Carbon-14 discharges from the nuclear fuel cycle: 2. Local effects

Environemtnal ¹⁴C levels around various types of nuclear installations within the UK have been monitored during recent years. Enhanced ¹⁴C levels have been detected around both the nuclear fuel reprocessing plant as Sellafield and the thermal nuclear power station complex at Hunterston. From these measurements, the radiological impact of the ¹⁴C discharges on the local population is assessed. It is conservatively estimated that the ¹⁴CO₂ emissions from Sellafield between 1952 and 1985 could have delivered an 8·4 man Sv collective effective dose equivalent commitment to the population living within 40 km of the site. The maximum possible collective dose to the population within 15 km of Hunterston in 1984 was 15 × 10⁻³ man Sv. Conservative estimates of maximum annual effective dose equivalents to individuals around Sellafield and Hunterston are 0·2 mSv (in 1982) and 12 μSv (in 1984), respectively. These dose levels do not exceed the limits recommended by ICRP but the former value clearly indicates that, for the larger discharges at least, consideration and optimisation of ¹⁴C releases are fully justified. The same ¹⁴C measurements are also used to test the validity of two atmospheric dispersion models, the Gaussian plume and the so-called ‘hyperbolic’ models. The former is excellent in predicting downwind ¹⁴C levels around Hunterston but is unsatisfactory when applied to Sellafield, whereas the latter proves reliable at both sites. Further investigations suggest that the Gaussian plume model's poor performance at Sellafield can be explained by inaccurate input data.     

The influence of hot particle contamination on Sr and Cs transfers to milk and on time-integrated ingestion doses

Most models for transfers of radionuclides through the food chain typically assume that the radioactivity is initially deposited in chemically available forms. It is known, however, that releases of radionuclides in the form of hot particles may significantly influence their environmental transfers and uptake to the food chain. This study presents models for time changes in ⁹⁰Sr and ¹³⁷Cs in milk which incorporate hot particle contamination using observed rates of hot particle dissolution following the Chernobyl accident. A general equation is presented for the influence of hot particles on overall ingestion doses. As expected from previous work, fallout of hot particles significantly influences time changes in radionuclide activity concentrations in foodstuffs. It is also shown that incorporation of radionuclides in hot particles influences time-integrated ingestion doses. For a situation in which a large proportion (90–100%) of fallout is in slowly dissolving hot particles, time-integrated ingestion doses from ⁹⁰Sr and ¹³⁷Cs are reduced by a factor of approximately two compared to the case where all radioactivity is deposited in bioavailable forms. However, the influence of rapidly dissolving hot particles on time-integrated ingestion doses is relatively minor. Remaining significant uncertainties in dose estimates are discussed.     

Artificial radioactivity in Cumbria: Summary of an assessment by measurement and modelling

At the Harwell laboratory, the distributions of the artificial radionuclides discharged by British Nuclear Fuels at Sellafield have been measured within Cumbria, with particular emphasis on the transfer between environmental media. The results of the measurements have been incorporated into a model of the Cumbrian environment.The object of this work is to estimate the radiological impact upon man by exploring the pathways leading to external irradiation, to inhalation and to the ingestion of foodstuffs.Distributions have been established for caesium-137, plutonium isotopes and americium-241. Transfer from sea to land, of actinide radioactivity discharged to the sea, occures on a very small scale. The relative contributions to deposition and airborne radioactivity from sea-to-land transfer, fallout from nuclear weapons testing and atmospheric releases from Sellafield are compared. The dose resulting from sea-to-land transfer of actinides to a resident of Seascale peaked in 1973 at less than 1% of the ICRP annual limit for the general public and should fall steadily up to the year 2000.     

Aspects of the uptake of radionuclides by sheep grazing on an estuarine saltmarsh. 1. The influence of grazing behaviour and environmental variability on daily intake

Sea water contaminated with diluted radioactive effluent originating from the Sellafield reprocessing plant inundates saltmarshes in the Esk estuary in west Cumbria (UK). Much of the radioactivity on the saltmarsh vegetation was found to be associated with a surface deposit of silt, brought onto the area during tidal inundation. Large temporal variations in the radionuclide concentrations of the vegetation were found, these being due probably to seasonal fluctuation in the extent of silt deposition.The grazing habits of sheep were studied on one of these saltmarshes and the consequent ingestion of radionuclides by the sheep was estimated. The sheep ingested different quantities of radionuclides according to time of year as a result of a combination of two factors; the considerable temporal variation in the concentration of radionuclides on the saltmarsh vegetation and the seasonal grazing behaviour of the sheep.     

Modelling radioactivity in the Irish Sea: From discharge to dose

In order to support authorised discharges of low level radioactive liquid effluent into coastal regions, mathematical models are required to robustly predict radiological impacts on critical groups of current and proposed changes to liquid discharges. The grid model presented here simulates the long term dispersion and transport of radioactivity discharged from the Sellafield site in Cumbria, UK, and the subsequent exposure of critical groups in Cumbria and across the Irish Sea in Northern Ireland. The fine grid of the model allows a good resolution of the seabed sediment distribution. This benefits the predictions for the last decades of low discharge level, when bed sediment can become a source of contamination by bringing back the legacy of past high discharges. This is highlighted by the dose comparison, where the predicted dose to Cumbria critical group follows well the dose estimated from environmental data during the low discharge level period.     

Polybrominated diphenyl ethers in domestic indoor dust from Canada, New Zealand, United Kingdom and United States

Because of the similarities in European and North American dietary exposure, it has been suggested that the order of magnitude higher body burdens in North Americans may be due to international variations in exposure via ingestion of indoor dust. Furthermore, ingestion of indoor dust has been suggested as a possible source of PBDEs in the blood serum of New Zealanders. Hence, polybrominated diphenyl ethers (PBDEs) were measured in domestic indoor dust from: Amarillo/Austin, Texas, US; Birmingham, UK; Toronto, Canada; and Wellington, New Zealand. Concentrations of BDE 209 in two UK samples were - at 520,000 and 100,000 ng g(-1) - the highest ever recorded in a domestic (or office) indoor dust sample. Median concentrations in ng g(-1) were: in Canada 620 and 560 for Sigmatri-hexa-BDEs and BDE 209 respectively; in New Zealand 96, BDE 209 not determined; in the UK 59 and 2,800; and in the US 1600 and 1300. With respect to BDE 209, concentrations were in the order: UK approximately US>Canada. For Sigmatri-hexa-BDEs, the order of concentrations was US approximately Canada>New Zealand approximately UK. Combined with principal component analysis of congener patterns, this suggests that, while North American dusts are contaminated by both Deca- and Penta-BDE commercial formulations, UK dusts are contaminated predominantly by Deca-BDE. The Octa-BDE formulation appears of minimal importance in accordance with available market demand figures. Despite the commercial formulations of PBDEs never having been manufactured in, nor imported into New Zealand, their presence in dusts from that country suggests international trade in PBDE-containing goods is an important pathway effecting their global distribution.     

Model testing using data on 131I released from Hanford

The Hanford test scenario described an accidental release of 131I to the environment from the Hanford Purex Chemical Separations Plant in September 1963. Based on monitoring data collected after the release, this scenario was used by the Dose Reconstruction Working Group of BIOMASS to test models typically used in dose reconstructions. The primary exposure pathway in terms of contribution to human doses was ingestion of contaminated milk and vegetables. Predicted mean doses to the thyroid of reference individuals from ingestion of 131I ranged from 0.0001 to 0.8 mSv. For one location, predicted doses to the thyroids of two children with high milk consumption ranged from 0.006 to 2 mSv. The predicted deposition at any given location varied among participants by a factor of 5-80. The exercise provided an opportunity for comparison of assessment methods and conceptual approaches, testing model predictions against measurements, and identifying the most important contributors to uncertainty in the assessment result. Key factors affecting predictions included the approach to handling incomplete data, interpretation of input information, selection of parameter values, adjustment of models for site-specific conditions, and treatment of uncertainties.     

Factors influencing the food transition in riverine communities in the Brazilian Amazon

The objective of this study was to determine the main patterns and factors influencing food transition in riverine people in the Brazilian Amazon. Through interviews with a semi-structured questionnaire, we inferred their food habits and provide information about general demographic, socioeconomic, resource use and environmental context. Data from the questionnaires were categorized and analyzed using a logistic regression model to assess the relative influence of socioeconomic and environment factors on the local diet. Based on a logistic regression data analysis, it was found a greater consumption of processed food significantly associated with multiple factors such as market participation, sex (female and male), government aid to forest conservation and environment context (upland and wetland). Although the local diet is composed mainly of local resources such as fish and cassava flour, increasing incomes due to direct government subsidy programs and marketing of cassava flour have influenced these local practices and habits. Through the analysis of factors influencing food transition, it was possible to evaluate those having the greatest effect on this Amazon region and propose an alternative method to subsidy food policy grounded in local opinion surveys.     

Government intervention in green industries: lessons from the wind turbine and the organic food industries in Denmark

Government intervention in green infant industries may be justified as a strategy to increase the provision of public goods. How should government policies be designed to promote such industries? One way to analyse this question is to compare government intervention in green infant industries in which it has been successful with green infant industries in which it has been less successful. The Danish government has intervened intensively in the wind turbine industry and organic farming sector mainly for environmental reasons since 1992 and 1987, respectively, but with very different impacts. While the electricity market share of wind energy reached 20% in 2007, organic food consumption lags behind with a food market share of approximately 8.5% in 2007. This paper compares the packages of policy instruments applied in the two industrial sectors and assesses whether differences in instrument choice may explain the significant differences in market shares. It is demonstrated that government intervention in the wind turbine industry has emphasized the use of policy instruments designed to increase demand for wind energy, whereas organic farming policy has put more emphasis on instruments motivating farmers to increase supply. This may be an important factor explaining variance in growth. Finally, the paper analyses whether the lessons from government policy aimed at promoting the wind turbine industry can be transferred to organic farming policy.     

A process-based model for the partitioning of soluble, suspended particulate and bed sediment fractions of plutonium and caesium in the eastern Irish Sea

A dynamic model of plutonium behaviour in the marine environment has been developed, representing the oxidation state distribution and partitioning of plutonium between the soluble, colloidal, suspended particulate and seabed sediment fractions. With simple re-parameterisation, this model can also be applied to (137)Cs. The model, which is calibrated and validated against field data, has been used to predict concentrations of Pu(alpha) and (137)Cs in both water and seabed sediments from the vicinity of the Sellafield Ltd. reprocessing plant in Cumbria, UK. The model predicts that sediment reworking and transport are the key environmental processes as the Sellafield Pu(alpha) and (137)Cs discharge continues to decline. Inventory calculations generated by the model are consistent with previous estimations. For a hypothetical post-discharge scenario, the concentrations of these radionuclides in both seawater and surface sediments are predicted to decrease sharply, concurrent with a downward vertical migration of the activity retained in sediments.     

Sea to land transfer of anthropogenic radionuclides to the North Wales coast, Part II: aerial modelling and radiological assessment

Modelling calculations have been performed to predict the radiological impact of the sea to land transfer pathway to members of the public in North Wales from 1952 to 2004. The radionuclides of interest were (99)Tc, (137)Cs, (239,240)Pu and (241)Am and the exposure routes considered were food consumption, external and inhalation. The consumption of locally grown terrestrial food in the early to mid 1980s was the most significant source of exposure to all of the groups considered, with (239,240)Pu being the radionuclide contributing most to the dose. A maximum dose of 1.46muSvy(-1) was calculated for adult members of the critical consumption group in 1985, with doses for 2004 reducing to 0.59muSvy(-1). Despite the conservative approach of the dose calculations, the dose rate values are very low, less than 0.15% of the annual limit of 1000muSvy(-1) for the UK public from controlled radiation sources (excluding medical).     

Areal distribution of 129I in west cumbrian solis

¹²⁹I has been released during operations at the BNFL nuclear fuel reprocessing plant at Sellafield in west Cumbria over the past thirty years with about 95% being discharged into the sea and 5% into the atmosphere. Soil samples have been taken within a 40 km radius of Sellafield to determine the extent to which the ¹²⁹I is deposited in the immediate vicinity of the plant. The ¹²⁹I content has been determined by a sensitive neutron activation technique and levels in soil were found to be elevated above global levels in all samples. The areal distribution of ¹²⁹I was consistent with direct deposition following release to the atmosphere from Sellafield and the relationship between ¹²⁹I activity and the distance from Sellafield was of a form predicted by atmospheric dispersion models. The absence of any observable return of ¹²⁹I from the sea has implications for assessments of dose.     

Overview of regulatory/policy/economic issues related to carbon dioxide

This is an overview of Session 2c dealing with the regulatory, policy and economic issues related to carbon dioxide and its impact on global climate change. The information is taken from the two papers presented in this session (the U.S. Perspective by Dennis Leaf and the European Perspective by Hans J.H. Verolme) and from the panel discussion that took place at the end of the session. The overview focuses primarily on the policy responses of both the United States (US) and the United Kingdom (UK) to changes in global atmospheric pollution. To a lesser extent, the progress of policy responses to these changes is discussed. The United Nations Framework Convention on Climate Change (UNFCCC) has been signed and ratified by over 180 countries. The UNFCCC contained no binding targets or timetables for emissions reductions. The Kyoto Protocol [United Nations. Kyoto Protocol to the United Nations Framework Convention on Climate Change. UNEP.IUC/99/10. Chatlelaine, Switzerland: United Nations Environment Programme's Information Unit for Conventions, for the Climate Change Secretariat, 1997] to the UNFCCC did contain targets and timetables for reductions of greenhouse gases on the part of developed countries. The US has signed but not ratified the Kyoto Protocol. The US has experienced some movement to reduce greenhouse gas emissions on the part of various levels of government, as well as the private sector. The UK's commitment to reducing green house gases is laid down in the UK Climate Change Programme 2000. The UK is a member of the European Union (EU). In this context, an example of EU-wide progress, the voluntary agreement with car manufacturers to reduce CO(2) emissions in new vehicles, will be discussed. In addition, there will be some discussion on the UK CO(2) trading scheme that created the first market in the world in April 2001. Overall, the policy process is constantly informed by scientific research. In the case of climate change, much of this work is carried out under the auspices of international scientific panels.     

The transfer of radionuclides from saltmarsh vegetation to sheep tissues and milk

Radionuclides released into the Irish Sea by the Sellafield reprocessing plant are deposited onto tide-washed pastures along the western coast of the United Kingdom. Many of these pastures are grazed by sheep or cattle. This paper describes a controlled feeding study, in which saltmarsh vegetation harvested from close to the Sellafield plant, was fed to lambs and adult female sheep for a period of 8 weeks. Activity concentrations of (60)Co, (95)Nb, (106)Ru, (134)Cs, (137)Cs, (238)Pu, (239,240)Pu and (241)Am were determined in edible tissues and transfer parameters estimated. The activity concentrations of some of the radionuclides will not have been in equilibrium with those in the diet. Nevertheless, the study was reasonably realistic in terms of agricultural management as the period of the study was similar to that for which lambs graze on the saltmarshes. A field study to determine the activity concentrations of (137)Cs and (239,240)Pu in the milk of ewes grazing a saltmarsh close to Sellafield is also described.     

Radiological risk assessment and biosphere modelling for radioactive waste disposal in Switzerland

Long-term safety assessments for geological disposal of radioactive waste in Switzerland involve the demonstration that the annual radiation dose to humans due to the potential release of radionuclides from the waste repository into the biosphere will not exceed the regulatory limit of 0.1 mSv. Here, we describe the simple but robust approach used by Nagra (Swiss National Cooperative for the Disposal of Radioactive Waste) to quantify the dose to humans as a result to time-dependent release of radionuclides from the geosphere into the biosphere. The model calculates the concentrations of radionuclides in different terrestrial and aquatic compartments of the surface environment. The fluxes of water and solids within the environment are the drivers for the exchange of radionuclides between these compartments. The calculated radionuclide concentrations in the biosphere are then used to estimate the radiation doses to humans due to various exposure paths (e.g. ingestion of radionuclides via drinking water and food, inhalation of radionuclides, external irradiation from radionuclides in soils). In this paper we also discuss recent new achievements and planned future work.     

Some observations on the geochemistry and isotopic composition of uranium in relation to the reprocessing of nuclear fuels

In order to determine whether or not uranium depleted in ²³⁵U and derived from the British Nuclear Fuels Ltd (BNFL) nuclear fuel reprocessingg plant at Sellafield, Cumbria, UK can be detected in environmental samples, we have investigated the isotopic composition of uranium in ammonium carbonate leachates from marine and terrestial samples from near Sellafield. Some show a depletion in ²³⁵U and the presence of ²³⁶U which unequivocally identifies the presence of uranium derived from BNFL. The ²³⁴U/²³⁸U activity ratio and total uranium content of samples are not significantly different from those of natural uranium abundances. The highest concentrations of uranium are found in anaerobic organic-rich silts and the lowest in sandy silts and coarse-grained sands.     

Quantifying 137Cs aggregated transfer coefficients in a semi-natural woodland ecosystem adjacent to a nuclear reprocessing facility

Radiocaesium (137Cs) activity concentrations and aggregated transfer factors (Tag values) were calculated for vascular plants, fungal fruiting bodies and invertebrates in a semi-natural Picea sitchensis woodland (Lady Wood) adjacent to the British Nuclear Fuels plc. reprocessing facility at Sellafield, Cumbria, UK. The Tag values for vascular plants ranged from 7.1 x 10(-4) - 1.9 x 10(-2) m2 kg(-1), the maximum value being for Pteridium aquilinum. Fungal fruiting bodies had higher Tag values (1.9 x 10(-3) - 1.8 x 10(-1) m2 kg(-1)) than vascular plants, with a maximum value for Mycena galericulata. None of the activity concentrations for edible foodstuffs collected within this study (fungi and berries) exceeded the EC recommended limits of 137Cs in foodstuffs grown within the UK. The invertebrate community sampled during the study had Tag values ranging from 3.4 x 10(-4) to 1.3 x 10(-2) m2 kg(-1). There were no systematic differences in 137Cs activity concentration between invertebrate guilds, or between seasonal cohorts within guilds. The invertebrates in Lady Wood were exposed to a dose from 137Cs (internal gamma + beta and external gamma) ranging between 4.37 x 10(-4) and 6.40 x 10(-4) mGy day(-1). Including dose from radionuclides other than 137Cs and accounting for uncertainties due to the relative biological effectiveness of differing radionuclides could increase total dose by approximately an order of magnitude. These dose rates are at least three orders of magnitude lower than the 1 mGy d(-1) level at which harm may be caused to terrestrial biota, hence the risk to the invertebrate community from the effects of ionising radiation in Lady Wood is low.     

Health and environmental impacts of a fertilizer plant--Part II: assessment of radiation exposure

In the previous paper the authors have studied the radioactive pollution caused by a complex fertilizers production plant. In this paper, the effective doses to the plant workers and to members of the population surrounding the industrial site are estimated. The authors have considered external irradiation, inhalation and ingestion of dust and inhalation of radon and radon daughters as the main occupational exposure routes. After estimating the single contributions, the total effective dose has been calculated as the sum of said contributions. Calculations have been differentiated according to the different tasks of the company employees. The estimated annual effective doses range from 0.6 to 1.4 mSv y(-1). Annual individual effective doses to local residents, resulting from internal and external irradiation caused by particulate matter emitted into the atmosphere by the plant have been estimated. The maximum individual dose rate is estimated to be about 4 microSv y(-1).     

Identifying optimal agricultural countermeasure strategies for a hypothetical contamination scenario using the strategy model

A spatially implemented model designed to assist the identification of optimal countermeasure strategies for radioactively contaminated regions is described. Collective and individual ingestion doses for people within the affected area are estimated together with collective exported ingestion dose. A range of countermeasures are incorporated within the model, and environmental restrictions have been included as appropriate. The model evaluates the effectiveness of a given combination of countermeasures through a cost function which balances the benefit obtained through the reduction in dose with the cost of implementation. The optimal countermeasure strategy is the combination of individual countermeasures (and when and where they are implemented) which gives the lowest value of the cost function. The model outputs should not be considered as definitive solutions, rather as interactive inputs to the decision making process. As a demonstration the model has been applied to a hypothetical scenario in Cumbria (UK). This scenario considered a published nuclear power plant accident scenario with a total deposition of 1.7x10(14), 1.2x10(13), 2.8x10(10) and 5.3x10(9)Bq for Cs-137, Sr-90, Pu-239/240 and Am-241, respectively. The model predicts that if no remediation measures were implemented the resulting collective dose would be approximately 36 000 person-Sv (predominantly from 137Cs) over a 10-year period post-deposition. The optimal countermeasure strategy is predicted to avert approximately 33 000 person-Sv at a cost of approximately 160 million pounds. The optimal strategy comprises a mixture of ploughing, AFCF (ammonium-ferric hexacyano-ferrate) administration, potassium fertiliser application, clean feeding of livestock and food restrictions. The model recommends specific areas within the contaminated area and time periods where these measures should be implemented.     

The marine impact of caesium-134 and -137 from the Chernobyl reactor accident

¹³⁴Cs and ¹³⁷Cs from the Chernobyl reactor accident were detected in UK shoreline seawater very quickly after activity from the accident reached this country. Concentrations were highest in areas adjacent to those where deposition over land was highest, but they declined quickly and did not reach radiologically significant levels in terms of public radiation exposure. Subsequently, the distribution in seawater was investigated further afield. Radiocaesium attributable to the Chernobyl accident was found to be widespread: it was readily distinguished from other sources by having a different ¹³⁷Cs:¹³⁴Cs ratio (about 2:1). Its presence was especially noticeable in northern UK waters rather than those to the south; much of the North Sea has been surveyed as well as the Norwegian Sea. Evidence of Chernobyl radiocaesium was found as far north as 70°N and in many of these areas, including the northern North Sea, it overshadowed the effect of BNFL (British Nuclear Fuels plc) Sellafield discharges, previously the main source of these radionuclides.