DAMAGE OF FUSION MATERIALS UNDER VARIABLE IRRADIATION CONDITIONS

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Though it is expected that the irradiation conditions such as the temperature and the neutron flux are change widely under operation of fusion reactors, most of the irradiation experiments for fusion material development have been carried out at constant conditions. In this projects, therefore, irradiation experiments were performed at various temperature conditions to understand the fundamental damage mechanism under various conditions.In the case of pure metals and alloys, where no segregation are expected, it was revealed that the temporal unbalance of interstitial atoms and vacancies during the change of the temperature greatly affected the accumulation of damage by comparing the experimental results and numerical calculation of defect accumulation based on the rate theory.On the other hand, in the case of P-modified austenitic stainless steel, which is known as high swelling resistance material due to the sink effects of FeィイD22ィエD2P properties, voids are formed easily by short pre-irradiation at low temperature, because of the formation of unstable FeィイD22ィエD2P precipitates during the pre-irradiation. It was also found that co-addition of Ti with P enhanced the stability of FeィイD22ィエD2P precipitates even in the pre-irradiation at low temperature.It was cleared that the effects of temperature variation on the formation of Ti-oxide is important in the V-4Cr-4Ti alloy. Pre-irradiation at low temperature enhances the formation of high density Ti-oxides, and this results in the large influence on the structure and hardiness of the material. It was also revealed that the suppression of penetration of oxygen through the specimen surfaces is indispensable for the further studies of radiation damage. We will therefore establish the method for the prevention of oxygen penetration at first and continue the studies on the temperature variation effects in the V-4Cr-4T alloy.