From right to left:The steam generator istransported on SPMTs tothe JS500 jack-up system.

The JS500 raises thesteam generator to theheight of the temporaryhatch.

The steam generator isskidded along a track intothe plant.

A temporary lifting device,a 900 metric ton strand jackon a gantry, raises thesteam generator.

The generator is maneu-vered by the temporary lift-ing device mounted on thepolar crane.

The reinforced polar crane,with its temporary liftingdevice, rotates the steamgenerator around the plantand lowers it into place.

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Usually, replacement projects in nuclear power plantsare performed by creating a temporary hatch in theplant’s wall, big enough to skid the old steamgenerators out and the new ones in before they areinstalled. However, the floor level height inside theplant made it necessary to create a temporary hatchsix meters above the outside ground. This wouldrequire Mammoet to lift the steam generators. Andthat is where the third and biggest complication camein: above the point where the temporary hatch had to

be constructed, power lines exit the plant, deliveringthe generated electricity to the grid. The plant wouldstill provide power during the steam generatorreplacement operation, so temporary removal ofthe power lines was not an option. According tosafety regulations, a minimum safety distance of sixmeters (20 feet) has to be observed betweenoperating equipment and the high voltage powerlines. This ruled out the use of our cranes to simplylift the steam generators in and out of the plant.

…and a comprehensive approachMammoet proposed a

comprehensive approach thatwould deal with all three

obstacles in the safestpossible manner.

At the southwest shore of Lake Erie, in OakHarbor, Ohio (USA) lies the Davis-Besse NuclearPower Plant. In 1978, it was the 50th nuclearpower plant to come online in the USA. Apressurized water reactor and two steamgenerators are at the core of this plant andprovide more than 7,000 Gigawatt-hours ofelectricity annually. In 2009 it was decided thatthe reactor vessel closure head (RVCH) andthe two steam generators had to be replaced.

Three complications…The replacement was set for 2014, and at that timethere were three known complications. First, the

polar crane in the plant was not strong enoughto lift an entire steam generator for

replacement. Second, the floor levelinside the Davis-Besse nuclear

power plant is around sixmeters higher than

ground leveloutside.

IN AND OUTTHE HATCHSqueezing time and space for nuclear outage in Ohio

“Our deadline was suddenlymoved forward by three years.”

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Project manager Stefan ten Hoeve explains: “Themost challenging issue was to find a way to dealwith the power lines. We could not lift thecomponents from above, but we could push themup from below, positioning them at the correctheight to move them through the temporary hatch.This was made possible by the JS500 jack-upsystem– an innovation that had just beenintroduced by Mammoet, and the only availableequipment able to handle such an operation. Thiswas the safest and most efficient solution.”

On the inside, Mammoet needed to reinforce thepolar crane. As the girders were not strong enoughfor the operation, Mammoet had proposed toreinforce them using a temporary support tower.The polar crane needed to rotate during its liftingoperations so the support tower was connected tothe bottom of the girders with a turntable. On topof the polar crane, Mammoet installed a temporarylifting device consisting of a 900 ton strand jack ona travelling gantry system that provided theadditional lifting capacity needed for the entireoperation.

Dealing with the unforeseenMammoet signed an agreement in 2009, stipulatingthat the replacement operation take place during apower outage in 2014. We had five years to prepareand it seemed like smooth sailing, but a complicationsoon arose that seriously upset the timetable: theNuclear Regulatory Commission, which is in chargeof issuing and renewing operating licenses, did aninspection in 2010. It ruled that the RVCH at Davis-Besse was nearing the end of its 20 year life-spanearlier than anticipated, and had to be replacedsooner in order for the license to be renewed. TheCommission decided that this had to take placeduring a mid-cycle outage in the fall of 2011.

Stefan ten Hoeve explains the consequences of theCommission ruling: “This meant our deadline wassuddenly moved forward by three years, which calledfor us to respond immediately. Now the work had tobe divided into two parts: replacing the RVCH in2011, and then replacing the two steam generatorsin 2014. It would be a tight squeeze, but we wereconfident we had the know-how and determinationto do it.”

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Replacing the RVCHWe immediately set about speeding up theengineering and test phases, without compromisingquality or safety, in order to beat the accelerateddeadline. By working around the clock, the technicalcrew managed to meet the new deadline andcomplete the test-loading and fit-testing by thesummer of 2011. Mammoet was ready to replace the140 ton RVCH during the planned outage, asrequested. Things went safely and smoothly threeyears ahead of our original deadline. Immediatelyafter the RVCH replacement we started preparationsfor the removal of the two steam generators.

Leaving nothing to chanceBy 2013, the engineering phase for the remainingwork was completed and all equipment had beenprepared and tested at our yards in the US and theNetherlands. Stefan describes one of the mostcomplicated challenges posed by the project: “Wereplicated the polar crane girders so that we couldload-test the temporary lifting device designed forthe top of the polar crane. The tests were successfuland we were ready to go.”

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nuclear outagesMichel Bunnik is Global Sales Director at Mammoet. Since 2000,he has been involved in most of the nuclear construction, outageand decommissioning projects that Mammoet has executed.

There are 435 civil nuclearpower reactors

operational in the world and some70 more under construction. Eachof these plants was customizedaccording to the technology andinsight at the time of theirconstruction. But often they were

not designed with efficient outages in mind.

‘Outages’ are scheduled shutdown periods for nuclearplants during which fuel is replaced, maintenance takesplace and components may be changed out. For manynuclear plants this process was not included in theirdesign and their infrastructure does not allow for theeasy and swift change-out of large key componentssuch as steam generators and reactor vessels. Asdowntime is very costly, innovative approaches to thelifting and transport of these components are needed toensure outages are executed as efficiently as possible.

Plant owners are often unaware of this when they startworking on the mechanical engineering for maintenanceprojects. It makes a significant difference in theefficiency of these projects when engineered heavylifting and transport activities are integrated from thebeginning. They define the critical path of a maintenanceoperation and therefore the actual downtime.

The timing depends on many factors, particularly theinternal layout and installations that define the roomto maneuver, the capacity to lift and potentialcomplications along the way. Therefore, the mechanicalengineering plan should be integrated with a detailedlogistics plan to encompass all lifting, transport andchange-out of the large key components involved.

Current heavy lifting and transport technology offersmany opportunities to minimize downtime in safe waysthat were not foreseen at the time of the plant’sconstruction. As demonstrated by the Davis-Besseproject, an integrated approach offers significantbenefits: it optimizes processes and can completeoutages faster while maintaining the highest safetystandards.

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The equipment and new steam generators hadarrived on site by October 2013. Everything waspre-assembled and in position by January 2014. Itall appeared to be under control and the rest ofthe operation seemed as if it would be a walk inthe park. We were soon reminded that Mammoetcan control a lot of things … except the weather.

Against the elementsWhen the replacement operation officially gotunderway in February 2014, the region was beingravaged by the worst winter in 30 years and theidyllic location had been transformed into a

freezing wasteland. There were three meters ofsnow on the ground and temperatures hadplummeted to between -10°C and -40°C. Thiscaused all kinds of problems for Stefan and theteam, who worked in two rotating shifts of twelvehours, six days a week for ten weeks. Workingoutside was grueling, fighting against theconstant snowfall and artic winds that whippedoff the lake, constantly filling the air with anominous howling.

Real troopersThe weather was dark and grey with gun-metalskies and bad visibility because of the ceaselesswind and stinging sleet. The team had to wearbulky, double-lined protective clothing thathampered their movements, making it even moredifficult to move along the icy, slippery paths.Team members could only work outside for anhour before having to go indoors to rest and thawout. The weather also required special measuresto keep the equipment running. The machineswere covered in thermal blankets and kept idlingat all times so that the engines wouldn’t freeze.Special industrial heaters were also mounted onthe power packs against the severe cold. It wasan extreme challenge, but the team worked withdogged determination to keep everything runningsmoothly and efficiently. “The team was amazing”,says Stefan. “Real troopers. They never grumbled;just knuckled down and completed the job!”

Steam generator extractionOnce the plant had cooled down, a temporaryhatch was made in the plant’s concrete wall. Thislarge entrance allowed us to move all ourequipment and transport the steam generatorsin and out. The JS500 was arranged in front ofthe work platform and a connecting skid way ontop of it provided the route inside the plant thatthe generators would travel – both ways. Onceeach steam generator was skidded out of theplant, it was quickly transferred to its final restingplace in the mausoleum, a concrete bunker withwalls so thick that no residual radiation canescape. Then the whole process was repeated forthe second steam generator. The new steamgenerators were installed using the sameprocedure, but in reverse.

A tough job, well doneStefan looks back on the project: “The first steamgenerator was extracted on 28 February 2014and the last new steam generator was set on itsfoundation on 11 March 2014. It was the first timethat the procedure had ever been carried out andit was specifically developed for this project. Ourplan enabled us to work quickly; every day savedmeant saving a million dollars for our client. Webeat the revised deadline for replacement of theRVCH and delivered everything without incident.Our customer was delighted with the outcome.” n

“It was the first time that theprocedure had ever been carriedout and it was specificallydeveloped for this project.”