JPS597552B2 - Manufacturing method of composite member for neutron shielding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a neutron shielding member provided near the core of a nuclear reactor, particularly a neutron shielding member with excellent oxidation resistance in which the outer peripheral surface of a Ta member is coated with a stainless steel outer skin material. be.

Various studies have been made for neutron shielding members, and representative metals such as stainless steel (SUS316), vanadium alloy, and Ta (tantalum) have been published in literature.

However, this stainless steel has a problem with its neutron absorption ability when placed near the reactor core, and vanadium alloys and Ta have high neutron absorption ability, and Ta in particular has excellent shielding ability. , both of which use liquid Na as a cooling medium.
Alternatively, it reacts with trace amounts of oxygen contained in water to form an oxide, and since this oxide has poor adhesion to the base material and has the property of being extremely easy to peel off, it is easily peeled off and cooled. It will migrate into the medium. The migrated oxides circulate together with the medium within the cooling system, causing not only radioactive contamination of the cooling system, but also accumulating within the cooling system and clogging it, potentially causing a serious accident. Therefore, in order to prevent the formation of this oxide, a method of thermally spraying oxidation-resistant Ni, etc. has been considered and attempted in some cases, but the thermally sprayed layer becomes porous, and it cannot penetrate through the pores. It has been found that an oxidation reaction occurs due to the oxygen, and the generated oxide peels off, causing the thermal sprayed layer itself to peel off.Therefore, there has been a demand for the development of other effective oxidation prevention techniques.

In view of the current situation, the present invention is based on Ta, which has a particularly high neutron shielding ability and is highly practical. This method solves the above-mentioned problems caused by oxidation by firmly joining easily processable stainless steel outer skin materials using the hot isostatic pressing method (hereinafter referred to as HIP method) to create a composite member. .

The HIP method has been actively researched in recent years as a method for firmly joining objects such as metal powders in a high-temperature, high-pressure gas atmosphere to obtain dense compacts, and has already been put into practical use in some cases. In the present invention, this HIP method is used to firmly diffusion bond and integrate a stainless steel outer skin material that prevents oxidation onto the outer peripheral surface of a Ta member that serves as a neutron shielding member. be.

The present invention will be specifically explained below.

FIG. 1 shows an example of the method for manufacturing the neutron shielding composite member of the present invention. The container 2 has an extremely simple bottomed cylindrical shape with an opening, and a predetermined shape is preliminarily inserted into the container 2. The formed Ta member 1 is charged, and the Ta member 1
After filling the space between the container 2 and the container 2 with stainless steel powder 8, the lid with the degassing pipe 4 is welded onto the lid, and the degassing pipe 4 is connected to a vacuum pump (not shown) according to a conventional method. Deaeration pipe 4
The inside of the container is degassed and sealed, and the container is charged into a high temperature and high pressure HIP furnace and HIPed at a temperature of 900 to 1200°C.
Through the treatment, the stainless steel powder 8 is made into a dense sintered body with a true density of approximately Y, and is also integrated with the Ta member by diffusion bonding.

When the HIP process is completed, the sintered body around the Ta member 1 is cut and removed along the shape of the Ta member as shown by the two-dot chain line in the figure, thereby forming a stainless steel outer skin layer 9 on the outer peripheral surface of the member 1. form a layer. In addition, in this method, since the outer cover material is formed of powder, it is possible to easily cover the outer circumferential surface of the Ta member 1 no matter what shape it is, and the shape of the container 2 is different from the Ta member. Since this is unrelated to the shape of 1 and the container material does not serve as the outer skin material of the Ta member, the container 2 can be made of a material that is easy to form such as mild steel and has a simple shape such as a cylindrical shape. . Therefore, regardless of the shape of the Ta member, an oxidation-resistant stainless steel outer shell can be formed from the simple-shaped container 2 and the stainless steel powder 8 by the HIP method. This can be said to be a suitable method for manufacturing a neutron shielding member. As mentioned above, stainless steel powder is used as the stainless steel shell material used in this method, but in cases where it is difficult to powder, or when only a small amount of powder is required and it is not economical to powder, powder may be used. If it is difficult to obtain, as shown by the dotted line in FIG. 1, stainless steel blocks 10a to 10d cut into a shape matching the shape of the gap between the container 2 and the Ta member 1 can be used instead of powder to fill the gap. It is also possible to place it in a section and then perform deaeration and sealing and HIP treatment as in the case described above.

As the material for the above-mentioned outer skin material, any metal can be used as long as it has particularly oxidation resistance and is easy to diffusion bond.
Stainless steel is the most practical and effective in the high temperature range of HlP temperatures up to . In addition, these outer skins are not only difficult to react with trace amounts of oxygen in the cooling medium, but also the oxides produced by oxidation reactions form a stable oxide film that firmly adheres to the base material, so this peels off and absorbs the cooling fluid. This prevents migration into the interior.

Another possible method is to form the container material from stainless steel and integrate it with the Ta member by diffusion bonding using the HIP method, and use the container part as the outer skin material of the Ta member, but this method requires molding of the container material itself. This is troublesome and not a good idea.

Next, HIP of stainless steel material and Ta used in the present invention
A processing test example will be explained.

Figure 2 shows the arrangement of the container and test pieces used in this test.Inside the container 2 formed of SUS3O4, MO board A, Ta board B, Ni board C, and SUS3O board are placed from below.
A plug D manufactured by No. 4 was placed as shown in the figure, and the plug D was degassed and sealed from the degassing pipe 4, and the air was heated at 1000 Kf/, in an argon gas atmosphere.
HIP processing was performed under the conditions of D, l2OO'C, lhr, and the bonding conditions between each metal in parts (a) to (f) were observed.

As a result, the joints of part (A) (SUS-SUS) were firmly joined, part (mouth) (SUS-Ni), part (c) (Ta-Ni), and part (d) (Ta-Ni). SUS) EPM
It was found that alloy layers formed by interdiffusion were formed in all of the joints made by A, and there were no problems with diffusion joining by the HIP method in either case. However, (Ta-MO) is
It was found that under these HIP conditions, since the temperature was low, no alloy layer was formed and no diffusion bonding occurred. Therefore, when MO is used as the outer skin material, S is preliminarily applied to the outer surface of the Ta member.
There is a disadvantage that the US must be coated in advance by thermal spraying or the like, and the MO must be placed on the outer layer. In addition, when stainless steel is used as the outer skin material as shown in this test example, the HIP treatment is performed by the conventional method, that is, heating → HIP treatment → furnace cooling (slow cooling).
When using this process, if the HIP treatment is performed at a temperature below 900°C, it is necessary to perform another solution treatment after the HIP treatment, but in the case of P, high pressure gas is used as the pressure medium, so HIP is completed. The gas pressure medium recovered during the subsequent depressurization process also carries the heat of the container, resulting in a faster cooling rate than in a general heat treatment furnace, which lowers the HIP treatment temperature to the solution treatment temperature of stainless steel (900 ~ 12
0 "C), and if the container is cooled in the press after the P treatment, the solution treatment will be performed there at the same time as the HIP treatment, and there will be no need to perform the solution treatment again after the HIP treatment. There are advantages.

Of course, the same effect can be achieved even if the material is taken out of the press and cooled.

Hereinafter, a specific example of manufacturing a composite material for neutron shielding using the method of the present invention will be given, and at the same time, it will be shown that the composite material for neutron shielding according to the present invention has excellent anti-oxidation ability. This will be revealed through a sex test.

Example 1 Two thick plates made of SUS3l6, each 11mm in length and width, and 5mm thick, and a Ta plate, 11mm thick in both length and width, were prepared, and after degreasing these, a thick plate made of SUS3l6 was prepared. It was assembled into a sandwich shape with a Ta plate sandwiched between both sides.

Then, this was placed in a square container made of mild steel, and the top cover with a degassing pipe was welded to the lid.The degassing pipe was connected to a vacuum pump to evacuate the inside of the container, and then the degassing pipe was closed. The product was degassed and sealed, then charged into a high-temperature and high-pressure furnace, and heated to 110
HIP treatment was carried out at 0°C and 1000K9/RA for 1 hour.

After the treatment, the treated material was taken out of the furnace and machined to create a sample of a sandwich-like composite material with a thickness of 10 WIJII 1 thickness 3V 11 in the vertical and horizontal directions, and each SUS3L6 plate on both sides and the Ta plate in the middle were 1 mm thick each. did.

On the other hand, for comparison, Ta is also 10 in length and width and 1 in thickness.
A sample was prepared by coating both sides of the plate with molybdenum and SUS3l6 by plasma spraying to form a coating layer of 1 VI thickness. Furthermore, in order to compare the SUS3l6 plate and the Ta plate, each length and width are 10Tf1J11 and the thickness is 3v1t.
Prepared as a board. Next, for each of the above-mentioned samples, a two-part holder container consisting of a lower holder 11 and an upper holder 12 as shown in FIG. Then, both ends are stopped with end stoppers 15 and 16, and liquid sodium is introduced through a passage 17 formed through the center of both upper and lower holders 11 and 12, and the N of each sample is
Corrosion resistance test was conducted during A. The test conditions at this time were as follows.

(a) Temperature of liquid sodium: 400'C (b) Flow rate of liquid sodium: 1-2 m/8e0 (c) Concentration of 02 in liquid sodium: 2 ppm The results of the above test were as shown in the following table.

In addition, in the table, the corrosion resistance was determined as follows. As detailed above, according to the method of the present invention, the outer circumferential surface of a neutron shielding member of any shape can be easily coated with a stainless steel sheathing material by using the HIP process, and the resulting composite member Because they are composited by HIP processing with stainless steel as the outer skin material at high temperatures of 900 to 1200°C, they are formed by strong diffusion bonding, so they do not peel off from each other, and Ta is removed from oxygen in the cooling medium. The members are completely protected, and the various adverse effects caused by Ta oxide as described above can be completely prevented, and the safety of the nuclear reactor can be further improved.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a container loaded with Ta members for manufacturing a neutron shielding composite member by the method of the present invention, and Fig. 2 is a sectional view showing samples for HIP processing various metal materials. be. Further, FIG. 3 is a partially cutaway perspective view showing a sample holder used for the corrosion resistance test in Na. 1...Ta member, 2
... Container, 8... Stainless steel, 9... Outer skin layer, 10a to 10d... Block.

Claims (1)

[Claims] 1. In a method for manufacturing a neutron shielding composite member in which the outer peripheral surface of a Ta member as a neutron shielding member is coated with a stainless steel outer skin material, a Ta member previously formed into a predetermined shape is placed in a container having an opening. Stainless steel powder or a stainless steel block having a shape corresponding to the shape of the gap is charged into the gap between the container and the Ta member, and the Ta member is surrounded and loaded with stainless steel, and then the inside of the container is degassed and sealed. The Ta member and the stainless steel are integrated by diffusion bonding by hot isostatic pressing at a temperature of 900°C to 1200°C, then the container is cooled, and then the outer skin of the stainless steel is A method for manufacturing a composite member for neutron shielding, characterized by removing unnecessary parts of the material.