Pipe stress allowables for operating reactors

During 1979, the NRC issued a series of bulletins which expressed concern on the seismic adequacy of piping systems in operating nuclear plants. Owners of these operating plants have had to reassess the original designs of the piping systems, and in many cases, make design upgrades to make the piping systems meet code requirements. In some cases, the magnitude of the design upgrades has been large enough to require four years for engineering and construction. During this interval, guidelines are required to justify continued plant operation. This paper presents is a suggested 'operability' pipe stress allowable of 2Sy under faulted (SSE) short term conditions. This stress allowable is greater than ASME NC, ND or B31.1 stress allowables of 2.4Sh. The 2Sy value is developed recognizing plastic capacity of pipe elements, conservatisms in conventional elastic stress analysis assumptions, and flexible piping systems. In addition, this operability allowable is convenient as a practical engineering solution to efforts in a backfit piping analysis situation. (orig.)