Independent Peer Review of - Low Level Waste Repository Ltd

Peer Review of LLWR Response to S9R2LLWR_2008-8-2Version 144. The peer review panel agrees that construction of a final cap is bestpractice in near-surface radioactive waste disposal and will be essential (tolimit infiltration and reduce the potential consequences of inadvertenthuman intrusion), but considers that further optimisation of the cap designmay be needed. For example, we are yet to be convinced that theproposed profile for the cap incorporating a central valley (see Figure 2.3of LLWR 2008c) is optimal, and we have concerns that it may berelatively more susceptible to cracking and failure due to differentialsettlement of the underlying waste than possible alternative designs.45. The peer review panel suggests that the SLC should consider a stagedprogramme of cap construction because this would provide an opportunityto trial and improve the cap construction process, to monitor capperformance, and to gather data on which to base models of capperformance.46. The peer review panel is not fully convinced by the justifications providedfor the vertical drains, the vault base liner, or the cut-off walls.Collectively these features (together with the cap) are designed to prevent‘bath-tubbing’ 2 and terrestrial discharge. The peer review panel considersthat the avoidance of bath-tubbing and terrestrial discharge should be akey design aim, but we are yet to be convinced that the proposed systemwill achieve this. For example, we are not convinced that with theircurrent proposed design, the vertical drains would continue to operate forthe required period and would not become clogged. The peer reviewpanel considers that a simpler facility design with a permeable vault basemight be better.47. We acknowledge that the SLC is planning further optimisation work onthe facility design and we support this. We would also encourage the SLCto review LLW disposal practices in other waste managementprogrammes (e.g., within Europe), with the aim of identifying examplesthat support the disposal practices and engineering measures beingproposed at the LLWR.3.2.3 Geology and Hydrogeology48. The geology and hydrogeology of the LLWR site and its immediatesurroundings are lithologically and spatially complex, and there have beenseveral attempts leading up to the 2002 PCSC and subsequently todevelop models of the geological structure and of groundwater andsurface water flows. Different modelling teams have had different viewson how the system should be represented and modelled, and over theyears, considerable resources have been put into the problem. LLWR(2008d) summarises the most recent work. However, some of the2Bath-tubbing is when the facility fills with water and this becomes contaminated and dischargesover the top of the facility walls into shallow groundwaters, the surrounding land or into streamsetc.TerraSalus Limited 12 2 September 2008