United States Nuclear Regulatory Commission - Protecting People and the Environment

A Quantitative Impact Assessment of Hypothetical Spent Fuel Reconfiguration in Spent Fuel Storage Casks and Transportation Packages (NUREG/CR-7203)

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Publication Information

Manuscript Completed: April 2015
Date Published: September 2015

Prepared by:
J. M. Scaglione, G. Radulescu, W. J. Marshall, K. R. Robb

Oak Ridge National Laboratory
Managed by UT-Battelle, LLC
Oak Ridge, TN 37831-6170

M. F. Bales, NRC Project Managerr

NRC Job Code N6789/N6686

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

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Abstract

Based on the current knowledge, commercial spent nuclear fuel (SNF), including high burnup fuel (burnup > 45 GWd/MTU) in the United States can be stored and transported safely in accordance with the respective regulatory requirements. The NRC periodically conducts research activities to confirm the safety of operations and enhance the regulatory framework to address any changes in technology, science, and policies. This includes analyses of beyond design basis conditions to confirm that regulatory requirements continue to provide reasonable assurance for safe storage and transportation of spent nuclear fuel. The research documented in this report is an effort of such nature.

This report documents an evaluation of the impact of a wide range of extremely unlikely postulated fuel reconfigurations under non-mechanistic causes of fuel assembly geometry change with respect to four technical disciplines: criticality, shielding (dose rates), containment, and thermal. The term “fuel reconfiguration” refers to any change to the storage and transportation system nominal intact fuel assembly configuration used for the basis of cask certification. Many configurations were considered to be physically unlikely realizable scenarios.

Three fuel reconfiguration categories were considered: configurations characterized by (1) cladding failure, (2) rod/assembly deformation without cladding failure or (3) changes to assembly axial alignment without cladding failure. The analyses considered representative SNF designs and storage cask/ transportation packages, and a range of fuel initial enrichments, discharge burnup values, and decay times.

Overall, the safety impacts of fuel reconfiguration are system design, content type, and loading dependent. The areas and magnitude of the impact vary from cask/package design to cask/package design. It should also be noted that some of the scenarios are extreme and physically unlikely to occur; they represent bounding values. The spent fuel storage systems and transportation packages approved by the NRC to date provide reasonable assurance that they are safe under normal, off-normal, and hypothetical accident conditions as prescribed in 10 CFR Part 71 and 72 regulations.

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