STUDY ON THE MICROSTRUCTURE EVOLUTION OF A508–3 STEEL UNDER PROTON IRRADIARION

Irradiation embrittlement of reactor pressure vessel (RPV) steels is one of the critical issues for integrity and safety in long-life operation of light water reactors. The em- brittlement is attributed to three main nano-scale microstructural features including copper rich precipitates, matrix damage and grain boundary segregation. The relevance of matrix component of damage can be high in low copper content alloys and also in the case of high doses. Some recent works have been done in trying to clarify the exact nature of this component of the dam- age in irradiated commercial steels. This is still an open question: how the irradiation-induced microstructure will evolve in the A508-3 steel in the high dose range. In the present work, in order to emulate the neutron irradiation damage in the RPV steels, 190 keV proton irradiations were conducted on a A508-3 steel to 0.108, 0.216 and 0.271 dpa at room temperature. The irradiation -induced microstructure was examined by TEM. The obtained results show that the irradiation induced defects are mainly dislocation loops, majority of which are both of � 100� type and of interstitial type, without the observation of the micro-voids. Dislocation loops distribute roughly evenly in the matrix, and some dislocation loops decorate the pre-existing dislocation lines.