JPH10226848A - Neutron absorbing alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make excellent the ductility, matteability and rollability of an alloy, to facilitate machining therefor and to obtain larger neutron absorging characteristics by using stainless steel as a base material and adding specified weight% of samarium and hafnium thereto. SOLUTION: A neutron absorbing alloy is composed by adding stainless steel with, by weight, 1 to 5% samarium and 0.5 to 4% hafnium. Though this neutron absorbing alloy has neutron absorbing characteristics equivalent to those of boron-contg. stainless steel added with 2% boron, its ductility is not remarkably deteriorated compared to that of general stainless steel such as SUS 304 or the like, so that it is easy to be subjected to machining. Furthermore, there is no problem as for its rollability as well, so that the sheet material is inexpensively produced. A storing rack and a shielding material for a used fuel aggregate or the like are economically and easily produced with increased high shielding properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutron-absorbing alloy suitable for use mainly in facilities such as storage of spent nuclear fuel assemblies and storage racks.

[0002]

2. Description of the Related Art In a facility for storing spent fuel, for example, taking a storage rack as an example, in order to absorb neutrons, conventionally, 1% by weight of boron (B) is contained in stainless steel.
A stainless steel containing boron mixed and alloyed to some extent is used. However, the above stainless steel containing boron is
Relatively brittle, difficult to machine, not easy to weld, requires careful handling.

On the other hand, in order to increase the neutron absorption capacity, it is necessary to further increase the boron concentration. However, with the increase in the boron concentration, the above mechanical properties become worse.
Since the difficulty in production also increases, the above boron concentration is substantially limited to about 1% by weight.

[0004] Among the boron, the use of the boron enriched for B ₁₀ large isotopic neutron absorption, it is also possible to reduce the boron concentration, it has not been realized for economic reasons.

[0005]

SUMMARY OF THE INVENTION The present invention addresses the above-mentioned situation, and is easy and economical to machine by adding the required amount of other metals to stainless steel and finding new neutron absorbing alloys. It is intended to obtain an effective neutron absorption alloy.

[0006]

That is, the feature of the neutron absorbing alloy of the present invention is that, with stainless steel as a base material, 1 to 5% by weight of summarynium and 0.5 to 4% by weight of the entire alloy.
% By weight of hafnium.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

In order to obtain neutron absorption characteristics equivalent to those of the conventional boron-containing stainless steel, the equivalent amounts of the above-mentioned summarynium (Sm) and hafnium (Hf) are as follows:
It is about four times, which is about twice the weight of the above boron. ○ In contrast, hafnium is 0.1% of boron in atomic number.
And about 1.6 times by weight the boron.

That is, since the thermal neutron absorption cross-sectional area of summarynium is about seven times that of boron, the number of atoms is about 0.14.
It is equivalent to double and about twice in weight. However, for thermal neutrons, the absorption of samarium is small. Therefore, in the present invention, hafnium is mixed for neutron absorption of the epithermal group. Since hafnium has several resonance absorption bands between neutron energies of 20 eV to 0.8 eV, the absorption of epithermal neutrons is very large.

Although similar effects can be obtained by using cadmium instead of samarium, cadmium is difficult to put into practical use because of its high toxicity. Further, since the thermal neutron absorption cross section of cadmium is less than half of that of samarium, there is a problem that the amount of cadmium added is large.

[0011]

EXAMPLE Using a stainless steel such as SUS304 or SUS316 as a base material, this alloy was obtained by mixing 3.8% by weight of summarynium and 3.2% by weight of hafnium in the same alloy to form an alloy having a uniform composition. A neutron absorbing alloy according to the invention example was manufactured.

The neutron absorbing alloy of the present invention contains boron
Although it has a neutron absorption characteristic equivalent to that of boron-containing stainless steel mixed with%, the ductility and malleability are not significantly inferior to those of general stainless steel such as SUS304, so that machining is easy. In addition, there is no problem in rollability, and plate materials and the like can be manufactured at low cost. Utilizing this processability, storage of spent nuclear fuel assemblies, equipment such as storage racks, or handling equipment,
It can be applied to structural materials such as plutonium fuel inspection devices and shielding materials.

As described above, by mixing 1-5% by weight of summarynium and 0.5-4% by weight of hafnium into stainless steel and alloying the same, about 0.8-5% in terms of boron-containing stainless steel is obtained. A neutron absorbing alloy corresponding to boron-containing stainless steel mixed with boron by weight of boron is obtained. In addition, in the present invention, since summarynium is mixed, an alloy having good absorption characteristics for epithermal neutrons can be obtained. In addition, when the above-mentioned summarynium and hafnium are mixed into stainless steel, if the content of the summarynium exceeds 5% and the content of the hafnium exceeds 4%, it becomes increasingly difficult to produce a composition having a uniform composition. However, when the value is not more than the above value, the production of the alloy of the present invention is easy.

[0014]

As described above, the neutron-absorbing alloy of the present invention is obtained by adding a predetermined amount of samarium and hafnium to stainless steel, and is more ductile and more malleable than conventional boron-containing stainless steel. It is easy to machine, has excellent neutron absorption characteristics, and has excellent absorption of epithermal neutrons, so it can be used for storage racks and shielding materials for spent fuel assemblies. It has a remarkable effect that it can be manufactured economically and easily, and can be manufactured with enhanced shielding properties.

Claims (1)

[Claims] 1. A stainless steel as a base material, wherein 1-5% by weight of samarium and 0.5-4% by weight are based on the whole alloy.
A neutron absorbing alloy characterized by the addition of hafnium.