Mike Thorne and Associates Ltd

Thorne and, United Kingdom

Mike Thorne and Associates Ltd

Thorne and, United Kingdom
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Becker J.K.,National Cooperative for the Disposal of Radioactive Waste | Lindborg T.,Svensk Karnbranslehantering AB | Thorne M.C.,Mike Thorne and Associates Ltd
Journal of Environmental Radioactivity | Year: 2014

In safety assessments of repositories for radioactive wastes, large spatial and temporal scales have to be considered when developing an approach to risk calculations. A wide range of different types of information may be required. Local to the site of interest, temperature and precipitation data may be used to determine the erosional regime (which may also be conditioned by the vegetation characteristics adopted, based both on climatic and other considerations). However, geomorphological changes may be governed by regional rather than local considerations, e.g. alteration of river base levels, river capture and drainage network reorganisation, or the progression of an ice sheet or valley glacier across the site. The regional climate is in turn governed by the global climate. In this work, a commentary is presented on the types of climate models that can be used to develop projections of climate change for use in post-closure radiological impact assessments of geological repositories for radioactive wastes. These models include both Atmosphere-Ocean General Circulation Models and Earth Models of Intermediate Complexity. The relevant outputs available from these models are identified and consideration is given to how these outputs may be used to inform projections of landscape development. Issues of spatial and temporal downscaling of climate model outputs to meet the requirements of local-scale landscape development modelling are also addressed. An example is given of how climate change and landscape development influence the radiological impact of radionuclides potentially released from the deep geological disposal facility for spent nuclear fuel that SKB (the Swedish Nuclear Fuel and Waste Management Company) proposes to construct at Forsmark, Sweden. © 2014 Elsevier 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.


Mitchell N.,Grant Harris Ltd | Perez-Sanchez D.,CIEMAT | Thorne M.C.,Mike Thorne and Associates Ltd
Journal of Radiological Protection | Year: 2013

The U-238 series of radionuclides is of relevance in a variety of environmental contexts ranging from the remediation of former uranium mining and milling facilities to the deep geological disposal of solid radioactive wastes. Herein, we review what is known concerning the behaviour of radionuclides from the U-238 decay chain in soils and plants. This review is intended to provide a single comprehensive source of information to anyone involved in undertaking environmental impact assessment studies relating to this decay chain. Conclusions are drawn relating to values and ranges of distribution coefficients appropriate to uranium, thorium, radium, lead and polonium in different soil types and under various environmental conditions. Similarly, conclusions are drawn relating to plant:soil concentration ratios for these elements for different plant and soil types, and consideration is given to the distribution of these elements within plants following both root uptake and foliar application. © 2013 IOP Publishing Ltd.


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.


Perez-Sanchez D.,CIEMAT | Thorne M.C.,Mike Thorne and Associates Ltd | Limer L.M.C.,Limer Scientific Consulting Ltd
Journal of Radiological Protection | Year: 2012

Se-79 is a long-lived radionuclide of potential radiological significance in relation to the deep geological disposal of solid radioactive wastes. In the context of release to the terrestrial environment, its main radiological impact is delivered through food chain pathways. Therefore, its accumulation in soils and uptake by plants is an important consideration in post-closure safety assessment studies. However, representation of its behaviour in the soil-plant system requires consideration of the multiple valence states that it can exhibit under different redox conditions and its susceptibility to volatilisation. A simple model is described that includes seasonal variations in soil hydrology and their effects on the mobility and root uptake of Se-79. Illustrative calculations are undertaken with the model, to demonstrate its capabilities for interpreting experimental data on the behaviour of Se-79 in soils and plants, and for making projections on the long-term behaviour of Se-79 transported to soils. © 2012 IOP Publishing Ltd.


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.


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.


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.


Thorne M.C.,Mike Thorne and Associates Ltd
Journal of Radiological Protection | Year: 2012

The International Commission on Radiological Protection (ICRP) has reviewed recent epidemiological evidence suggesting that, for the lens of the eye, the threshold in absorbed dose for the induction of deleterious health effects is about 0.5Gy. On this basis, the Commission recommends that for occupational exposure in planned exposure situations, the equivalent dose limit for the lens of the eye should be 20mSv in a year, averaged over defined periods of 5yr, with exposure not exceeding 50mSv in any single year. This paper summarises the data that have been taken into account by the ICRP and critically examines whether the proposed downward revision of the dose limit is justified. Overall, it is concluded that the accumulating radiobiological and epidemiological evidence makes it more appropriate to treat cataract induction as a stochastic rather than a deterministic effect. Within this framework, it is illogical to have the same dose limit for the lens of the eye as for the whole body irradiated uniformly. This could be addressed either by removing the special dose limit for the lens of the eye, assigning it an appropriate tissue weighting factor and including it in the computation of the effective dose, or through a composite approach involving the use of a tissue weighting factor for effective dose computations together with a special limit on the equivalent dose to the lens of the eye to ensure that no individual was subject to an unacceptably high risk of induction of clinically significant cataracts. © IOP 2012 Publishing Ltd.


Thorne M.C.,Mike Thorne and Associates Ltd
Journal of Radiological Protection | Year: 2012

On 26 January 2012, the Blue Ribbon Commission on America's Nuclear Future released a report addressing, amongst other matters, options for the managing and disposal of high-level waste and spent fuel. The Blue Ribbon Commission was not chartered as a siting commission. Accordingly, it did not evaluate Yucca Mountain or any other location as a potential site for the storage or disposal of spent nuclear fuel and high-level waste. Nevertheless, if the Commission's recommendations are followed, it is clear that any future proposals to develop a repository at Yucca Mountain would require an extended period of consultation with local communities, tribes and the State of Nevada. Furthermore, there would be a need to develop generally applicable regulations for disposal of spent fuel and high-level radioactive waste, so that the Yucca Mountain site could be properly compared with alternative sites that would be expected to be identified in the initial phase of the site-selection process. Based on what is now known of the conditions existing at Yucca Mountain and the large number of safety, environmental and legal issues that have been raised in relation to the DOE Licence Application, it is suggested that it would be imprudent to include Yucca Mountain in a list of candidate sites for future evaluation in a consent-based process for site selection. Even if there were a desire at the local, tribal and state levels to act as hosts for such a repository, there would be enormous difficulties in attempting to develop an adequate post-closure safety case for such a facility, and in showing why this unsaturated environment should be preferred over other geological contexts that exist in the USA and that are more akin to those being studied and developed in other countries. © IOP 2012 Publishing Ltd.

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