Effects of the neutron spectrum on mechanical property changes in low dose irradiations

Abstract

Mechanical property measurements from comparative low dose irradiations of metals and alloys are reviewed. The emphasis is on recent experiments involving miniature tensile specimens irradiated at the Rotating Target Neutron Source II (RTNS-II) at Lawrence Livermore National Laboratory and the Omega West Reactor at Los Alamos National Laboratory. Pure metals, model alloys and structural alloys have been irradiated in RTNS-II from room temperature to 723 K to fluences as high as 8 × 10 22 n/m 2. Where temperature effects are apparent, the effect of increasing the irradiation temperature is to delay the onset of irradiation hardening to higher fluences. Companion fission reactor irradiations have been more limited in scope, but comparative information has been obtained on tensile properties at irradiation temperatures of 363 K and 563 K. For most of the materials tested the differences in the neutron energy spectrum can be accounted for by using displacements per atom (dpa) as a correlation parameter. The exceptions are all pure metals: copper, niobium and vanadium. There is also evidence for rate effects in some of the data. The rate effects obscure the spectral effects and prevent examination of dpa as a damage correlation parameter.