Theoretical Development of Cross-section Uncertainty Library FOR CORE Simulators

The current regulatory process allows for the use of models employing realistic assumptions as opposed to conservative bounding approaches. Achieving that requires a concerted use of best-estimate modeling and comprehensive estimation of uncertainties, collectively referred to as BEPU (best-estimate-plus-uncertainty) methods. This necessitates access to an integrated and automated procedure for the propagation and understanding of key sources of uncertainties. Focusing here on neutronic reactor core simulation, this manuscript lays the theoretical foundations for an uncertainty framework that is comprehensive, informative, and efficient, implying its ability to propagate all sources of uncertainties and identify key contributors to quantities of interest in a computationally efficient manner, suitable for routine day-to-day calculations. This represents the overarching objective of our work, demonstrated here for the propagation of multi-group cross-sections uncertainties through lattice physics calculations and core-wide simulation. This requires the evaluation of few-group parameters uncertainties in terms of a wide range of local conditions, e.g., burnup, fuel temperature, etc., which results in a very high dimensional uncertainty space. This manuscript employs an accuracy-preserving compression approach relying on the use of range finding algorithms to construct all few-group parameters variations to a very small preset tolerance. In a separate co-submitted manuscript, this framework is demonstrated to thermal reactors including both light and heavy water systems using a number of computer codes, including NESTLE-C, SERPENT, SCALE's NEWT and SAMPLER codes.