Abstract
Identifying and evaluating the factors that might impact on the long-term integrity of a deep Geological Disposal Facility (GDF) and its surrounding geological and surface environment is central to developing a safety case for underground disposal of radioactive waste. The geological environment should be relatively stable and its behaviour adequately predictable so that scientifically sound evaluations of the long-term radiological safety of a GDF can be made. In considering this, it is necessary to take into account natural processes that could affect a GDF or modify its geological environment up to 1millionyears into the future. Key processes considered in this paper include those which result from plate tectonics, such as seismicity and volcanism, as well as climate-related processes, such as erosion, uplift and the effects of glaciation. Understanding the inherent variability of process rates, critical thresholds and likely potential influence of unpredictable perturbations represent significant challenges to predicting the natural environment. From a plate-tectonic perspective, a one million year time frame represents a very short segment of geological time and is largely below the current resolution of observation of past processes. Similarly, predicting climate system evolution on such time-scales, particularly beyond 200ka AP is highly uncertain, relying on estimating the extremes within which climate and related processes may vary with reasonable confidence. The paper highlights some of the challenges facing a deep geological disposal program in the UK to review understanding of the natural changes that may affect siting and design of a GDF.
Highlights
A key component of deep geological disposal is the emplacement of wastes within an engineered facility, constructed at depths of hundreds of meters below the surface, making use of the surrounding geological environment as one of the containment barriers (NDA, 2010)
In contrast, future climate models predict that cycles of glacial advance and retreat are likely to affect the UK within the 1 Myr which are likely to drive glacial isostatic adjustment and climate-linked denudational isostacy depending on the location and extent of the resulting ice sheets
Understanding and predicting the long-term changes in the natural environment significantly contributes to the evidence underpinning the safety case of deep geological disposal facility
Summary
The disposal of radioactive waste represents a significant challenge for those countries that have utilised nuclear materials for defence, power generation and medicinal purposes. Geological disposal of radioactive waste differs from other sub-surface exploitation in that it requires significant assessment, to understand the impact of potential fugitive radionuclides, for up to 1 million years into the future. This timescale reflects the length of time for the radioactivity of typical waste materials to reach an acceptable risk level solely by natural decay (NDA, 2010). Atmospheric processes, including climate, have a strong influence on surface processes, such as rates of erosion and composition of sedimentary deposits, modifying the topography and redistributing very significant volumes of sedimentary material. This includes gradual trends of warming and cooling driven by tectonic processes on time scales of 105 to 107 years, rhythmic or periodic cycles driven by orbital processes with 104- to 106-years, and rare rapid climatic aberrations (for example, catastrophic methane release) with durations of 103 to 105 years (Zachos et al, 2001)
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