JPS62235595A - 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 nuclear reactor control rod that adjusts and controls the reactor power of a nuclear reactor, and particularly relates to a long-life nuclear reactor control rod. .

(Prior Art) A control rod for a nuclear reactor is constructed by loading a large number of neutron absorption rods into a plurality of wings formed by attaching an elongated U-shaped sheath to a central tie rod. The neutron absorption rod is 5
The usz tube is filled with boron carbide (B4C) powder, and partitions are placed at regular intervals in the cladding tube to prevent powder movement.

The B4C filled in the neutron absorption rod absorbs neutrons and gradually loses its neutron absorption ability, and during this time boron-10 (B) reacts with the neutrons to generate He gas and increase the pressure inside the cladding tube. let Is the lifetime determined by the neutron absorption capacity a nuclear standard? The life determined by the gas pressure inside the cladding tube is called the mechanical life.

By the way, control rods that are moved in and out of the core of a nuclear reactor are not uniformly irradiated with neutrons; for example, the side edges and upper ends of each wing are exposed to strong neutron irradiation. For this reason, the neutron absorbing rods near the side edges and upper ends of each wing of the control rod absorb a large number of neutrons, and therefore reach their nuclear lifetime earlier than the other neutron absorbing rods. As a result, the control rod had to be disposed of as radioactive waste, even though the other neutron-absorbing rods still had sufficient nuclear lifespan.

In order to solve such problems, the applicant has developed a nuclear reactor control rod in which a long-life neutron absorber with a long nuclear life is placed near the side edge of the wing, which is exposed to strong neutron irradiation. This control rod for a nuclear reactor is disclosed in Japanese Patent Application Laid-open No. 74697/1983.

However, the life of the nuclear reactor control rod disclosed in JP-A-53-74697 was only about twice that of a conventional control rod, and was not necessarily sufficient to extend the life of the control rod.

In order to address this problem of longer life, the present applicant has developed a control rod for nuclear reactors of a much superior long life type. This reactor tIIJIIl rod is published in Japanese Patent Application Publication No. 58-55887.
As disclosed in the publication, a solid neutron absorbing plate made of a long-life neutron absorbing material is loaded inside the raku wing of the vItll rod. This neutron absorption plate is designed so that a small amount of plate material is removed in areas where the axial distribution of the reactor shutdown margin is small, and conversely, a large amount of plate material is removed in areas where the axial distribution of the reactor shutdown margin becomes large. has been established.

(Problems to be Solved by the Invention) However, this control rod for a nuclear reactor uses an expensive hafnium (Hf) metal plate as a neutron absorbing material, so it is very heavy and expensive. It was necessary to change the design of the lateral drive mechanism of the υJtll rod drive machine that handles this control rod, and the conventional l1fj rod drive mechanism could not be used.

However, there is still room to remove the hafnium metal plate, which is a long-life neutron absorbing material used in ailJIIl rods for nuclear reactors, in terms of weight, and if the weight can be reduced by 8, the control rod drive mechanism can be used without changing the design. was confirmed in subsequent studies.

The present invention has been made in consideration of the above-mentioned circumstances, and by effectively reducing the need for long-life neutron absorbers, it is possible to create control rods for nuclear reactors that can be used without changing the design of the control rod drive mechanism. The purpose is to provide.

[Structure of the invention]

(Means for Solving the Problems) A 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 has a deep U-shaped cross section in each protrusion of the central tie rod. A plate-like long-life neutron absorber is inserted into the sheath, and the neutron absorber is divided into a plurality of neutron absorbing elements in the axial direction of the central tie rod, and A neutron absorber has a gap formed between opposing neutron absorbing elements to guide a moderator.

(Function) The control rod for a type nuclear reactor according to the present invention has a long-life neutron absorber disposed along the axial direction of the central tie rod that connects the tip structural member and the terminal structural member. deep U
It is housed within a sheath having a letter-shaped cross section. The neutron absorber is divided into a plurality of neutron absorbing elements in the axial direction of the central tie rod, and the neutron absorber is divided into opposing neutron absorbing elements! ! A gap is formed between the cables to guide the moderator, and this gap is used as a moderator flow path to increase the reactivity and reduce the weight of the neutron absorber.

(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. 1 is an overall perspective view showing a nuclear reactor control rod according to the present invention, and this nuclear reactor control rod 10 integrally connects a tip structure member 12 provided with a handle 11 and an end structure member 13. It has a central tie rod 14 having a cross-shaped cross section. A high purity stainless steel sheath 15 having a deep U-shaped cross section is fixed to each protruding leg of the central tie rod 14 to form a webbing 16. 1 inside the sheath 15. A plate-shaped long-life neutron absorber 18 made of a hafnium (Hf) metal plate is inserted.

There are a plurality of neutron absorbers 18 in the axial direction of the central tie 14, for example, as shown in FIG. 2, there are four neutron absorbers 18a serving as metal neutron absorbing plates.

It is divided into 18b, 18c, and 18d. In FIG. 2, the right half shows the state in which the neutron absorption elements 188 to 18d are not inserted, and the left half shows the state in which they are inserted. Among the neutron absorbing elements at each stage, the neutron absorbing elements 18a, 18b, and 18C, excluding the neutron absorbing element 18d on the terminal structural member 13 side, are supported by the absorbing element support piece 20. The support pieces 20 are provided protruding from each of the protruding legs of the central tie rod 14 at appropriate intervals to prevent vertical movement of the neutron absorption elements 518a to 18C.

The lowest neutron absorbing element 18d is held by the terminal structure member 13.

The neutron absorption elements 188 to 18d of each stage are the tip structure material 12
The structure is such that the neutron absorption characteristics gradually decrease from the end structure member 13 toward the end structure member 13. Specifically, neutron absorber 1
8 is divided into four stages of neutron absorbing elements 188 to 18d, each stage of neutron absorbing elements 188 to 18d is the tip structure material 1.
The thickness is gradually reduced from 2 to the terminal structural member 13, and as a result of this thinning, the reactivity effect, that is, the neutron absorption property is gradually reduced as shown in 3rd rj4.

Further, the tip side of the first stage neutron absorption element 18a adjacent to the tip structure member 12 (for example, an area within 35 feet from the tip)
The control rod design and the method of using the l+1111 rod may increase the neutron absorption characteristics to improve the scram characteristics, or may be made smaller to reduce the fluctuation range of reactor power due to the withdrawal of the v4IIl rod. Also, at least the first
The neutron absorbing elements 18a of the stages are formed so that the neutron absorbing characteristics on the side end portion facing the central tie rod 14 side are increased.

By the way, in the control rod 10 for a long-life nuclear reactor, the tip structural member 12 is exposed to a very large amount of neutron irradiation, and there is a possibility that it will become brittle due to this neutron irradiation. Therefore, high-purity stainless steel is used. It alleviates the problem of brittleness. Furthermore, the tip structural member 12, the terminal structural member 13, and the speed limiter 22 attached to the terminal structural member 13 are made as thin as possible and lightweight. In addition, reactor aI1
1, the control rod 10 has a gap 23 formed at the bottom of the tip structure member 12, and this gap 23 is configured as an auxiliary handle part.

The auxiliary handle portion 23 is a portion that does not require a neutron absorbing material in terms of neutron absorption performance, and the reactor control rod 10 is further lightened by the void 1123 of the auxiliary handle portion.

On the other hand, it has been experimentally determined that the fast neutron irradiation fJ4ffi at the upper part of the auxiliary handle is approximately 1/3 to 1/5 or less than the amount of fast neutron irradiation at the upper part of the handle. From this, the embrittlement of the auxiliary handle part 23 due to neutron irradiation is about 173 to 175 or less than the embrittlement of the handle part, so providing the auxiliary handle part 23 provides a very healthy handle backup in case of an emergency. It becomes a function.

Moreover, the neutron absorber 18 inserted into the sheath 15 is
As shown in FIG. 4, two plate-shaped neutron absorption elements 18a are made of hafnium metal plates.

18a are installed facing each other. Both neutron absorption elements 18a
, 18a are spaced apart by spot-shaped spacers 24. This spacer 24 allows the neutron absorbing element 18a to
In addition to improving the strength of the neutron absorbing element 188
．． A flat section FJ that guides the moderator inside 18a! 25 is formed, and this 1111 m25 is formed as a moderator flow path. A plurality of water holes 26 communicating with the 1II 125 are formed at corresponding locations between the sheath 15 and the neutron absorbing element 18a. In principle, the water holes 26 do not penetrate the wing 16 in a straight line.

The plate-shaped neutron absorption element 18a, isa is, for example, 0
．． It is a thin plate with a thickness of 5 mm to 2.0 mm, and the end sides of the wings 16 are curved in opposite directions, and a small gap is formed at the tip to ensure flexibility of the neutron absorbing element 18a.

Next, the operation of the nuclear reactor control rod 1o will be explained.

In a boiling water reactor, the axial fission nuclide concentration distribution curve $1A of the reactor core in which combustion has progressed to a certain extent is expressed representatively as shown in FIG. Nuclear reactor core combustion 11
Since the control is divided into four equal parts in the axial direction of the reactor core, it is convenient to divide the reactor control rods 10 into four equal parts.

At the bottom of the reactor core, the progress of combustion is delayed during combustion, so
The fission nuclide concentration value is increasing, and when the axial length of the reactor core is L, the neutron spectrum hardens due to the generated air bubbles (voids) from the center (2/4L) to the top. . As a result, the plutonium production reaction (neutron reaction) is promoted, and the thermal neutron flux decreases due to the generated voids, and this decrease causes a combustion delay, so the fission nuclide concentration distribution is expressed as shown in Figure 5. It will be done.

When the nuclear fission nuclide concentration shown in FIG. 5 exists in the reactor core, the neutron multiplication factor at the time of reactor shutdown has an axial partial surface 11B shown in FIG. 6.

The larger the value of the neutron multiplication factor, the smaller the reactor shutdown margin and the shallower the subcriticality. Figure 6 shows that the neutron multiplication factor decreases at the lower and upper ends of the reactor core. This is a phenomenon caused by neutron leakage.

Figure 7 shows tA III rod 1 rod 0 for nuclear reactor according to the present invention.
It is an axial neutron irradiation dose distribution curve C of the nuclear reactor control rod 10 when used. From this distribution -$90, there is a region in the upper end of the nuclear reactor control rod 10 where the neutron irradiation R rapidly increases in a very limited region (usually about 30α from the tip). The other portions continuously and smoothly decrease toward the lower end of the reactor control rod 10.

The nuclear reactor control rod 10 according to the present invention is configured to provide a satisfactory control effect on the neutron multiplication factor characteristics shown in FIG. 6 and the neutron irradiation ω characteristics shown in FIG. In other words, at the tip of the V4Ill rod 10 for a nuclear reactor (length of 1/4 m, for example, about 90s to 953), the neutron multiplication factor increases (that is, the shutdown margin becomes small) and the neutron irradiation table becomes high, causing the shutdown margin to decrease. The company is dealing with the fact that it tends to decline.

Further, as shown in FIG. 3, the neutron absorption element becomes thinner from the tip structure member 12 to the end structure member 13,
The neutron absorption effect is gradually decreasing. In particular, the neutron absorption characteristics of the 1/4 L region from the lower end (upper end of the terminal structural member 13) of the reactor ajj control rod 10 are 1/4
It is slightly smaller than between L and 2/4L. In terms of neutron irradiation, as shown in Figure 7, the lower region from the bottom to 1/4L is the next adjacent region (1/4
This is because the neutron multiplication factor becomes relatively large, as shown in FIG. 6, although it is considerably smaller than that of 2/4 L).

In addition, FIG. 8 shows a typical neutron irradiation population distribution curve 1 in the width direction of each wing 16 of a 1IJII1 rod 10 for a nuclear reactor.
i1D, and as can be seen from this distribution -SO, it increases rapidly on the outside of the wing, and increases slightly on the side of the center tie rod 14 inside the wing. From this, the reactivity effect E of the neutron absorber 18 can be set as shown in the ninth factor by changing the neutron absorption characteristics in the width direction of the wing 16. , At that time, in the nuclear reactor control rod 10 of the present invention, each neutron absorption element 188 to 1ad of the plate-shaped long-life neutron absorber 18 is
fl is formed from a flesh plate, and a flat space Fj is formed between the neutron absorption elements.
i25 was formed, and during this period, the inside of Fl125 was used as a flow path for the moderator, so the neutron absorber 1 accommodated in the wing 16
Conventional F1a between 8 and 11.

This can be significantly reduced compared to neutron absorbers that do not form. Therefore, for nuclear reactors! The overall weight of the 1lIil rod 10 can be reduced, and the existing control rod drive mechanism can be used as is without any design changes.

Next, another example of the 4IJII1 rod for nuclear reactors will be described.

FIG. 10 to FIG. 12 show the uji for nuclear reactor according to the present invention.
11 shows a second embodiment of the ll rod.

The nuclear reactor rod 10A shown in this embodiment has two neutron absorbing elements 28a and 28b constituting a plate-like long-life neutron absorber 18A and a spot-like spacer 29.
The outer ends of the opposing neutron absorbing elements 28a and 28b, that is, the wing end side, are fixed by side end tie rods 30 to strengthen them.

The outer edges of the neutron absorption elements 28a and 28b are exposed to neutron irradiation a.
The side tie rods 30 can effectively improve the reactivity. The central tie rod 14 sides of the opposing neutron absorbing elements 28a, 28b are curved so as to approach each other, and the neutron absorbing elements 28a, 28b absorb the elongation due to neutron irradiation growth.

The other configuration is the reactor control rod 1 shown in Figures 1 to 4.
Since it is the same as 0, the same reference numeral is given and the explanation is omitted.

In this case as well, the reactor UtS rod 10 shown in one embodiment
It has a similar effect.

Figure 13 shows aI1111 rod 10B for nuclear reactor according to the present invention.
This shows a third embodiment of the invention.

In the reactor control rod 10B shown in this embodiment, the neutron absorber 18B housed in the sheath 15 constituting the wing 16 has two neutron absorbing elements 31a and 31b made of hafnium metal plates in a deep U. The neutron absorbing elements 318 and 31b are curved into a letter shape and installed with their U-shaped openings facing each other via a stiffener 32 which also serves as a spacer. Neutron absorption elements 31a, 3 curved into a U-shape
A gap 25 is formed inside 1b to guide the moderator.

The gap 25 within the neutron absorbing element 318.31b is secured by the engagement step of the stiffener 32 or the corrugated plate 33. The corrugated plate 33 is preferably made of a long-life neutron absorbing material such as hafnium, and is disposed so as to be interposed on the outside of the wing 16 .

FIG. 14 shows a fourth embodiment of a control rod for a nuclear reactor according to the present invention.

This reactor control rod 10C is the sheath 15 of the wing 16.
The long-life neutron absorber 18C housed inside is formed of a neutron absorbing element 36 curved into a deep U-shape, and a gap 25 for guiding a moderator is formed within this neutron absorbing element 36.

The neutron absorbing element 36 is formed of a hafnium metal plate, and is formed into concave and convex portions so that the center portions in the width direction of the wings 16 mutually protrude inwardly, and the protruding portions 36a,
The gap 25 is secured by the gap 36b, and also serves as an escape area for irradiation growth during neutron irradiation. Neutron absorption element 36
The opening expands in a tapered shape toward the center tie rod 14, and is tapered into engagement with the protruding leg of the center tie rod 14 with a gap therebetween.

FIG. 15 shows a fifth embodiment of a nuclear reactor control rod 10D according to the present invention.

This 1lIII rod 100 for a nuclear reactor has a stiffener 37 interposed in the sheath 15 of the wing 16, and a sheath 1
5, plate-shaped long-life neutron absorbers 18D are interposed on both sides of the stiffener 37, respectively. This neutron absorber 18D has two neutron absorbing elements 388 and 38b installed facing each other, and both ends thereof are folded inward to form an FJi 25 for guiding a moderator inside.

At this time, since the neutron absorption elements 38a and 38b are folded back at a position where the amount of neutron irradiation is high, the wall becomes substantially thick in this part, and the reactivity effect (neutron absorption characteristics) can be effectively enhanced. . In particular, the folding amount of the neutron absorbing element 38b on the blade tip side of the wing 16 is 1
Approximately 1 to 31 is desirable.

FIG. 16 shows a sixth embodiment of the present invention.

In the reactor tII111 rod 10E shown in this embodiment, the long-life neutron absorber housed in the sheath 15 of the wing 16 is formed by bending two plate-shaped neutron absorbing elements 39° 39 into a deep U-shape. The U-shaped neutron absorbing elements 39 are accommodated in the sheath 15 in an aligned state facing the width direction of the wings 16.

The opening of the neutron absorbing element 39 is largely curved from one side toward the other side, thereby creating a gap 25 within the neutron absorbing element 39.
In addition to holding the neutron irradiation, it also forms an escape margin during neutron irradiation growth.

FIG. 17 shows a seventh embodiment of the present invention.

The nuclear reactor control rod 10F shown in this embodiment has a stiffener 40 interposed in the sheath 15 of the wing 16, and plate-shaped long-life neutron absorbers 18F are placed facing each other on both sides of the stiffener 40. This is what I did. The neutron absorber 18F includes two neutron absorbing elements 41a made of hafnium metal plates.

41b are arranged to face each other, and a gap 11i25 is formed therein as a moderator flow channel.

One end of the neutron absorbing element 418.41b is slightly curved, and the other end is greatly curved so as to wrap around one end of the opposing neutron absorbing element. In this case as well, the gap 25 within the neutron absorber is maintained by the curved forming of both ends of the neutron absorbing elements 41a, 41b, and a countermeasure against irradiation growth is taken.

Although various embodiments of the nuclear reactor control rod according to the present invention have been described, various other modifications can be made without departing from the spirit of the invention.

〔Effect of the invention〕

As described above, in the nuclear reactor control rod according to the present invention, the neutron absorber is divided into a plurality of neutron absorbing elements in the axial direction of the central tie rod, and the moderator is inserted between the opposing neutron absorbing elements. Because we created a guiding gap,
During this time, at least the neutron absorber can be relieved by the simple act. Therefore, the control rod for a nuclear reactor can be made lighter and more effective, and the existing control rod drive mechanism can be backfitted as is without changing the design.

Further, by guiding the moderator into the gap between the neutron absorbers, the reactivity can be improved, and the neutron absorber can be reduced accordingly. Furthermore, since the neutron absorbing elements of the neutron absorber can be effectively arranged at important positions with sufficient shutdown margin, the reactivity is effectively increased and the shutdown margin of the reactor is improved.

[Brief explanation of drawings]

Fig. 1 is an overall perspective view showing one embodiment of the υ1111 rod for nuclear reactor according to the present invention, and Fig. 2 is the &lJ II rod for nuclear reactor mentioned above.
A diagram showing the arrangement relationship of neutron absorbers incorporated in the I rod,
Figure 3 is a diagram showing the relationship between the height direction of TSM rods for nuclear reactors and the reactivity effect (neutron absorption characteristics), and Figure 4 is the rV of Figure 1.
- A partial plan cross-sectional view along the rV line, Figure 5 is a diagram showing the fission nuclide concentration distribution in the axial direction of the nuclear reactor core, and Figure 6 is a diagram showing the neutron multiplication factor distribution in the axial direction of the nuclear reactor core. , FIG. 7 is a diagram showing the neutron irradiation dose distribution in the axial direction of the 1i1J control rod for a nuclear reactor according to the present invention, FIG. 8 is a diagram showing the neutron irradiation distribution in the wing width direction of the control rod for a nuclear reactor, Figure 9 shows the reactivity effect in the wing width direction of the 1IIJII1 rod for nuclear reactors, and Figure 10 shows a second embodiment of the control rod for nuclear reactors according to the present invention, which is a long-life neutron absorber. The partial diagram shown in Fig. 11 is (G-) of Fig. 10.
12 is a plan sectional view showing a wing of a control rod for a nuclear reactor according to the second embodiment of the present invention, and FIGS. 13 to 17 are sectional views taken along line G. The third control rod for the reactor
FIG. 7 is a plan sectional view of a wing showing examples to a seventh example, respectively. 10.10A, 10B, IOC, 100, 10E, 10
F...III control rod for nuclear reactor, 12...Tip structural material,
13... End structure material, 14... Center tie rod, 1
5...Sheath, 16...Wing, 18.18A. 188.18G, 180.18E, 18F... Neutron absorber, 18a, 18b, 18c, 18d, 28a, 2
8b, 31a, 31b, 36.38a. 38b, 39.41a, 41b...neutron absorption element,
20... Absorption element support piece, 23... Auxiliary handle part, 25... ff! l1lEi, 26... Water hole, 3
0...Side end tie Otsu'do, 33...Corrugated plate. Applicant's agent Hisasai Hatano Bottom of Figure 6 it it Fang L
Kamikohide 7 times

Claims (1)

[Claims] 1. The tip structural member and the terminal structural member are connected by a central tie rod, and a sheath having a deep U-shaped cross section is fixed to each protrusion of the central tie rod, and a plate-shaped In the control rod for a nuclear reactor in which a long-life neutron absorber is inserted, the neutron absorber is divided into a plurality of neutron absorbing elements in the axial direction of the central tie rod, and the neutron absorber is divided into a plurality of neutron absorbing elements facing each other. A control rod for a nuclear reactor, characterized in that a gap for guiding a moderator is formed between the rods. 2. The neutron absorbing element is configured such that the wall thickness of the neutron absorbing element is gradually reduced from the tip structural member to the terminal structural member, and the neutron absorption characteristics gradually decrease toward the terminal structural member. Control rods for nuclear reactors. 3. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorbing element is gradually thinned from the tip structural member to the terminal structural member. 4. Among the neutron absorbing elements, at least the neutron absorbing element adjacent to the tip structure material has a side end facing the central tie rod that has greater neutron absorbing characteristics than other parts. Control rods for nuclear reactors. 5. Absorbing element supporting pieces are provided on each protruding leg of the central tie rod at intervals in the axial direction, and each supporting piece engages and supports a neutron absorbing element. Control rods for nuclear reactors. 6. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorbing element adjacent to the tip structure member is provided with an auxiliary handle adjacent to the neutron tie rod. 7. The control rod for a nuclear reactor according to claim 1, wherein the sheath and the neutron absorption element within the sheath are provided with water holes communicating with the moderator guide gap at corresponding locations. 8. The neutron absorbing element is composed of two metal neutron absorbing plates such as hafnium metal plates that are housed in a sheath facing each other, and the opposing metal neutron absorbing plates are spaced apart by a spot-shaped spacer, so that both metal neutron absorbing elements The control rod for a nuclear reactor according to claim 1, wherein a gap for a moderator flow path is formed between the plates. 9. The neutron absorbing element consists of two metal neutron absorbing plates housed in a sheath facing each other, and the outer ends of the wings of the two facing metal neutron absorbing plates are fixed to the side end tie rods. A control rod for a nuclear reactor according to claim 1. 10. The metal neutron absorption plates are configured in a rectangular shape, and both ends of the opposing metal neutron absorption plates are folded back, and the distance between the opposing metal neutron absorption plates is maintained by the folded portions.Claim 8 Or a control rod for a nuclear reactor according to item 9. 11. Both ends of the two opposing metal neutron absorption plates are curved with different curvatures, so that one end of one metal neutron absorption plate is wrapped with the opposite end of the other metal neutron absorption plate. Claim 8 or 9 as constructed
Control rods for nuclear reactors as described in Section 1. 12. The neutron absorption element is made of a metal neutron absorption plate such as a hafnium metal plate, and the metal neutron absorption plate has a deep U
The atoms according to claim 1, which are curved and formed to have a letter-shaped cross section, and a spacing piece is provided at the center in the width direction of this U-shaped metal neutron absorption plate to maintain a gap for guiding a moderator. Control rod for furnace. 13. The neutron absorbing element is made of a metal neutron absorbing plate such as a honey metal plate, and the metal neutron absorbing plate is curved to have a deep U-shaped cross section, and the central part in the width direction is formed to have a concave and convex shape to form a moderator. The control rod for a nuclear reactor according to claim 1, wherein the interval between the guide gaps is maintained. 14. The neutron absorbing element is made of a metal neutron absorbing plate such as a hafnium metal plate, and the neutron absorbing plate is curved to have a deep U-shaped cross section, and the opening thereof is held by a spacing piece. A control rod for a nuclear reactor according to item 1.