TVA readies Watts Bar 27 July 2015
The second unit at the Watts Bar nuclear power plant in southeastern Tennessee is set to come online in December, making it the first new US power reactor to begin operation in almost 20 years. Thecla Fabian looks back at one of the longest reactor construction projects in history.
The last US reactor to start up was Watts Bar 1, which began operation in May 1996. Like its twin, it is a 1150MWe Westinghouse-designed four-loop pressurised water reactor where construction first began in 1973. Federally owned US power utility the Tennessee Valley Authority (TVA) halted construction on both units in 1985, with unit 1 essentially complete and unit 2 about 80% complete. TVA restarted construction on Watts Bar 2 in 2007, and expects the final cost of the restart will be $4-4.5 billion, TVA spokesman Scott Brooks told Nuclear Engineering International.
In October 2000, at the request of TVA, the US Nuclear Regulatory Commission (NRC) pushed back the expiration of the construction permit for unit 2 to 31 December 2010. TVA informed NRC in November 2006 that the utility planned to study the feasibility of completing unit 2, with the goal of producing power by 2013. Based on an evaluation of energy needs, schedule, projected costs, environmental impacts and financial risks, TVA's board of directors approved restarting construction and notified the director of NRC's Office of Nuclear Reactor Regulation (ONR) of its decision.
Bechtel was brought in as lead contractor for the completion project. It also served as project manager between 2007 and 2012, when TVA brought project management back in house with Bechtel continuing as lead contractor.
TVA updated its original June 1976 application for an operating licence in March 2009. It had to submit separate applications for a construction licence and an operating licence, because it had submitted its original licence applications for Watts Bar 2 years before NRC had approved the option of a combined construction and operating licence (COL).
The NRC staff published the Final Environmental Impact Statement for operation of Watts Bar 2 (NUREG-0498) in May 2013, and in November 2013 NRC issued an order extending the construction completion date once again, this time to 30 September 2016.
ONR monitors and inspects work on Watts Bar 2 and identifies requirements TVA must meet before it receives the final operating licence. On 26 May 2015, the NRC Commissioners unanimously voted to give the ONR director authority to issue a full-power operating licence for Watts Bar 2.
NRC chairman Stephen Burns noted that in the past, NRC issued a low-power operating licence to allow fuel loading and low power testing, followed by a full-power operating licence after the licensee demonstrated its ability to operate the facility within design and licensing parameters. However, Burns said this two-step process was not necessary if the application was uncontested, as was the case for Watts Bar 2. He further noted that TVA had operated Watts Bar 1 for almost 20 years, and that the two reactors shared a similar design and licensing basis.
On 12 February 2015, NRC's independent adjudicatory body, the Advisory Committee on Reactor Safeguards (ACRS) -- recommended proceeding with the Watts Bar 2 licence and noted that there was "reasonable assurance" that it could operate "without undue risk to the health and safety of the public." In a 13 February statement, TVA chief nuclear officer Joe Grimes said the ACRS conclusion on TVA's readiness and ability to operate a two-unit plant at Watts Bar resulted from six years of discussions, interactions, and meetings through which TVA demonstrated that unit 2 "is being completed the right way -- safely -- with quality, and in a manner to protect the general public."
The Commission's 26 May vote on the full-power licence was a critical regulatory step necessary to keep the plant on track to become the first new US nuclear generation of the 21st century, said Grimes. Delegation of the licensing authority signified confidence that NRC inspections showed Watts Bar 2 is being built according to regulatory requirements and industry standards.
Only finishing touches remain
Bulk construction on Watts Bar 2 is complete and TVA is finishing work on a few remaining systems so it can perform final testing, Mike Skaggs, senior vice president for Watts Bar Operations & Construction, told a public meeting in Athens, Tennessee, on 26 March.
So far, TVA has expended more than 34 million person-hours on the project without a lost-time accident, he said. In quality control inspections more than 97% of the work was accepted.
When construction resumed in 2007, TVA estimated that, with changes in technology and regulation, the project was 30-40% complete, Brooks said.
Major plant components were tested and found to be useable. These included the reactor vessel, containment, steam generators, and ice condenser. However, the long hiatus in construction has led to extra work. Core bore sampling was needed on all previously installed concrete. The samples underwent destructive testing to verify that they could meet or exceed the original design specifications, Skaggs said. TVA also had to evaluate steel rebar embedded in the concrete. All buildings successfully passed inspections for cracking or any unexpected movement.
Miles of new cabling had to be installed, after previously installed cable was voltage-tested to determine whether conductors and insulation had degraded over the years. TVA also had to replace piping, much of it because of design revisions that called for different sizes or grades of material. Borescope inspections were used to verify the internal condition of some piping. Pipes deemed acceptable were flushed to meet cleanliness requirements.
A number of pumps had to be reinstalled when vibration problems during testing showed that an unnamed vendor had supplied unsatisfactory equipment, Skaggs said. Watts Bar already has onsite all the staff needed to run a two-unit plant, Skaggs told a local Tennessee television station in March.
One key element of the construction project was to make sure the control rooms for units 1 and 2 were fundamentally the same, so operators could work in either unit, Brooks said. One of the upgrades to unit 2 when construction resumed was installation of digital instrumentation and control (I&C) systems on both units. However, Brooks said the control rooms still look like 1970s control rooms. The manual systems are still in place and everything is hardwired. If a digital system fails, it will not take the plant offline. Rather, operators will switch to manual controls. Monitoring is digital, but functions critical to shutdown can still be performed manually.
Pre-operational testing is now the critical-path item on the construction schedule, Brooks explained. TVA has completed open vessel testing of safety-related systems used to inject water into the reactor and determined that they operate as designed. It also completed cold hydrostatic testing to verify reactor coolant integrity.
TVA has energised the main transformer and placed it in service, and has drawn the initial vacuum on the secondary side of the plant, identifying a few problems that had to be corrected before it could begin hot functional testing, which is the final group of tests. Hot functional testing was scheduled to begin in June, Brooks said. Pumps and the steam generators will be used to bring the reactor up to operating temperature and pressure without fuel in the reactor.
Any problems found during hot functional testing, such as a valve or hose failure, will be repaired before NRC issues the final full-power operating licence, which TVA hopes to have before the third quarter, and possibly as early as July.
TVA finished loading all of the ice into the ice condenser in the last week in May, Brooks said. The ice condenser is designed to rapidly absorb heat released in the containment building during a loss of coolant accident or steam line rupture, thereby reducing pressure in the containment building.
Once TVA has its full-power licence, it will load the fuel. TVA will then begin full temperature and pressure testing, followed by first criticality. It will gradually increase power to 100%. A final test involves a unit trip and restart, followed by re-increase of power to 100% and an initial 20-day generation period. After that, TVA can declare the unit commercially operational.
Meeting all post-Fukushima requirements
In March 2015, TVA notified NRC that Watts Bar 2 had achieved full compliance with the regulator's Fukushima mitigating strategies order, becoming the first US reactor to do so. It was the first US reactor to pass NRC's stringent post-Fukushima inspection, and it is one of a handful of US plants that they have certified to have completed all the required work, Brooks said.
Watt Bar 2 began planning and implementing enhanced emergency preparedness before NRC issued its guidance, because it wanted to ensure that the post-Fukushima changes would not delay the licensing schedule, Brooks said. As a result, it became the pilot for post-Fukushima plant enhancements. "What we did went above and beyond what NRC later required," he said.
The unit has installed multiple redundant cooling systems including a 500,000-gallon water tank; added a hardened "Flex" building to store emergency equipment; and provided additional diesel generators and portable and pre-staged Flex emergency equipment, including diesel-driven water pumps and electric generators, ventilation fans, hoses, fittings, cables and communication gear.
Station blackout plans include three layers of protection: backup diesels within the concrete reactor building that can withstanding flooding and worst-case seismic events; a second set of generators and pumps in the Flex building; and access to equipment stored at the multi-plant Flex centre in Memphis, Tennessee, which can ship emergency equipment to Watts Bar 2 within 24 hours.
TVA also installed a smaller backup emergency diesel generator on top of the containment building to provide power to critical controls if onsite power is lost.
When completed, Watts Bar 2 will have satellite communications, portable electric generators, portable water pumps, more fire hoses and fittings than any other US reactor, portable battery carts, spare electrical equipment (cable, breakers, insulators), emergency kits, and an enormous number of radiation monitoring devices. It will have a 3MWe diesel generator as backup to existing onsite diesel generators, and a 150kW diesel generator for recharging the plant's backup battery banks.
TVA says the plant can withstand a major earthquake, flooding resulting from failure of a large nearby dam, a tornado throwing a 4000-pound missile (e.g. a car or a bunch of utility poles) at 360mph, or a major airliner crash. There are no tsunamis expected at the east Tennessee site for at least 200 million years, TVA said.
NRC region II administrator Victor McCree told a March public meeting in Tennessee that inspections by NRC's onsite and regional inspectors had not identified any significant safety concerns that would preclude NRC from issuing the full-power licence.
NRC has expended more than 73,000 hours on inspections at Watts Bar 2 since construction resumed, including more than 23,000 hours in 2014. McCree said he expects NRC will spend the same amount of time, or more, on inspections in 2015.
TVA estimates it will be able to operate Watts Bar 2 for at least 60 years at load factors of 90% or more, producing 700TWh of electricity over its lifetime.
Once the plant comes online, TVA plans to obtain 40% of its power from nuclear. However, when it will reach this goal depends on when it retires its older coal plants, now expected by the end of 2017, Brooks told NEI.
TVA's current generation mix is 36% nuclear, 43% coal, 12% hydro, 9% natural gas and a small amount of oil-based generation. Less than 1% is non-hydro renewables. With plans to retire its old coal plants, TVA estimates it will need 9600MWe of new capacity by 2019.
While the utility does not have plans to build additional reactors, it does plan to uprate three of its six existing reactors - Browns Ferry 1,2 and 3 sited 32 miles west of Huntsville, Alabama. The reactors, all BWRs, are licensed to operate into the 2030s. Final decisions on the size of the uprates will come after Watts Bar 2 is in operation.
TVA also has two more partially completed reactors in preservation status, at the Bellefonte site in Hollywood, Alabama. Both are 1256MWe Babcock & Wilcox PWRs where construction began in 1974 and was halted in 1988. Plans to resume construction are on hold, because TVA does not expect sufficiently strong demand growth in the next decade. It estimates resuming construction at Bellefonte would cost $6-8billion.