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Hamsterley, United Kingdom

Walke R.C.,Quintessa Ltd. | Thorne M.C.,Mike Thorne and Associates Ltd | Norris S.,NDA RWMD
Mineralogical Magazine | Year: 2012

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.

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.

Perez-Sanchez D.,CIEMAT | Thorne M.C.,Mike Thorne and Associates Ltd
Journal of Environmental Radioactivity | Year: 2014

In a previous paper, a mathematical model for the behaviour of 79Se in soils and plants was described. Subsequently, a review has been published relating to the behaviour of 238U-series radionuclides in soils and plants. Here, we bring together those two strands of work to describe a new mathematical model of the behaviour of 238U-series radionuclides entering soils in solution and their uptake by plants. Initial studies with the model that are reported here demonstrate that it is a powerful tool for exploring the behaviour of this decay chain or subcomponents of it in soil-plant systems under different hydrological regimes. In particular, it permits studies of the degree to which secular equilibrium assumptions are appropriate when modelling this decay chain. Further studies will be undertaken and reported separately examining sensitivities of model results to input parameter values and also applying the model to sites contaminated with 238U-series radionuclides. © 2013 Elsevier Ltd.

Thorne M.C.,Mike Thorne and Associates Ltd
Journal of Radiological Protection | Year: 2013

The ERICA Tool has become widely accepted as an appropriate approach to assessing radiological impacts of environmental concentrations of radionuclides on wildlife. Although generally a comprehensive and state-of-the-art approach in this type of assessment, its treatment of uncertainty at Tier 2 is extremely limited and is not likely to be valid in the assessment contexts in which it will typically be employed. A more appropriate approach to the treatment of uncertainties is described. This leads to the conclusion that where data are lognormally distributed, it is appropriate to use the arithmetic mean of the distribution in reasonably cautious assessment calculations (as is done in the ERICA Tool) rather than to use the geometric mean, but that the uncertainty factor adopted should be larger than the range of 3 to 5 currently recommended at Tier 2 of the ERICA Tool. © 2013 IOP Publishing Ltd.

Thome M.C.,Mike Thorne and Associates Ltd | Smith G.M.,GMS Abingdon Ltd.
15th International High-Level Radioactive Waste Management Conference 2015, IHLRWM 2015 | Year: 2015

In post-closure radiological safety assessments of geological disposal facilities for radioactive wastes, models are developed and applied for transport of radionuclides through the engineered barriers and surrounding host rock towards the biosphere. Whereas the role of the engineered barriers and host rock is generally to prevent or retard the migration of radionuclides, in the more superficial strata retardation may be of less importance compared with dilution and dispersion. However, in determining the radiological impacts of possible releases of radionuclides in relation to the regulatory criteria typically employed, there is a need to evaluate the degree of dilution and dispersion in the superficial strata, together with any re-concentration that may occur. This means that appropriate conceptual and mathematical models are required to define the region between the deeper geosphere and the superficial biosphere. This region is described as the geosphere-biosphere interface and its characterization is discussed herein, based on work carried on work carried out with the BIOPROTA international collaborative forum.

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