Papers by Keyword: Nuclear Piping

Abstract: The current in-service inspection (ISI) strategy for the nuclear piping in many countries consists of both the code requirements such as ASME B & PV Code Sec. XI and the country-specific regulatory requirements, so called as the enhanced ISI. The enhanced ISI reflects the operating experience of piping failure, while the ASME Code Sec. XI requirement is based on random sampling for the inspection points. In this study, a new strategy for ISI of nuclear piping was proposed based on piping failure frequency. This strategy basically reflects the operating experience because the piping failure frequency is based on the piping failure database. The new concept of minimum inspection rate was also introduced in this new ISI strategy. As pilot study, the new ISI strategy was applied to the Class 1 piping system such as reactor coolant system and safety injection system of Ulchin Unit 5 which is the 1,000 MWe Korean Standard PWR. The results from the proposed new strategy were compared to those from the ASME Code Sec. XI. The results show that the new ISI strategy reasonably reflects the operating experience. The results also show that the concept of the minimum inspection rate can compensate the unbalance in the number of inspection points between the very large differences in the piping failure frequency.

Abstract: Class 1 piping components of a certain old vintage nuclear power plant were designed by ANSI B31.1 code without a detailed fatigue evaluation such as the one required by recent ASME Section III code. These components may undergo fatigue damage when considering the continued operation beyond the design life whilst the inherent fatigue resistances of those may satisfy the corresponding implicit limits. In this paper, the alternative fatigue evaluation has been carried out explicitly for Class 1 piping of old nuclear power plant. At first, four representative nuclear piping systems were selected to check the operational adequacy. After characterization of conservative loading conditions based on design features, a series of finite element analyses have been performed and the cumulative usage factors were calculated to guarantee if the components at each system sustain adequate fatigue resistance. Finally, comparisons were drawn between the implicit fatigue design specifications and alternative explicit fatigue analysis results. Even though there were some exceptions, it was demonstrated that most components satisfied the current explicit fatigue criterion.