The presence of non-aqueous phase liquids (NAPLs) in radioactive wastes has the potential to adversely affect their long-term management. The buoyancy of light NAPLs can represent a separate pathway for their migration from a waste management facility, such as a deep repository, to the accessible environment. Their inherent toxicity and potential burden of radionuclides need to be addressed. Nirex is currently developing an understanding of the behaviour of NAPLs and exploring the means of mitigating any adverse impact. NAPLs such as oils and solvents are present in existing wastes, but NAPLs can also be generated by degradation of some solid organic materials, such as plastics. Wastes arising in the United Kingdom that may contain NAPLs include liquids and sludges contaminated with oils, and waste items containing trapped oil, for example gearboxes and pumps. The reference inventory being assessed by Nirex also contains significant quantities of organic materials which can be considered to be potential precursors to the generation of NAPLs. A programme of work has been instigated by Nirex to develop a better understanding of the behaviour of NAPLs. The programme includes the following aspects: understanding the mechanisms by which NAPLs might be produced and existing NAPLs degraded and destroyed: • consideration of the containment that could be offered by packaging of wastes containing NAPLs; • investigating the extent to which radionuclides may be entrained in NAPLs; • understanding the migration of NAPLs in the near-field and in geological systems; • the impact of NAPLs on the surface properties of repository backfill and the geosphere; • development of assessment tools to quantify the potential risk due to NAPLs. This paper will describe the scope of this programme of work, and will provide examples from the ongoing programme to demonstrate that suitable long-term waste management solutions can be developed for NAPL containing wastes.

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