JPH01203994A - Control rod for nuclear reactor - Google Patents

Abstract

PURPOSE:To increase the stop margin of the nuclear reactor effectively by putting a long-life type neutron absorber diluting alloy in a neutron absorber filled space on its insertion tip side and filling a neutron absorber except the long-life type in the hole of the diluting alloy. CONSTITUTION:The 1st area X of a wing 15 has an insertion tip area X1 irradiated with intense neutrons, a high reaction area X2 adjoining to said area X1, and an insertion terminal area X3. Then the long-life type neutron absorber diluting alloy 20 obtained by diluting, for example, a long-life type neutron absorber with a diluting material such as zirconium is filled in the area X1. One storage hole 21 is formed in the wing width direction within a range of about 5mm from the insertion tip. Boron carbide which swells by neutron high irradiation is not filled in this storage hole 21, a gas plenum pat is filled in at least one storage hole 21 at the area X11 on the tip insertion side of the area X1, and a hafnium material 22 is filled in the storage hole of the area X12. Consequently, the nuclear reactor stop margin is increased effectively.

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 controls the reactor power of a light water reactor such as a boiling water reactor, and particularly relates to a control rod for a nuclear reactor that controls the reactor power of a light water reactor such as a boiling water reactor. increase,
This article relates to control rods for high-reactivity, long-life nuclear reactors that have a long service life.

(Prior art) A conventional control rod 1 for a boiling water reactor is shown in FIGS. 9 and 1.
As shown in FIG. 0, a large number of neutron absorbing rods 5 are loaded into a plurality of wings 4 formed by fixing an elongated U-shaped sheath 3 to a central tie rod 2. Neutron absorption rod 5
is prepared, for example, by filling a stainless steel cladding tube with boron carbide (84C) powder as a neutron absorbing material.

When this nuclear reactor control rod 1 is inserted into the reactor core of a boiling water reactor, etc., the neutron absorbing material filled in the sheath 3 is irradiated with neutrons and gradually loses its neutron absorption ability. 1 is periodically replaced after being operated for a predetermined period of time.

By the way, t, IJ used in the core of a nuclear reactor
The III rod is not uniformly irradiated with neutrons over the entire surface of each wing; for example, the insertion tip region and the outer edge region of each wing are subjected to intense neutron irradiation. Therefore, the neutron absorbing material filled in that region absorbs a large amount of neutrons and is consumed faster 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, it is uneconomical to discard the entire reactor control rod as radioactive waste. On the other hand, if the 11J control rod for the nuclear reactor is replaced frequently, the replacement work takes a long time, which reduces the operating rate of the reactor and causes a major economic disadvantage. There is also a risk that radiation exposure will increase the most on the last day of the crop.

In order to resolve such concerns, nuclear reactor control rods have been developed in which a long-life neutron absorbing material such as hafnium, which has a long nuclear life, is partially placed in the area of the control rod that is subject to intense neutron irradiation. The inventor has developed this.

This nuclear reactor ff1lJ m rod is JP-A RFR453-
As disclosed in Japanese Patent No. 74697, it has a hybrid structure in which long-life neutron absorbers are placed at the tip and rabbit ends of the wings. This hybrid type nuclear reactor control rod has achieved a lifespan approximately twice that of a conventional control rod.

On the other hand, in conventional A11TLL 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 each area in the axial direction is adjusted to be equal. As mentioned above, the reactivity varies over time due to non-uniform neutron irradiation,
At the end of a nuclear reactor's operating cycle, there is a possibility that the reactor shutdown margin will partially decrease.

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 (subcritical trace) in the reactor core axis direction is determined by the design specifications of the fuel assembly or the reactor operating method. Although there will be slight differences depending on the situation, the distribution will basically be as shown in Figure 5 (A>. In other words, the reactor shutdown margin will be large at the upper and lower ends of the core, while it will be minimum at a position slightly below the upper end. Takes a value.

Possible causes of this are as follows.

When the effective length of the reactor core in the axial direction is L, the bubble rate (void skewer) during operation is high, especially in the vicinity of the upper end region of the reactor core from the position 3/4 L from the lower end of the reactor core to the upper end. Since the power density of uranium (LJ-235>
There is a relatively large amount of residual a. Further, the generated air bubbles (voids) cause a hardening phenomenon of neutron radiation. As a result, the plutonium production reaction (neutron absorption reaction) is promoted. For this reason, after the reactor has been operated, the concentration of fissile material in the upper part of the reactor core increases, causing a relative reduction in the reactor shutdown margin in that area.

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 along with this, there is a strong demand for control rods for nuclear reactors that have a long nuclear life and a large margin for reactor shutdown.

(Problem to be solved by the invention) When conventional nuclear reactor control rods are used in a nuclear reactor loaded with highly enriched nuclear fuel, the reactor shutdown margin is relatively reduced, and the reactor control rods are required to be used for each short operation cycle. Rods must be replaced frequently. However, replacing control rods for a nuclear reactor 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 for control rod replacement occur frequently, and the shutdown periods (111) are prolonged, resulting in a significant drop in the operational efficiency and economic efficiency of the nuclear reactor. Additionally, administrative effort can be significantly increased.

The present invention has been made in consideration of the above-mentioned circumstances, and it increases the reactivity of the portion where subcriticality becomes shallow during reactor shutdown, effectively increasing the reactor shutdown margin and prolonging the nuclear life. The purpose of this research is to provide a control rod for a nuclear reactor with high reactivity and long life.

[Structure of the invention]

(Means for Solving the Problems) A control rod for a nuclear reactor according to the present invention has an atom structure in which a tip structure member and a terminal structure member are connected by a tie rod, and a metal sheath is fixed to the tie rod to form a wing. In the reactor control rod, the neutron absorbing material filling space formed in the wing is divided into a first region on the insertion tip side and an iT2 region on the insertion end side adjacent to the first region, and the first region has a high reactivity region containing a long-life neutron absorber diluted alloy obtained by diluting a long-life neutron absorber with a diluent, and a plurality of holes are bored in a row in the diluted alloy, and the above-mentioned The hole is filled with a neutron absorbing material other than the long-life neutron absorbing material.

Further, in the control rod for a nuclear reactor according to the present invention, the high reactivity region formed in the first region is a space with a length of at least approximately 1/4 of the axial length of the neutron absorbing material filling space; The high-reactivity region is divided into a high-reactivity, long-life region on the insertion tip side and a high-reactivity, long-life region on the insertion end side. The 11 degrees of the neutron absorbing material is changed in the direction of decreasing, and the diluent is made of a substance containing zirconium or titanium as a main component.

Furthermore, the Ill W rod for nuclear reactors of the present invention is made of gold TA ￥J
The neutron absorbing material filling space in the sheath is formed with a first region having a length of at least 1/4 or more of the total length of the filling space from the insertion tip to the insertion end, and a long-life neutron absorbing material is formed in this first region. accommodating a diluted alloy and forming a row of horizontal holes extending in the wing width direction in the diluted alloy, and the horizontal hole near the insertion tip of the diluted alloy forming a gas blennium;
At least one horizontal hole on the insertion end side following this horizontal hole is filled with a long-life neutron absorbing material, and the insertion end side next to the horizontal hole filled with this long-life neutron absorbing material is subcritical when the reactor is shut down. Each horizontal hole in the region where the depth becomes shallow is filled with a neutron absorbing material such as boron carbide with long holes or a dense pitch between the holes, and furthermore, the horizontal hole on the insertion end side of the first region following these horizontal holes is filled with a neutron absorbing material such as boron carbide. A neutron absorbing material is arranged, and a second region on the insertion end side of the first region is filled with a neutron absorbing material such as boron carbide.

Furthermore, in order to achieve the above-mentioned object, the control rod for a nuclear reactor according to the present invention has an atom structure in which a tip structure member and a terminal structure member are connected by a tie rod, and a metal sheath is fixed to the tie rod to form a wing. In the reactor control rod, a long-life neutron absorber diluted alloy is housed in the neutron absorber filling space formed in the wing over almost the entire length from the insertion tip side to the insertion end side, and the long-life neutron absorber diluted alloy is formed in the diluted alloy. The accommodation hole is filled with a neutron absorbing material such as boron carbide.

(Function) This control rod for a nuclear reactor is divided into a first region on the insertion tip side and a second region on the insertion end side. A long-life neutron absorber diluted alloy, such as a hafnium alloy, is diluted with a diluent contained in a metal sheath, and multiple holes are drilled in a row, and 8 holes are filled with pellet-shaped or powdered medium other than hafnium. A neutron absorbing material is filled to form a high reactivity region, and neutron absorbing rods filled with a neutron absorbing substance such as boron carbide are arranged in the second region to provide a high reactivity r! In the IT4 region, the long-life neutron absorbing material and powdered or pellet-like neutron material contained in the diluted alloy increase the reactivity of this part, effectively increasing the reactor shutdown margin, and increasing the long-life neutron absorption material. Since the absorbing material and the neutron absorbing material share the absorption of neutrons, a longer life can be achieved.

In addition, the insertion tip region of each wing, where the amount of neutron irradiation is especially high, is filled with long-life neutron absorbing material.
Its neutron absorption ability does not decline over a long period of time and its nuclear lifespan is long. Therefore, the life of the reactor control rod as a whole can be significantly extended.

Furthermore, the long-life neutron absorber, which has a long life and is expensive and has a high specific gravity, is diluted with a diluent that has a low specific gravity, and the required amount is l' l [! This reduces the manufacturing cost and weight of the entire reactor control rod, making it possible to backfit it into existing plants.

Furthermore, due to the complementary and cooperative neutron absorption effect of the long-life neutron absorber such as hafnium contained in the diluted alloy as the base material and the neutron absorber filled in the accommodation hole, the reactivity value is high and the life is long. It is. In addition, it has a large specific gravity (
13,3) By creating a solid-state alloy with the necessary amount of long-life neutron absorbing material such as hafnium, and using a diluted alloy diluted with a diluent such as zirconium or titanium, which has a low specific gravity, physical Chemically stable and lightweight, it can be easily backfitted into existing nuclear reactors.
can do.

In this reactor control rod, more neutron absorbers are placed in areas where subcriticality becomes shallow during reactor shutdown, and long-life neutron absorbers are placed in areas where neutron irradiation is extremely high. In addition, the gas plenum was arranged as optimally as possible in areas other than these two, so the neutron absorbing material contained gas such as helium released when it reacted with neutrons, suppressing the gas pressure and reducing the mechanical life. It's improving.

(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.

The overall appearance of the nuclear reactor control rod of the present invention is substantially the same as the conventional control rod shown in FIG. This reactor control rod 1
0, as shown in FIG.
A deep O-shaped metal sheath 14 is fixed to each protrusion of the tie rod 13 to form a wing 15. The inside of the metal sheath 14 of the wing 15 is formed as a flat and elongated space filled with a neutron absorbing material. The insertion tip side and the insertion end side of the wing 15 are fixed to the tip structure member 11 and the end structure member 12, respectively, thereby reinforcing the mechanical strength.

The tip structure member 11 is integrally provided with a handle 16 for operation, and is also provided with guide rollers 17 that guide the control rod 10 in and out of the reactor core.

Further, the sheath 14 fixed to the tie rod 13 is provided with a large number of water holes (not shown) in its longitudinal direction, and the moderator can freely flow through the sheath 14 through these water holes. It looks like this.

Each sheath 14 accommodates neutron absorbers having various neutron absorption characteristics depending on the characteristics of the nuclear reactor.

This reactor control rod 10 has an effective length corresponding to the axial height of the reactor core (corresponding to the axial length of the neutron absorbing material filling space), and has an effective length corresponding to the axial height of the neutron absorbing material filling space. The first region X is formed to have a longitudinal length 11 of 1/2·L. The length Jl of the first region X in the longitudinal direction may be approximately 1/4 or more. wing 15
A second region as a normal neutron absorption region is formed on the insertion end side adjacent to the first region X on the insertion end side.

The first region X of the wing 15 has an insertion tip region X1 that receives strong neutron irradiation, a high reactivity region X2 adjacent to this insertion tip region x1, and an insertion end region x3. The insertion tip region x 1 has a length of, for example, about 51 or more and 32α or less from the insertion tip of the neutron absorbing material filling space to the insertion end side, and is determined by the usage conditions of the nuclear reactor control rod 10. This insertion tip region It may be filled with a long-life neutron material absorbing and diluting alloy 20 diluted with a diluent such as IF4.5), and this insertion tip region x 1 constitutes a tip long-life section.

On the other hand, in the reactor control rod 10, approximately 5
The range up to aR is constantly irradiated with neutrons from the reactor core, and the neutron flux changes significantly. At least one receiving hole 2 formed
1 is made into the blenheim part of the cavity, and boron carbide (84
G) is avoided. This is because if swelling occurs due to filling with 84C, a large stress will be generated in the accommodation hole 21, causing cracks in the base material, and the integrity of the control rod 10 is expected to be impaired.

In FIG. 1, the insertion light f! of the insertion tip region×1 is shown. a(
At least one accommodation hole 21 in the X1 part of III is inserted into the gas plenum part, and a hafnium material 22 in which the neutron absorbing material is not substantially diluted, for example, is inserted into the accommodation hole in the X12 part.

This accommodation hole (horizontal hole) may be filled with a long-life neutron absorbing material whose main neutron absorbing material is a rare earth oxide such as europium oxide or dysprosium oxide, or with silver-indium-cadmium (silver-indium-cadmium). AQ-I n-Cd
) May be filled with an alloy material. When a long-life neutron absorber dilution alloy 2o using hafnium is used as the base material for the insertion tip region x 1, the neutron absorption effect is large because it contains hafnium. Since the material is diluted with zirconium with a specific gravity of .5 and titanium with a specific gravity of 4.5), its neutron absorption life is reduced compared to long-life neutron absorbers that are not diluted with a diluent. In order to improve
Long in the accommodation hole of the section! It is preferable to fill the mold with hafnium material 22 as a sample absorbing material. When a long-life neutron absorbing material, such as a hafnium material, is used as the base material of the insertion tip region x 1, there is no need to fill the accommodation hole in the X12 portion.

On the other hand, in the combustion management of a nuclear reactor, adjustment of the relative position between the fuel assembly and the control rod is carried out every 15 to 16 α, which is the effective length of the reactor core divided into 24 equal parts. The length 12 is preferably set to a unit length of 15 to 161 or 30 to 32α, which is twice the unit length. This insertion tip region × 1, especially the X11 part, usually has a small contribution to the reactor shutdown margin, so boron carbide <84
There is no need to add other neutron absorbing substances as in 0).

In addition, the high reactivity region x2 of the first region An insertion end region x3 that is broadly divided and extends in the wing width direction is formed on the insertion end side of the high reactivity section x22.

The high reactivity long-life region X formed in the high reactivity region x 2 of the first region X and the high reactivity region x 22 have approximately the same longitudinal length, but The length may be set so that (insertion tip area x 1 + high reaction scar long life area x 21) and (high reaction area x 22) are approximately the same, or may be set to other length ratios. .

In any case, in the high reactivity region x 2 of the first region
24. Plate-shaped long-life neutron absorber diluted alloy made by diluting a long-life neutron absorber such as hafnium with a diluent.
25 is accommodated. Of these, high reactivity long life part x 21
In the example shown in FIG. 1, the diluted alloy 24 accommodated in the diluted alloy 20 is molded integrally with the diluted alloy 20 disposed in the insertion tip region x 1, and contains hafnium (Hf) contained in the diluted alloy 20.24.
is, for example, 50 cents by weight (wt%).

This diluted alloy 20.24 is an alloy with a specific gravity of 9.9, which is obtained by diluting hafnium as a long-life neutron absorbing material with zirconium (Zr) as a diluent. Also, high reactivity section x 2
The long-life neutron-absorbing diluent alloy 25 housed in 2 has, for example, 20 cents of hafnium, and has a specific gravity of 7, which is obtained by diluting this hafnium with zirconium as a diluent.
．． 9 alloy. A plurality of horizontal holes 26 extending in the width direction of the wing 15 are arranged in each diluent alloy 24, 25 in a row with equal diameter and equal pitch in the longitudinal direction of the control rod 10. Inside each horizontal hole 26, except for the insertion tip region x 1, the diluted alloy 2
A neutron absorbing material 28 different from the long-life neutron absorbing material contained in 4.25 is filled. This neutron absorbing material 28 is made of boron compounds such as natural boron (B), boron carbide (B4C) which is concentrated boron-10 (''B), boron titanide (BN>), europium oxide, dysprosium oxide, gadolinium oxide, etc. It is a powder or pellet material whose main neutron absorbing substance is a rare earth oxide such as samarium oxide, a mixture of a rare earth oxide and hafnium oxide, or a compound of boron and a rare earth element.

In addition, the concentration of long-life neutron absorbers such as hafnium contained in the long-life neutron absorber diluted alloy 24.25 placed in the high-reactivity area x 2 is shown in Figure 1. It changes stepwise in the life part X21 and the high reactivity part X22,
An example was shown in which the concentration of neutron irradiation was high in the high-reactivity long-life section x21, and lower in the relatively low-reactivity high-reactivity section x22, but the content concentration of this long-life neutron absorbing material was It is also possible to change it continuously.

Furthermore, the blade tip of the wing 15 in the first region X portion is subjected to intense neutron irradiation along with the insertion tip region x1. For this reason, a long-life neutron absorbing rod 3 such as an elongated flat hafnium material is provided on the open end side (wing false end side) of the horizontal hole 21.26 formed in the insertion tip region x1 and the high reactivity region x2.
0 is inserted, and the opening of the horizontal hole 21.26 is closed.

Each horizontal hole 21.26 is communicated with each other by a gap 26 between the long-life neutron absorbing rod 30, and the gas pressure in each horizontal hole 21.26 is equalized, while the long-life neutron absorbing material diluted alloy 20, 24, and 25 are curved to wrap around the neutron absorbing rod 30 after inserting the neutron absorbing rod 30 into the open ends of the horizontal holes 21, 26. It is sealed by welding as shown in C).

The base material of the high-reactivity part X adjacent to the insertion end side of the high-reactivity long-life part is generally smaller than that of the high-reactivity long-life section It has become. The reactivity value is only slightly inferior to area x1 and x21 parts. That is, the high reactivity portion x22 is a high reactivity region.

An insertion end region x 3 is formed on the insertion end side adjacent to the high reactivity region TaX2 where the subcriticality of the first region X is shallow, and this region x 3 has a length of 13 (2
A gap 31 extending in the wing width direction is formed except for the adjacent border S9 aI
1 is filled with metal wool made of hafnium or the like.

This gap 31 is, for example, 0.5 in the longitudinal direction of the wing 15.
It has a length l of about ~1.51ff. Part 14 is the first
Then, it absorbs the expansion and contraction of the second regions X and Y due to thermal cycles or neutron irradiation, and the long-life neutron absorbing material 32 of the X31 section is brought into close contact with the second region Y side, thereby reducing the gap where the neutron absorbing material does not exist. It has been reduced as much as possible.

By the way, &IJ III rod 10 for nuclear reactor is wing 1
A second region Y is formed on the insertion end side adjacent to the first region X of No. 5. This second area Y is the first area X of the wing 15.
The neutron absorbing rods 33 are arranged in the metal sheath 14 in the second region Y in the wing longitudinal direction, and are arranged in rows in the wing width direction. This neutron absorption rod 33 is made of stainless steel with a circular or rectangular cross section. A powdered or pelleted neutron absorbing material such as 84C is filled into the cladding tube made of No. 4.

Among the neutron absorption rods 33 arranged in the second region Y, one to three neutron absorption rods arranged at the outer edge of the wing 15 may be replaced with hafnium rods as necessary.

Furthermore, when the neutron absorption rod 33 filled with a neutron absorption material such as 84C is arranged in the second region Y of the wing 15,
Since a plug which is a neutron non-absorbing material is attached to the top of the neutron absorbing rod 33, a non-neutron absorbing material region is inevitably formed structurally, and if the adjacent boundary part x 31 does not exist, the first and second
The neutron absorber-free space between regions x and Y is expanded,
Causes reactivity loss. That is, if the space in which no neutron-absorbing substance exists becomes long, the integrity of the neutron-absorbing rod 33 will be impaired and the nuclear lifetime will be affected, so it is necessary to make the space as short as possible. In view of this relationship, the long-life neutron absorbing material 32a is placed and fixed on the top of the neutron absorbing rod 33 in the insertion end region x 3 of the first region X, so that the gap due to space etc. does not become large.

Next, in FIG. 1, as an example, a long-life neutron absorber diluted alloy 20.24 used for the base material of the insertion tip region IIi x 1 of the first region X and the high reactivity long-life section x 2° Using a diluted alloy with a specific gravity of 9.9 in which 50 weight percent (wt%) hafnium is diluted with zirconium, 20 weight percent (wt%) hafnium is used as the base material of the high reactivity part X22 of the high reactivity region X2. Long-life neutron absorber diluted alloy 2 with a specific gravity of 7.9 diluted with
5, and each horizontal hole 26 arranged at an equal pitch in the high reactivity region x2 is filled with B4C, and each horizontal hole 21 in the X12 portion of the insertion tip region X is filled with hafnium 22. Hafnium (H) contained in the reactor control rod 10
f) The axial distribution of ffi and B4Cff1 is shown in Figure 2 (A).
and (B).

Hafnium is a long-lived neutron-absorbing element, and B4C is a neutron-absorbing substance with a relatively short lifetime but a high reactivity value. Insertion tip side of first region X (insertion arrow #i region
Since the neutron irradiation r is high in the high reactivity long life part x 21) of the first region
In the high-reactivity section x 22), the content concentration is kept low to suppress weight increase and cost increase due to Hf.

The concentration of Hf disposed in the first region
It is desirable that the content is 0 wt% or more.

If the concentration of Hf is 20 wt% or less on the insertion end side of the first region The insertion tip of the first region
,,,) side rHflflJ becomes less than 50wt%,
Problems may arise in terms of long life. t-1fff
A decrease of 1 degree indicates a relative increase in the neutron absorption rate of 84G as shown in FIG. 6(B), and since B4C is not a long-life neutron absorber, the neutron absorption lifetime becomes short.

In addition, in FIG. 1, since the horizontal holes filled with 84C are arranged at equal dimensions and at equal pitches, B4Cff1
are almost equal in the high reactivity region x 2 of the first region X.

Next, the operation of the AI control rod for a nuclear reactor will be explained.

This reactor control rod 10 divides the wing 15 into a first region X on the insertion end side and a second region Y on the insertion end side adjacent to the first region X, and the first region X is neutron! ! A long-life neutron absorbing material 20 with increased f concentration is placed in the insertion tip region x 1 that constantly receives radiation, creating a long-life region, and the insertion end side following this insertion tip region X1 is a high reactivity region. ×
A large number of horizontal holes 26 are arranged in rows in the longitudinal direction of the wing in the long-life neutron absorbing material diluted alloy 24 housed in this X21 section. Powdered or pelleted neutron absorbing material 2 such as boron carbide with concentrated natural boron or boron-10 in 26
8, it is possible to increase the reactivity of the X21 part, where the degree of subcriticality becomes shallow during reactor shutdown, and increase the reactor shutdown margin.

In addition, a long-life neutron absorbing material diluted alloy 24 such as a hafnium plate and a B4C% neutron absorbing material 28 are placed in this high-reactivity long-life section x 21 to create a multiple hybrid and increase the amount of neutron absorbing material. Therefore, Figure 5 (B) and (C
) As shown in 1, a high reactivity can be obtained, and the absorption of neutrons can be shared between different neutron absorbers 24 and 28, and the long-life neutron absorber diluted alloy 24 has a large share of neutron absorption. Since the neutron absorption rate of the other neutron absorbing material 28 is reduced, it can be used for a long period of time, and its life can be extended. As a result, the high reactivity of 1q is increased by 5 to 10% compared to conventional reactor control rods, and the reactivity is increased by 2.5 to 3
．． It is possible to extend the service life by about 0 times.

In this reactor control rod 10, the reactivity region x 2 of the first region An example in which absorbent diluted alloy 24.25 is used and each hole 26 of this diluted alloy 24.25 is uniformly filled with B4C28 is shown in FIG. 6(A). In this case, the neutron absorption rate ( ) is the plate thickness t of the diluted alloy.
, the hole pitch p, and the hole diameter d, but in a control rod of suitable dimensions for a boiling water reactor (BWR), for example, Hf-
When a Zr diluted alloy is used, this is shown in FIG. 6(B).

When Hf is not included in the base material, neutron absorption is performed only by B4C. When the Hf concentration increases, the neutron absorption rate of B4C suddenly decreases, the neutron absorption rate of Hf increases, and the neutron absorption rate of (84C+Hf) increases as a whole.

Hf content is from around 20wt% (84C111f)
The neutron absorption rate of increases slowly and shows saturation characteristics. Therefore, in areas where the neutron absorber is not very large and only the reactivity value needs to be increased, there is not much need to increase the Hf content of the Hf'-Zr diluted alloy.

On the other hand, the insertion tip side of the first region X (X1 region and X21 section)
In areas where long life is required, such as (Hf+84G
), it is necessary to increase the neutron absorption rate of Hf
The higher the temperature is, the better the Hf concentration is, for example, 9qwt.
i more than %! (Even if the temperature is 715 degrees, there is no significant effect on the neutron absorption rate, so realistically, a culm degree of 5 qwt% or more, for example, 7 qwt% is sufficient.

In addition, Hf contained in the long-life neutron absorber diluted alloy
The relationship between the specific gravity of c4 degrees changes almost linearly as shown in Figure 6 (C), and from Figure 6 (A) and (B), the Hf' concentration that meets the operating conditions of the reactor control rods is determined. It is determined.

Next, a second embodiment of this nuclear reactor control rod is shown in FIG. 7(A).
, (B) and FIG. 8.

The overall configuration of this nuclear reactor control rod 10A is wing 15.
The reactor control rod 1 shown in FIG. 1 except for the first region X of
Since it is not different from 0, the explanation will be omitted. The reactor υ control rod 10A shown in the second embodiment has wings 15 as shown in FIG.
The structure is as shown in A) and (B). The difference from the first embodiment lies in the configuration of the first region X.

In the first example, the first region
It may be divided into an X21 part and an X22 part and fixed by welding or the like. ), HfF 4 degrees higher on the ×21 side, X22
The horizontal holes formed in each diluted alloy 24 and 25 were uniform (same shape, same size, and same pitch). That is, the insertion end side of the first region

On the other hand, in the second embodiment, the base material long-life neutron absorber diluted alloy 40 accommodated in the first region
A long life region and a high reactivity region are formed in the axial direction by changing the shape of the storage holes (horizontal holes) formed in the diluted alloy 40 and the pitch between adjacent storage holes. The insertion tip region X and the insertion end region x3 of the first region
Same as the example. The insertion tip region x1 is divided into x11 and x12 parts from the insertion tip in the same manner as in the first embodiment.

In this second embodiment, the high reactivity region X of the first region X is
It is divided into a large reactivity long life section X'21 on the insertion tip side, an extra large reactivity section x'22 in the middle, and a high reactivity section X' on the insertion end side. The reactivity of the 21 parts of X' and the reactivity of the 122 parts of X' do not need to be very high.

Therefore, the X122 portion of the high reactivity region
A long-life neutron absorber housed in a metal sheath with a slightly larger pitch between storage holes to provide sufficient mechanical strength to the diluted alloy (base material), and a neutron absorber housed in each horizontal hole. Even if B4C, which has a high reactivity value as a steel, swells when exposed to a large number of neutron irradiations, it is designed to exhibit a certain level of proof strength. In this part, by increasing the ratio of Hf to 84C, the share of the neutron absorption rate of 84C is reduced, so that a longer life can be achieved. The reactivity value hardly decreases even if the ratio of Hf to B4C decreases a little, and when this part is filled with B4C powder, the packing density may be slightly lower than the normal density, for example, 60% TD. With this level of packing density, a swelling space is secured within each hole when irradiated with neutrons, so
It is possible to alleviate the stress generated in each hole and to delay the timing of stress generation, which is suitable for extending the life.

Roughly speaking, in order to make the packing density of 84C powder approximately 70% of the theoretical density, multiple types of neutron absorbing materials with different particle sizes (
B4C powder, etc.) must be mixed and filled, but 6
At about 0% TD, no consideration is needed for mixing unless the particle size is very fine or particularly large. Furthermore, since the base material is perforated in the horizontal direction, the problem of reduced reactivity due to powder deposition does not occur. Since the base material contains long-life neutron absorbing material 1-1 f, even if the structure is such that deposition occurs, even if a space is created where no neutron absorbing material such as 84C exists due to deposition. Since Hf in the base material takes over neutron absorption, reactivity loss and neutron flux peaking do not pose a problem.

The extra-large high-reactivity region x'22 with two high-reactivity regions is formed into a long hole by connecting several holes, and the long hole is filled with B4C powder. Various shapes can be considered for the elongated hole, and some examples are shown in FIG.

If the elongated hole is filled with 84C powder, more 84C can be filled as a neutron absorbing material, so a reactivity value can be obtained. By making the holes elongated, the Hf111 degree in the base metal substantially decreases, and the contribution rate of Hf to neutron absorption decreases, but B
Since the contribution rate of neutron absorption by 4C increases significantly,
High reactivity can be achieved. If the actual depth of Hf decreases, it is not suitable for extending the lifespan, but X122
In general, the neutron irradiation dose in the section is smaller than that in the insertion tip region x 1 or the high reactivity long-life section You can do something like this.

The neutron irradiation chamber of the high reactivity section x'23 in the high reactivity region First, the pitch in the direction of adjacent holes is made slightly smaller, and B4C
The filling port is only slightly larger than before. Depending on the core, it may be the same as the conventional one. In addition, the code|symbol 43 is a protrusion for support.

In this case, the first region X forms a high reactivity and long life region,
Among them, the insertion tip region x 1 and the insertion tip region x 21 of the high reactivity region X form long-life regions.

FIG. 8(A) or G) shows the first area X of the wing 15.
FIG. 8 (A>
Δ is the same as that shown in Figure 7 (B), and Δ is the same as that shown in Figure 8 (8
) of each horizontal hole 41 formed in the high reactivity region x 2 of the diluted alloy 40B, a plurality of adjacent horizontal holes are grouped h1 to h.
, and the pitch between the horizontal holes 41 of each group is reduced. The diluted alloy 400 shown in FIG. 8(C) has elongated holes 42 formed by interconnecting the horizontal holes of each group shown in FIG. 8(B).

Furthermore, as shown in the diluted alloy 710D in FIG. 8(D), a small-diameter horizontal hole 43, a normal horizontal hole 41, and a long hole 44 are combined, and the diluted alloy 40E in FIG. 8(E) has a high A small-diameter horizontal hole 45 is bored between the long holes 44 of two reactivity regions. Furthermore, the horizontal holes in the high reactivity region X2 are shown in Figure 8 (
A rectangular hole 46 may be used as shown in the diluted alloy 40F in F), or a modified rectangular hole 47 and a triangular hole 48 may be combined as shown in the diluted alloy 40G in FIG. 8(G). In addition, each storage hole may be a horizontal hole of various shapes.

In each of the diluted alloys 40, a large amount of neutron absorbing material such as 84C is filled in the portion where the subcriticality becomes shallow when the nuclear reactor is shut down to increase the reactivity.

Further, the packing density of B4C filled in each horizontal hole of the diluted alloy 40 can be set to 30 to 65% of the theoretical packing density especially at the high insertion tip side of the neutron source 11). In existing control rods, 84C powder is filled with 70% TD ± 5% TD, but if the filling amount of B4C powder changes by about 5% TO, the neutron irradiation amount to keep the swelling stress the same will change by about 20%. It is possible that 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 increased by π.

As shown in FIG. 8 (A) to (G), diluted alloy 40A
~ If a horizontal hole is drilled in 40G, there is virtually no problem of B4C powder deposition, so it is possible to lower the density to some extent, and when filling 70% of 84C powder as in the past, It is necessary to use a mixture of 84C powders with different particle sizes, but at around 60% TD or less, only one type of B4C powder is required, which has a cost reduction effect and does not require particle size control. becomes.

On the other hand, if the particle size of the B4C powder is set to 30% TD or less, B-10 is quickly consumed due to neutron reaction, which is inappropriate for extending the service life. Furthermore, although it is difficult to achieve no sedimentation with low density packing, this can be easily overcome by reducing the particle size of the powder up to 30% TD of 84C powder.

The nuclear reactor control rod 10B may be configured as shown in FIGS. 9(A) and 9(B).

This nuclear reactor control rod 10B has a long-life neutron absorber diluted alloy 50°51 over almost the entire length from the insertion tip to the insertion end in the neutron absorber filling space formed in the gold sheath 14 of the wing 15. May be accommodated. In FIGS. 9(A) and (B), a long-life neutron absorber diluted alloy 50.51 is disposed in the first ffi region X,
It is divided into those arranged in the second area Y. The long-life neutron absorber diluted alloy 50 disposed in the first region X is almost the same as the diluted alloy 40 disposed in the first region X in FIG. The same reference numerals (symbols) are given and explanations are omitted.

In addition, the long-life neutron absorbing material diluted alloy 51 disposed in the second region Y is a diluted alloy diluted with a diluent of a HD-type neutron absorbing material such as hafnium, such as zirconium, and hafnium contains 2 wt% or more. . This diluted alloy 51
An example of this is natural zirconium. Natural zirconium has hafnium of about 2.5 to 3. O
It has about wt%. A neutron absorbing material 52 different from a long-life neutron absorbing material such as 84C is filled in a horizontal hole as a housing hole formed in this diluted alloy 51.

Furthermore, the neutron absorbing material filling space formed in the wing 15 of the reactor control rod 10B is shown in FIGS. 9(A) and 9(B).
As shown in the figure, it is not necessary to separate the first region may be accommodated. In this case, the diluted alloy may be integrally molded over the entire length or divided into several parts, and the diluted alloy may be accommodated except for at least one of the upper and lower ends of the neutron absorber filling space. In addition to filling the neutron absorbing material shown in FIGS. 9(A) and 9(B) in the horizontal holes serving as accommodation holes for the diluted alloy, it is also possible to fill the same neutron absorbing material made of 84C or the like in each horizontal hole. good.

At this time, the long-life neutron absorber diluted alloy that is filled over the entire area of the neutron absorber filling empty circuit is a long-life neutron absorber diluted alloy such as hafnium diluted with a diluent such as zirconium or titanium. For example, when hafnium is an alloy with zirconium, it contains about 1Qwt% of hafnium, and when it is an alloy with titanium, it contains about 3Qwt% of hafnium.

〔Effect of the invention〕

As described above, the nuclear reactor IT according to the present invention! In the J control rod, the wing of the control rod is divided into a first region on the insertion end side and a second region on the insertion end side adjacent to this first region, and the first region has a long-life type inside the sheath. A long-life neutron absorber diluted alloy made by diluting a neutron absorber with a diluent is accommodated, and a high reactivity region is formed in the first region, and a plurality of long-life neutron absorbers are disposed in this high reactivity region. By forming holes in a row and filling each hole with a neutron absorbing material other than hafnium, the reactivity in the region where subcriticality becomes shallow during reactor shutdown is increased, effectively increasing reactor shutdown margin. In addition, by using at least two types of neutron absorbers, a long-life neutron absorber and a neutron absorber other than hafnium, in the high reactivity region, the nuclear energy can be increased by complementary and cooperative neutron absorption effects. A long-life control rod with high reactivity and a large reactor shutdown margin can be provided.

Furthermore, in the first region, a long-life neutron absorber diluted alloy, which is a long-life neutron absorber diluted with a diluent with a small specific gravity, is placed at least in a limited manner to reduce the weight of control rods and make them subcritical when the reactor is shut down. It is possible to increase the reactivity of the shallow part, extend the life, and reduce the overall use of the long-life neutron absorber, which reduces costs.
Furthermore, the weight reduction allows it to be backfitted into existing plants.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of a control rod for a nuclear reactor according to the present invention, and FIG. 2 (A) and FIG. 2 (B) are a sectional view of a wing of the control rod. A diagram showing the axial distribution of hafnium fit and 84CM housed in the wing, Figure WS3 (A> is an enlarged view of the first region of the wing shown in Figure 1, Figure 3 (B) is shown in Figure 3 (
The cross-sectional view taken along the line ■-■ of A), the fourth factor (A), (B), and (C) are the cross-sectional view along the line A-A, line B-B, and C- of Fig. 3 (A).
A plan sectional view taken along line C, FIG. 5(A) is a diagram showing the subcriticality of a conventional nuclear reactor control rod, and FIG. 5(8) is a diagram showing the neutron absorption characteristics of the nuclear reactor control rod of the present invention. Figure 5 (C) is a diagram comparing the subcriticality of the conventional nuclear reactor control rod and the nuclear reactor control rod of the present invention, Figure 6 (A>
is a cross-sectional view of a long-life neutron absorber diluted alloy (Hf-Zr diluted alloy) accommodated in the first region of the wing;
B) and (C) are diagrams showing the relationship between the hafnium concentration contained in the diluted alloy, the neutron absorption rate, and the ratio m, and Figures 7 (A) and (B) are diagrams showing the control rod for a nuclear reactor according to the present invention. 8(A) to 8(G) are cross-sectional views showing the second embodiment of the invention, and FIGS. 8(A) to 8(G) respectively show modified examples of the long-life neutron absorber diluted alloy accommodated in the first region of the wing of the Hill m bar. 9(Δ) and (B) are views showing a third embodiment of the control rod for a nuclear reactor according to the present invention, FIG. 10 is a perspective view showing a conventional atomic control rod 111111, and FIG. is a plan cross-sectional view of a conventional υ control rod for a nuclear reactor. 10.10A, 10B... υJilt rod for nuclear reactor, 1
1...Tip structure material, 12...Terminal disease construction material, 13...
・Tie 0d, 14... Gold ff1l sheath, 15...
・Wing, 20.24.25.40.50.51...
・S life type neutron absorber diluted alloy, 21.26...Horizontal hole (accommodation hole), 22.32...Long life type neutron absorber, 28°52...Neutron absorber, 30... long'ti
Life-type neutron absorption rod, 40A to 40G...Long-life neutron absorption material diluted alloy. x3 u (ε) Fig. 4 111 Juizunohara J7F scrap type S # glue - JR1 @ I) II child Shuuripi ladder top j wao top end
Horizontal stripes (A) (15) (C) $5 figure (C) $6 figure $lθ figure

Claims (1)

[Claims] 1. The tip structure member and the end structure member are connected by a tie rod,
In the nuclear reactor control rod in which a metal sheath is fixed to the tie rod to form a wing, a neutron absorbing material filling space formed in the wing is arranged in a first region on the insertion tip side and adjacent to the first region. and a second region on the insertion end side, and the first region has a high reactivity region containing a long-life neutron absorber diluted alloy obtained by diluting a long-life neutron absorber with a diluent, A control rod for a nuclear reactor, characterized in that a plurality of holes are bored in a row in the diluted alloy, and the holes are filled with a neutron absorbing material other than the long-life neutron absorbing material. 2. The high reactivity region formed in the first region is at least approximately 1/4 of the axial length of the neutron absorbing material filling space, and this high reactivity region is the high reactivity region on the insertion tip side. The diluted alloy contained in the first region is divided into a long-life region and a high-reactivity region on the insertion end side, and the concentration of the long-life neutron absorber contained therein decreases from the insertion end side to the insertion end side. 2. The control rod for a nuclear reactor according to claim 1, wherein the diluent is a substance containing zirconium or titanium as a main component. 3. The neutron absorbing material filling space in the metal sheath is formed with a first region having a length of at least 1/4 or more of the total length of the filling space from the insertion tip to the insertion end, and this first region has a long life. A type neutron absorber diluted alloy is accommodated, horizontal holes extending in the wing width direction are formed in a row in the diluted alloy, and the horizontal hole near the insertion tip of the diluted alloy forms a gas plenum, which continues to the horizontal hole. At least one horizontal hole on the insertion end side is filled with a long-life neutron absorbing material, and a region adjacent to the horizontal hole filled with the long-life neutron absorbing material is where the degree of subcriticality becomes shallow at the time of reactor shutdown on the insertion end side. Each horizontal hole is filled with a neutron absorbing material such as boron carbide with a long hole or a dense hole pitch, and the neutron absorbing material is placed in the horizontal hole on the insertion end side of the first region following these horizontal holes. Claim 1, wherein neutron absorbing rods filled with a neutron absorbing material such as boron carbide are arranged in the second region on the insertion end side of the first region.
The described control rod for a nuclear reactor. 4. Connect the tip structure material and the end structure material with tie rods,
In a nuclear reactor control rod in which a metal sheath is fixed to the tie rod to form a wing, long-life neutrons are emitted over almost the entire length from the insertion tip side to the insertion end side in the neutron absorbing material filling space formed in the wing. 1. A control rod for a nuclear reactor, characterized in that a neutron absorbing material such as boron carbide is filled in a housing hole formed in the diluted alloy, and a neutron absorbing material such as boron carbide.