Modification to the flow properties of repository cement as a result of carbonation

The current UK repository concept for low- and intermediate-level radioactive wastes involves using large quantities of cementitious materials for both construction and buffer/backfill. CO2 generated from degradation of waste organic material results in cement carbonation and associated mineralogical changes. Hydraulic and gas permeability tests were performed at 4 MPa and 40 °C. Carbonation halved the permeability of Nirex Reference Vault Backfill (NRVB) cement under these repository conditions. Mineralogical changes occurred in a narrow zone along the leading edge of a migrating reaction front and decreased porosity. The small reduction in permeability (and slightly elevated pressures) that resulted is considered to have minor impact on the permeable characteristics of the NRVB.