Hydrogen analysis and slow strain rate test in Ar gas for irradiated austenitic stainless steel

Hydrogen concentration in austenitic stainless steel irradiated with neutrons in boiling water reactors (BWRs) was measured and the effect of hydrogen in the austenitic stainless steel on intergranular cracking was investigated by the slow strain rate test (SSRT) in Ar gas. The hydrogen concentration decreased at low neutron fluences and increased at high neutron fluences. The decrease was attributed to the effect of heating or γ-ray irradiation at the early stage of reactor operation. The increase at high fluences was considered mainly due to the generation of hydrogen by nuclear transmutation. Intergranular cracking was not found for the specimen irradiated to a high fluence (1.4×1026 n/m2) in the SSRT at a very low strain rate (1.0×10−8 s−1). This meant that the hydrogen concentration was too small to induce cracking, or hydrogen could not diffuse because of being trapped in irradiation defects at the test temperature.