Nuclear Technology / Volume 164 / Number 3 / December 2008 / Pages 309-319
Technical Paper / Fission Reactors
Acoustic oscillations in nuclear steam supplies have caused structural vibration leading to plant modifications in both pressurized water reactor and boiling water reactor (BWR) systems. Power increases (i.e., uprates) in some BWR designs have resulted in acoustic oscillations in the steam supply that have caused fatigue failures in steam dryer assemblies. Standing waves in side branch lines are identified as one important acoustic source for waves in the main lines. The side branch standing waves are driven by vortex shedding across the branch opening. The side branch lines couple acoustically with standing waves in the main line, extending the range of physical behavior beyond that normally considered in the literature. There are many side branches mounted where there is flow in the main steam line, creating multiple acoustic sources, many of nearly the same frequency. These multiple sources cause time variation in the acoustic performance that may extend over many seconds, and these attributes must be considered during data acquisition, component load simulation, and stress simulation. Wet steam sound speed models appropriate to BWR steam supply conditions are also presented.