Periodic (inservice) inspection of nuclear station piping welds, for the minimum overall radiation risk

A method is presented for determining the optimal number of piping welds to inspect which results in the minimum overall radiation risk. This risk has two parts, a) that incurred by inspection personnel, and b) the ''expected'' risk to the public due to piping system failure. The probability of system failure may be quantified in terms of the number of welds inspected. Radiation exposures are evaluated by a method based on radiation detriment optimization measures advocated in the revised ALARA concept. Knowing the release to the public due to failure, it is possible to quantify the overall radiation risk in terms of the number of welds inspected. Optimization methods allow determination of the optimal number of welds to inspect, to minimize this overall radiation risk. The method was applied to the example of a typical piping system in a CANDU station, with the apparent conclusion that no weld periodic inspection would be required for the purposes of safety. Further review of the specific assumptions involved would be necessary to confirm this result. (orig./HP)