Just two weeks ago, a mammoth crane hoisted a 659-ton containment vessel “top head” onto the Sanmen 1 reactor being built in China’s Zhejiang province.
The successful feat, akin to placing the star atop a decorated Christmas tree, was watched closely by U.S. engineers because both sites are using the new Westinghouse AP1000 modular reactor design that will make future nuclear plants as similar as Wal-Marts.
The China project, begun two years ahead of Vogtle, serves as a crystal ball of sorts that can help predict successes and identify challenges at Vogtle.
“The (Vogtle) builders, Shaw and Westinghouse, are gaining a lot of good lessons learned from a design and construction perspective,” said Mark Rauckhorst, Southern Nuclear’s construction vice president for Plant Vogtle’s Units 3 and 4.
Although the $14 billion Vogtle expansion involves the first new U.S. reactors built in decades, the Sanmen 1 unit – scheduled to begin generation in October 2014 – will be the world’s first AP1000 unit to go into service.
The two Vogtle units are scheduled to begin operation in 2016 and 2017, but contractors have said there could be delays of a year or more. Negotiations remain under way to determine a new completion schedule.
Although placement of major containment vessel components remains far into the future at Vogtle, the next major milestone is expected to occur in March, with the first pouring of “nuclear concrete” into Unit 3’s nuclear island.
Some of the beneficial changes that have occurred at Vogtle are a direct result of lessons learned from the Sanmen project, Rauckhorst said.
One example involved changing onsite fabrication of certain components from a horizontal to vertical alignment, which engineers say makes the welds stronger and easier to accomplish.
Subtle design changes made as a result of lessons learned at Sanmen have also helped at Vogtle, he said.
“Lessons are learned during their construction phase, then it allows our design for Units 3 and 4 to already have incorporated those lessons before we get to the field.”
One of the biggest advantages the China project will offer to Vogtle engineers is the opportunity to observe the testing and startup functions at Sanmen 1.
“That will be very important to our operational and engineering folks,” he said. “Our plan is to have people at that plant, more in an observation capacity.”
The AP1000 design is much different than traditional units that rely on electric or diesel pumps to provide cooling water that would prevent a meltdown.
Each new unit includes tanks on the top of the containment vessel that hold enough water to cool the reactor for 72 hours. The emergency water supply requires no electricity or pumps, and relies only on the force of gravity to flow into the reactor during a power outage.
Other than Vogtle, the only U.S. project under way with AP1000 construction is in South Carolina, where two new units are being added to SCANA’s V.C. Summer Plant.