Quantification of the maximum heat flux bias introduced by modelling assumptions on the basis of the BR2 LEU representative core

In this study the potential underprediction of the actual maximum heat flux due to different modelling assumptions, is quantified in order to account any possible bias in the future thermal hydraulic safety limit evaluation of Belgian Reactor 2 (BR2) LEU driver fuel. To do so, the maximum heat flux along the hottest fuel plate, and for different fuel element locations in the foreseen Low Enriched BR2 core configuration was computed using the MCNP-6.2 code. The base case, where all the fuel materials of the core were depleted up to 30 days, assumed that the outer-most fuel plate of an assembly of interest is burned as one homogenous azimuthal region. From there, two modeling variations were investigated. For the first variant, the outer-most fuel plate of interest was now depleted with a heterogeneous 60-bin mesh that was azimuthally imposed on the fuel material. For the second variation, the latter heterogeneous assembly model was azimuthally rotated 180°.