Development of a Phenomena Identification and Ranking Table (PIRT) for Thermal-Hydraulic Phenomena during a PWR (Pressurized Water Reactor) Large-Break LOCA (Loss-of-Coolant Accident).

摘要

The U.S. Nuclear Regulatory Commission (NRC) is proposing to amend its regulations to permit the use of best-estimate safety analysis codes to demonstrate that the emergency core cooling system would protect the reactor core during a postulated loss-of-coolant accident (LOCA). A key feature of the proposed rule is that the licensee will be required to quantify the uncertainty of the best-estimate calculations and include that uncertainty when comparing the calculated results with the Appendix K limits. The NRC has further proposed a Code Sealing, Applicability, and Uncertainty (CSAU) evaluation methodology. One of the cornerstones of that methodology is the identification and ranking of all the processes that occur during a specific scenario. The ranking is done according to importance during the scenario and is used to limit the uncertainty analysis to a sufficient, but cost effective scope. The work reported in the document identifies the thermal-hydraulic phenomena that occur during a large-break loss-of-coolant accident (LBLOCA) in a Westinghouse four-loop pressurized water reactor and ranks the relative importance of each with respect to peak cladding temperature.