Asymmetric Blowdown Loads on PWR Primary Systems – Resolution of Generic Task Action Plan A-2 (NUREG-0609)

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Publication Information

Manuscript Completed: November 1980
Date Published: January 1981

Prepared by:
S. B. Hosford, Task Manager, R. Mattu, R. 0. Meyer, E. D. Throm, C. G. Tinkler

Diviison of Safety Technology
Office of Nuclear Reactor Regulation
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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The NRC staff, after being informed of newly identified asymmetric loadings resulting from postulated ruptures of primary piping, initiated a generic investigation, Task Action Plan A-2. This investigation was limited to pressurized-water-reactor (PWR) plants because of their higher primary system pressures and potential for larger asymmetric loads. The intent of the investigation was to develop a better understanding of this complicated phenomenon and then to develop acceptable criteria and guidelines for the staff to use for evaluating plant analyses.

The staff has completed its investigation and concludes that an acceptable basis is provided in this report for performing and reviewing plant analyses for asymmetric LOCA (loss-of-coolant accident) loads. Guidelines and criteria were developed for the following areas: evaluation of the loading transients, evaluation of the structural components, and evaluation of the fuel assembly.

The staff reviewed and approved computer programs and modeling techniques submitted by each PWR nuclear-steam-supply-system vendor for development of the subcooled blowdown- and cavity-pressure components of the loading transient. Audit models were developed to evaluate the structural computer programs and modeling techniques. The audit evaluation has been completed and the methods have been approved for the structural-analysis method submitted by Westinghouse for the Indian Point Unit 3 plant. Structural-analysis methods developed by Babcock and Wilcox and Combustion Engineering will be evaluated when their plant analyses are submitted to NRC. Criteria and guidelines are provided to perform a detailed evaluation of the fuel assembly. Acceptance criteria are also provided so deformed fuel-assembly spacer grids may be evaluated.

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