Institute for Radiation Protection and Nuclear Safety (IRSN)
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Thermal characterization of downward ventilation flows through a smoke layer
No full textInternational audienceUnderstanding the behaviour of downward flows of fresh air in temperature-stratified compartments is crucial for improving oxygenation of fire in confined compartment. This study investigates the axial temperature profiles of such flows and their sensitivity to injection rates. Experimental tests in a stratified compartment reveal a naturally bounded flow that transitions between a plume and a collapsing fountain, with the ability to transport heat and to affect the thermal stratification. However, different injection rates reveal potential distinct flow configurations. Low rates limit heat transfer potential to upper locations, while high rates lead to colder air reaching the lower part of the compartment. These findings highlight the significance of injection conditions in predicting the fire source environment. Improving such predictions is critical for ensuring accurate prediction of oxygen concentration in the near field of a fire
A Step Towards a Comprehensive Uncertainty Quantification in Transient Analysis
No full textInternational audienceContinuing one long-term research program intended on the development, validation, and deployment of the comprehensive multi-physics simulations in the practice of the nuclear safety assessment, we are studying some issues resulted from the coupling of the modules of different physics and different fidelity. One issue -a consistency of the use of weighted average fuel temperature to the power feedback -can be considered as a kind of unavoidable simplification inherent to the multi-physical modelling. At the same time, the way the concept of this effective temperature has been involved in the content of the multi-physics simulations follows the same logic as so-called implicit coupling strategy. By studying these kinds of simplifications, one could elaborate an approach suitable to an assessment of emerging phenomena in the complex simulation tools. In such a context, we considered such typical for the Light Water-cooled nuclear Reactors cases as Rod Ejection and Main Steam Line Break accidental transients. The considerations have been illustrated via simulations performed using an in-house developed large-scale three-dimensional multi-physics code system. To assess the consistency of these simplifications, the models have been challenged by variations of the "law of averaging" in the calculations of the effective temperatures. It gave an opportunity to assess the impacts due to simplifications inherent to the modeling and, to a certain extent, due to an imperfect coupling of the models of different physics. These parametric studies have been extended onto the arbitrary varied laws of averaging by a brute-force sampling of one surrogate "soft" reduced order model. According to the results of these simulations and their analysis, the ultimate uncertainties due to the simplifications remain limited for all scenarios. It confirms, in its order, if not full consistency, but, at least, robustness of the coupled best-estimate modeling
Measures of fragmentation of rest activity patterns: mathematical properties and interpretability based on accelerometer real life data
No full textInternational audienceAccelerometers, devices that measure body movements, have become valuable tools for studying the fragmentation of rest-activity patterns, a core circadian rhythm dimension, using metrics such as inter-daily stability (IS), intradaily variability (IV), transition probability (TP), and self-similarity parameter (named α ). However, their use remains mainly empirical. Therefore, we investigated the mathematical properties and interpretability of rest-activity fragmentation metrics by providing mathematical proofs for the ranges of IS and IV, proposing maximum likelihood and Bayesian estimators for TP, introducing the activity balance index (ABI) metric, a transformation of α , and describing distributions of these metrics in real-life setting. Analysis of accelerometer data from 2,859 individuals (age=60-83 years, 21.1% women) from the Whitehall II cohort (UK) shows modest correlations between the metrics, except for ABI and α . Sociodemographic (age, sex, education, employment status) and clinical (body mass index (BMI), and number of morbidities) factors were associated with these metrics, with differences observed according to metrics. For example, a difference of 5 units in BMI was associated with all metrics (differences ranging between -0.261 (95% CI -0.302, -0.220) to 0.228 (0.18, 0.268) for standardised TP rest to activity during the awake period and TP activity to rest during the awake period, respectively). These results reinforce the value of these rest-activity fragmentation metrics in epidemiological and clinical studies to examine their role for health. This paper expands on a set of methods that have previously demonstrated empirical value, improves the theoretical foundation for these methods, and evaluates their empirical use in a large dataset
Outcomes of the experimental and numerical work on the operational behavior of passive autocatalytic recombiners in the late phase of a severe accident in the framework of the Amhyco Project
No full textInternational audienceThe molten core-concrete interaction in the ex-vessel phase of a severe accident in a light water reactor is a source of significant amounts of gaseous products including carbon monoxide. The European project AMHYCO addresses open issues related to the understanding of the impact of carbon monoxide on safety-relevant accident phenomena and on hydrogen mitigation measures. In order to support the simulation of accident sequences and the assessment of safety measures, Task 3.2 aimed to provide realistic models considering the influence of carbon monoxide on the operating behavior of passive auto-catalytic recombiners. The work program included conducting new experiments, analyzing existing experimental data, and further developing numerical models. The experimental program performed within Task 3.2 involved the REKO facilities at FZJ to study the impact of predicted accident atmospheres including oxygen-lean mixtures and the presence of carbon monoxide on the hydrogen recombination efficiency of different generic catalysts. More specifically, criteria were derived to predict the atmospheric conditions leading to catalyst poisoning. At the same time, a unified database including selected datasets from the various OECD/NEA-THAI projects was developed. The available experimental data were used to further advance numerical models such as the manufacturer’s engineering correlation for Framatome PARs as well as the scientific models SPARK (IRSN), PARUPM (UPM), and REKO-DIREKT (FZJ)
Analysis of postulated severe accidents in generic integral pwr small modular reactors in the frame of the horizon euratom saspam-sa project
No full textInternational audienceInvestigation of postulated SA scenarios in integral water-cooled Small Modular Reactors (SMRs) by using best estimate analytical tools has been hardly addressed in a systematic way. The HORIZON-EURATOM SAPSAM-SA project, coordinated by ENEA (Italy), was launched in 2022 aiming at filling this gap and at transferring the knowledge and know-how of large LWR to integral iPWRs in view of the European licensing needs with respect to severe accident and Emergency Planning Zone (EPZ). This paper provides an overview of the preliminary outcomes of the large calculation campaign of postulated Design Basis Accident (DBA) and SA scenarios currently ongoing in the SASPAM-SA project performed by means of state-of-art European and non-European integral codes. The primary goal is the evaluation of such tools to predict the key physical phenomena occurring during such postulated scenarios in generic iPWR systems
Sensitivity analysis and uncertainty quantification in PWR irradiation ageing like problems
No full textInternational audienceThe lifespan of nuclear power plants is a critical aspect of energy production, with reactor vessel ageing being one of the main challenges. Over time, ageing under neutron irradiation of the Pressurized Water Reactor (PWR) vessels leads to changes in the material's micro-structure. These changes adversely affect the mechanical properties, making the material more brittle and susceptible to fractures, especially under strong temperature gradients. Beyond the vessel, the aging of other elements, such as concrete structures, also poses significant concerns. Accurate calculations of neutron fluence and the associated uncertainties throughout and beyond the reactor vessel are essential to ensure safety. This study aims at addressing this issue by applying a specific methodology to a simplified model, providing a foundational step to quantify the uncertainty in Monte-Carlo simulations related to irradiation ageing in nuclear reactors
In-vessel corium thermochemistry benchmark based on MASCA-CORDEB2 experimental data
No full textInternational audienceThis paper presents the first two steps of a benchmark on in-vessel corium thermochemistry, which is part of the IAEA Coordinated Research Project on In-Vessel Melt Retention. The benchmark focuses on the stratification of corium in the lower plenum of a reactor vessel during a severe accident. The experimental data from the MASCA test facilities are used to validate/calibrate the models of the different codes used by the participants. The paper gives an overview of the different models, including their underlying assumptions. The results show that the models are generally in good agreement with the experimental data, but further experimental data is needed for model validation. Besides the need for further work, this paper highlights the fact that integral models (published in the open literature for most of them) are available to account for the first-order phenomena associated with in-vessel corium. Accordingly, this paper may be useful for code developers that would like to upgrade their models in order to take into account transient stratification kinetics, a prerequisite for a state-of-the-art analysis of in-vessel melt retention
Low Cycle Fatigue of Alloy 690 in the PWR Environment
No full textInternational audienceEnvironmentally Assisted Fatigue (EAF) is one of the concerns for the extended operation of nuclear power plants. Over time, certain components experience thermal cycling while being exposed to the chemically active environment of Pressurized Water Reactors (PWRs). While many components in the primary loop are constructed from stainless steel, some critical parts are made from Alloy 690, a nickel-based alloy. Compared to the extensive research on EAF in stainless steels, only a limited focus has been placed so far on Alloy 690.This study aims to assess the impact of the PWR environment on the fatigue life of Alloy 690. Low cycle fatigue tests were conducted in two different environments, namely air and PWR environments, at different strain amplitudes and strain rates. To investigate the mechanisms of EAF in Alloy 690, fracture surfaces were analyzed. In particular, fatigue crack growth rates as a function of crack depth were derived from striation spacing measurements. Additionally, microstructural changes, as influenced by Dynamic Strain Aging, in the air were examined using Transmission Electron Microscopy (TEM) on the specimens from interrupted tests at different stages of the fatigue life. A twofold ratio was expected according to the design rules, but the results indicate that there is minimal or almost no influence of the environment on the fatigue life of Alloy 690 in PWR conditions when compared to its behavior in an air environment. This observation is consistent with the crack growth rates, which demonstrate a constant growth in both the environments
Improving cable tray fire modelling with AI techniques
No full textInternational audienceModelling cable tray fires remains a complex issue, and existing models such as the FLASH-CAT model still have limitations due to the lack of information on certain input data. This paper discusses improvements in cable tray fire modelling by finding appropriate input data using an artificial intelligence (AI) technique. An AI-driven expert system was developed to assess missing data from a fire test database of 29 large scale cable tray fire experiments in open atmosphere. The expert system quantifies the dependencies between input and output data, helps identify influential parameters and refine model inputs. It also guides modelling efforts by identifying areas for model improvement. In this way, the applicability of an expert system in obtaining reliable input data for simulation tools to simulate a real fire scenario that has already been tested is demonstrated. Cable tray fire simulation results show improved accuracy compared with the use of default values for uncertain parameters
Les radionucléides en médecine nucléaire : applications courantes, nouveautés et radioprotection associée
No full textNational audienceLa médecine nucléaire connaît actuellement un fort développement en thérapie et en diagnostic dans le monde, généralement au travers d’une approche théranostique, notamment en raison des nouvelles applications thérapeutiques à large échelle du Lutétium-177 dans le cadre de certains cancers métastatiques de la prostate (177Lu-PSMA).Dans ce contexte de forte évolution, l’Autorité de sûreté nucléaire (ASN) a saisi l’IRSN en avril 2020 afin de réaliser une expertise sur les perspectives d’utilisation clinique de nouveaux radionucléides en médecine nucléaire en France et les questions de radioprotection associées.Entre 2020 et 2023, l’IRSN a ainsi conduit successivement des travaux qui ont permis l’élaboration de plusieurs rapports :1. En février 2021, le rapport IRSN n°2021-00083 propose un classement des radionucléides jugés les plus prometteurs par l’IRSN concernant leur probabilité de développement en France dans le futur et présente les données biologiques pertinentes disponibles au regard de la radioprotection recueillies dans la littérature pour ces radionucléides (rétention/excrétion, débit de dose autour du patient, etc.).2. En juin 2021, le rapport IRSN n°2021-00484 est consacré aux questions de radioprotection des patients dans le contexte d’une utilisation thérapeutique (planification individuelle du traitement), et de leur entourage.3. En octobre 2021, le rapport IRSN n°2021-00753 traite des questions de radioprotection des travailleurs dans les établissements de santé, des transporteurs sanitaires (ambulanciers, etc.) et des travailleurs des systèmes d’assainissement (égoutiers, etc.).4. En janvier 2023, le rapport IRSN n°2023-00026 traite du cas de décès de patients après un acte de médecine nucléaire et se concentre particulièrement sur la radioprotection des travailleurs effectuant leur prise en charge. Des estimations de dose et des recommandations sont formulées pour le personnel des pompes funèbres et les agents de chambre mortuaire hospitalière effectuant le transport avant la mise en bière et les soins au corps (toilette, habillage, thanatopraxie) et également pour les personnels des crématoriums.La présentation développera tout d’abord les radionucléides les plus courants en médecine nucléaire et les applications cliniques associées.Seront ensuite abordés les nouveaux radionucléides qui commencent à être utilisés cliniquement, en présentant les travaux ayant conduit au rapport de l’IRSN de février 2021 précité, complétés de quelques informations plus récentes.Enfin, seront abordées certaines des thématiques de radioprotection pertinentes pour les PCR dans l’usage des nouveaux radionucléides, ayant fait l’objet des études pour l’élaboration des trois autres rapports de l’IRSN précités (juin et octobre 2021, et janvier 2023)