Identifying root causes of feedwater transients at Dresden 3

In response to the significant feedwater transients experienced at the Dresden 3 BWR in the summer of 1987, Commonwealth Edison set up a team to investigate the problem. Subsequent tests identified valve instability as the root cause of the transients. It was determined that the instabilities were associated with the specific operating positions of the two main feedwater regulating valves. The unstable behaviour was mitigated by replacing the air to open and air to close undamped valve operators with springs to open and air to close hydraulically damped valve operators. (U.K.)