Identification of Quad Cities Main Steam Line Acoustic Sources and Vibration Reduction

The Quad Cities Nuclear Power Station, Units 1 and 2, have a history of steam line vibration issues. The implementation of an Extended Power Uprate resulted in significant increases in steam line vibration as well as acoustic loading of the steam dryers, which led to equipment failures and fatigue cracking of the dryers. This paper discusses the extensive data collection on the Quad Cities Unit 2 replacement dryer and the Main Steam Lines. This data was taken with the intent of identifying acoustic sources in the steam system. Review of the data confirmed that vortex shedding coupled column resonance in the relief and safety valve standpipes were the principal sources of large magnitude acoustic loads in the main steam system. Modifications were developed in subscale testing to alter the acoustic properties of the valve standpipes and add acoustic damping to the system. The modifications developed and installed consisted of acoustic side branches that were attached to the Electromatic Relief Valve (ERV) and Main Steam Safety Valve (MSSV) attachment pipes. Subsequent post-modification testing was performed in plant to confirm the effectiveness of the modifications. The modifications have demonstrated a reduction in the acoustic pressure loads at full Extended Power Uprate (EPU) conditions to levels below those at Original Licensed Thermal Power (OLTP).