|Easy Does It. For generator rewind, 208-ton, 53-ft-long rotor was shipped back to manufacturer for high-speed balance.|
The Tennessee Valley Authority and its contractors had a distinct advantage when they set about the $1.8-billion job of restarting Unit 1 at the Browns Ferry nuclear plant in Alabamathey had already finished that task on the sites other two units.
As a result, TVAs latest unit overhaul will cost less and require fewer man hours, says Jon Rupert, the federal utilitys Unit 1 restart vice president. The project began in May 2002 and was scheduled for completion in five years. Officials say it is now running ahead of schedule, with construction about 65% complete and a projected on-line date as early as November 2006.
Browns Ferry was the largest nuclear powerplant in the world when it was completed in 1977, say TVA officials. Its three boiling-water reactors produced 2,285 MW of power. Unit 1 went on line in 1974, but was shut down in 1985 because of "design control problems," says a former reactor engineer there. Safety concerns shut down the other two units the same year.
By 2001, TVAs board began to consider restarting Unit 1. Over the next six months, it hired a team of site-experienced experts from inside and outside the utility, including those from Bechtel Group Inc. and Stone & Webster Engineering Corp., now part of Shaw Group, Baton Rouge. They prepared a detailed cost estimate that advocated standardizing the units design with the others. "We studied lessons learned in engineering, design, and maintenance from the other restarts," says Rupert. "We also looked at modifications that were planned on units 2 and 3 through 2007."
At the same time, TVA officials were preparing a detailed cost estimate to upgrade Unit 1s output from 1,100 MW to 1,280 MW and to relicense it through 2033. Its current license expires in 2013.
TVA originally budgeted $2 billion for the Unit 1 restart. But by including the estimated 8% savings from lessons learned in restarting Unit 3, and the 5% projected savings on man-hours, the cost would drop by $200 million, Rupert says. "We saved 18% on the design phase just from doing it twice before," he says.
The restart of Unit 2 took 74 months to complete and cost $1.4 billion in 1990. On Unit 3, completed in 1995, work lasted 60 months and cost $1.3 billion. Unit 1 will cost $500 million more, but officials claim the job includes significantly more work in the same amount of time.
Developing the project team and the plan were key challenges, with 45,000 separate activities required, says Rupert. In the end, via competitive bidding, TVA awarded the work to the same core team that completed the Unit 3 restart. The infusion of experienced people led to huge efficiencies, he adds.
|Energy-Intensive. Rewinding the sator coil took 18,000 man hours.|
Bechtel Power Corp., Frederick, Md., the Unit 3 engineer, rejoined the team for Unit 1. "We were also involved in Unit 2, so it was a matter of repeating," says Rick Jackson, Bechtel project manager. The firm completed design in March 2004. With design standardization, "it really was more an issue of the volume of work than the technical challenge," he says.
The bigger challenge lay in boosting the entire teams output, Jackson says. Bechtel brought in many site-experienced staffers, using them to mentor younger workers who might not have had sufficient training. "This allowed new people to be more efficient," he says. The firm assigned mentors for specific electrical, civil, structural and mechanical engineering disciplines and to improve drawings.
Design changes required 27,600 major calculations and preparation of 18,000 drawings. "This is not a construction project; it is a modification in a controlled environment," says TVAs Rupert, adding that 1,600 craft workers and 350 support personnel on site will invest a total of nearly 11.8 million man-hours.
Required Unit 1 activities may also disrupt ongoing operations at Units 2 and 3, says Don Olson, Stone & Webster regional director for TVA projects and a veteran of the previous restarts. "We have to make sure the overall schedule is integrated, crisp and efficient," he says. "Other than that, its just a lot of work."
The team developed a logical sequence of work, refurbishing the drywell first, then the reactor, control and turbine buildings. Crews used a library of work orders developed from Bechtels design documents to control work flow. "We have a work in-tegration and scheduling group to assure things are done in sequence," a TVA spokesman says. That avoids impacts on the two operating units and minimizes rework, he adds.
Daily schedule meetings with all groups keep construction on track and their management teams meet daily with the schedule integration group to meld the various tasks. Workflow is tracked in the "war room," which is staffed by representatives from all firms and entities working at the site. They include Rupert and TVA managers in plant operations, restart activities and quality assurance.
A jobsite problem that cant be resolved within 30 minutes is earmarked for the war room. Supervisors and first responders there have direct access to all site managers and can take problem-solving as high up the chain of command as necessary.
Workers decontaminated Unit 1s primary containment structure, which houses its reactor vessel, and most other unit systems to reduce radiation before work began, says Rupert. "It was a business decision that made the work safer, more efficient and cheaper in the long run," he says. Workers can work in plain clothes all day long, he says. Fuel from Unit 1s reactor was removed and stored in the plants spent-fuel pools after the unit was shut down.
|Two Up, One To Go. Browns Ferrys Unit 1 is to be back in service in 2007.|
Workers also replaced contaminated dry well piping because it was easier than refurbishing pipes and qualifying welds, Rupert says. Crews will eventually replace about 16,000 ft of large-bore pipe, between 2 and 42 in. in diameter, and install 1,700 hangers to support the large-bore pipe. Five miles of small-bore pipe, less than 2 in. in diameter, also must be replaced. That job will require 5,900 new hangers. TVA will also install more than 30 miles of conduit, along with the most modern cable-tray system.
TVA is replacing or completely refurbishing all major pumps, motors and valves. All large valves will be new. The utility will also inspect all boiling-water reactor welds and, below the water line, recoat the interior of the 31-ft-dia torus surrounding the reactor.
About 40% of all work will be done in the reactor building. That includes reworking all Unit 1 control panels to mirror those in Units 2 and 3. TVA is buying new turbine generators, condenser tubes and heat exchangers, finding that its less costly than refurbishment, says Rupert. It is also replacing the main bank of transformers, erecting additional breakers in the switchyard to protect the transmission grid and upgrading two substations and a mile of 161-kV line to improve reliability in the region.
Officials contend that the Unit 1 restart is progressing well so far. The unit is very likely to beat its May 2007 target date to come on line, but TVA officials have not officially changed the date. This fall, the project will begin to transition from a modification to a system-driven project, says Rupert. By February, component testing will begin. "This will be the oldest brand-new plant around," he contends.
(Photos courtesy of The Tennessee Valley Authority)