Thermal hydraulic investigations of a molten salt burner reactor

Molten Salt Reactors (MSRs) can be used as effective burners of TRU from LWR spent fuel. For this paper a study was made to examine the thermal hydraulic behaviour of the conceptual study of the MOlten Salt Advanced Reactor Transmuter (MOSART) (Ignatiev et al. 2003a). The molten salt fuel is a ternary NaF-LiF-BeF2 system fuelled with 1% mole typical compositions of TRU trifluorides from LWR spent fuel. The reactor core does not contain graphite structure elements, so the neutron spectrum is relatively hard in order to improve the burning performance. Without structure elements in the core, the flow pattern is potentially complex and may affect significantly the fuel temperature distribution in the core. Therefore, some optimizations of the salt flow may be needed. Here, the main attention has been paid to the fluid dynamic simulations of the MOSART core with the code SIMMER-III (Kondo et al. 1999). For the simulation, a complete equation of state (EOS) for this liquid fuel had to be developed and implemented in the SIMMER-III code. Through those simulations it was concluded that the thermal hydraulic behaviour appeared to be very important in molten salt reactors concerning design and safety. A distribution plate design was found effective to optimize the flow pattern in the core region. Further investigations are under way to obtain optimal flow fields without exceeding design limits. (authors)