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) evaluations 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 × 1020 n/cm2 (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 to 5 × 1018 n/cm2 at a neutron flux of 4 × 1011 n/cm2˙s, radiation embrittlement is stronger than in irradiation at a neutron flux of 3 to 4 × 1012 n/cm2˙s. A tendency has been observed for the values of the radiation embrittlement coefficients AF, 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 × 1011 n/cm2˙s.

The main results obtained from studying recovery of irradiation embrittlement of reactor vessel steels are presented. Investigations were carried out using WWER-440 vessel materials (base metal, weld metal). The irradiation temperature was 270°C, which corresponded to the operation temperature of the vessel wall. The effect of the annealing temperature and annealing time, neutron fluence, and phosphorus and copper impurity contents on recovery of the ductile-to-brittle transition temperature was studied. Recovery of the transition temperature depends mainly on the annealing temperature. At a phosphorus content exceeding 0.02%, recovery of properties in annealing is complicated. The effect of copper at contents lower than 0.2% has not been observed. At an annealing temperature of 420°C, residual postannealing embrittlement does not depend on neutron fluence. The results obtained in irradiation-annealing-reirradiations are also presented. After annealing, the tendency of the steel to irradiation embrittlement is not increased over that in its initial state.

No abstract