Institute for Radiation Protection and Nuclear Safety (IRSN)
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Improving variance estimation for time-dependent detectors in Monte Carlo dynamic calculations using adaptive sampling of neutrons
No full textInternational audienceMonte Carlo methods have been used for nuclear applications since the beginning of scientific computing. Decades of method refinements now allow to perform simulations of steady-state fissile systems with quite accurate results and relatively accessible computation time. Timedependent calculations such as reactivity insertion accident simulations on the other hand still present issues. Indeed, reaching a sufficient accuracy implies high computational costs which prohibit industrial use of time-dependent Monte Carlo simulations. Dynamic calculations which include thermal feedback effects using coupled calculation schemes might especially suffer from high statistical fluctuations due to the non-linearity of multiphysics solvers. To address this issue, with the aim of reducing variance in Monte Carlo transient neutronics simulations, this article proposes a strategy based on adaptive sampling of neutron histories. The method which is proposed here is adapted from the Adaptive Multilevel Splitting method for particle transport and can make use of an importance map provided by the user. A first test of the method was conducted on a 2-dimensional 3x3 UOX assembly cluster to produce detailed and spatially integrated power distributions over time. Increases of the figure of merit up to a factor 30 were observed for detailed and spatially integrated results at the end of the neutronics transient. Such improvements of the figure of merit could eventually prove to be efficient to reduce potential amplifications of statistical fluctuations due to non-linearity of other multiphysics solvers with affordable calculation costs
Radiocarbon dating of Angkorian art and monuments - Direct dating of iron reinforcements
No full textInternational audienc
Ion recombination correction factors and detector comparison in a very-high dose rate proton scanning beam
No full textInternational audienceAccurate dosimetry is paramount to study the FLASH biological effect since dose and dose rate are critical dosimetric parameters governing its underlying mechanisms. With the goal of assessing the suitability of standard clinical dosimeters in a very-high dose rate (VHDR) experimental setup, we evaluated the ion collection efficiency of several commercially available air-vented ionization chambers (IC) in conventional and VHDR proton irradiation conditions. Methods: A cyclotron at the Orsay Proton Therapy Center was used to deliver VHDR pencil beam scanning irradiation. Ion recombination correction factors (k s) were determined for several detectors (Advanced Markus, PPC05, Nano Razor, CC01) at the entrance of the plateau and at the Bragg peak, using the Niatel model, the Twovoltage method and Boag's analytical formula for continuous beams. Results: Mean dose rates ranged from 4 Gy/s to 385 Gy/s, and instantaneous dose rates up to 1000 Gy/s were obtained with the experimental setup. Recombination correction factors below 2 % were obtained for all chambers, except for the Nano Razor, at VHDRs with variations among detectors, while k s values were significantly smaller (0.8 %) for conventional dose rates. Conclusions: While the collection efficiency of the probed ICs in scanned VHDR proton therapy is comparable to those in the conventional regime with recombination coefficiens smaller than 1 % for mean dose rates up to 177 Gy/s, the reduction in collection efficiency for higher dose rates cannot be ignored when measuring the absorbed dose in pre-clinical proton scanned FLASH experiments and clinical trials
Insights into the modes of action of tritium on the early-life stages of zebrafish, Danio rerio, using transcriptomic and proteomic analyses
No full textInternational audienceIn the environment, populations are exposed to different kinds of ionizing radiation. Little is known about their modes of action on non-human species, and whether or not they are similar for alpha, beta and gamma radiations, considered as the reference. In this context, tritium effects (beta emitter) under the form of tritiated water (HTO) were investigated in zebrafish, a common model in toxicology and ecotoxicology with a fully sequenced genome. Experiments were conducted on early life stages, considered to be highly sensitive to pollutants, byexposing eggs to 0.4 mGy/h of HTO until 10 days post fertilization. Tritium internalization was quantified, and effects were investigated using a combined approach of transcriptomic and proteomic analyses. Results highlighted similarities in the biological pathways affected by HTO by both techniques, such as defence response, muscle integrity and contraction, and potential visual alterations. These results correlated well with previous data obtained on earlier developmental stages (1 and 4 dpf). Interestingly, HTO effects were partly overlapping those obtained after gamma irradiation, underlying potential common modes of action. This study, therefore, brought a body of evidence on the effects of HTO observed at the molecular level on zebrafish larvae. Furtherstudies could investigate if the effects persist in adult organisms
Contribution of IRSN R&D to reducing the risks of airborne pollutants dispersion during the dismantling of nuclear facilities
No full textInternational audienceThis paper presents a general overview of IRSN research activities for assessing and reducing the risksof airborne dispersion of radioactive contamination during the dismantling operations of nuclearfacilities. Four main topic areas are addressed: aerosol source term, contamination transfers, behaviorof containment equipment and contamination metrology. Firstly, the various experimental and numericalmeans involved are presented
Prediction of DNA rejoining kinetics and cell survival after proton irradiation for V79 cells using Geant4-DNA
No full textCorrigendum to “Prediction of DNA rejoining kinetics and cell survival after proton irradiation for V79 cells using Geant4-DNA” [Phys. Med. 105 (2023) 102508] (S1120179722021032) : 10.1016/j.ejmp.2024.103375International audiencePurpose:Track structure Monte Carlo (MC) codes have achieved successful outcomes in the quantitative investigation of radiation-induced initial DNA damage. The aim of the present study is to extend a Geant4-DNA radiobiological application by incorporating a feature allowing for the prediction of DNA rejoining kinetics and corresponding cell surviving fraction along time after irradiation, for a Chinese hamster V79 cell line, which is one of the most popular and widely investigated cell lines in radiobiology.Methods:We implemented the Two-Lesion Kinetics (TLK) model, originally proposed by Stewart, which allows for simulations to calculate residual DNA damage and surviving fraction along time via the number of initial DNA damage and its complexity as inputs.Results:By optimizing the model parameters of the TLK model in accordance to the experimental data on V79, we were able to predict both DNA rejoining kinetics at low linear energy transfers (LET) and cell surviving fraction.Conclusion:This is the first study to demonstrate the implementation of both the cell surviving fraction and the DNA rejoining kinetics with the estimated initial DNA damage, in a realistic cell geometrical model simulated by full track structure MC simulations at DNA level and for various LET. These simulation and model make the link between mechanistic physical/chemical damage processes and these two specific biological endpoints
The intercellular communications mediating radiation-induced bystander effects and their relevance to environmental, occupational, and therapeutic exposures
No full textInternational audiencePurpose: The assumption that traversal of the cell nucleus by ionizing radiation is a prerequisite to induce genetic damage, or other important biological responses, has been challenged by studies showing that oxidative alterations extend beyond the irradiated cells and occur also in neighboring bystander cells. Cells and tissues outside the radiation field experience significant biochemical and phenotypic changes that are often similar to those observed in the irradiated cells and tissues. With relevance to the assessment of long-term health risks of occupational, environmental and clinical exposures, measurable genetic, epigenetic, and metabolic changes have been also detected in the progeny of bystander cells. How the oxidative damage spreads from the irradiated cells to their neighboring bystander cells has been under intense investigation. Following a brief summary of the trends in radiobiology leading to this paradigm shift in the field, we review key findings of bystander effects induced by low and high doses of various types of radiation that differ in their biophysical characteristics. While notable mechanistic insights continue to emerge, here the focus is on the many means of intercellular communication that mediate these effects, namely junctional channels, secreted molecules and extracellular vesicles, and immune pathwaysConclusions: The insights gained by studying radiation bystander effects are leading to a basic understanding of the intercellular communications that occur under mild and severe oxidative stress in both normal and cancerous tissues. Understanding the mechanisms underlying these communications will likely contribute to reducing the uncertainty of predicting adverse health effects following exposure to low dose/low fluence ionizing radiation, guide novel interventions that mitigate adverse out-of-field effects, and contribute to better outcomes of radiotherapeutic treatments of cancer. In this review, we highlight novel routes of intercellular communication for investigation, and raise the rationale for reconsidering classification of bystander responses, abscopal effects, and expression of genomic instability as non-targeted effects of radiation
Renal toxicity and biokinetics models after repeated uranium instillation
No full textInternational audienceDuring nuclear fuel processing, workers can potentially be exposed to repeated inhalations of uranium compounds. Uranium nephrotoxicity is well documented after acute uranium intake, but it is controversial after long-term or protracted exposure. This study aims to analyze the nephrotoxicity threshold after repeated uranium exposure through upper airways and to investigate the resulting uranium biokinetics in comparison to reference models. Mice (C57BL/6J) were exposed to uranyl nitrate (0.03-3 mg/kg/day) via intranasal instillation four times a week for two weeks. Concentrations of uranium in urines and tissues were measured at regular time points (from day 1 to 91 postexposure). At each exposure level, the amount of uranium retained in organs/tissues (kidney, lung, bone, nasal compartment, carcass) and excreta (urine, feces) reflected the two consecutive weeks of instillation except for renal uranium retention for the highest uranium dose. Nephrotoxicity biomarkers, KIM-1, clusterin and osteopontin, are induced from day 4 to day 21 and associated with changes in renal function (arterial fluxes) measured using non-invasive functional imaging (Dopplerultrasonography) and confirmed by renal histopathological analysis. These results suggest that specific biokinetic models should be developed to consider altered uranium excretion and retention in kidney due to nephrotoxicity. The threshold is between 0.25 and 1 mg/kg/day after repeated exposure to uranium via upper airways
Did the Younger Dryas to Holocene climate transition favour high seismicity rates in the north-western Alps ?
No full textInternational audienceIn the French north-western Alps, several lakes of glacial origin, such as Aiguebelette and La Thuile, present some mass-transport deposits within their sedimentary sequences. These event layers can result from lake sediment destabilization eventually triggered by earthquakes. On Lake Aiguebelette, based on sedimentological, geochemical and magnetic analyses, and high-resolution seismic and bathymetric surveys a ca 1 m thick event layer was identified in the deepest lake basin and a synchronous ca 2 cm thick deposit in the shallow basin. Age-depth models based on radiocarbon ages reveal that both mass-transport deposits in Lake Aiguebelette occurred around the Younger Dryas - Early Holocene climatic transition (i.e. 11 700 cal bp) time range. In Lake La Thuile, located 30 km away, unique mass-transport deposits (translational slide type) were recorded at the same time range in sedimentary records. Additionally, high-resolution seismic profiles previously acquired in Lake Annecy and Lake Bourget support the hypothesis of significant mass-transport deposits occurring at the Younger Dryas - Early Holocene time range. These outcomes on four north-western peri-Alpine and Alpine lakes highlight the regional occurrence of mass-transport deposits in the Younger Dryas - Early Holocene time range. Seismic and rockfall events are discussed as potential sources of these significant and similarly aged mass-transport deposits. Based on this study and a literature review, the authors suggest that mechanisms induced by rapid climate change and glacial retreat, such as crustal rebound and erosional unloading, could favour the triggering of earthquakes and rockfall events. In the case of mass-transport deposits archived in north-western Alpine lakes during this time period, this study favours the hypothesis of increased seismicity as the primary source driving process involved
Ecosystem modelling in the Northwestern Mediterranean Sea: Structure and functioning of a complex system
No full textInternational audienceEcopath mass-balanced models are widely-used tools to address various challenges in the understanding and protection of ecosystems. To track the continuing improvements in data and the evolving environment (climate change, anthropic pressure), new models are regularly being developed. In this study, we built a Gulf of Lion Ecopath model, focused on the continental shelf, featuring enhanced representation of benthic invertebrates and a realistic assessment of catches, and which takes into account the significant changes observed after 2008–2009 in the trophic structure of this ecosystem as well as related changes in fisheries activities. The model is composed of 68 functional groups, including 6 primary producers, discards and detritus, 27 invertebrate groups, 31 fish groups, dolphins and seabirds. New datasets were taken into account for biomasses, as well as for diets. P/B and Q/B parameters were calculated to include the most recent and geographically closest data. Model results highlight a food web diagram, ranging over 5 trophic levels and placing Prionace glauca, Squalus acanthias and dolphins as top predators. The mixed trophic impact analysis showed that the groups with the highest accumulated negative impacts are, in decreasing order, benthic trawls, nets and carnivorous echinoderms. The groups with the highest accumulated positive impacts are, in decreasing order, detritus, microphytoplankton and nanoplankton. The flux analysis shows that a major part of the flows occurs at trophic level 2 with 35.1% of the model total throughput and 43.8% of the total biomass. The catches have a mean trophic level of 3.47, higher than in previous studies, reflecting the changes in the fisheries activities