While testing equipment last year, workers at the V.C. Summer nuclear plant discovered a small oil leak in a section of pipe that served one of the most important backup safety systems in the facility northwest of Columbia.
A crack had developed around the pipe in the plant's diesel generator system, and the leak appeared to be getting worse. If left uncorrected, the crack would likely make the diesel generator inoperable during a nuclear emergency, a federal report found. Without a working diesel generator, nuclear fuel can overheat in an emergency and release radiation into the air.
So repairs were done. But in investigating the issue, federal nuclear safety officials made a discovery that was perhaps more unsettling than the problem from 2022.
They identified a pattern of cracks and leaks in the plant's emergency generator system going back 20 years. On five different occasions since 2003, the power company has been forced to repair cracks in the emergency diesel generator system, according to an agency inspection report released in August.
Diesel oil leaks have focused attention on why VC Summer plant operators did not resolve the cracking problems -- and how that might have affected the company's ability to prevent a radiation leak if an emergency occurred.
Officials with the Nuclear Regulatory Commission say they are concerned because the problems keep recurring. Few other nuclear plants in the Southeast have had the same number of cracking problems in diesel generator systems, say officials in the agency's Atlanta office.
NRC officials now are considering enforcement action against Dominion over the issue.
Although the power company has plugged leaks in the generator system through the years, the NRC is pushing the company to get to the bottom of why the cracks keep happening.
"They did some corrections, but it happened multiple times,'' said David Dumbacher, the NRC's regional reactor projects chief. "We're wondering if the corrections were enough.''
"There's something wrong that we don't understand,'' he continued. "We are telling them we are not sure they understand.''
Dumbacher's recent letter to Dominion said the power company had failed to identify and correct problems that left the piping system vulnerable to premature cracks.
Dominion, which acquired SCE&G after a nuclear construction project at the site went awry in 2017, said a small number of minor fuel leaks have occurred in the past 20 years.
The Virginia-headquartered energy company said it fixed the problems, but it also said the November 2022 leak prompted the nuclear power plant to review the diesel generator fuel delivery system.
The company "has implemented a plan to improve the system's reliability,'' spokesman Darryl Huger said in an email. Huger's statement did not elaborate on what the plan entails.
Emergency diesel generators are important to safety at atomic power plants, and must be kept in good working condition in the event they are ever needed.
These generators, huge machines that are roughly the size of train engines, are supposed to provide power in an emergency so that nuclear fuel inside the plant's reactor doesn't melt and release radiation to the surrounding community.
Nuclear plants like V.C. Summer have two generators. The generators provide energy if electricity from the power grid is unavailable.
A nuclear meltdown is perhaps the worst accident that can happen at an atomic energy plant. Without power to keep water circulating inside a containment area, the highly radioactive fuel will overheat and melt over a period of days, if not sooner.
David Lochbaum, a former NRC instructor and expert on the inner workings of nuclear power plants, said properly operating diesel systems ensure safety after hurricanes and earthquakes. South Carolina has had a higher than usual number of small earthquakes since January 2021, The State reported earlier this year.
Lochbaum said a backup diesel generator system helped keep a nuclear station in South Florida operating safely after Hurricane Andrew knocked out power for several days in 1992.
But in 2011, an earthquake and tidal wave shut down the main power and knocked out the emergency diesel backup power at the Fukushima atomic power plant in Japan, he said. Without the diesel system working, atomic fuel partially melted and radioactive material leaked, the BBC reported.
Continued diesel generator problems at V.C. Summer have caught the NRC's attention, he said.
The NRC, in its recent letter to Dominion, is sending a message "on a pretty big billboard'' that Dominion needs to get to the bottom of the cracking problems because they are continuing, Lochbaum said.
"If it's an isolated case, it's a different story,'' Lochbaum said. "But when you raise their antenna like it is now, they will turn over more rocks, and if they find more problems, it doesn't bode well.''
According to the NRC's August inspection report, five issues involving cracking in diesel generator systems started in 2003 and continued to this past November. The NRC learned of the problems from Dominion.
In addition to the 2022 crack and leak, the following problems occurred:
Oct. 21, 2003: A fuel line for the plant's A diesel generator ruptured. SCE&G, Dominion's predecessor, said the problem was related to what it called "manual manipulation of the pipe.'' The issue later was attributed to equipment fatigue.
Aug. 20, 2014: A pipe connection serving the A generator system developed a 120-drops-per-minute fuel oil leak. As repairs were being made, mechanics found a hairline crack in a grooved area of the pipe.
Nov. 4, 2014: A pipe connection serving the B generator system developed a small leak. During repairs, workers found a hairline crack in a grooved area of pipe. The power company said it most likely resulted from a "single impact event,'' followed by high stress fatigue.
March 2, 2020: Dominion found a crack on a coupling in the A generator system. A test on March 5 of that year found fuel oil was leaking. After repairs had been made, Dominion found a leak and crack on a newly installed pipe fitting.
Fortunately, the problems at the VC Summer plant were discovered during testing rather than an actual emergency, officials said.
But the issues have produced questions, and they follow another set of shortcomings discovered in the plant's generator system last year.
Those shortcomings, which were unrelated to the pattern of cracks noted in the August NRC letter, resulted from an electrical problem with the plant's B generator system. In October 2022, the NRC said the plant's B generator had such problems that it was not operable for several weeks.
The NRC said Dominion "inadequately assessed" erratic system behavior during a test. The Oct. 18, 2022, letter from the NRC to Dominion said the company failed to correct a situation that caused the emergency diesel generator not to work for several weeks.
The matter was serious enough that the NRC issued what is known as a "white finding,'' a relatively uncommon assessment of safety shortcomings at a nuclear plant. The most common safety assessment findings are green. Yellow and red are more significant safety assessment ratings.
Dumbacher, of the NRC, said it's too soon to say whether his agency would issue another white finding, this time for the latest problems with cracks on the diesel generator system, if it issues any at all. He expects the agency to make a decision next month.
The V.C. Summer nuclear plant, first licensed in 1982, is about 25 miles northwest of Columbia in rural Fairfield County. The plant site contains a single reactor near the shores of Lake Monticello.
Dominion Energy, headquartered in Virginia, is one of South Carolina's largest energy providers, serving customers in the Columbia, Charleston and Hilton Head Island areas.
The company acquired SCANA, SCE&G's parent company, in 2018 as part of a $14.6 billion deal. SCANA had been weakened by its failure to build two additional nuclear reactors at the VC Summer site, despite raising customer rates and spending billions of dollars.
Dominion, which has other nuclear plants in its fleet of generating stations, is now seeking a new license for the VC Summer plant. If approved, it would extend the plant's life another 20 years.
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