On the effects of pre- and post-transient rod positions for TREAT temperature-limited transient powers

A set of KENO models to simulate select TREAT temperature-limited transients using the Transient Reactor eXcursion simulator (T-ReX), a hybrid deterministic-stochastic code, has been prepared. These transients are from the M8CAL experiment series, which are a set of experiments performed to determine the relationship between the fission power generated in the TREAT core and the fission power generated in experiment fuel located in an experiment vehicle. The experiments were performed to provide necessary calibration information specifically needed for planning and analysis of the M8 test series. The models have been prepared using best available information on materials and geometry. These models resulted in somewhat different reactivity values than those that were reported. Control rod positions prior to and post transient were adjusted to yield the reported critical values as well as the reactivity insertions. The effect of using different cross-section libraries as well as continuous energy vs. multigroup treatments were assessed. Finally, transient analyses were performed using T-ReX for both unmodified and modified cases and compared to experimental results. It was observed that the modified rod positions result in better agreement for maximum yield measured during the M8CAL experiments.