Tritium in precipitation on 5 sites in North-West France during the 2017-2019 period.

Between October 2017 and May 2019, measurements of tritium in rainwater were carried out at several sites in north-west France. Tritium is an important tracer for hydroclimatic studies and this work provided up-to-date data that we compared with Global Network for Isotopes in Precipitation (GNIP) measurements. Of the various sites studied, some could potentially be affected by atmospheric gaseous emissions from the nuclear industries in the region (reprocessing plant, nuclear power plant). On our reference site, the activities measured in rainwater are often below the decision threshold (<0.15 Bq.L-1). Two other sites with little impact from nuclear industries have mean activities of less than 0.7 Bq.L-1. At the two Cherbourg sites closer to the nuclear industries, the activities in rainwater are slightly higher on average, though still close to 1 Bq.L-1, but the activities are more variable when the rainfall accompanies an air mass from the Orano La Hague nuclear site. Using existing GNIP data and a simple model to simulate predicted data up to 2019, it is shown that all our measured data are comparable with the predicted activities for GNIP stations with a marine influence, in the case of the reference site and the sites with little impact from nuclear industries, and for GNIP stations with a continental influence, in the case of the other sites. Seasonal variation in activities was detected, with greater activities in the spring-summer period corresponding to the well known 'spring leak' phenomenon. This study also reveals significant differences between the activities measured on the western side of France (influenced by the Atlantic Ocean) and those measured in a continental zone. The mean levels of tritium in rainwater in France, excluding any nuclear influence, can be estimated on average at less than 0.3 Bq.L-1 in the western marine zone, and at around 1 Bq.L-1 in the continental zones.

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.

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.

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.

In situ measurements of tritium evapotranspiration (³H-ET) flux over grass and soil using the gradient and eddy covariance experimental methods and the FAO-56 model.

The behaviour of tritium in the environment is linked to the water cycle. We compare three methods of calculating the tritium evapotranspiration flux from grassland cover. The gradient and eddy covariance methods, together with a method based on the theoretical Penmann-Monteith model were tested in a study carried out in 2013 in an environment characterised by high levels of tritium activity. The results show that each of the three methods gave similar results. The various constraints applying to each method are discussed. The results show a tritium evapotranspiration flux of around 15 mBq m(-2) s(-1) in this environment. These results will be used to improve the entry parameters for the general models of tritium transfers in the environment.

Probing the surface of a sweet protein: NMR study of MNEI with a paramagnetic probe.

The design of safe sweeteners is very important for people who are affected by diabetes, hyperlipemia, and caries and other diseases that are linked to the consumption of sugars. Sweet proteins, which are found in several tropical plants, are many times sweeter than sucrose on a molar basis. A good understanding of their structure-function relationship can complement traditional SAR studies on small molecular weight sweeteners and thus help in the design of safe sweeteners. However, there is virtually no sequence homology and very little structural similarity among known sweet proteins. Studies on mutants of monellin, the best characterized of sweet proteins, proved not decisive in the localization of the main interaction points of monellin with its receptor. Accordingly, we resorted to an unbiased approach to restrict the search of likely areas of interaction on the surface of a typical sweet protein. It has been recently shown that an accurate survey of the surface of proteins by appropriate paramagnetic probes may locate interaction points on protein surface. Here we report the survey of the surface of MNEI, a single chain monellin, by means of a paramagnetic probe, and a direct assessment of bound water based on an application of ePHOGSY, an NMR experiment that is ideally suited to detect interactions of small ligands to a protein. Detailed surface mapping reveals the presence, on the surface of MNEI, of interaction points that include residues previously predicted by ELISA tests and by mutagenesis.

On the structural stability of a small bioactive peptide of potential use in biotechnology.

A tridecapeptide with the sequence CCEICCNPACFGC has been synthesized to reproduce the active moiety of a heat stable enterotoxin from Vibrio cholerae. The proton NMR analysis indicates, for the active synthetic fragment, a rigid secondary structure stabilised by three disulfide bridges. Such a rigid peptide, suitably detoxified and activated, could be a good candidate to be used as a carrier for linear bioactive peptides or other functional groups.

Carotid endarterectomy: a retrospective analysis. Microendarterectomy and transcranial Doppler ultrasound monitoring.

BACKGROUND: Analyses of the results obtained following our protocol for the surgical therapy of carotid artery stenosis is the aim of this study. METHODS: Ninety-one procedures were performed on 84 patients by the same surgical team. Indications for carotid endarterectomy (CEA) were 50-70% internal carotid artery (ICA) stenosis in 8% of the patients (100% symptomatic), 70-90% stenosis in 67% (64% symptomatic) and 90-99% ICA stenosis in 25% of our patients (33% symptomatic). Carotid shunt during arterial cross-clamp was only used in 4 cases (4.4%) following trans-cranial Doppler ultrasound (TCD) intraoperative monitoring findings. Operative microscope or surgical loupes were used for the complete removal of atheroma and the direct suture of the arteriotomy. Heparin was only antagonised in selected cases. RESULTS: No mortality and no permanent deficit related to ischemic events were present in our patients; a transient neurological deficit occurred in 1 case (1.1%). Two patients died (2.2%): 1 due to myocardial infarction and the second one to bronchopneumonia. Transient peripheral nerve deficits were noted in 2 cases. CONCLUSIONS: In order to reduce to a minimum ischemic risks during CEA, our preliminary experience advises microsurgical technique for the complete removal of the atheroma and suture, TCD evaluation of collateral reserve during cross-clamping, and the use of randomised multicenter studies guidelines for the selection of patients. More attention must also be given to postoperative care, since hemodynamic instability represents the main risk for our patients. Overnight intensive care unit (ICU) surveillance in all patients may help to avoid fatal complications.

In situ metrology of 85Kr plumes released by the COGEMA La Hague nuclear reprocessing plant.

The IRSN (Institut de Radioprotection et de Sûreté Nucléaire, France) has started an in situ study of the behaviour of atmospheric releases close-by the COGEMA La Hague nuclear reprocessing plant. The study is designed to improve information on the dispersion of radioactive pollutants very close to the emission point--a 100 m height chimney. In this situation, close to the emission and height of the emission, Gaussian models generally used to predict the behaviour of atmospheric releases are not well adapted. The study is based on the characterisation of the 85Kr emitted during normal operations of the reprocessing process. Temporal and spatial variations of the plume shape were investigated with intensive in situ measurements. Live in situ techniques to measure the electrons and the photons emitted by the 85Kr have been implemented and will be described. Preliminary results showing the interest of the techniques were presented. Variations of the dose rates created by the photon flux of a plume were directly measured and correlated to other quantities.

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.

TOCATTA: a dynamic transfer model of ¹4C from the atmosphere to soil-plant systems.

Many nuclear facilities release ¹4C into the environment, mostly as ¹4CO2, which mixes readily with stable CO2. This complete isotopic mixing (equilibrium) is often used as the basis for dose assessment models. In this paper, a dynamic compartment model (TOCATTA) has been investigated to describe ¹4C transfer in agricultural systems exposed to atmospheric ¹4C releases from nuclear facilities under normal operating or accidental conditions. The TOCATTA 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 have been designed to be relatively simple, minimizing the number of compartments and input parameters required, appropriate to its use in an operational mode. This paper describes in detail ¹4C transfer in agricultural plants exposed to time-varying concentrations of atmospheric ¹4C, with a consideration also of the transfer pathways of ¹4C in soil. The model was tested against in situ data for ¹4C activity concentration measured over two years on a grass field plot located 2 km downwind of the AREVA NC La Hague nuclear reprocessing plant. The first results showed that the model roughly reproduced the observed month-to-month variability in grass ¹4C activity, but under-estimated (by about 33%) most of the observed peaks in the ¹4C activity concentration of grass. This tends to prove that it is not suitable to simulate intra-monthly variability, and a fortiori, the response of vegetation to accidental releases that may occur during the day. The need to increase the temporal resolution of the model has been identified in order to simulate the impact of intermittent ¹4C releases occurring either the day or night, such as those recorded by the AREVA NC plant.

Modelling the transfer of 14C from the atmosphere to grass: a case study in a grass field near AREVA-NC La Hague.

Radioactive (14)C is formed as a by-product of nuclear power generation and from operation of nuclear fuel reprocessing plants like AREVA-NC La Hague (North France), which releases about 15 TBq per year of (14)C into the atmosphere. Since the autumn of 2006, (14)C activity concentrations in samples from the terrestrial environment (air, grass and soil) have been monitored monthly on grassland 2 km downwind of the reprocessing plant. The monitoring data provides an opportunity to validate radioecology models used to assess (14)C transfer to grassland ecosystems. This article compares and discusses the ability of two different models to reproduce the observed temporal variability in grass (14)C activity in the vicinity of AREVA-NC La Hague. These two models are the TOCATTA model which is specifically designed for modelling transfer of (14)C and tritium in the terrestrial environment, and PaSim, a pasture model for simulating grassland carbon and nitrogen cycling. Both TOCATTA and PaSim tend to under-estimate the magnitude of observed peaks in grass (14)C activity, although they reproduce the general trends. PaSim simulates (14)C activities in substrate and structural pools of the plant. We define a mean turn-over time for (14)C within the plant, which is based on both experimental data and the frequency of cuts. An adapted PaSim result is presented using the 15 and 20 day moving average results for the (14)C activity in the substrate pool, which shows a good match to the observations. This model reduces the Root Mean Square Error (RMSE) by nearly 40% in comparison to TOCATTA.

Modelling tritium flux from water to atmosphere: application to the Loire River.

Tritium (³H or T) is one of the major radionuclides released by nuclear power plants (NPP) into rivers. However, tritiated water (HTO) flux from water to air is seldom considered when assessing health effects of such releases. The aim of this paper is to present the result of a research program, called LORA, conducted on the Loire River (France). To improve our understanding of HTO flux from surface water to air, three field campaigns were organised during the NPP's radioactive releases to measure simultaneously the activity concentrations in air on the riverbank, using an innovative system, and in river water. The measurements showed that during radioactive releases, water vapour was enriched in ³H. These results were used to calibrate exchange velocities. The average of these estimated exchange velocities was more than one order of magnitude higher than those calculated in the literature from indoor experiments. The variability of these values was also larger, showing that outdoor studies cover a wide range of conditions influencing HTO flux. No correlation was observed between exchanges velocities and meteorological conditions. However, there was a significant difference between day and night with a higher value observed during the day. Two approaches used to calculate HTO evaporation from water (i.e. the approach based on water evaporation and the approach considering that HTO follows its own concentration gradient) were included in a hydrodynamic model, which was used to evaluate HTO air activity along the Loire River. In conclusion, only the approach considering that HTO follows its own gradient led to a good agreement between measurements and predictions. A one-year simulation was done to estimate the contribution of this process to the dose. Its contribution can be considered as negligible in this case compared to the other pathways such as ingestion of water or foodstuffs.

A study of the atmospheric dispersion of a high release of krypton-85 above a complex coastal terrain, comparison with the predictions of Gaussian models (Briggs, Doury, ADMS4).

Atmospheric releases of krypton-85, from the nuclear fuel reprocessing plant at the AREVA NC facility at La Hague (France), were used to test Gaussian models of dispersion. In 2001-2002, the French Institute for Radiological Protection and Nuclear Safety (IRSN) studied the atmospheric dispersion of 15 releases, using krypton-85 as a tracer for plumes emitted from two 100-m-high stacks. Krypton-85 is a chemically inert radionuclide. Krypton-85 air concentration measurements were performed on the ground in the downwind direction, at distances between 0.36 and 3.3 km from the release, by neutral or slightly unstable atmospheric conditions. The standard deviation for the horizontal dispersion of the plume and the Atmospheric Transfer Coefficient (ATC) were determined from these measurements. The experimental results were compared with calculations using first generation (Doury, Briggs) and second generation (ADMS 4.0) Gaussian models. The ADMS 4.0 model was used in two configurations; one takes account of the effect of the built-up area, and the other the effect of the roughness of the surface on the plume dispersion. Only the Briggs model correctly reproduced the measured values for the width of the plume, whereas the ADMS 4.0 model overestimated it and the Doury model underestimated it. The agreement of the models with measured values of the ATC varied according to distance from the release point. For distances less than 2 km from the release point, the ADMS 4.0 model achieved the best agreement between model and measurement; beyond this distance, the best agreement was achieved by the Briggs and Doury models.

Structural characterization and thermal stability of Notothenia coriiceps metallothionein.

Fish and mammalian metallothioneins (MTs) differ in the amino acid residues placed between their conserved cysteines. We have expressed the MT of an Antarctic fish, Notothenia coriiceps, and characterized it by means of multinuclear NMR spectroscopy. Overall, the architecture of the fish MT is very similar to that of mammalian MTs. However, NMR spectroscopy shows that the dynamic behaviour of the two domains is markedly different. With the aid of absorption and CD spectroscopies, we studied the conformational and electronic features of fish and mouse recombinant Cd-MT and the changes produced in these proteins by heating. When the temperature was increased from 20 to 90 degrees C, the Cd-thiolate chromophore absorbance at 254 nm of mouse MT was not modified up to 60 degrees C, whereas the absorbance of fish MT decreased significantly starting from 30 degrees C. The CD spectra also changed quite considerably with temperature, with a gradual decrease of the positive band at 260 nm that was more pronounced for fish than for mouse MT. The differential effect of temperature on fish and mouse MTs may reflect a different stability of metal-thiolate clusters of the two proteins. Such a conclusion is also corroborated by results showing differences in metal mobility between fish and mouse Zn-MT.

NMR studies of protein surface accessibility.

Characterization of protein surface accessibility represents a new frontier of structural biology. A surface accessibility investigation for two structurally well-defined proteins, tendamistat and bovine pancreatic trypsin inhibitor, is performed here by a combined analysis of water-protein Overhauser effects and paramagnetic perturbation profiles induced by the soluble spin-label 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl on NMR spectra. This approach seems to be reliable not only for distinguishing between buried and exposed residues but also for finding molecular locations where a network of more ordered waters covers the protein surface. From the presented set of data, an overall picture of the surface accessibility of the two proteins can be inferred. Detailed knowledge of protein accessibility can form the basis for successful design of mutants with increased activity and/or greater specificity.