SIMMER-III. A coupled neutronics-thermohydraulics computer code for safety analysis

The SIMMER-III code is a two-dimensional, multi-velocity-field, multi-phase, multi-component, Eulerian, fluid-dynamics code coupled with a fuel-pin model and a space- and energy-dependent neutron transport kinetics model. Since SIMMER-III is expected to become a standard tool for fast reactor safety analysis with likely application to licensing calculations, the code must be demonstrated to be sufficiently robust and reliable. For this purpose, a systematic assessment program of the code has been conducted in cooperation with European partners. The philosophy behind the code development was to generate a versatile and flexible tool, thus SIMMER-III has been applied to safety analyses of various reactor types with different neutron spectra and coolants. Since the three-dimensional representation of the core enables realistic distribution of the materials constituting the core including control rods, the development of SIMMER-IV has been performed to be a direct extension of SIMMER-III to three dimensions with retaining exactly the same physical models as SIMMER-III. Recently, the parallelization of SIMMER-IV has been made to allow applications to reactor calculation within available computational resource. A three-dimensional calculation with SIMMER-IV is presented to indicate more realistic accident scenario. (author)