PRAISDPD: An aging pipe reliability analysis PC code

A double guillotine break of primary piping when a reactor is at full power has long been considered a bounding accident. But just what is its probability of occurrence? This paper presents a review of attempts to assess the probability of this never occurring event from WASH-1400 through the Thomas model to efforts using probabilistic fracture mechanics as exemplified in the PRAISE code which resulted in a revision of the Code of Federal Regulations to recognize the tendency of pipe to leak-before-break. The interactive PC code PRAISDPD implements the PRAISE algorithms and was used to perform safety optimizing parametric studies of Oak Ridge National Laboratory's Advanced Neutron Source (ANS) reactor. From this, the sensitivity of the pipe break probability to the piping parameters were determined and suggestions were made to minimize the break probability. Qualitative conclusions are: 1. • Pipe lengths should be minimized. 2. • Large diameter pipe is more reliable than smaller pipe because of the greater wall thickness through which a crack must grow and the larger circumference around which a crack must grow before becoming unstable with subsequent breakage. 3. • The probability of leakage and breakage is significantly reduced by periodic non-destructive examination (NDE—specifically ultrasound testing). 4. • Aging increases the probability of leak/break.