JPS6314833A - Ti-base alloy excellent in neutron-absorption capacity - Google Patents

Abstract

PURPOSE:To obtain a Ti-base alloy excellent in neutron-absorption capacity by adding specific amounts of Gd or further Ta to Ti and by alloying them. CONSTITUTION:A Ti-base alloy containing, by weight, 0.1-2% or 0.1-3% Gd and 4-6% Ta is refined and cast into an ingot. This ingot is hot-rolled and cold-rolled to be worked into a sheet of 1mm thickness, which is subjected to vacuum annealing at 550 deg.C for 1hr. In this way, the Ti-base alloy excellent in workability, mechanical properties, weldability, and corrosion resistance, having high neutron-absorption capacity, and suitable for use as material for equipments constituting a nuclear fuel cycle can be obtained.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to so-called nuclear fuel, such as equipment for producing, handling, transporting, storing, storing nuclear fuel, reactor auxiliary equipment, and radioactive waste processing equipment. The present invention relates to a Ti-based alloy that has excellent neutron absorption ability and is used in equipment that constitutes a cycle.

[Prior Art] In the above-mentioned nuclear fuel cycle equipment, etc., there is a fundamental requirement to ensure subcriticality of fissile material. In other words, U235 contained in nuclear fuel, spent nuclear fuel, radioactive waste, etc.
Nuclear fissile materials such as p u 23 fl emit thermal neutrons (number e
Since the bonding energy with V (lower than V) is high, it is easy to create a highly excited state, and there is a danger that the critical point can be easily exceeded.

Therefore, in order to avoid such a situation, it is necessary to lower the thermal neutron flux density in the above equipment to increase subcriticality.

On the other hand, in radioactive waste processing facilities, spent nuclear fuel is melted, purified, recovered, and disposed of using acids or alkalis, which raises concerns about equipment corrosion and deterioration of soundness. may be leaked. Therefore, it is necessary to use materials with high corrosion resistance when constructing the above facilities.

As mentioned above, in nuclear fuel cycle equipment, etc., it is required to ensure subcriticality and high corrosion resistance.In order to meet these two different requirements, conventional materials such as stainless steel, Ti, and Zr, which have excellent corrosion resistance, have been used. A response was taken to configure equipment using the above method and inject a neutron poison such as Gd2O3 into the solution to be treated.

[Problems to be solved by the invention] However, in order to solve the above problems, the concentration of neutron poison in each process must be appropriately controlled to ensure subcriticality, and especially in the nuclear fuel cycle, the concentration of neutron poison must be appropriately controlled. Since various processing operations such as extraction, filtration, and concentration are added, there is a drawback that the control of the neutron poison concentration becomes complicated.

The inventors of the present invention have focused on these circumstances, and have attempted to provide a means to achieve the two objectives of ensuring subcriticality and preventing equipment corrosion, while also being easy to manage.
Various considerations were made. As a result, they came up with the idea that the problem could be solved all at once if the equipment component materials themselves had excellent corrosion resistance and a large neutron absorption capacity.

[Means for Solving the Problems] The alloy of the present invention has been completely absorbed as a result of further research based on the above policy, and contains G d : 0.1 to 2%, with the balance being Ti and The first gist is that it consists of unavoidable impurities, and G d : 0.1 to 3%.

The second point lies in the fact that it contains 4 to 6% Ta, with the remainder consisting of Ti and unavoidable impurities.

[Function] Examples of materials that have a large neutron absorption capacity and excellent corrosion resistance include Hf and Cd, but these materials are extremely expensive and have poor m-contract properties as structural materials, so they are not practical. It is not something that can withstand. In other words, it goes without saying that the constituent materials for the nuclear fuel cycle construction, etc. must satisfy the above requirements, but before satisfying such requirements, they must also have the basic properties as a structural material, and must also have the desired properties. It is also necessary to have good workability, weldability, etc. when processing into the shape. However, since no material has been available that satisfies all of these requirements, it has been necessary to use a method that combines the use of corrosion-resistant materials and the addition of neutron poison as described above.

In response, the present inventors have conducted research on additive elements that can be added to corrosion-resistant materials to provide thermal neutron absorption ability without impairing the properties of the base material for structural materials, especially elements with large thermal neutron absorption cross sections. advanced. As a result, as shown in Table 1, Gd has a significantly large thermal neutron absorption cross section and
The present invention was found to be optimal for achieving the purpose of the present invention without adversely affecting the property of contracting, etc., and the present invention as shown in the above structure was completed.

Table 1 * Relative values when natural boron is 1.0, that is, the Ti alloy and Ti-Ta alloy according to the present invention are materials that exhibit excellent corrosion resistance against acids or alkalis, and have various properties as structural materials. This makes it suitable for use in fields such as the aforementioned nuclear fuel cycle equipment.

The Ti--Ta alloy in the present invention contains 4 to 6% Ta, thereby further improving corrosion resistance. However, if the Ta amount is less than 4%, no improvement in corrosion resistance can be obtained, while if it exceeds 6%, workability deteriorates slightly and no further improvement in corrosion resistance can be expected.

In the present invention, Gd is added to the above-mentioned corrosion-resistant structural material, but when the base material is Ti, the amount added is 0.1 to 2%.
0 if the base material is a Ti-Ta alloy.
．． It is necessary to set it to 1-3%. In any case, if the amount of Gd added is less than 0.1%, the addition has no effect and the thermal neutron absorption ability cannot be improved. On the other hand, the amount of Gd added is Ti
If it exceeds 2% in the case of Ti-Ta alloys, and 3% in the case of Ti-Ta alloys, the workability of forging, rolling, etc. will deteriorate, and the corrosion resistance and material properties of the welded part will deteriorate significantly.

Incidentally, the amount of solid solution of Gd in Ti and Ti-5%Ta alloys is small, and in Ti-based alloys containing 1% or more of Gd,
A d-rich second phase (5-10 μm in diameter) is present. This Gd-rich second phase often exhibits a higher oxygen content than the parent phase, and the volume fraction of the Gd-rich phase increases as the Gd content increases. For these reasons, when the amount of Gd added is excessive, the Gd-rich phase increases and the workability and material properties deteriorate.

[Example 1] After arc melting the various alloys shown in Table 2, hot rolling and cold rolling were performed sequentially to evaluate workability, and the thickness was
IIll plate material was created. After vacuum annealing at 550°C for 1 hour, the properties of the metal phase, corrosion resistance in acids and alkalis, and welded part properties were investigated.
The results shown in the table were obtained.

As is clear from Table 3, the Ti-based alloy of the present invention has a workability of 9
It was confirmed that the alloy has excellent mechanical properties, weldability, and corrosion resistance, and has thermal neutron absorption ability.

Table 2 [Effects of the Invention] The present invention is constructed as described above, and the above-mentioned nuclear fuel cycle equipment manufactured using the alloy of the present invention can obtain excellent corrosion resistance over a long period of time, and Subcriticality can be guaranteed with certainty. Furthermore, since the alloy of the present invention has good workability and weldability, equipment of a desired shape can be manufactured without any problems, and since the alloy has satisfactory mechanical properties, it can be used with confidence as a structural material.

Claims (2)

[Claims] (1) Gd: 0.1 to 2% (meaning of weight %, same below)
A Ti-based alloy with excellent neutron absorption ability, characterized in that the remainder consists of Ti and unavoidable impurities. (2) A Ti-based alloy with excellent neutron absorption ability, characterized by containing Gd: 0.1-3%, Ta: 4-6%, and the remainder consisting of Ti and unavoidable impurities.