Institute for Radiation Protection and Nuclear Safety (IRSN)
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Iodine uptake in brown seaweed exposed to radioactive liquid discharges from the reprocessing plant of ORANO La Hague
No full textInternational audienceIodine-129 is present in controlled liquid radioactive waste routinely released in seawater by the ORANO nuclear fuel reprocessing plant in La Hague (Normandy, France). Brown algae are known for their exceptional ability to concentrate iodine from seawater. They also potentially emit volatile iodine compounds in response to various stresses, such as during emersion at low tide. For these reasons, brown seaweed is routinely collected for radioactivity monitoring in the marine environment (Fucus serratus and Laminaria digitata). Despite the high concentration ratio, the exact mechanism of iodine uptake is still unclear. Chemical imaging by laser desorption/ionization mass spectrometry provided evidence that iodine is stored by kelps as I−. In this study we investigate in vivo iodine uptake in kelps (L. digitata) with an emphasis on seawater iodine chemical speciation. Our results showed that kelp plantlets were able to take up iodine in the forms of both IO3− and I−. We also observed transient net efflux of I− back to seawater but no IO3− efflux. Since the seaweed stores I− but takes up both IO3− and I−, IO3− was likely to be converted into I− at some point in the plantlet. One major outcome of our experiments was the direct observation of the kelp-based biogenic conversion of seawater IO3− into I−. On the basis of both IO3− and I− uptakes by the seaweed, we propose new steps in the possible iodine concentration mechanism used by brown algae
Improved metamodels for predicting high-dimensional outputs by accounting for the dependence structure of the latent variables: application to marine flooding
No full textInternational audienceMetamodelling techniques (also referred to as surrogate modelling) have shown high performance to overcome the computational burden of numerical hydrodynamic models for fast prediction of key indicators of marine flooding (e.g. total flooded area). To predict flood maps (e.g. spatial distribution of maximum value of water depth during a flood event), a commonly-used approach is to rely on principal component analysis to reduce the high dimensionality of the flood map (related to the number of pixels typically of several 1000 s) by transforming the spatial output into a low number of latent variables (typically < 10). One commonly-used approach is to build one metamodel per latent variable by assuming independence between the latent variables. Using two real cases of marine flooding, we show that the predictive performance of the metamodelling approach (relying on kriging metamodels) can significantly be improved when the dependence structure of the latent variables is accounted for. Our tests show that the most efficient approach relies on the clustering in the space of the latent variables (here with k-means algorithm). Complementing the approach with a kriging metamodel specifically dedicated to handle vector-valued variables allows an additional increase of predictability, but only if two conditions are jointly met: (1) the number of training samples is sufficiently high to learn the dependence structure over the respective clusters; (2) a careful selection of the number of clusters has been performed
Effets sub-léthaux du tritium sous forme organique chez les embryons et larves de poisson zèbre.
No full textInternational audienceLes populations naturelles d'organismes aquatiques sont exposées à des radionucléides émetteurs de différents types de rayonnements (α, β, γ) [1]. Ces expositions peuvent mener à l'apparition d'effets délétères qui dépendent de plusieurs facteurs tels que le type de rayonnement, la dose absorbée, le temps d'exposition et la répartition subcellulaire du radionucléide dans l'organisme. Deux études ont entre autres mis en avant que l'exposition du poisson zèbre au tritium libre pendant son développement entraîne une modification de l'expression de certains gènes et une augmentation du taux de dommages à l'ADN menant à des altérations musculaires et à une modification du comportement natatoire des larves [2,3]. Cette étude se concentre sur le tritium sous forme organique, plus spécifiquement la thymidine tritiée. Des expériences préliminaires ont permis de mettre en place des expositions à ce polluant, réalisées dans le but d'étudier différents effets sub-léthaux. Des embryons de poisson zèbre ont été exposés à trois différentes activités de thymidine tritiée (7,5; 40 et 110 kBq/mL) pendant 4 jours et différents effets ont été étudiés sur les individus exposés. Le développement a été étudié par le biais d'un suivi de la cinétique d'éclosion, mais également par le biais de la mesure de différentes caractéristiques développementales (longueur de la larve, diamètre de l'œuf, diamètre de l'œil). L'activité spontanée dans le chorion et du rythme cardiaque après 1 et 3 jours d'exposition ont également été mesurés, tout comme le comportement natatoire des larves après 4 jours d'exposition. Après 1 et 4 jours, le test des comètes a également été réalisés afin de vérifier si une dégradation de l'ADN était observable. Les résultats expérimentaux ont mis en avant un ralentissement du développement, avec une éclosion retardée chez les individus exposés aux deux plus fortes activités. Aux deux plus faibles activités, des différences significatives ont été observées sur différents marqueurs de développement, mais ces différences étaient réversibles, avec une absence de différence significative au quatrième jour de développement. Le comportement natatoire a également été impacté, avec une vitesse de nage plus élevée chez les individus exposés à l'activité intermédiaire de tritium, mais aussi avec des réactions différenciées aux stress tactiles et lumineux après exposition au tritium. Pour finir, une augmentation des dommages à l'ADN a été observée après exposition à toutes les activités, et ce aux deux stades de développement. D'autres marqueurs tels que γ-H2AX, l'état des muscles des larves, et l'expression de différents gènes d'intérêt sont encore en cours d'étude. Ces effets, compilés avec ceux déjà connus du tritium libre, permettront d'améliorer les connaissances déjà acquises sur les mécanismes de toxicité du tritium
Cohort profile: ORICAMs, a French cohort of medical workers exposed to low-dose ionizing radiation
No full textInternational audienceMedical personnel represent the largest group of workers occupationally exposed to ionizing radiation. Although the health risks associated with occupational exposure to low doses of ionizing radiation in the medical field have been investigated in several national cohorts, no study has been conducted in France to date. The ORICAMs (Occupational Radiation Induced Cancer in Medical staff) cohort is a nationwide French longitudinal cohort of medical workers exposed to ionizing radiation aiming to investigate the risk of radiation-associated cancer and non-cancer mortality. The ORICAMs cohort was set up in 2011 and includes all medical personnel monitored for ionizing radiation exposure with at least one dosimetric record in the SISERI database (the national registry for monitoring ionizing radiation exposure in workers) over the period 2002–2012. Causes of death were abstracted from death certificates and coded according to ICD-10. The follow-up ended on 31/12/2013. Standardized mortality ratios (SMRs) were calculated by cause of death to compare the mortality in the cohort to that in the French population, by gender, age group and calendar period. Among the 164,015 workers included in the cohort (60% women) a total of 1,358 deaths (892 in male and 466 in female) were reported. The observed number of all-cause deaths was significantly lower than expected based on national rates in both male (SMR = 0.35; 95% CI: 0.33, 0.38; n deaths = 892) and female (SMR = 0.41; 95% CI: 0.38, 0.45; n deaths = 466). This analysis leads to the conclusion that mortality in French workers exposed to medical radiation is significantly lower than the national reference rates. However, these results based on a comparative analysis with national rates may be impacted by the healthy worker effect towards low SMRs, and do not enable to establish a potential relationship between occupational exposure and mortality risk, even if we may suspect an impact of high SES of these professionals on the observed decreased mortality. Thus, further dose-response analyses based on individual ionizing radiation exposure and job’s type will be conducted to characterize correlation between risk of cancer mortality and occupational exposure
Dosimetry of a self-shielded gamma irradiator small animal whole-body irradiations: comparisons between ionisation chamber and alanine
No full textInternational audienceAbstract Because of reproducibility and repeatability problems with reference measurements made with an ionisation chamber in a self-protected GSRD1 irradiator, a comparison was made with alanine dosimetry for a whole-body mouse irradiation setup in a sterile box. The twisting of the cables in the cable duct and in the irradiator cell and the irradiation of the ionisation chamber connector are likely to have caused the problems encountered. These problems are not observed on other types of irradiators with more suitable cable passages. A difference up to 8.4% was observed between the alanine dosimetry and ionisation chamber. The influence of the number of animals in the sterile box on the whole-body dose of the animals was also evaluated with alanine and found to be <2%
Pulses of South Atlantic water into the tropical North Atlantic since 1825 from coral isotopes
No full textInternational audienceDecadal and multidecadal changes in the meridional overturning circulation may originate from either the subpolar North Atlantic or the Southern Hemisphere. New records of carbon and oxygen isotopes from an eastern Martinique Island (Lesser Antilles) coral reveal irregular, decadal, double-step events of low ∆ 14 C and enhanced vertical mixing, high δ 18 O and high δ 13 C values starting in 1885. Comparison of the new and published ∆ 14 C records indicates that the last event (1956-1969) coincides with a widespread, double-step ∆ 14 C low of South Atlantic origin from 32°N to 18°S, associated with a major slowdown of the Caribbean Current transport between 1963 and 1969. This event and the past Martinique ∆ 14 C lows are attributed to pulses of northward advection of low ∆ 14 C Sub-Antarctic Mode Waters into the tropical Atlantic. They are coeval with changes of the tropical freshwater budget and likely driven by meridional overturning circulation changes since ~1880
Chemical evolution of the full glass/steel/cement/claystone system in a HLW disposal cell
No full textInternational audienceThe Belgium, Dutch and French concepts for the disposal of vitrified high-level waste (HLW) are based on underground disposal facilities located in clay formation. The first two ones rely on supercontainers containing HLW and carbon steel overpack encased in a concrete buffer to keep steel passivation. In the French concept, the annular gap between carbon steel sleeve and host rock is filled with a low-pH/bentonite grout that imposes a corrosion-limiting environment during the operating period but has to be readily neutralized afterwards. The HYTEC code was used to assess of the chemical evolution of the full system including the “vitrified waste – steel overpack – concrete buffer – clay host rock” over 100,000 years. The modelling of the full system showed that the driving force was the chemical destabilization of the cement phases of the concrete buffer by the clay rock. This slowly propagated by diffusion towards the steel overpack with a pH decrease. Therefore, the durability of the cement buffer would strongly affect the duration of the containment properties of the complete multi-barrier system as a whole. As long as the high-pH buffering capacity lasted, steel generalized corrosion was minimized and magnetite was the main corrosion products. The loss of such high-pH conditions led to the speed-up of the corrosion with Fe(II)-silicate formation. The important formation of Fe-silicates corrosion products at the glass/overpack-steel interface sustained glass dissolution
An integrative systems biology strategy to support the development of adverse outcome pathways (AOPs): a case study on radiation-induced microcephaly
No full textInternational audienceAdverse Outcome Pathways (AOPs) are useful tools for assessing the potential risks associated with exposure to various stressors, including chemicals and environmental contaminants. They provide a framework for understanding the causal relationships between different biological events that can lead to adverse outcomes (AO). However, developing an AOP is a challenging task, particularly in identifying the molecular initiating events (MIEs) and key events (KEs) that constitute it. Here, we propose a systems biology strategy that can assist in the development of AOPs by screening publicly available databases, literature with the text mining tool AOP-helpFinder, and pathway/network analyses. This approach is straightforward to use, requiring only the name of the stressor and adverse outcome to be studied. From this, it quickly identifies potential KEs and literature providing mechanistic information on the links between the KEs. The proposed approach was applied to the recently developed AOP 441 on radiation-induced microcephaly, resulting in the confirmation of the KEs that were already present and identification of new relevant KEs, thereby validating the strategy. In conclusion, our systems biology approach represents a valuable tool to simplify the development and enrichment of Adverse Outcome Pathways (AOPs), thus supporting alternative methods in toxicology
Mineralogical Evolution and Expansion of Cement Pastes in a Sulfate-Confined Environment
No full textInternational audienceThe geologic disposal of radioactive waste could lead to confined conditions in which cementitious materials impose a moderate alkaline pH, in which the rocks supply sulfate ions at rather low concentrations. In this context, the purpose of this work was to study the degradation of cement pastes under such conditions using a non-renewed 30 mmol/L Na 2 SO 4 solution without pH regulation. Samples were investigated through laboratory testing and numerical modeling. XRD, SEM-EDS, and micro-indentation acquisitions were performed to follow the evolution of chemical, mineralogical, and mechanical properties during the weak external sulfate attack. Reactive transport modeling was performed with the HYTEC code. Based on these results, the Young's moduli of the degraded zones were estimated using analytical homogenization. Decalcification occurred despite the high pH value of the solution and significantly affected the mechanical properties. Macroscopic swelling and cracking were caused by the formation of expansive sulfate minerals after 60 days, despite the low sulfate content of the tank solution. The modeling supported the discussion on the evolution of the mineral fronts (ettringite, portlandite, and gypsum)
Experimental investigation of the effects of a sidewall and cable arrangement on a horizontal cable tray fire in an open atmosphere
No full textInternational audienceThe work deals with the influence of a sidewall and cable arrangement on the behavior of a fire involving horizontal cable trays in the framework of fire safety assessments in nuclear installations. The analysis is based on large-scale fire tests performed in open atmosphere in the frame of the OECD Nuclear Energy Agency (NEA) PRISME 3 project and on the corresponding simulations applying the FLASHCAT model for predicting the fire heat release rate. The fire configuration consists in five horizontal trays filled with PVC insulated power cables. The parameters investigated are the presence or absence of a sidewall and the cable arrangement (loose or tight bundles). The results show that the presence of a sidewall increases the fire HRR in comparison to a scenario without a sidewall. This effect is due to the increase of the flame spread velocity on the lower trays. Regarding cable arrangement, a tight configuration in bundles reduces the fire HRR in comparison to a scenario with a loose arrangement. This result is due to the reduction of the fire heat release rate per unit of area (HRRPUA) as well as the flame spread velocity. The performance of the FLASHCAT model in predicting the effects of the sidewall and the cable arrangement was also assessed on the basis of the fire tests and satisfactory agreements are reported. The presented analysis demonstrates that the fire scenario with horizontal cable trays against a sidewall and with a loose cable arrangement represents a conservative scenario for fire risk assessment. In addition, on the basis of these experiments, the effect of cable arrangement is more substantial than the sidewall effect