Radiation Stability of WWER-440 Vessel Materials

The main results of a complex investigation of radiation embrittlement of WWER-440 reactor vessel (RV) materials, carried out in the former USSR are presented. The object of the investigation was surveillance specimen (SS) evaluation of RV materials. It has been found that at an irradiation temperature of 270 C neither the base metal (steel 15 Kh2MFA) nor weld metal exhibits saturation of radiation embrittlement in irradiation of specimens up to neutron fluences of 7 {times} 10{sup 20} n/cm{sup 2} (E > 0.5 MeV). Regularities in the influence of impurity elements (copper and phosphorus) on radiation embrittlement of RV materials have been investigated. It is shown that radiation embrittlement 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 radiation embrittlement 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 {times} 10{sup 18} n/cm{sup 2} at a neutron flux of 4 {times} 10{sup 11} n/cm{sup 2} {center_dot} s, radiation embrittlement is stronger than in irradiationmore » at a neutron flux of 3 to 4 {times} 10{sup 12} n/cm{sup 2} {center_dot} s. A tendency has been observed for the values of the radiation embrittlement coefficients A{sub F}, characterizing sensitivity of the steel to radiation embrittlement, to reduce with an increase of neutron fluence in irradiation of specimens with a neutron flux of 4 {times} 10{sup 11} n/cm{sup 2} {center_dot} s.« less