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Science and Technology of Nuclear Installations
Volume 2012, Article ID 767096, 9 pages
Research Article

A Two-Step Approach to Uncertainty Quantification of Core Simulators

1Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109, USA
2Reactor Safety Research Division, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, Boltzmannstraße 14, 85748 Garching bei München, Germany
3Reactor and Nuclear Systems Division, Oak Ridge National Laboratory, P.O. Box 2008 MS6172, Oak Ridge, TN 37831, USA

Received 30 July 2012; Accepted 7 December 2012

Academic Editor: Kostadin Ivanov

Copyright © 2012 Artem Yankov et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


For the multiple sources of error introduced into the standard computational regime for simulating reactor cores, rigorous uncertainty analysis methods are available primarily to quantify the effects of cross section uncertainties. Two methods for propagating cross section uncertainties through core simulators are the XSUSA statistical approach and the “two-step” method. The XSUSA approach, which is based on the SUSA code package, is fundamentally a stochastic sampling method. Alternatively, the two-step method utilizes generalized perturbation theory in the first step and stochastic sampling in the second step. The consistency of these two methods in quantifying uncertainties in the multiplication factor and in the core power distribution was examined in the framework of phase I-3 of the OECD Uncertainty Analysis in Modeling benchmark. With the Three Mile Island Unit 1 core as a base model for analysis, the XSUSA and two-step methods were applied with certain limitations, and the results were compared to those produced by other stochastic sampling-based codes. Based on the uncertainty analysis results, conclusions were drawn as to the method that is currently more viable for computing uncertainties in burnup and transient calculations.