In recent years, the nuclear industry experienced adverse flow effects that caused structural damage to safety-related and nonsafety-related components as a result of flow-induced acoustic resonance in both Boiling Water Reactor (BWR) and Pressurized Water Reactor plants. In particular, fatigue failures and cracks in steam dryers occurred in certain BWR plants during the extended power uprate operation with generation of loose parts that can adversely affect safety-related components within the reactor vessel and the reactor coolant system. The acoustic resonance occurs when the main steam line flow exceeds a critical value such that the vortices over the cavity of the closed side branch pipe are excited by the acoustic modes of the stagnant fluid in the branch. The occurrence of this phenomenon is highly dependent on plant-specific operating conditions and the piping as-built configuration. The U.S. nuclear industry has initiated extensive activities to address this phenomenon in BWR plants. The staff of the U.S. Nuclear Regulatory Commission (NRC) has been monitoring generic industry activities, as well as reviewing the evaluation of potential adverse flow effects that might result from power uprates at current operating plants, and during the design certification and licensing of new reactors. This paper discusses operating experience with adverse flow effects at nuclear power plants from the acoustic resonance phenomenon, industry actions to address and resolve the phenomenon, and NRC staff review activities related to this issue.

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