Failure analysis of a heater drain line at Millstone Point Unit 2

A formal Flow-Accelerated Corrosion (FAC) program has been in place at Millstone Point Unit 2 since 1991. In spite of this, the unit experienced a pipe break in a heater drain pump recirculation line in August 1995. The failure occurred during a water hammer event in a straight, 8 inch pipe that had experienced wall thinning as the result of FAC. This paper describes the pipe rupture and the thermal hydraulic events that resulted in wall thinning as well as the thermal hydraulic conditions that initiated a water hammer with a pressure spike of sufficient magnitude to rupture the thinned pipe. Also discussed are the programmatic and organizational aspects surrounding the failure and the actions taken to prevent a similar occurrence