This is Part 1 of a three-part series.
Ten years after the March 2011 meltdown of a reactor in Fukushima, Japan, Browns Ferry Nuclear Plant officials say constant upgrades like those they are performing now on Unit 2, advanced computer modeling and lower seismic and flooding risks protect the Limestone County plant from a similar fate.
Unit 2 is undergoing one of the largest construction projects since it went online 47 years ago, the highlight of which is replacing the massive turbines that convert nuclear-generated steam into electricity.
The project was timed to coincide with a planned refueling outage. Unit 2's outage began 654 days after the last refueling was completed. The Tennessee Valley Authority has added 1,500 workers to the 1,400 employees at the plant during the outage.
For the first time in a decade, the Tennessee Valley Authority this month allowed a tightly controlled media tour of the plant. The nine reporters in attendance wore masks and were required to have a negative COVID-19 test before attending. They also went through multiple metal detectors and were tested by a mechanical bomb-sniffing device, the same security procedures used for employees and contractors.
About a third of the fuel in each of Browns Ferry's three reactors is replaced every two years, and outages are planned around that timetable. During the current outage, TVA is performing an extensive upgrade aimed at expanding energy production by about 7 megawatts, enough to power 4,000 homes. Other work during the outage includes installing 320 new fuel assemblies, inspecting reactor components and conducting 14,800 work activities.
“The work that we’re doing up on the turbine deck is the largest construction project that we’ve done at this station on the turbine decks since construction in the late '60s and early '70s,” said Browns Ferry Site Vice President Matt Rasmussen. “A lot of work is going on.”
Browns Ferry’s three units are boiling water reactors, the same type used at the Fukushima plant. Bombarding with neutrons the uranium packed in fuel rods triggers a chain reaction that generates heat. The heat is used to convert water into steam, and pressurized steam turns the turbines to power electric generators. The chain reaction can be stopped or slowed through insertion of neutron-absorbing control rods into the pool holding the fuel bundles.
During the outage there will be more than 600 crane lifts, including of low-pressure turbines that weigh up to 164 tons. Unit 2, like the other two units, has a high-pressure turbine that receives the steam first, and three low-pressure turbines that generate electricity from steam as it loses pressure.
Properly managing outages every two years is essential to maximizing power production, TVA Chief Nuclear Officer Tim Rausch explained to The Decatur Daily during a break from the media tour, and poorly executed refueling outages cause some nuclear plants to struggle to maintain optimal power production.
“On refueling, either you’re taking too long to refuel it, or you’re not doing the right work the right way and when you put it back together and start it up it doesn’t run reliably for the next two years,” Rausch said.
Rausch, who also is TVA executive vice president and is a former chief nuclear officer at Browns Ferry and at non-TVA plants, said a key part of his role is to generate as much power as possible. While Browns Ferry’s capacity has been maxed out at 3,954 megawatts — enough to power more than 2.2 million homes, manufacturing plants and businesses — he said the three units have room for improvement in terms of maintaining that output between refueling outages.
To accomplish maximizing output, Rausch said, a nuclear plant needs solid leadership, skilled workers that work as a team and a system that anticipates equipment failures before they happen.
“You need to have an analytical system maintenance process that anticipates wear and tear on equipment and prevents failure,” he said. “You use your computer system, you use data trending, you use analytics, remote monitoring, all those sorts of things.
“It’s kind of like Disney. You’ll never see a lightbulb burned out at Disney. What they do is they know the lifetime of the lightbulb and they know the curve of failure starts at, say, 75% of that lifetime. They’ll change all lightbulbs at 75% so they don’t have an unexpected failure. That’s the trick here.”
Redundancy is part of the secret, he said. If two pumps are needed for a unit to operate efficiently, there should be four in place. That way one can be taken out of operation for maintenance, and even if another fails, there’s a spare. That prevents any lost production time.
“We run very well, but we can run better,” Rausch said. “And that’s our goal.”
Aggressive equipment replacement has helped Browns Ferry maximize output, Rasmussen said, and also protects it from disasters such as the one in Japan a decade ago.
Control of river vegetation also plays a role in avoiding disruptions in power production. During the tour a helicopter hovered over the Tennessee River, just outside Browns Ferry. Rasmussen explained it was tracking vegetation that had floated downstream from Guntersville. If it appeared to pose a risk to Browns Ferry’s intake pipes, dams could be adjusted to speed the vegetation’s passage.
Extensive training at Browns Ferry is designed to avert problems like those that beset Fukushima before they start. Much of this is accomplished through an advanced simulator that is identical to the reactors' control rooms. Software is tweaked frequently to mimic performance of the control rooms and to reflect conditions of each unit.
"This thing is modeled to look just like the plant," said Browns Ferry's Christopher Baxter, who is training for his operator's license. "We have a group of engineers and they are constantly looking at data from the plant and tweaking and making adjustments. ... What you're looking at is definitely a marvel of modern technology."
A decade ago, a nuclear disaster was unfolding in Japan at the Fukushima Daiichi Nuclear Power Plant triggered by a March 11, 2011, earthquake and tsunami. A 46-foot tidal wave swamped the generators that were designed to continue pumping coolant water into the spent fuel pools to prevent heat from increasing. The end result was the meltdown of three reactors, the release of radioactive contamination and the evacuation of 154,000 people. The boiling water reactors at Fukushima, complete with elevated spent fuel pools, are nearly identical to those at Browns Ferry.
The disaster resulted in new regulations in the United States.
“Our TVA fleet meets all the requirements post-Fukushima,” Rausch said. “I went to Fukushima a year after it happened. I spent a week over there. It will never leave me.”
Rausch said important lessons were learned from Fukushima, but Browns Ferry does not face the same risks as the Japan plant.
“It’s amazing how many earthquakes that Japan has every single year when you compare it to the United States,” he said. “And its seismic activity is much more significant in terms of magnitude. Then when you look where they were built, on the ocean, and the way they were built, they were basically built at sea level.”
He said the Fukushima plants also failed to take appropriate steps to protect the plant from known risks, especially when it came to the height of a flood wall designed to block tsunami-caused tidal waves.
“Over the course of years they would recalculate the potential tsunami, what its maximum height could be. Well, they built the wall for the maximum height, but then as time went on they actually recalculated and said, ‘The tsunami could be bigger than that.’ But they never reconfigured the wall. So they made some bad technical decisions. We have to apply all those lessons learned here.”
Rasmussen said TVA is constantly analyzing risks based on worst-case models, such as an assumption of seven straight days of rain and multiple dam failures. Those models, Rausch said, are incorporated into design changes.
“So if that (model) resulted in a higher maximum water level here because of all those multiple ‘what ifs,’ we would have to update the plant today,” Rausch said.
Edwin Lyman, director of nuclear power safety at the nonprofit Union of Concerned Scientists, wrote a book on Fukushima and recently published a paper critical of the Nuclear Regulatory Commission’s response to the disaster. He said earthquakes and flooding both present risks to Browns Ferry.
Lyman said Browns Ferry’s location puts it in the top 10 of U.S. sites at risk of a seismic meltdown, and because three reactors are located there the risk is actually greater.
“The seismic risk is relatively high at Browns Ferry,” Lyman said. “The NRC did not take any action at any nuclear plant in the country after Fukushima to require seismic or flooding upgrades. The NRC did require plants to reevaluate their external hazard risks, like flooding and earthquakes, and they found 96% of the plants actually had higher flood heights than what they were designed to protect against, and Browns Ferry is in that category. But the NRC didn’t actually require any plant to make any changes.”
He said Browns Ferry has redone its methodology on flooding analysis, but the NRC hasn’t reviewed it.
“I think they just put a Band-Aid on the Fukushima problem without really solving it,” Lyman said of the NRC.
One of the lessons of Fukushima is that the failure of generators can cause disaster if conventional AC electric current is disrupted. Post-Fukishima, much effort has been expended to ensure a reliable electrical supply to run the all-important pumps that inject water into the reactor and spent fuel pool to prevent a meltdown when other systems fail.
Browns Ferry completed implementation of a FLEX (for flexible strategies) system housed in a separate FLEX building in 2018. It contains high-volume diesel pumps capable of drawing water from Wheeler Lake, diesel generators, batteries and towable tanks containing diesel fuel.