Application of the leak-before-break approach to Westinghouse PWR [pressurized water reactor] piping: Final report

NUREG 1061, Volume 3, puts forth criteria that can be used to demonstrate leak-before-break for high energy piping systems. An accepted leak-before-break methodology for PWR primary loop piping already exists. The purpose of this effort was to extend the leak-before-break methodology to high energy piping systems other than the reactor coolant loop piping. A detailed leak-before-break evaluation of the pressurizer surge line is presented in this report. The pressurizer surge line was selected as a typical case because this line would typically yield large fatigue crack growth because of the steady state fluctuations associated with the pressurizer fluid. Based on the evaluation it is concluded that for the typical surge line considered in this investigation, guillotine breaks should not be used as a part of the structural design basis. As a second part of this investigation, the high energy piping systems inside containment were prioritized from the standpoint of determining the applicability of the leak-before-break approach. The priorities were based on three considerations. First, the potential for pressure boundary failure in high energy lines with diameters 6 inches and larger was reviewed qualitatively by addressing six potential failure mechanisms. As the second consideration, the piping systems were prioritized based on cost benefit assessment. As the final consideration, the piping systems were prioritized based on quantitative assessment to determine the feasibility of demonstrating leak-before-break. An overall priority to demonstrate leak-before-break was established based on the above considerations