United States Nuclear Regulatory Commission - Protecting People and the Environment

Overview of Nuclear Data Uncertainty in Scale and Application to Light Water Reactor Uncertainty Analysis (NUREG/CR-7249, ORNL/TM-2017/706)

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Publication Information

Manuscript Completed: December 2017
Date Published: December 2018

Prepared by:
W. Wieselquist
M. Williams
D. Wiarda
M. Pigni
U. Mertyurek

Oak Ridge National Laboratory
Bethel Valley Road
Oak Ridge, TN 37831

Mourad Aissa, NRC Project Manager

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

This report presents the current state of the art in SCALE for nuclear data uncertainty analysis capability, and it provides an overview of the uncertainty in multigroup cross sections, fission product yields, and decay data. The effect of nuclear data uncertainty is demonstrated for a typical light water reactor (LWR) depletion analysis problem involving a Combustion Engineering 14 × 14 assembly irradiated in Calvert Cliffs Unit 1. A single fuel rod from assembly D047, designated as MKP109, has been subjected to destructive radiochemical assay to measure the isotopic contents.

The 95% range width (difference between the 97.5th and 2.5th percentiles) is used in this study to assess the calculation uncertainty. This approach uses the actual distribution of the data and does not make any assumptions about the normality of the distributions. If the distribution were normal, then the 95% range width would correspond to 4-sigma range, or +/- 2 sigma.

The calculation uncertainty determined in nuclide concentrations for the MKP109 rod ranges from a few percent to 50%. The power factor for this fuel rod shows a very low uncertainty of less than 0.5%.

Uncertainties in the macroscopic cross sections, reactivity, and power distributions are generally low, in the few percent range. The effective delayed neutron fraction, βeƒƒ, shows higher uncertainty of 20–100%.

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