Verdantas Flow Labs (formerly Alden Research Laboratories) was contracted to help identify the cause of elevated vibration levels in the feedwater system after steam generator replacement and to find solutions to mitigate these vibrations.

A half scale model of the WF3 RSG Feedring was constructed at the Alden Campus. The loop was commissioned with the intention of identifying the pressure fluctuations due to flow instabilities that were thought to be the cause of the vibration. Early testing showed that the cause of the vibration was not fluid structure interaction (FSI), but was in fact cavitation in the feedring inlet tee, which shifted the focus of the testing from what was laid out in the Test Plan.

Baseline testing was completed, which successfully replicated the vibration experienced at the plant. The cause of vibration was identified as cavitation in the vortex core formed in the feedring inlet tee. Suitable scaling criteria were developed to match model behavior to measured and observed full scale performance with a high degree of confidence.

Following baseline testing, several concepts were tested. The best-performing concept was a wedge-shaped insert that could be mounted inside the inlet tee. The “Wedge” was found to reduce the feedring pressure loss by a factor of 4; reduce the pressure fluctuations by a factor of 7; and completely eliminate cavitation – which was determined to be the primary cause of vibration – well beyond the full load operating conditions at WF3.