Flux of tritium from the sea to the atmosphere around a nuclear reprocessing plant: Experimental measurements and modelling for the Western English channel.

Tritium is released to the environment by nuclear industries in various forms, mainly HTO. In impact studies leading to estimated doses for the population, atmospheric discharges are mainly taken into consideration because they generally lead to values higher than those related to liquid discharges. However, the tritium released in liquid environments can be transferred to the atmosphere by evaporation and then be transported to terrestrial ecosystems by wind. This study was carried out in France near a fuel reprocessing plant (RP) which discharges tritium into the western English Channel. We highlighted the influence of a mass of water enriched with tritium on the HTO levels in atmospheric water vapour downwind through 18 field campaigns. A hydrodynamic model able to simulate tritium activity in the water was coupled with an evaporation an atmospheric transport model. It allows to reconstitute variations in atmospheric tritium on the coast, depending on liquid discharges of tritium from the reprocessing plant. On this basis, when seawater containing 20-100 Bq.L-1 of tritium flows between 0 and 10 km off the coast, variations in atmospheric activity onshore can increase of 2-15 Bq.L-1. Mean tritium quantities released by the sea into the atmosphere in the Western English Channel reached 130 TBq.y-1 over the 2017-2020 period. Emissions were estimated at 0.9-11.3 GBq km-2.y-1 and depends principally on the distance from the liquid discharge point. If we compare the "marine" source term, in HTO form, with the direct source term for gaseous discharges, the marine source term is one order of magnitude greater for the marine region affected by liquid discharges. Finally, we estimate that approximately 1.1% of tritium stock discharged at sea (regulated and controlled) return to the atmosphere each year at the scale of the Western English Channel.

Tritium forms discrimination in ryegrass under constant tritium exposure: From seed germination to seedling autotrophy.

Uncertainties remain regarding the fate of atmospheric tritium after it has been assimilated in grasslands (ryegrass) in the form of TFWT (Tissue Free Water Tritium) or OBT (Organically Bound Tritium). One such uncertainty relates to the tritium forms discrimination during transfer from TFWT to OBT resulting from photosynthesis (OBTphoto), corresponding to the OBTphoto/TFWT ratio. In this study, the OBT/TFWT ratio is determined by experiments in the laboratory using a ryegrass model and hydroponic cultures, with constant activity of tritium in the form of tritiated water (denoted as HTO) in the "water" compartment (liquid HTO) and "air" compartment (HTO vapour in the air). The OBTphoto/TFWT ratio and the exchangeable OBT fraction are measured for three parts of the plant: the leaf, seed and root. Plant growth is modelled using dehydrated biomass measurements taken over time in the laboratory and integrating physiological functions of the plant during the first ten days after germination. The results suggest that there is no measurable discrimination of tritium in the plant organic matter produced by photosynthesis.

Atmospheric tritium concentrations under influence of AREVA NC La Hague reprocessing plant (France) and background levels.

In-air tritium measurements were conducted around the AREVA NC La Hague reprocessing plant, as well as on other sites that are not impacted by the nuclear industry in northwest of France. The results indicate that the dominant tritium form around the AREVA site is HT (86%). HT and HTO levels are lower than 5 and 1 Bq. m-3 for hourly samples taken in the plume. No tritiated organic molecules (TOM) were detected. 26 measurement campaigns were performed and links were established between near-field 85Kr, HT and HTO activities. Environmental measurements are in line with those taken at the discharge stack, and tend to demonstrate that there are no rapid changes in the tritium forms released. Out of the influence of any nuclear activities, the levels measured were below 13 mBq.m-3 for HT and 5 mBq.m-3 for HTO (<0.5 Bq. L-1). HTO level in air seems to be influenced by HTO activities in surrounding seawater.

The VATO project: Development and validation of a dynamic transfer model of tritium in grassland ecosystem.

In this paper, a dynamic compartment model with a high temporal resolution has been investigated to describe tritium transfer in grassland ecosystems exposed to atmospheric 3H releases from nuclear facilities under normal operating or accidental conditions. TOCATTA-χ model belongs to the larger framework of the SYMBIOSE modelling and simulation platform that aims to assess the fate and transport of a wide range of radionuclides in various environmental systems. In this context, the conceptual and mathematical models of TOCATTA-χ have been designed to be relatively simple, minimizing the number of compartments and input parameters required. In the same time, the model achieves a good compromise between easy-to-use (as it is to be used in an operational mode), explicative power and predictive accuracy in various experimental conditions. In the framework of the VATO project, the model has been tested against two-year-long in situ measurements of 3H activity concentration monitored by IRSN in air, groundwater and grass, together with meteorological parameters, on a grass field plot located 2 km downwind of the AREVA NC La Hague nuclear reprocessing plant, as was done in the past for the evaluation of transfer of 14C in grass. By considering fast exchanges at the vegetation-air canopy interface, the model correctly reproduces the observed variability in TFWT activity concentration in grass, which evolves in accordance with spikes in atmospheric HTO activity concentration over the previous 24 h. The average OBT activity concentration in grass is also correctly reproduced. However, the model has to be improved in order to reproduce punctual high concentration of OBT activity, as observed in December 2013. The introduction of another compartment with a fast kinetic (like TFWT) - although outside the model scope - improves the predictions by increasing the correlation coefficient from 0.29 up to 0.56 when it includes this particular point. Further experimental investigation will be undertaken by IRSN and EDF next year to better evaluate (and properly model) other aspects of tritium transfer where knowledge gaps have been identified in both experimental and modelling areas.

The VATO project: An original methodology to study the transfer of tritium as HT and HTO in grassland ecosystem.

Tritium (3H) is mainly released into the environment by nuclear power plants, military nuclear facilities and nuclear reprocessing plants. The construction of new nuclear facilities in the world as well as the evolution of nuclear fuel management might lead to an increase of 3H discharges from the nuclear industry. The VATO project was set up by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and EDF (Electricité de France) to reduce the uncertainties in the knowledge about transfers of 3H from an atmospheric source (currently releasing HT and HTO) to a grassland ecosystem. A fully instrumented technical platform with specifically designed materials was set up downwind of the AREVA NC La Hague reprocessing plant (Northwest of the France). This study, started in 2013, was conducted in four main steps to provide an hourly data set of 3H concentrations in the environment, adequate to develop and/or validate transfer models. It consisted first in characterizing the physico-chemical forms of 3H present in the air around the plant. Then, 3H transfer kinetics to grass were quantified regarding contributions from various compartments of the environment. For this purpose, an original experimental procedure was provided to take account for biases due to rehydration of freeze-dried samples for the determination of OBT activity concentrations in biological samples. In a third step, the 3H concentrations measured in the air and in rainwater were reconstructed at hourly intervals. Finally, a data processing technique was used to determine the biological half-lives of OBT in grass.

Near-field krypton-85 measurements in stable meteorological conditions around the AREVA NC La Hague reprocessing plant: estimation of atmospheric transfer coefficients.

The aim of this work was to study the near-field dispersion of (85)Kr around the nuclear fuel reprocessing plant at La Hague (AREVA NC La Hague - France) under stable meteorological conditions. Twenty-two (85)Kr night-time experimental campaigns were carried out at distances of up to 4 km from the release source. Although the operational Gaussian models predict for these meteorological conditions a distance to plume touchdown of several kilometers, we almost systematically observed a marked ground signal at distances of 0.5-4 km. The calculated atmospheric transfer coefficients (ATC) show values (1) higher than those observed under neutral conditions, (2) much higher than those proposed by the operational models, and (3) higher than those used in the impact assessments.

Molecular cloning of a new member of the p53 family from the Pacific oyster Crassostrea gigas and seasonal pattern of its transcriptional expression level.

Like other sessile filter-feeding molluscs, oysters may be exposed in the natural environment to a variety of contaminants. Long-term exposure to pollutants may be one factor affecting prevalence of cancerous-like disorders, such as neoplasia. Environmentally induced alterations in p53 protein expression, in relation to leukemia, have been reported in various mollusc species inhabiting polluted water, suggesting that p53 proteins can also be used as a marker for environmental research. This work reports the cloning and sequencing of a p53-like cDNA in the mollusc bivalve Crassostreagigas. The deduced amino acid sequences of p53 shared a high degree of homology with the homologues from other mollusc species, including typical eukaryotic p53 signature sequences. We examined the p53 transcription expression pattern during the annual cycle in oyster gills and whole soft tissues in four locations along the French coasts. Real-time PCR analysis suggested that strong variations at p53 mRNA level are probably synchronized with the seasonal cycle at the four locations investigated.