THERMAL HYDRAULIC CALCULATIONS OF THE IRT-SOFIA RESEARCH REACTOR WITH LEU FUEL IRT-4M, SOFIA

The neutronic calculations of the IRT-Sofia research reactor with fuel assemblies (FA) of the IRT-4M type, containing low enriched uranium (19.75%), confirmed the justness of the selection of its initial core configuration. On the basis of the neutronic calculation results the thermal-hydraulic calculations were done by PLTEMP code. Three possible operational regimes have been considered. For each of them the margin coefficients of the water onset of the nucleate boiling (ONB) have been determined. An analysis has been made on the fuel element surface for the particular fuel assembly with maximum power density. The calculations have been accomplished for the core water inlet temperature of 45 degrees C. The results are in compliance with the thermal-hydraulic safety requirements. This is valid for all analyzed regimes.