NRC perspective on through-wall leakage in ASME code class components

摘要

A new item entitled, "Leakage Disposition Flow Chart" was introduced during the August 1998 meetings of Section XI of the American Society of Mechanical Engineers (ASME) Working Group on Pressure Testing (WGPT). The flow chart accompanied an action to re-write Subparagraph IWA-5250, "Corrective Action." The proposed re-write resulted from the WGPT's desire to investigate and develop better Code requirements for the disposition of leakage detected during a pressure test. This paper presents a discussion of the Nuclear Regulatory Commission (NRC) perspective on through-wall leakage with regard to structural integrity and consequences of continued operation. The discussion does not include leakage through bolted connections or gaskets. Leakage through packing or gaskets, for example, are common occurrences that are not likely to compromise the structural integrity of a system or component. Emphasis is placed on NRC regulations and guidelines which govern U.S. commercial nuclear power plants. These regulations do not allow through-wall leakage in, for example, the reactor coolant system (RCS). The stated NRC position is compared to the contention occasionally expressed by the industry that the ASME Code allows through-wall leakage. This opinion periodically emerges and is debated during ASME Section XI Code meetings.