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概要

Since structural materials used in a fission reactor are subjected to irradiation by high energy neutrons, materials degradation due to irradiation should be taken into account when reactor design and maintenance are made. One of significant issues to be solved for a realization of long term operations beyond 40 years is to clarify the validity of a predictio n of material’s degradation due to long term irradiation that is not experienced yet. Material’s behavior due to 60 years irradiation in a reactor should be understood using accelerated irradiation conditions provided by a different irradiation facility from the actual reactor environment. Therefore, we should obtain a precise, quantitative relationship between irradia tion conditions and materials degradation on a basis of damage mechanisms. To do this, in the present study, material’s degradation under various irradiation conditions has been evaluated by numerical calculations based on the defect reaction rate theory. Our calculation results have showed that volume swelling due to irradiation is very much different depending on irr adiation facilities such as HFIR, JOYO, KUR, 14MeV fusion neutrons that are quantitatively characterized by the irradiation dose rate of dpa/s. An establishment of irradiation correlation rule is discussed, where material’s degradation due to long term irradiation are precisely predicted using material’s irradiation data obtained at the existing irradiation facilities.

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