Reaction and alteration of mudstone with cement pore fluids

Bateman, K.; Amano, Yuki   ; Tachi, Yukio  

The construction of a repository for the geological disposal of nuclear waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository and the use of cement will result in the development of a highly alkaline porewater in the case of Ordinary Portland cement (OPC). The alkaline fluid will migrate and react with the host rock, affecting the long-term performance of the repository altering the physical and chemical properties, including radionuclide behaviour. This study focused on the alteration due to OPC-type leachates on mudstone, a potential candidate host rock in Japan. A series of batch (to provide long-term equilibrium data) and flow experiments (to provide spatial and temporal data) were conducted inside a Nitrogen gas atmosphere glove box, with Horonobe mudstone, and simplified OPC leachates. Fluid analysis was by Inductively Coupled Plasma (ICP) and Ion Chromatography (IC), and determination of pH, and Eh. Solids were examined by scanning electron microscopy (SEM). In summary, the reaction of the mudstone with OPC type fluids demonstrated that long term, the chemical buffering capacity leading to a reduction in the pH of the leached fluid and the precipitation of CSH phases. This is consistent with previous similar studies, though this study suggests that the presence of pyrite in the Horonobe mudstone could result in an acidic pulse could precede the alkaline fluid in this host rock.