Showing papers in "Journal of Radiological Protection in 2010"

A multi-criteria weight of evidence approach for deriving ecological benchmarks for radioactive substances

Abstract: Dose rate benchmarks are required in the tiered approaches used to screen out benign exposure scenarios in radiological ecological risk assessment. Such screening benchmarks, namely the predicted no-effect dose rates (PNEDR), have been derived by applying, as far as possible, the European guidance developed for chemicals. To derive the ecosystem level (or generic) PNEDR, radiotoxicity EDR(10) data (dose rates giving a 10% effect in comparison with the control) were used to fit a species sensitivity distribution (SSD) and estimate the HDR(5) (the hazardous dose rate affecting 5% of species with a 10% effect). Then, a multi-criteria approach was developed to justify using an assessment factor (AF) to apply to the HDR(5) for estimating a PNEDR value. Several different statistical data treatments were considered which all gave reasonably similar results. The suggested generic screening value of 10 microGy h(-1) (incremental dose rate) was derived using the lowest available EDR(10) value per species, an unweighted SSD, and an AF of 2 applied to the estimated HDR(5). Consideration was also given to deriving screening benchmark values for organism groups but this was not thought to be currently appropriate due to few relevant data being currently available.

Modelling particle retention in the alveolar–interstitial region of the human lungs

Abstract: Better information is available now on long-term particle retention in the human lungs than there was in 1994, when the human respiratory tract model (HRTM) was adopted by the International Commission on Radiological Protection (ICRP). Three recent studies are especially useful because they provide such information for groups of people who inhaled very similar aerosols. For all three the HRTM significantly underestimates lung retention of insoluble material. The purpose of this work was to improve the modelling of long-term retention in the deep lung. A simple physiologically based model developed to predict lung and lymph node particle retention in coal miners was found to represent lung retention in these studies adequately. Instead of the three alveolar-interstitial (AI) compartments in the HRTM, it has an alveolar compartment which clears to the bronchial tree and to a second compartment, representing the interstitium, which clears only to lymph nodes. The main difference from the HRTM AI model is that a significant fraction of the AI deposit is sequestered in the interstitium. To obtain default parameter values for general use, the model was fitted to data from the three recent studies, and also the experimental data used in development of the HRTM to define particle transport from the AI region for the first year after intake. The result of the analysis is that about 40% of the AI deposit of insoluble particles is sequestered in the interstitium and the remaining fraction is cleared to the ciliated airways with a half-time of about 300 days. For some long-lived radionuclides in relatively insoluble form (type S), this increased retention increases the lung dose per unit intake by 50-100% compared to the HRTM value.

Protection of the environment from ionising radiation in a regulatory context--an overview of the PROTECT coordinated action project.

Abstract: The outcome of the PROTECT project (Protection of the Environment from Ionising Radiation in a Regulatory Context) is summarised, focusing on the protection goal and derivation of dose rates which may detrimentally affect wildlife populations. To carry out an impact assessment for radioactive substances, the estimated dose rates produced by assessment tools need to be compared with some form of criteria to judge the level of risk. To do this, appropriate protection goals need to be defined and associated predefined dose rate values, or benchmarks, derived and agreed upon. Previous approaches used to estimate dose rates at which there may be observable changes in populations or individuals are described and discussed, as are more recent derivations of screening benchmarks for use in regulatory frameworks. We have adopted guidance and procedures used for assessment and regulation of other chemical stressors to derive benchmarks. On the basis of consultation with many relevant experts, PROTECT has derived a benchmark screening dose rate, using data on largely reproductive effects to derive species sensitivity distributions, of 10 µGy h − 1 which can be used to identify situations which are below regulatory concern with a high degree of confidence.

Predicting the radiation exposure of terrestrial wildlife in the Chernobyl exclusion zone: an international comparison of approaches

Abstract: There is now general acknowledgement that there is a requirement to demonstrate that species other than humans are protected from anthropogenic releases of radioactivity. A number of approaches have been developed for estimating the exposure of wildlife and some of these are being used to conduct regulatory assessments. There is a requirement to compare the outputs of such approaches against available data sets to ensure that they are robust and fit for purpose. In this paper we describe the application of seven approaches for predicting the whole-body (90Sr, 137Cs, 241Am and Pu isotope) activity concentrations and absorbed dose rates for a range of terrestrial species within the Chernobyl exclusion zone. Predictions are compared against available measurement data, including estimates of external dose rate recorded by thermoluminescent dosimeters attached to rodent species. Potential reasons for differences between predictions between the various approaches and the available data are explored.

An international model validation exercise on radionuclide transfer and doses to freshwater biota

Abstract: Under the International Atomic Energy Agency (IAEA)'s EMRAS (Environmental Modelling for Radiation Safety) programme, activity concentrations of 60Co, 90Sr, 137Cs and 3H in Perch Lake at Atomic Energy of Canada Limited's Chalk River Laboratories site were predicted, in freshwater primary producers, invertebrates, fishes, herpetofauna and mammals using eleven modelling approaches. Comparison of predicted radionuclide concentrations in the different species types with measured values highlighted a number of areas where additional work and understanding is required to improve the predictions of radionuclide transfer. For some species, the differences could be explained by ecological factors such as trophic level or the influence of stable analogues. Model predictions were relatively poor for mammalian species and herpetofauna compared with measured values, partly due to a lack of relevant data. In addition, concentration ratios are sometimes under-predicted when derived from experiments performed under controlled laboratory conditions representative of conditions in other water bodies.

Background dose-rates to reference animals and plants arising from exposure to naturally occurring radionuclides in aquatic environments.

Abstract: In order to put dose-rates derived in environmental impact assessments into context, the International Commission on Radiological Protection (ICRP) has recommended the structuring of effects data according to background exposure levels. The ICRP has also recommended a suite of reference animals and plants (RAPs), including seven aquatic organisms, for use within their developing framework. In light of these propositions, the objective of this work was to collate information on activity concentrations of naturally occurring primordial radionuclides for marine and freshwater ecosystems and apply appropriate dosimetry models to derive absorbed dose-rates. Although coverage of activity concentration data is comprehensive for sediment and water, few, or in some cases no, data were found for some RAPs, e.g. for frogs (Ranidae) and freshwater grasses (Poaceae) for most radionuclides. The activity concentrations for individual radionuclides in both organisms and their habitat often exhibit standard deviations that are substantially greater than arithmetic mean values, reflecting large variability in activity concentrations. To take account of variability a probabilistic approach was adopted. The dominating radionuclides contributing to exposure in the RAPs are 40K, 210Po and 226Ra. The mean unweighted and weighted dose-rates for aquatic RAPs are in the ranges 0.07–0.39 µGy h − 1 and 0.37–1.9 µGy h − 1 respectively.

Estimation of seasonal correction factors through Fourier decomposition analysis--a new model for indoor radon levels in Irish homes.

Abstract: Radon concentrations in homes have been shown to vary considerably with season. It is important to account for this by applying a correction factor to any home radon measurement of less than one year. To date, Irish radon measurement services have used correction factors based on data derived for the UK in the 1980s. In the absence of similar data for Ireland at the time, these were considered suitable for use due to the similarities between the climates, house types and lifestyles in the two countries. In order to better estimate the long-term radon concentration, measurements from 5640 Irish homes were used to derive a set of correction factors specifically for Ireland. These were generated by means of Fourier decomposition analysis and the new correction factors compared, using 95% confidence intervals, to those derived for the UK using the same analysis and to those currently in use for Ireland. In both cases, a significant difference was found between 10 of the 12 monthly seasonal correction factors. This paper presents the methods used in detail and the results of the analysis.

Short-lived variations in the background gamma-radiation dose.

Abstract: Sudden increases in the background gamma-radiation dose may occur due to the removal of 222Rn and 220Rn progeny from the atmosphere by wet deposition mechanisms. This contribution has been measured using a Geiger–Muller detector at the Atomic Weapons Establishment (Aldermaston, UK) during July 2005–April 2006. The results are approximated by a log-normal distribution and there were nine separate occurrences of the gamma-radiation dose exceeding 125% of the geometric mean value. The increases were associated with periods of heavy rainfall, although no correlation was evident between the dose rate and the amount of rainfall, as increased rainfall dilutes the activity further rather than increasing its atmospheric removal. The events were preceded by periods of fine weather and atmospheric stability that allow for the build-up of 222Rn and 220Rn progeny. Similar increases in gamma-radiation dose have been measured at a nearby monitoring station situated approximately 11 miles from Aldermaston. Increases in gamma-radiation dose during heavy rainfall have also been observed throughout the UK, that followed the trajectory of an air mass. All events decreased to typical values within 1–2 h as the water permeated into the ground below and the radioactivity decayed away.

Absorption of plutonium compounds in the respiratory tract.

Abstract: In order to optimise the monitoring of potentially exposed workers, it is desirable to determine specific values of absorption for the compounds handled. This study derives specific values of absorption rates for different chemical forms of plutonium from in vitro and animal (monkeys, dogs, mice, rats) experiments, and from human contamination cases. Different published experimental data have been reinterpreted here to derive values for the absorption parameters, fr, sr and ss, used in the human respiratory tract model currently adopted by the International Commission on Radiological Protection (ICRP). The consequences of the use of these values were investigated by calculating related committed effective doses per unit intake. Average and median estimates were calculated for fr, sr ,a ndss for each plutonium compound, that can be used as default values for specific chemical forms instead of the current reference types. Nevertheless, it was shown that the use of the current ICRP reference absorption types provides reasonable approximations. Moreover, this work provides estimates of the variability in pulmonary absorption and, therefore, facilitates analyses of the uncertainties associated with assessments, either from bioassay measurements or from prospective calculations, of intake and dose.

Incomplete data on the Canadian cohort may have affected the results of the study by the International Agency for Research on Cancer on the radiogenic cancer risk among nuclear industry workers in 15 countries.

Abstract: In 1995 the International Agency for Research on Cancer (IARC) completed a study that involved nuclear workers from facilities in the USA, UK and Canada. The only significant, though weak, dose-related associations found were for leukaemia and multiple myeloma. The results for the Canadian cohort, which comprised workers from the facilities of Atomic Energy of Canada Limited (AECL), were compatible with those for the other national cohorts. In 2005, IARC completed a further study, involving nuclear workers from 15 countries, including Canada. In these results, the dose-related risk for leukaemia was not significant but the prominent finding was a statistically significant excess relative risk per sievert (ERR Sv − 1) for 'all cancers excluding leukaemia'. Surprisingly, the risk ascribed to the Canadian cohort for all cancers excluding leukaemia, driven by the AECL sub-cohort, was significantly higher than the risk estimate for the 15-country cohort as a whole. We have attempted to identify why the results for the AECL cohort were so discrepant and had such a remarkable influence on the 15-country risk estimate. When considering the issues associated with data on the AECL cohorts and their handling, we noted a striking feature: a major change in outcome of studies that involved Canadian nuclear workers occurred concomitantly with the shift to when data from the National Dose Registry (NDR) of Canada were used directly rather than data from records at AECL. We concluded that an important contributor to the considerable upward shift in apparent risk in the 15-country and other Canadian studies that have been based on the NDR probably relates to pre-1971 data and, in particular, the absence from the NDR of the person-years of workers who had zero doses in the calendar years 1956 to 1970. Our recommendation was for there to be a comprehensive evaluation of the risks from radiation in nuclear industry workers in Canada, organisation by organisation, in which some of the anomalies that we have identified might be addressed.

Risk analysis using fuzzy set theory of the accidental exposure of medical staff during brachytherapy procedures

Abstract: Using fuzzy set theory, this paper presents results from risk analyses that explore potential exposure of medical operators working in a high dose rate brachytherapy irradiation plant. In these analyses, the HEART methodology, a first generation method for human reliability analysis, has been employed to evaluate the probability of human error. This technique has been modified on the basis of fuzzy set concepts to take into account, more directly, the uncertainties of the so-called error-promoting factors on which the method is based. Moreover, with regard to some identified accident scenarios, fuzzy potential dose was also evaluated to estimate the relevant risk. The results also provide some recommendations for procedures and safety equipment to reduce the occurrence of radiological exposure accidents.

A study of the relationship between peak skin dose and cumulative air kerma in interventional neuroradiology and cardiology.

Abstract: A study of peak skin doses (PSDs) during neuroradiology and cardiology interventional procedures has been carried out using Gafchromic XR-RV2 film. Use of mosaics made from squares held in cling film has allowed doses to the head to be mapped successfully. The displayed cumulative air kerma (CAK) has been calibrated in terms of cumulative entrance surface dose (CESD) and results indicate that this can provide a reliable indicator of the PSD in neuroradiology. Results linking PSD to CESD for interventional cardiology were variable, but CAK is still considered to provide the best option for use as an indicator of potential radiation-induced effects. A CESD exceeding 3?Gy is considered a suitable action level for triggering follow-up of patients in neuroradiology and cardiology for possible skin effects. Application of dose action levels defined in this way would affect 8% of neurological embolisation procedures and 5% of cardiology ablation and multiple stent procedures at the hospitals where the investigations were carried out. A close relationship was observed between CESD and dose?area product (DAP) for particular types of procedure, and DAPs of 200?300? Gy?cm2 could be used as trigger levels where CAK readings were not available. The DAP value would depend on the mean field size and would need to be determined for each application.

Radium isotopes in Estonian groundwater: Measurements, analytical correlations, population dose and a proposal for a monitoring strategy

Abstract: In some areas of Estonia, groundwater contains a significant number of natural radionuclides, especially radium isotopes, which may cause radiation protection concern depending on the geological structure of the aquifer. Indeed, the parametric value of 0.1 mSv y⁻¹ for the total indicative dose established by European Directive 98/83/EC, adopted as a limit value in Estonian national legislation, is often exceeded. A Twinning Project between Estonia and Italy was carried out within the framework of the Estonian Transition Facility Programme, sponsored by the European Union. Its aims were to assess the radiological situation of Estonian groundwater and related health consequences. The first step was a study of Estonian aqueducts and the population served by them, and a thorough analysis of the radiological database for drinking water, from which the relevant effective doses for the population were obtained. Particular attention was devoted to doses to children and infants. Correlations between the chemical parameters were investigated, in order to suggest the best possible analytical approach. Lastly, a monitoring strategy, i.e. sampling points and sampling frequencies, was proposed.

Measurement of soil gas radon and its correlation with indoor radon around some areas of Upper Siwaliks, India

Abstract: Radon is a radioactive gas which makes the primary contribution to the natural radiation to which people are exposed. For that reason, great importance is attributed to the determination of radon concentration levels in water, indoor air and soil gas and outdoors. In this paper, measurements of radon concentration in soil gas have been carried out around some areas of the Upper Siwaliks of the Kala Amb, Nahan and Morni Hills, India, using a portable AlphaGUARD PQ 2000 device into which the soil gas is drawn using active pumping. The soil gas radon concentration around the Upper Siwaliks was found to vary from 11.5 ± 0.9 to 78.47 ± 3.1 kBq m − 3. The annual average indoor radon concentration in the study area was measured in the range from 71.7 ± 21.0 to 421.7 ± 33.6 Bq m − 3 using LR-115 type II cellulose nitrate films in the bare mode. The values of soil gas radon concentration in the study area were compared with those from the adjoining low-radioactive areas of Punjab. Since the soil or bedrock beneath a building is one of the sources of radon gas in the indoor air, an effort has been made to find a possible correlation between soil gas radon with the indoor radon. A satisfactory positive correlation has been observed between soil gas radon and indoor radon in the study area.

Testicular cancer risk associated with occupational radiation exposure: a systematic literature review

Abstract: Testicular cancer is a rare disease, affecting mainly young men aged 15-49. There have been some recent reports that it might be associated with radiation exposure. We have systematically reviewed this topic. English-language articles published between 1990 and 2008 studying the relationship between occupational radiation exposure and testicular cancer were included. Risk of bias was assessed using a modified version of the EPHPP checklist. For ionising radiation we subdivided study populations into occupational groups. No pooled analysis was performed due to the heterogeneity of studies. Seven case-control and 30 cohort studies were included in the review. For radiation workers, one incidence study showed a significant increase and four showed no effect. Eight mortality studies did not indicate an effect while four showed a non-significant increase. Incidence among persons with military exposure was not increased in two studies and non-significantly increased in another two. Among aircrew studies, one showed no effect against five with slight increases. Medical exposure studies showed no increases. For EMF exposure, three studies showed no effect, two reported a significant and four a non-significant increase in incidence. Overall, there was very limited evidence for associations between occupational ionising radiation and testicular cancer, while there were some positive associations for EMF. Testicular cancer mortality is generally low and was not associated with radiation. New incidence studies are recommended to investigate the association between radiation exposure and testicular cancer where exposure is better specified and individually estimated.

Assessment of risk to wildlife from ionising radiation: can initial screening tiers be used with a high level of confidence?

Abstract: A number of models are being used to assess the potential environmental impact of releases of radioactivity. These often use a tiered assessment structure whose first tier is designed to be highly conservative and simple to use. An aim of using this initial tier is to identify sites of negligible concern and to remove them from further consideration with a high degree of confidence. In this paper we compare the screening assessment outputs of three freely available models. The outputs of these models varied considerably in terms of estimated risk quotient (RQ) and the radionuclide-organism combinations identified as being the most limiting. A number of factors are identified as contributing to this variability: values of transfer parameters (concentration ratios and K(d)) used; organisms considered; different input options and how these are utilised in the assessment; assumptions as regards secular equilibrium; geometries and exposure scenarios. This large variation in RQ values between models means that the level of confidence required by users is not achieved. We recommend that the factors contributing to the variation in screening assessments be subjected to further investigation so that they can be more fully understood and assessors (and those reviewing assessment outputs) can better justify and evaluate the results obtained.

Preliminary clinical findings on NEUMUNE as a potential treatment for acute radiation syndrome

Abstract: 5-androstenediol (5-AED) has been advanced as a possible countermeasure for treating the haematological component of acute radiation syndrome (ARS). It has been used in animal models to stimulate both innate and adaptive immunity and treat infection and radiation-induced immune suppression. We here report on the safety, tolerability and haematologic activity of 5-AED in four double-blinded, randomized, placebo-controlled studies on healthy adults including elderly subjects. A 5-AED injectable suspension formulation (NEUMUNE) or placebo was administered intramuscularly as either a single injection, or once daily for five consecutive days at doses of 50, 100, 200 or 400 mg. Subjects (n = 129) were randomized to receive NEUMUNE (n = 95) or the placebo (n = 34). NEUMUNE was generally well-tolerated; the most frequent adverse events were local injection site reactions (n = 104, 81%) that were transient, dose-volume dependent, mild to moderate in severity, and that resolved over the course of the study. Blood chemistries revealed a transient increase (up to 28%) in creatine phosphokinase and C-reactive protein levels consistent with intramuscular injection and injection site irritation. The blood concentration profile of 5-AED is consistent with a depot formulation that increases in disproportionate increments following each dose. NEUMUNE significantly increased circulating neutrophils (p < 0.001) and platelets (p < 0.001) in the peripheral blood of adult and elderly subjects. A dose–response relationship was identified. Findings suggest that parenteral administration of 5-AED in aqueous suspension may be a safe and effective means to stimulate innate immunity and alleviate neutropenia and thrombocytopenia associated with ARS.

Considerations for the integration of human and wildlife radiological assessments.

Abstract: A number of tools and approaches have been developed recently to allow assessments of the environmental impact of radiation on wildlife to be undertaken. The International Commission on Radiological Protection (ICRP) has stated an intention to provide a more inclusive protection framework for humans and the environment. Using scenarios, which are loosely based on real or predicted discharge data, we investigate how radiological assessments of humans and wildlife can be integrated with special consideration given to the recent outputs of the ICRP. We highlight how assumptions about the location of the exposed population of humans and wildlife, and the selection of appropriate benchmarks for determining potential risks can influence the outcome of the assessments. A number of issues associated with the transfer component and numeric benchmarks were identified, which need to be addressed in order to fully integrate the assessment approaches. A particular issue was the lack of comparable benchmark values for humans and wildlife. In part this may be addressed via the ICRP's recommended derived consideration reference levels for their 12 Reference Animals and Plants.

The in vivo relationship between cross-sectional area and CT dose index in abdominal multidetector CT with automatic exposure control.

Abstract: The relationship between patient cross-sectional area and both volume CT dose index (CTDI) and dose length product was explored for abdominal CT in vivo, using a 16 multidetector row CT (MDCT) scanner with automatic exposure control. During a year-long retrospective survey of patients with MDCT for symptoms of abdominal sepsis, cross-sectional areas were estimated using customised ellipses at the level of the middle of vertebra L3. The relationship between cross-sectional area and the exposure parameters was explored. Scans were performed using a LightSpeed 16 (GE Healthcare Medical Systems, Milwaukee, WI) operated with tube current modulation. From a survey of 94 patients it was found that the CTDI increased with the increase in patient cross-sectional area. The relationship was logarithmic rather than linear, with a least-squares fit to the data (R(2) = 0.80). For abdominal CT the cross-sectional area gave a measure of patient size based on the region of the body to be exposed. Exposure parameters increased with increasing cross-sectional area and the greater radiation exposure of larger patients was partly a consequence of their size. Given increasing obesity levels we believe that cross-sectional area and scan length should be added to future dose surveys, allowing patient size to be considered as a factor of relevance when examining population doses.

Patient skin dose measurements during coronary interventional procedures using Gafchromic film.

Abstract: Interventional cardiology (IC) procedures are known to give high radiation doses to patients and cardiologists as they involve long fluoroscopy times and several cine runs. Patients' dose measurements were carried out at the cardiology department in a local hospital in Penang, Malaysia, using Gafchromic XR-RV2 films. The dosimetric properties of the Gafchromic film were first characterised. The film was energy and dose rate independent but dose dependent for the clinically used values. The film had reproducibility within ? 3% when irradiated on three different days and hence the same XR-RV2 dose?response calibration curve can be used to obtain patient entrance skin dose on different days. The increase in the response of the film post-irradiation was less than 4% over a period of 35 days. For patient dose measurements, the films were placed on the table underneath the patient for an under-couch tube position. This study included a total of 44 patients. Values of 35?2442?mGy for peak skin dose (PSD) and 10.9?344.4?Gy?cm2 for dose?area product (DAP) were obtained. DAP was found to be a poor indicator of PSD for PTCA procedures but there was a better correlation (R2 = 0.7344) for CA + PTCA procedures. The highest PSD value in this study exceeded the threshold dose value of 2?Gy for early transient skin injury recommended by the Food and Drug Administration.

An estimation of the annual effective dose to the Canadian population from medical CT examinations.

Abstract: This study was carried out to assess the annual per capita effective dose from medical diagnostic procedures using computed tomography (CT) in Canada Relevant data concerning the nature and the frequency of various diagnostic CT examinations were obtained from the reports on Medical Imaging in Canada and Diagnostic Services in Ontario Doses associated with examinations of different types were based primarily on typical effective doses used in the National Council on Radiation Protection and Measurements Report 160 with considerations of limited dose information surveyed in Canada The results show that the per capita annual effective dose from diagnostic CT exams was 074 mSv in 2006, up from 019 mSv in 1991 This significant increase in population radiation dose from CT scans is due mainly to a more than doubling in the examination rate and to a higher radiation dose per procedure from the newer generation of multi-detector CTs

The ambient dose equivalent at flight altitudes: a fit to a large set of data using a Bayesian approach

Abstract: The problem of finding a simple, generally applicable description of worldwide measured ambient dose equivalent rates at aviation altitudes between 8 and 12 km is difficult to solve due to the large variety of functional forms and parametrisations that are possible. We present an approach that uses Bayesian statistics and Monte Carlo methods to fit mathematical models to a large set of data and to compare the different models. About 2500 data points measured in the periods 1997-1999 and 2003-2006 were used. Since the data cover wide ranges of barometric altitude, vertical cut-off rigidity and phases in the solar cycle 23, we developed functions which depend on these three variables. Whereas the dependence on the vertical cut-off rigidity is described by an exponential, the dependences on barometric altitude and solar activity may be approximated by linear functions in the ranges under consideration. Therefore, a simple Taylor expansion was used to define different models and to investigate the relevance of the different expansion coefficients. With the method presented here, it is possible to obtain probability distributions for each expansion coefficient and thus to extract reliable uncertainties even for the dose rate evaluated. The resulting function agrees well with new measurements made at fixed geographic positions and during long haul flights covering a wide range of latitudes.

A gamma radiation dose calculation method for use with Lagrangian puff atmospheric dispersion models used in real-time emergency response systems

Abstract: The paper presents the development of a model for the calculation of the gamma radiation dose rate from a cloud or plume of radionuclides. The model has been implemented in the Lagrangian puff dispersion model DIPCOT which is used in the framework of the RODOS system for nuclear emergency management. The basic characteristics of the model are its speed of execution and its ability to calculate the gamma dose rates from clouds or plumes of random shape formed under non-homogeneous meteorological conditions or over complicated topography. The three-dimensional integral that would normally have to be numerically calculated in such circumstances has been transformed to a one-dimensional one through a coordinate transformation for each model puff and by using a separation of variables technique. The resulting one-dimensional integrals have been pre-calculated and their values stored for a range of parameters that cover the possible ranges of photon energies, puff dimensions and distances encountered in cases of atmospheric dispersion. During runtime the model calculates the exact values by interpolation from stored tables of values. This is a very fast and accurate method, as the evaluation study has proved. The model performance has been evaluated through simulations of a real-scale experiment involving routine emissions of (41)Ar from a reactor and comparisons of model predictions with measured fluence rates. The comparisons have revealed a satisfactory level of agreement and the model performance statistical indices are well above the acceptance criteria that are suggested in the literature.

Mortality and cancer registration experience of the Sellafield workers known to have been involved in the 1957 Windscale accident: 50 year follow-up

Abstract: This paper studies the mortality and cancer morbidity of the 470 male workers involved in tackling the 1957 Sellafield Windscale fire or its subsequent clean-up. Workers were followed up for 50 years to 2007, extending the follow-up of a previously published cohort study on the Windscale fire by 10 years. The size of the study population is small, but the cohort is of interest because of the involvement of the workers in the accident. Significant excesses of deaths from diseases of the circulatory system (standardised mortality ratio (SMR) = 120, 95% CI = 103–138; 194 deaths) driven by ischaemic heart disease (IHD) (SMR = 133, 95% CI = 112–157, 141 deaths) were found when compared with the population of England and Wales but not when compared with the population of Northwest England (SMR = 105, 95% CI = 90–120 and SMR = 115, 95% CI = 97–136 respectively). When compared with those workers in post at the time of the fire but not directly involved in the fire the mortality rate from IHD among those involved in tackling the fire was raised but not statistically significantly (rate ratio (RR) = 1.11, 95% CI = 0.92–1.33). A RR of 1.11 is consistent with an excess relative risk of 0.65 Sv − 1 as reported in an earlier study of non-cancer mortality in the British Nuclear Fuels plc cohort of which these workers are a small but significant part. There was a statistically significant difference in lung cancer mortality (RR = 2.18, 95% CI = 1.05–4.52) rates between workers who had received higher recorded external doses during the fire and those who had received lower external doses. Comparison of the mortality rates of workers directly involved in the accident with workers in post, but not so involved, showed no significant differences overall. On the basis of the use of a propensity score the average effect of involvement in the Windscale fire on all causes of death was − 2.13% (se = 3.64%, p = 0.56) though this difference is not statistically significant. The average effect of involvement in the Windscale fire was − 5.53% (se = 3.81, p = 0.15) for all cancers mortality and 6.60% (se = 4.03%, p = 0.10) for IHD mortality though neither figure was statistically significant. This analysis of the mortality and cancer morbidity experience of those Sellafield workers involved in the 1957 Windscale fire does not reveal any measurable effect of the fire upon their health. Although this study has low statistical power for detecting small adverse effects, due to the relatively small number of workers, it does provide reassurance that no significant health effects are associated with the 1957 Windscale fire even after 50 years of follow-up.

Enhancement of tritium concentrations on uptake by marine biota: experience from UK coastal waters

Abstract: Concentrations of tritium in sea water and marine biota as reported over the last approximately 10 years from monitoring programmes carried out by this laboratory under contract to the UK Food Standards Agency are reviewed from three areas: near Cardiff; Sellafield; and Hartlepool. Near Cardiff, enhancement of concentration factors (CFs) above an a priori value of approximately 1 have already been studied, and attributed to compounds containing organically bound tritium in local radioactive waste discharges. Further data for Cardiff up to 2006 are reported in this note. Up to 2001, CFs increased to values of more than approximately 7000 in flounders and approximately 4000 in mussels, but have subsequently reduced; this variability could be due to changes in the organic constitution of compounds discharged. Near Sellafield and Hartlepool, enhancements to the tritium concentration factor are observed but they are relatively small compared with those near Cardiff. Near Sellafield, plaice and mussels appear to have a CF for tritium of approximately 10; in some cases concentrations of tritium in winkles are below detection limits and positively measured values indicate a CF of approximately 3. The variation could be due to mechanisms of uptake by the different organisms. Near Hartlepool there were only a few cases where tritium was positively measured. These data give a value of approximately 5 for the CF in plaice (on the basis of two samples); approximately 15 in winkles (eight samples); and > 45 in mussels (two samples). Any differences between the behaviours at Sellafield and Hartlepool would need to be confirmed by improved measurements. Possible causes are the organic composition of the effluent and differences in environmental behaviour and uptake by organisms near the two sites. These potential causes need further investigation. It is emphasised that results from tritium analyses are heavily method dependent; thus comparison with results from other programmes needs to take this into account. Further, the results for enhancement of CF will also depend on the definition of CF itself.

Retention of tritium in reference persons: a metabolic model. Derivation of parameters and application of the model to the general public and to workers.

Abstract: Tritium ( 3 H) is a radioactive isotope of hydrogen that is ubiquitous in environmental and biological systems. Following debate on the human health risk from exposure to tritium, there have been claims that the current biokinetic model recommended by the International Commission on Radiological Protection (ICRP) may underestimate tritium doses. A new generic model for tritium in mammals, based on energy metabolism and body composition, together with all its input data, has been described in a recent paper and successfully tested for farm and laboratory mammals. That model considers only dietary intake of tritium and was extended to humans. This paper presents the latest development of the human model with explicit consideration of brain energy metabolism. Model testing with human experimental data on organically bound tritium (OBT) in urine after tritiated water (HTO) or OBT intakes is presented. Predicted absorbed doses show a moderate increase for OBT intakes compared with doses recommended by the ICRP. Infants have higher tritium retention—a factor of 2 longer than the ICRP estimate. The highest tritium concentration is in adipose tissue, which has a very low radiobiological sensitivity. The ranges of uncertainty in retention and doses are investigated. The advantage of the new model is its ability to be applied to the interpretation of bioassay data.

Measurement of thoron gas in the environment using a Lucas scintillation cell.

Abstract: A simple and fast method for measuring the concentration of 220Rn in the environment was developed based on the AB-5 portable radon measuring device. First, background counts were measured with a Lucas scintillation cell (LSC), then air sampling measurement was started immediately and lasted for 1 min; the 220Rn concentration could be calculated from the counts before and after sampling as well as the theoretical detection efficiency. Results of theoretical calculations showed that in a pure 220Rn environment the lower detection limit of the LSC would be some 65 Bq m−3 (with a confidence level of 70%). The experimental results showed that compared with a RAD7 monitor in pure 220Rn or mixed 222Rn/220Rn environments the deviations were less than ± 10%. This method can also be used for quantitative measurement of 220Rn concentration.