A safety case for the disposal of intermediate level waste (ILW) in a deep Geological Disposal Facility (GDF) requires consideration of the potential for a discrete light non-aqueous phase liquid (LNAPL) to form in disposal vaults, and the subsequent potential impact that might arise. A team from AMEC, Quintessa and the University of Birmingham has recently completed a study for the Nuclear Decommissioning Authority (NDA) Radioactive Waste Management Directorate (RWMD) that developed and documented a series of long-term safety arguments concerning NAPLs in a GDF containing Intermediate Level Waste (ILW).
The study drew together information from a wide range of sources to investigate the potential for a discrete buoyant NAPL phase to migrate through each of the barriers that comprise the multi-barrier system of a GDF. The work included estimation of the nature and quantity of NAPL that might be associated with ILW, consideration of the likely properties of the resulting NAPL mixture, and a scoping-level modelling study to explore the potential for this NAPL mixture to migrate out of a waste package.
The safety arguments developed support the case that it is unlikely that significant quantities of NAPL would be able to escape from the waste packages, and even less likely that NAPL would be sufficiently persistent in the disposal environment that it could accumulate at the highest point of a vault and migrate under buoyancy into the geosphere. These conclusions are valid for all of RWMD’s generic environments. While some uncertainties remain, and will be managed in the safety case, the approach taken has aimed to provide multiple lines of evidence to support the proposition that the release of a discrete NAPL phase originating from the ILW will not present a significant challenge to the Environmental Safety Case. The report is available from the NDA Radioactive Waste Management Bibliography and the poster can be downloaded here.
Update October 2014: A paper describing this work (Potential migration of buoyant LNAPL from Intermediate Level Waste (ILW) emplaced in a geological disposal facility (GDF) for UK radioactive waste) has now been published in the Journal of Contaminant Hydrology.
Image courtesy of NDA RWMD