Small angle neutron scattering analysis of the radiation susceptibility of reactor pressure vessel steels

The irradiation induced microstructure for two reactor pressure vessel (RPV) steel types after irradiation at different neutron exposure levels and annealing treatments were investigated by means of small angle neutron scattering (SANS). The radiation susceptibility changes with the type of steel. Therefore the role of particular material parameters in defect evolution was worked out. The characteristics of the irradiation-induced defects such as number density, size distribution, and volume content were determined and potential defect compositions were estimated. The type of RPV steel influences the volume content but hardly the size distribution. The evolution of the defect content for a particular steel is not linear in response to the irradiation damage described in displacements per atom. The defect type is not uniform. The average composition of defects is partly changed with increasing dpa-doses. Additionally, the redissolving behaviour of irradiation induced defect clusters was studied after gradual thermal treatments. The analysis bases on the hypothesis that the radiation defects are not ferromagnetic. The consistency of the results supports the correctness of the hypothesis