Changing priorities in nuclear piping design

The nuclear industry has had basic piping design rules for Class 2/3 piping for 39 years, and for Class 1 piping, 25 years. Most of the code changes since 1971 have been incremental changes to resolve technical questions. Now, the Working Group on Piping Design is working on significant enhancements or improvements--seismic stress limits, design for vibration, rules for buried pipe, integration of the design and fabrication requirements, and a commentary. The design of piping systems has been significantly impacted by seismic loads. One of the biggest problems the nuclear industry has had is deciding on appropriate analytical methods for use. Basically, the Section III Code provides stress criteria based on linear elastic analysis methods. NRC has defined acceptable linear elastic analysis methods through regulations. In the author's opinion, the code should define acceptable and appropriate analytical methods through the consensus process. For piping design for seismic loads, it is unreasonable to ignore the benefits of inelastic energy absorption. The seismic issue brings into focus the need for minimum acceptable standards for analysis of piping systems--an area that has not been within the scope of Section III in the past. The time has come for a complete technical review and rewrite of the code. The industry needs to gather together their experience over the last 23 years and case studies on problem areas. Then they start from the beginning with the idea of simplifying the requirements. They also need to figure out how to be more responsive. There are many critical needs, but the resources to accomplish meaningful changes in the code are lacking