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Watts Bar Unit 2 Timeline

Today—Complete and Commercial

The nation’s first new nuclear generation in 20 years officially entered commercial operation on October 19, 2016.

The $4.7 billion capital construction project was completed on budget. The unit now moves to working asset status.

It now joins six other operating TVA nuclear units to supply more than one-third of the region’s generating capacity, and meeting the electric needs of more than 4.5 million homes.

Watts Bar Nuclear Plant

October—Power Ascension Testing Complete

Workers at Watts Bar Unit 2 have completed an extensive series of tests designed to validate the safety and reliability of the unit.

Power Ascension Testing was a highly detailed series of tests performed at various power levels to ensure all systems operate safely as designed.

The unit is now in a pre-commercial operations reliability period of extended full power generation.

Dual Operations

August 2016—Power Ascension Testing

Watts Bar Unit 2 staff has completed six of seven power ascension testing periods:

  • Initial core loading
  • Post-core load pre-critical
  • Initial criticality/low power
  • 30% power plateau
  • 50% power plateau
  • 75% power plateau

The final test plateau involves taking the unit to 100% power for the first time and conducting multiple tests at full power.

Control Room

June 2016 – Unit 2 Produces Power for the First Time

Watts Bar nuclear Unit 2 generated electricity onto its power grid for the first time on Friday, June 3.

The unit is officially synced to the power grid and licensed reactor operators have begun an initial test run of generation equipment. The team is using this run to collect data to be sure generating equipment is prepared for continuous full-power operation later this summer.

Watts Bar Unit 2, like Unit 1, produces electricity using controlled nuclear fission to generate heat, which is used to produce steam to turn turbines and a single, large generator.

Watts Bar Unit 2 - Initial Electricity Generation - Reactor Operator Bill Hahn 6-3-2016

Reactor Operator Bill Hahn synchronizes Watts Bar Unit 2 to the TVA power grid on Friday, June 3, 2016.

Watts Bar Unit 2 - Initial Electricity Generation - Reactor Operator Eric Silvers - 6-3-2016

Reactor Operator Eric Silvers monitors the Unit 2 Control Room screen displaying 49 megawatts of electric output.

Initial Criticality Achieved May 23, 2016

RO Greg Ratliff

Watts Bar Nuclear Plant Unit 2 Reactor Operator Todd Blankenship monitors reactor conditions ahead of initial criticality, which was achieved at 2:16 a.m. EDT, May 23, 2016.

Watts Bar Unit 2 is generating heat under its own power for the first time. Known as “initial criticality,” this milestone means the reactor has achieved its first sustained nuclear fission reaction, and is operating safely as it is designed.

Like its sister, Unit 1, Watts Bar Unit 2 is designed to produce electricity by using controlled nuclear fission to generate heat, which is then used to produce steam to turn turbines and a single, large generator.

The reactor is now operating in a stable condition at low power levels. Power levels will be slowly increased as part of scheduled power ascension testing and the unit will begin producing electricity that will flow onto TVA’s transmission system.

Plant systems and controls will be monitored and tested at various power levels up to 100 percent. These tests will be repeated multiple times to ensure the entire system operates safely as designed.

Once all tests have been completed successfully, the unit will provide a sustained 1,150 megawatts of safe, low-cost, reliable, carbon-free electricity to the Tennessee Valley. Combined with Watts Bar Unit 1, the plant will supply power to roughly 1.3 million homes in the TVA service area.

May 2016

As part of continued testing, we are heating up plant systems reaching “Mode 4” then “Mode 3,” a first for the new unit. This new level of operation is another step leading up to power generation.

Watts Bar April 2016

December 2015 – Fuel Load Completed

We completed loading the 193 new fuel assemblies into the Unit 2 reactor, marking the first initial core load of a commercial nuclear reactor in the United States in nearly two decades.

With fuel loaded and the reactor reassembled, the Watts Bar team can begin testing the unit's performance as its power output is gradually increased to full capacity. Power ascension testing is an extension of the pre-operational tests and is the final phase designed to ensure that Unit 2 is capable of delivering electricity safely, reliably and efficiently to TVA’s power system.

Fuel Load

November 2015 – Preparation for Fuel Load

The Watts Bar Nuclear Plant team began preparations to transfer 193 new fuel assemblies into the Unit 2 reactor vessel. Fuel assemblies were staged in the used fuel pool.

Fuel Load

October 2015 – Operating License Issued

Issuance of the operating license for Watts Bar Unit 2 by the U.S. Nuclear Regulatory Commission on Oct. 22, 2015, is the culmination of a good team completing a tremendous amount of hard work and complex testing the right way – safely and with quality – and demonstrating that Unit 2 can be operated in a manner that ensures regulatory compliance

September 2015 – Last Major Pre-Operational Testing Milestone Complete

Work at Watts Bar Unit 2 is focused on activities that support license readiness after successfully completing the last in a series of major testing milestones required before fuel can be loaded into the reactor.

  • Integrated Safeguards Test – Verified the integrated performance of the Engineered Safety Features Actuation System which is designed to automatically trip the reactor and activate safety systems in response to specific plant conditions. The testing included the automatic actuation of hundreds of design safety feature components.
  • Structural Integrity Testing – Involved increasing pressure inside the containment structure to check welds and other seals to make sure they function as designed.
  • Containment Integrated Leak Rate Testing – Increased pressure in the steel containment structure to higher than normal levels to check openings for valves, piping, cable penetrations and airlock doors for excessive leaking.


August 2015 – Unit 2 is Substantially Complete

On August 10, the Watts Bar team completed hot functional testing, marking the first time nearly 60 important systems operated together. The testing was a critical pre-operational requirement leading up to TVA requesting an operating license from the Nuclear Regulatory Commission. The data gathered builds on earlier testing milestones—open vessel testing, cold hydrostatic testing and secondary hydrostatic testing—and further ensures that Watts Bar Unit 2 systems will support safe operation as designed and according to established NRC regulations.

August 2015 at Watts Bar

TVA has notified the Nuclear Regulatory Commission that Watts Bar Unit 2 is substantially complete. This is a major construction milestone. The notification also provides a listing of key activities that remain to be finished prior to operation, and requests that an operating license be issued for the unit. The letter follows recent completion of comprehensive testing on major Unit 2 systems to demonstrate operational readiness. Called hot functional testing, the tests showed that nearly 60 important systems can function together at operational temperatures and pressures as designed and built.

June 2015 – Watts Bar is First in the U.S. to Complete Post-Fukushima Upgrades and Inspection

Safety first! Watts Bar is the first nuclear plant in the nation to complete the inspection process for a FLEX post-Fukushima safety program. The site passed the inspection by the Nuclear Regulatory Commission— affirming that Watts Bar is prepared to respond to external challenges that could lead to a loss of offsite power and cooling water.

FLEX June 2015

Upgrades for the FLEX program include:

  • A concrete building that houses backup emergency diesel generators and pumps
  • A 500,000-gallon water storage tank
  • New response procedures and training for employees.

May 2015—Important Step Toward License

The Commissioners of the U.S. Nuclear Regulatory Commission (NRC) voted to delegate authority to the director of its Office of Nuclear Reactor Regulation (NRR) to issue a full power-operating license for Watts Bar Unit 2, pending applicable regulatory requirements being met.

“The commission’s action was a critical regulatory step necessary to keep Watts Bar Unit 2 on track to become the nation’s first new nuclear generation of the 21st century,” says TVA’s Chief Nuclear Officer Joe Grimes. “The delegation of this authority signifies confidence that NRC inspections show Watts Bar Unit 2 is being built according to rigorous regulatory requirements.”

The issuance of the NRC’s Staff Requirements Memorandum (SRM) delegates authority to issue the Watts Bar Unit 2 operating license to the part of the oversight agency that monitors and inspects the work that's been done and notes requirements TVA must meet before the license can be issued.

"We have a responsibility to complete Watts Bar Unit 2 the right way—safely and with quality. That's what we're doing,” adds Sr. VP of Watts Bar Operations and Construction Mike Skaggs. “The Watts Bar team has made tremendous progress getting us to this point and is focused on the work and challenges ahead to successfully complete, test and license Unit 2 and to integrate the unit into TVA’s nuclear fleet."

April 2015 – Pride in our Progress

Our people are the key to success at Watts Bar Unit 2. In this video, nuclear unit operator Camille Stringfellow shares her pride in the work TVA is doing to bring online the first new nuclear generation of the 21st century.

March 2015—Preparations for More Critical Testing

Critical systems on Unit 2 are being readied for a major pre-operational milestone—hot functional testing. The unit will be brought up to operational temperatures and pressure without fuel in the reactor to ensure major systems important for making and moving the steam used to generate electricity will function together as designed. Important safety functions will also be tested.

Preparations include:

  • Energizing the main Unit 2 transformers and parts of the electrical distribution system
  • Using normal plant procedures to place systems and components that will be used during hot functional testing into the alignment that will be used for power operations
  • Confirming through testing the operability of motors, pumps, valves, circuits and other devices in nearly 60 systems

Hot functional testing will be conducted over a period of about 45 days during which Watts Bar systems will largely operate as a dual-unit nuclear plant for the first time.

February 2015—Major Regulatory Milestone

Watts Bar Nuclear Plant Unit 2 has cleared a major milestone toward becoming the nation’s first new nuclear generation of the 21st century. Based on detailed analysis and review, a key advisory group for the Nuclear Regulatory Commission has recommended the Commission approve the Watts Bar Unit 2 operating license, once TVA completes the remaining work and NRC inspections. The Advisory Committee on Reactor Safeguards made its recommendation after reviewing documents and inspections focusing on safety-related items.

Watts Bar

January 2015—Control Rooms

The control rooms of both Watts Bar Unit 1 and Unit 2 are being made to support monitoring and control of many critical systems.

  • More digital links for monitoring allow operators to better respond to equipment or system issues
  • Upgraded control rooms that ensure little or no difference for operators training on the units

Upgrades to the Unit 2 control room also include the installation of more than 15 miles of new electrical wire, replacement of nearly 800 hand switches and reconfiguring more than 900 alarm indicators.

The control rooms will be essentially identical by the time Unit 2 comes on line.

January 2015—On Track for First New Nuclear

Watts Bar Unit 2 is on track to be the nation’s first new nuclear generation in the 21st century. Work at the project is building on proven technology, using established engineering and design standards, and a plant that was initially started in the 70s is being updated through a comprehensive refurbishment effort.

December, 2014—Cold Hydro Tests Complete

Another major milestone for the Watts Bar Unit 2 project is complete. Cold Hydrostatic Testing took place during three separate tests over several months—and verified that welds, joints, pipes and other components in the reactor coolant system, steam-supply system and associated high-pressure systems do not leak and will hold pressure.

December 2014 - Watts Bar

The final pressure test was successfully conducted in mid-December. That test involved pressurizing the systems at above normal operating conditions, and set the stage to move these systems and components forward from construction to operation status.

December 2014—Another Safety Milestone

Workers at Watts Bar Unit 2 continue to put safety first—and have now logged more than 30 million work-hours without a lost-time incident.

November 2014—Project on Track

  • The latest quarterly update to the Watts Bar Unit 2 Estimate to Complete covers the work accomplished between May and July 2014.
  • One year ago, the project was in final stages of bulk construction. There has been good progress since then as demonstrated by the focus on system specific construction work to support testing milestones and the successful completion of open vessel testing during the quarter.
  • The update validates that overall project targets continue to be met for safety, quality, cost, and schedule.

October 2014—TVA Meets with NRC Officials

On October 30, TVA nuclear leadership briefed the U.S. Nuclear Regulatory Commission in a public session at NRC headquarters in Rockville, Md. As part of the licensing process for Watts Bar Unit 2, TVA provided an update on key aspects of the Watts Bar project, including TVA’s ability to safely operate and maintain two units.

Prior to that meeting, NRC member Kristin Svinicki toured Watts Bar on October 22. While at the site, she was briefed on the work to complete Watts Bar Unit 2, transitioning Watts Bar to dual-unit operation, and integrating the dual-unit site into TVA’s nuclear fleet.

Mke Skaggs and Svinicki

Commissioner Svinicki’s visit is the fourth tour of Watts Bar Unit 2 by an NRC commissioner this year. The visits provide a first hand look at the completion project and how TVA is ensuring Unit 2 is being built safely, with quality and in a manner designed to ensure excellence in operation following licensing. 

October 2014—Cold Hydrostatic Testing

Watts Bar Unit 2 passes a major pressure test: Primary Cold Hydrostatic Testing, or Cold Hydro. By demonstrating that the systems and components that are central to nuclear operations can safely hold pressure above the normal operating value of 2250 psi, the team completed a major testing milestone. That’s puts Watts Bar Unit 2 one step closer to becoming the nation’s first new nuclear power generation of the 21st century.

hydrostatic Oct 2014

September 2014—Safety Milestone

Safety is top priority at Watts Bar Unit 2. The team has logged more than 28.8 million hours without a lost-time incident.

August 2014—Reactor Vessel Is Assembled

The Watts Bar Unit 2 team safely completed the first and largest portion of assembling the reactor vessel: placing the core barrel into the reactor vessel. Inspections were performed at every stage as the 282,000-pound barrel was lifted and then lowered into the reactor. The entire lift process took approximately 12 hours to safely set up and complete—and was executed perfectly.

Reactor Vessel

This was the first of three lifts that need to be completed to assemble the Unit 2 reactor for Cold Hydro, a pressure test that requires the reactor vessel to be assembled and tests the reactor coolant system and the high-pressure portions of the residual removal system, the steam generator and the chemical and volume control system and the safety injection system.

July 2014—FLEX Buildings Mean Safety

Watts Bar Unit 2 is the first nuclear plant in the U.S. to meet new Nuclear Regulatory Commission regulations established after the 2011 earthquake and tsunami that struck Fukushima Nuclear Plant in Japan. Watch the construction of one of the first functional FLEX buildings in the industry, complete with a 16-foot-tall tornado-proof door, designed to protect emergency equipment from missiles created in tornado situations, including flying cars.

FLEX Building

July 2014—Open Vessel Testing

On July 1, 2014, Watts Bar Unit 2 completed Open Vessel Testing, which tests key safety and safety-support systems designed to deliver water to the reactor vessel. The time-lapse video below shows approximately 185,000 gallons of water flowing into the Watts Bar Unit 2 reactor vessel over a 23-minute period of testing.

Watts Bar team members now are reassembling the reactor in preparation for a second major testing milestone, Cold Hydro. This test verifies that welds, joints, pipes, components of the reactor coolant system and associated high-pressure systems meet quality standards.

June 2014—Cooling Tower Turned Over to Operations

Watts Bar Unit 2’s massive cooling tower was transferred from Nuclear Construction to Nuclear Operations, signaling its readiness for operations.

When a plant is operating, cooling water from the condenser is distributed through pipes and baffles inside the cooling tower and falls like rain about 60 feet, which cools the water before it is continuously recycled to condense more steam. Water in the vapor rising from the cooling tower is replenished to the condenser cooling system with water from the Tennessee River.

May 2014—Coolant System Ready for Testing

Watts Bar Unit 2 completed a significant amount of work to release the reactor coolant system to the site’s pre-operational startup engineering team after completing more than 192,000 craft hours and more than 1,200 work orders.

The system is the heart of the nuclear plant, constantly circulating highly pressurized water through the reactor, four steam generators, a pressurizer and the piping that connects them to the reactor. Inside the steam generators, the heat from the water coming from the reactor is transferred to a second separate supply of water that turns to steam that powers the turbine generator. See how Watts Bar Nuclear Plant uses steam to make power.

April 2014—Prepping for Testing

Engineers get an early jump on preparations for Open Vessel Testing, the first in a series of major milestones to lead Watts Bar Unit 2 to regulatory approval to load fuel. Open Vessel Testing ensures key safety systems and safety support systems work as designed to deliver water to the reactor vessel. Open Vessel Testing will culminate in water flowing into the reactor at about 10,000 gallons a minute.

April 2014—Operators Presented with Licenses

Eight nuclear professionals were formally presented with their Watts Bar Unit 2 operator licenses by Nuclear Regulatory Commission officials at an awards dinner in Cleveland, Tenn. The ceremony marked the licensed operators’ completion of 18 months of training and testing requirements.

January 2014—Shifting Gears

The focus of work on the Watts Bar Unit 2 is shifting from large-scale construction to completion and testing of individual plant systems.

Watts Bar - January 2014

October 2013—Meeting Challenges

Safety and quality continue to be excellent as workers move toward delivering Watts Bar Unit 2 on time and within budget.

However, some challenges are arising, too. These include:

  1. Completing complex work and required documentation
  2. Performing testing on shared Unit 1 and Unit 2 systems without impacting the safe and reliable operation of Unit 1
  3. Addressing regulatory and licensing issues
  4. Successfully transitioning the site to dual-unit operations

July 2013—Review Yields Good News

The latest quarterly review of the Watts Bar 2 Estimate to Complete found:

  • Workers continued to deliver good safety performance.
  • Quality performance remained high, improving to 97 percent.
  • Overall, cost performance continued to be better than projected in the revised estimate to complete.
  • Schedule performance met expectations.
  • Challenges are anticipated as the as some systems move into testing mode, and others are completed.
  • No new risks emerged that currently compromise completion of the project; regulatory and licensing issues remain the primary concerns.

April 2013—Goals Exceeded

One year after the TVA Board approved the further construction of Watts Bar Unit 2, a quarterly review showed that the project continued to meet or exceed goals for quality, schedule and safety. 18 million work hours had been logged without a lost-time incident, and the overall quality acceptance rate was at 96 percent or better. However, despite the excellence, there will be challenges as the team works to deliver a safe, reliable unit.

February 2013—Moving the Vessel Head

Lifting an assembly made of 144 tons of carbon steel and precisely crafted control rods from a reactor vessel and moving it into a specially built holding stand and then putting it back again is a complex job. But the team achieved the right results and moved the 288,000-plus pound Watts Bar Unit 2 reactor pressure vessel head from its holding stand to the top of the reactor pressure vessel safely.

Head Lift

December 2012—Construction Moves Forward

The Watts Bar Unit 2 project focused on efficiently performing construction activities; maintaining the overall pace of installing commodities, such as valves, piping and cable; and continuing to implement improvement initiatives.

September 2012—Safety First

Building a nuclear plant is a complex task with lots of inherent safety hazards. But workers at Watts Bar Unit 2 recognize this, and by keeping safety first, surpassed 16 million work hours without an accident.

Watts Bar Unit 2 construction workers are demonstrating their commitment to keeping themselves and others safe by:

  1. Wearing the right personal protective equipment for every job
  2. Taking 2 minutes before they start work to identify potential hazards
  3. Immediately reporting potential safety issues and every injury so appropriate steps can be taken to prevent future injuries
  4. Intervening to protect each other from unsafe acts and to reinforce safe behaviors


April 2012—Green Light for Watts Bar Unit 2

The TVA Board of Directors approved continuing the construction of Watts Bar Unit 2 with a revised estimate to complete of $4 billion to $4.5 billion. Estimates have it that the unit will be completed between September 2015 and June 2016. Once operational, Watts Bar Unit 2 will produce the first new nuclear generation in the United States—providing energy that is low-cost and carbon-free. When completed, Watts Bar Unit 2 will generate 1,150 megawatts of electricity—enough for about 650,000 homes in the Tennessee Valley