Molten salt related extensions of the SIMMER-Ⅲ code and its application for a burner reactor

摘要

Molten salt reactors (MSRs) can be used as effective burners of plutonium (Pu) and minor actinides (MAs) from light water reactor (LWR) spent fuel. In this paper a study was made to examine the thermal hydraulic behaviour of the conceptual design of the molten salt advanced reactor transmuter (MOSART) [Ignatiev, V., Feynberg, O., Myasnikov, A., Zakirov, R., 2003a. Neutronic properties and possible fuel cycle of a molten salt transmuter. Proceedings of the 2003 ANS/ENS International Winter Meeting (GLOBAL 2003), Hyatt Regency, New Orleans, LA, USA 16-20 November 2003]. The molten salt fuel is a ternary NaF-LiF-BeF_2 system fuelled with ca. 1 mol% typical compositions of transuranium-trifluorides (PuF_3, etc.) from light water reactor spent fuel. The MOSART reactor core does not contain graphite structure elements to guide the flow, so the neutron spectrum is rather hard in order to improve the burning performance. Without those structure elements in the core, the molten salt in core flows freely and the flow pattern could be potentially complicated and may affect significantly the fuel temperature distribution in the core. Therefore, some optimizations of the salt flow pattern 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, Sa., Morita, K., Tobita, Y, Shirakawa, K., 1992. SIMMER-Ⅲ: an advanced computer program for LMFBR severe accident analysis. Proceedings of the ANP' 92, Tokyo, Japan; Kondo, Sa., Tobita, Y., Morita, K., Brear, D.J., Kamiyama, K., Yamano, H., Fujita, S., Maschek, W, Fischer, E.A., Kiefhaber, E., Buckel, G., Hesselschwerdt, E., Flad, M., Costa, P., Pigny, S., 1999. Current status and validation of the SIMMER-Ⅲ LMFR safety analysis code. Proceedings of the ICONE-7, Tokyo, Japan], which was originally developed for the safety assessment of sodium-cooled fast reactors and recently extended by the authors for the thermo-hydraulic and neutronic models so as to describe the molten salt reactors. For the adaptation to molten salt reactor, a complete equation of state (EOS) for this liquid fuel had to be developed and implemented into 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, operation and safety. A flow 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.