Carbon-14 has been identified as one of the more significant radionuclides in solid radioactive wastes in a repository, due to the potential radiological impact arising if 14C were to be released and enter the biosphere. However, the assessment of radiation doses is complicated by the major role of carbon in biological processes, and this has tended to lead to the adoption of a cautious assessment approach.

An international comparison of five models used to predict uptake of 14C to agricultural crops has been undertaken, within the BIOPROTA framework. Processes investigated include conversion of 14C-labelled CH4 into CO2 in soils, carbon accumulation in and release from soil carbon pools, gaseous emanation to, and dispersion from, the plant canopy atmosphere and, incorporation into plants by photosynthesis.

For a unit rate of entry of 14C to soil, modelled activity concentrations in cereal crops differ by three to five orders of magnitude. This reflects, in part, differing assumptions for mixing and dispersion of air above the soil surface and within the crop canopy layer. For a unit activity concentration of 14C in air, the modelled uptake to cereal crops converges significantly. Following an assumed irrigation of crops with groundwater containing unit activity of 14C, the predicted uptake to crops varied by two to four orders of magnitude, again largely dominated by assumptions regarding the canopy atmosphere. In all cases, there is some convergence in model predictions as field size increases.

A continuing programme of field research is being undertaken in parallel with the assessment work.

Radioactive Waste Management Limited (RWM) is tasked with implementing geological disposal of the United Kingdom's (UK) higher activity radioactive wastes. This paper describes how RWM's biosphere modelling capability has been extended from a solely terrestrial model to allow potential contaminant releases to estuarine, coastal and marine systems around the UK to be represented. The new models aim to strike a balance between being as simple as can be justified, erring on the side of conservative estimates of potential doses, while also representing the features and processes required to reflect and distinguish UK coastal systems. Sediment dynamics (including meandering of estuaries and sediment accumulation) are explicitly represented in a simplified form that captures the accumulation and remobilization of radionuclides. Long-term transitions between biosphere systems (such as from a salt marsh to a terrestrial system) are outside the scope of the study. The models and supporting data draw on information about the UK that is representative of present-day conditions and represent potential exposures arising from both occupational and recreational habits.?

Generic calculations demonstrate that potential doses to humans arising from releases to estuarine, coastal and marine systems are typically more than two orders of magnitude lower than those for equivalent releases to terrestrial systems via well water and groundwater discharge to soil. The extended capability (i) ensures that RWM is able to undertake assessments for potential coastal site contexts, if and when required, and (ii) provides RWM with quantitative evidence to support the principal focus on terrestrial releases ( particularly for more generic assessments).

Carbon-14 (C-14) is a key radionuclide in the assessment of a geological disposal facility (GDF) for radioactive waste. In the UK a significant proportion of the national C-14 inventory is associated with reactor-core graphite generated by the decommissioning of the UK's Magnox and AGR reactors.

There are a number of uncertainties associated with the fate and transport of C-14 in a post-closure disposal environment that need to be considered when calculating the radiological impacts of C-14-containing wastes. Some of these uncertainties are associated with the distribution of C-14-containing gaseous species such as 14CH4 and 14CO2 between the groundwater and gaseous release pathways. As part of the C14-BIG programme, a modelling framework has been developed to investigate these uncertainties. This framework consists of a biogeochemical near-field evolution model, incorporating a graphite carbon-14 release model, which interfaces with a geosphere/biosphere model. The model highlights the potential impact of the microbial reduction of 14CO2 to 14CH4, through the oxidation of H2, on C-14 transport. The modelling results could be used to inform the possible segregation of reactor graphite from other gasgenerating wastes.

This article proposes an assessment of the ingestion doses potentially received by peopleliving in the Japanese areas most severely affected by the radioactive deposits due to theFukushima nuclear accident. The assessment distinguishes two consecutive periods: thefirst 2 months (March 15th to May 15th 2011) and the rest of the year 2011, according tothe two main foodstuff contamination periods identified (Renaud et al.,2013). On the basis of the worst-case hypothesis that can reasonably be made, theestimated doses are much lower than they might have been in other circumstances, onaccount of generally moderate levels of contamination for most foods, early evacuation ofthe most severely affected areas and the consumption bans ordered by the Japaneseauthorities. Thus, a single ingestion of 100 g of leafy vegetables in the early days by aone-year-old child living in non-evacuated localities near Iitate and Kawamata could haveled to an equivalent dose to the thyroid of about 25 mSv; and to a thyroid dose of about140 mSv for the rather unrealistic scenario of a daily consumption. Because of the rapiddecrease in the contamination of vegetables and a much weaker contamination of othercrops, and thanks to measures taken by the authorities (prohibition of consumption, use ofcertain fodder, etc.), the ingestion doses potentially received during the remainder ofthe year 2011 are estimated to be below 1 mSv. In the event that sales limits would havebeen ignored, only repeated consumption of mushrooms would have led to doses above thatlevel. Even with the worst-case hypotheses, the doses potentially caused by ingestion aremuch lower than those resulting from outdoor exposure to radioactive deposits:approximately several millisieverts in a year for the population living in thenon-evacuated localities near Iitate and Kawamata.

L’uranium est naturellement présent dans l’alimentation,à un niveau très variable, conduisant à des activités détectablesdans les excréta, indépendamment d’une éventuelle exposition professionnelle.L’interprétation des résultats de surveillance radiotoxicologiqueindividuelle des travailleurs exposés professionnellement au dioxyded’uranium doit donc prendre en compte l’apport alimentaire pourétablir une estimation dosimétrique. Pour ce faire, les auteursont testé différentes approches dans le suivi d’un travailleur et proposentune méthode originale d’interprétation des données radiotoxicologiquespar comparaison des résultats obtenus dans un groupe de travailleursexposés à ceux collectés dans une population de référence. Cetteméthode a permis d’estimer une dose efficace engagée annuelle pourun groupe de travailleurs exposés au dioxyde d’uranium.

During an accidental release of tritium, mechanisms of hydrogen transferfrom air to man are very numerous, dependent on multiple climate,physiological and biological parameters, and the kinetic is highlyvariable from one environmental compartment to another. To evaluatethe impact of an acute tritium release requires either an overallassessment of the state of the environment during the release and thefollowing hours from a number of restricted data, or the establishmentof a significant data bank, a complex model and a system of dataacquisition in real time whose potential for daily purposes is veryhypothetical. To facilitate the first approach, this paper discussesthe key elements of the mechanisms to guide the choice of parametersfor a rapid assessment of the situation, and to clarify the typesof measurements to carry out and their interpretation.

In 2011 the IRSN conducted several assessments of atmosphericradioactive releases due to the Fukushima Daiichi NPP accident (March11, 2011) and of their impact on Japan’s terrestrial environment.They were based on the IRSN’s emergency management tools and onthe abundant information and technical data gradually publishedin Japan. According to these assessments, the main release phaselasted from March 12 to 25, 2011 and impacted Japanese land in twoevents, the first on 15 and 16 March, in which the main radioactivedeposits were formed, and the second from March 20 to 23, whichwas less significant. The highest amounts of radioactive deposits werefound in an area extending upwards of several tens of kilometersnorthwest of the plant. Lower amounts were discontinuously scatteredin an area extending up to over 250 km away. Initially composedmainly of short-lived radionuclides, the deposits’ activity sharplydecreased in the subsequent weeks. Since the summer of 2011, cesium-134and cesium-137 have become the residual deposits’ main components.According to IRSN estimates, in the absence of protection, the dosesdue to exposure to the radioactive plume during the atmosphericrelease phase may have been potentially higher for people who remainedin coastal areas up to several tens of kilometers north and southof the damaged plant. Thereafter, people living up to 50 km northwestof the plant, outside the 20-km emergency evacuation zone, were potentiallymost vulnerable to residual radioactive deposits over time.

The activity concentrations of 226Ra, 232Th and 40K infifty granite samples collected from five different quarry industries in Ondo State,Nigeria, were determined using gamma-ray spectrometry. The mean activity concentrationsfor each industry ranged from 16.7(6.4) to 85.4(23.0), 62.4(10.1) to 113.6(7.6), and1315(136) to 1551(84) Bq.kg-1 for 226Ra, 232Th and40K, respectively. The values in parenthesis are the standard deviations.When compared with results from some parts of the world, the 226Ra and232Th contents were lower, whereas the 40K content was similar.Using different approaches to estimate the potential radiological hazard of the samples,the results obtained were below the recommended maximum limits. This shows that theradiological hazards associated with the use of the granites examined in this study asbuilding material are within the acceptable limit.

Bitumen samples and soil samples around a bituminous deposit in Ondo State, Nigeria, wereanalysed for 40K, 226Ra and 232Th employing gamma-rayspectrometry. The activity concentrations of 40K, 226Ra and232Th in soil varied from (45.2 ± 5.3) to (484.2 ± 25.9), BDL (belowdetectable limit) to (27.7 ± 2.1) and (22.8 ± 2.7) to (62.4 ± 6.8) Bq.kg-1,respectively. The corresponding mean values were (240.2 ± 133.5), (13.3 ± 8.0) and (40.0 ±10.2) Bq.kg-1, respectively. The mean activity concentrations of theradionuclides in the bitumen were (58.4 ± 36.4), (16.1 ± 13.3) and (32.5 ± 13.1)Bq.kg-1, respectively, for 40K, 226Ra and232Th. The mean absorbed dose and effective dose for the soil samples were(41.5 ± 8.9) nGy.h-1 and (50.7 ± 10.9) μSv.y-1, respectively, whilethose of the bitumen samples were (29.5 ± 15.6) nGy.h-1 and (36.1 ± 19.1)μSv.y-1, respectively. For radiological hazard assessment, the radiumequivalent activity and the external hazard index were determined. The values of theradium equivalent activity and external hazard index obtained for the soil and bitumensamples were lower than the recommended limit.

Bien que le tritium soit un radionucléide existant à l’état naturel, sa présence dans l’environnement est souvent associée à la production d’électricité d’origine nucléaire. À l’occasion de la construction du nouveau réacteur EPR à Flamanville et de renouvellement d’autorisations de rejets pour des sites existants, cette publication a pour objectif de résumer la connaissance scientifique, les mesures réalisées autour des sites et les études d’impact dans l'environnement et chez l'homme pour ces deux radionucléides.

En 2000, des flux de rayonnement anormalement élevés ont été détectés sur certaines plages du littoral camarguais. Les sables du littoral camarguais ont alors fait l’objet d’une caractérisation radiologique montrant des activités moyennes de quelques dizaines de Bq kg-1 en uranium-238 et thorium-232 d’une part, et l’existence de points chauds à plus de 1000 Bq kg-1 d’autre part ; voire plus sur deux plages : l’une située à l’Est du phare de Beauduc, l’autre située à l’Est du phare de l’Espiguette. Cette radioactivité, d’origine naturelle, est responsable de l’exposition des personnes fréquentant ces deux dernières plages relativement isolées, mais néanmoins accessibles à tout public. L’Institut de radioprotection et de sûreté nucléaire a réalisé une évaluation des doses susceptibles d’être reçues par des personnes fréquentant ces deux dernières plages, en se basant sur des mesures et des prélèvements effectués in situ, en établissant expérimentalement la solubilité des sables dans les fluides gastrique et intestinal, et en formulant des hypothèses sur la fréquentation des lieux (scénarios). La dose annuelle maximale ainsi évaluée est de l’ordre de 0,8 mSv pour des adultes et 0,5 mSv pour les enfants ; valeurs vraisemblablement très prudentes dans lesquelles la dose par exposition externe prédomine largement.

Lors d'une suspicion d'exposition accidentelle aux rayonnements ionisants, la détermination de la dose reçue au moyen de paramètres biologiques est une part importante de la stratégie thérapeutique, en complément des signes cliniques et de la dosimétrie physique. Le dénombrement des aberrations chromosomiques instables dans les lymphocytes du sang périphérique est aujourd'hui la méthode de référence. La préparation des échantillons biologiques dépend cependant du but à atteindre, de l'expertise précise de suspicions d'irradiations ou du tri rapide en cas d'accident de grande envergure. Une adaptation peut être nécessaire s'il s'agit d'irradiation hétérogène ou ancienne. Malgré cette robustesse et ces adaptations, la cytogénétique conventionnelle reste une technique lourde, longue, réservée à du personnel spécialisé. Le dénombrement des micronoyaux dans les lymphocytes binucléés peut constituer une alternative, apparemment plus facile et plus simple que le test des dicentriques. À partir de l'expérience acquise par l'IPSN ces dernières années sur l'expertise des suspicions d'irradiation, ce papier a pour but de dresser un bilan technique quoique succinct de ces différentes approches telles que nous les avons adaptées aux suspicions d'irradiation récente.

Nos connaissances sur les sources naturelles de rayonnements ont beaucoup progressé au cours de ces quinze dernières années. Il est aujourd'hui possible d'établir un bilan assez précis desdoses qui en résultent en moyenne pour les populations. Il s'avère aujourd'hui que les incertitudes principales entachant les estimations de dose sont dues aux incertitudes des modèlesdosimétriques permettant la conversion d'exposition en dose. Le radon est sans doute le radionucléide pour lequel les incertitudes sont les plus grandes, mais il en existe aussi pour lesrayonnements cosmiques et les radionucléides ingérés.

La Commission Internationale de Protection Radiologique (CIPR), dans ses nouvelles recommandations, propose l'utilisation de paramètres déterminés expérimentalement pour effectuer uncalcul de dose efficace par unité d'incorporation (DPUI) spécifique pour chaque composé. Le but de cette étude est de définir une méthodologie (techniques d'analyse, test in vitro de dissolutionet test in vivo sur rats) permettant d'accéder à ces données et de présenter les méthodes de calcul utilisées, comme le logiciel GIGAFIT pour l'interprétation des données de transfert sanguin, etle logiciel LUDEP pour le calcul de dose. Ce travail a permis de déterminer pour un composé UO2 (uranium appauvri), utilisé dans la fabrication du combustible MOX, les principaux paramètresphysico-chimiques et biologiques qui entrent dans le calcul de dose : le Diamètre Aérodynamique Médian en Activité ou DAMA de 6,5 microns; la Surface Spécifique SS= 2,68 m2.g-1; et lesfraction et taux de transfert sanguin respectivement fr, entre 2,5% et 44,4%, Sr, entre 0,09 et 1,7 j-1, et Ss, entre 6,4x10-4 et 1,5x10-3 j-1. Ces résultats intégrés dans LUDEP conduisent à une DPUI spécifique par inhalation pour ce composé UO2 égale à 2,84x10-6 Sv.Bq-1.