Thermal-hydraulic analysis of a superheat BWR design using two fluid model

In the present study a sub-channel analysis of a superheat BWR fuel assembly with annular fuel rods, is carried out. Since the existing commercial codes are not capable of analyzing and designing the superheat fuel assembly with downward and upward flow, for thermal-hydraulic calculations, the two-fluid THERMIT-2 code was modified and used. The performed modification was based on enhanced adaptive routines for fuel-gap heat transfer and CHF estimation models. Finally, the thermal-hydraulic results such as Axial coolant temperature for liquid and vapor, Radial and axial fuel and cladding temperature, Axial gap conductance variations, Axial void fraction, pressure drop and evaluation of MCHFR, are investigated in this paper. The achieved results show that by using two-fluid and adapted CHF models, the MCHFR is reduced compared with EPRI model. The comparison of obtained results with the previous works, indicate that the fuel and cladding temperature, due to the consideration of the appropriate fuel-gap heat transfer model, are achieved higher.