JP2563434B2 - Control rod for nuclear reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a control rod for a reactor that adjusts and controls the reactor power, and in particular, may increase the weight of the entire control rod. The present invention relates to a long-life reactor control rod that does not have a high reactor shutdown margin.

(Prior Art) As a reactor control rod for controlling the output of a nuclear reactor, for example, a plurality of connecting members are arranged in the central axis direction, and four stainless steel wings are integrated in the cross direction in the connecting members. A new type of control rod has been developed in which a large number of accommodating holes formed inside the wing are filled with neutron absorber powder such as boron carbide (B ₄ C) at a uniform density.

When the control rod for this reactor is inserted into the core part of a boiling water reactor or the like, the neutron absorbing material filled in the accommodation hole is irradiated with neutrons and gradually loses its neutron absorbing capacity, so that it was operated for a predetermined period. Later it will be replaced regularly.

(Problems to be Solved by the Invention) By the way, a control rod used in a core part of a nuclear reactor does not uniformly receive neutron irradiation over the entire surface of each wing. The lateral edge region receives intense neutron irradiation. for that reason,
The neutron absorbing material filled in that region absorbs a large amount of neutrons and is consumed faster than other regions, and ends its nuclear life early. Therefore, despite the fact that the neutron absorber filled in other areas still has a sufficient nuclear life, there is an uneconomical situation in which the entire nuclear reactor control rod must be discarded as radioactive waste. If the replacement frequency is high, it takes a long time to perform the replacement work, so that the operation rate of the reactor decreases, the operating economy decreases, and the social impact is large. In addition, there is also a problem that the radiation dose to workers increases.

Further, conventional control rods for nuclear reactors are filled with neutron absorbing material at a uniform density over the entire region of the wing, and are prepared so that the neutron absorbing ability in the axial direction, that is, the reactivity becomes equal. As described above, the reactivity may vary over time due to uneven neutron irradiation dose, and the reactor shutdown margin may be partially reduced at the end of the operation cycle of the reactor.

That is, the axial distribution of the reactor shutdown margin (subcriticality) after the reactor is operated for a predetermined period using the reactor control rod is determined by the fuel assembly design specifications or the reactor operating method. However, the distribution is basically shown in FIG. That is, the reactor shutdown margin is large at the upper end and the lower end of the core, and takes a minimum value at a position slightly lower than the upper end. The possible causes are as follows.

If the axial length of the reactor core is L, it is 3 /
In the upper end region from the 4L position to the upper end, the bubble ratio (void ratio) during operation is high, and the power density of the furnace is slightly reduced. Therefore, the fissile material uranium (U-235) with mass number 235 (U-235) The residual amount is relatively large, and the hardening phenomenon of the neutron spectrum occurs due to the generated bubbles (voids). As a result, the plutonium production reaction (neutron absorption reaction) is promoted, and as shown in FIG. 4, the nuclear fission nuclide concentration in the upper part of the core increases after the operation of the reactor, and the reactor shutdown margin in that region decreases. .

On the other hand, in the future, it is inevitable that the nuclear reactors will be shifted to higher burnup of nuclear fuel and longer operating cycle from the demand for improvement of operating economy. As a concrete measure for this, the adoption of highly enriched nuclear fuel has advanced, and along with this, there is a strong demand for reactor control rods with a long life and a large reactor shutdown margin.

However, when the conventional control rods for a nuclear reactor are adopted in a nuclear reactor loaded with highly enriched nuclear fuel, the control rods for a nuclear reactor must be frequently replaced every short operating cycle. When replacing the control rod for the reactor, shut down the reactor,
The complicated work of preliminarily excluding a large number of fuel assemblies arranged around the control rod to be replaced from the core is required. Therefore, there are frequent reactor shutdowns for control rod replacement,
In addition, while the shutdown period is prolonged, the operating efficiency and economic efficiency of the reactor are significantly reduced, while the management labor may be significantly increased.

On the other hand, in order to meet the demand for longer life of control rods, the applicant has developed a remarkably excellent long-life type control rod for nuclear reactors. This reactor control rod is, as disclosed in Japanese Patent Laid-Open No. 58-55887, a neutron absorbing plate formed of hafnium, which is a long-life type neutron absorber, in each wing formed of stainless steel. It is formed by loading. The long-life neutron absorbing plate made of hafnium or the like significantly extends the life of the control rod.

However, in this reactor control rod, since the plate-shaped hafnium (Hf) metal plate, which is expensive and has a large density, is used as the neutron absorber, the total weight of the control rod is very large and expensive. The control rod drive mechanism that handles the control rod requires a design change in weight resistance, and cannot be used as it is in the conventional control rod drive mechanism.

The present invention has been made to solve the above problems, aiming to reduce the weight of the entire control rod for a reactor, and also increase the anti-concentration value, in the area where the reactor shutdown margin tends to decrease, In particular, by partially arranging the necessary minimum amount of neutron absorber with high reactivity or long life, it is possible to effectively and inexpensively increase the reactor shutdown margin and prolong the nuclear life. It is an object of the present invention to provide a control rod for a long-life nuclear reactor, which can be obtained and used as it is in an existing nuclear reactor.

[Structure of Invention]

(Means for Solving the Problems) A reactor control rod according to the present invention is a reactor control rod in which a plurality of rectangular wings are formed in a cross shape, and the wings are long-life neutron absorbing materials such as hafnium. Is formed of a diluting alloy diluted with a diluting material such as zirconium or titanium, and the accommodating hole is formed in the diluting alloy, and the neutron absorbing material is filled in the accommodating hole.

The content of the diluted alloy forming the wing is constant over the entire length in the axial direction of the wing, and the content is set to 20 to 90% by weight.

Furthermore, the dilution alloy forming the wings may be configured so that the content of hafnium gradually decreases from the core insertion tip to the insertion end.

Further, the neutron absorber filled in the accommodation hole is boron carbide.

Further, two or more regions are provided in the upper region corresponding to half of the entire length from the insertion tip in the axial direction of the wing, and the long-life neutron absorber and the high-reactivity neutron absorber are sequentially arranged from the insertion tip side of this region. Should be filled.

Also, in the upper region corresponding to half the entire length from the axial insertion tip of the wing, at least the accommodation hole located in the region of the insertion tip side, hafnium, hafnium-containing alloy, Ag-In-Cd alloy and europium oxide, While filling at least one selected from rare earth oxides such as dysprosium oxide, gadolinium oxide, and samarium oxide, most of the accommodation holes located in regions other than the above are filled with boron carbide. Characterize.

Further, in the upper region corresponding to half the entire length from the axial insertion tip of the wing, two or more regions are further provided, and the hole diameter in the axial direction of the accommodation hole located at least in the region at the insertion end side in the upper region. Is preferably larger than the hole diameter of the accommodation hole located in the lower region corresponding to half the total length from the insertion end.

Further, two or more regions are provided in the upper region corresponding to half of the entire length from the insertion end in the axial direction of the wing, and the center-to-center distance of the accommodation holes located at least in the region at the insertion end side in the upper region is It is advisable to make the accommodation holes denser by making the distance smaller than the center-to-center distance of the accommodation holes located in the lower region corresponding to half of the entire length from the insertion end.

Furthermore, the hole diameters of the plurality of accommodation holes arranged on the insertion tip side in the axial direction of the wing may be smaller than the hole diameters of the accommodation holes arranged on the insertion end side.

Further, accommodating holes filled with boron carbide may be arranged in a region corresponding to half of the entire length from the insertion end in the axial direction of the wing, and accommodating holes not filled with the neutron absorbing material may be dispersively arranged.

(Operation) According to the reactor control rod having the above structure, each wing is formed of a diluted alloy obtained by diluting a long-lived neutron absorber such as hafnium having a high density with a diluent such as zirconium or titanium having a low density. Since the diluted alloy is formed of a solid solution containing zirconium or titanium, a physicochemically stable lightweight control rod can be manufactured. Therefore, the existing control rod drive mechanism can be used as it is in a conventional nuclear reactor without changing the design of load bearing performance.

Also, as a long-lived neutron absorbing material such as hafnium contained in the diluted alloy that composes each wing, and the complementary neutron absorbing effect of the neutron absorbing material filled in the accommodation holes of each region, it can be used as a reactor control rod. The value of the reactivity is increased, the reactor shutdown margin is increased, and the nuclear life can be significantly extended.

Also, by increasing the hafnium content in the diluted alloys that make up the wings to a range of 20 to 90% by weight, depending on the neutron absorption characteristics required for reactor control rods, the overall weight of control rods can be increased. It is possible to obtain a control rod for a reactor that has a better reactor shutdown margin than before.

In addition, the amount of expensive hafnium used can be reduced to the necessary minimum by configuring the content of hafnium in the diluted alloy to decrease from the insertion tip to the insertion end according to the life characteristics required for the control rod. Is possible
It is possible to provide a control rod for a nuclear reactor that is highly economical.

Further, as described in claims 4 to 6, by appropriately changing the kind of the neutron absorbing substance to be filled in the accommodation hole arranged in the predetermined region of the wing, the reactivity value of the region,
It is possible to adjust characteristics such as reactor shutdown margin and nuclear life.

Further, as described in claims 7 to 10, the filling of the neutron absorbing material by changing the hole diameter or the center-to-center distance of the accommodation holes arranged in a predetermined region with the hole diameter or the center-to-center distance of the accommodation holes in other regions. The density can be varied, as can the properties of the region.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a front view showing an embodiment of a nuclear reactor control rod according to the present invention. The nuclear reactor control rod 1 has a plurality of coupling members 2 arranged at predetermined intervals in the axial direction. , The inner ends of a plurality of rectangular wings 3 are connected to each other in a cross shape through the connecting member 2, and the accommodation hole 4 bored in the wings 3 is inserted in the vertical direction from the insertion tip H of the wings 3. Is a control rod for a nuclear reactor arranged in multiple rows over a length L corresponding to the entire axial length of the core.
Is a long-life neutron absorber such as hafnium (Hf) made of a diluted alloy diluted with a lightweight diluent such as zirconium (Zr) or titanium (Ti), while the accommodation hole is formed in the wing 3 above. 4 is filled with a neutron absorbing material.

Here, the diluting alloy forming the wing 3 is the wing 3
The hafnium content is adjusted to be constant over the entire axial length L, and the content is set to 20 to 90% by weight.

On the other hand, the hafnium content may be gradually reduced substantially from the core insertion tip toward the insertion end, corresponding to the reactivity distribution in the axial direction.

Further, as shown in FIG. 1 and FIG. 2, the accommodation hole in each region of each wing is filled with a neutron absorber having different characteristics depending on the amount of neutron irradiation and the required reactivity value, or A gas plenum is formed.

That is, the region l ₄ of the insertion tip is large neutron irradiation amount, significantly higher reactivity worth by hafnium contained in the wings 3 is applied. Therefore, the accommodation hole 4 is used as the gas plenum 6 without filling the accommodation hole in the region l _{4 with} the neutron absorbing material.

Further, in the accommodation hole 4 of the region l ₅ adjacent to the lower end of the region l _{4 in which} the gas plenum 6 is arranged and where the neutron irradiation amount is particularly high,
The long-life neutron absorber 7 formed of a hafnium material is filled. When the region l ₅ is filled with boron carbide (B ₄ C), the life may be shortened rapidly depending on the usage of the control rod, so a hafnium material having a long life is preferable.

Further, the region l ₆ adjacent to the lower end of the region l ₅ has a relatively high neutron irradiation amount, but since it is necessary to secure a certain degree of reactivity, a high reactivity neutron absorbing material such as boron carbide (B ₄ C) 8 To fill. This is because boron carbide has a higher reactivity than hafnium material in the case of the same filling volume.

Here, as the neutron absorber 5 to be filled in the accommodation hole 4 at the tip of the core insertion, hafnium (Hf), hafnium-zirconium (Hf-Zr) alloy, hafnium-titanium (Hf-Ti)
Alloy, silver - indium - cadmium (Ag-In-Cd) alloy and europium oxide (Eu ₂ O _3), dysprosium oxide (Dy ₂ O _3), gadolinium oxide (Gd ₂ O _3), samarium oxide ( If one prepared from one or more substances selected from rare earth oxides such as Sm ₂ O ₃ ) is adopted, the life can be extended. In addition, the neutron absorbing material 5
Does not generate helium gas by reaction with neutrons, so swelling in the accommodation hole 4 is prevented, and excessive stress does not act on the wings 3.

Of the upper area l ₂ of each wing 3, areas l ₄ , l ₅ , l ₆
The region W except for is a region where the neutron irradiation amount becomes relatively small, while the subcriticality decreases during the reactor shutdown, so it is necessary to fill a large amount of highly reactive neutron absorber. , housing hole 4a to dispose, as shown in Fig. 12 (a), the center distance P from the accommodation hole 4 in the other region l _3, l ₆ and set short, or the first view, As shown in FIGS. 2 (A), 12 (C), and (D), the diameter in the axial direction is enlarged to form an elongated hole shape, and the accommodation hole 4a formed in this elongated hole diameter is formed in the lateral direction. Place them next to each other. A large amount of the high reactivity neutron absorbing material 8 is filled in the accommodation hole 4a.

Furthermore, in the lower region l ₃ of each wing 3, since a large reactivity value is not required, boron carbide (B ₄
Storage hole 4 filled with high reactivity neutron absorber 8 such as C)
And the gas plenum 6 coexist. That is, the gas plenums 6 are dispersedly arranged in the region l ₃ within 1/2 L of the axial total length L from the insertion end O of each wing 3 toward the insertion tip H,
The gas plenum 6 is formed by the accommodation hole 4 which is not filled with the neutron absorbing material. Since the reactivity value may be small in the vicinity of the insertion end O, the gas plenums 6 may be arranged relatively densely as shown in FIG.

The openings of the accommodation holes 4, 4a of each wing 3 are communicated with each other by a passage 9 provided at the outer edge of the wing 3, and the helium gas generated in each region l ₂ , l ₃ passes through the passage 9. , The gas plenum 6 provided in the regions l ₃ and l ₄ . Therefore, the helium gas pressure in the receiving holes 4 and 4a in the entire regions l ₂ and l ₃ is uniform.

As shown in FIGS. 2C to 2F, a hafnium rod 10 having a semi-cylindrical cross section is attached to the passage 9, and a wing end 11 is bent so as to wrap the hafnium rod 10 and the wing thereof is bent. The joints of the ends 11 are axially seam welded to form the integral wing 3.

As shown in FIG. 3 (A), each wing 3 is composed of a dilute alloy in which a solid solution of hafnium (Hf) and zirconium (Zr) is formed, and a receiving hole 4 is formed from the side of the dilute alloy. It is configured by filling the accommodation hole 4 with a neutron absorbing material 5 such as B ₄ C.

The reactivity value of the wing 3, that is, the neutron absorption characteristic changes depending on the plate thickness t of the Hf-Zr diluted alloy, the arrangement pitch P of the accommodation holes 4, the accommodation hole diameter D, the Hf content of the alloy material, and the like. That is, as shown in FIG. 3 (B), when the alloy material does not contain Hf, neutrons are absorbed only by B ₄ C.
Then, as the Hf content increases, the neutron absorption by B ₄ C decreases, and the total neutron absorption by both increases at a slow rate. In the composition where the Hf content exceeds 30% by weight, the growth of the total neutron absorption rate slows down, and even if the Hf content is increased thereafter, there is no great increase.

Therefore, the content of hafnium having a long life is set low in a region where the neutron irradiation dose is relatively small and only the reactivity value needs to be increased. It should be noted that the neutron absorption rate does not completely reach the saturation state due to the Hf content rate, and the reactivity gradually increases as the Hf content rate becomes higher. However, as shown in FIG. 3 (C), the specific gravity of the diluted alloy increases almost proportionally to the increase of the Hf content.
It is not a good idea to set the Hf content more than a predetermined value because the weight increase and the cost increase drastically.

On the other hand, in the region where long life is required, Hf for B ₄ C
The Hf content should be increased in order to set a large absorption ratio of H., but as shown in FIG. 3 (B), even if it is 90 wt% or more, the effect of increasing the neutron absorption is small. Therefore, the Hf content is usually determined in the range of 20 to 90 wt%, but in reality, a value of about 70 wt% is optimal.

Further, the diluted alloy forming the wings 3 is more economical when the Hf content is set differently in the upper region l ₂ which receives intense neutron irradiation and the lower region l ₃ which has a relatively small irradiation amount. In other words, the amount of expensive hafnium used can be minimized by gradually decreasing the hafnium content from approximately the tip of the core to the end O of the core.

Further, as shown in FIG. 3 (C), the specific gravity of the diluted alloy changes in proportion to the change in Hf content. Therefore, the optimum Hf content is determined in consideration of the load bearing strength of the control rod drive mechanism, the required reactivity, and the life.

Next, the operation of the reactor control rod according to the present embodiment will be described.

In a boiling water reactor, the axial fission nuclide concentration distribution curve A of the reactor core in which combustion has advanced to some extent is generally represented as shown in FIG. Since the combustion management target region of the core of the nuclear reactor is divided into four equal parts in the axial direction of the core, it is convenient to compare the control rods for nuclear reactor 1 into four equal parts.

At the lower end of the reactor core, the progress of combustion is delayed at the time of combustion, so the fission nuclide concentration value is large. On the other hand, when the axial length of the reactor core is L, the central part (2 / 4L)
From the top to the top, the hardening phenomenon of the neutron spectrum occurs due to the generated bubbles (voids). As a result, the plutonium production reaction (neutron capture reaction) is promoted, and the generated neutron flux decreases the thermal neutron flux, and this decrease causes combustion delay, so the fission nuclide concentration distribution is as shown in Fig. 4. Represented.

When the nuclear fission nuclide concentration shown in FIG. 4 exists in the core of the nuclear reactor, the neutron multiplication factor when the reactor is stopped is the axial distribution curve B shown in FIG. As the neutron multiplication factor increases, the reactor shutdown margin decreases and the subcriticality decreases. From Fig. 5, the neutron multiplication factor decreases at the lower and upper ends of the reactor core. Is a phenomenon caused by the leakage of neutrons.

FIG. 6 is an axial neutron dose distribution curve C of the reactor control rod 1 when the reactor control rod 1 according to the present invention is used. From this distribution curve C, the control rod for reactor 1
Has a region where the neutron dose rises rapidly in a very limited area at the upper end (usually about 30 cm, especially about 5 cm from the tip). The other portions are continuously and smoothly reduced toward the lower end of the reactor control rod 1.

The reactor control rod 1 according to the present invention is configured so that a satisfactory control effect can be obtained with respect to the neutron multiplication characteristic shown in FIG. 5 and the neutron irradiation amount characteristic shown in FIG. That is, at the tip of the reactor control rod 1 (total length of the regions l ₄ , l ₅ , l ₆ ; for example, about 90 cm to 95 cm), the neutron multiplication factor rises (that is, the stop margin decreases) and neutrons increase. It deals with the fact that the irradiation dose becomes high and the stop margin easily decreases.

That is, in the reactor control rod of this embodiment shown in FIG. 1, the wings 3 are formed of a dilute alloy of zirconium containing 50 wt% of hafnium, and the hafnium content in the dilute alloy is uniform over the entire axial length L. Is.

A gas plenum is provided in the upper end region of each wing 3, the type of neutron absorber (B ₄ C, haunium) to be filled in the accommodation hole is changed, and the dispersion ratio of the gas plenum is increased in the lower region to allow axial reaction. The degree value (neutron absorption characteristics) distribution is set as shown in FIG. That is, since the region l ₄ provided with the gas plenum 6 and the region l ₅ filled with the haunium material are provided at the upper end portion, a portion where the reactivity value is slightly lowered appears.
The accommodation hole 4a located in the region W is formed in a long hole shape, and the accommodation hole is filled with a large amount of B ₄ C having a high reactivity, so that a region having a high reactivity value is formed. Further, in the region from the middle part (2 / 4L) to the lower end, the reactivity value decreases toward the lower end because the arrangement ratio of the gas plenum 6 is gradually increased.

The nuclear life distribution in the axial direction of the reactor control rod of this embodiment is as shown in FIG. The reason why there is a lowered portion at the upper end of the insertion is that the accommodating hole is not filled with the neutron absorbent and the accommodating hole is arranged as a gas plenum. This is because the hafnium content is as low as 50 wt%. The part where the life is reduced is limited to a very small part of the insertion tip, and there is almost no effect on the subcriticality.

A region with a long life appears adjacent to the lower part of the region with a reduced life. Approximately 97 wt% in the accommodation hole in this area
This is because the high-concentration hafnium material is inserted and the nuclear life in that region is significantly extended.

Next, a region whose life is slightly reduced appears. The reason for this is that the arrangement pitch of the accommodation holes in the region is set large and then the accommodation holes are filled with B ₄ C. Originally, in this region, since the neutron irradiation is relatively high, hafnium material is preferable from the viewpoint of maintaining the life, but B ₄ C is used from the viewpoint of keeping the reactivity value higher.

On the other hand, when B ₄ C receives strong neutron irradiation, it causes swelling, presses the accommodation hole from the inside, and generates large stress in the wing base material. Therefore, when the accommodating hole is formed in a long hole shape, the base material for connecting both surface portions of the wing is insufficient, and the strength of the wing as a structural material may be reduced. Therefore, it is necessary to form the accommodating holes generally in a circular shape, and to retain the strength by leaving the meat of the base material between the adjoining accommodating holes.

Here in order to prevent the pressing force from inside the accommodation hole by swelling of the B ₄ C is the packing density of the B ₄ C may decrease below a certain value. That is, the packing density of the boron carbide (B ₄ C) powder packed in the accommodation hole in the region where intense neutron irradiation occurs is preferably set to 30 to 65% of the theoretical density. By thus securing the space for absorbing the B ₄ C swelling, the pressing force can be absorbed. Even when the space is provided, the accommodation hole is formed in the horizontal direction, so that the problem of depositing the filled neutron absorber does not occur. Further, in the above range, the particle size of B ₄ C is about 50 to 300 mesh, and the production is easy and the filling operation is easy.
Usually, the density is about 60%.

Also, returning to FIG. 8, the central portion in the axial direction of each wing (2 /
4L), the nuclear life is decreasing from the bottom to B ₄ C.
This is because the ratio of the accommodation holes used as the gas plenum to all the accommodation holes filled with is increased downward.

The distribution characteristics of the neutron multiplication factor after using the control rod for a reactor of the present embodiment for a certain period is shown in FIG. 9 in comparison with the conventional example. The reactivity control value of the conventional reactor control rod shown by the broken line in FIG. 9 is set uniformly over the entire axial length, and the neutron multiplication factor increases immediately below the insertion tip and near the insertion end. There is a ridge, and the reactor shutdown margin in that area is reduced.

On the other hand, in the case of the reactor control rod of this embodiment adjusted to have the reactivity value distribution as shown in FIG. 7, as shown by the solid line in FIG. Throughout, the neutron multiplication factor was suppressed to be uniformly low. In particular, the neutron multiplication factor in the region from the upper end L to 3 / 4L, where the subcriticality tends to decrease in the past, is greatly reduced. Therefore, the subcriticality of the above region is increased, and the reactor shutdown margin is sufficiently secured.

Next, the distribution characteristic of the actual nuclear life of the control rod for a reactor of this embodiment is shown in FIG. 10 in comparison with the conventional example. In a conventional reactor control rod having a uniform composition over the entire axial length,
As shown by the dashed line, the nuclear life is short in the upper region of each wing, while it is excessive in the lower region.

On the other hand, the actual nuclear life of the reactor control rod according to the present embodiment is determined by multiplying the neutron irradiation dose for each position shown in FIG. 6 and the nuclear life of the control rod shown in FIG. . In the present embodiment, as shown by the solid line in FIG. 10, the nuclear life is almost uniform over the entire axial length, and the life is greatly extended especially in the region from the insertion tip to 2 / 4L.
Although it is slightly descending at the upper end, there is almost no effect on the neutron multiplication factor when the reactor is shut down, so there is no adverse effect. The peak near the upper end appears because the accommodation hole in that region is filled with a neutron absorber having a long life. In addition, valleys adjacent to the peaks occur because the containment holes in that region are filled with B ₄ C, which has a relatively short life.

Next, another embodiment of the present invention will be described with reference to FIG.

The reactor control rod 1 according to the present embodiment is different from the embodiment shown in FIG. 1 in that an elongated hole-shaped accommodation hole is not provided in the upper end region l ₂ , and the accommodation hole 4 is provided for each wing. 3 having the same diameter are arranged over the entire length L in the axial direction. Further, the accommodation hole 4 in the region W of the insertion tip portion is filled with a boron compound (for example, B ₄ C) or EuB _{6 in} which boron (B-10) having a mass number of 10 is concentrated. The hafnium content in the diluted alloy of hafnium and zirconium forming the wing 3 is set to a slightly higher value from the viewpoint of improving the reactivity value. It is possible to provide a control rod for a nuclear reactor having a particularly high reactivity value.

Next, an example of the shape and arrangement of the receiving holes 4 and 4a arranged in the region W where the subcriticality decreases during the reactor shutdown is shown in FIG.
This will be described with reference to (G).

That is, as shown in FIG. 12 (A), by setting the center-to-center distance P of the accommodation hole 4a to be shorter than the other regions l ₃ and l ₆ , B
_It is possible to increase the filling amount of ₄ C and increase the reactivity value of the region.

Further, as shown in FIG. 12 (B), a plurality of accommodation holes 4 having a small diameter are formed side by side in the axial direction to form an accommodation hole group 12, and the accommodation hole groups 12 are continuously arranged in the axial direction at intervals. You may comprise. According to this embodiment, the filling volume of the neutron absorbing material is increased, and the structural strength of the wings 3 is secured by the base material interposed between the accommodation hole groups 12.

FIG. 12 (C) shows the distance P between the centers of the accommodation holes 4
This is an example in which a plurality of accommodation holes 4 are set to have a diameter smaller than that of 4 to communicate with each other to form an elongated hole-shaped accommodation hole 4a. Also in this case, the same effect as in the case of FIG. 12 (B) is exhibited.

In FIG. 12 (D), the small-diameter accommodation holes 4b are continuously provided in the tip end regions l ₄ and l ₅ , the large-diameter accommodation holes 4 are provided in the region l ₆ , and the region W
An example in which a slot-shaped accommodation hole 4a is formed is shown in FIG. In this embodiment, even when the insertion tip receives strong neutron irradiation and B ₄ C causes swelling, since the accommodation hole 4b is formed to have a small diameter, the pressing force generated from the inside of the accommodation hole 4b to the outside is generated. Have strong resistance to. Therefore, excessive stress is prevented from being generated in the wings.

FIG. 12 (E) shows that a small-diameter accommodation hole 4c is provided between the accommodation holes 4a formed in the shape of an elongated hole to further increase the filling volume of the neutron absorber.

FIG. 12 (F) shows an accommodation hole 4d formed in the shape of an elongated hole, and by making the accommodation hole 4d have a rectangular cross-sectional shape,
The filling volume of B ₄ C is further enlarged as compared with the oval-shaped accommodation hole 4d shown in FIGS.

FIG. 12G shows an example in which the accommodation holes 4e and 4f having a modified quadrangular or triangular cross section are formed adjacent to each other. In the case of the present embodiment, the filling volume is increased, and in particular, the base material formed between the accommodation holes 4e and 4f has a triangular truss structure, which has the effect of increasing the structural strength of the wings.

〔The invention's effect〕

As described above, according to the reactor control rod of claim 1,
Each wing is formed of a diluted alloy obtained by diluting a long-lived neutron absorber such as hafnium with a small density with a diluting material such as zirconium or titanium with a small density.The diluted alloy is formed with a solid solution containing zirconium and titanium. Therefore, a lightweight control rod that is physically and chemically stable can be manufactured. Therefore, the existing control rod drive mechanism can be used as it is in a conventional nuclear reactor without changing the design of load bearing performance.

Hafnium, which is a long-lived neutron absorber contained in the diluted alloy that composes each wing, and the neutron absorber that is filled in the accommodation holes of each region complement each other by the complementary neutron absorption effect, and as a control rod for a reactor. The reactivity value is increased, the reactor shutdown margin is increased, and the nuclear life can be significantly extended.

In the reactor control rod according to claim 2, the hafnium content in the diluted alloy forming the wing is set to 20 to 90 wt%, and within the above range, the total weight of the control rod does not increase. The optimum neutron absorption rate can be obtained. That is, the amount of expensive hafnium material used can be suppressed to a necessary minimum amount, which is economical.

According to the reactor control rod of claim 3, the hafnium content in the diluted alloy is reduced from the insertion tip toward the end according to the required life characteristics, and the content distribution according to the characteristics is formed. By doing so, expensive hafnium is used only in the necessary minimum amount, which is economical.

Further, as described in claims 4 to 6, by appropriately changing the kind of the neutron absorbing substance to be filled in the accommodation hole arranged in the predetermined region of the wing, the reactivity value of the region,
It is possible to adjust characteristics such as reactor shutdown margin and nuclear life.

Further, as described in claims 7 to 10, the filling of the neutron absorbing material by changing the hole diameter or the center-to-center distance of the accommodation holes arranged in a predetermined region with the hole diameter or the center-to-center distance of the accommodation holes in other regions. The density can be varied, as can the properties of the region.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a control rod for a nuclear reactor according to the present invention, FIG. 2 (A) is an enlarged sectional view of a IIA portion in FIG. 1, and FIG. 2 (B) is a second view. FIG. 2A is a sectional view taken along the line BB in FIG. 2A, and FIGS. 2C to 2F are views taken along the line CC in FIG. , F-
FIG. 3A is a sectional view showing the arrangement pitch of the accommodation holes, and FIG. 3B is a sectional view showing the relationship between the hafnium content of the Hf-Zr diluted alloy material and the neutron absorption rate. Graph showing, third
Figure (C) is a graph showing the relationship between hafnium content and density, Figure 4 is a graph showing the relationship between control rod position and fission nuclide concentration, and Figure 5 is the control rod position, neutron multiplication factor, and reactor shutdown. A graph showing the relationship with the margin, FIG. 6 is a graph showing the relationship between the control rod position and the neutron irradiation dose, and FIG. 7 is a graph showing the axial distribution of the neutron absorption characteristics of the control rod of this example.
FIG. 8 is a graph showing the axial distribution of the nuclear life of the control rod of the present embodiment, and FIG. 9 is a graph showing the axial distribution of the neutron multiplication factor of the control rod of the present embodiment in comparison with the conventional example. FIG. 10 is a graph showing the axial distribution of the actual nuclear life of the control rod of this embodiment in comparison with the conventional example, FIG. 11 is a front view of another embodiment, and FIGS. (G) is a side sectional view showing a shape and an arrangement example of the accommodation holes formed in each wing. 1 ... Reactor control rod, 2 ... Coupling member, 3 ... Wing, 4,4a, 4b, 4c, 4d, 4e, 4f ... Accommodation hole, 5 ... Neutron absorber, 6 ... Gas plenum, 7: long-life neutron absorber, 8: high reactivity neutron absorber, 9: passage, 10:
Hafnium rod, 11 ... wing end, 12 ... accommodation hole group,
H ... insertion tip, O ... insertion end, W, l ₂ , l ₃ , l ₄ , l ₅ , l ₆ ...
... area, P ... distance between centers of accommodation holes, D ... accommodation hole diameter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 59-138987 (JP, A) JP-A 60-3584 (JP, A) JP-A 62-212592 (JP, A) JP-A 62- 218893 (JP, A) JP 62-239087 (JP, A) JP 63-221289 (JP, A)

Claims (10)

(57) [Claims] 1. A reactor control rod in which a plurality of rectangular wings are formed in a cross shape, wherein the wings are made of a diluted alloy obtained by diluting a long-lived neutron absorber such as hafnium with a diluent such as zirconium or titanium. Then, a storage hole is bored in the dilution alloy, and the storage hole is filled with a neutron absorbing material. 2. The reactor control according to claim 1, wherein the diluted alloy forming the wing has a constant hafnium content over the entire length in the axial direction of the wing, and the content is set to 20 to 90% by weight. rod. 3. The control rod for a nuclear reactor according to claim 1, wherein the dilution alloy forming the wing is configured so that the content of hafnium gradually decreases from the core insertion tip end toward the insertion end. 4. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorbing material filled in the accommodation hole is boron carbide. 5. An upper region corresponding to half the entire length from the axial insertion tip of the wing is further provided with two or more regions, and the long-life neutron absorber and the high reaction are sequentially provided from the insertion tip side of this region. The reactor control rod according to any one of claims 1 to 3, wherein the control rod is filled with a neutron absorbing material. 6. A hafnium, a hafnium-containing alloy, an Ag—In—Cd alloy, and an alloy containing Ag—In—Cd and Europium oxide,
While filling at least one selected from rare earth oxides such as dysprosium oxide, gadolinium oxide, and samarium oxide, most of the accommodation holes located in regions other than the above are filled with boron carbide. The reactor control rod according to any one of claims 1, 2, 3, and 5, which is characterized. 7. A shaft of a receiving hole which is further provided with two or more regions in the upper region corresponding to half of the entire length from the axial insertion tip of the wing and which is located at least in the region at the insertion end side in the upper region. 7. The nuclear reactor according to claim 1, wherein a hole diameter in a direction is made larger than a hole diameter of a receiving hole located in a lower region corresponding to half of the entire length from the insertion end. Control rod. 8. A center of a receiving hole located in at least an insertion end side region in the upper region, in which two or more regions are further provided in an upper region corresponding to half of the entire length from the axial insertion tip of the wing. 7. The inter-distance is made smaller than the inter-center distance of the accommodation holes located in the lower region corresponding to half of the total length from the insertion end, and the accommodation holes are densely arranged. The control rod for a nuclear reactor according to item 1. 9. The hole diameter of a plurality of housing holes arranged on the insertion tip side in the axial direction of the wing is smaller than the hole diameter of the housing holes arranged on the insertion end side. The control rod for a nuclear reactor according to any one of items. 10. An accommodation hole filled with boron carbide is arranged in a region corresponding to a half of the entire length from an axial insertion end of the wing, and accommodation holes not filled with neutron absorbing material are dispersedly arranged. Claims 1 to 9
The control rod for a nuclear reactor according to any one of 1.