Concentration of osmoregulated periplasmic glucans (OPGs) modulates the activation level of the RcsCD RcsB phosphorelay in the phytopathogen bacteria Dickeya dadantii

International audienceOsmoregulated periplasmic glucans (OPGs) are general constituents of many Proteobacteria. Synthesis of these oligosaccharides is repressed by increased osmolarity of the medium. OPGs are important factors required for full virulence in many zoo-or phytopathogens including Dickeya dadantii. The phytopathogen enterobacterium D. dadantii causes soft-rot disease on a wide range of plant species. The total loss of virulence of opg-negative strains of D. dadantii is linked to the constitutive activation of the RcsCD RcsB phosphorelay highlighting relationship between this phosphorelay and OPGs. Here we show that OPGs control the RcsCD RcsB activation in a concentration-dependent manner, are required for proper activation of this phosphorelay by medium osmolarity, and a high concentration of OPGs in planta is maintained to achieve the low level of activation of the RcsCD RcsB phosphorelay required for full virulence in D. dadantii

Putting residential flexibility management into action with pilot sites in Europe: From Mas2tering to DRIvE projects

The Mas2tering and DRIvE European projects develop a software platform to manage the residential and tertiary energy flexibility in local communities of prosumers. This platform includes forecasting, optimization, cybersecurity and fast-response capabilities modules. Business models and use cases were developed, taking into account the regulatory challenges. The platform will be implemented in five pilot sites across three countries

Bibliographic review of the computer codes and experiments dealing with steam explosion in Europe

Since the Three Miles Island accident in 1979, steam explosion has been considered as a potential risk for PWR nuclear power plants. Among the hypothetical severe accidents induced by a core melting, steam explosion has been intensely studied because it might lead to potentially catastrophic environmental consequences caused by an early and massive containment failure. Assuming that the loss of coolant caused a degradation of the reactor core and its melting, the principal accident sequences can be summarized as follows:- The corium relocates from the core area into the lower plenum and premix coarsely with the water.- A trigger causes a fine scale fragmentation of the corium drops which increases strongly the corium thermal exchange surface and allows the explosive vaporization of the water due to high energy transfers between the corium and the water. During a very short initial period, the pressure rises quickly in the premixing zone and expands through the lower head. The resulting dynamic forces may reach a magnitude sufficient enough to fail the lower head vessel.- At the same time, the interaction zone expands upwards what can cause the acceleration of all the materials above the explosion zone. This slug may fail part of the reactor upper head, thus creating missiles which may be hurled against the containment roof and damage it. In Europe, several research centers have been working on steam explosion for several years. The whole work has been organized so as to share out the study set necessary to fully understand the matter between the different research centers and countries and to pool the final knowledge. The European research program is organized around three main themes: the premixing phase, the steam explosion and the slug impact. For each issue, test-facilities and numerical computations have been realised. This paper comprises a review of the test-facilities and codes available at the present time in Europe concerning steam explosion.On the one hand, the research program is based on the understanding of the local phenomena governing the explosion by means of several complementary test-facilities such as KROTOS, ECO, MICRONIS and TREPAM. On the other hand, it is based on the development of numerical computer codes able to predict globally the pressure pulse propagation like IDEMO, CULDESAC and CASTEM-PLEXUS or codes specialized in the local description of the steam explosion as MC3D and COMETA

Bibliographic synthesis of the experimental and numerical German and French research programs concerning slug impact

International audienceSlug impact is considered as a potential risk for PWR power plants in case of a severe accident. A loss of coolant can cause the degradation of the core and its melting. By falling down in the water remaining in the lower plenum, the corium transfers quickly its energy to the water which vaporizes and causes a steam explosion. The explosion may be powerful enough to accelerate upwards all the materials above the explosion zone and causes, in turn, a slug impact.During this process, the mechanical energy of the explosion is transformed into kinetic energy for the slug. If the slug is energetic enough, it can crush and fail the upper structures. Then the mixture of slug and upper structure pieces may hit the upper head vessel. The impact may fail the upper head or part of it and thus create missiles, ung upwards thanks to the remaining energy.The slug impact is studied by the german and french research centers FZK and CEA-Saclay. FKZ aims at the quantification of the maximum mechanical energy which would not lead to fail the upper head. They investigate this issue by means of the reduced-scale experiments BERDA.The transfer of the experimental results to reactor dimensions using scale factors are based on similarity laws whose validity is checked thanks to the german test-facilities FLIPPER. The understanding of the slug material influence and the extrapolation to the corium is investigated with the french test-facilities SKIPPY.In order to deepen the understanding of the impact process and to extrapolate the experimental results to other combinations of parameters, corresponding theoretical work is being performed with the code ABAQUS for the impact of solid structures and with the code CASTEM-PLEXUS developped by CEA-Saclayfor the impact of liquid projectile against solid structures

A porosity method to model the internal structures of a reactor vessel

International audienceTo take into account the influence of a structure net among a fluid flow, without modelling exactly the structure shape, a concept of "equivalent porosity method" was developped. The structures are considered as solid pores inside the fluid. The method was studied for HCDA in LMFBR, but it can be applied to any problem involving fluid flow getting through a solid net

Comparison of Various Models for the Simulation of a Core Disruptive Accident in the MARA 10 Mock-up.

Abstract not availableJRC.G-Institute for the Protection and the Security of the Citizen (Ispra

A pipe-model to assess the hydrodynamic effects of a blowdown in a 4-loop PWR

Proceedings of the 8th International Conference on Nuclear Engineering (Icone8); Baltimore, USA, April 2-6International audienceDuring the first milliseconds of a Loss Of Coolant Accident in a PWR, a depressurization wave propagates from the break through the whole primary circuit and the reactor. Then the circuit empties progressively with a diphasic regime. The propagation delay of the depressurization wave causes local transient pressuredifferences between various zones of the reactor. The pressure differences around the core zone may damage the fuel assemblies and the core structures. Consequently, the reactor pressure map must be assessed during the blowdown phase. As the depressurization process is very dependent on the break conditions, it is important to model precisely the break hydrodynamic regime and to represent the complete primary circuit.This paper presents CASTEM-PLEXUS hydrodynamic calculations of the blowdown due to a LOCA, in the primary circuit of a four-loop-PWR. The hydraulic circuit isrepresented with a pipe model respecting the 3D component volumes and the average journey of the diphasic water. Specic laws complete the description for section changes and multi-pipe links. The hydraulic peculiarities (pumps, pressure losses and the break) are taken into account thanks to additional constitutive laws and bounding conditions. The initial conditions are those of the reactor nominal rating. The calculation describes the pressure transient coupled with diphasic water mass transfers, due to the break opening and the beginning of the circuit emptying

A porosity model to represent the influence of structures on a fluid flow - Application to a hypothetical core disruptive accident

International audienceIn case of a Hypothetical Core Disruptive Accident (HCDA) in a Liquid Metal Fast Breeder Reactor, the interaction between fuel and liquid sodium creates a high pressure gas bubble in the core. The violent expansion of this bubble loads the vessel and the internal structures, whose deformation is important. An experimental programme was undertaken in France during the 80s to understand the HCDA physical process. Based on a 1/30 scale model of the SUPER-PHENIX reactor, the MARA programme involved ten tests of gradual complexity due to the addition of internal deformable structures.The numerical simulation of the HCDA mechanical effects on the reactor vessel has been carried out with the CASTEM-PLEXUS software. For this purpose, a specific constitutive law was added to this general ALE fast dynamics finite element code.In order to demonstrate the CASTEM-PLEXUS capability to predict the reactor behaviour, axisymmetrical computations of the MARA serie have been confronted with the experimental results. Whereas the CASTEM-PLEXUS results and the MARA tests with few internal structures are in a good agreement, the simulation of the last test (including all the significant internal components) is too conservative. The main reason comes from the fact that the CASTEM-PLEXUS model does not represent several non axisymmetrical structures which have a protective effect on the containment by acting as porous barriers, absorbing energy and slowing down the fluid impacting the containment. A new fluid constitutive law was developped to take into account the presence of the internal structures (without meshing them) by means of an equivalent porosity method. The structures are only described by means of three parameters: a porosity, a shape coefficient and a pressure loss. This paper briefly describes the porosity model implemented in the HCDA constitutive law of the CASTEM-PLEXUS code. The model is numerically validated on an analytical shock tube test. A parametric study assessing the solid parameter influence proves that the internal structures really have a shield effect on the fluid wave impacting the LMFBR vessel in case of a HCDA

Assessment of a clay barrier resaturation in isothermal conditions

Many projects of underground repositories for high level radioactive wastes involve an engineered clay barrier, placed between the waste canister and the surrounding rock. By hydrating progressively, the barrier swells, seals the gaps and provides a good global watertightness. In a high level radioactive waste repository, the maximum admissible temperature for the barrier governs the space between canisters and consequently the cost of the civil engineering works. Thus a precise assessment of this criterion is compulsory. Even though the barrier behaviour depends on the thermal-hydro-mechanical interactions with the canister and the host rock, the study is only focused on the hydraulic behaviour of the barrier without phase change in a first step.A chamber containing one high level radioactive waste canister is simulated for the East of France repository site. A 2D-plane computation is done with the CASTEM2000 code. A cylindrical geometry, composed of a barrier layer surrounded by a site layer, is represented. Two kinds of clay are studied for the barrier.The clay foreseen for the french repository sites is the FoCa clay. But in order to compare our results with those of other european countries, we studied the spanish La Serrata clay too for the barrier. The East of France site is made of a clay, different from the barrier one. To understand the influence of the boundary conditions on the barrier resaturation time, two sorts of boundary conditions are considered for the external site limit: an imposed water pressure or no water flow. On the internal barrier limit, we enforce a water flow equal to zero. Initially, the site is saturated whereas the barrier is partially unsaturated. Neglecting the initial ventilation phase in the repository site, we suppose that the barrier is in thermal equilibrium with the surrounding site. Their average temperature is 50°C.The models implemented in the CASTEM-2000 code are based on the mixed-hybrid finite element formulation. The numerical model used for this computation supposes that air remains at a constant pressure and water only exists in a liquid state. This paper is devoted to the analysis of the barrier resaturation by the site water. A parametric study on the barrier material and the boundary conditions is realised. The results are the water pressure and the saturation versus time and along a radius

Modélisation en dynamique rapide d'accidents dans le circuit primaire des réacteurs à eau pressurisée

CHATENAY MALABRY-Ecole centrale (920192301) / SudocSudocFranceF