JPH01284796A - Control rod for nuclear reactor - Google Patents

Abstract

PURPOSE:To prevent corrosion products from being formed between a sheath and a diluted alloy plate by preventing the diluted alloy plate and the sheath which covers it from coming into surface contact with each other, and holding the gap between the diluted alloy plate and sheath constant at the same time and allowing a reactor cooling material to flow. CONSTITUTION:The diluted alloy plate 9a of a long-lived neutron absorbing material does not come into surface contact with the internal surface of the sheath 3a between wings 4a of the control rod, and a flow passage for reactor cooling water is secured between the diluted alloy plate 9a and sheath 3a. Consequently, corrosion products are prevented from being deposited on the gap between the diluted alloy plate 9a and sheath 3a and oxygen which is decomposed with radiation never stays in the gap, thereby improving the corrosion resistance of the sheath. Further, the gap between the diluted alloy plate and sheath is held constant, so even if the corrosion products are deposited on the gap, no press spreading force resulting from wedge operation operates on the sheath and large bending stress is not generated.

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, and particularly to a control rod for a nuclear reactor equipped with a long-life neutron absorbing material that controls the output of a nuclear reactor. Concerning control rods.

(Prior Art) A reactor control rod 1 of a conventional boiling water reactor has a plurality of wings formed by attaching an elongated U-shaped sheath 3 to a central tie rod 2, as shown in FIGS. 9 and 10. It is constructed by loading a large number of neutron absorption rods 5 into the neutron absorbing rod 4.

The neutron absorption rod 5 is prepared by filling a stainless steel cladding tube with poron carbide (84C) powder as a neutron absorption material.

When this reactor control rod 1 is inserted into the core of a boiling water reactor, the neutron absorbing material filled in the sheath 3 is irradiated with neutrons and gradually loses its neutron absorption ability. After being operated for a predetermined period of time, it is periodically converted.

By the way, the control rods used in the core of a nuclear reactor are not uniformly irradiated with neutrons over the entire surface of each wing 4. For example, the insertion tip region and outer edge region of each wing are irradiated with intense neutrons. . Therefore,
The neutron absorbing material filled in that area absorbs a large amount of neutrons and is consumed more quickly than other areas, reaching its nuclear lifetime earlier. Therefore, even though the neutron absorbing material filled in other areas still has sufficient nuclear life left, it is uneconomical that the entire reactor control rod must be disposed of as radioactive waste. On the other hand, if the control rods for a nuclear reactor are replaced frequently, the replacement work takes a long time, which reduces the operating rate of the reactor and causes a major economic disadvantage. Additionally, there is also the possibility that workers' radiation exposure will increase.

In order to solve the above-mentioned problems, a control rod for a nuclear reactor has been proposed that uses a long-life neutron absorbing material such as hafnium, which has a long nuclear life, in the region of the control rod that is subjected to intense neutron irradiation. One example of such a reactor control rod is the first
The structure shown in FIG. 1 and FIG. 12 is obtained. That is, in a nuclear reactor control rod 1a in which a tip structural member 7 and a terminal structural member 8 are connected by a central tie rod 2, and a stainless steel sheath 3 is attached to the central tie rod 2 to form a wing 4, the wing 4 is A diluted alloy plate 9 of a long-life neutron absorber, which is made by diluting a long-life neutron absorber such as hafnium with a diluent such as zirconium or titanium, is placed between the neutron absorber fillings formed in the neutron absorber. A plurality of long holes 10 are formed in a row in 9, and the long holes 1
0 is filled with a neutron absorbing material such as B4C, and a neutron absorbing rod 11 made of a long-life neutron absorbing material is wrapped at the tip of the wing 4 with a sheath 3 made of stainless steel.

In the nuclear reactor control rod 1a configured in this way,
The concentration of the long-life neutron absorber contained in the diluted alloy 9 can be changed in the axial direction of the reactor control rod 1a in consideration of the neutron irradiation dose, and the long-life neutron absorber and neutron absorber The absorption of neutrons can be shared between the two, and the life of the reactor control rod as a whole can be significantly extended.

(Problems to be Solved by the Invention) In the above-mentioned control rod for a nuclear reactor, as shown in FIG. The diluted alloy plate of the long-life neutron absorber is in surface contact with the stainless steel sheath 3, or an extremely fine gap is created.

The sheath 3 is provided with a plurality of water holes 12,
The dilution alloy plate 9 is cooled by the reactor cooling water that has passed through the water holes 12, but as described above, the sheath 3 and the dilution alloy plate 9
There is not enough clearance between the sheath 3 and the dilution alloy plate 9, and the reactor cooling water stagnates in the minute clearance between the sheath 3 and the diluent alloy plate 9. When water stagnates between the sheath 3 and the dilution alloy plate 9, corrosion resistance decreases due to electrochemical causes caused by contact between the sheath 3 and the dilution alloy plate 9, which are dissimilar metals, and corrosion products are more likely to occur.

When corrosion products are generated between the sheath 3 and the diluted alloy plate 9, a wedge action acts to force the sheath to expand, generating large bending stress.

The sheath 3 has reduced corrosion resistance, and when a large tensile stress is applied to it, water is further radiolyzed to create an oxygen-rich atmosphere, so stress corrosion cracking occurs and cracks are likely to occur.

The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a diluted alloy plate of a long-life neutron absorber and a plurality of long holes drilled in a row in the diluted alloy plate to transmit neutrons. An object of the present invention is to provide a long-life nuclear reactor control rod filled with an absorbing material and having a long nuclear life, which has high strength and reliability and does not cause stress corrosion cracking in its sheath.

[Structure of the invention]

(Means for Solving the Problems) In the nuclear reactor control rod according to the present invention, a tip structural member and an end structural member are connected by a central tie rod, and each protrusion of the central tie rod has an elongated U-shaped cross section. A sheath is fixedly attached to form a wing, and a diluted alloy plate of a long-life neutron absorbing material is placed inside the wing, and neutrons are absorbed through a plurality of long holes drilled in a row in the diluted alloy plate. In a control rod for a nuclear reactor filled with fuel, the dilution alloy plate and the sheath covering it are prevented from making surface contact, and at the same time, the gap between the dilution alloy plate and the sheath is maintained constant to allow the reactor coolant to flow through the control rod. It is characterized by being configured so that it can be distributed.

(Function) Inside the wing of the reactor control rod, the dilution alloy plate of the long-life neutron absorber no longer comes into surface contact with the inner surface of the sheath, and there is also a flow path for reactor cooling water between the dilution alloy plate and the sheath. As a result, corrosion products are prevented from being deposited in the gap between the diluted alloy plate and the sheath, and radiolyzed oxygen is also prevented from remaining in the gap, improving the corrosion resistance of the sheath. can.

In addition, since the gap between the diluted alloy plate and the sheath is maintained at a constant interval, even if corrosion products are deposited in the above gap, there will be no pushing force applied to the sheath due to the wedge action, and large bending stress will not occur. Does not occur. Therefore, the sheath can be protected from stress corrosion cracking in combination with the effect of improving corrosion resistance described above.

(Example) A first example of the control rod for a nuclear reactor according to the present invention will be explained with reference to FIGS. 1 and 2.6 FIG. 2 shows details of the wing portion of the control rod for a nuclear reactor. FIG. 3 is a cutaway perspective view. Moreover, FIG. 2 is a cross-sectional view of the wing portion.

A central tie rod 2a is arranged at the center of the nuclear reactor control rod and extends in the axial direction of the nuclear reactor control rod. The central tie rod 2 has a cross-shaped cross section, and wings 4a each consisting of a U-shaped sheath 3a with an elongated cross section are fixed to each of its four protrusions. A tip structure member and an end structure member (not shown) are fixed to the upper and lower ends of the central tie rod 2a and the four sheaths 3a, respectively.

In the neutron absorbing material filling space inside the sheath 3a.

A dilute alloy plate 9a of a long-life neutron absorber made by diluting a long-life neutron absorber such as hafnium with a diluent such as zirconium or titanium is provided, and a plurality of long holes 10a are formed in the dilute alloy plate 9a. Long holes 10a are drilled in rows.
The inside is filled with a neutron absorbing material other than the long-life neutron absorbing material, such as 84C. The above diluted alloy plate 9
The thickness of a is 1.5 to 2 m longer than the distance of the inner surface of the sheath 3a.
Set it as short as possible.

In this case, the thickness of the diluted alloy plate is thinner than the diluted alloy plate 9 of the long-life neutron absorber housed in the reactor control rod 1a shown in FIG. 12, but the long-life type contained in the diluted alloy plate 9a is Neutron absorption capacity can be maintained by increasing the concentration of the neutron absorption material.

The end of the diluent alloy plate 9a on the center tie rod 2a side forms a curved surface so that the contact area with the center tie rod side surface 13 is small.

On the other hand, at the other end of the dilution alloy plate 9a, neutrons made of a long-life neutron absorbing material such as hafnium are inserted so as to cover the open ends 14 of the long holes 10a formed in rows in the dilution alloy plate 9a. The absorption rod 11a is attached.

The neutron absorption rod 11a is a rod having a semicircular cross-sectional shape, with a crescent-shaped notch cut out in the axial direction.
5 is provided in consideration of reducing the contact area of the tip of the wing 4a with the inner surface of the curved portion of the sheath 3a. The width Q□ of the neutron absorption rod 11a is equal to the distance between the inner surfaces of the sheath 3a, and the cross-sectional radius of the neutron absorption rod 11a is set between the sheath 3a at the tip of the wing 4a.
It is configured to be equal to the inner radius of the bend.

After filling the elongated hole 10a drilled in the diluted alloy plate 9a with a neutron absorbing material such as B4C, the end face of the neutron absorbing rod 11a is attached to the diluted alloy plate 9a by axial fillet welding 16.
At this time, the plate thickness center line of the dilution alloy plate 9a and the center of the cross-sectional radius of the neutron absorption rod 11a are made to coincide with each other.

A support pin 17 made of a long-life neutron absorbing material such as hafnium is attached to the center tie rod 2a side of the diluted alloy plate 9a.
penetrates the diluted alloy 98 in a direction perpendicular to the side surface of the diluted alloy plate 9a, and is fixed thereto by fillet welding 18 all around. The total length of the support pin 17 is equal to the distance between the inner surfaces of the sheath 3a and the width dimension Q□ of the neutron absorption rod 11a, and the protrusion dimension of the support pin 17 from the surface of the diluted alloy plate 9a is equal to the front and back sides of the diluted alloy plate 9a. are adjusted to be equal.

The sheath 3a encloses the diluted alloy plate 9a and the neutron absorption rod 11a, which are configured as a pair as described above, and has one end fixed to a lip 19 provided on the central tie rod 2a by axial butt welding 20. The other end is connected to the end of the other sheath 3a by an axial butt weld 21 at the tip of the wing 4a.

Next, the operation of the first embodiment will be explained.

According to the above embodiment, the neutron absorption rod 11a and the support pin 1
7 prevents the surface of the dilution alloy plate 9a from coming into contact with the inner surface of the sheath 3a, and furthermore, a certain gap 22 is formed between the sheath 3a and the dilution alloy plate 9a. Therefore, as shown in FIG. 2, the water passage hole 12 (
Since the reactor cooling water that has flowed into the sheath 3a from (not shown in FIG. 1) flows through the gap 22,
Water no longer stagnates between the sheath 3a and the diluted alloy plate 9a, and the surface contact between the sheath 3a and the diluted alloy plate 9a is eliminated, as well as corrosion products between the sheath 3a and the diluted alloy plate 9a. This prevents corrosion and improves corrosion resistance. Further, a certain gap 22 is provided between the sheath 3a and the dilution alloy plate 9a.
Even if corrosion products were to accumulate between the sheath 3a and the diluted alloy plate 9a, the sheath 3a would not be subjected to any pushing force due to the wedge action, and no large bending stress would be generated.

Therefore, the sheath 3a can be protected from stress corrosion cracking.

Further, according to the above embodiment, a curved surface is formed at the end of the dilution alloy plate 9a on the center tie rod 2a side, and the neutron absorption rod 1
1a has a crescent-shaped notch, so the contact area with the other party is small, and the sheath 3a
Similar improvement in corrosion resistance is expected between the diluted alloy plate 98 and the diluted alloy plate 98.

Furthermore, since the joint between the sheath 3a and the central tie rod 2a has been changed from the conventional insertion type shown in Fig. 12 to a butt type, water does not stay in the insertion part of the sheath 3a and the central tie rod 2a, improving corrosion resistance and stress corrosion. Efforts are made to prevent cracking.

Although the support pin 17 used in this example has a cylindrical shape, it is also effective to provide a spherical roundness at the tip of the support pin 17 in order to further reduce the contact area between the support pin 17 and the sheath 3a. be.

Next, second to fourth embodiments of the present invention will be described with reference to FIGS. 3 to 8. Figure 3.

5 and 7 are cutaway perspective views showing details of the control rod wing sections for reactors in the second to fourth embodiments, and FIGS. 4, 6, and 8 are respectively cutaway views of the wing sections. FIG.

The second embodiment shown in FIGS. 3 and 4 is based on the diluted alloy plate 9 used in the first embodiment explained in FIGS. 1 and 2.
A short pin z3 having a short height is used instead of the support pin 17 passing through a. The height dimension of the short pin 23 is configured to be equal to the gap dimension provided between the dilution alloy plate 9a and the sheath 3a, and the dilution alloy plate 9a is connected by fillet welding 24 all around the circumference.
is fixed directly to the surface. Instead of the short pins 23 described above, a flat washer may be used, or a long-life neutron absorbing material may be used to build up the surface of the diluted alloy plate 98.

The third embodiment shown in FIGS. 5 and 6 has a sheath 3a
In order to maintain a gap between the diluted alloy plate 9a and the diluted alloy plate 9a, a protrusion is provided on the sheath 3a side instead of on the diluted alloy plate 9a side. The protrusions are realized by a plurality of chevron-shaped dimples 25 obtained by bending the sheath 3a. This dimple 25 has the same function as the support pin, short pin, or overlay in the embodiments described above.

On the other hand, in the fourth embodiment shown in FIGS. 7 and 8, the diluted alloy plate 9a is formed into a wavy shape by bending, and the diluted alloy plate 9a is supported by the sheath 3a at the top 26 of the wavy shape. ing. After bending the diluted alloy plate 9a,
Long hole 10a for filling with neutron absorbing material such as B4C
Process. Since the thickness of the diluted alloy plate 9a hardly changes even when it is bent, its neutron absorption capacity remains unchanged.The second to fourth embodiments described above can be summarized as follows. ■The width of the neutron absorption rod installed inside the tip of the wing is equal to the distance between the inner surfaces of the wing and is larger than the thickness of the diluted alloy plate of the long-life neutron absorption material. ■Multiple dimples provided on the sheath prevent surface contact between the sheath and the diluted alloy plate, and
It is characterized by maintaining a constant gap between the diluted alloy plates. ■The diluted alloy plate is bent into a wave shape, and the diluted alloy plate is supported by the sheath at the top of the wave shape, preventing surface contact between the sheath and the diluted alloy plate and maintaining a constant gap between the sheath and the diluted alloy plate. It is characterized by Also in these embodiments, water does not remain between the sheath and the diluted alloy plate, improving corrosion resistance and preventing stress corrosion cracking.

〔Effect of the invention〕

According to the present invention, a gap is formed between the diluted alloy plate and the sheath of the long-life neutron absorber to prevent surface contact between dissimilar metals such as the diluted alloy plate and the sheath, and to allow reactor cooling water to flow between the diluted alloy plate and the sheath. be done.

Therefore, by allowing reactor cooling water to flow into the gap, generation of corrosion products between the sheath and the diluent alloy plate can be prevented, and corrosion resistance can be improved.

In addition, because a certain gap is maintained between the sheath and the diluted alloy plate, even if corrosion products are deposited between the sheath and the diluted alloy plate, the sheath will not be subjected to any pushing force due to the wedge action, resulting in large bending stress. does not occur. Therefore, the sheath can be protected from stress corrosion cracking.

As described above, according to the present invention, a long-life nuclear reactor with a long nuclear life in which a long-life neutron absorber diluted alloy plate and a plurality of long holes drilled in rows in this diluted alloy plate are filled with neutron absorber. A structure that prevents stress corrosion cracking from occurring in the sheath can be added to the control rod, and a long-life reactor control rod with high strength and reliability can be obtained.

[Brief explanation of the drawing]

Figures 1 and 2 show a first diagram of a control rod for a nuclear reactor according to the present invention.
Fig. 1 is a perspective view of a control rod wing, Fig. 2 is a sectional view of the control rod wing, and Figs. 3 to 8 are diagrams showing a control rod for a nuclear reactor according to the present invention. Embodiments 2 to 4 are shown, and FIGS. 3, 5, and 7 are perspective views of control rod wings, and FIGS. 4, 6, and 8 are sectional views of control rod wings. Figure 9 is a partially cutaway perspective view of a conventional nuclear reactor control rod, Figure 10 is a sectional view of a wing of a conventional nuclear reactor control rod, and Figure 11 is a long-life neutron absorber. FIG. 12 is a partially cutaway perspective view showing a long-life control rod using a diluted alloy plate, and FIG. 12 is a sectional view of a wing of the long-life control rod using the diluted alloy plate. 1, la... Reactor control rod 2... Central tie rod 3, 3a... Sheath 4.
4a... Wing 7... Tip structure material 8... End structure material 9, 9a... Diluted alloy plate 10, 10a...
・Long hole 11. lla...neutron absorption rod 12.
...Water hole 17...Support bin 22...Gap 23 Short pin 25...Dimple 2
6... Wavy shape top agent Patent attorney Yoshiaki Inomata (one person) Figure 2 Figure 4 Figure 6 Figure 92 Yuu 10 Figure 11

Claims (1)

[Claims] The tip structural member and the terminal structural member are connected by a central tie rod, and a sheath having an elongated U-shaped cross section is fixed to each protrusion of the central tie rod to form a wing, and a long-life neutron is inserted into the sheath. A diluted alloy plate of the absorbent and a plurality of long holes are drilled in a row in this diluted alloy plate,
In the control rod for a nuclear reactor, the elongated hole is filled with a neutron absorbing material, and a neutron absorbing rod made of a long-life neutron absorbing material is wrapped in a sheath at the tip of the front wing. A control rod for a nuclear reactor, characterized in that a plurality of protrusions are attached to a dilution alloy plate to prevent surface contact between the sheath and the dilution alloy plate and to maintain a constant gap between the sheath and the dilution alloy plate.