Contribution of the Tricalcium Silicate Hydration Products to the Formation of Radiolytic H₂: A Systemic Approach

Abstract

Because they contain residual water, cementitious materials produce radiolytic dihydrogen under irradiation, which can pose a safety concern for some nuclear applications. The estimation of H₂ emissions by current models takes into account the contribution of pore water but not that of solid hydrates, which is considered negligible. Gamma irradiation (dose rate of 359 Gy h^-1 up to 6 months in a closed system under Ar gas) of hydrated tricalcium silicate pastes, the main constituent of Portland cement, shows however an initial contribution of solid hydrates to H₂ formation. A systemic study combining the source term of solid hydrates and the pore water radiolysis using simulation shows that the primary radiolytic yield devoted to portlandite and cementitious C-S-H (together) is of the order of 2.5 × 10^-8 mol J^-1, and that the contribution of the solid phases is decreasing and becomes negligible in the long term, suggesting a saturation effect with dose. Even if limited in time, the effect of the additional H₂ source term is very sensitive on the radiolysis of the pore water with the very strong solicitation of the recycling reaction chain (equivalent to the Allen chain in basic medium) and leads to a frankly reducing medium (Eh ≈ − 470 mV NHE).