On-Site, Near Surface Disposal of Graphite Wastes in the UK

Reactor graphite makes up about 30% by volume of the UK’s inventory of intermediate level waste (ILW). There is estimated to be about 15,000m³ of graphite arisings prior to 2040, mainly comprising operational waste streams (Magnox and AGR fuel sleeves), along with core graphite from the decommissioning of experimental and prototype reactors. A further 65,000m³ of graphite is forecast to arise after 2040, comprising core graphite from the final decommissioning of the Magnox and AGR reactors. Consequently, the management and disposal of graphite wastes is of key strategic importance in the UK. The current baseline strategy for reactor graphite wastes in the UK is to encapsulate them upon retrieval using a cementitious grout in stainless steel containers, in compliance with NDA Radioactive Waste Management Directorate (RWMD) Generic Waste Package Specifications and Letter of Compliance (LoC) process, and to dispose of them, following a period of interim storage, to the UK’s planned geological disposal facility (GDF), when this becomes available (currently planned for 2040). Using Magnox’s Hunterston A site as a Pathfinder, EnergySolutions and its partner organisations have been engaged with the feasibility assessment, options assessment, engineering concept design and environmental safety case (ESC) development for a proposed on-site, near surface disposal facility for operational wastes. The proposal is consistent with Scotland’s Higher Activity Radioactive Waste Policy. The operational wastes comprise more than 90% graphite by volume, with small volumes of other materials present (although these have higher activity concentrations for some radionuclides). The Pathfinder project also included a preliminary assessment for core graphite (which represents a more homogeneous waste form). Following production of detailed feasibility assessments and a concept/location options assessment, the ongoing engineering design work package has focused on delivery of a viable concept design for the facility. In parallel with this, the ESC and performance assessment work packages are concerned primarily with the radiological performance of the facility against the key requirements set out in the Scottish Environmental Protection Agency’s (SEPA) Near Surface Guidance on the Requirements for Authorisation (NS-GRA). The concept under development is for a facility comprising one or more concrete lined, cylindrical disposal cells, sited within the near-surface environment at tens of meters below ground level, making of use of a series of engineered multi-barrier systems. The construction of the disposal cells relies on mature engineering, and standard technology readily available within the civil engineering field. This work may in due course support applications for regulatory and planning approval and subsequent placement of contracts for detailed design and build of a disposal facility at Hunterston A, subject to the confirmation of feasibility and agreement from the NDA to pursue implementation.