TECHNICAL CHALLENGES FOR DEEP BOREHOLE DISPOSAL (Invited Presentation)
Based on the information presented at the workshop, the NWTRB recommends: 1) Independent expert review of the design and implementation of drilling to assure that down-hole testing and sampling requirements are adequately planned and integrated. 2) Comprehensive risk assessment of the drilling and waste emplacement program including, specifically, analysis of options available in the event of an accident during emplacement. 3) Full consideration of the potential heterogeneity of the subsurface environment at five kilometers and the complex interactions and feedbacks among the engineering activities related to drilling and sealing boreholes and the conditions of the natural geologic system at depth. 4) Inclusion of pre-drilling surface-based geophysical surveys to evaluate subsurface characteristics prior to drilling and help build an understanding of how data from a potentially complex system at a site can be applied to other sites. 5) Utilize the DBFT to investigate waste package performance, demonstrate seal emplacement, and test the efficacy of seal materials in dealing with damage zones around a borehole when exposed to in situ conditions. 6) Simulate emplacement of radioactive wastes in the DBFT to develop an operational safety strategy to limit exposure risks. 7) Engage regulators to define retrievability requirements, determine the technical information needed and collect that information to the extent practicable in the DBFT. 8) Use the DBFT to gain experience in consent-based siting of nuclear facilities by incorporating new standards of transparency and data access, and engaging stakeholders. Finally, NWTRB found that available performance assessments indicate that DBD does not offer any discernable improvement in long-term safety over disposal of waste in a mined geologic repository.