JPH0684993B2 - Control rod for nuclear reactor - Google Patents

Description

The present invention relates to a reactor control rod for adjusting and controlling reactor power of a nuclear reactor, and particularly to a long-life boiling water reactor. Regarding control rod.

(Prior Art) A control rod for a boiling water reactor has an elongated U-shaped central tie rod.
A large number of neutron absorbing rods are loaded in a plurality of wings formed by attaching a V-shaped sheath. The neutron absorbing rod is composed of a SUS cladding tube filled with boron carbide (B ₄ C) powder, while partition balls for preventing powder movement are arranged at regular intervals in the cladding tube.

B ₄ C filled in the neutron absorbing rod absorbs neutrons and gradually loses its ability to absorb neutrons.
10 ( ¹⁰ B) reacts with neutrons to generate He gas, increasing the pressure in the cladding. The life determined by the neutron absorption capacity is called the nuclear life, and the life determined by the gas pressure in the cladding is called the mechanical life.

By the way, the control rods taken in and out of the reactor core do not receive uniform neutron irradiation, and, for example, the side edges and upper ends of the wings receive strong neutron irradiation. For this reason, the neutron absorbing rods near the side edges and upper ends of the wings of the control rod absorb a large amount of neutrons, and thus reach the nuclear life earlier than other neutron absorbing rods. Therefore, the control rods had to be discarded as radioactive waste, even though the neutron absorbing rods in other parts had a sufficiently long nuclear life.

In order to solve such a problem, the present applicant has developed a control rod for a reactor in which a long-lived neutron absorbing plate having a long nuclear life is arranged near the side edge of a wing that receives strong neutron irradiation. This control rod for a nuclear reactor is disclosed in JP-A-53-74697.

However, the reactor control rod disclosed in Japanese Patent Laid-Open No. 53-74697 has a life of about twice as long as that of a normal type control rod, and is not necessarily satisfactory in extending the life of the control rod. There wasn't.

In order to address this problem of extending the service life, the present applicant has developed a control rod for a nuclear reactor of markedly superior life, as disclosed in Japanese Patent Laid-Open No. 58-55887. In this control rod for reactors, each wing of the control rod is loaded with a solid neutron absorbing plate made of a long-life neutron absorbing material. With this neutron absorbing plate, a small amount of plate material is cut at a part where the axial distribution of the reactor shutdown margin becomes small, and conversely a large amount of plate material is cut at a part where it becomes large. Has been set.

(Problems to be solved by the invention) However, in this control rod for a nuclear reactor, since a plate-shaped hafnium (Hf) metal plate that is expensive and has a large specific gravity is used as a neutron absorbing plate, the weight is very large, In addition to being expensive, the control rod drive mechanism for handling this control rod requires a weight-resistant design change, and the conventional control rod drive mechanism cannot be used as it is.

On the other hand, the hafnium metal plate, which is a long-lived neutron absorber used for reactor control rods, has room to be removed by weight, and if the weight of reactor control rods can be reduced by removing excess thickness, control rod drive mechanism It was confirmed in the subsequent study that the product can be used as it is without changing the design.

The present invention has been made in consideration of the above circumstances, and by effectively reducing the weight of the long-life neutron absorbing plate, a long-life nuclear reactor that can be used without changing the design of the control rod drive mechanism. The purpose is to provide a control rod for.

[Structure of Invention]

(Means for Solving the Problems) The control rod for a reactor according to the present invention connects the tip structural member and the end structural member by a central tie rod, and a sheath is fixedly provided on each protrusion of the central tie rod. In what inserted a plate-like long-life neutron absorbing plate in the sheath, the neutron absorbing plate is divided into a plurality of stages of neutron absorbing elements in the axial direction of the central tie rod, each stage of the neutron absorbing element is the flesh of the wing. Comprised of a plurality of neutron absorbing plates that are accommodated in opposition to each other in the thickness direction, while forming a gap that guides the moderator between the opposing neutron absorbing plates, between the neutron absorbing plates of the neutron absorbing elements that are adjacent in the axial direction. The gap formed in is formed so as to be masked by the opposing neutron absorbing plate.

(Operation) In the reactor control rod according to the present invention, a long-life type neutron absorbing plate is arranged along the axial direction of the central tie rod connecting the tip structural member and the end structural member, and the neutron absorbing plate is sheathed. Housed inside to form a wing. Then, the neutron absorbing plate disperses the weight, and absorbs the difference in elongation due to thermal expansion, etc., and is divided into a plurality of neutron absorbing elements in the axial direction of the central tie rod, and each neutron absorbing element is the meat of the wing. Consists of a plurality of neutron absorbing plates housed opposite to each other in the thickness direction, forming a gap that guides the moderator between the facing neutron absorbing plates, and increasing the reactivity by using this gap as a moderator flow path, Moreover, the weight of the neutron absorbing plate is reduced.

Further, the gap formed between the neutron absorbing plates of the neutron absorbing elements adjacent to each other in the axial direction is masked by the neutron absorbing plates arranged so as to face each other, and the neutron absorbing characteristic of the gap portion is smoothed.

(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 schematically showing a nuclear reactor control rod according to the present invention. The nuclear reactor control rod 10 is a cross-sectional view of a tip structural member 12 having a handle 11 and an end structural member 13. They are integrally connected by a cross-shaped central tie rod 14. 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 wing 16. A plate-shaped long-life neutron absorption plate 18 typified by a hafnium (Hf) metal plate or the like is inserted into the sheath 15.

A plurality of neutron absorption plates 18 are arranged in the axial direction of the central tie rod 14,
For example, as shown in FIG. 2, eight neutron absorption elements 18a-1
It is divided into 8h. The neutron absorbing elements 18a-18h in each stage are supported by a plurality of supporting spacers 20, respectively. As shown in FIG. 2, the supporting spacers 20 are fixed to the wings 16 at appropriate intervals to prevent the neutron absorbing elements 18a to 18h from moving up and down.

The neutron absorbing elements 18a to 18h in each stage are configured so that the neutron absorbing characteristics gradually decrease from the tip structure material 12 toward the end structure material 13. Specifically, when the neutron absorbing plate 18 is divided into eight stages of neutron absorbing elements 18a to 18h, the neutron absorbing elements 18a to 18h in each stage are gradually thinned from the tip structure material 12 toward the end structure material 13. As a result of this thinning, as shown in FIG. 3 (A), the reactivity effect, that is, the neutron absorption characteristic is gradually reduced.

In addition, in FIG. 3 (A), the example in which the neutron absorbing elements 18a to 18h of all the stages are thinned in stages in the axial direction has been described, but as shown in FIG. The neutron absorbing elements may have a plurality of stages, for example, two stages each having the same plate thickness. Further, as shown in FIG. It may be configured such that the thickness changes thinly.
It is also possible to combine the neutron absorbing elements shown in Figures (A) to (C) with each other.

Also, the first stage neutron absorbing element adjacent to the tip structure material 12
The tip side of 18a (for example, the area within 35 cm from the tip) has a neutron absorption characteristic that is increased to improve scrum characteristics, or a control rod is drawn to reduce the control rod extraction furnace. The fluctuation range of the output may be reduced. Also, at least the first stage neutron absorbing element 18
It is also possible to form a so that the neutron absorption characteristics on the side end side facing the central tie rod 14 side become large.

By the way, in the long-life reactor control rod 10, the tip structure material 12
Since the central tie rod 14, the sheath 15, and the like are irradiated with a very large amount of neutrons and this neutron irradiation may cause embrittlement, high-purity stainless steel is used to alleviate the problem of embrittlement due to neutron irradiation. There is. Also, advanced structural materials
12, the end structure material 13, and the speed limiter 22 attached to the end structure material 13 are made as thin as possible and lightened.

Further, as shown in FIG. 4, the neutron absorbing elements at each stage of the neutron absorbing plate 18 inserted into the sheath 15 are plate-shaped neutron absorbing plates 18 _a1 . 18 _a2 ; 18 _b1 ,
18 _b2 ... 18 _h1 and 18 _h2 are installed facing each other in the thickness direction of the wing 16. The neutron absorbing plates 18 _a1 , 18 _a2 ; As shown in FIG. 5, the supporting spacer 20 has a coma structure, and a supporting leg 20b is projectingly provided at the center of the spacing member 20a. The supporting leg 20b is formed on the neutron absorbing plates _18a1 and _18a2 ; Loosely pierce the hole 23
It is fixed to the inner wall of 15 by welding or the like. The holes 23 formed in the neutron absorbing plates facing each other in each stage of the neutron absorbing elements are the supporting legs.
It is formed with a diameter larger than 20b and can absorb expansion and contraction due to temperature changes. While supporting the neutron absorbing plate facing the support spacer 20 in the sheath 15,
A flat gap 25 for guiding the moderator is formed in the neutron absorbing plates 18 _a1 , 18 _a2, ... And this gap 25 is formed as a moderator flow path. As shown in FIG. 6, a plurality of water holes 26 communicating with the gap 25 are formed at the corresponding positions of the sheath 15 and the neutron absorbing elements at each stage of the neutron absorbing plate 18. In principle, the water passage hole 26 does not penetrate the wing 16 in a straight line.

The plate-shaped neutron absorbing elements 18a to 18h at each stage are, for example, 0.
It is a thin metal neutron absorption plate with a thickness of 5 mm to 2.0 mm. As shown in FIG. 3 (A), the tip structure material 12 side has a thickness of 1.5 mm to 2.0 mm.
The thickness of the end structure 13 side is 0.5 mm to 1.0 mm, and the middle portion thereof is appropriately set to the middle thickness.

7 is an enlarged view of the portion A of FIG. 2 with the support spacer omitted, and FIG. 8 is a side sectional view taken along the line VII-VII of FIG. 7.

Neutron absorbing elements 18a at each stage adjacent in the axial direction of the control rod 10,
18b… 18h neutron absorbing plates 18 _a1 . 18 _a2 ； 18 _b1 , 18 _b2 … 18
_A plurality of gaps 30 extending in the axial direction of the wing 16 between _h1 and 18 _h2
a, 30b are formed. Each of the gaps 30a and 30b has a stepped structure so as to be masked by the neutron absorbing plates facing each other. That is, the plurality of gaps 30a, 30b formed between the neutron absorbing elements between adjacent steps are masked by the neutron absorbing plates facing each other, and each gap does not have a common plane of the same height. Thus, the planes including the gaps 30a and 30b are formed at different positions.

FIGS. 9 to 11 show respective modifications of the neutron absorbing elements between adjacent stages, and the gaps 31a, 31b; 32a formed between the adjacent neutron absorbing elements shown in the respective modifications. ,
32b; 33a and 33b are the ones in which the front side of the wing and the rear side (rear surface) of the wing intersect each other, and the overlapping portion is made as small as possible. By reducing the overlapping portion of the gaps formed on the wing front surface side and the back surface side, it is possible to prevent the reactivity position of the control rod from being lowered.

The gap formed between the neutron absorbing elements of each adjacent stage is
Various modifications other than those shown in FIGS. 9 to 11 are easily conceivable.

Next, the operation of the reactor control rod 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 represented as shown in FIG. Combustion management of the reactor core is divided into four equal parts in the axial direction of the reactor core.
It is convenient to divide 10 into four equal parts.

At the lower end of the reactor core, the progress of combustion is delayed during combustion,
When the fission nuclide concentration value is large and the axial length of the reactor core is L, the hardening phenomenon of the neutron spectrum occurs from the central part (2 / 4L) to the upper end due to the generated bubbles (voids). . As a result, the plutonium production reaction (neutron absorption reaction) is promoted, and the generated neutron flux decreases the thermal neutron flux, and this decrease causes combustion delay. Therefore, the fission nuclide concentration distribution is as shown in Fig. 12. Represented.

When the nuclear fission nuclide concentration shown in FIG. 12 is present in the core of the reactor, the neutron multiplication factor at the time of reactor shutdown is in the form of a distribution curve B shown in FIG. The larger the neutron multiplication factor, the smaller the shutdown margin of the reactor and the shallower the subcriticality. The thirteenth
From the figure, the decrease in neutron multiplication factor at the lower and upper ends of the reactor core is a phenomenon caused by neutron leakage.

FIG. 14 is an axial neutron irradiation distribution curve C of the reactor control rod 10 when the reactor control rod 10 according to the present invention is used. From this distribution curve C, the control rod 10 for a nuclear reactor has a region where the neutron irradiation dose rapidly rises in a very limited region (usually about 30 cm from the tip) at the upper end. The other portion is continuously and smoothly reduced toward the lower end of the reactor control rod 10.

The reactor control rod 10 according to the present invention is configured so that a satisfactory control effect can be obtained with respect to the neutron multiplication characteristics shown in FIG. 13 and the neutron dose characteristics shown in FIG. That is, the tip of the reactor control rod 10 (1 / 4L length, for example 90
cm ~ 95 cm), the neutron multiplication factor is high (that is, the stop margin is small) and the neutron irradiation is high, and the stop margin is likely to decrease.

Further, as shown in FIGS. 3 (A) to (C), the neutron absorbing element is made thinner as it goes from the tip structure material 12 to the end structure material 13, and the neutron absorption effect gradually decreases. In particular, the lower end of the reactor control rod 10 (end structure material 13
Neutron absorption characteristics in the 1 / 4L region from 1 / 4L)
It is slightly smaller than between 2 / 4L. this is,
As shown in Fig. 14, the lower region from the lower end to 1 / 4L is much smaller than the next adjacent region (1 / 4L to 2 / 4L) in neutron irradiation dose, but the neutron multiplication factor is Fig. 13 This is because it becomes relatively large as shown in.

Further, the neutron absorber 18 housed in the wing 16 of the reactor control rod 10 is divided in the axial direction into the neutron absorbing elements 18a, 18b, ...
The gaps 30a and 30b formed at the boundaries of 18a, 18b ... 18h are provided so as to be stepped or crossed so as not to have a common plane. The gaps 30a and 30b are adjacent to each other in the axial direction by the neutron absorbing plate 18
It is formed between _a1 , _18a2 ; _18b1 , _18b2 ... _18h1 , _18h2 , but one of the gaps 30a, 30b is masked by the neutron absorbing plates facing each other, so that it is formed in the thickness direction of the wing 16. Each gap 30
The a, 30b (31a, 31b; 32a, 32b; 33a, 33b) are never aligned.

Therefore, when the neutron absorbing elements 18a, 18b ... 18h are arranged while being divided in the axial direction, it is possible to suppress the decrease in reactivity due to the gaps 30a, 30b generated at the boundaries of the neutron absorbing elements in each stage. .

Although various modifications have been described for the reactor control rod according to the present invention, various other modifications are possible without departing from the spirit of the invention.

〔The invention's effect〕

As described above, in the control rod for a reactor according to the present invention, the neutron absorber is divided into a plurality of stages of neutron absorbing elements in the axial direction of the central tie rod, and each neutron absorbing element is opposed to the wing thickness direction. Since a plurality of neutron absorbing plates accommodated in the neutron absorbing plate are formed, and a gap for guiding the moderator is formed between the neutron absorbing plates facing each other, it is possible to reduce the weight of the neutron absorber by at least the gap. Therefore, it is possible to surely and effectively reduce the weight of the control rod for a nuclear reactor, and it is possible to backfit the existing control rod drive mechanism without changing the design.

In addition, while guiding the moderator into the gap of the neutron absorber, the gap formed between the neutron absorbing plates of the neutron absorbing elements that are adjacent to each other in the axial direction is masked by the opposing neutron absorbing plates so that the gaps do not overlap. Therefore, the neutron reaction can be improved, and the neutron absorbing material can be reduced accordingly. Further, since the neutron absorbing element of the neutron absorber can be effectively arranged at an important position in the stop margin, the reactivity is effectively increased and the stop margin of the reactor is improved.

[Brief description of drawings]

FIG. 1 is an overall perspective view showing an embodiment of a nuclear reactor control rod according to the present invention, FIG. 2 is a diagram showing a positional relationship of neutron absorbers incorporated in the nuclear reactor control rod, and FIG. A) ~
(C) is a diagram showing the relationship between the reactor control rod height direction and reactivity effect (neutron absorption characteristics), and FIG. 4 is IV-IV in FIG.
5 is a partial plan sectional view taken along the line, FIG. 5 is a view showing a support spacer for supporting the neutron absorbing element at each stage, FIG. 6 is a plan sectional view taken along the line VI-VI of FIG. 1, and FIG. Is a partial view showing an enlarged part A of FIG. 2, FIG. 8 is a side sectional view taken along the line VIII-VIII of FIG. 7, and FIGS. 9 to 11 are examples of modified arrangements of neutron absorbers. Figure, Figure 12 is a diagram showing the fission nuclide concentration distribution in the axial direction of the nuclear reactor core, Figure 13 is a diagram showing the neutron multiplication distribution in the axial direction of the nuclear reactor core, Figure 14 is an atom according to the present invention It is a figure which shows the neutron dose distribution in the axial direction of the control rod for reactors. 10,10A, 10B, 10C, 10D, 10E, 10F ... Reactor control rods, 12 ...
... tip structural member, 13 ...... end structural member, 14 ...... central tie rod, 15 ...... sheath, 16 ...... wings, 18 ...... neutron absorbers, 18a, ～18H ...... neutron absorbing elements, 18 _a1. 18 _a2 ； 1
8 _b1 , 18 _b2 … 18 _h1 , 18 _h2 …… neutron absorption plate, 20 …… support spacer, 25 …… gap, 26 …… water passage hole, 30a, 30b, 31a, 31
b, 32a, 32b, 33a, 33b …… Gap.

Front page continuation (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location 9117-2G G21C 7/10 GDB J

Claims (7)

[Claims] 1. A tip structural material and an end structural material are joined by a central tie rod, a sheath is fixedly provided on each protruding portion of the central tie rod, and a plate-shaped long-life neutron absorber is inserted into the sheath. In a control rod for a reactor in which wings are formed, 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 facing each other in the thickness direction of the wings. Is formed of a plurality of neutron absorbing plates, a gap is formed between the neutron absorbing plates to guide the moderator between the neutron absorbing plates, while the gap formed between the neutron absorbing plates of the neutron absorbing element adjacent in the axial direction is opposed. A control rod for a nuclear reactor, which is configured to be masked by a neutron absorbing plate. 2. The plurality of gaps formed between the neutron absorbing plates of the neutron absorbing elements adjacent to each other in the axial direction are arranged such that the planes including the gaps are different from each other. Control rod for nuclear reactor. 3. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorbing element is configured so that the neutron absorbing characteristic gradually decreases from the tip structural material toward the terminal structural material. 4. The neutron absorbing element according to claim 1, wherein the neutron absorbing element is gradually thinned from the tip structure material toward the end structure material.
2. The control rod for a nuclear reactor according to item 2 or item 2. 5. The control rod for a nuclear reactor according to claim 1, wherein the neutron absorbing element has a wing absorption characteristic at an outer end portion of the wing larger than that of other portions. 6. The control for a nuclear reactor according to claim 1, wherein support spacers are arranged in the sheath at intervals in the axial direction, and each support spacer engages and supports a neutron absorbing element. rod. 7. The neutron absorbing element is composed of a plurality of neutron absorbing plates such as hafnium metal plates which are housed facing each other in the wall thickness direction of the wing, and the facing metal neutron absorbing plates are spaced by a support spacer. Claim 1, wherein a moderator gap is formed between the metal neutron absorbing plates.
A control rod for a nuclear reactor according to the item.