It has been established that copper and other trace elements have a detrimental effect on the notch-impact properties of ferritic pressure vessel steels irradiated at reactor operating temperatures of about 288°C (550°F). The underlying cause, however, of this trace element effect has not been established. But based on radiation damage work on vanadium containing oxygen and iron containing nitrogen, a possible mechanism appears to involve stabilization of radiation-produced defects as a result of migration of impurity atoms to the defects where they become trapped. The evidence for this impurity-defect interaction in vanadium and iron is described, and its effect on radiation hardening and embrittlement is discussed. The influence of dislocation channeling in promoting the early onset of plastic instability is also discussed, and the possible relevance of dislocation channeling is indicated with regard to the radiation-produced increase in ductile-brittle transition temperature and decrease in ductile shelf energy.

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