Planning for the disposal of spent nuclear fuel is at an advanced stage in several nations around the world. Licensing of the disposal facility requires correspondingly detailed assessment of the future performance of the facility. With increased site-specific detail available to the assessment, local characteristics play an increasingly important role in determining the potential radiological risk posed by releases to the biosphere. In this paper we go beyond existing reference biosphere models and investigate the potential for specific accumulation mechanisms. The implications for the modelling carried out in long timescale performance assessment are discussed.

The two-chamber (water and bottom sediments) model was used to analyze factors influencing magnitude of 137Cs accumulation factor in bottom sediments of rivers and lakes with concentration of the radionuclide close to background levels. The most probable values of the factor are given. It is proposed to use the factor for assessments of 137Cs activity in water on the base of its observed activity in bottom sediments.

Observations carried out in the frame of the ISTC project 3547 [1] were used to parametrize and validate the model of radionuclides transport from Siberian Chemical Combine (SCC) by the Tom and Ob rivers and also to assess discharges of radioactive substances from SCC to the Tom River and to estimate possible contamination of the rivers in case of accidents.

The aim of this study is to assess the interception and transfer to edible part of wet deposited 134Cs and 85Sr to spring oilseed rape and spring wheat and the dependency of the intercepted fraction on the development stage e.g. the total plant biomass. The radionuclides, 134Cs and 85Sr, were deposited at six different development stages using a rainfall simulator. The results showed that there was a positive correlation between the interception fraction for 134Cs and 85Sr and the biomass both for spring oilseed rape and spring wheat. The interception fraction and transfer factors were highest at growing stage of senescence (ripening) for both crops.

Long-term observations on the effects of a fertilization treatment on 137Cs concentrations in forest vegetation are scarce. Needles of Scots pine were used as biological indicators of radionuclide uptake of trees. The fertilization experiments are located in western Finland in an area where radioactive contamination from the Chernobyl accident in 1986 was relatively high (22–75 kBq m−2) compared to other parts of Finland. Fertilization treatments included different combinations of major nutrients, i.e. nitrogen, phosphorus, potassium and calcium. Needle 137Cs concentrations of Scots pine were analyzed during 1991–2006. The effect of fertilization on 137Cs concentration was tested 5 to 20 years after radioactive contamination from the Chernobyl accident in 1986. Fertilization clearly decreased 137Cs concentration in Scots pine needles 1–21 growing seasons after application. Single K fertilization decreased significantly 137Cs concentration 21 growing seasons after radioactive deposition on a drained mire. Mineral nutrients (application of commercial fertilizer or wood ash) can well be recommended for remediation of forests contaminated by accidental radionuclide deposition. The site conditions need to be taken into account in planning of remediation.

For appropriate safety assessment of TRU waste disposal, the dominant chemical species of 14C-gas was studied. [1,2-14C] sodium acetate was added to flooded paddy soil samples, and the content of 14C in the soil, solution, and the emitted CO2 gas during incubation period was determined. Recovery ratios of the total 14C activity to the initial 14C activity were 97.9% at day 1, 86.4% at day 3, and 83.5% at day 7 of incubation. The result of the day 1 means that the emitted 14C-gas was almost 14CO2. At day 7 of incubation, about 16.5% of 14C was failed to recover. Even if the unknown 14C was gases other than 14CO2, the dominant chemical species of the emitted 14C-gas will be 14CO2, because the recovery ratio of the 14CO2 was 48.9% (¿16.5%). Sodium 2-bromoethane-sulfonate was used to ensure the emission of CH4, but there was no effect of the regent to the recovery ratio of 14CO2. Methane emission may be little under our experimental conditions. These results suggest that the dominant chemical species of the emitted 14C-gas from the flooded paddy soil samples was 14CO2.

In this study it is shown how the behaviour of radionuclides in agricultural soils can be quantitatively estimated. The sorption of those nuclides onto soil particle surfaces is a key process which every predictive model has to take into account. This has been accomplished by implementing a component additivity (CA-) model into the well known geochemical code PHREEQC that includes the most important sorbents clay, amorphous iron oxide and organic matter. For uranium and cesium it is shown that model calculations are in excellent agreement with experimental data.

The toxicity and oxidative stress responses of 19-day old Arabidopsis seedlings induced by U (66 μM) and Cd (20 μM) alone or in a binary mixture set-up (equitoxic mixture) are studied in function of time. After 48h a significant decrease in root and shoot growth and a simultaneous increase in anthocyanin production was evident in all treated plants.

Production of O−2 or H2O2 was visualized by staining freshly harvested leaves with nitrobluetetrazolium or diaminobezidine, respectively. With this method production of O−2 was only significantly measurable after 168 h treatment which coincides with a significant decrease in biomass production and probably also plant cell death. For Cd treated plants a significant increase in H2O2 production was measurable from 24h onwards. In contrast, a similar H2O2 production could not be measured in U or U + Cd treated plants. Both water and lipophilic soluble antioxidants significantly increased in U treated plants after 48 h. These high antioxidant levels might detoxify potential H2O2 produced in the U treated plants. In contrast for Cd treated plants only after 168h a significant increase in water soluble antioxidants was measured whereas no difference in the lipophilic fraction was visible.

Adaptive responses were observed using the micronucleus frequency in bullfrog tadpoles. In tanks in which control tadpoles were placed in contact with tadpoles that were previously housed in tritiated water (3.0 × 104 Bq/L), the cells from all animals responded as though they were “adapted”. This suggests that direct exposure to 3.0 × 104 Bq/L tritium contributes to an increased resistance to a high dose of radiation in liver cells. It also suggests that being in contact with tadpoles that were previously exposed to 3.0 × 104 Bq/L tritium (bystander effect) contributes to an increased resistance to a high dose of radiation in liver cells.

In vitro exposures were also conducted using primary cultures of liver cells obtained from an unexposed-non-bystander tadpole. In these control cells, it was observed that exposure to 100 mGy of 60Co gamma radiation (delivered at a dose rate of 5 mGy/min) did not affect the micronucleus frequency whereas exposure to 4 Gy (delivered at a dose rate of about 10.2 Gy/min) increased the micronucleus frequency. Prior exposure to a low dose of 60Co gamma radiation (100 mGy delivered at a dose rate of 5 mGy/min) induced an adaptive response, protecting the cells from harm caused by exposure to subsequent high doses of 60Co gamma radiation (4 Gy delivered at a dose rate of about 10.2 Gy/min). Using the adaptive response (determined using micronucleus assay) as a biomarker, the data obtained suggest that bystander effects do play a role in wild populations since bullfrog tadpoles that were not exposed to tritium responded like the tadpoles that were directly exposed to tritium after being placed in contact with them.

The aim of the present work was to study the impact of chemical climate (i.e. the chemical composition of precipitation) on radioactive caesium in soil and plants. This was done through field studies and a laboratory experiment. Three types of precipitation regimes were considered in both cases, representing a natural range found in Norway: Acidic precipitation (southernmost part of the country); precipitation rich in marine cations (coastal areas); and low concentrations of sea salts (inland areas). Results indicate that acid rain increases the mobility and the plant availability of radioactive caesium.

The FASTer-lite model is multi-compartmental model that can be used to simulate transfer through a simple terrestrial food-chain. The model uses allometric relationships to describe dietary intake rates and radionuclide biological half-lives; the latter were mostly derived from published literature. This type of conventional modelling, for simulating the transfer of radionuclides to representative animals such as birds, results in the observation that activity concentrations associated with ecological compartments approach an equilibrium after a certain time interval. Whilst this approach has validity, however, it is not biologically plausible as it ignores reproduction. In this study we calculate how activity concentrations may vary if transfer to eggs and subsequent growth dilution occurring within juvenile birds is accounted for.

CHERPAC is a code developed by AECL to predict the time-dependent concentrations of 25 radionuclides in environmental compartments and the resulting radiation dose (ingestion, inhalation, immersion and groundshine) to humans, following an accidental release to the atmosphere from a nuclear facility. CHERPAC was used to investigate environmental sensitivities in agricultural and forest ecosystems. Given the assumptions in the CHERPAC code, it was concluded that doses to humans from agricultural food products are higher than those from groundshine and forest food products. Doses from agricultural products are highest from radionuclide deposition in summer because all plants are at their peak growth and are ingested fresh after the deposition event. The dose is higher if the deposition occurs in dry conditions rather than during heavy rain, because radionclides adhere better to dry plant leaves. For Cs-137, ingestion dose is higher for adults than other age groups, but for Sr-90 and I-131, ingestion dose is highest for infants. This is due to relative food product concentrations, intake rates and DCFs (dose conversion factors). In the forest ecosystem, adult doses are higher than those for children and infants because of the higher rates of intake by adults of forest food products.

Model intercomparison exercises have identified radionuclide transfer predictions as the greatest source of uncertainty in biota dose assessments. One wildlife group for which few transfer data exist is reptiles, Given that reptiles are an important, and often protected, component of many ecosystems and that assessments of radiation impact on ecosystems are becoming increasingly necessary due to the current nuclear renaissance, there is a need to further develop our current database on transfer to reptiles or find alternative approaches to estimate reptile transfer parameters. Three approaches that have the potential to increase the availability of parameters to predict radionuclide transfer to reptiles are the use of non-lethal sampling techniques, phylogenetic relationships and allometric relationships. Non-lethal sampling is an attractive long term option for deriving transfer parameters, but the derivation of phylogenetic and allometric relationships could provide ways of predicting transfer in the interim.

Since January 1959, Health Canada has monitored environmental levels of radioactive fallout, to ensure the health and well being of Canadians. This work has evolved to include explosion verification for the Comprehensive nuclear-Test-Ban Treaty by monitoring the concentration of radioxenon in the atmosphere. Detection of Xe at Yellowknife by the monitoring system of Health Canada combined with the atmospheric transport and dispersion models (ATDM) of Environment Canada and seismic timing data have shown that the source of this Xe was most likely from the North Korean nuclear test of October 9th, 2006. Historical and real time monitoring data on the distribution of Xe releases from Chalk River Labs, the major source of anthropogenic background to Yellowknife were studied. Careful review of other large Xe-133 measurements at Yellowknife with ATDM was used to understand the October 2006 measurements of Xe. This allowed us to conclude that the Xe-133 detected at Yellowknife could be attributed to a release from the October nuclear test in North Korea. Health Canada and Environment Canada have demonstrated that Xe detection combined with ATDM is a viable technology for treaty verification.

Although aim of the environmental protection is conservation of ecosystem, there are only a few studies focusing on the effect of radiation on ecosystem. To understand the ecological effect of irradiation, microbial ecosystem, “microcosm”, which contains minimum components of ecosystem such as producer, consumer and decomposer, is useful because the natural ecosystem is too complex. The microcosm consists of three species, i.e. Euglena (producer), Tetrahymena (consumer), and E. coli (decomposer). The mathematical model and computer simulation model were also developed to understand the mechanism of ecological interaction using the results of acute exposure experiments of the microcosm, and we predicted Tetrahymena, which is the most radio-resistant among the constituent species, would be most sensitive in the chronically irradiated microcosm as a result of an indirect effect due to population decrease in E. coli. Recently we started chronic exposure experiments. The microcosms were irradiated with γ-rays at dose rate of 1.2Gy/day, 5Gy/day, 10Gy/day and 23Gy/day. From preliminary results, we found that the prediction from the models was different from the experimental results. Therefore, in this study, we improved our mathematical model and discuss the difference between the model and experiments.

This paper describes transport modeling performed by the Swedish Nuclear Fuel and Waste Management Company (SKB) within the recently completed SR-Site safety assessment. SR-Site is a part of the license application for building a deep geological repository for spent nuclear fuel in Sweden; this application was submitted to the authorities in March 2011. In the safety assessment, a suite of transport models was used to quantify radionuclide transport through the engineered and geological barriers and in the biosphere. The present paper is focused on the transport in the upper part of the bedrock and in the regolith (the Quaternary deposits overlying the rock). The results presented provide input to the assessment of uncertainties in calculated discharge locations for radionuclide-bearing groundwater from the considered repository volume and to analyses of solute spreading in near-surface and surface systems.

Chlorine 36 is considered as part of the group III of radioactive wastes composed of the moderate radiotoxic radionuclides such as Carbon 14. As such and along with its long half-life (3.01 × 105 years) and its chemical form (chloride anion), it is a very important radionuclide to be taken into account in the environment thereby making its modelling an important goal.

We present in this paper the phenomenological approach developed at IRSN for modelling the behaviour of chloride 36 in the continental ecosystems. This model is a part of the SYMBIOSE programme (SYstemic approach for Modelling the fate of chemicals in the BIOSphere and the Ecological systems) whose main goal is to develop a modelling platform able to sustain an environmental chemical risk assessment. Such an approach has been found necessary for Chlorine 36 when the classic models (conventional transfer factor models and specific activity models) fail (for instance in case of acute release of radionuclides). Only the part of the model dealing with the agricultural soil-plant system is described here in detail: interaction matrices, components description, components equations, independent variables, and data. Then, we present an application of this model to investigate chlorine 36 behaviour in soils and uptake by plants after its discharge in groundwater from a radioactive waste deep storage site. Finally, we present results from an intercomparison study performed under the BIOPROTA international cooperation framework.

The comparison of strength of bystander effect induction in human lymphocytes by rho0 (complete loss of mitochondrial DNA) and rho+ (with fully functional mtDNA) strains of Saccharomyces cerevisiaewas carried out. The cultures of human peripheral blood were experimentally contaminated with nonirradiated or X-ray irradiated yeast cells (haploid rho0 and rho+ strains of S. cerevisiae). The doses of irradiation were 1 and 10 Gy. Well spread human metaphases were scored for chromosomal aberrations (CA). It was found that nonirradiated yeast cells (no matter rho0 or rho+) had no effect on lymphocytes chromosomal stability. Statistically significant increased level of CA was observed in lymphocytes incubated with irradiated rho+ yeast cells. The increasing of the CA was dose independent. However, after cocultivation with irradiated rho0 cells the bystander effect was revealed for dose 10 Gy only and his manifestation was mild in comparison with rho+ data. Thus, our findings suggest that strength of bystander effect depends on existence of mitochondrial DNA and normally functioning mitochondria.

The uptake of radioceasium and radiostrontium in biota in dose assessment models is mostly estimated on the basis of Concentration Factors (CF). For accidental releases, the dynamical foodweb model BURN has been implemented in the coastal model POSEIDON (part of the Decision Support System RODOS). BURN can be applied on water bodies with different salinity levels, since in the model the uptake of radioceasium and radiostrontium in phytoplankton is governed by potassium and calcium in the water, which are calculated via the easier-to-obtain parameter salinity. Recently a dataset on radiocaesium and radiostrontium has been collected for various aquatic organisms in the Dnieper-Bug Estuary (DBE) in Ukraine, which enabled model validation with BURN. Considering the limitation of compartment models and the fact BURN is a predictive model, with fixed model parameters, the model results are within a reasonable range with the measurement data. Besides comparison with measurement data, the model calculations were also used to derive values for CF and compared with literature, which gave reasonable results for Cs-137 in fish and molluscs. For Sr-90 however, the calculated values exceeded the levels given in literature, since equilibrium between radionuclides in biota and water is not reached. Longer time periods for the radionuclide flux into the DBE, both from the Dnieper and the Black Sea are required to obtain high quality model results for the years after 1989.

The complex radioecological investigations of the East-Ural Radioactive Trace were conducted. Three transects were established in EURT area: central, eastern and western. The current levels of soil contamination near the epicenter of the accident reach 30 × 103 kBq/m2 for 90Sr and 1 × 103 kBq/m2 for 137Cs. Contamination levels are reduced in accordance with a power function with increasing distance from the accident site and at a distance of more than 100 km become close to background values. In the EURT impact area vegetation is a complex of synanthropic and semi-natural plant communities in various stages of degradation and restoration successions. The current state of phytocenosises on the sites of the demolished local villages is largely determined by the degree of human impact in the pre-accident period, and remediation activities. For most species the viability of their seed progeny, formed in a gradient of radioactive contamination, are either not different from background samples or reduced half a century after the accident. Mutability of seed progeny in impact coenopopulations in all studied species was high. Radioadaptation phenomenon, i.e. increased resistance to provocative irradiation is rare and unstable.