May-June 2018 NPJ

Water Pump Isolation Valve Repair By Dan Frey, Entergy. Dan Frey Daniel Frey is the Senior Manager of Site Projects and Maintenance Services at Entergy Nuclear, Waterford 3 in Killona, Louisiana. He is responsible for the oversight of all station projects, maintenance support activities, reactor, turbine, and dry fuel storage activities. Daniel is also responsible for the management, oversight, development and continuous evaluation of all department direct reports. Frey started his nuclear career in the Navy in 1980 and later served as the Lead Engineering Laboratory Technician. He received a Bachelor’s degree of Science in Nuclear Technology from Excelsior College. Nuclear Energy Institute’s Top Innovative Practice Awards highlight the nuclear industry’s most innovative techniques and ideas. This innovation won the 2017 AREVA Vendor Award. The team members who participated included Laurie Murray, Waterford 3 Project Manager; Doug Philips, Waterford 3 Project Engineer; Nigel Elias, Waterford 3 Project Engineer; John Sheppard, Framatome Tooling Engineering Manager; Corey Claybrook, Framatome Outage Manager. Summary On January 9, 2016, Circulating Water Pump C Discharge Isolation Valve failed closed and the disc appeared to be stuck in its seat. Further investigation identified the valve shaft could rotate when the valve was stroked open/closed but no movement of the valve disc was detected. Based on this, it appeared that CW-103C had a valve disc to upper stem separation (there was OE to support this conclusion) which rendered the valve unable to open or close, causing the Circulating Water Pump to be inoperable. This limited the plant to three out of four pump operations. Based on the information from the valve vendor, if the pins connecting the upper shaft and disc are separated, then the disc could pinwheel. The disc was resting in the cast body of the seat, preventing the disc from pinwheeling, however this dynamic failure mechanism could occur in the future. Circulating Water Pump C Discharge Isolation Valve is one of four 96" butterfly valves which all feed to a common discharge header. If CW Discharge Valve C would have inadvertently opened, flow from the common discharge header would have been diverted from circulating water back to the Mississippi River, reducing the cooling water to the plant loads, as described below. With the disc of CW-103C not mechanically secured, there was a risk the back pressure would push the disc through the seat of CW-103C and cause the valve disc to open or pinwheel. This would have diverted some of the Circulating Water flow from the Condenser, Turbine Closed Cooling Water (TCCW) and Blowdown (BD) Heat Exchangers back to the Mississippi River. The amount of flow is approximately 300,000 gpm with three Circulating Water Pumps operating. If backflow were to occur several things would most likely have happened:  Condenser Vacuum would drop to the point that manual actions would be required.  TCCW temperatures would rise affecting several turbine building component’s ability to reject heat and operate within its parameters.  Backflow from the transition block #1 would spin the idle Circulating Water Pump backwards and could possibly damage the pump.  CW103C disk would pinwheel, causing pressure pulses in the Circulating Water piping and components.  With three pump operations, water velocities through the waterboxes would be reduced, causing increased silting of the Condenser tubes. This would increase the potential for tube leaks, which would impact the Chemistry Index.  If one of the three operating Circulating Water Pumps was taken out of service, during the summer months, the unit would have to be de-rated to reduced power levels.  Blowdown Heat Exchanger performancewould be impacted, with the potential of lowering blowdown flow if Hx outlet temperatures could not be maintained.  Cleaning and maintenance would increase due to the increased silting. Based on the potential consequences of the CW-103C condition, a project team was established to investigate on- line repair options. The Project Team along with Framatome established two (2) separate tasks to achieve the ultimate goal: 1. The first task was to stabilize the disc for CW-103C to secure it closed to ensure that the CW-103C would not open and render the valve stabilized by inserting two holding pins through the valve body and locking the disc in place. 2. After the valve was secured closed with stabilization pins, the next task was to insert a separate pin through the valve body into the valve disc and stem, restoring the ability to cycle CW-103C, thereby restoring the ability of the Circulating Water Pump C to operate, and restoring 4 pump operations. This had to be accomplished at normal system pressure and flows. 42 NuclearPlantJournal.com Nuclear Plant Journal, May-June 2018