Granite Recrystallization - The Key to an Alternative Strategy for HLW Disposal?
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*UDQLWH5HFU\VWDOOL]DWLRQ±7KH.H\WRDQ$OWHUQDWLYH6WUDWHJ\IRU+/:'LVSRVDO" Fergus G.F. Gibb Immobilisation Science Laboratory, Department of Engineering Materials, University of Sheffield, Sheffield S1 3 JD, U.K. $%675$&7 An alternative strategy is proposed for the disposal of spent nuclear fuel (SNF) and other forms of high-level waste (HLW) whereby the integrity of a mined and engineered repository for the bulk of the waste need be preserved for only a few thousand years. This is achieved by separating the particularly problematic components, notably heat generating radionuclides (HGRs) and very long lived radionuclides (VLLRs) from the waste prior to disposal. Such a solution requires a satisfactory means of disposing of the relatively minor amounts of HGRs and VLLRs removed from the waste. This could be by high-temperature very deep disposal (HTVDD) in boreholes in the continental crust [1,2]. However, the viability of HTVDD, and hence the key to the entire strategy, depends on whether sufficient melting of granite host rock can occur at suitable temperatures and whether the melt can be completely recrystallized. The high-temperature, high-pressure experiments reported here demonstrate that granite can be partially melted and completely recrystallized on a time scale of years, as opposed to millennia as widely believed. Furthermore, both can be achieved at temperatures and on a time scale appropriate to the disposal of packages of heat generating HLW. It is therefore concluded that the proposed strategy, which offers, environmental, safety and economic benefits, could be a viable option for a substantial proportion of HLWs. ,1752'8&7,21 Most countries with inventories of HLW are looking to eventual disposal in so-called “deep”, mined and engineered repositories utilising the multi-barrier approach. While designs differ in detail, they almost all involve the wastes being encapsulated in metal and cement before being sealed into a system of tunnels, caverns and silos at depths between 300 and 1000 metres, i.e. in geological terms they are quite shallow. The technical problems associated with such repositories are well known and can have serious consequences, e.g. the failure to progress an ILW repository in the UK in the late 1990’s. Most of the difficulties arise either from the siting of the repository within the zone of active near-surface groundwater circulation or from the inherent properties of the HLW itself (and frequently both). The HLW based problems are essentially of two kinds. Firstly, the waste contains substantial amounts of heat generating radionuclides (HGRs) which puts constraints on the design and materials of the repository and, more importantly, necessitates that the HLW be packaged in relatively small units. Further, each of these units requires its own multi-barrier system and they have to be dispersed throughout a large volume of host rock to avoid potentially damaging temperature rises. Secondly, the waste contains sufficient quantities of very long lived radionuclides (VLLRs) to n
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