Watts Bar Nuclear Plant

Based on Wikipedia: Watts Bar Nuclear Plant

In October 2016, something happened in eastern Tennessee that hadn't occurred anywhere in America for two decades: a brand new nuclear reactor went online. The Watts Bar Nuclear Plant's Unit 2 became the first commercial reactor to begin operation in the United States since 1996. But here's the remarkable part—construction on that very same reactor had started in 1972.

That's a forty-four year journey from groundbreaking to generating power. The story of Watts Bar is really the story of American nuclear energy itself: ambitious beginnings, decades of doubt, cost overruns that would make a Pentagon contractor blush, and ultimately, a quiet persistence that defies the conventional narrative about nuclear power's demise.

The Tennessee Valley's Nuclear Twins

Watts Bar sits on about 1,800 acres of Tennessee countryside, nestled between Chattanooga and Knoxville along the Tennessee River. The plant is run by the Tennessee Valley Authority, that Depression-era creation of Franklin Roosevelt's New Deal that transformed one of America's poorest regions through dams, electrification, and what we'd now call infrastructure investment.

The facility houses two reactors, both of them pressurized water reactors built by Westinghouse. In this design, water serves two crucial purposes: it cools the nuclear fuel and acts as what engineers call a "moderator"—slowing down the neutrons released by splitting uranium atoms so they can trigger more fissions. The water is kept under such intense pressure that even at temperatures far above boiling point, it remains liquid, carrying heat away from the reactor core to generate steam in a separate system.

Together, these twin reactors can generate about 2,330 megawatts of electricity. To put that in perspective, that's enough to power roughly 1.2 million homes. A typical household might use a kilowatt or two at peak times, so Watts Bar could theoretically supply the electricity needs of a city larger than San Antonio.

A Construction Timeline Unlike Any Other

When workers first broke ground on Unit 1 in January 1973, Richard Nixon was president, the Vietnam War was still grinding on, and the oil embargo that would reshape American energy policy was still months away. The plan called for two reactors to be built in sequence, a common approach for nuclear plants designed to achieve economies of scale.

Construction progressed through the 1970s, that strange decade when nuclear power seemed simultaneously to be the future and increasingly controversial. Three Mile Island's partial meltdown in 1979 shook public confidence, though the reactor's containment structure performed exactly as designed, preventing significant radiation release. But the political and regulatory climate had shifted. New safety requirements multiplied. Costs climbed.

By 1985, with Unit 1 still incomplete and Unit 2 about 60 percent finished, the Tennessee Valley Authority made a painful decision: stop everything. The projected demand for electricity had fallen short of earlier forecasts. The economics no longer made sense, or so it seemed at the time.

For seven years, the partially built reactors sat idle. Concrete aged. Equipment waited. The billions already spent represented a sunk cost that accountants could only shake their heads at.

Resurrection and the Long Road to Completion

In 1992, construction on Unit 1 resumed. Four more years of work followed before the reactor finally achieved what nuclear engineers call "criticality"—the point at which a controlled, self-sustaining nuclear chain reaction begins. This happened on New Year's Day, 1996. Commercial operation started that May, twenty-three years after construction began.

Unit 2's story would prove even more dramatic. After sitting dormant for over two decades, the Tennessee Valley Authority's board voted in August 2007 to complete the second reactor. The initial budget estimate was $2.5 billion. The facility was expected to employ about 2,300 construction workers and eventually create 250 permanent jobs.

Then came March 2011 and the Fukushima Daiichi disaster in Japan. A massive earthquake and tsunami overwhelmed a nuclear plant's backup power systems, leading to three reactor meltdowns and the worst nuclear accident since Chernobyl in 1986. The disaster prompted nuclear regulators worldwide to reassess safety requirements.

The Nuclear Regulatory Commission, the American agency responsible for overseeing civilian nuclear power, issued nine new orders aimed at improving safety at domestic plants. Two of these directly affected Watts Bar Unit 2: the Mitigation Strategies Order, requiring enhanced capabilities to respond to extreme events, and the Spent Fuel Pool Instrumentation Order, mandating better monitoring of the pools where used nuclear fuel is stored.

These weren't minor paperwork exercises. They required actual design modifications to a reactor that was already substantially built according to earlier specifications. The project ran over budget and behind schedule. The final cost of Unit 2 alone reached $4.7 billion—nearly double the original estimate. Combined with Unit 1, the total investment in Watts Bar exceeded $12 billion.

The Last of Its Kind

When Unit 2 finally began commercial operation in October 2016, it earned a distinction that sounds impressive but actually carries a melancholy undertone: it will likely be the last Generation II reactor ever completed in the United States.

Nuclear reactor generations are a way of categorizing design evolution. Generation I reactors were the experimental prototypes of the 1950s and 1960s. Generation II encompasses most of the commercial reactors operating today, designed primarily in the 1960s and 1970s. These are proven workhorses but lack some of the passive safety features engineered into later designs.

Generation III and III+ reactors incorporate lessons learned from Three Mile Island, Chernobyl, and decades of operating experience. They're designed so that in an emergency, natural forces like gravity and convection can cool the reactor without requiring active intervention—pumps that need power, valves that need operators. The Vogtle Electric Generating Plant in Georgia, which brought two new reactors online in 2023 and 2024, represents this newer generation.

Generation IV remains largely theoretical, promising radical improvements in efficiency, safety, and waste reduction. These designs exist mostly on paper and in small research projects.

Watts Bar Unit 2, then, is a monument to an earlier era: conceived when bell-bottoms were fashionable, designed when disco dominated the airwaves, and finally completed when smartphones were ubiquitous. It embodies both the enormous staying power of nuclear technology and the glacial pace at which America has built new capacity.

Early Troubles and Steam Generator Surgery

Nuclear plants are extraordinary feats of engineering, but they're also complex systems subject to wear, corrosion, and occasional failure. Within months of Unit 2's commercial debut, problems emerged.

In March 2017, the reactor went offline due to failures in its condenser—the equipment that converts steam back into water after it has spun the turbines. The condenser dated from the original 1970s construction, meaning it had sat for decades before finally being put into service. One section suffered a structural failure. Repairs took four months.

Both units have also required major surgery on their steam generators, the heat exchangers where water from the reactor transfers its thermal energy to the secondary system that actually drives the turbines. The original steam generators were vulnerable to a phenomenon called stress corrosion cracking, where the combination of mechanical stress, heat, and corrosive conditions causes metal to develop microscopic cracks over time.

For Unit 1, replacement happened in the early 2000s. Unit 2's steam generators—also originals from the 1970s—were replaced in 2022. The new units are made from a nickel-chromium alloy called Inconel 690, which resists corrosion far better than earlier materials. The replacement process required cutting large holes in the containment building, that thick concrete-and-steel dome designed to prevent any radioactive release. The old steam generators, now contaminated with radioactive material, will remain on site until the plant is eventually decommissioned.

Nuclear Weapons and Peaceful Power Plants

Here's a detail about Watts Bar that rarely makes headlines: since 2003, it has been producing tritium for America's nuclear weapons stockpile.

Tritium is a radioactive isotope of hydrogen, containing one proton and two neutrons in its nucleus instead of the single proton found in ordinary hydrogen. It's essential to modern thermonuclear weapons—hydrogen bombs—serving as the fusion fuel that provides much of their destructive power. But tritium is unstable, decaying at a rate of about 5.5 percent per year. After twelve years and four months, half of any given amount will have transformed into helium-3.

This means that nuclear arsenals require a constant supply of fresh tritium, regardless of whether any weapons are actually used. During the Cold War, the United States produced tritium at dedicated government reactors. But those facilities have closed, and commercial nuclear plants now shoulder the burden.

In September 2002, the Nuclear Regulatory Commission modified Watts Bar's operating license to permit the irradiation of what are called tritium-producing burnable absorber rods. These specially designed rods can absorb up to 2,000 rods per reactor cycle, exposed to the intense neutron flux inside the reactor core. The neutrons convert lithium-6 within the rods into tritium through nuclear transmutation.

After irradiation, the rods are shipped to the Savannah River Site in South Carolina, where the tritium is extracted. The Department of Energy reimburses the Tennessee Valley Authority for the costs and pays an additional fee for each rod processed.

There's a fascinating regulatory wrinkle here. When Watts Bar produces tritium, it must use what's called "unobligated uranium"—fuel that isn't subject to international agreements restricting its use to peaceful purposes. Most commercial reactor fuel comes with such restrictions, a legacy of nonproliferation treaties designed to prevent the spread of nuclear weapons. The technology and equipment involved must also be of American origin. So even this seemingly civilian power plant, serving Tennessee households, maintains a carefully firewalled connection to national defense.

Living in the Shadow

Every nuclear power plant in America has two invisible circles drawn around it on emergency planners' maps.

The first, with a radius of ten miles, defines the plume exposure pathway zone. If something goes wrong at the reactor, this is the area where people might be exposed to airborne radioactive contamination or need to take shelter. Residents within this zone receive potassium iodide tablets, which can block the thyroid gland from absorbing radioactive iodine—one of the most dangerous short-term byproducts of a nuclear accident.

The second circle extends fifty miles and defines the ingestion pathway zone. Here, the concern shifts from breathing contaminated air to eating contaminated food or drinking contaminated water. In a serious accident, authorities might need to prevent the consumption of locally produced milk, vegetables, or tap water.

About 18,500 people lived within ten miles of Watts Bar as of the 2010 census, a number that had grown about four percent over the previous decade. The fifty-mile circle encompasses nearly 1.2 million people—a significant population that includes portions of both the Chattanooga and Knoxville metropolitan areas.

Earthquake Country

When most Americans think about earthquakes, they picture California or perhaps Alaska. But the southeastern United States has its own seismic risks, centered on the New Madrid fault zone along the Mississippi River and the Southern Appalachian seismic zone that runs through eastern Tennessee.

In August 2010, the Nuclear Regulatory Commission published a study estimating earthquake risks at American nuclear plants. For Watts Bar, the annual probability of a quake severe enough to potentially damage the reactor core was assessed at about one in 27,778. Those are reassuring odds for any given year, though over decades of operation, probabilities compound.

The assessment became more than theoretical in August 2018, when a magnitude 4.4 earthquake struck with its epicenter just two miles east of Watts Bar. The Southern Appalachian earthquake, as it became known, was felt across multiple states. The Tennessee Valley Authority reported that all its facilities, designed to withstand seismic events, were unaffected, though inspectors conducted additional checks as a precaution.

A Chilled Work Environment

Not all of Watts Bar's challenges have been technical. In March 2016, as Unit 2 approached completion, the Nuclear Regulatory Commission issued a troubling assessment: inspectors described the project as having a "chilled work environment."

In nuclear regulatory parlance, this is a significant concern. It means that employees feel reluctant to raise safety issues for fear of retaliation from supervisors or colleagues. A healthy nuclear safety culture depends on workers at every level feeling empowered to stop work, ask questions, and report concerns without facing professional consequences.

The finding didn't halt the project—Unit 2 received its operating license and began generating power later that year. But it serves as a reminder that nuclear safety isn't just about engineering margins and containment structures. It depends on human factors: organizational culture, communication, and the willingness of individuals to speak up when something seems wrong.

The Economics of Endurance

More than twelve billion dollars for two reactors, with construction spanning more than four decades. By almost any conventional measure, Watts Bar should be considered an economic failure, a cautionary tale about the folly of nuclear power.

Yet the plant will likely operate for many more decades, generating carbon-free electricity around the clock regardless of whether the sun is shining or the wind is blowing. The fuel costs for nuclear power are minimal compared to natural gas or coal. Once a plant is built and the capital costs are absorbed—however painfully—the electricity flows at very low marginal cost.

Nuclear plants also provide what grid operators call baseload power, running continuously at near-full capacity. Unlike solar or wind installations, they don't require backup generation or energy storage to maintain reliability. Unlike natural gas plants, they don't produce carbon dioxide emissions during operation.

The Tennessee Valley Authority, as a federal corporation, can take a longer view than private utilities facing quarterly earnings pressure. Whether that longer view justifies the staggering investment at Watts Bar is a question that economists and energy policy analysts will debate for years. But the plant now exists. It works. And for better or worse, it represents America's most recent addition to its nuclear fleet—at least until the next generation of reactors finally moves from drawing boards to construction sites.

What Comes Next

Watts Bar's operating licenses run for forty years from their respective approval dates. Unit 1's license expires in 2035, Unit 2's in 2055. The Tennessee Valley Authority will likely seek renewals, as most American nuclear operators have done. The Nuclear Regulatory Commission has granted twenty-year license extensions to dozens of reactors, and some are now pursuing second renewals that would allow operation for eighty years.

Whether Watts Bar will join this geriatric nuclear fleet depends on factors both technical and political. The reactors will need continued maintenance, component replacements, and safety upgrades. The economics will need to remain favorable compared to alternatives. Public acceptance will need to persist through whatever incidents or accidents occur elsewhere in the nuclear industry.

For now, the plant sits along the Tennessee River, its cooling towers occasionally pluming steam into the humid Southern air, its reactors splitting uranium atoms in controlled chain reactions that have run continuously since the Clinton administration (Unit 1) and the Obama administration (Unit 2). It powers homes and businesses across the region. It produces tritium for weapons that everyone hopes will never be used. It employs hundreds of workers who monitor gauges, perform maintenance, and ensure that the invisible dance of neutrons and nuclei proceeds exactly as intended.

Watts Bar is neither the future of nuclear power nor its past. It's something stranger: a bridge between eras, a machine conceived in one world and completed in another, quietly generating electricity while the debates about energy and climate and safety swirl around it. Whatever you think about nuclear power, Watts Bar demands respect for sheer persistence. Very few human endeavors span four decades from inception to completion and then keep running for decades more.