Features of recovery annealing after low temperature irradiation of supporting structures materials of WWER-440 reactor vessels

Abstract

The annealing temperature effect on the degree of properties recovery has been studied for supporting structures (SS) materials of WWER-440 reactor pressure vessels. SS materials such as ferritic-pearlitic steels have been investigated in unirradiated state, after irradiation at low temperatures (50 … 90 °C) and after post-radiation annealing. The degrees of radiation embrittlement of SS materials and the properties recovery under annealing have been determined on the basis of tension tests, impact strength tests, fracture toughness tests and microhardness investigations. The mechanical test results have been interpreted on the basis of the obtained data of APT analysis. The dependence of the properties recovery coefficient on annealing temperature has been quantified. The main processes occurring under post-radiation annealing and affecting the recovery degree of the properties of SS materials have been revealed.

It is shown that for SS material with high copper content the annealing in the temperature range (150–275) °С does not lead to any recovery of the properties of SS materials. At temperatures higher than 300°С the recovery of properties begins, and at 400°С there is practically a complete recovery of the SS material properties with high copper content. For SS materials with low copper content the annealing at temperatures below 300°С can be quite effective. The influence of impurities (phosphorus and copper) on the embrittlement of the material under irradiation and on the recovery of its properties after annealing has been considered.