Probability of pipe failure in the reactor coolant loops of Babcock and Wilcox PWR plants. Volume 2. Guillotine break indirectly induced by earthquakes

The requirements to design nuclear power plants for the effects of an instantaneous double-ended guillotine break (DEGB) of the reactor coolant loop (RCL) piping have led to excessive design costs, interference with normal plant operation and maintenance, and unnecessary radiation exposure of plant maintenance personnel. This report describes an aspect of the NRC/Lawrence Livermore National Laboratory sponsored research program aimed at exploring whether the probability of DEGB in RCL Piping of nuclear power plants is acceptably small and the requirements to design for the DEGB effects (e.g., provision of pipe whip restraints) may be removed. This study estimates the probability of indirect DEGB in RCL piping as a consequence of seismic-induced structural failures within the containment of Babcock and Wilcox supplied pressurized water reactor nuclear power plants in the United States. The median probability of indirect DEGB was estimated to range between 6 x 10/sup -11/ and 1 x 10/sup -7/ per year. Using very conservative assumptions, the 90% subjective probability value (confidence) of P/sub DEGB/ was found to be less than 1 x 10/sup -5/ per year. 19 refs., 19 figs., 11 tabs.