Influence of hydrogen on the toughness of irradiated reactor pressure vessel steels

The influence of hydrogen on the mechanical behaviour of different reactor pressure vessel (RPV) steels was investigated by tensile tests in correlation to the chemical composition, the neutron fluence, the hydrogen charging condition, the strain rate, and the temperature. Small-angle neutron scattering (SANS) experiments, hydrogen analyses and thermal desorption investigations were performed to prove the evidence of hydrogen trapping at irradiation defects. An increasing susceptibility to hydrogen embrittlement indicated by reduction of area was observed at room temperature with in situ hydrogen-charged specimens when loaded by low strain rates or with specimens which had been irradiated at low temperature. Generally, the susceptibility increases with increasing strength of the steels. At 250 °C hydrogen embrittlement was not evident. The results do neither prove that irradiation defects are favoured traps for hydrogen nor give evidence that hydrogen affects the RPV integrity under normal operating conditions.