EMPIRICAL CORRELATION OF OBSERVED THREE STAGES OF FAST NEUTRON IRRADIATION HARDENING AND EMBRITTLEMENT IN WWER-440 PRESSURE VESSEL MATERIALS

摘要

Correlations between irradiation hardening and embrittlement of 10 different WWER-440 pressure vessel materials has been investigated. The presence of three stages of fast neutron irradiation hardening (RH) and embrittlement (RE) has been detected. Good empirical correlation between RH and RE was found in the first stage of the irradiation hardening stage. In the second stage, the RE process appears less intensive compared with the first one. In fact, there was only slight hardening and, in some cases, softening occurred; consequently, there was no correlation between RH and RE in the second stage. It is indicated that the RH and RE processes take place in or on different surfaces (grain bulk, grain boundaries and on precipitates) and therefore have local character. It is possible that the delay of RH and RE appearance is related to the nucleation and subsequent growth of precipitates.