Development and first application of a new tool for the simulation of the initiating phase of a severe accident on SFR

In order to improve the safety level of Sodium Fast Reactors, low probability events such as Hypothetical Core Disruptive Accident (HCDA) are analyzed for their potential consequences. The initiating phase of such accidents is of particular interest both for the prevention and the mitigation of routes leading to a large core disruption and recriticalities. Up to now, analysis of the initiating phase of HCDA has been performed with the SAS4A code. The SAS4A accident calculations are based on a multiple-channel approach, which requires that subassemblies or groups of similar subassemblies be represented together as independent channels. The SAS4A severe accident calculation scheme resorts to a simplified treatment in which an average pin is used to represent a channel. A point kinetics model coupled with a feedback reactivity model is also used to provide an estimate of the reactor power level. Both to increase the accuracy and decrease the uncertainties in the prediction of reactor safety margins, a new computational tool is currently under development at CEA Cadarache. The main features of this tool are the ability to provide a detailed sub-channel meshing of the sub-assembly as well as three-dimensional kinetics during severe accident conditions. To fulfill these goals, the fluid-dynamics SIMMER-III code has been coupled to the SNATCH solver using a MPI environment. This coupling allows both to compute the multi-phase and multi-component flows encountered in severe accident conditions and to model the power shape variation during voiding and melting of the different reactor materials. This new calculation scheme relies on a SAS-like multiple-channel treatment, where channel-to-channel heat and momentum exchanges are neglected. In this paper, an overview of the SIMMER-III/SNATCH coupled tool capabilities is provided. A first application of this new tool is also performed and compared with a SAS4A reference calculation. The new SIMMER-III/SNATCH tool proved to be able to model accurately the major phenomenon of the initiating phase i.e. sodium heating and boiling, clad and fuel melting and relocation of the different materials

Thyrotropin receptor, still much to be learned from the patients

In the absence of crystal available for the full-length thyrotropin receptor, knowledge of its structure and functioning has benefitted from the identification and characterization of mutations in patients with various thyroid dysfunctions. The characterization of activating mutations has contributed to the elaboration of a model involving the extracellular domain of the receptor as an inverse tethered agonist which, upon binding of the ligand, relieves the transmembrane domain from an inhibiting interaction and activates it. The models derived from comparisons with other receptors, enriched with the information provided by the study of mutations, have proven useful for the design of small-molecule agonists and antagonists that may be used in the future to treat thyroid dysfunctions. In this review, extrathyroidal expression of the thyrotropin receptor is described, the role of which is still poorly defined

Improvements in simulation tools to be developed within the framework of the ASTRID project

International audienceThe ASTRID design comprises innovative features compared to past designs. The simulation tools being very important to support the ASTRID design option selection and to assist a robust Safety demonstration, the CEA and its industrial partners have launched a large program for developing a new generation of simulation tools. Within the framework of the ASTRID project, the strategy for simulation is to continuously improve the simulation tools and their verification and validation (VetV). Furthermore, this new generation of tools is implemented for the basic design of ASTRID in compliance with the regulatory and schedule requirements. Several examples of computation tool developments in the fields of neutronics, fuel behavior, core mechanics, thermal-hydraulics and severe accident analyses are given. The VetV process, described here for the core studies, is also carried out for others domains by the industrial partners.The approach is closely linked to the realization of the RandD experimental programs, aimed to complete the existing experimental data base and so to validate the new model developments and to decrease the calculation uncertainties. The development program of new simulation tools is ambitious in order to meet the challenges which arise from the innovative design options implemented in ASTRID and for the will to comply with the objectives of the 4th generation reactors

The ‘Coral Bulker’ Fuel Oil Spill on the North Coast of Portugal: Spatial and Temporal Biomarker Responses in Mytilus galloprovincialis

In December 2000, the ship ‘Coral Bulker’ ran aground at the entrance of the port of Viana do Castelo (North–west coast of Portugal). A large amount of fuel oil was spilled and part of it reached the shore. To evaluate the spatial and temporal impact of this oil spill, a field study, and several laboratory toxicity tests were performed using Mytilus galloprovincialis as biological indicator of environmental contamination and the biomarkers glutathione S-transferases (GSTs) and acetylcholinesterase (AChE) as indicative criteria. Fifteen days after the oil spill, mussels collected at stations located near the ship presented higher and lower values of GSTs and AChE activity, respectively. These results, and those obtained in the laboratory toxicity tests, evidence that these biomarkers were sensitive indicators of exposure to this kind of pollution and were able to monitor a spatial impact of the oil spill of at least 10 km, confirming the higher level of contamination near the ship and a contamination gradient along the sampling stations. One year after the accident, such a contamination gradient was no longer evident. This study highlight the potential suitability of a biomarker approach for assessing spatial and temporal impacts of marine pollution accidents, such as fuel oil spills, suggesting the inclusion of these biomarkers in risk assessment studies, as cost-effective and early warning recognized tools. Major advantages and limitations of the biomarker approach used in this study are further discussed