Abstract :
This report describes the SIMMER calculation and analysis of the Special Power Excursion Reactor Tests SPERT-I 12/25 destructive test series using highly enriched fuel plates. The SIMMER-III code combines an advanced multicomponent multiphase fluid dynamics part including multicomponent heat and mass transfer with a fuel pin and structure model and neutron space-time kinetics. Previously, the code had been adapted to zero power plate-type water-moderated research reactors by developing additional physical models. These models had first been used to calculate destructive accidents in low enriched cores. There, the Doppler coefficient dominates all other counter or feedback reactivities. This report shows that for SPERT with highly enriched fuel, additional fluid-dynamic and structure models are needed to explain the power transient for the whole range of reactivity insertions. The new models are proposed which are necessary to recalculate the SPERT tests with a single input parameter set. A selection of transients that extend over reactor periods of 3.2–118 ms of the D-12/25 series is presented. It has been found, that using approximated fuel swelling data that have been extracted from in-pile experiments, additional water evaporation is necessary to find enough counter or feedback reactivity. Measurements of out-of-pile experiments could have been used to shed some light on nucleate boiling, but only qualitative information was found and used in the modeling. The significance is being shown of the physical phenomena leading to counter or feedback reactivities. Because these equally have influence on the time and way the fuel plate disintegrates the destructive tests of SPERT are presented in detail.
