When leaks were detected on a nuclear reactor vessel head at the North Anna Power Station, the implication was that it was cracked. The leaks were found during routine checks at the time of a refuelling outage. The reactor vessel head was going to have to be replaced, something that had never been done before during an outage in the USA, according to the client Dominion Power.
Three months later the 72t (160,000 lb) replacement head landed by cargo plane at night from France. Soon after, lifting contractors Rigging International took the decision not to wait until morning to get the cargo moving. It was after midnight when Carolina Crane operator Ricky Barton and two colleagues got the call. After parking their Liebherr LTM 1300/1 at the Richmond (Virginia) International Airport, they had gone back to a hotel nearby to wait for the load to land. The nuclear power station it was going to, some 130km away, was waiting.
The lift
On paper, the lift seemed simple enough the crane was to lift up the reactor head off of the skids that brought it out of the plane, slew around and drop it on to a 19-axle heavy transport trailer. But because of the load’s value, Carolina had to add in an additional 12% safety factor, so that it lifted at a maximum of 75% capacity. Carolina equipped the crane with 39t (86,000 lb) of counterweight and lifted a total of 104t (230,000 lb) at a 7.3m (24ft) radius.
It also had to use a custom three-spoke spreader bar. Although the reactor head had lifting attachments built into its tapering sides, access to these was blocked by a mating ring installed on the head. Rigging International had to install lifting lugs in three of the 50-odd stud holes around the bottom edge of the head and design the spreader to lift the head from these improvised lugs.
The Carolina Crane team started lifting about 5am and finished a few hours later. ‘The most rewarding part for us was getting a letter from the CEO of Dominion Power complimenting us on a job well done,’ says All Carolina Crane managing director Earl Johnson III.
When the head arrived at the plant four hours later, workers were ready for it. Because it would not fit through the reactor’s equipment hatch, Rigging International had to blast a hole through the side of the reactor. It installed a 20ft by 30ft aerial work platform 20ft above the ground for this purpose, according to Pat Glennon, Rigging International engineer.
To minimise any radiation leakage, teams worked around the clock to finish the job. Rigging International installed beams to roll out the old head, sprayed with a rubber insulation coating in case it was slightly radioactive. The head was picked on a 33ft radius, slewed and lowered on to a six-axle Goldhofer trailer with a 500t Demag AC 1200 leased to Rigging International by All Erection. Then they did the job in reverse, lifting the new head on to the work platform and then rolling it inside. The whole exchange job took a day and a half, and finished in the last days of 2002.
Dominion Power completed another head change at the site in March 2003, was scheduled to do another last month at time of going to press, and will do another later in the year. Bechtel was the primary construction contractor.
