ABSTRACT
Time requirements and economic considerations do not allow for full-scale experiments to be conducted for clay-engineered barriers intended for use as engineered multi-barrier systems or as clay buffers in repositories housing canisters containing radioactive waste. In particular, if we are to provide reliable performance information on clay-engineered barriers over their service life, full-scale experiments would need to be conducted over a period of at least 35 years for engineered multi-barrier systems and 100,000 years for clay buffers in repositories. In attempts to shorten the time requirement in long-term experiments, laboratory scale-up and full-scale experiments, methods, devices and techniques have been devised to (a) accelerate physical and chemical reactions in the clay; (b) heighten and increase biological activities; and (c) shorten time-dependent processes and increasing rate-dependent processes etc. without compromising their effect. These, however, have not proven to be successful or reliable in producing the spectrum of information needed to allow decision-makers to render their judgements on anticipated performance of the candidate clay to be used in multi-barrier systems in the long term. For these, and many other reasons, organizations responsible for safe disposal of high-level radioactive wastes (HLWs) and hazardous solid wastes (HSWs), and especially the former, have tended to rely on conceptual and theoretical system-performance models for prediction of long-term performance.
