Nuclear Plant Journal - Digital Versions

Gimbaled Heads Improve VesselHead InspectionsBy Margie Jepson, Entergy Nuclear.On March 6, 2002, workers repairinga CRDM nozzle at the Davis-BesseNuclear Power Station in Ohio discovereda football-sized cavity in the reactorvessel head. Their finding is linked totwo other discoveries 15 years earlier.The Nuclear Regulatory Commissionsubsequently required all owners ofpressurized water reactors, includingDavis-Besse, to take specific measures toprotect plant equipment from boric acidcorrosion caused by primary water stresscorrosion cracking.Entergy has a boric acid corrosioncontrol program to identify and dispositionboric acid leaks. Palisades will replacethe reactor head, but until that time, hasgreatly improved the inspection devicesfor both Control Rod Drive Mechanisms(CRDMs) and the In Core Instrumentation(ICI) nozzles.In 2004, 2006 and 2007 refuelingoutages, challenges to schedules forvolumetric inspections for CDRMs andICI nozzles caused by repetitive scansled the Palisades and AREVA team toexplore new solutions to improve theoverall inspection process.“We are very proud of our Palisadesemployees and their persistent spirit inbuilding this device over a number ofyears until it resulted in a breakthroughadvance for Entergy that ultimatelynow benefits the entire industry,” saidEntergy Nuclear President and CEO,Entergy Nuclear employees at PalisadesPower Plant and AREVA took home thehighest honor at the Nuclear EnergyAssembly in the 2010 Top IndustryPractice Awards. The Entergy Palisadesteam from Covert, Michigan, was themaintenance category winner and alsoearned the top honor, the B. Ralph Sylvia“Best of the Best” Award, over 14 othercategory winners at the meeting held inSan Francisco by the Nuclear EnergyInstitute. The coveted Top IndustryPractice awards rank among the nuclearindustry’s most prestigious recognitions.John Herron. Herron also serves as theChief Nuclear Officer for the EntergyNuclear fleet, the second largest nuclearfleet in the U.S. operating or providingmanagement services to facilities inArkansas, Louisiana, Massachusetts,Michigan, Mississippi, Nebraska, NewYork and Vermont.Gimbaled headA gimbaled head contains ultrasonictransducers configured into arrays in anassembly. There are pivoting mechanismsthat are spring-loaded to allow thetransducer arrays to move smoothly overthe surface of the nozzles. Wear-resistantfeet on a transducer unit enable slidingcontact with the surface without damageto the transducers. The information fromthe scan is collected and transmitted to aremote computer for analysis and captureon hard-drives.The concept of transducers“following the surface” is not new, from adesign standpoint, but is very difficult inthe weld region due to distortion causedby the fabrication process.From L to R: John Herron – Entergy Nuclear President, CEO and CNO;Chad Main – Project Manager and team lead, Palisades; Kelle Barfield– Vice President Communications, Entergy Nuclear Public Affairs; JimLeto -Superintendant Maintenance Support, Palisades; John Broschak,Control Room Supervisor and manager project sponsor, Palisades;John Sheppard, Manager NDE Solutions – AREVA NP; Alan Blind –Engineering Director, Palisades; Mike Rencheck, President and CEO –AREVA NPThe Palisades challenge wasthreefold: obtain a smaller transducerfootprint with a gimbaled motion that wasretractable; getting adequate couplant tothe transducers; and collecting data inhard-to-reach areas.Initially, the ICI nozzle inspectionsrequired use of inner and outer diametertools. Use of these tools took excessivetime and consistently exceeded outageschedule goals. The breakthrough advanceof the final device is that the newICI gimbaled head design does the workfor both inspections with one deviceshortening critical path time while greatlyimproving overall quality of the scans.(Continued on page 58)56 www.NuclearPlantJournal.com Nuclear Plant Journal, July-August 2010