A multi-mode electromagnetic stirring technology (MM-EMS) delivered by Danieli-Rotelec Company has been implemented in ArcelorMittal Gent CC2. This solution is able to control the liquid steel flows in CC mould by braking, accelerating or stirring them through the use of three different modes: EMLS, EMLA and EMRS. This paper presents the methodology followed in order to optimize the working of this new technology for improving the quality of products in terms of slivers defects. Different tools were developed and used by ArcelorMittal Maizières R&D to reach this objective: Numerical simulation with MagnetoHydroDynamics (MHD) tool to simulate the fluid flows in mould under the influence of magnetic fields, Submeniscus Velocity Control (SVC) tool to directly measure the liquid steel flows in the mould and finally some quality investigation tool like Automatic Surface Inspection System to detect defects directly on coils and qualify quality of products. Numerical and experimental approaches were associated to finally deliver to ArcelorMittal Gent steelplant an optimized actuator efficient for reducing defects in slabs and improving the final quality of products.

In the framework of the research and development on GEN IV sodium fast reactors (SFRs), the phenomenology of sodium boiling during a postulated unprotected loss of flow (ULOF) transient has been investigated with the CATHARE 2 system code. This study focuses on a stabilized boiling case: in such a regime, no flow redistribution occurs from the subassemblies which have reached the saturation temperature to those that are still single-phase. In this paper, for a subassembly design featuring no restrictive structures above the fuel bundle, a quasi-static approach is first developed to get an upper bound of the reactor core power at boiling onset that would be compatible with the well-known Ledinegg criteria for diphasic flow static equilibrium. Then, dynamics results achieved through simulation with the CATHARE 2 code for a postulated ULOF are presented: boiling is shown to remain stable during the transient for such a core power at boiling onset. Another important outcome of the simulation is the calculation of a dynamic instability, in the form of a two-phase hydrodynamic chugging phenomenon. The predicted phenomenology of this stabilized boiling case should be studied further in order to consider its dependency on the underlying closure laws and to eliminate the possibility of a numerical instability.

The computational codes used in the evaluation of the ESFR-SMART reactor performance and specifically their sodium boiling models are assessed using two KNS-37 LOF experiments, i.e. L22 and L29 tests, where boiling onset and two-phase flow regime up to dry-out occurred. The well-equipped KNS-37 experimental facility provided very valuable information for understanding the physical phenomena occurring in a 37-pin subassembly under LOF conditions, as well as experimental data to be used for computational tools validation. NATOF-2D, SAS-SFR, TRACE, ASTEC-Na, CATHARE-2 & CATHARE-3 and NEPTUNE_CFD codes have been used in this exercise in order to compare the various boiling models and conclude on the advantages and limitations of them based on the comparison against the experimental data. Beyond boiling onset, the various sodium two-phase flow approaches determine the ability of the code to correctly represent the rewetting and voiding phases as well as cladding dry-out onset. A simulation performed by a CFD approach (NEPTUNE_CFD code) considering liquid-vapor interfaces by an interface-tracking method is also shown and compared with the others approaches. Conclusions on each code performance are presented where the improvements needed to solve the issues encountered are included. This paper provides a first step in the process to investigate the required evaluation of the sodium two-phase flow models able to assess the safety of new SFR core designs (e.g. low void cores) under accidental conditions such as ULOF transients.