Overview of key thermal–hydraulic phenomena in severe accident unfolding: Current knowledge and further needs

Severe Accidents (SA) developments are closely and deeply linked with thermal-hydraulics, that is, fluid flow combined with heat and mass transfer. The present paper synthesizes this relation during an accident unfolding and provides an overview of the remaining gaps associated to thermal-hydraulics that need to be addressed to reduce the uncertainties associated to SA and to optimize their management. Some of those thermal–hydraulic phenomena are common to other areas, but most of them are genuine to the SA domain. In addition to thermal–hydraulic phenomena affecting SA development, there are others major SA consequences, like fission product transport and eventual release to the environment, that are heavily affected by thermal–hydraulic boundary conditions and need to be investigated under the anticipated accident conditions. There is a consensus that any investigation to be launched in the coming years should have a direct impact on either reducing the uncertainties associated to their modelling or on optimizing their management, or on both; such consensus was soundly built in the EC EURSAFE project and has been renewed under the frame of the SARNET projects and the SNETP/NUGENIA/TA2 activities

NUGENIA/TA2 Achievements in Severe Accidents Research (2015-2020)

Severe accident research is the only way to achieve the best possible management in case such unlikely events eventually happen. Early this century, the Severe Accident Research NETwork (SARNET) was born as an EC project and about 10 years later it became the technical area 2 of NUGENIA, the SNETP (Sustainable Nuclear Energy Technological Platform) pillar devoted to research on Gen. II and Gen. III Light Water Reactors (LWRs). This paper describes the most relevant outcomes from NUGENIA/TA2 research in the last five years concerning coolability of in-vessel and ex-vessel corium/debris, in-containment phenomena and source term; besides, the progress made and underway on severe accident modelling is outlined. Finally, the NUGENIA/TA2 commitment to knowledge dissemination through courses and conferences is highlighted

Main Outputs from the OECD/NEA ARC-F Project

The Analysis of Information from Reactor Buildings and Containment Vessels of Fukushima Daiichi Nuclear Power Station (FDNPS) (ARC-F) project was initiated in January 2019 for three years with 22 signatories from 12 countries. Three main tasks were implemented in the ARC-F project, which were relevant to 1) refinement of analysis for accident scenarios and associated fission product (FP) transport and dispersion, 2) compilation and management of data and information, and 3) discussion for the next-phase project. Various activities were performed in Task 1, covering improvement of analysis for accident scenarios, and in-depth analyses for specific phenomena such as in-vessel melt progression, molten core/concrete interaction, FP transport and source term, hydrogen combustion and atmospheric dispersion of FPs. Through these studies, analyses for accident scenarios with severe accident codes were refined and important phenomena with large uncertainties were clarified. In order to share well selected and organized information from the FDNPS with the project partners, two databases, information source database and sample database, were built under Task 2. The analysis techniques including the separation of iodine species were developed also in Task 2 and applied to the analysis of FPs in several samples taken from the FDNPS. The next-phase project was discussed in Task 3, resulting in launching the Fukushima Daiichi Nuclear Power Station Information Collection and Evaluation (FACE) project. The FACE project officially started in July 2022 with the participation of 23 organizations from 12 countries and the European Commission

Evaluation of the Impact That PARs Have on the Hydrogen Risk in the Reactor Containment: Methodology and Application to PSA Level 2

This paper presents a methodology and its application to a Level 2 Probabilistic Safety Assessment (PSA-2), to evaluate the impact of the Passive Autocatalytic Recombiners (PARs) on the hydrogen risk in the reactor containment in case of a severe accident. Among the whole set of accidental scenarios calculated in the framework of the PSA-2, nine have been selected as representative in terms of the in-vessel hydrogen production rate and in-vessel total produced hydrogen mass. Five complementary scenarios have been added as representative of the core reflooding situations. For this set of selected scenarios the evolution of the conditions in the containment (i.e., pressure, temperature, and composition) during the in-vessel phase of the accident has been evaluated by means of a lumped parameter approach. The use of spray systems in the containment has also been considered as well as the presence of recombiners. Moreover, the ignition by recombiners of the flammable atmosphere has been considered

The role of protein modifications in senescence of freeze-dried Acetobacter senegalensis during storage

Background Loss of viability is one of the most important problems during starter culture production. Previous research has mostly focused on the production process of bacterial starters, but there are few studies about cellular protein deterioration causing cell defectiveness during storage. In the present study, we investigated the influence of storage temperature (−21, 4, 35°C) on the cellular protein modifications which may contribute to the senescence of freeze-dried Acetobacter senegalensis. Results Heterogeneous populations composed of culturable cells, viable but non-culturable cells (VBNC) and dead cells were generated when freeze-dried cells were kept at −21 and 4°C for 12 months whereas higher storage temperature (35°C) mainly caused death of the cells. The analysis of stored cell proteome by 2D-DiGE demonstrated a modified pattern of protein profile for cell kept at 4 and 35°C due to the formation of protein spot trains and shift of Isoelectric point (pI). Quantification of carbonylated protein by ELISA showed that the cells stored at 4 and 35°C had higher carbonylated protein contents than fresh cells. 2D-DiGE followed by Western blotting also confirmed the carbonylation of cellular proteins involved in translation process and energy generation. The auto-fluorescent feature of cells kept at 35°C increased significantly which may be an indication of protein glycation during storage. In addition, the percentage of cellular unsaturated fatty acid and the solubility of cellular proteins decreased upon storage of cells at higher temperature suggesting that peroxidation of fatty acids and possibly protein lipidation and oxidation occurred. Conclusions High storage temperature induces some deteriorative reactions such as protein oxidation, lipidation and glycation which may cause further protein modifications like pI-shift, and protein insolubility. These modifications can partly account for the changes in cell viability. It can also be deduced that even moderate carbonylation of some critical cellular proteins (like ribosomal proteins) may lead to VBNC formation or death of freeze-dried bacteria. Moreover, it seems that other mechanisms of biomolecule deterioration preceding protein carbonylation lead to VBNC formation under very low storage temperature

Etude protéomique de la reprogrammation métabolique lors de la transformation tumorale des astrocytes

Metabolic reprogramming is one of the main characteristics of cancer cells that adapt their energy metabolism to promote cell survival and tumor proliferation. This reprogramming includes all metabolic, enzymatic, proteic or genetic adaptations, allowing cancer cells to create a favorable microenvironment for their survival and growth. In fact, cancer cells display an aberrant metabolic behavior generating ATP through an inefficient glycolysis pathway even in the presence of adequate oxygen supply. Recent works have shown that the genetic alterations that contribute to cancer development affect a number of oncogenic signaling pathways driving several tumor metabolic modifications that are essential for malignancy. Those changes in metabolic pathways allow cancer cells to facilitate their uptake and release of nutrients that can be transformed into building blocks for nucleotide, protein and lipid synthesis necessary for macromolecule assembly and tumor growth.We exploited the analytical potential of the 2D-DIGE (two-dimensional differential in-gel electrophoresis) quantitative proteomic analysis to characterize the proteomes of mouse astrocytes that underwent in vitro cancerous transformation, and of their normal counterparts. We aimed to identify and characterize the protein signature of those in vitro transformed cells in an attempt to understand their neoplastic behavior and the effect of transformation on metabolic processes.Metabolic reprogramming effects on enzymatic and structural protein expression as well as associated metabolites abundance were quantified. A total of 143 unique proteins were found to be affected by this transformation process. Using enzymatic activity measurements and zymography, we documented and confirmed several changes in abundance and activity of various isoenzymes likely to participate in metabolic reprogramming. We found that after transformation, the cells increase their expression of glycolytic enzymes, thus acquiring the ability to use aerobic glycolysis (Warburg effect). An increased capacity to dispose of reducing equivalents through lactate production was also documented. Major effects on carbohydrates, amino acids and nucleotides metabolic components were also observed. Conversely, the transformed cells reduced their capacity for tricarboxylic acid oxidation, for neurotransmitters (glutamate and GABA) metabolism and their expression of astroglial markers.&#8195

Advances in the analysis and management of accidents and future challenges: the OECD/NEA WGAMA

International audienceThe OECD Nuclear Energy Agency (NEA) Working Group on Analysis and Management of Accidents (WGAMA) is responsible for activities related to potential accidental situations in nuclear power plants (NPPs) address the safety aspects of existing power reactors and the emerging safety challenges required to enable safety design and operation of advanced and innovative nuclear technologies, including the ones used for small modular reactors. The objective is to assess and, where necessary, strengthen the technical basis needed for the prevention, mitigation and management of potential accidents in NPPs, and to facilitate international convergence on safety issues and accident management (AM) analyses and strategies. As a result, the WGAMA's achievements have been outstanding in preparing technical reports, becoming reference materials, and in organizing workshops and conferences to discuss innovative methods, materials and technologies in the fields of thermal-hydraulics (T/Hs), computational fluid dynamics (CFD) and severe accidents (SAs). The paper aims to review and summarize the recent WGAMA activities and outcomes with focus on in nuclear reactor thermal hydraulics analysis in water cooled reactors and possible applications to advanced designs. Particularly, applicability of major outcomes is discussed in the relevant subjects of passive system (PS), modelling innovation in CFD, severe accident management (SAM) countermeasures, advanced measurement methods and instrumentation, and modelling robustness of safety analysis codes