Design Options for the UK’s ILW Geological Disposal Facility

Abstract

Over the last few years, a major national programme of public consultation has been under way in the UK resulting, in 2006, in the announcement by government of geological disposal as the most appropriate solution for the long-term management of the UK’s long-lived and higher-activity radioactive waste and the launch, in 2008, of an implementation programme. The approach being pursued is to solicit volunteer communities to host a geological disposal facility, which may contain not only intermediate-level waste (ILW) and some low-level waste (LLW), but also high-level waste (HLW), any spent fuel (SF) declared as waste, and potentially other materials that may be declared as waste. These wastes have different physical, chemical, thermal and radiological characteristics, and different concepts will be required to accommodate their disposal, potentially in a single facility. The volunteer approach means that the geological environment that might eventually emerge as the preferred location is not known at the outset. Indeed, the siting process may require evaluation of several different geological environments because the UK has rich geological variability for such a small landmass. Consequently, the Nuclear Decommissioning Authority (NDA), which is charged with designing, developing and implementing a geological disposal facility, has investigated facility designs that could be appropriate for a wide range of host rocks and geological environments. This paper presents the results of a project carried out on behalf of the NDA to collate and report information on concepts for the geological disposal of ILW/LLW; a separate project carried out a parallel evaluation of options for disposing of HLW and SF. Initially, the range of geological disposal facility design options available worldwide for the disposal of ILW/LLW was evaluated. Nine disposal concepts were identified and reviewed that would cater for any geological environment likely to arise in the UK. These concepts have different engineering and operational aspects. The appropriateness of each option for implementation in five different generic geological environments was assessed using expert judgement, with input from the NDA, consultants and the UK regulatory agencies. The paper presents a set of generic designs derived from the study and discusses the key issues that would need to be addressed should any of these designs be considered for implementation in specific geological environments in the UK. The findings of this work are intended to provide a resource to support comparisons of alternative disposal concepts and the identification of designs suitable for the disposal of UK ILW/LLW in different geological environments.

Dramatic loss of microbial viability in bentonite exposed to heat and gamma radiation: Implications for deep geological repository

“…Subsequently, there is a hot and dry phase lasting a decade, dependent on initial moisture content and host rock type. Standard repository designs assume canister surface temperatures to reach 100°C within a few years, while bentonite buffer temperatures are anticipated to stay below 100°C (Hicks et al 2009). The temperature on canister-bentonite interface can reach 150°C in the initial hot phase due to very low thermal conductivity of dried bentonite (Johnson et al, 2002;SKB, 2010).…”

Extremophilic microbial metabolism and radioactive waste disposal

“…Bentonite clay contains the phyllosilicate mineral montmorillonite, which swells upon contact with water. The swelling of montmorillonite is the main safety feature of a bentonite barrier, generating a high pore pressure that provides lower permeability and porosity (Hicks et al 2009 ). Understanding bentonite barrier evolution is important for controlling microbial activity, which is anticipated to be inhibited by swelling pressures.…”

Interactions between Simulant Vitrified Nuclear Wastes and high pH solutions: A Natural Analogue Approach

“…In addition to 450,000 m 3 of cement-encapsulated waste 1 , the facility may also use a cementitious backfill as part of the engineered barrier, which will be optimised to physically and chemically impede the transport of radionuclides to the biosphere 2 . Over geological time scales, groundwater will interact with the cementitious components of the facility resulting in high pH conditions in the repository 3 . Should vitrified intermediate level waste be placed in this environment, an understanding of the effect of cement leachates on the longevity of glass is required.…”