PWR secondary system pipe thinning

Nuclear power plants have been experiencing significant thinning of pipe walls from wet steam at least since 1962, when a leak occurred in an extraction line at Dresden Unit 2. Many plants have had valves and piping dow-stream of valves damaged by flashing water. However, it was not until Surry Unit 2 experienced a dramatic pipe rupture in December 1986 at the suction of a feedwater pump that thinning in high energy lnes carrying only liquid water attracted widespread attention, although a similar failure had occurred in a pipe on the discharge side of a heater drain pump at Trojan about 20 months earlier.Seven months after the Surry incident the Nuclear Regulatory Commission issued a bulletin (IEB 87-01) requiring utilities to report their programs to identify and control erosion-corrosion. The NRC also sent out a questionnaire to collect information on the secondary water chemistry of PWRS. Analysis of their responses indicates that not only is erosion-corrosion widespread but that there is need for an easy way to understand its causes in a particular plant, evaluate alternative actions for its correction and arrive at practical, cost-effective programs to control it. This paper suggests how to fill that need in ways that will stop or nearly stop the progress of wall thinning and provide convincing evidence that it has been arrested. Specifically, it identifies water chemistry changes as the most cost-effective way to arrest widespread erosion-corrosion