. When europium oxide is used as a main neutron absorber and another neutron absorber not containing boron is used together, the large-reaction change and also a long lifetime can be attained.

Description

Detailed Description of the Invention (Objective of the Invention) (Industrial Field of Application) The present invention provides a
[This article relates to I rods, and particularly to control rods for long-life nuclear reactors that have a large reactivity value during reactor shutdown.

(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 arranging a connecting member in the center. A new type of control rod has been developed in which a large number of accommodation holes formed inside the rod are filled with powder of a neutron absorbing material such as bocon carbide (B4C) 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 region absorbs a large number of neutrons and is consumed more quickly than other regions, reaching the end of its nuclear lifetime earlier. Therefore, even though the neutron absorbing material filled in other areas still has sufficient nuclear life left, there was a risk that the entire reactor control rod would have to be disposed of as radioactive waste. On the other hand, if the number 11 control rods for the reactor are replaced frequently, the replacement work will take a long time, which will reduce the operating rate of the reactor and cause a major economic disadvantage. In addition, there is a possibility that the amount of ll1iFJ received by the worker may 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 shown in the figure, the unevenness of the neutron irradiation amount causes variations in reactivity over time, and there is a possibility that the margin for reactor shutdown may partially decrease at the end of the nuclear reactor's operation.

In other words, the axial distribution of the reactor shutdown margin (subcriticality) when the reactor is operated for a predetermined period using the above reactor control rods is determined by the design specifications of the fuel assembly or the reactor operating method. Although there are slight differences depending on the situation, the distribution is basically as shown in Figure 2 (A>.In other words, the reactor shutdown margin is large at the upper and lower ends of the core, while the minimum is at a position slightly below the upper end. The 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 No. 9 area from the 4L position to the upper end,
The void ratio during operation is high and the power density of the reactor is slightly reduced, so the remaining amount of uranium (U-235) with a mass number of 235, which is a fissile material, is relatively large, and the generated air bubbles ( (void) causes 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 relatively high 53 days after the reactor is operated, and the margin for reactor shutdown in that region decreases.

On the other hand, due to the demand for improved operating economy, it is inevitable that the current nuclear reactors will shift to higher burn-up of nuclear fuel and longer operating cycles. 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 high reactivity value when the reactor is shut down.

(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. 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, as the outage period for control rod replacement becomes longer, the operating efficiency of the reactor decreases, I! This can significantly reduce administrative efficiency while significantly increasing administrative 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 neutron absorbing materials with a long life, it is possible to inexpensively and effectively increase the reactor shutdown margin and extend the nuclear life! The purpose is to provide control rods for long-life nuclear reactors that can be used for II.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above-mentioned problems, a control rod for a nuclear reactor according to the present invention forms a wing including a plate-shaped metal in at least a part of the neutron absorption part, and In a nuclear reactor control rod in which a metal is provided with a plurality of accommodation holes extending in the wing width direction and a neutron absorbing material is housed in the accommodation hole, a long-life neutron absorbing material is installed in the accommodation hole in the wing insertion tip area where the neutron absorbing material is large. In addition to inserting the material, each accommodation hole in the region where the subcriticality becomes shallow when the reactor is shut down is configured into an elongated hole shape, and a dimple for absorbing swelling is installed on the side of the sheet metal in which the elongated accommodation hole is formed. We have established this.

(Function) This control rod for a nuclear reactor uses a neutron absorbing element in which a neutron absorbing material is filled in a housing hole extending in the wing width direction of a sheet metal. Hafnium (Hf), silver, indium, cadmium (
AO-I n-Cd) alloy, Eu2O3, Dy2O3,
Rare earth oxides such as Gd2O3 or rare earth oxides and H
A long-life neutron absorber made of a mixed oxide with fO2 or the like is arranged. A long-life neutron absorber does not generate gas even when it absorbs neutrons, and hardly causes swelling in sheet metal. In addition, most long-life neutron absorbing materials have a nuclear long life because each atomic nucleus originally has the ability to absorb neutrons many times. Since there is no gas generation or swelling, there is almost no stress generated in the accommodation hole that accommodates the long-life neutron absorber, and the mechanical life can be extended.

In addition, when the reactor is shut down with full insertion, the accommodation hole in the fr4 region, where the subcriticality of the reactor becomes shallow, is formed into a long hole shape, and this accommodation hole is filled with B4C or B- Fill with neutron absorbing material such as 84C concentrated 10. 8-10 in 84C reacts with neutrons to form He gas and li.

) (Most of the e stays inside the B4C powder grains, causing the grains to swell and applying local force from the inside to the outside of the accommodation hole, and He released from the B4C powder grains enters the accommodation hole. Solve the problem of applying uniform force.

In addition to the excellent feature of having a large reactivity effect, B4C also has the advantage of being inexpensive and having a light enclosure, but (above)! As shown in i, it may generate internal reaction horns in the machine and shorten the mechanical life.
A single neutron capture reaction results in 1-1e or Li, which has a small neutron absorption ability, so it has the disadvantage of a short nuclear lifetime.

In this reactor control rod, by making the accommodation hole in the part where the subcriticality is 1 (1) into a long hole shape, more neutron absorbing material such as B4C powder particles is filled and the reactivity value is increased. In addition to improving the nuclear lifetime to some extent, a swelling-absorbing dimple was constructed on the side of the plate metal in the long hole so that the stress caused by the swelling of B4C in the long hole can be absorbed, so that neutron irradiation progresses. When B4C causes swelling, the dimple part is pushed out,
The force caused by the swelling of the neutron absorbing material is released by the escape of the dimple portion.

This control rod for a nuclear reactor has a structure that allows the swelling of the swelling absorbing dimples to escape from the swelling of the neutron absorbing material, so it is possible to significantly delay the occurrence of mechanical stress. (As for uniform He gas, since the technique of making each accommodation hole communicate with each other has been established, it is only necessary to solve the above-mentioned local stress). Stainless steel plates are usually used as metal plates with accommodation holes, but for example, Hf
A new stable alloy plate of a completely solid solution type such as a plate or an alloy plate obtained by diluting Hf with a diluent of Zr or Ti may be used. In this case, since the alloy plate itself has the ability to absorb neutrons, the neutron absorption rate of the neutron absorber such as 84C accommodated in the accommodation hole is reduced, and the timing of slinging of the neutron absorber is accordingly reduced. As a result, a longer mechanical life can be achieved than when using a stainless steel plate.

(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.

Control rods for nuclear reactors are basically divided into those with a sheath on the wing and those without a sheath.

A control rod for a nuclear reactor without a sheath has a neutron absorbing element fixed directly between a tip structural member and a terminal structural member. In addition, in a nuclear reactor control rod equipped with a sheath, the tip structural member and the terminal structural member are fixed with a tie rod, and a sheath with a deep U-shaped cross section is fixed to each protruding leg of the tie rod, and neutrons are absorbed within this sheath. It contains elements.

FIGS. 1(A) and 1(B) show a nuclear reactor control rod 10 according to the present invention without a sheath, and this nuclear reactor control rod 10 is made of four rectangular plates made of stainless steel plates, for example. It has a wing 11.

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. The tip structure material 1 is attached to the insertion tip of the wing 11.
3 is integrally or integrally formed, and this tip structure material 1
3, the operating handle 14 is fixed.

Wing 11 is made of Hefni ram instead of stainless steel plate.
A long-life neutron absorber diluted alloy containing hafnium, such as a zirconium alloy or a hafnium-diquine alloy, may also be used. In this case, the neutron absorption effect of hafnium is added, and the life of the control rod 10 can be extended and the reactivity can be increased.

An end structure member 15 is integrally or integrally provided on the insertion end side of the wing 11 of the D71 sub-reactor control rod 10, and a connection portion to a speed limiter and control rod drive mechanism (not shown) is provided at the bottom of this end structure member 15. is provided.

The wing 11 of the reactor control rod 10 receives strong neutron irradiation on the insertion tip side and the outer edge side (wing tip side), while the reactor control rod 10 has an insertion tip region X that makes a small contribution to the reactivity value. a high reactivity region Y, which is a second region adjacent to the first region and whose subcriticality becomes shallow during reactor shutdown; and a high reactivity region Y adjacent to the high reactivity region Y on the insertion end side. It is divided into a third area Z. Each wing 11 of the reactor control rod 10 has accommodation holes 17, 18, and 19 as horizontal holes extending in the wing width direction from the insertion tip to the insertion end of the wing. ;9 has been done.

It should be noted that the region indicated by the dashed diagonal line on the upper left side of FIG. 1(A) is the region filled with the long-life neutron absorbing material.

On the other hand, the insertion light fa formed in the first region of the wing 11
The region is about 5 cm or less from the insertion tip and about 16 cm or less. Each accommodation hole 17 formed in the insertion tip region A long-life neutron absorbing material 20.21 is filled.

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 1.51 from the inner edge and a constant length from the insertion tip to the insertion end, for example, 1.
A long-life neutron absorbing material of about 5 to 40 u may be arranged.

Further, on the wing outer edge side of the insertion tip region However, in a nuclear reactor control rod 10 whose main purpose is to increase the reactivity, a long-life neutron absorber 21 is used.
Since B4C is often inferior in reactivity value to B4C, the region width 15 may be set to about 0.51. This area width 15
The wing longitudinal length 11 of the portion may be short in the case of a control rod whose main purpose is to increase reactivity, but it may be short if the control rod is inserted into the reactor core during reactor operation and whose main purpose is to control reactor operation. For a 1M control rod for a nuclear reactor, the length must be at least 1/4 of the effective length in the axial direction. If the method of using the control rod is not specific, set the area width I5 to 0.5 to 1 cm.
If the degree (1-13> is about 1/2L), a large reactivity can be achieved without reducing the reactivity value.The outer edge of the wing 11 is attached to the opening side of each accommodation hole by welding or the like. is closed via a long-life neutron absorbing material 21 or the like.

By the way, as long-life neutron absorbing material 20.21,
1 selected from rare earth oxides such as hafnium metal (11f), octium-zirconium alloy, hafnium-ditane alloy, silver-indium-cadmium alloy, europium oxide, dysprosium oxide, sumari-cum oxide, etc. A solid or powdered neutron absorbing material containing one or more types of substances is adopted, and the neutron irradiation intensity,
The optimal combination is determined by taking into consideration the operating period, etc.

In addition, the second gA area Y of the wing 11 is the reactor control center 1.
In order to obtain a large reactivity value of 0, each accommodation hole 18 is formed into a long hole shape, and the hole volume per unit length in the longitudinal direction of the wing is equal to the insertion tip area iIl! x and the pore volume of the 3rd!1 region Z. Specifically, by making each accommodation hole 18 in the second region Y a long hole, the capacity of the neutron absorbing material 23 such as 84C is increased by 14 m, and the reaction in the region where the degree of subcriticality becomes shallow during reactor shutdown is increased. This increases the degree of reaction.

The region where subcriticality becomes shallow during reactor shutdown is shown in Figure 2 (A).
As shown in Figure 2, it is formed in the second region Y, and although the neutron irradiation dose in this region NY is relatively high, 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, europium oxide is expensive and is not suitable for achieving high reactivity compared to enriched boron, so europium 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 18 of the second region 11Y elongated, it is possible to fill it with 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 hole diameter of the accommodation hole 18 is constant, when the distance between hole centers (hole pitch) is changed, the filling Ll'-reactivity value (relative value) of the neutron absorbing material 23 changes to the third figure(
It can be changed as shown in B).

In a typical design example of this type of control rod, the plate 19t is 8M
The R1 hole straightness 1d is 6#I, and the hole center open circuit @ (pitch: p) is 8#I. 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. 3(B). When the diameter and pitch of the accommodation holes are the same, the amount of neutron absorbing material is about 1.3 times more than the conventional one, and when the accommodation holes almost overlap,
Therefore, the plate is divided into two pieces of thickness (t-d)/2,
When the absorbent material is filled in a plate shape (lii limit), it is approximately 1.
It will be 7 times more. Relative changes in reactivity value are affected by core configuration, fuel enrichment, water gap width, burnable poison, etc., so it cannot be discussed uniformly, but as an example, Figure 3 ( It looks like the two-dot chain line in B). In this example, the increase is 4% in the state g (p-d) where the accommodation holes are adjacent without overlapping, and about 7.5% in the state where they completely overlap.

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 there is a state of 0, the idea of reducing this pitch p is to group several adjacent convergence holes, reduce the inter-hole pitch p between them, and place the base material between other groups. If the configuration is as shown in Figure 1 where the meat (wings) is left, effectively p = 4 ~ 5 M (d =
(3 Maro), which is fully achievable. In this case, FIG. 3(B) shows that the reactivity 1iffiii can be improved by about 5%.

The above is the principle of improving reactivity value in the present invention. If the region Y where the reactivity value becomes large has a length in the longitudinal direction of 14, the axial neutron absorption characteristic distribution will be as shown in FIG. 2(B). Therefore, the axial distribution of subcriticality during reactor shutdown is improved from Fig. 2 (△) to Fig. 2 (C), and the second region where the subcriticality is extremely shallow is eliminated, and the axial distribution almost uniform.

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 840, but the third!
Since there is no need to greatly increase the reactivity value in the region formed within L/2 from the insertion end side in zone 1 Z, a part of each accommodation hole 19 is not filled with a neutron absorbing material, and instead It may be set to 26. In this case, it is desirable that the gas plenum 26 be provided so as to avoid the accommodation holes 19 that are adjacent to each other.

Further, each accommodation hole formed in the second region Y of the wing 11 is configured, for example, as shown in FIG. 4, and the neutron absorbing material of 500 ml is filled in a limited region.

Accommodation hole 1 formed in the second region IJY of this wing 11
8 is formed as follows.

First, in the second region Y of the wing 11, a long hole-shaped accommodation hole 18 is formed as shown in FIG. Form as shown. Subsequently, this accommodation hole 18 is opened as shown in FIG.
As shown in B), press so that the wing thickness becomes thinner. As a result of this suppression, the continuous hole portion of each accommodation hole 18 is crushed as shown by a broken line to a solid line, and a swelling absorbing dimple 28 is formed. After forming the dimples 28, a heat treatment is performed as necessary to release the residual stress in the continuous hole portion of each accommodation hole 18, and then neutron absorbing $423 such as 84C powder particles is placed inside each accommodation hole 18. Let it fill.

The second area Y of the wing 11 is shown in FIGS. 4 and 5 (A).
, When the reactor control rod configured as shown in (B) is inserted into the reactor core and irradiated with neutrons, the 84C powder grains serving as the neutron absorbing material will swell due to the generated He etc., and each accommodation hole 1B Press from the inside to the outside.

In this case, the continuous hole portion of each accommodation hole 18 provided in the second region bAY of each wing 11 is crushed in the thickness direction of the wing 11 to form a swelling absorbing dimple 28, ), so even if the swelling force is applied from the inside, the local stress will be reduced to almost no damage. It can swell to the state shown.

Moreover, the volume change rate due to swelling of 840 grains as a neutron absorbing material is small, and the swelling absorbing dimples 28 formed in the continuous hole portion of each accommodation hole 18 reach the state shown in FIG. 5(A). In order to recover, the 84C powder requires considerable swelling. For this reason, by forming a swelling absorbing gain pull 28 in each accommodation hole 18 in the second region Y of the wing 11, this dimple 28 absorbs the swelling of the 84C powder grains, so each accommodation hole 18 absorbs the swelling of the 84C powder grains. Even if swelling occurs, stress generation on B4C swelling can be effectively and significantly prevented.
Mechanical life can be extended.

FIG. 6 shows another embodiment of the control rod for a nuclear reactor.

The reactor control rod shown in this example is wing 11.
neutron high irradiation fri area Y1 on the tip side
and a neutral calf irradiation area Y2 on the insertion end side. Each accommodation hole 1 formed in the neutral calf irradiation area Y2
8a is almost the same as the flower shape of each accommodation hole 18 shown in FIG. 4 and FIGS. 5(A) and (B).
The difference is that the inner surface of the hole a is smoothed in advance. In this case, more B4C can be filled.

In addition, the accommodation hole 1 formed in the neutron high illuminance olJ region Y1
8b is a round blind hole crushed in the thickness direction of the wing 11 to form an elongated hole shape, and this accommodation hole portion includes:
Dimples 28a are formed to absorb swelling stress.

Further, an accommodation hole (Yokotomi hole) 17a for filling 84C is also formed in the insertion tip region X of the first region, but this accommodation hole 17a is filled with neutron high light 04 ffi lI! The hole diameter is smaller than that of the accommodation hole 18b of Y1, and the thickness of the leg 11 is increased to increase the swelling resistance. Since the insertion tip side has a particularly high neutral dried fish t)J concentration, Hf is filled as a long-life neutron absorbing material.

In one embodiment of the present invention, a nuclear reactor control rod without a sheath has been described, but the present invention can be similarly applied to a nuclear reactor control rod with a sheath.

Moreover, various other shapes are conceivable for the accommodation hole formed in the wing second ifl region of this nuclear reactor control rod.

(Effect of the invention) As described above, the υJil for nuclear reactor according to the present invention
In the rod, a long-life neutron absorber is inserted into the accommodation hole in the plate metal formed in the tip region where the large wing of the neutron absorber is inserted, and each accommodation hole in the area where subcriticality becomes shallow when the reactor is shut down is inserted. Since the hole is made into a long hole shape, the hole volume can be increased, and a large amount of neutron absorbing material can be filled, resulting in a high reactivity, and a control rod for a large reactivity, long-life reactor can be made by 1q. can.

In addition, we provided swelling-absorbing dimples on the side surfaces of the metal plate in which the elongated accommodation holes were formed, so even if the neutron absorbing material filled in the accommodation holes swells when irradiated with neutrons, this swelling will not occur. Since it can be absorbed by the swelling of the dimples, it is possible to mechanically improve Et and D life.

[Brief explanation of the drawing]

FIG. 1(A) is a diagram showing one embodiment of a control rod for a nuclear reactor according to the present invention, FIG. 1<8) is a sectional view taken along the line A-A in FIG. (A), (B), and (C) are diagrams showing changes in subcriticality, neutron absorption characteristics, and improved subcriticality in the effective length direction of the neutron absorption part of a nuclear reactor control rod, respectively. Figure (A) is a principle diagram showing an example of an elongated accommodation hole drilled in the plate metal of this reactor control rod, and Figure 3 (B) is the accommodation hole shown in Figure 3 (A). A diagram showing the relationship between the hole pitch, reactivity value, and neutron absorption characteristics. Figure 4 is an enlarged view of the second region of this reactor control rod. Figures 5 (A) and (B) ) is shown in Figure 1 (B
) and an enlarged view of part B in FIG. 4, which shows the molding procedure for the second region, and FIG. 6 is a diagram showing a modification of FIG. 5. 10... Nuclear reactor control rod, 11... Wing, 12
... Connecting member, 13... Tip structure material, 15... End structure material, 17.17a, 18. ．． 18a, 18b. 19...Accommodation hole, 20.21...Long-life neutron absorber, 23; 25...Neutron absorber (B4C),
26... Blenheim, 28... Dimple for swelling absorption, X... Insertion tip region (first region), Y...
Highly reactive region (second region), Z...inserted end chain ll1
t (third region). Yoko Shufu Upper CR1n stop trout) (Hara 1g stop nafyo) (A) (C) Figure 2 Figure 1 (,4) Breast layer Pino+! (B) Nap Nap Nap

Claims (1)

[Claims] A control for a nuclear reactor, wherein a wing including a plate metal is formed in at least a part of the neutron absorption part, a plurality of accommodation holes extending in the wing width direction are provided in the plate metal, and a neutron absorbing material is accommodated in the accommodation hole. In the rod, a long-life neutron absorbing material is inserted into the accommodation hole in the wing insertion tip area where the neutron irradiation amount is large, and each accommodation hole in the area where the degree of subcriticality becomes shallow when the reactor is shut down is configured into a long hole shape. A control rod for a nuclear reactor, characterized in that a dimple for absorbing swelling is provided on the side surface of the metal plate in which the elongated accommodation hole is formed.