Modeling Burnup at NRU Loop Sites Using MCNP

Abstract

NRU loop sites offer a unique irradiation capability to test fuel assembly performance at high flux and reactor operating temperatures. Accurate prediction of burnup at the scale of individual fuel pin-segments is a challenge in this highly heterogeneous environment, but must be pursued both to better interpret historic data, and to offer future clients more precise burnup time series.Bundles with different geometries have at times been irradiated simultaneously, in many permutations, and new configurations might be of interest. The preparation of high-fidelity models of these configurations presents a challenge, as the model of the irradiation of a single string of six fuel bundles requires the composition and tracking of approximately 2000 cells. An automated model generation tool is discussed and preliminary simulation results presented.