Investigation of irradiation embrittlement and recovery properties of pressure vessel steels of WWER reactors in the USSR

The paper presents the main results of a complex program on investigations of irradiation embrittlement of WWER-440 reactor vessel (RV) materials, carried out in the USSR. The object of investigations was surveillance specimens (SS) of RV materials. It has been found that at an irradiation temperature of 270 deg. C neither the base metal (steel 15 Kh2MFA) nor weld metal exhibit saturation of irradiation embrittlement (IE) in irradiation of specimens up to fluences of neutrons 7x1020n/cm2. Regularities in the influence of impurity elements (copper and phosphorus) on IE of RV materials have been investigated. It is shown that IE of the weld metal is determined by at least four processes associated with the individual effects of copper and phosphorus, their joint effect and the mechanism of direct buildup of radiation defects in the metal. The effect of dependence of the IE characteristics of the WWER-440 RV materials on the neutron flux has been found. It is shown that within the range of fluences from 1 to 5x1019n/cm2 at a neutron flux 4x1011n/cm2.s IE is stronger than in irradiation at a neutron flux 3-4x1012n/cm2.s. A tendency has been observed for the values of the irradiation embrittlement coefficients AF, characterizing sensitivity of the steel to IE, to reduce with increase of neutron fluence in irradiation of specimens with the neutron flux 4x1011n/cm2.s. (author). 14 refs, 13 figs, 2 tabs