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Harwell, United Kingdom

Alexander W.R.,Bedrock Geosciences | Milodowski A.E.,British Geological Survey | Pitty A.F.,Pitty EIA Consulting | Hardie S.M.L.,Scottish Universities Environmental Research Center | And 5 more authors.
Clay Minerals

Bentonite is one of the more safety-critical components of the engineered barrier system in the disposal concepts developed for many types of radioactive waste. It is used due to its favourable properties (including plasticity, swelling capacity, colloid filtration, low hydraulic conductivity, high retardation of key radionuclides) and its stability in relevant geological environments. However, bentonite is unstable under alkaline conditions and this has driven interest in low-alkali cements (leachate pH of 10 À 11). To build a robust safety case, it is important to have supporting natural analogue data to confirm understanding of the likely long-term performance of bentonite. In Cyprus, the presence of natural bentonite in close proximity to natural alkaline groundwaters permits the zones of potential bentonite/alkaline water reaction to be studied as an analogy of the potential reaction zones in the repository. Here, the results indicate minimal volumetric reaction of bentonite, with production of a palygorskite secondary phase. © 2013 Mineralogical Society. Source

Towler G.,Quintessa Ltd. | Bond A.E.,Quintessa Ltd. | Watson S.,Quintessa Ltd. | Norris S.,NDA RWMD | And 2 more authors.
Mineralogical Magazine

Understanding the behaviour of gas in a geological disposal facility (GDF) is an essential component of analysing the facility evolution and long-term (post-closure) safety performance. This includes the impacts of gas on the physico-chemical evolution of the GDF, and the release and migration of radionuclides in water and gas. The Nuclear Decommissioning Authority Radioactive Waste Management Directorate is participating in the EC FORGE (fate of repository gases) project (www.forgeproject.org) and conducting independent research. Key research themes are modelling the impacts of different host rocks on facility evolution including coupled processes, and upscaling the effects of small scale features that can significantly influence the evolution of the whole facility. Recent code developments have enabled coupled processes to be represented more realistically in models. This has significantly advanced understanding of facility evolution, as discussed in this paper, and will improve future assessment models. There is potential to further improve approaches to upscaling the effects of small scale features on strongly coupled processes, within the context of the EC FORGE project. © 2012 The Mineralogical Society. Source

Walke R.C.,Quintessa Ltd. | Thorne M.C.,Mike Thorne and Associates Ltd | Norris S.,NDA RWMD
Mineralogical Magazine

Higher activity radioactive wastes remain hazardous for extremely long timescales, of up to hundreds of thousands of years. Disposing of such wastes deep underground presents the internationally accepted best solution for isolating them from the surface environment on associated timescales. Geological disposal programmes need to assess potential releases from such facilities on long timescales to inform siting and design decisions and to help build confidence that they will provide an adequate degree of safety. Assessments of geological disposal include consideration of the wastes, the engineered facility, the host geology and the surface and near-surface environment including the biosphere. This paper presents an overview of recent post-closure biosphere assessment studies undertaken in support of the Nuclear Decommissioning Authority Radioactive Waste Management Directorate disposal system safety case for geological disposal of the United Kingdom's higher activity radioactive wastes. Recent biosphere studies have included: (1) ensuring that the United Kingdom's approach to consideration of the biosphere in safety case studies continues to be fit for purpose, irrespective of which site or sites are considered in the United Kingdom's geological disposal programme; (2) updating projections of global climate and sea level, together with consideration of the potential importance of transitions between climate states; (3) considering geosphere - biosphere interface issues and their representation, including redox modelling and catchment-scale hydrological modelling; and (4) identifying key radionuclides and developing a series of reports describing their behaviour in the biosphere together with an evaluation of associated implications for post-closure assessment calculations. © 2012 The Mineralogical Society. Source

Ikonen A.T.K.,Posiva Oy | Smith K.,Eden Nuclear and Environment | Robinson C.A.,Cove Environmental Consulting Ltd | De La Cruz I.,Facilia AB | And 4 more authors.

A programme of work, commissioned within the BIOPROTA collaborative forum, has recently been undertaken to assess the quantitative and qualitative elements of uncertainty associated with non-human biota (NHB) dose assessment in relation to the potential long-term release of radionuclides from a geological disposal facility (GDF). This was achieved through combining quantitative sensitivity and qualitative knowledge quality analyses based on the EC ERICA assessment approach and default assessment parameters. The results of the project demonstrate that this combination of approaches may be used to identify important parameters that could be significant in assessments of the impacts of any radionuclide release from a GDF on NHB, and for which there is low confidence. The output is intended to provide information on those parameters that may need to be considered in more detail for site-specific assessments. Such information should help users to enhance the quality of their assessments and build greater confidence in the results. © 2011 EDP Sciences. Source

Morris J.,Galson Sciences Ltd | Wickham S.,Galson Sciences Ltd | Nicholls D.,AREVA | Walshh C.,NDA RWMD | McKinney J.,NDA
Proceedings of the International Conference on Radioactive Waste Management and Environmental Remediation, ICEM

The NDA's Upstream Optioneering project has examined the potential implications of using an alternative type of waste package and its influence on the waste management lifecycle across the NDA estate. Robust Shielded Containers (RSCs) are radioactive waste packages that provide integral radiological shielding, reducing the need for remote handling. The robustness of the container could remove the need to immobilise waste by cement encapsulation. RSCs are routinely used to package ILW for interim storage in Germany and have fairly recently been considered for use in the UK because RSCs have the potential to simplify the waste management lifecycle and enable risk and hazard reduction. In particular, the current baseline (included in Magnox Limited lifetime plans) follows the strategy set out in the Magnox Operating Decommissioning Programme (MODP), in which Type II MOSAIK and Type VI Ductile Cast Iron Containers (DCICs) are used to package (in non-encapsulated form) most Magnox ILW arising prior to 2050. By considering representative types of Intermediate Level Waste (ILW) and exploring potential packaging options for these wastes, this paper identifies the factors that could differentiate between cases in which RSCs would, or would not, be an appropriate option. The potential role of RSCs across the waste management lifecycle is examined, from retrieval of waste through to emplacement at a Geological Disposal Facility (GDF), including consideration of other potential uses of RSCs, such as temporary storage of raw wastes for which appropriate treatment and conditioning measures have yet to be developed. Copyright © 2013 by ASME. Source

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