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October 20A P U B L I C A T I O N O F T H E A M E R I C A N N U C L E A R S O C I E T Y

Nuclear Power PlantMaintenance46-page Special Section begins on page 41

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BY CHARLES VALLANCE,

MARK MALZAHN,AND JOHN PATTERSON

IN 2009 AND 2010, Southern CaliforniaEdison (SCE), an electricity utility serv-ing 14 million residents in southern and

central California, undertook the replace-ment of the four original steam generatorsin Units 2 and 3 at the San Onofre NuclearGenerating Station (SONGS), in SanClemente, Calif. (Unit 1 completed a 25-year run in November 1992 and has sincebeen decommissioned.) The steam genera-tors had been part of the plant from the timeof the commercial startups of the two unitsin 1983 and 1984, respectively. The deci-sion to replace the steam generators wasbased on the forecast of degradation ofsteam generator tubing and the corre-sponding tube plugging.

The removal and replacement job waslarge and complicated. What remained tobe done after the original steam generatorswere removed from the Unit 2 and Unit 3containment buildings was to cut them upand ship them to the EnergySolutions sitein Clive, Utah, for disposal. Some of thesections from the segmented steam genera-tors have already been shipped, but some ofthe cutting work was still ongoing in mid-September.

The first steam generator was disassem-bled on site in April, and the underwatercutting work on the last of the four steamgenerators was completed on September 14.External cutting is under way, as of thiswriting, on the last two steam generators.The first shipment left the San Onofre siteduring the night of July 31 and arrived atthe Clive site on August 18. The lower as-

sembly (the part that houses the steam gen-erator tubes) from a Unit 2 steam generatorwas on the road as of this writing.

Work planningEach of the original four steam generators

measured more than 65 feet long by 22 feetin diameter at its largest point. With thesteam generators weighing almost 700 tonseach and containing irradiated components,the process of cutting and packaging themfor shipment off site represented a challenge.

The scope of work required the develop-ment of an effective work plan for stagingthe steam generators on site after they had

been removed from containment, cuttingthem down to a manageable shipping size,packaging the cutup sections, and trans-porting the sections off site, all while en-suring the prevention of the spread of radi-ological contamination and minimizing ex-posure to workers.

Each aspect of the project was unique. Toaddress the challenges, SONGS selectedseven separate vendors to make up the seg-mentation and disposal team, which in-cluded a diving contractor, a specialty cut-ting contractor, a shipper, and a disposalcontractor. In addition, a transportationroute had to be coordinated with the feder-

The removal of the four original steam generators

at San Onofre-2 and -3 and the subsequent task of

cutting them up for shipment off site required a

great deal of work and advance planning.

San Onofres steam generator disposal project

Charles Vallance () is

vice president of the nuclear division of UESI/

Underwater Engineering Services Inc. Mark

Malzahn is the SONGS project manager. John

Patterson (), of

PSA Consultants, is a consultant for the project.

Nuclear Power Plant Maintenance Special Section San Onofres Steam Generator Disposal Project

October 2011 N U C L E A R N E W S 43

A temporary tent served as the radiologically controlled area where the segmenting of the

steam generators was done. (Photos: Underwater Engineering Services Inc.)

As seen in the October 2011 issue ofNuclear NewsCopyright 2011 by the American Nuclear Society

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ing on the tents exterior to avoid affectingplant personnel.

The steam generators support pedestalsprovided a strong base for the cutting ac-tivities. To prepare for the job, steel baseplates were set up, followed by the support

pedestals. Asphalt was then hand-placedaround the sharp edges of the steel baseplates to prevent damage to the site trans-porters rubber tires and the spill berms lin-er material. The top of each pedestal con-tained a steel plate, a steel shim, and a ply-

wood softener plate. The shim height wasset to allow the site transporter to be raisedslightly to position the steam generator sothat it could be lowered onto the supportpedestal bearing plates.

The spill berm, manufactured by Inter-state Products Inc., covered almost the en-tire asphalt floor area of the tent, measuring102 feet by 88 feet by 14 inches high, andhad a maximum capacity of 57 000 gallonswith the pedestals and other material insideof it. Specially designed to fit within thetent, the berm was made from XR-5 fabric,which is strong enough to allow vehiculartraffic to enter and exit while maintainingits function to contain any spill material.

In addition, protective barrier measuresto impede the inflow of rainwater and oth-er material were installed around the pe-riphery of the tent. These devices were in-tegrated into the fabric and structure of thetent.

Three separate radiation barriers were es-tablished outside the tent: a shield wall con-sisting of large cargo containers called seavans; lead blankets to provide protectionfrom skyshine (scattered radiation of a pri-mary gamma radiation source generated byaerial dispersion) and the higher dose chan-nel head nozzles; and the rolling shieldwalls of lead blankets. The measured doserates in the tent when a Unit 2 steam gen-erator was on the stands varied between 1.5

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October 2011 N U C L E A R N E W S 45

The steam generators lower assembly that housed the steam tubes. Shielding was installed

over the penetrations and along the top of the lower assembly to reduce radiation dosewithin the tent.

http://www.ludlums.com/

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millirem and 0.15 millirem at ground lev-el. This was with the lead blankets on thehigher-dose channel head nozzles.

The shield wall made of the sea vans wasconstructed with standard 20-foot cargo

containers, the exterior sides of which wereplated with half-inch-thick steel plates. Thesea vans were then stacked so that theyblocked the dose from reaching the siteswest boundary, where the general public

could possibly be exposed. The sea-vanwall also served as the radiation barrier dur-ing the time of the steam generator domeremoval and the tube bundle cover installa-tion.

Internal cuttingSegmentation of the steam generators

was essentially a two-phase process. Beforethe outer shell could be segmented, it wasnecessary to cut and remove certain inter-nal structures and components. Because ofradiation dose levels and the potential forrelease of radiological contamination, thedecision was made to flood the secondaryside of the steam generators with clean wa-ter and use divers to make these cuts.

The horizontal staging of the steam gen-erators provided an optimal working envi-ronment. An access hole for the divers wascut using a petrogen torch at top dead cen-ter in the 4-inch-thick outer shell to allowsafe entry and egress. The access also had toaccommodate the segmented componentsas they were lifted out of the steam genera-tor. About 76 000 gallons of water were re-quired to fill each steam generator, whichadded 630 000 pounds to the weight of eachone and required special design considera-tions for the supporting saddles.

To allow the divers to work safely, de-tailed plans were developed for cutting, rig-ging, and moving the segmented compo-

San Onofres Steam Generator Disposal ProjectNuclear Power Plant Maintenance Special Section

46 N U C L E A R N E W S October 2011

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nents in a confined space, preventing radi-ological contamination, and managing ra-diation exposure. Of particular concern wasthe potential to breach the steam tubes dur-ing the cutting process. The tube bundlescontained contaminated radioactive waterthat if released would have posed the riskof contamination and unwanted radiationexposure to the divers and the supportworkers topside and would have preventedthe completion of the remainder of the cut-ting and disposal work. To ensure that thiscould be avoided, Underwater EngineeringServices Inc. (UESI) and SONGS engineersperformed a mock-up before the actual pro-cedure to practice the most difficult part ofthe cutting operation.

Divers worked in special suits and hel-mets that fully encapsulated them to preventskin contamination. Air for breathing andthe connection for hard-wired radio com-munication were supplied by an umbilicalhose to the surface. Closed-circuit under-water cameras were mounted on the divershelmets so that every aspect of their under-water work could be closely monitored bysurface support personnel. UESI also pro-vided a manual diver extraction system thatwas integrated with the dive platform. Thesystem met all regulatory requirements andwas the primary retrieval tool in case of adiver emergency.

The water acted as a shield to reduce ex-posure to a fraction of the dose that wouldhave been present in air. Working in wateralso allowed for easier mobility of thedivers within the complex geometry of thesteam generator internals. Components tobe segmented during the wet-cutting oper-ation included steel beams supporting thetube bundles, the half-inch carbon steel

wrapper plate (or shroud) surrounding thetube bundles, and various other componentsblocking diver access to interior work areas.

The divers plan identified the cuttingtools to be used and mapped out the exactsize and weight of each segment that wouldresult from the cuts. This was essential todiver safety, because any shifting of heavysegmented components within the confinedspace could pose danger. In some areas,structural bracing was welded in place bydiver welders prior to cutting to eliminatethe risk of a components shifting. All weldsmet the requirements of AWS 3.6M, ASMESection IX, and ASME Section XI.

A sound cutting plan was also essentialto the success of the segmentation. Any in-complete cuts would keep the larger partsfrom being separated during the externalsegmentation, and inaccuracies in cuttingtolerances could also prevent separation,thereby preventing the installation of thesteam tube bundle cap required to seal thetubes prior to transport.

The primary underwater cutting tool usedwas a plasma arc torch, which uses a plas-ma that is hot enough (around 45 000 F) tomelt the metal being cut. The plasma movesat a velocity sufficient to blow molten met-al away from the cut. The process is accu-rate, efficient, and relatively clean.

As cutting commenced, divers assessedthe clearance at the feedwater ring thatblocked the path to the steam tube shroud.This area was very confining and extreme-ly congested because of the tubing and pip-ing, requiring careful maneuvering by thediver and vigilance by his topside tendersto avoid entanglement.

The first circumferential shroud cut wasmade 1 foot up the baffle cone from the areawhere the steam tube shroud transitions froma cylindrical shape to a cone shape. This cutwas necessary to allow at least 5 inches ofclearance on all sides of the cylindrical sec-tion of the lower assembly when the steamdome was separated. Once a high-heat-re-sistant rubber mat was placed between thetube bundle and the baffle plate, divers be-gan the cuts at the 3 oclock position andworked down past the 6 oclock position onboth sides of the baffle plate. They stoppedthe cut at approximately the 5 and 7 oclockpositions to ensure that there was no breachof any tube bundles.

A second circumferential cut was madeat the transition of the cylindrical section to

Nuclear Power Plant Maintenance Special Section

48 N U C L E A R N E W S October 2011

The lower assembly after the steam dome was severed and removed. The top of the tube

bundle and portions of the remaining steam tube support beams are visible.

The steam dome after the lower assembly that housed the steam tubes was removed.

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the conical section, with the diver directingthe torch as close to parallel to the cylindri-cal section as possible to reduce the poten-tial for a tube breach.

The divers made a portion of the circum-ferential cuts and then sectioned these cutsto create pieces that could be handled andlowered to the bottom of the steam dome.

When cutting the tube bundle supports,divers first made longitudinal cuts along theweb of the 24-inch beam to remove materi-al and reduce weight to below 160 poundsper segmented piece, to ensure that theywould be small enough for a diver to handlecomfortably. During underwater cutting op-erations, SONGS personnel and other con-tractors provided support that was essentialto the safety of the divers and the efficiencyof the work. Radiological control personnelclosely monitored diver exposure and theprocesses required to prevent contamination.Expert riggers and operators worked close-ly with the dive team to rig and remove seg-mented pieces from the steam generator, oneof the riskiest tasks that had to be performed.

Diving work, which was done five daysa week, was carried out April 1227, 2011,for the first steam generator (a total of 12days of diving); May 417 for the secondsteam generator (10 days of diving); andAugust 15September 5 for the third steamgenerator (9 days of diving). Diving workin the fourth steam generator was complet-ed in the first half of September and took 10days of diving.

External cuttingWith the divers work completed, the

steam generator was drained so that exter-

nal cuts could be made to sever the steamdome from the lower assembly that housedthe steam tubes.

During external cutting operations, thesteam generators thick outer shell providedshielding to minimize radiation exposure, asthe general area dose rates were elevated

above background dose rates. Even thoughthe shell is over 4.5 inches thick, the dose isabout 4 millirem at 6 feet in some locations.Other radiation dose minimization mea-sures, such as the use of stationary andmoveable lead blanket shadow shields andremote camera monitoring of the cutting, theremoval of the steam dome, and the instal-lation of the tube bundle cover, were em-ployed.

Separating the lower assembly from thesteam dome required a 17238-inch cutthrough 478 inches of SA533 carbon steel.Welding Services Inc. used a split-frameouter-diameter cutting machine that incor-porates a clamshell-style cuttera Hy-dratight MM180said to be the worldslargest gear-driven split-frame lathe.

The clamshell cutter was operated re-motely and monitored using the SONGSHealth Physics Departments CARE cam-era system. Remote monitoring continuedup to the point at which the cutter was aboutto complete the severance, which was thenmonitored from a shielded observation area.The lower assembly and the steam domewere securely supported on multiple standsto minimize movement and the potential forbinding as the final cut was made. The ex-ternal cutting for each steam generator tookabout two days, with total personnel dosefor each of about 45 millirem.

Rigging and handlingOnce the steam dome and lower assem-

bly were separated, the clamshell cutter was

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October 2011 N U C L E A R N E W S 49

Divers entered a steam generator through an access hole cut in the top of the steam dome.

The diver supervisor watches the divers on a video screen in order to direct their work by

radio communication. The supervisor also controled power to the plasma torch and

engaged it only when the diver was set to cut, and he monitored the divers air supply and

coordinated with topside support personnelsuch as the dive tenders (who held the

divers umbilical hose), the crane operator, and the riggersas the work progressed.

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removed and the work area was demobilizedfrom cutting operations and prepared for rig-ging and handling operations. Air samplesof the interior environment were taken con-tinuously throughout the shell-cutting pro-cess to verify that the air remained below de-tectable radiological activity.

When rigging and handling preparationswere complete, a site transporter was movedinto the tent and positioned under the steamdome, and the tube bundle cover was stagedon a second site transporter in preparation forinstalling the steam tube shield cap. Thesteam dome was then secured and removedfrom the tent, allowing the second trans-porter to position the shield cap, a procedurethat was monitored through the use of theCARE camera system. The tube bundle cov-er was properly fitted up to the lower as-sembly and was tack-welded into place, atask requiring temporary shielding to lowerthe dose rate to the welders. Weld-out of thecap was performed by an automated machinewelding system similar to the clamshell cut-ter tooling. The success of the welding pro-cess was confirmed by the use of a magnet-ic particle nondestructive examination, andthe components were moved to a transfer lo-cation for off-site shipment.

On the road to UtahAfter the installation of all of the lower as-

sembly covers and plugs and the applicationof transport coatings, SONGS personnelperformed a verification of acceptability pri-or to shipment of the components to the En-ergySolutions disposal site. A quarter-inchcarbon steel plate was welded over each ofthe hollow sections of the center of the steamgenerator stand. In addition, SONGS healthphysicists surveyed and conditionally re-leased each component for transportationbefore its release to the disposal facility.

Perkins Specialized Transportation Con-tracting Services custom-designed and built

the transporter for shipping the lower as-semblies from SONGS to the disposal site.The transporter measures 399 feet long by20 feet wide by almost 17 feet high, and has192 wheels to support the load. The trans-porter had to meet all state and DOT re-quirements and have all approved permitsin place prior to the delivery of the lowerassemblies to the transfer point, from whichdelivery of the lower assemblies to Clivewas made.

Perkins completed a route analysis thatrequired coordination with the DOT, theNuclear Regulatory Commission, the Fed-eral Bureau of Investigation, the CaliforniaDOT, the California Highway Patrol, theCalifornia Public Utilities Commission, theCalifornia Coastal Commission, the Neva-da DOT, the Nevada Highway Patrol, the

Utah DOT, the Utah Highway Patrol, theSan Diego County Sheriff, the RiversideCounty Sheriff, the San Bernardino Sheriff,and numerous towns and municipalitiesalong the route.

Each steam generator has already or willtravel 832 miles at an average speed of lessthan 30 miles per hour. The highest eleva-tion along the transport route is 7000 feet,and the lowest is 35 feet above sea level.

After SONGS had approved the trans-port route, Perkins provided all informationrequired for the preparation of the Trans-port Emergency Response Plan (TERP) inaccordance with 49 CFR Parts 107 and 173.The TERP contains contingency plans foremergent situations that could arise duringthe transport and describes the specifictransport route between SONGS and theClive site, including detailed proceduresfor all handling and tiedown activities, aswell as any major procedures to be per-formed in preparation for and during thetransport.

Meanwhile, SCE personnel undertookcommunications outreach efforts with com-munity officials, utility regulatory agencies,and media outlets along the route to ensureadequate public communication to supportthis transportation project.

At the time of this writing, the project hasbeen a resounding success, according toproject manager Mark Malzahn. Even withthe usual project delays, work has pro-gressed much faster than expected. The proj-ect is on schedule and Malzahn said that it isanticipated that the project will enjoy a sav-ing in radiation exposure. The original as-low-as-reasonably-achievable plan estimat-ed a total project dose of 21 person-rem; to-tal expected project dose is now projected tobe less than 8 person-rem.

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50 O t b 2011

A map of the route taken by the steam generator shipments to the disposal site in Utah.

San Onofres Steam Generator Disposal Project

A retired steam generator aboard a 24-axle trailer system makes its way to Utah for

disposal. (Photo: John Patterson)