Elevated temperature tensile properties of irradiated 20/25/Nb stainless steel fuel pin cladding at low and high strain rates

Tensile specimens were prepared from 20/25/Nb stainless steel fuel pin cladding irradiated in a Commercial Advanced Gas-cooled Reactor (CAGR) at temperatures in the range 622-866K and integrated fast neutron doses up to 16 x 1024 n/m2. The tests were performed in air at temperatures in the range 298-873K at strain rates from 2 x 10-5/s to 7.2/s. The tensile properties varied with irradiation temperature, test temperature and strain rate. At lower irradiation temperature, strengthening produced by fast neutron damage was accompanied by reduced elongation. Strengthening was also observed at higher irradiation temperatures, possibly due to precipitation phenomena. The maximum irradiation embrittlement was observed in tests at 873K at low strain rates between 2 x 10-4/s and 2 x 10-5/s. The failure mode of embrittled specimens irradiated at higher temperatures was characterised by prematurely ruptured ductile fibres, rather than by intergranular cracking. (author)