Nonstationary thermohydraulic code – UNSCELM

The UNSCELM code was developed to perform nonstationary thermohydraulic fuel-assembly calculations over cells cooled by a single-phase coolant. In contrast to previously developed codes, the assumption that the pressure is constant in a transverse section of a fuel assembly is not used in this code. This makes it possible to take account of large local nonuniformities over a transverse cross section of a fuel assembly (right up to reverse flows) as well as hydraulically isolated cells. The UNSCELM code was tested on the results of experiments performed at the Physics and Power Engineering Institute (FEI) on a 25-rod assembly cooled by the coolant 22%Na–78%K. The assembly simulated square packing of the fuel elements in a fuel assembly in the core of a lead-cooled BREST-OD-300 reactor. The satisfactory agreement between the computed and experimental distributions attests to the serviceability of the proposed algorithm in the code and the correctness of the closure relations for liquid-metal coolant.