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Limer L.,Limer Scientific Consulting Ltd | Klos R.,Science 37 | Walke R.,Quintessa Ltd. | Shaw G.,University of Nottingham | And 2 more authors.
Radiocarbon | Year: 2013

The need to address radiological impacts from radiocarbon released to the biosphere has been recognized for some time. In 2011, the Swedish Radiation Safety Authority (SSM) commissioned a study to develop a 14C model of the soilplant-atmosphere system that would provide them with an independently developed assessment capability. This paper summarizes that study, which comprised a review of contemporary models, the development of a new conceptual model, SSPAM14C, and the application of SSPAM14C to a set of experimental data relating to the atmospheric exposure of cabbages. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona. Source

Paulley A.,Quintessa Ltd. | Metcalfe R.,Quintessa Ltd. | Egan M.,Quintessa Ltd. | Maul P.R.,Quintessa Ltd. | And 2 more authors.
Energy Procedia | Year: 2013

Underground CO2 storage facilities are designed to contain CO2 permanently and the expected performance scenario is that no CO2 leakage from the storage complex will occur. However, it is necessary to assess the possible environmental impacts of CO2 leakage in the unlikely event that a storage system evolves differently from the design aim. The RISCS project is being undertaken under the European Union's 7th Framework Programme to research these potential impacts. To help focus RISCS research and aid communication of the results, a set of reference terrestrial and marine European receptor environments and associated impact scenario descriptions were defined systematically by evidence-based expert elicitation. Source

Klos R.A.,Science 37 | Limer L.,Limer Scientific Consulting Ltd | Shaw G.,University of Nottingham | Perez-Sanchez D.,CIEMAT | Xu S.,Swedish Radiation Safety Authority SSM
Journal of Radiological Protection | Year: 2014

Recent developments in the modelling of key radionuclides in long-timescale assessments of the safety of geological disposal of spent fuel and other radioactive wastes emphasise the influence of the redox conditions of the soil column. Models with higher spatial resolution than typically employed in standard modelling approaches have been shown to capture important features of experimental observations that are not otherwise manifested. Furthermore, models with monthly, rather than annually, averaged parameters and with dynamic transfers between soil and plant have been shown to lead to key differences compared with standard models employing soil-plant concentration ratios. This paper looks at the potential for the inclusion of a higher spatio-temporal resolution in models for long-timescale dose assessments and includes representations of measured plant-root distributions as well as the effects of bioturbation. Focusing here on the distribution and dynamics of radionuclides in the soil column, the effects of different spatial and temporal resolution are compared, together with an investigation of the way in which the hydrology of the soil column is represented. The approach has been successfully incorporated into a practical assessment-level model. Results indicate the potential importance of higher spatio-temporal resolution in modelling soil column dynamics, particularly of weakly sorbing radionuclides in long-timescale assessments featuring sudden transitions between ecosystem types. © 2014 IOP Publishing Ltd. Source

Mobbs S.,Eden Nuclear and Environment | Shaw G.,University of Nottingham | Norris S.,Nuclear Decommissioning Authority NDA | Marang L.,Electricite 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. Source

Limer L.M.C.,Limer Scientific Consulting Ltd | Thorne M.C.,Mike Thorne and Associates Ltd | Cummings R.,Low Level Waste Repository Ltd
Radioprotection | Year: 2011

The LLW Repository Limited has recognised the potential importance of the processes being considered in the BIOPROTA 14C working group and funded the development a new 14C model that addresses the exchange of gas in a soil-plant-atmosphere system. This model considers two regions in the above-ground atmosphere and utilises concepts from the field of micrometeorology to describe the exchange of air between these regions and losses from the area of interest. The lower layer only experiences molecular diffusion processes in relation to the movement of molecules of CO2, whereas the upper layer experiences some degree of turbulent mixing as a result of winds which flow over the area of interest. The thicknesses of these layers depend upon the canopy density, which will affect the light intensity and thus the rate of photosynthetic uptake of carbon in the canopy profile. Model results demonstrate the impacts of 14C-labelled gas from the soil upon the calculated 14C concentration in plants for a variety of plant species (pasture and garden crops) and subsequent doses to human exposure groups. The technical modelling work described has been funded by the LLW Repository Ltd in support of its 2011 Environmental Safety Case. © 2011 EDP Sciences. Source

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