Neutron Irradiation-Induced Embrittlement in Hastelloy-X at Elevated Temperatures

Synopsis : Ductility loss of neutron-irradiated Hastelloy-X at elevated temperatures has been examined by post irradiation tensile test. The results were analysed as a function of test temperature, strain rate, thermal neutron fluence and the associated helium content. The contribution of helium production due to the 58Ni (n, ƒÁ) 59Ni (n, ƒ¿) 56Fe reaction in addition to the 1813 (n, ƒ¿) 7Li reaction was considered. The results obtained are summarized as follows : ( 1 ) The post irradiation ductility decreased with strain rate decrease and test temperature increase up to 1000 °C. ( 2 ) As for the helium embrittlement attributed to (n, ƒ¿) -reaction, the 10B (n, ƒ¿) 7Li reaction was dominant at lower fluences, and Ni-two step reaction became predominant with fluence increase. ( 3 ) Extrapolations of the results of irradition at low temperature gave the ductility values of about 3.5% at 900•Ž and about 1.5% at 1 000•Ž for the thermal neutron fluence of 1022n/cm2. ( 4 ) The threshold thermal neutron fluences for embrittlement were estimated as 6•~ 1016n/cm2 at 900°C and 2 × 1016n/cm2 at 1 000°C, corresponding to the calculated atomic helium fractions of 9.4 × 10-10 and 3.2×10-10, respectively.