Model development of relocation of molten metal fuel in SFR; Comparison between MESFRAC and SAS4A

Among the general GEN IV reactors, SFR (Sodiumcooled Fast Reactor) in Korea choose to use metal fuel because of its inherent safety for severe accidents. There has been a lot of results about safety analysis of SFR using metallic fuel core. There are two representative severe accidents, and, they are seriously studied about CDAs (Core Disruptive Accidents). One is UTOP (Unprotected Transient Over Power) and the other is ULOF (Unprotected Loss Of Power). If power of core is increased or coolant flow in the coolant channel stops, the temperature starts to increase up to its melting temperature. If reactivity exceeded over 1, core power excursion can make further core temperature increase. This can induce the extension of molten fuel which means the molten fuel pool. There is probability of in-vessel retention. The final goal of this study is developing the code model which can predict the relocation of molten fuel inside SFR coolant channel and calculate the criticality to ensure the success of accident termination. In this paper, molten fuel behavior inside coolant channel is calculated and compared to SAS4A accident code to recognize the weakness of the code. This molten fuel analysis code (MESFRAC; MEtal fuel SFR Accident analysis Code) has simple form rather than other code. Heat transfer in cladding and structure, solidification of molten fuel, fuel behavior modeling have been done. In the case of SFR severe accident, to calculate the reactivity of disrupted core, the relocation of molten fuel inside coolant channel is modelling with FORTRAN base. This simple code calculates the inchannel hydrodynamics with 1 dimensional and calculates heat transfer with 2 dimensional way. Up to now, only 3 component is modelled in the channel; liquid molten metal fuel, solidified molten metal, sodium vapor.