JPH066767B2 - Ti-based alloy with excellent neutron absorption - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to so-called nuclear fuel such as facilities for manufacturing, handling, transportation, storage, storage, etc. of nuclear fuel, nuclear reactor auxiliary facilities, and radioactive waste treatment facilities. The present invention relates to a Ti-based alloy having an excellent neutron absorption ability, which is used for facilities that constitute a cycle.

[Prior Art] In the nuclear fuel cycle facility and the like, it is a basic requirement to ensure the subcriticality of the fissile material. That is, fissionable substances such as U ²³⁵ and Pu ²³⁹ contained in nuclear fuel, spent nuclear fuel, radioactive waste, etc. have a high binding energy with thermal neutrons (several eV or less), so it is easy to create a high excited state, and the critical point is easily set. There is a danger of exceeding. Therefore, in order to avoid the occurrence of such a situation, it is necessary to lower the thermal neutron flux density in the above equipment and increase the subcriticality.

On the other hand, in radioactive waste treatment facilities, etc., when dissolving, refining, recovering, or disposing of spent nuclear fuel, it is feared that the equipment will be corroded and its soundness deteriorated because it is treated with acid or alkali. May leak. Therefore, it is necessary to use materials with high corrosion resistance when constructing the above equipment.

As mentioned above, in nuclear fuel cycle equipment, etc., it is required to secure subcriticality and high corrosion resistance. In order to satisfy these two different requirements, conventionally, materials such as stainless steel, Ti, Zr, etc. having excellent corrosion resistance were used. Use to configure equipment,
A countermeasure has been taken to add neutron poison such as Gd ₂ O ₃ to the solution to be treated.

[Problems to be Solved by the Invention] However, in the above measures, the neutron poison concentration in each process must be appropriately controlled in order to ensure subcriticality. Since various treatment operations such as extraction, filtration, and concentration are added, there is a drawback that the control of neutron poison concentration becomes complicated.

The inventors of the present invention have paid attention to such a situation, and have thought to provide a means for achieving the two purposes of ensuring subcriticality and preventing equipment corrosion, and for facilitating management therefor.
Various studies were repeated. As a result, it has been decided that the problem can be solved all at once if the equipment constituent material itself has excellent corrosion resistance and large neutron absorption capacity.

[Means for Solving Problems] The alloy of the present invention has been completed as a result of further research under the above-mentioned policy, and contains Gd: 0.1 to 2%, the balance being Ti and unavoidable impurities. The first gist exists in the point consisting of, and the second gist exists in the point that Gd: 0.1 to 3% and Ta: 4 to 6% and the balance is Ti and inevitable impurities.

[Function] Hf, Cd and the like are mentioned as materials having high neutron absorption capacity and excellent corrosion resistance, but these materials are disadvantageous in that they are extremely expensive and have poor mechanical properties as structural materials. Can not stand. That is, as a constituent material of the nuclear fuel cycle equipment and the like, it goes without saying that the above requirements are satisfied, but it is necessary to have basic properties as a structural material before satisfying such requirements, and further desired It is also necessary that the workability and weldability in processing the shape be good. However, since a material satisfying all of these requirements has not been provided so far, it was unavoidable that the above-mentioned combined use of the corrosion-resistant material and addition of neutron poison was unavoidably adopted.

On the other hand, the present inventors have studied additional elements, especially those having a large thermal neutron absorption cross section, that can impart thermal neutron absorption ability without impairing the base material properties for structural materials even when added to corrosion resistant materials. Advanced. As a result, as shown in Table 1, it was found that Gd has a remarkably large thermal neutron absorption cross section and does not adversely affect mechanical properties, etc., and is optimum for achieving the object of the present invention. The present invention having the above-described structure has been completed.

That is, the Ti alloy and the Ti-Ta alloy according to the present invention are materials exhibiting excellent corrosion resistance against acids or alkalis and have various properties as structural materials, and are used in the fields including the nuclear fuel cycle facility described above. Can withstand.

The Ti-Ta alloy according to the present invention contains Ta in an amount of 4 to 6%, which is intended to further improve the corrosion resistance. However, if the Ta amount is less than 4%, the corrosion resistance improving effect cannot be obtained, while if it exceeds 6%, the workability is slightly deteriorated, and the corrosion resistance improving effect cannot be expected any more.

In the present invention, Gd is added to the corrosion resistant structural material, but when the base material is Ti, the addition amount is 0.1 to 2%.
If the base material is a Ti-Ta alloy, the content should be 0.1 to 3%. In either case, if the Gd addition amount is less than 0.1%, the addition effect is not obtained and the thermal neutron absorption capacity cannot be improved. On the other hand, the amount of Gd added is T
If it exceeds 2% in the case of i and 3% in the case of Ti-Ta alloy, the workability such as forging and rolling deteriorates, and the corrosion resistance and the deterioration of the material properties of the welded portion become remarkable.

By the way, the solid solution amount of Gd in Ti, Ti-5% Ta alloy is small, and in a Ti-based alloy containing 1% or more of Gd,
There is a d-rich second phase (diameter 5-10 μm). 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 this reason, when the amount of Gd added is excessive, the Gd rich phase increases and workability and material properties deteriorate.

[Example] Various alloys shown in Table 2 were arc-melted, and then hot-rolled and cold-rolled in order to evaluate workability, and a plate material having a thickness of 1 mm was prepared. Then, after vacuum annealing at 550 ° C. for 1 hour, the metal phase, mechanical properties, corrosion resistance in acid and alkali, and weld characteristics were examined, and the results shown in Table 3 were obtained.

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

[Advantages of the Invention] The present invention is configured as described above, and in the above-described nuclear fuel cycle equipment manufactured by using the alloy of the present invention, excellent corrosion resistance can be obtained for a long period of time, and it is possible to ensure that The criticality can be guaranteed. Further, since the alloy of the present invention has good workability and weldability, it is possible to manufacture equipment having a desired shape without any trouble, and since it has satisfactory mechanical properties, it can be safely used as a structural material.

Claims (2)

[Claims] 1. A Ti-based alloy having excellent neutron absorption ability, characterized by containing Gd: 0.1 to 2% (meaning weight%; the same applies hereinafter), the balance being Ti and unavoidable impurities. 2. A Ti-based alloy having excellent neutron absorption ability, characterized by containing Gd: 0.1 to 3% and Ta: 4 to 6%, the balance being Ti and inevitable impurities.