Understanding feedwater line pressure surges

The phenomenon of waterhammer is one aspect of steam plants with which most operators become familiar. An unusual type of waterhammer distinguished by the difficulty in understanding its mechanism as well as by its potential intensity has been experienced recently in feedwater systems of several nuclear power plants. A summary of these experiences has been collected by the Nuclear Regulatory Commission and published by Creare. The waterhammer to be discussed is associated with a bottom discharge feedwater header in which it is possible to isolate a volume of high temperature saturated steam inside the feedring header in contact with highly subcooled feedwater. Steam systems which can operate with the boundary between the steam and water phases below as well as above the feedwater sparger are susceptible to this kind of waterhammer. This includes most PWR systems with U tube steam generators as well as most BWR systems