Small angle neutron scattering study on the effect of hydrogen in irradiated reactor pressure vessel steels

Hydrogen uptake can potentially enhances the neutron embrittlement of reactor pressure vessel (RPV) steels. This suggests that irradiation defects act as hydrogen traps. The evidence of hydrogen trapping was investigated using the small angle neutron scattering (SANS) method on four RPV steels. The samples were examined in the unirradiated and irradiated state and both in the as-received condition and after hydrogen precharging. Despite the low bulk content of hydrogen achieved after precharging with low current densities, an enrichment of hydrogen in small microstructural defects could be identified. Preferential traps were the microstructural defects in the size range of approx. > 10 nm in the unirradiated as well as in the irradiated samples. However, the results do not show any evidence for hydrogen trapping in irradiation defects.