Doel 3 & Tihange 2 - Some Peer-reviewed Scientific Papers & Reports

J. Koutskj:, K. ,~plichal

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Significant increase of hydrogen content was achieved within l h charging time. Fur ther charging time up to 48 h had little effect. The hydrogen content was higher for the irradiated specimens compared with the unirradiated ones (Fig. 11). The decisive factor for interaction of hydrogen with traps is the current density of hydrogen charging. By increasing current density from 20 to 300 A m- 2 the total elongation decreased and was lower for irradiated specimens practically throughout the whole range of hydrogen charging times (Fig. 12). The hydrogen release during 48 h degassingtime at room temperature resulted in recovery of ductility. For the specimens charged at 20 A m -2 and those unirradiated and charged at 300 A m -2 (for 1-24 h) the total elongation and the total hydrogen content reverted nearly to their initial values. For the irradiated specimen and an unirradiated specimen hydrogen-charged for 48h we can assume that the interaction of hydrogen with structural defects (charging at 300Am -2) results in stable defects which prevent recovery of ductility even when the hydrogen content falls to the same values as those of unirradiated specimens, as was found by Hrub~ e t a l . 4 DISCUSSION AND CONCLUSIONS The CrMoV steel in both unirradiated and irradiated states was sensitive to hydrogen embrittlement at hydrogen contents above 2-5 ppm after charging at current densities of 10-50Am -2. The hydrogen content apparently increased with decrease of irradiation temperature from 290°C to 130°C. This means that the effect of radiation-induced defects on trapping and maintaining hydrogen appears to be substantially higher in comparison with that of structural defects of unirradiated steel. A substantial decrease of elongation observed above those values is controlled by the hydrogen content or by the current density of charging. Irradiat ion at 130 and 180"C for a neutron fluence >2.6 x 1 0 2 3 nm -2 (E > 0-5 MeV) followed by hydrogen charging suggested mutual super- position of hydrogen and radiation embrittlement, which was proved by the decrease of elongation with hydrogen content over 8-10ppm, when full loss of ductility may appear. Radiat ion embrittlement decreases the uniform elongation; hydrogen embrittlement affects the decrease of local necking elongation.