Competitive effects of deuterium and hydrogen in RAFM steels under gas mixture co-exposure

Abstract

In the deuterium (D)- tritium (T) operation phase, T retention in the structural materials of the tritium breeding blanket will raise safety concerns. These materials will face D-T mixture conditions, making it essential to understand hydrogen isotope effects on retention in RAFM steels. This work investigated D retention behavior in RAFM steels CLF-1 under 1:1 H₂+D₂ mixture gas and pure D₂ gas exposure for various duration times at 673 K. D retention was detected by thermal desorption spectrum (TDS) and elastic recoil detection analysis (ERDA) experiments. Relative to 0.05 MPa D₂, co-exposure to 0.1 MPa 1:1 H₂+D₂ (i.e., the same D₂ partial pressure) reduced low-temperature (<650 K) D retention by 39 %. Meanwhile, the ERDA results showed that the maximum D concentration at the near surface (<100 nm depth) was 0.16 % under the condition of 0.05 MPa pure D₂ exposure. As a comparison, the D concentration was only 0.03 % under the condition of 0.1 MPa 1:1 H₂+D₂ mixture gas exposure, indicating an 81 % reduction. The TDS and ERDA results suggested that the introduction of H₂ reduced the D retention in the RAFM steels and decreased the D concentration in the surface area. In addition, the D retention at low temperature and the surface D concentration in the RAFM steels have reached saturation within the uncertainty of the measurements when the exposure duration times of 0.1 MPa pure D₂ gas and 0.1 MPa 1:1 H₂+D₂ mixture gas exceeded 2 h.