Possibility of a life-time extension for wwer-1000 reactor pressure vessels beyond the design period

Abstract

At present a life-time extension for WWER-1000 reactor pressure vessels is an actual issue in Ukraine. For a decision about the life-time extension it is needed to assess mechanical properties and the critical brittleness temperature TK for the RPV materials as well as to perform the brittle strength calculations. The surveillance test data for the reactor pressure vessel in ques- tion are used for an estimation of changes in the mechanical properties. For today dose dependences of the temperature TK for weld metal in the fluence range of fast (E ≥ 0.5 MeV) neutrons, corresponding to the RPV lifetime more than 40 years, have been obtained. This paper analyzes the surveillance test data for the WWER-1000 reactor pressure vessels, whose welds have a high content of nickel and manganese and are prone to considerable radiation embrittlement. The surveillance specimens have been irradiated within the fluence range, the maximum value of which exceeds the design fluence 57·1022 m–2. The analysis has shown that the experimental dependences of the temperature TK on the neutron fluence for welds are consistent with the design embrittlement model with the exponent of 1/3. The results of comparison between the critical brittleness temperature and the maximum allowable value TKa indicate a possibility of the life-time extension for WWER-1000 reactor pressure vessels beyond the design period.