Current status of thermohydraulic validation studies at CEA-Grenoble for the SIMMER-III code

SIMMER-III (SIII) is a two-dimensional, three-velocity-field, multiphase, multicomponent, Eulerian, fluid-dynamics code coupled with a space- and energy-dependent neutron kinetics model, to investigate postulated core disruptive accidents in LMFRs. It is developed by PNC, Japan. The paper makes the synthesis of the SIII assessment performed at CEA-Grenoble since 1996, which covers a large variety of multiphase flows, from two-phase flow basic modelling to LMFR accident simulation experiments with real materials. Single bubbles or droplets equilibrium radii and velocities, air/water experiments in tubes, and comparisons with the literature, are used to qualify the interfacial area convection equation and the momentum exchange functions. Using the second order differencing scheme of the Navier-Stokes equation, a turbulence model for two-phase recirculating flows is implemented. It is successfully validated on an adiabatic air/water experiment, and on the Sebulon boiling pool simulation experiment, which is a box of water internally heated, with a cover gas, and cooled at the walls. The successful calculations of the SGI experiment and of a reactor scale case contribute to the code validation for LMFR expansion phase. Besides, the large scale UO2/sodium interactions of the Termos T1 experiment, and the UO2 boiling pool laterally cooled with sodium flow at the wall of the Scarabee BF2 experiment, is also studied with SIM Lastly, satisfying results are obtained with the calculation of the Scarabee APL3 slow pump run down without scram. It is shown that SIII is a state-of-the-art tool to simulate transient multiphase phenomena. The paper also discusses those areas, identified through these assessment calculations, which require further research and development. (author)