Study on degradation phenomenon of nuclear reactor materials (Thesis)

Shibata, Akira 

The degradation of materials, the exposing to high-dose neutron and gamma irradiation, the high temperature and the high pressure water environment are important issues for nuclear reactors. Due to the public concern, plants will inevitably be used for a long term, thereby facing problems of degradation materials due to ageing. In addition, "high burn-up" is being promoted. This prolongs period of operation cycles. The major objective of the thesis is to understand the degradation phenomenon of reactor materials and to improve the evaluation test techniques. Zirconium alloys have been used as fuel cladding material. Advanced Zr-Nb alloys gradually replaced Zircaloy-4 in PWR. Corrosion tests under simulated PWR water conditions were conducted on those materials and formation of oxide layers was studied via EIS. Mechanical properties of oxide layers on Zircaloy-4 and M5 were evaluated by Nano indentation with FEM analysis. Stainless steel is widely used as structure material of nuclear reactors. Tensile tests and SSRTs were conducted on specimens irradiated to higher than threshold fluence of IASCC. The integrity and the IASCC susceptibility were evaluated.