Acoustics, stability, and compensation in boiling water reactor pressure control systems

An analysis is provided of the effects of steam pipe acoustics on the control of steam pressure in boiling water reactors. A model is developed for the process which encompasses the reactor vessel, the main steam piping, the bypass system piping, the turbine throttle valve and bypass valve, and associated control equipment. It is shown that instability of the closed loop can occur unless the acoustics are suitably accounted for. Moreover, it is shown that although classical compensation schemes may lead to adequate controller designs in some situations, such regulators are limited in their ability to provide fast pressure recovery and can thus contribute to undesirable oscillations between reactor pressure and water level control loops. State variable methods are shown to lead to fundamentally different control structures which eliminate this difficulty but other considerations are noted which can limit their application. These are, however, minor when compared to the benefits attainable.