Jun. 14—Less than six years after the Tennessee Valley Authority completed construction of America's newest commercial nuclear reactor, workers cut a giant hole in the containment building of the new structure this spring to replace key components deemed to be potentially unreliable.
Over the past three months, with the aid of more than 2,000 extra TVA and contract workers on site, four 67-foot-long steam generators have been removed and newer versions of the GE equipment installed in their place in the Unit 2 reactor at the Watts Bar Nuclear Plant near Spring City, Tennessee
"The four new steam generators are in place, and all the primary welding to connect the new generators into the plant is complete," Tim Rausch, TVA's chief nuclear officer, said in an interview last week with the Chattanooga Times Free Press.
Over the weekend, TVA began refueling the Unit 2 generator at Watts Bar and is expected to begin pressure tests of the containment building next week after workers resealed the structure that houses the reactor, TVA spokesman Jim Hopson said in a phone interview Monday.
With a price tag of more than $500 million for planning, design and implementation, the project is the biggest nuclear refueling and maintenance outage at TVA in nearly a decade since similar steam generators were replaced at the Sequoyah Nuclear Plant.
WEATHER DELAYS REPLACEMENT
Rausch said the project has proceeded safely so far, but it was delayed by the weather when there was wind above the Unit 2 containment building that made it too risky to lift and lower the 850,000-pound steam generators into place using a giant Demag Outdoor Lift System Crane with a 300-foot boom— the world's second biggest crane. The crane is capable of lifting 3 million pounds, but with its elevation and 1.4 million pounds of counterweights, the crane also is restricted from operating in windy conditions.
"In order for the boom on the crane to be up with these size loads, the wind had to be below 22 miles an hour, and at the top of the boom, it was not hard to get winds of that magnitude," Rausch said. "So we did experience some weather delays early on when we were taking the old equipment out of the building. But our priority has always been on safety over speed."
Rausch said the new generators should help improve the efficiency of the Watts Bar unit but will not have a major effect on boosting power output. TVA has set a goal of boosting its nuclear capacity factor — or the share of time a reactor is running at maximum power — from about 90% five years ago to 95% by 2025.
In 2021, the capacity factor of all nuclear power plants in the United States averaged 92.7%, slightly up when compared to the previous year, according to the Nuclear Energy Institute.
"We're moving from the bottom quartile (lowest 25% of performance among all U.S. utilities) to become a top performer in the industry," Rausch said.
THE HEAT IS ON
The Unit 2 reactor, which is capable of supplying enough power for about 650,000 homes, won't be available for power generation this week. With the National Weather Service calling for temperatures to top out in the mid-90s across much of TVA's seven-state region, electricity demand in the Tennessee Valley is projected to reach the highest so far this summer this week.
Hopson said TVA doesn't expect any problem in meeting the peak demand, which will still be far below TVA's all-time summer peak of of 33,482 megawatts reached in the summer of 2007, when temperatures across the valley averaged 102 degrees.
Although TVA has operated its newest reactor at Watts Bar for less than six years, the steam generators being replaced were built in the 1970s using designs that are nearly a half century old. The existing steam generators were found to be built with a metal alloy that has prematurely developed leaks and other problems at other nuclear plants.
The Watts Bar project this spring is the last of four such steam generator replacement projects TVA has done at its pressurized water reactors in East Tennessee. The four steam generators in each of the Watts Bar reactors act as heat exchangers to convert water into steam from heat produced in a nuclear reactor core.
DECADES OF CONSTRUCTION
The potentially unreliable equipment was installed at Watts Bar in the 1980s before TVA suspended work at the site due to cost overruns, employee safety concerns and a drop in the projected power demand in the valley. TVA determined it would be too costly to replace the original steam generators when construction was resumed at Watts Bar Unit 2, so TVA operated with the original steam generators through a couple of earlier refueling outages before beginning the installation of the new units.
In 2014, TVA ordered the four new Westinghouse steam generators even before the Unit 2 reactor began generating power in 2016 as the most recent nuclear reactor in the country to be started up by a U.S. utility. TVA paid $160 million for Westinghouse to make the giant steam generators, and TVA has spent millions of dollars more to transport them and store them at the Watts Bar site even before the giant cranes and construction crews were brought to the plant this year to install the new generators.
Contact Dave Flessner at email@example.com or at 423-757-6340. Follow him on Twitter @dflessner1.
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