Institute for Radiation Protection and Nuclear Safety (IRSN)
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PASTELS project - overall progress of the project on experimental and numerical activities on passive safety systems
No full textInternational audienceNuclear accidents such as Fukushima Daiichi have highlighted the potential of passive safety systems to replace or complement active safety systems as part of the overall prevention and/or mitigation strategies. In addition, passive systems are key features of Small Modular Reactors (SMRs), for which they are becoming almost unavoidable and are part of the basic design of many reactors available in today’s nuclear market. Nevertheless, their potential to significantly increase the safety of nuclear power plants still needs to be strengthened, in particular the ability of computer codes to determine their performance and reliability in industrial applications and support the safety demonstration. The PASTELS project (September 2020–February 2024), funded by the European Commission “Euratom H2020” programme, is devoted to the study of passive systems relying on natural circulation. The project focuses on two types, namely the SAfety COndenser (SACO) for the evacuation of the core residual power and the Containment Wall Condenser (CWC) for the reduction of heat and pressure in the containment vessel in case of accident. A specific design for each of these systems is being investigated in the project. Firstly, a straight vertical pool type of SACO has been implemented on the Framatome’s PKL loop at Erlangen. It represents a tube bundle type heat exchanger that transfers heat from the secondary circuit to the water pool in which it is immersed by condensing the vapour generated in the steam generator. Secondly, the project relies on the CWC installed on the PASI test loop at LUT University in Finland. This facility reproduces the thermal-hydraulic behaviour of a Passive Containment Cooling System (PCCS) mainly composed of a CWC, a heat exchanger in the containment vessel connected to a water tank at atmospheric pressure outside the vessel which represents the ultimate heat sink. Several activities are carried out within the framework of the project. Different tests are conducted on these integral test facilities to produce new and relevant experimental data allowing to better characterize the physical behaviours and the performances of these systems for various thermo-hydraulic conditions. These test programmes are simulated by different codes acting at different scales, mainly system and CFD codes. New “system/ CFD” coupling approaches are also considered to evaluate their potential to benefit both from the accuracy of CFD in regions where local 3D effects are dominant and system codes whose computational speed, robustness and general level of physical validation are particularly appreciated in industrial studies. In parallel, the project includes the study of single and two-phase natural circulation loops through a bibliographical study and the simulations of the PERSEO and HERO-2 experimental facilities. After a synthetic presentation of the project and its objectives, this article provides the reader with findings related to the physical analysis of the test results obtained on the PKL and PASI installations as well an overall evaluation of the capability of the different numerical tools to simulate passive systems
Sensitivity analysis of simulated premixed layer and vapour explosion in stratified configuration
No full textInternational audienceExperiments of fuel-coolant interaction in stratified geometry at the PULiMS and SES (KTH, Sweden) test facilities resulted in spontaneous steam explosions. Prior to the explosion, a premixed layer of ejected melt drops in the water layer was observed in the experiments. Based on the experimental and analytical knowledge, we have recently developed a model for premixed layer formation in the Fuel-Coolant Interaction code MC3D and applied it to estimate steam explosion energetics. In the paper, a sensitivity study of this model is performed on the three main uncertain parameters of the premixed layer formation model, which define the melt fragmentation rate, the size of the ejected melt drops and the ejected melt drop velocity. The analysis is performed against the SES S1 and the PULiMS E6 experimental results. The chosen tests were selected as in both of them the same material was used, the geometry was similar, and both of them resulted in a spontaneous steam explosion. The effects can be observed in all the performed analyses and they are consistent in simulations of both experiments, affecting the premixed layer height as well as the explosion strength and duration. Some uncertainty of the experimental results is assessed, with the main limitation related to the visual observations. The combination of both analyses provides us with the assessment of future work necessity and prioritization. The presented sensitivity analysis of the premixed layer formation model enables a more reliable assessment of the stratified vapour explosion risk and its uncertainty in nuclear power plants and other industries
First CIP1-2B post-test calculations with scanair
No full textInternational audienceThe CIP1-2B test is part of the CABRI International Program (CIP) which general objective is to study the behavior of fuel rods submitted to a Reactivity Initiated Accident (RIA) under representative Pressurized Water Reactor conditions. It is the fourth test of the CIP program and the second one in the renovated CABRI reactor, equipped with the pressurized water loop.The test rodlet was refabricated from a high burnup UO2 fuel rod (72 GWd/tU) with a M5 TM cladding. The test was successfully carried out in the CABRI reactor on November 14 th , 2022.CIP1-2B is a very valuable test to challenge numerical simulations because, for the first time, the boiling crisis under thermal-hydraulic conditions representative of a PWR has been reached with an irradiated rod submitted to a RIA transient and without cladding failure.The father rod irradiation was calculated with FRAPCON V4.0 Patch 1, and the RIA transient was simulated with SCANAIR 2022.A study related to influent parameters and models allowed to reduce the discrepancies between available measurements and simulations. This analysis shows that:• The prediction of the cladding residual mechanical hoop strain is improved with the "2D multi-species" gas flow model associated to direct flow towards the free volumes. • The prediction of the boiling crisis duration is improved with the increase of the cladding-to-coolant heat exchange coefficient during the film boiling regime. • The prediction of the fission gas released fraction is improved with the reduction of the grain boundary rupture limit in the high burnup structure zone at the pellet periphery. • The prediction of the cladding residual mechanical hoop strain is improved thanks to the modelling of a permanent thermal contact between fuel and cladding during the whole duration of the accidental transient.</p
Quantitative analysis of iron-based coloring material by means of p-XRF spectrometry.
No full textInternational audienceThe study of red and yellow coloring materials based on iron oxides and hydroxides found in prehistoric archaeological contexts have benefited from an important methodological renewal in recent years. The analysis of their elemental composition has proved to be a relevant tool for discriminating geological sources and identifying the origin of materials. Although its sensitivity to trace elements can be limiting, pXRF analysis is an interesting technique for in-situ analysis of large collections in the preliminary phase of studies. However, the composition of these natural materials varies widely (eg. 15%wt of iron for bauxite, over 60%wt for pure iron oxide), and the quantification these matrices is complex. Furthermore, these issues require the comparison of large set of archaeological and geological samples (sometimes analyzed by different teams or system), and the reuse of these data over a long period of time. For this purpose, we have initiated a calibration of XRF data by analyzing rock and ore standards, combined with quantification by the fundamental parameter method using PyMCA software. We have also developed an add-on to automate the analysis of large corpora. This work has helped us to increase the precision of quantifications, to better assess quantification errors and biases for the different elements, and thus to improve data interoperability and reliability
ELSMOR – towards European Licensing of Small Modular Reactors: Methodology recommendations for light-water small modular reactors safety assessment
No full textPDF non généré, le texte complet est dans le lien éditeurInternational audienceDecarbonization of energy production is key in today’s societies and nuclear energy holds an essential place in this prospect. Besides heavy-duty electricity production, other industrial and communal needs could be served by integrating novel nuclear energy production systems, among which are low-power nuclear devices, like small modular reactors (SMRs). The ELSMOR (towards European Licensing of Small Modular Reactors) European project addresses this topic as an answer to the Horizon 2020 Euratom NFRP-2018-3 call. The consortium includes 15 partners from eight European countries, involving research institutes, major European nuclear companies and technical support organizations. The 3.5-year project, launched in September 2019, investigates selected safety features of light-water (LW) SMRs with focus on licensing aspects. Providing a comprehensive compliance framework that regulators can adopt and operate, the licensing process of such SMRs could be optimized, helping their deployment. In this prospect, as a result of ELSMOR’s work, this article gives an overview of the specific issues that LW-SMRs may bring about in the different domains of nuclear safety, in terms of: • Methodological standpoints: safety goals, safety requirements, safety principles (defence-in-depth implementation); • Main safety functions of reactivity control, decay heat removal and confinement management; • Severe accident management; • Other safety issues particular to SMRs: use of shared systems; performing of multi-unit probabilistic safety assessment (PSA); spent fuel management, transport and disposal management. In this article, adequate methodologies are developed to deal with these issues and to help assess the safety of LW-SMRs. This work gives a precious synthesis of the safety assessment issues of LW-SMRs and of the associated methodologies developed in the context of the ELSMOR European project
IER 480: TEX-Pu Benchmark (PU-MET-THERM-004) to Test Polyethylene and Lucite Thermal Scattering Laws [Slides]
No full texthttps://ncsp.llnl.gov/program-management/ncsp-technical-program-review/nuclear-criticality-safety-program-ncsp-technical-program-review-2024International audienceThis presentation finds that PMT-004 has four new benchmark cases highly sensitive to PE TSL (2 cases) and PMMA TSL (2 Cases). PE cases were well predicted using MCNP6.2 and ENDF/B-VIII.0. PMMA cases overpredicted by approximately 0.6-0.7% in keff at 20°C. Accepted into 2023 version of the ICSBEP Handbook. Temperature had a large impact on reactivity of the critical configuration. Implications for validation work for thermal cases- need to adjust TSL data to correct temperature as it can have hundreds of pcm effects for a few °C. Future thermal experiments should try and measure reactivity at multiple temperatures to aid in data testing and benchmark adjustment
Rod bundle cooling by a spray system in spent fuel pool accident conditions
No full textInternational audienceThe knowledge of the phenomenology of loss of coolant/cooling scenarios in spent fuel pools is of prime interest since a huge amount of fission product can be released in accident conditions. In this context, the ASPIC facility is dedicated to the study of the heat transfers that occur at the scale of one rod bundle stored in a spent fuel pool cell. Investigations have been carried out on a full high assembly composed of 17 × 17 electrically heated rods. The water level in the cell is controlled and set, in this test series, so that about one meter of the assembly is uncovered. Therefore, the upper part of the assembly gets overheated unless some counter measure is undertaken. In this contribution, the ability of a spray system to limit the temperature rise of the uncovered part of the rod bundle is assessed. It has been observed that the water spray reduces the temperature level on the whole cross section of the assembly and lowers significantly the risk of degradation of the rod bundle. Besides, for a bundle heat power of 20 kW, a spray mass flow rate of 10 gs−1 or higher leads to rod temperatures lower than 480 °C
Exploration of genetic algorithms to build a balanced neutron spectra dataset useful to train unfolding techniques based on artificial neural networks
No full textInternational audienceDiverse domains need neutrons unfolding technics to assess the incident neutron energy spectrum. Examples are radiation protection, nuclear reactor physics or criticality safety. Traditionally, methods based on the Bayesian approach requires an initial guess of the solution which may significantly impact the unfolding result. This work proposes a novel method for neutron spectrum reconstruction using machine learning (ML) techniques trained on a large dataset. To ensure the ML algorithm to perform on a large domain of application particular attention has been paid to the dataset creation. We propose a comparison of two methods of building large dataset where the most adequate solution is obtained using a dynamic genetic algorithm (GA). This GA targets optimal combinations of 48 parameters to generate a variety of neutron spectra. The resulting dataset is then used to train a new convolutional neural network architecture for unfolding neutron spectra. Obtained performance metrics of the tested architecture show high efficiency and emphasize the added value of the built dataset
Additive Printed Structures for Optical Fiber Sensing in Concrete
No full textInternational audienceDistributed Fiber Optic Sensing (DFOS) is a potent technique for measuring internal strain distribution in civil engineering structures. This method relies on measuring the axial strain of an optical fiber, which is protected by a sensing cable providing mechanical support and coupling to the surrounding material. However, due to the fiber’s sensitivity solely to axial strain, installing the cable along complex paths is often necessary to capture desired data accurately. Precise cable placement is critical for accurate data analysis, as locating the sensing cable within deep concrete or soil layers is challenging. This study introduces a novel approach employing 3D-printed polymer support structures to facilitate the installation of sensing cables along intricate paths. In addition, a novel crack detection method based on computing strain rates is proposed. This innovative technique shows promise for advancing crack monitoring in civil engineering structures, offering enhanced accuracy and efficiency in identifying structural vulnerabilities
Burning Rate and Carbon Monoxide Production for an elevated pool fire in a weakly ventilated compartment
No full textInternational audienceThis work concerns the study of fires in ventilated compartments, and in particular scenarios involving fire located in the upper part of a room near ceilings and in under-ventilated conditions. These complex scenarios are poorly understood and require better knowledge for fire risk assessment. A reduced-scale experimental study with dodecane pool fires was carried out to investigate the coupled influence of fire elevation and compartment ventilation flowrate. The fire characteristics of interest are burning rate and CO production. The results show that fire elevation and ventilation flow rate have opposite influence on burning rate. The net balance is a positive effect of elevation, increasing the burning rate even in an oxygen-poor environment. On the contrary, elevation and ventilation flowrate have a same positive influence on CO production and contribute to its increase. This work shows the complexity of a fire in the upper part of a poorly ventilated room and provides new knowledge to improve its prediction for safety assessments