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

Magnetic field effects on three-dimensional natural convection (S23)

We study the structure of a magnetoconvective flow. The magnetic field modifies the heat fluxes at the walls. It tends to destroy the three-dimensional patterns in favor of two-dimensional rolls. The last part of this paper consists in an extent to the marginal stability theory, thanks to a finite difference scheme. We also present the validation of the developments of the finite volume code Jadim, thanks to the simulation of magnetohydrodynamic (MHD) flows that have analytical solutions

On the EU-Japan roadmap for experimental research on corium behavior

A joint research roadmap between Europe and Japan has been developed in severe accident field of light water reactors, focusing particularly on reactor core melt (corium) behavior. The development of this roadmap is one of the main targets of the ongoing EU project SAFEST. This paper presents information about ongoing severe accident studies in the area of corium behavior, rationales and comparison of research priorities identified in different projects and documents, expert ranking of safety issues, and finally the research areas and topics and their priorities suggested for the EU-Japan roadmap and future bilateral collaborations. These results provide useful guidelines for (i) assessment of long-term goals and proposals for experimental support needed for proper understanding, interpretation and learning lessons of the Fukushima accident; (ii) analysis of severe accident phenomena; (iii) development of accident prevention and mitigation strategies, and corresponding technical measures; (iv) study of corium samples in European and Japanese laboratories; and (v) preparation of Fukushima site decommissioning

A promising method for polyurethane recycling: vitrimerization through the activation of carbamate exchange by organic catalysts

International audienceIn this work, we studied the effect of several organic catalysts on lab synthesized and industrial PU, and compared them to reference organometallic catalysts. We evaluated the activity of catalysts through rheology, DMA and stress-relaxation measurements with several PU formulations and the continuous reprocessing in internal mixer of the industrial PU with the best catalysts

A promising method for polyurethane recycling: vitrimerization through the activation of carbamate exchange by organic catalysts

International audienceIn this work, we studied the effect of several organic catalysts on lab synthesized and industrial PU, and compared them to reference organometallic catalysts. We evaluated the activity of catalysts through rheology, DMA and stress-relaxation measurements with several PU formulations and the continuous reprocessing in internal mixer of the industrial PU with the best catalysts

Fukushima Daiichi fuel debris simulant materials for the development of cutting and collection technologies

International audienceCutting fuel debris (solidified corium) is an important issue for the decommissioning of Fukushima Daiichi Nuclear Power Station. The main reasons for developing and using fuel debris simulants are presented. The relative merits of the various types of materials (stainless steel, zirconium, sintered alumina-zirconia, cast fused zirconia, metal+zirconia, melted inactive simulants, prototypic fuel debris simulant, irradiated fuel debris simulant) that can be used to simulate fuel debris cutting have been assessed against criteria relevant for the cutting technique itself (hardness, melting temperature, elastic modulus, toughness, heterogeneity) as well as relevant to (radioactive) aerosol and combustible gas generation. It appears that simplified simulants can be used for the development of fuel debris cutting techniques but have some limitations in terms of representativity so that melted inactive fuel debris simulant must be used to assess the cutting performance. Concerning combustible gas generation, zirconium plates will provide an upper bound in term of underwater generation of hydrogen. Finally, for aerosol and dust generation, it appears that non-radioactive simulant cannot correctly represent the aerosol formation during cutting. Prototypic fuel debris simulant, using depleted uranium and natural isotopic composition for the fission product elements are the best available option for determination of cutting secondary outlet

Steel oxidation phenomena during Molten Corium siliceous Concrete Interaction (MCCI)

International audienc