RADIATION-INDUCED GRAIN-BOUNDARY SEGREGATION IN NUCLEAR-REACTOR STEELS

The paper will review the various mechanisms of grain boundary segrega tion. These are: thermal equilibrium segregation (TES); neutron irradi ation enhanced equilibrium segregation; thermal non-equilibrium segreg ation; and radiation-induced segregation (RIS). The neutron irradiatio n-induced mechanisms will be discussed in detail. Modelling of the neu tron irradiation segregation effects will be outlined with reference t o two approaches: non-equilibrium theory based models and rate theory models. Both models have been successful in predicting phosphorus grai n boundary segregation in pressure vessel steels as a function of irra diation conditions and examples of this success will be given in the p aper. 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 sta te of grain boundaries as a function of reactor operating conditions w ill be emphasised. The influences of neutron dose, dose rate, temperat ure and microstructure will be mentioned. (C) 1997 Elsevier Science B. V.