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Fuyushima, Takumi; Takabe, Yugo; Sayato, Natsuki; Kimura, Akihiro; Takemoto, Noriyuki
The IV International Scientific Forum "Nuclear Science and Technologies"; AIP Conference Proceedings 3020, p.040007_1 - 040007_6, 2024/01
We studied irradiation tests of structural materials simulating fast reactor conditions in JMTR. We fabricated capsules that can simulate fast reactor irradiation in JMTR by using He/dpa ratio as index. To simulate fast reactor, cadmium, which shield thermal neutrons, was placed inside the capsule to adjust the neutron spectrum. According to the result of irradiation tests by neutron spectrum adjusting capsule, we confirmed that it can simulate the He/dpa ratio of fast reactor. Currently, since it is impossible to conduct irradiation tests in Japan, a plan is underway to partly replace the irradiation function of JMTR with overseas reactors. The alternative irradiation will be carried out by succeeding and developing the irradiation technology accumulated in the JMTR, and as a part of this, a trial of such irradiation in which the neutron spectrum is adjusted is under consideration.
Hirota, Noriaki; Nakano, Hiroko; Fujita, Yoshitaka; Takeuchi, Tomoaki; Tsuchiya, Kunihiko; Demura, Masahiko*; Kobayashi, Yoshinao*
The IV International Scientific Forum "Nuclear Science and Technologies"; AIP Conference Proceedings 3020, p.030007_1 - 030007_6, 2024/01
Dynamic strain aging (DSA) and intergranular stress corrosion cracking (intragranular SCC) occur in high temperature pressurized water simulating a boiling water reactor environment due to changes in dissolved oxygen (DO) content, respectively. In order to clearly understand the difference between these phenomena, the mechanism of their occurrence was summarized. As a result, it was found that DSA due to intragranular cracking occurred in SUS304 stainless steel at low DO 
1 ppb, while DSA was suppressed at DO 100 to 8500 ppb due to the formation of oxide films on the surface. On the other hand, when DO was increased to 20000 ppb, the film was peeled from the matrix, O element diffused to the grain boundary of the matrix, resulting in intergranular SCC. These results are indicated that the optimum DO concentration must be adjusted to suppress crack initiation due to DSA and intergranular SCC.
