Investigation of samples taken from Kozloduy unit 2 reactor pressure vessel

Radiation Service Life of the Vessel Metal in Operating VVER Reactors

“…• the characteristics (critical temperature of embrittlement, fracture resistance) currently used to assess radiation embrittlement of vessel material [10] following the normative documents in use since 1960-1970 are not included in the program of delivery tests -instead of the critical temperature of embrittlement, based on analysis of the temperature dependence of the impact viscosity, obtained from tests on impact bending of Charpy samples with a V-shaped notch, the impact viscosity of Charpy-type samples with a U-shaped notch at room temperature were determined; • it is impossible to make a direct determination of the critical temperature of the brittleness of vessel material in the initial state because there is no archived metal; • a system for inspecting the state of vessel material using control samples has not been provided for first-generation reactors; • data on the content of phosphorous and copper in the weld-seam material -the elements determining the tendency of steel toward radiation embrittlement -have not been available [1, 2,4]; to obtain predictive estimates of radiation embrittlement the content of phosphorous and copper in the steel and the initial temperature of the vis- cobrittle transition were found by a computational method using empirical relations established by Prometei, Central Scientific-Research Institute of Composite Materials [11]; later investigations showed that this approach is inadequate [12]. An approach to substantiate the service life of vessels after annealing was developed and termed the "conservative scheme" [13].…”