Examination of the materials from operating WWER pressure vessels

The data of the materials taken from operating VVER-440 pressure vessels studied in the framework of TACIS and WANO are performed. The degree of radiation embrittlement in metal from NVNPP Units 1,3,4 and 'Kozloduy' Units 1,2 after long-term operation has been determined. The efficiency of recovery annealing has been confirmed as the method removing radiation damages in the materials and also the way to prolong the lifetime of NPP Units. The efficiency of the studies applied to templets cut off the internal surfaces of operating reactors for evaluation of the state of reactor pressure vessel metal has been demonstrated. The correlative relations between the data obtained in sub-size and full-size specimens have been revealed. The degree of radiation embrittlement occurring in pressure vessel metal as a result of re-irradiation in operating conditions has been determined and workability of the 'lateral shift' scheme for evaluation of the changes in ductile/brittle transition temperature resulting from re-irradiation of the steel has been validated. (authors)