Development of models for the sodium version of the two-phase three dimensional thermal hydraulics code THERMIT

Abstract

Several different models and correlations were developed and incorporated in the sodium version of THERMIT, a thermal- hydraulics code written at MIT for the purpose of analyzing transients under LMFBR conditions. This includes: a mechanism for the inclusion of radial heat conduction in the sodium coolant as well as radial heat loss to the structure surrounding the test section. The fuel rod conduction scheme was modified to allow for more flexibility in modelling the gas plenum regions and fuel restructuring. The formulas for mass and momentum exchange between the liquid and vapor phases were improved. The single phase and two phase friction factors were replaced by correlations more appropriate to LMFBR assembly geometry. The models incorporated in THERMIT were tested by running the code to simulate the results of the THORS Bundle 6A experiments performed at Oak Ridge National Laboratory. The results demonstrate the increased accuracy provided by the inclusion of these effects.