[en] Highlights: • Progress of the IRSN R&D activities related to the safety assessment of the ITER installation. • Simulation of an accidental scenario with the ASTEC code: loss of coolant in port cell and in vacuum vessel. • Location and chemical speciation of beryllium dusts and tritium. - Abstract: The French “Institut de Radioprotection et de Sûreté Nucléaire” (IRSN) in support to the French nuclear safety authority performs the safety analyses of the ITER experimental installation. We present the progress in the R&D activities related to a better evaluation of the source term in the event of an accident in this installation. These improvements are illustrated by an evaluation of the source term of a LOCA transient with the dedicated ASTEC code.

[en] This paper is devoted to the presentation of a numerical scheme for the simulation of gravity currents of non-Newtonian fluids. The two dimensional computational grid is fixed and the free-surface is described as a polygonal interface independent from the grid and advanced in time by a Lagrangian technique. Navier-Stokes equations are semi-discretized in time by the Characteristic-Galerkin method, which finally leads to solve a generalized Stokes problem posed on a physical domain limited by the free surface to only a part of the computational grid. To this purpose, we implement a Galerkin technique with a particular approximation space, defined as the restriction to the fluid domain of functions of a finite element space. The decomposition-coordination method allows to deal without any regularization with a variety of non-linear and possibly non-differentiable constitutive laws. Beside more analytical tests, we revisit with this numerical method some simulations of gravity currents of the literature, up to now investigated within the simplified thin-flow approximation framework

[en] We propose a numerical method to calculate unsteady flows of Bingham fluids without any regularization of the constitutive law. The strategy is based on the combination of the characteristic/Galerkin method to cope with convection and of the Fortin-Glowinsky decomposition/coordination method to deal with the non-differentiable and non-linear terms that derive from the constitutive law. For the spatial discretization, we use low order finite elements, with, in particular, linear discretization for the velocity and the pressure, stabilized by a Brezzi-Pitkaeranta perturbation term. We illustrate this numerical strategy through two well-known problems, namely the hydrodynamic benchmark of the lid-driven cavity and the natural convection benchmark of the differentially heated cavity. For both, we assess our numerical scheme against previous publications, for Newtonian flow or in the creeping flow regime, and propose novel results in the case of Bingham fluid non-creeping flows

[en] In 2009, EDF started its project to extend the operating life of its Gen II PWRs beyond 40 years. It implied : •a specific program for ageing management, • a safety reassessment in light of the requirements applicable to new reactors (EPR) and the state of the art of nuclear technologies → Prevention of basemat melt-through in case of a severe accident was one issue considered in that framework. Then, post-Fukushima actions were launched in France and the importance of that issue was confirmed.

[en] Highlights: • Deterministic and probabilistic approaches are used for Source Term evaluations. • The Phébus FP results contribute to improve the Source Term evaluations for PWRs. • Iodine and ruthenium behavior have a large impact on the Source Term consequences. • Iodine oxide seems to be one of the major iodine species in releases. - Abstract: The Phébus FP program had a major importance in the development of knowledge on severe accident in the international nuclear safety community and has been helpful for the validation of phenomenological assumptions related to the core melt accident progression and then for the validation of simulation tools. The paper presents the contribution of the Phébus FP program to the calculation of radioactive releases to the atmosphere for reference accident scenarios (named “reference Source Term”) in case of a severe accident in a French PWR. The system-level code ASTEC is used for these evaluations. This approach has then been completed by the probabilistic approach (L2 PSA) which includes calculations of radioactive release for a very large number of accident scenarios. Several years after the last Phébus FP experiment, the paper presents the status of the modeling used for these Source Term calculations, presents some important results, highlights the contribution of previous research programs and explains how more recent results from the ISTP project have also been taken into account. Further expectations for the next few years are presented in conclusion

[en] Highlights: ► IRSN has a first version of ASTEC able to model an accident in ITER. ► Models are developed to make possible water/air ingress simulations in the vessel. ► Some thermal-hydraulic calculations in agreement with MELCOR are discussed. -- Abstract: ASTEC is a code system aiming to compute severe accident scenarios and their consequences in nuclear fission Pressurized Water Reactors (PWRs). Its capabilities have been recently extended to address the main accident sequences which may occur in the fusion installations, in particular in ITER. The purpose of this paper is to present a synthesis of the work that has been performed on ASTEC as part of its adaptation to fusion ITER facility, in particular concerning the development of some specific models (dust behavior, jet impaction and wall oxidation), the state of validation of the code and some first calculations for accident transients considered in the basis design. Comparisons with the MELCOR code, selected by ITER for their own safety analysis are provided and show a good agreement between both codes