Reactor Pressure Vessel Failure Probability Following Through-Wall Cracks Due to Pressurized Thermal Shock Events.

摘要

A fracture mechanics model was developed at the Pacific Northwest Laboratory (PNL) to predict the behavior of a reactor pressure vessel following a through-wall crack that occurs during a pressurzed thermal shock (PTS) event. The study contributed to a U.S. Nuclear Regulatory Commission (NRC) program to study PTS risk. The model predicts the arrest, reinitiation, and direction of crack growth for a postulated through-wall crack and thereby predicts the mode of vessel failure. A Monte-Carlo type of computer code was written to predict the probabilities of the alternative failure modes with the fracture mechanics properties of the various welds and plates of a vessel as random variables. Plant-specific calculations for the Oconee-1, Calvert Cliffs-1, and H.B. Robinson-2 reactor pressure vessels for the conditions of postulated transients predicted that 50% or more of the through-wall axial cracks will turn to follow a circumferential weld. The predicted failure mode results in a potential vertically-directed missile consisting of the upper head assembly. Missile arrest calculations predict that such vertical missiles, as well as all potential horizontally directed fragmentation type missiles, will be confined to the vessel enclosure cavity. The PNL failure mode model is recommended for use in future evaluations of other plants, to determine the failure modes that are most probable for postulated PTS events.