H2 Production under Gamma Irradiation of a Calcium Aluminate Cement: an Experimental Study on Both Cement Pastes and Its Stable Hydrates

The objective of this paper is to investigate the use of calcium aluminate cements as alternative cements within the context of nuclear waste stabilization by solidification. Using an external Co-60 source, the effect of gamma-radiation on H-2 gas production of one of the calcium aluminate cement-based materials (cement "Ciment Fondu") and its stable hydrates, was studied. The amount of H-2 produced by these cement pastes is found to be much lower (up to five times less) than that of the Portland cement pastes containing the same amount of water, especially in the low range of water to cement ratios (W/C <= 0.4) where water is essentially engaged in the hydrates. The H-2 production of the two major hydrates of Ciment Fondu, gibbsite AH(3) and katoite hydrogarnet C(3)AH(6), is very low compared with that of the main hydrates of other cements (Portland cement, Calcium Sulfo-Aluminate and Magnesium Phosphate cements). The type of water engaged in the hydrates, as hydroxyl groups and/or molecular water, influences significantly the H-2 production. Thus, the nature of the hydrate is a key parameter to the aim of optimizing cement matrices with respect to the gas production under irradiation. XRD analysis shows that the crystal structures of gibbsite and katoite are preserved up to very high doses under electron irradiation (3 GGy). This makes calcium aluminate cements (CAC) potential good candidates for nuclear waste conditioning from the point of view of their stability under irradiation.