United States Nuclear Regulatory Commission - Protecting People and the Environment

Examination of Spent PWR Fuel Rods After 15 Years in Dry Storage (NUREG/CR-6831)

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Publication Information

Manuscript Completed: August 2002
Date Published: September 2003

Prepared by:
RE. Einziger, H. Tsai, M.C. Billone, B.A. Hilton*

Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439

*Argonne National Laboratory-West
P.O. Box 2528
Idaho Falls, ID 83403

S. Basu, NRC Project Manager

NRC Job Code Y6248

Prepared for:
Division of Systems Analysis and Regulatory Effectiveness
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

For 15 years 15 x 15 PWR fuel (35.7 GWd/MTU) was stored in a dry inertatmosphere Castor V/21 cask as peak cladding temperatures decreased from =350 to 150°C. Before storage, the loaded cask was subjected to extensive thermalbenchmark tests, during which time the peak temperatures were >400°C. The cask was opened to examine the fuel rods for degradation and to determine if they were suitable for extended storage. In the central region of the fuel column, the measured hydrogen content of the cladding is consistent with the thickness of the oxide layer. At higher elevations, there is less hydrogen than would be expected from the oxide thickness. Migration of hydrogen to the cooler ends of the rod probably occurred during dry storage. The volume of hydrides varies azimuthally around the cladding but all of the hydrides appear to have retained a circumferential orientation. Little or no cladding creep occurred during thermalbenchmark testing and dry storage. Poststorage creep testing indicated that the cladding retains significant creep ductility after dry-cask storage. It is anticipated that the creep would not increase appreciably during additional storage because of the low temperature after 15 years. Based on the Surry fuel rod data, no deleterious effects of 15-years of dry cask storage were observed.

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