JPH0833475B2 - Control rod for nuclear reactor - Google Patents

Description

The present invention relates to a control rod for a nuclear reactor that adjusts and controls the reactor power, and in particular, has high mechanical strength against external force and wear due to corrosion. Related to control rods for nuclear reactors.

(Prior Art) A conventional boiling water reactor control rod is configured by loading a large number of neutron absorbing rods into a plurality of wings formed by fixing a long U-shaped sheath to a central tie rod. .
The neutron absorbing rod is prepared, for example, by filling a stainless steel cladding tube with boron carbide (B ₄ C) powder as a neutron absorbing material. The filled B ₄ C absorbs neutrons in the reactor and gradually loses its ability to absorb neutrons.

By the way, the control rod inserted into or removed from the core of the nuclear reactor does not receive uniform neutron irradiation over the entire region thereof, and for example, the side edge region or the upper end region of the wing receives a strong neutron beam. Therefore, the neutron absorbing rods arranged in the side edges and upper end regions of each wing of the control rod absorb a large amount of neutrons and end their nuclear life earlier than the neutron absorbing rods in other regions. Therefore, there has been an uneconomical situation in which the control rod must be discarded as radioactive waste even though the neutron absorbing rods arranged in other regions have a sufficiently long nuclear life.

In order to solve such problems, nuclear control rods with long nuclear life in the region of control rods that receive strong neutron irradiation, for example, long-lived neutron absorbers such as hafnium are partially arranged. Applicant has developed. This reactor control rod, as disclosed in JP-A-53-74697,
The life was about twice as long as that of a conventional control rod.

After that, in response to the demand for high burnup operation of the nuclear reactor and transition to long-term continuous operation, and the demand for longer life of the control rods increased further, the applicant of the present invention filed Japanese Patent Application No. 61-78746. As described in, we have developed a long-life type control rod for reactors that can dramatically extend the life.

This reactor control rod has a structure in which a metal neutron absorbing plate such as a hafnium metal plate which has a long life and does not use B ₄ C as a neutron absorbing member is disposed inside the sheath so as to face each other.
The specific structure is shown in FIGS. 7 and 8. That is, in the control rod 1 for a nuclear reactor, the tip structural member 3 having the handle 2 and the end structural member 4 are integrally joined by a central tie rod 5 having a cross-shaped cross section. A wing 7 is formed by fixedly installing a sheath 6 made of stainless steel having a deep U-shaped cross section on each protruding portion of the central tie rod 5.

A plate-shaped long-life neutron absorber 8 represented by a hafnium (Hf) metal plate or the like is housed in the sheath 6.

This neutron absorber 8 is divided into a plurality of neutron absorbing elements 8a in the axial direction of the central tie rod 5, and the neutron absorbing elements 8a at each stage are arranged so as to face each other in the thickness direction of the wings 7, as illustrated in FIG. It is composed of, for example, two neutron absorbing plates 8b, and both are integrally joined via a plurality of spacers 9. A flow path 10 through which the moderator flows is formed between the two neutron absorbing plates 8b. Further, the sheath 6 is provided with a large number of water passage holes 21a and 21b for allowing the reactor water, which is a moderator, to flow into or out of the sheath 6.

According to this hafnium plate trap type reactor control rod, the cladding tube filled with B ₄ C unlike the conventional case is not required,
Since the hafnium plate having a long life is used, the life of the control rod itself is remarkably extended. However, hafnium is slightly inferior to B ₄ C in neutron absorption capacity and has a large specific gravity, so it is necessary to attach a thick hafnium plate to ensure the same neutron absorption function as conventional control rods. There is. Therefore, the weight of the control rod is significantly increased, and the load design needs to be changed, which is a problem that the existing control rod drive mechanism cannot be used as it is.

In order to solve the problem, as shown in FIG.
It was proposed to form a flow path 10 for circulating water, which is a moderator, between neutron absorbing plates 8b made of hafnium facing each other in the sheath, and to utilize the neutron moderating effect of the moderator. . That is, when water is circulated in the flow path 10, the reactivity value of the control rod is improved by the neutron moderating effect of water. Therefore, the thickness of the hafnium plate as the neutron absorber can be relatively reduced.

By this result, while maximizing the width of the flow path 10 formed between the neutron absorbing plates 8b, the thickness of the neutron absorbing plate 8b formed of hafnium is reduced to the limit, and the total weight of the control rods is reduced. By suppressing the increase as much as possible, it became possible to adopt this hafnium plate trap type control rod in the conventional control rod drive mechanism.

By the way, as a result of confirming the reactivity value by using a criticality experiment device incorporating this full-scale model (mock-up) of the reactor control rod, for example, the flow path of the moderator formed in the sheath 6 of the control rod is confirmed. It was demonstrated that the wider the width of 10, the higher the reactivity value of the control rod. That is, as the width of the flow path 10 is increased, it becomes possible to reduce the plate thickness of the hafnium plate, and attention is focused on this point and studies are being made to reduce the total weight of the control rod.

(Problems to be solved by the invention) However, the distance between the surfaces of the U-shaped sheath of the control rod is about 8 mm as compared with the conventional one, and an increase of more than this value leads to a change in the entire core design, Is difficult. On the other hand, in order to reduce the weight of the control rod within this thickness range, it is necessary to make the thickness of the sheath thinner. However, because the strength of the sheath as a structural member decreases, the possibility of plastic deformation increases when excessive bending stress acts on the control rod, for example, when a large earthquake occurs, and the operation of inserting the control rod into the reactor core increases. May be adversely affected. That is, the sheath is plastically deformed outward due to excessive bending stress, and comes into contact with the fuel assemblies arranged facing each other,
It is difficult to completely rule out the possibility that it will interfere with the control rod insertion operation.

Further, in the conventional reactor control rod, the neutron absorber loaded in the sheath is not integrated in the axial direction but is divided into a plurality of stages in the axial direction. The effect of reinforcing the strength was small. Therefore, when a bending stress acts on the control rod, the stress concentrates on the above-mentioned dividing positions where the strength is relatively lowered.

Further, during the reactor scrum operation, a large axial load may act on the control rod due to the acceleration generated when the control rod is rapidly inserted into the core, and the sheath surface at the split position may be deformed. Some reinforcement measures are desired.
In particular, reactor control rods used for long-term continuous high burnup operation of the reactor are required to have sufficient soundness to maintain sufficient mechanical strength without being deformed even after a large number of scrum operations as a design standard. It

On the other hand, long-term corrosion integrity must also be guaranteed.

That is, when the width of the flow path of the moderator is expanded to increase the reactivity value of the control rod and to reduce the weight of the neutron absorbing plate to be mounted, the neutron absorbing plate adheres to the inner surface of the sheath and It may be possible to impede the smooth flow of the coolant in. When the coolant stagnates, it is possible that the heat removal operation of the neutron absorbing plate, which has absorbed neutrons and generated heat, does not proceed smoothly and locally becomes overheated. Also,
The contact between dissimilar metals such as the stainless steel forming the sheath and the stainless steel spacers that keep the distance between the opposing neutron absorbing plates and the hafnium forming the neutron absorbing plate may induce electrochemical corrosion. Conceivable.

Furthermore, since the inside of the reactor is under a strong radiation environment,
Water, which is a coolant, may be decomposed by radiolysis to create an oxygen-rich atmosphere, which may accelerate the induction of stress corrosion cracking.

The present invention has been made in order to solve the above problems, high mechanical strength with less deformation against external force,
Another object of the present invention is to provide a control rod for a nuclear reactor that can prevent wear due to corrosion.

[Structure of Invention]

(Means for Solving Problems) In a reactor control rod according to the present invention, a tip structural material and an end structural material are connected by a central tie rod, and a U-shaped sheath is provided on each protruding portion of the central tie rod. Fix it, insert a plate-shaped long-life neutron absorber into the sheath to form wings, and place a long hafnium material adjacent to the long-life neutron absorber at the outermost edge of each wing. On the other hand, the neutron absorber is divided into a plurality of stages of neutron absorbing elements in the axial direction of the central tie rod, the neutron absorbing elements of each stage are a plurality of neutron absorbing plates that are housed facing each other in the thickness direction of the wings. It is configured, while forming a flow path for guiding the moderator while holding the facing intervals of the neutron absorbing plates by locally interposing a plurality of spacers between the facing neutron absorbing plates, while contacting the inner surface of the neutron absorbing plate Spacer It is characterized in that a water passage groove is formed on the space holding surface.

Further, a water passage is formed between the outer surface of the neutron absorbing plate and the inner surface of the sheath.

(Operation) Since the reactor control rod having the above-described configuration has the long hafnium material disposed adjacent to the long-life neutron absorber at the outermost edge of each wing, the structural strength of the sheath is enhanced, The resistance of the control rod to external force is strengthened. That is, the outermost edge of each wing is reinforced by the long hafnium material provided, and the mechanical strength of the entire control rod is increased. Therefore, deformation due to bending stress due to an earthquake or the like is small, and mechanical soundness can be maintained even in many scram operations assuming long-term operation.

Further, since the water passage groove is formed on the space holding surface of the spacer which is in contact with the inner surface of the neutron absorbing plate, the coolant sufficiently flows into the water passage groove, and the neutron absorbing plate is less likely to be overheated and damaged. Further, since the contact ratio between the neutron absorbing plate which is a dissimilar metal and the spacer is reduced, the electrochemical corrosion between the two is also reduced.

Further, by forming the water passage between the outer surface of the neutron absorbing plate and the inner surface of the sheath, the coolant does not flow and stay sufficiently, so that the sheath is not locally overheated and damaged. In addition, since the outer surface of the neutron absorbing plate and the inner surface of the sheath are separated by the water passage, there is no risk of the two different metals coming into contact with each other and causing electrochemical corrosion, and the control rod for the reactor can be used for a long period of time. Can maintain the soundness of.

(Embodiment) An embodiment of a reactor control rod according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a front view of a control rod for a nuclear reactor according to the present invention, in which a sheath on the right side in the drawing is partially broken.
The same components and parts as those in the conventional example shown in FIGS. 7 and 8 are designated by the same reference numerals.

In the control rod 1 for a nuclear reactor of this embodiment, a tip structural member 3 having a handle 2 and an end structural member 4 are integrally joined by a central tie rod 5 having a cross-shaped cross section. Central tie rod 5
A wing 7 is formed by fixing a sheath 6 having a U-shaped cross section to each of the protruding portions. A plate-shaped long-life neutron absorber 8 typified by a hafnium metal plate is housed on the side of the central tie rod in the sheath 6.

In addition, a long hafnium material 11 is arranged at the outermost edge of each wing 7 adjacent to the neutron absorber 8. The long hafnium material 11 is, for example, formed in the shape of a round bar as shown in FIG. 2, and two to five pieces are arranged in parallel and arranged so as to penetrate the entire length of the wing in the axial direction. Further, as shown in FIG. 1, a space 32 for absorbing deformation due to thermal expansion is provided in the upper portion of the hafnium material 11 on the insertion tip side.

On the other hand, the neutron absorber 8 is divided into a plurality of neutron absorbing elements 8a in the axial direction of the central tie rod 5, and the neutron absorbing elements 8a at each stage are arranged in the thickness direction of the wings 7 as shown in FIG. A plurality of neutron absorbing plates 8b housed opposite to each other is formed, and a flow path 10 for guiding a moderator is formed between the facing neutron absorbing plates 8b. On the other hand, a water passage 12 is formed between the outer surface of the neutron absorbing plate 8b and the inner surface of the sheath 6. The neutron absorbing plates 8b, 8b arranged facing each other are side edge spacers 1
It is held by the sheath 6 at a predetermined interval by 3 and the spacer 14 for the center. The side edge spacer 13 and the center spacer 14 are made of hafnium material or stainless steel material.

Next, the structure of the attachment portion of the neutron absorbing plate 8b will be described more specifically with reference to FIG. Both ends of the neutron absorbing plates 8b, 8b arranged facing each other in the sheath 6 are short side edge spacers arranged at predetermined intervals in the axial direction of the wing.
It is partially joined to 13 by welding or the like.

The width of the plate mounting portion 13a of the side edge spacer 13 forms a flow path 10 at a predetermined interval between the neutron absorbing plates 8b and 8b, while a predetermined distance is provided between the inner surface of the sheath 6 and the outer surface of the neutron absorbing plate 8b. A water passage 12 having a width is formed.

In addition, at the corners of the protruding end edge of the central tie rod 5 and the side edge spacers 13 facing the protruding end edge, a water passage 30 is formed by chamfering as shown in FIG. The flow resistance of the reactor water, which is a moderator, is reduced, the cooling action is smoothed, and local overheating of the neutron absorbing plate 8b is prevented.

On the other hand, the central portion of the neutron absorption plate 8b is the central spacer 14
And it is fixed at a predetermined position via the ring-shaped spacer 15. Here, the central spacer 14 is, as shown in FIG.
Having a collar-shaped mounting seat 16 having a thickness corresponding to the width of the flow path 10, by abutting the neutron absorbing plates facing each other on both sides of the mounting seat 16, the facing interval of the neutron absorbing plate is a predetermined value. Held in. Water passages 17 are provided on both surfaces (space holding surfaces) of the mounting seat 16 for the flow of reactor water as a moderator.

Opposing neutron absorbing plates 8b, 8b are attached to both sides of the mounting seat 16 of the spacer 14 for the center, respectively, and the ring-shaped spacer 15
It is fixed to the sheath 6 via. The spacer 14 for the center is
It is integrally joined to the mounting hole 18 provided in the opposing sheath 6 by welding or the like. In order to obtain the same cooling effect, the spacer 14 for the center is also provided on the surface of the ring-shaped spacer 15.
Similarly to the above, it is preferable to provide the water passage groove 17a.

Further, a through hole 31 through which the central spacer 14 penetrates is formed in the neutron absorbing plates 8b, 8b. By setting the inner diameter of the through hole 31 to be larger than the outer diameter of the through portion of the center spacer 14 and forming a predetermined clearance therebetween, the difference in thermal expansion between the sheath 6 and the neutron absorbing plate 8b is caused. The displacement can be effectively absorbed, and thermal deformation can be prevented.

As shown in FIG. 1, a water passage hole formed on the surface of the sheath 6.
The reactor water flowing from 21a, 21b into the sheath 6 flows through the flow passage 10 and the water passage 12, removes the heat generated in the neutron absorbing plate 8b, and also acts as a moderator, and the wing 7 It flows out from the upper water passage holes 21a and 21b.

As described above, in the reactor control rod according to the present embodiment, since the long hafnium material 11 is arranged at the outermost edge of each wing 7, the structural strength of the entire sheath 6 is increased and control against external force is performed. Improves rod resistance. Therefore, it is useful as a control rod for a reactor that operates for a long period of time.

Further, in this embodiment, since the water passage 12 is formed between the outer surface of the neutron absorbing plate 8b and the inner surface of the sheath 6, the coolant is sufficiently circulated, and the sheath 6 or the neutron absorbing plate 8b is locally There is no possibility of overheating and damage.

In addition, the water passage 12 includes a side edge pacer 13 and a center spacer 14
Since the outer surface of the neutron absorbing plate 8b and the inner surface of the sheath 6 are formed by the ring-shaped spacer 15 so as to be separated from each other, there is no possibility that both dissimilar metals will come into contact with each other and cause electrochemical corrosion, and It is possible to maintain the soundness of the reactor control rod 1. Further, since the water passage groove 17 is also formed on the space holding surface of the mounting seat 16 of the central spacer 14 that comes into contact with the inner surface of the neutron absorbing plate 8b, the same cooling effect and anticorrosion effect can be obtained.

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

In this embodiment, a long hafnium material 11a formed in the shape of a hollow cylinder is arranged in the axial direction of the outer edge of each wing 7.

In this case, since a flow path of water as a moderator is secured in the hollow portion 19 of the long hafnium material 11a, it is possible to take over the neutron absorbing function of hafnium, and the material weight of the hafnium material is slightly increased. It can be reduced. It is also possible to provide a large number of through holes 22 on the side surface of the hafnium material 11a, diversify the flow path of the moderator to reduce the flow resistance, and further improve the cooling efficiency.

Further, a large number of dimples 20 projecting on the inner surface of the sheath 6 are formed on the surface of the sheath 6, and the tops of the dimples 20 are brought into contact with the neutron absorbing plate 8b so that the neutron absorbing plate 8b
The outer surface and the inner surface of the sheath 6 may be separated to form the water passage 12 having a predetermined width. The dimple ring 20 is preferably formed on the sheath 6 near the center spacer 14 and the side edge spacer 13.

In this case, the side edge spacer 13 has a shape that restricts only the width of the channel 10 formed in the central portion of the sheath 6. Therefore, its shape is simplified and processing and preparation are easy. Further, in the case of this embodiment, the ring-shaped spacer 15 (FIG. 2) for restricting the width of the water passage 12 is not necessary, and the wing 7
The assembly work of is simplified. In this embodiment, the side edge spacers 13 provided at the ends of the neutron absorbing plates 8b, 8b arranged facing each other are arranged at predetermined intervals in the axial direction of the wings 7, as shown in FIG. Arranged and spacers 13 for each side edge
Is fixed to one of the opposing neutron absorbing plates 8b, 8b by welding or the like. Therefore, even if one of the opposing neutron absorbing plates 8b, 8b is unexpectedly bent for some reason, both neutron absorbing plates 8b are affected by the effect.
It is prevented that b and 8b are integrally deformed greatly.

〔The invention's effect〕

In the reactor control rod according to the present invention, since the long hafnium material is arranged at the outermost edge of each wing, the structural strength of the sheath is increased, and the resistance of the reactor control rod to external force is enhanced. To be done. Therefore, it is possible to sufficiently safely cope with an earthquake or a large number of scrum movements that are expected during long-term use.

Further, since the water passage groove is formed on the space holding surface of the spacer which is in contact with the inner surface of the neutron absorbing plate, the coolant sufficiently flows into the water passage groove, and the neutron absorbing plate is less likely to be overheated and damaged. Further, since the contact ratio between the neutron absorbing plate which is a dissimilar metal and the spacer is reduced, the electrochemical corrosion between the two is also reduced.

Further, by forming the water passage between the outer surface of the neutron absorbing plate and the inner surface of the sheath, the coolant is sufficiently circulated and the sheath or the neutron absorbing plate is prevented from being overheated. Moreover, since the outer surface of the neutron absorbing plate and the inner surface of the sheath are separated by providing the water passage, both of the dissimilar metals are less likely to cause electrochemical corrosion, and the control rod Can maintain soundness.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view showing an embodiment of a nuclear reactor control rod according to the present invention, and FIG. 2 is a II- line in FIG.
II is a sectional view taken in the direction of the arrow, FIG. 3 is a detailed view of the III portion in FIG.
4 (A), (B), and (C) are perspective views, plan views, and cross-sectional views of the central spacer in FIG. 3, respectively. FIG. 5 is a cross-sectional view of a wing of another embodiment, and FIG. 5 is a sectional view taken along the line VI-VI in FIG. 5, FIG. 7 is an overall perspective view of a conventional reactor control rod, and FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 1 ... Reactor control rod, 2 ... Handle, 3 ... Tip structural material, 4 ... End structural material, 5 ... Central tie rod, 6 ...
… Sheath, 7 …… Wing, 8 …… Neutron absorber, 8a…
… Neutron absorbing element, 8b …… Neutron absorbing plate, 9 …… Spacer, 10 …… Flow path, 11,11a …… Long hafnium material, 12 ……
Water passage, 13 ... Side edge spacer, 13a ... Plate mounting part, 14
…… Center spacer, 15 …… Ring spacer, 16 ……
Mounting seat, 17,17a …… Water passage, 18 …… Mounting hole, 19 …… Hollow part, 20 …… Dimple ring, 21,21a, 21b …… Water passage hole, 22
…… Through hole, 30 …… water passage, 31 …… through hole, 32 …… space.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location 9216-2G G21C 7/10 GDB L

Claims (7)

[Claims] 1. A tip structural member and an end structural member are connected by a central tie rod, and U is provided at each protrusion of the central tie rod.
A letter-shaped sheath is fixed and a wing is formed by inserting a plate-shaped long-life neutron absorber into the sheath to form a wing. While arranging the hafnium material, the neutron absorber is divided into a plurality of stages of neutron absorbing elements in the axial direction of the central tie rod, and the neutron absorbing elements of each stage are accommodated in a plurality facing each other in the thickness direction of the wings. Of the neutron absorbing plate, a plurality of spacers are locally interposed between the facing neutron absorbing plates to form a flow path for guiding the moderator while maintaining the facing interval of the neutron absorbing plates, while absorbing the neutrons. A control rod for a nuclear reactor, wherein a water passage groove is formed on a space holding surface of a spacer that abuts on an inner surface of the plate. 2. The control rod for a nuclear reactor according to claim 1, wherein a water passage is formed between the outer surface of the neutron absorbing plate and the inner surface of the sheath. 3. The control rod for a nuclear reactor according to claim 1, wherein the long hafnium material is formed in a hollow circular tube shape. 4. The sheath has a dimple ring protruding to the inner surface of the sheath, the top of the dimple ring is brought into contact with the neutron absorbing plate, and a water passage having a predetermined width is provided between the outer surface of the neutron absorbing plate and the inner surface of the sheath. The control rod for a nuclear reactor according to claim 2, wherein the control rod is formed. 5. The nuclear reactor control rod according to claim 4, wherein the dimple ring is formed in the sheath near the spacer. 6. A control rod for a nuclear reactor according to claim 1, wherein a water passage is formed at a protruding edge portion of the central tie rod. 7. The neutron absorbing plate has a through hole through which the spacer penetrates, and the inner diameter of the through hole is set to be larger than the outer diameter of the spacer so as to absorb the difference in thermal expansion between the sheath and the neutron absorbing plate. The control rod for a nuclear reactor according to claim 1, wherein