Acoustic oscillations in main steam lines caused by side branch resonance

Acoustic oscillations in main steam lines have caused structural vibration leading to plant modifications in both PWR and BWR systems. Recent power increases (i.e., uprates) in some BWR designs have resulted in acoustic oscillations in the main steam lines that have caused fatigue failures in steam dryer assemblies. The physics of acoustic propagation in wet steam typical of BWR steam supplies is reviewed. The excitation of acoustic waves in the main steam lines by standing waves in side branch lines is also reviewed and relationships between standing waves in the main lines and standing waves in the side branch lines are examined experimentally. The side branch lines are found to couple acoustically with standing waves in the main line, leading to a range of frequency excitations from the branch lines.