JPS58120755A - Material for absorbing neutron - Google Patents

Abstract

PURPOSE:To make microscopically the resulting material for absorbing neutrons uniform and to enhance the neutron absorbing power and corrosion (crevice corrosion) resistance by preparing an amorphous Ni alloy contg. P, B and a specified amount or more of Cr. CONSTITUTION:This material for absorbing neutrons is made of an amorphous Ni alloy contg. P, B and >5 atomic% Cr. For example, the alloy consists of, by atom, about 0.5-2.5% P, about 15-25% B, about 15-25% Cr and the balance Ni. Since this material does not cause crevice corrosion, claddig is not required. For example, this material 4 for absorbing neutrons is used only by attaching to the outside of a square pipe 2, so sheets of the material 4 are easily superposed on each other, the neutron absorbing power is enhanced, and the density of a rack is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a neutron absorbing material that has high neutron absorbing ability, excellent strength, and corrosion resistance.

In recent years, there has been a demand for excellent neutron absorbing materials for use as shielding materials in storage pools for spent nuclear fuel rods, and the required properties include uniform neutron absorbing ability, corrosion resistance, and strength.

Conventionally, a rectangular tube made of austenite has been used, but its neutron absorption capacity is about 3.2c117100g, which is small. On the other hand, the composite board of B4C and AI is 77
It has a high absorption capacity of 5cd/100#, but the material is brittle, difficult to bend, and has poor corrosion resistance. Furthermore, attempts have been made to add boron to stainless steel to increase its neutron absorption capacity7. A neutron absorption capacity of 66j/ioog' is obtained by adding lat% of boron. However, if the boron content is increased any further, the rollability deteriorates and it cannot be put to practical use. This is t
Stainless steel material containing boron as a solution? Attempts have been made to pulverize and sinter, but from the viewpoint of processability,
The limit is 9.4 at%. In addition, when stainless steel powder containing boron and stainless steel powder not containing boron are mixed and sintered, stainless steel without boron works effectively as a binder, so boron TT can be increased to 34 at% as a total lid. However, in this case, the material is a combination of particles that contain boron and particles that do not, and the neutron absorption ability is microscopically uneven (rounded where boron is segregated).
This is a problem.

The object of the present invention is to relate to a neutron absorbing material that has a large neutron absorbing ability, is microscopically uniform, and has excellent corrosion resistance (crevice corrosion).

Generally, increasing the amount of poron added is used to increase the neutron absorption capacity.

The properties required for high-density racks are high uniform neutron absorption capacity, excellent corrosion resistance, and strength. Conventional materials used include 8U 8304 and Boral (a mixture of B, C and aluminum powder, sintered and sandwiched between aluminum plates). 8U830
The boron-added lid of No. 4 is about 9.2 at% or less, and if it exceeds this, it becomes brittle and cannot be processed. Therefore, the neutron absorption capacity is low. Further, although Boral has a high neutron absorption ability, it has a problem that uniform neutron absorption ability cannot be obtained because it is microscopically non-uniform.

The present invention focuses on amorphous alloys as a solution to these problems. Generally, in order for amorphous alloys to become amorphous, B,
A thin plate with high strength and toughness is obtained by ultra-rapid solidification (cooling rate: 10@C/8) of a molten metal containing one of p, c, si or ifiz in a liquid state. The distribution of boron in this thin plate is also completely uniform because it is ultra-rapidly cooled.

Amorphous alloys have excellent strength or thin plates (10 to 100
μm), so it cannot be used as a structural material like known materials. Therefore, the rack structure is such that it is attached around the 8U8304 rectangular tube. in this case,
In contact with approximately 55C pure water in the storage pool, SUB 304
A gap is created between the amorphous alloy and the amorphous alloy thin plate (because they are stacked), and crevice corrosion becomes a problem. The earlier application (reception number N05600003361) is 5US3
Since 04 was clad with an amorphous alloy thin plate and there was no gap, no corrosion occurred even with 1 to 5 at% Cr@. In the present invention, since it is used without cladding (to eliminate the cladding process and achieve low cost), the inevitable VC
This caused a problem in corrosion resistance in the composition of the previous application (corrosion is accelerated when a gap occurs). Therefore, it was thought that in order to improve the corrosion resistance, it would be sufficient to simply increase Cr1it. However, when the amount of Cr was increased, a phenomenon occurred in which amorphization was not achieved.

The present invention contains Cr which has excellent crevice corrosion resistance.

Moreover, it is a neutron absorbing material that is characterized by being amorphous.

FIG. 1 shows the relationship between B and Cr, which influence amorphization due to the N 1-2-5 P-B-Cr system. The manufacturing conditions are a quartz nozzle and a circumferential speed of 30? The molten metal was ejected onto the surface of a rotating roll at PI/8eC. In accordance with the P content request, maximum boron content has been obtained at 0.5 to 25 at%, and 2.5 at% P was adopted here. The mark ○ indicates a case where an amorphous substance is obtained, the mark ・ indicates a case where amorphous and crystalline substances are mixed, and the mark X indicates a case where a crystalline substance is obtained without becoming amorphous. As the amount of Cr added decreases, the B content decreases to 20! Since the OB content is about 25 at% in Lt%Cr, and the B-containing IL is reduced to about gat%, the neutron absorption ability is also reduced, which is considered to be disadvantageous.

However, since the material of the present invention does not require cladding and consists of overlapping thin plates, sufficient coverage can be achieved by increasing the number of sheets.In fact, increasing the number of sheets has the effect of increasing the neutron absorption capacity. come.

FIG. 2 shows the results of measuring the surface roughness of the free-solidifying surface of the produced thin plate. N i -2, S P-20B as one row
-20Cr system is shown. The surface roughness is reduced by a maximum of approximately 15 μm.

The surface roughness is good until the Cr content is about 5 it%, but as the Cr content increases, it tends to get worse as shown in the figure. If the surface roughness is poor, the space factor will deteriorate when thin plates are used in a stacked manner, which is not preferable. In order to improve this surface roughness, PE was added. Figure 3 shows the results.

It has been found that the surface roughness is improved when the amount of F added is about 15 at% or more. Figure 4 shows Ni-2,5P-20 as an example.
The results of measuring the surface roughness of B-20Cr-20Fe series are shown. Addition of Fe has the effect of improving surface roughness.

However, as shown in Figure 5, the amount of Fe added is approximately 30&t.
% or more, it becomes difficult to make it amorphous, so the content of pe is desirably 1ti 30 at % or less.

Table IHN i-2, 5P-20B-Cr system and Ni-7
These are the results of measuring the neutron absorption capacity, tensile strength, and crevice corrosion when changing the amount of Cr added in the -5P-20Fe-20B-Cr system. The neutron absorption capacity and tensile strength of conventional materials are also shown for comparison. Crevice corrosion condition F'i 2 sheets 5U
Ten amorphous alloy thin plates were stacked and sandwiched between S304 and subjected to an immersion test in 85C pure water for an aooo hour. As a result, some rust occurred in samples A1 and A7. This UCr content is Vc10! This is because it is as low as Lt%.

When the Cr content was 15 at % or more, no crevice corrosion was observed in both acid systems, and good results were obtained. Since the tricr content of the samples in Graves 5 and 410 exceeded the limit, the materials were not amorphous and were so brittle that they crumbled to pieces during handling, so their properties could not be measured. From these results, it is clear that the Cr content is 15 to 2, especially for the environment in which it is used.
5 at% is desirable.

The first effect of the present invention is that crevice corrosion does not occur, so there is no need for cladding, and it is sufficient to simply attach the neutron absorbing material 41 of the present invention to the outer periphery of the rectangular tube 2 shown in FIG. Because stacking is easy, the neutron absorption capacity is improved and the rack can be densified. Second Effect It is obvious that the surface roughness of the thin plate is improved by using the N1-pe-P-E3-cr-based material of the present invention containing hpe, but the use of the raw material 11CF e -B N1-P-B is now possible, and the raw material cost does not include PE.
-The cost is drastically reduced by about 1/4 compared to the Cr type (Fe
- Since the cost of B is about 1/7 of that of NB).

In the case of nuclear power, the use of fuel storage racks (t#-) shown in Figure 6 with K in one plan depends on the output, but for approximately 800 MW, 560 racks are required. Therefore, reducing the raw material cost to 1/4 has the effect of achieving great economic efficiency.

[Brief explanation of the drawing]

Fig. 1 shows the amorphous formation range of 1dN i-2,5P-B-Cr-based material, Fig. 2 shows the range of amorphous formation of N i-2,5P-208
- A diagram showing the surface roughness of a free solidifying surface of a 20Cr-based material. Figure 3 t! A diagram showing the surface roughness of the free solidification surface of Ni-15P-20B-200r-re based material, Figure 4 is N1-Z5P
-20B-20Cr-20Fe-based material diagram showing surface roughness of free solidification surface, Figure 5 is N1-Z5 P-20B-200
A diagram showing the range of amorphous formation of r-Fe-based materials, Figure 6 is an external view of a conventional high-density rack, and Figure 7 is a cross-sectional view of the neutron-absorbing amorphous thin plate of the present invention attached to a rectangular tube. shows. 1... Upper reinforcing material, 2... Square tube, 3... Lower reinforcing material. Engraving of the drawing (no changes to the contents) J1! 1st/θ /, 5” 2θ 2S30
B (At'/-), l ¥2 Engraving of drawings (no change in content) Fe (at'/-) /gfi Engraving of drawings ζNo change in content) /ρ 15 2θ 25
．． 10e<td%) 茅2月'47 目Proceedings Amendment Writing Method) % Formula % Display of the Case 1982 Patent Application No. 2745 Name of Invention Person who makes amendment for neutron absorbing material 41g) Related Patent Applicant (I Address: 5-1 Marunouchi, Chiyoda-ku, Tokyo
＃(51O+Hitachi, Ltd. representative)
3 1) Osamu Katsu Shigeyo Residence 5-1 Marunouchi-chome, Chiyoda-ku, Tokyo Drawings subject to amendment

Claims (1)

[Claims] 1. A neutron absorbing material comprising an amorphous alloy containing phosphorus, boron, and more than 5 at % of chromium. 2. Phosphorus is added to the amorphous alloy from 0.5 to 2. ．． 5 atom%,
The neutron absorbing material according to claim 1, which contains 15 to 25 at. % of boron, 15 to 25 at. % of chromium, and the balance is nickel. 3. The neutron absorbing material according to claim 2, wherein the nickel alloy contains 30 atomic percent or less of iron.