Investigation of irradiated metal of WWER-type reactor internals after 45 years of operation. Part 4. Mechanical properties and fracture mechanisms

Abstract

Experimental data are obtained for austenitic chromium-nickel steel of 18Cr–10Ni–Ti grade(analog of AISI 321 steel) irradiated with mixed neutron spectrum to various damage doses at temperature near 300 o C. Metal for investigations has been taken from decommissioned components of internals of WWER type reactor. On the basis of the tests of standard cylindrical specimens the strengthand the plasticity characteristics are determined over wide temperature range. The fracture mechanisms are studied by SEM examination. It is revealed that the fracture strain decreases with decrease of temperature and the transition occurs from transgranular ductile to intergranular brittle fracture. The performed review of other published works has shown that this phenomenonmay be observed for various austenitic steels irradiated with mixed neutron spectrum and for austenitic and ferritic steels with implanted helium. This phenomenon is termed as low temperature helium embrittlement (LTHE).