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.
Radioprotection | Year: 2011
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.
Mobbs S.,Eden Nuclear and Environment |
Shaw G.,University of Nottingham |
Norris S.,Nuclear Decommissioning Authority NDA |
Marang L.,Électricité de France |
And 7 more authors.
Radiocarbon | Year: 2013
Radiocarbon is present in solid radioactive wastes arising from the nuclear power industry, in reactor operating wastes, and in graphite and activated metals that will arise from reactor decommissioning. Its half-life of 5730 yr, among other factors, means that 14C may be released to the biosphere from radioactive waste repositories. These releases may occur as 14C-bearing gases, especially methane, or as aqueous species, and enter the biosphere from below via natural processes or via groundwater pumped from wells. Assessment of radiation doses to humans due to such releases must take account of the major role of carbon in biological processes, requiring specific 14C assessment models to be developed. Therefore, an intercomparison of 5 14C assessment models was organized by the international collaborative forum, BIOPROTA. The intercomparison identified significantly different results for the activity concentrations in the soil, atmosphere, and plant compartments, based upon the different modeling approaches. The major source of uncertainty was related to the identification of conditions under which mixing occurs and isotopic equilibrium is established. Furthermore, while the assumed release area plays a role in determining the calculated atmospheric 14C concentrations, the openness of the plant canopy and the wind profile in and above the canopy are the key drivers. The intercomparison has aided understanding of the processes involved and helped to identify areas where further research is required to address some of the uncertainties. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.
Meehan A.,EnergySolutions |
Sibley P.,EnergySolutions |
Lightfoot J.,Golder Associates |
Jackson D.,Eden Nuclear and Environment
Proceedings of the International Conference on Radioactive Waste Management and Environmental Remediation, ICEM | Year: 2011
Reactor graphite makes up about 30% by volume of the UK's inventory of intermediate level waste (ILW). There is estimated to be about 15,000m3 of graphite arisings prior to 2040, mainly comprising operational waste streams (Magnox and AGR fuel sleeves), along with core graphite from the decommissioning of experimental and prototype reactors. A further 65,000m3 of graphite is forecast to arise after 2040, comprising core graphite from the final decommissioning of the Magnox and AGR reactors. Consequently, the management and disposal of graphite wastes is of key strategic importance in the UK. The current baseline strategy for reactor graphite wastes in the UK is to encapsulate them upon retrieval using a cementitious grout in stainless steel containers, in compliance with NDA Radioactive Waste Management Directorate (RWMD) Generic Waste Package Specifications and Letter of Compliance (LoC) process, and to dispose of them, following a period of interim storage, to the UK's planned geological disposal facility (GDF), when this becomes available (currently planned for 2040). Using Magnox's Hunterston A site as a Pathfinder, EnergySolutions and its partner organisations have been engaged with the feasibility assessment, options assessment, engineering concept design and environmental safety case (ESC) development for a proposed on-site, near surface disposal facility for operational wastes. The proposal is consistent with Scotland's Higher Activity Radioactive Waste Policy. The operational wastes comprise more than 90% graphite by volume, with small volumes of other materials present (although these have higher activity concentrations for some radionuclides). The Pathfinder project also included a preliminary assessment for core graphite (which represents a more homogeneous waste form). Following production of detailed feasibility assessments and a concept/location options assessment, the ongoing engineering design work package has focused on delivery of a viable concept design for the facility. In parallel with this, the ESC and performance assessment work packages are concerned primarily with the radiological performance of the facility against the key requirements set out in the Scottish Environmental Protection Agency's (SEPA) Near Surface Guidance on the Requirements for Authorisation (NS-GRA). The concept under development is for a facility comprising one or more concrete lined, cylindrical disposal cells, sited within the near-surface environment at tens of meters below ground level, making of use of a series of engineered multi-barrier systems. The construction of the disposal cells relies on mature engineering, and standard technology readily available within the civil engineering field. This work may in due course support applications for regulatory and planning approval and subsequent placement of contracts for detailed design and build of a disposal facility at Hunterston A, subject to the confirmation of feasibility and agreement from the NDA to pursue implementation. Copyright © 2011 by ASME.
Jackson D.,Eden Nuclear and Environment |
Smith K.,Eden Nuclear and Environment |
Wood M.D.,University of Salford
Journal of Environmental Radioactivity | Year: 2014
Over recent years, a number of approaches have been developed that enable the calculation of dose rates to animals and plants following the release of radioactivity to the environment. These approaches can be used to assess the potential impacts of activities that may release radioactivity to the environment, such as the operation of waste repositories. A number of national and international studies have identified screening criteria to indicate those assessment results below which further consideration is not generally required. However no internationally agreed criteria are currently available and consistency in criteria between countries has not been achieved. Furthermore, since screening criteria are not intended to be applied as limits, it is clear that they cannot always form a sufficient basis for assessing the adequacy of protection afforded. Typically, exceeding a screening value leads to a regulatory requirement to undertake a further, more detailed assessment. It does not, per se, imply that there is inadequate protection of the organism types at the specific site under assessment. Therefore, there is a need to develop a more structured approach to dealing with situations in which current screening criteria are exceeded. As a contribution to the developing international discussions, and as an interim measure for application where assessments are required currently, a two-tier, three zone framework is proposed here, relevant to the long term assessment of potential impacts from the deep disposal of radioactive wastes. The purpose of the proposed framework is to promote a proportionate and risk-based approach to the level of effort required in undertaking and interpreting an assessment. © 2013 .
Mobbs S.,Eden Nuclear and Environment
Mineralogical Magazine | Year: 2012
Disposal in deep geological formations aims to provide isolation of long-lived radioactive waste for hundreds of thousands of years. This raises the question of the long-term governance of the repository throughout its lifetime. In the operational phase the repository is under active regulatory control. Once closed, there will be a phase of passive management control or indirect oversight. This will be followed, at some time in the future, by a period in which there is no oversight. This may be a result of a decision to cease management control or it may occur through loss of records or a change in priorities. The importance of the main exposure scenarios (exposure as a result of the gradual transport of radionuclides in groundwater, transport of radionuclides in gas, and exposure arising from inadvertent intrusion into the repository) are discussed with reference to these different phases. An interesting question is 'How do we minimize the risk of inadvertent intrusion in the far future?' Perhaps it is better to ensure that the repository is forgotten and should we try to plan for this? The different approaches are discussed and the importance of deciding on a strategy at an early stage is emphasized. © 2012 The Mineralogical Society.