Radiation-induced grain boundary segregation in nuclear reactor steels

The paper will review the various mechanisms of grain boundary segregation. These are: thermal equilibrium segregation (TES); neutron irradiation enhanced equilibrium segregation; thermal non-equilibrium segregation; and radiation-induced segregation (RIS). The neutron irradiation-induced mechanisms will be discussed in detail. Modelling of the neutron irradiation segregation effects will be outlined with reference to two approaches: non-equilibrium theory based models and rate theory models. Both models have been successful in predicting phosphorus grain boundary segregation in pressure vessel steels as a function of irradiation conditions and examples of this success will be given in the paper. In addition the models have recently been adapted to account for the behaviour of Cr in austenitic steels with a view to understanding irradiation-assisted intergranular stress corrosion (IASCC). The use of predictive modelling of this kind in forecasting the embrittled state of grain boundaries as a function of reactor operating conditions will be emphasised. The influences of neutron dose, dose rate, temperature and microstructure will be mentioned. (orig.)