JPS63196889A - Control rod for nuclear reactor - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a control rod for a nuclear reactor that adjusts and controls the reactor output, and in particular has a long life and less deformation due to external forces. Regarding the $11111 rod for nuclear reactors.

(Prior Art) A conventional control rod for a boiling water reactor is constructed by loading a large number of neutron absorption rods into a plurality of wings formed by fixing an elongated U-shaped sheath to a central tie rod. . A neutron absorbing rod is prepared, for example, by filling a stainless steel cladding tube with boron carbide (B4C) powder as a neutron absorbing material. The filled B4C absorbs neutrons in the nuclear reactor and gradually loses its neutron absorption ability.

By the way, control rods that are inserted into or extracted from the core of a nuclear reactor do not receive uniform neutron irradiation over their entire area; for example, the side edge area or upper end area of each wing is exposed to intense neutron irradiation. receive.

For this reason,! , II The neutron absorbing rods arranged at the side edges and upper end regions of each wing of the H rod absorb a large amount of neutrons and end their nuclear lifetime earlier than the neutron absorbing rods in other regions.

Therefore, it was uneconomical to discard the control rods as radioactive waste even though the neutron absorption rods placed in other areas had sufficient nuclear life remaining.

To solve such problems, control rods for nuclear reactors are partially placed with long-life neutron absorbers such as hafnium, which have a long nuclear lifetime, in the region of the 1-control rod that receives intense neutron irradiation. has been developed by the applicant. As disclosed in Japanese Unexamined Patent Publication No. 53-74697, this nuclear reactor control rod had a lifespan of about 2@ compared to a conventional control rod.

After that, there was a desire for a transition to high burnup operation and long II continuous operation of nuclear reactors, and in response to the increasing demand for longer life of t, lJ 1B rods, the present applicant filed a patent application in 1983.
As described in the specification of No. 1-78746, we have developed a long-life atomic control rod that can dramatically extend its life.

This nuclear reactor l111tl rod is used as a neutron absorber.
It has a structure in which metallic neutron absorbing plates such as hafnium metal plates, which do not use carbon and have a long life, are disposed facing each other inside the sheath.

III tan for this hafnium plate trap type atom
According to No. 1, there is no need for a cladding tube filled with 840 as in the past, and a long-life hafnium plate is used, so the life of the υ1111 rod itself is significantly extended. However, hafnium has a slightly inferior neutron absorption capacity compared to B4C and has a high specific gravity, so in order to ensure the same neutron absorption function as conventional control rods, it is necessary to install thick hafnium plates. As a result, the weight of the control rod increases significantly, requiring a change in load design, which poses a problem that it cannot be used as is in the existing 111till rod drive vJm structure.

In order to solve this problem, a flow path is formed between hafnium neutron absorbing plates that are placed opposite each other inside the sheath to allow water, which is a moderator, to flow through, thereby utilizing the neutron moderating effect of the moderator. It was suggested that. That is, when water is allowed to flow through the flow path, the reactivity value of the control rod is improved due to the neutron moderating effect of water. Therefore, the thickness of the hafnium plate as a neutron absorbing material can be relatively reduced.

This result allows us to maximize the width of the flow path formed between the neutron absorption plates, while minimizing the thickness of the neutron absorption plates made of hafnium, making it possible to increase the total weight of the control rod. Conventional control rod drive e! 1
It is now possible to use it horizontally.

By the way, as a result of confirming the function and operating status using a critical experiment device incorporating a full-scale model (mock-up) of this nuclear reactor control rod, we found that two hafnium neutron sheets placed inside the sheath of the control rod It was demonstrated that the wider the moderator flow path formed between the absorption plates, the higher the reactivity value of the control rod. That is, culms that expand the width of the channel,
It has become possible to reduce the thickness of the hafnium plate, and studies are underway to reduce the total weight of the control rod.

(Problem to be solved by the invention) However, the distance between the surfaces of the U-shaped sheath of the VLTLL rod is approximately 8 #lI than before, and increasing it beyond this value would lead to changes in the entire core design. Yes, it is realistically impossible. On the other hand, in order to reduce the weight of the control rod within this thickness range, it is necessary to make the sheath thinner. However, because the strength of the sheath as a structural member decreases, for example, in the event of a major earthquake, etc.
If excessive bending stress is applied to the l-rod, the possibility of plastic deformation increases, which may have a negative effect on the control rod's insertion into the reactor core. In other words, it is difficult to completely rule out the possibility that the sheath plastically deforms outward due to excessive bending stress and comes into contact with the fuel assembly arranged opposite, causing problems in the insertion operation of the uJ111 rod. It is.

In addition, during reactor scram operation, it is possible that large stress is applied in the axial direction of the control rods due to the acceleration generated when the control rods are inserted into the reactor core at normal speed, but even in such cases, excessive deformation may occur. is not allowed.

The present invention has been made to solve the above problems, and it is lightweight, has a long nuclear life, and has little deformation due to external forces, so smooth insertion operation is possible even in an emergency. The purpose is to provide a nuclear reactor control rod.

[Structure of the invention]

(Means for Solving the Problems) The l+ control rod for a nuclear reactor according to the present invention connects a tip structural member and an end structural member by a central tie rod, and each protrusion of the central tie rod has a substantially U-shaped cross section. A wing is formed by fixing a sheath having a wing, and a plate-shaped long-life neutron absorber is housed within the sheath, and the front two neutron absorbers are divided into multiple stages of neutron absorbing elements in the axial direction of the central tie rod. is,
Each stage of the neutron absorbing element is composed of a plurality of neutron absorbing plates arranged opposite to each other in the thickness direction of the wing, and a flow path through which the moderator flows is formed between the opposing neutron absorbing plates. A concave groove formed by curving the sheath inward so as to fit into the gap formed between the neutron absorbing plates of the neutron absorbing elements adjacent in the direction is provided in the direction perpendicular to the axis of each wing.

(Function) The III1 rod for a nuclear reactor according to the present invention has a plate-shaped long-life neutron absorption plate disposed within the sheath, so the nuclear life of the v control rod is long.

In addition, the neutron absorption plates are arranged facing each other in the wall thickness direction within the sheath, forming a flow path for the moderator between them, and since the neutron moderating effect of the moderator is utilized, the neutron absorption plates The thickness can be reduced. Therefore, an increase in the weight of the control rod is suppressed υ1, and the present invention can be applied to an additional control rod drive mechanism.

In addition, a concave groove is provided in the direction perpendicular to the axis of each wing, with the sheath curved inward. Even when stress due to earthquakes etc. is applied to the control rod, deformation occurring on the sheath surface is prevented by the concave groove. It is absorbed in Therefore, there is no hindrance to the vertical movement of the control rod, and smooth movement is possible at all times.

(Example) Hereinafter, an example of a control rod for a nuclear reactor according to the present invention will be described with reference to the accompanying drawings.

FIG. 7 is an overall perspective view schematically showing the nuclear reactor control rod 1 according to the present invention. They are integrally joined by a cross-shaped central tie 5. A sheath 6 made of stainless steel and having a deep U-shaped cross section is fixed to each protrusion of the central tie rod 5 to form a wing 7.

Inside the sheath 6, a root-shaped long-life neutron absorber 8, typically made of a hafnium (llf) metal plate, is housed.

This neutron absorber 8 is divided into a plurality of neutron absorbing elements 8a in the axial direction of the central tie 5, and the neutron absorbing elements 8a in each stage are opposed in the thickness direction of the wing 7, as illustrated in FIG. For example, two neutron absorbing plates 8b are arranged.
The two are integrally joined via a plurality of spacers 9.

A flow path 10 through which the moderator flows is formed between the two neutron absorption plates 8b.

Furthermore, a recessed groove 11 is formed in the direction perpendicular to the axis of the sheath 6 of each wing 7. As shown in FIGS. 1 and 2, this concave groove 11 is formed by a neutron absorbing element 8a adjacent in the axial direction.
The sheath 6 is curved inward so as to fit into the gap A formed between the neutron absorbing plates 8b.

Furthermore, this concave groove 11 is formed on the upper surface of the sheath 6 in the second region, which is equally divided in the axial direction from the upper end of the entire region of each wing 7 from the first region to the third region, in the axially perpendicular direction (width direction). ) are provided at least one or more. Furthermore, each concave groove 1
1 has 756 notched holes 12 in the wing 7fil 1m part.
a and a notch hole 12b provided in the sheath portion that is fixed to the central tie [1].

The procedure for machining the sheath 6 on the right side of this concave groove 11 is the third step.
As shown in the figure, first, both edges of the unfolded sheath material 6a are cut to form the cutout holes 12a.

12b is bored, and then the sheath material 6a is indented in the back direction in the figure along the bending line B-B connecting the notched holes 12a and 12b, thereby forming a curved concave groove 11. Since notch holes 12a and 12b are formed at both ends of the recessed groove 11, the bending operation is easy. Furthermore, the notch hole 12
A U-shaped sheath 6 is formed by deeply bending both sides of the sheath material 6a toward the back along the axial center line C-C1 passing through a.
form. The U-shaped sheath 6 having the concave groove 11 is
As shown in FIG. 2, it is fixed to each protrusion of the central tie rod 5 by spot welding or the like. Further, the concave groove 11 is provided at a position where it is recessed into the gap A formed between the adjacent neutron absorption plates 8b, 8b (see FIG. 5).

Furthermore, in order to facilitate the inflow and outflow of the moderator into the sheath 6, a plurality of water passage holes 13 are bored at predetermined positions on the surface of the sheath 6, as shown in FIG.

According to the 1I11tIl rod for nuclear reactors of this example, a long-life neutron absorption plate is installed in the sheath, so υ111
The nuclear lifespan of one rod is long. In addition, the neutron absorption plates are arranged facing each other in the thickness direction within the sheath, forming a flow path for the moderator between them, and since the neutron moderating effect of the moderator is utilized, the neutron absorption plates Thickness can be reduced. Therefore, it is possible to reduce the amount of expensive and heavy neutron absorption plates used, and an increase in the weight of the control rod can be suppressed.

Furthermore, since a concave groove is formed by curving the sheath inward in the direction perpendicular to the axis of each wing, in the event of a large earthquake or the like and excessive bending stress is applied to the control rod, Even when a large acceleration acts and stress is generated, the sheath does not bulge outward. Therefore, the control rod can be moved up and down smoothly. That is, when the above-mentioned external force acts on the control rod, the deformation occurring in the sheath 6 is absorbed by the expansion and contraction of the curved surface of the recessed groove 11, so that no outwardly protruding deformation occurs. Therefore, the sheath of the control rod will not come into contact with the opposing fuel assembly, thereby preventing smooth driving.

Further, it is effective to provide the concave groove 11 in the second iJI region, which is obtained by equally dividing the entire region of each wing 7 from the upper end into the first, second, and third regions. That is, the deformation due to the stress acting on the control rod 1 during an earthquake or the like is greatest in the second region at the axial center of the control rod 1. The gap A for the concave groove 11 is provided only in the second region at the center, and the neutron absorbing plates 8b are continuously arranged in the first region where the neutron radiation is large, so that the neutron absorption in the first region is Absorption capacity is not reduced, that is, sufficient margin for reactor shutdown is ensured.

In the third region J3, since the external force that acts is not as large as the central portion, there is little Q benefit in providing the concave groove 11. Further, the number and position of the recessed grooves 11 provided in the second region are determined by taking into account load conditions and the like.

Furthermore, the rigidity of the blade can be adjusted by changing the position where the recessed groove 11 is provided for each wing 7. moreover,
As illustrated in FIG. 4, the recesses 1M11 provided on both sides of each wing may be formed in different positions. The processing procedure for the sheath 6a in this case is almost the same as that illustrated in FIG. 3, but the cutout hole 12a provided at the wing side edge is an elongated hole. The sheath material 6a shown in FIG. 4 is processed into a U-shape and fixed to the central tie rod, and the state in which the neutron absorption plate 8b is accommodated is shown in FIG.
In this case, the gaps A, A of about 10 mm formed between the neutron absorbing plates 3a, 8a adjacent to each other in the axial direction of the sheath 6 are separated from each other by the neutron absorbing plates 8b disposed facing each other. It is constructed in a structure that is far apart so that it is masked.

In this case, unlike the case where the heights of the gaps A and A formed at the front and rear parts of the wing are made to match as shown in FIG. 5, according to the structure shown in FIG. Since the passing neutron beams are masked by the neutron absorption plates 8b provided facing each other, a decrease in the reactivity value of the control rods in the gap is prevented, and a decrease in reactor shutdown margin is avoided. can.

Note that if the corners of the neutron absorption plate 8b housed in the sheath 6 facing the concave grooves 11 are chamfered as illustrated in FIGS. 5 and 6, the curved portion of the sheath It is assumed that local stress acts on the material.

〔Effect of the invention〕

As described above, in the atomic control rod according to the present invention, since the plate-shaped long-life neutron absorption plate is disposed inside the sheath, the nuclear life of the control rod is long, and it lasts for a long period of time. It is suitable as a control rod for a nuclear reactor that operates continuously over a period of time.

In addition, a plurality of neutron absorption plates are arranged facing each other in the wall thickness direction inside the sheath, and a flow path is formed between them to allow the moderator to flow, and the neutron moderating effect of the moderator is utilized. ff1 of the number of neutron absorption plates corresponding to the effect
ffi can be reduced. Therefore, i/J
The increase in weight of the 111 rod is suppressed to υ1 as much as possible, and the existing control rod drive mechanism can be applied as is without modification.

Furthermore, a concave groove is provided in which the sheath is curved inward in the direction perpendicular to the axis of each wing. ! Even if an excessive stress is applied to the rod due to a stress, the deformation generated on the sheath surface is absorbed by the concave groove. Therefore, the t control rods do not come into contact with the fuel assemblies facing each other with a slight gap between them, and the lifting and lowering of the tIIIgB rods is not hindered (smooth operation is always possible).

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway front view showing an embodiment of the v-control rod for nuclear reactors according to the present invention, Fig. 2 is an enlarged front view of the number mark ■ in Fig. 1, and Fig. The figure is a developed view of the sheath showing the processing procedure of the sheath in Fig. 2, Fig. 4 is a developed view showing the processing procedure of other sheaths, Fig. 5 is a sectional view along the v-■ arrow in Fig. 1, and Fig. 6 is a developed view showing the processing procedure of the sheath in Fig. 2. The figure is a cross-sectional view of an example of a modified arrangement of concave grooves with respect to FIG. 5, and FIG.
FIG. 8, a perspective view of the body of II, is a cross-sectional view taken along the line -■ in FIG. 7. 1... υIII rod, 2... Handle, 3... Tip structure material, 4... End structure material, 5... Center tie, 6... Sheath, 6a... Sheath material ,7...
Wing, 8... Neutron absorber, 8a... Neutron absorbing element, 8b... Neutron absorbing plate, 9... Spacer,
10... Channel, 11, 11a, 11b... Concave groove,
12.12a, 12b...Notch hole, 13...Water hole, A...Gap. :%4 Figure Fa, Figure 5, Figure 6, Figure 6

Claims (1)

[Scope of Claims] 1. The tip structure member and the end structure member are connected by a central tie rod, and a sheath having a substantially U-shaped cross section is fixed to each protruding portion of the central tie rod to form a wing; A plate-shaped long-life neutron absorber is housed in the sheath, and the neutron absorber is divided into multiple stages of neutron absorbing elements in the axial direction of the central tie rod, and each stage of neutron absorbing elements is arranged in the thickness direction of the wing. It is composed of a plurality of neutron absorption plates disposed facing each other, and forms a flow path through which a moderator flows between the opposing neutron absorption plates, while forming a flow path between the neutron absorption plates of the axially adjacent neutron absorption elements. 1. A control rod for a nuclear reactor, characterized in that a concave groove formed by curving a sheath inward so as to fit into a gap between wings is provided in a direction perpendicular to the axis of each wing. 2. The control rod for a nuclear reactor according to claim 1, wherein the concave groove is connected to a cutout hole bored in a sheath portion fixed to the wing side end and the center tie rod. 3. The recessed groove is arranged in a second region that is obtained by dividing the entire region of each wing into a first region, a second region, and a third region equally in the axial direction from the upper end, as described in claim 1. Control rods for nuclear reactors. 4. The gap formed between the axially adjacent neutron absorbing plates of the neutron absorbing elements that are arranged oppositely in the sheath via the moderator flow path is A control rod for a nuclear reactor according to claim 1, which is configured to be masked. 5. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorption plate is made of a hafnium metal plate.