Environmental Effects of Extending Fuel Burnup Above 60 Gwd/MTU (NUREG/CR-6703)

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Publication Information

Manuscript Completed: November 2000
Date Published: January 2001

Prepared by:
J. V. Ramsdell, Jr., C. E. Beyer, D. D. Lanning,
U. P. Jenquin, R. A. Schwarz, D. L. Strenge,
P.M. Daling, R. T. Dahowski

Pacific Northwest National Laboratory
Richland, WA 99352

T. J. Kenyon, NRC Project Manager

Prepared for:
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code J2441

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Abstract

In 1988, the U. S. Nuclear Regulatory Commission published an environmental assessment (EA) of the effects of increasing nuclear reactor peak-rod fuel irradiation (burnup) up to 60 gigawatt days per metric ton of uranium (GWd/MTU). The EA was based, in large part, on the evaluation of environmental impacts of extended fuel burnup in NUREG/CR-5009. This report updates the information in NUREG/CR-5009 using current fuel designs, fuel performance data, and dose computational methods. It contains a best-estimate assessment of the environmental and economic impacts of extending peak-rod burnup above 60 GWd/MTU.

Inventories were calculated for burnup up to 75 GWd/MTU, and gap-release fractions were calculated up to 62 GWd/MTU. Evaluation of gap-release fractions is limited to 62 GWd/MTU by the methods for estimating release fractions. Gap-release fraction estimates for burnup up to 62 GWd/MTU remain below the release fractions assumed in current guidance associated with evaluation of the environmental consequences of potential accidents, although gap-release fractions for current fuel designs are larger than estimated in NUREG/CR-5009. The increase in gap-release fraction may lead to an increase in the potential environmental impacts of normal operation and accidents involving loss of reactor coolant, if the gap activity is released to the environment. However, even though burnup has been increasing, coolant activity has been decreasing as bumup has increased as a result of better control in fuel-rod fabrication.

There will be a reduction in the environmental effects of the front end of the fuel cycle with increased burnup because increases in burnup to 75 GWd/MTU can be achieved without further increases in enrichment.

The environmental consequences of normal operation are expected to remain small as peak-rod burnup increases because the regulatory limits on releases are independent of burnup. The requirements of 10 CFR 50.36a and Appendix I to 10 CFR Part 50 ensure that releases of radioactive materials to unrestricted areas are kept "as low as reasonably achievable." The volume of low-level waste should continue to decrease as the time between refueling outages increases to achieve higher burnups. The reduced fuel throughput associated with increased bumup will also reduce onsite spent fuel storage facility demands.

The potential environmental consequences of postulated accidents are not expected to increase significantly with increased burnup. The changes in potential consequences from postulated loss of coolant accidents, pressurized-water reactor (PWR) steam generator tube rupture accidents, boiling-water reactor (BWR) main steam line break accidents, and fuel handling accidents were all evaluated and found to be small. The potential doses from each of these accidents remain well below regulatory limits.

Potential environmental effects of incident-free transportation of spent fuel and the accident risks associated with spent-fuel transportation do not change significantly with increasing burnup up to 75 GWd/MTU, provided that fuel is cooled for at least 5 years before shipment. For all reactors, the estimated environmental impacts of transportation are bounded by the impacts in 10 CFR 51.52, Table S-4.

For those aspects of this assessment not significantly affected by the gap-release fraction, the findings indicate that there are no significant adverse environmental impacts associated with extending peak-rod burnup to 75 GWd/MTU. For those aspects affected by the gap-release fraction, the findings in the report indicate that there are no significant adverse environmental impacts associated with extending peak-rod burnup to 62 GWd/MTU.