Feds back away from harsh rating of SC nuclear plant, but will keep an eye on it

The U.S. Nuclear Regulatory Commission has toned down concerns it had raised about a safety system at the V.C. Summer power plant northwest of Columbia — but the agency says it will keep an eye on the facility.

After hearing from Dominion Energy, the federal oversight agency recently reduced a “yellow’’ safety finding to a “white’’ finding. Both ratings flag concerns about the quality of operations at nuclear plants, but yellow findings are more serious.

The NRC has had its eye on the Summer plant because the power company failed for two decades to stop cracks and leaks in its backup diesel generator system. The system is designed to provide electricity to parts of the nuclear plant in the event of a power outage.

Proper maintenance and operation of the backup diesel generators ensures that water will continue to circulate through the atomic reactor during an emergency. Without cooling water, reactor cores can overheat and release radiation.

In an email to The State this week, the NRC said it downgraded the yellow finding to white after Dominion presented more evidence that the emergency diesel generator system’s shortcomings were not as serious as originally thought.

The power company showed that the diesel generator system, even with the problems that had been outlined, could operate for six hours during an emergency. That would give plant workers time to take additional measures to avoid a problem, according to the nuclear agency.

“The insight into the generator’s capacity led the NRC to reassess the issue’s safety significance, ultimately concluding that it posed a lower risk than initially assessed,’’ the email from NRC spokesman Dave Gasperson said.

The NRC’s scale of severity for nuclear plant problems runs from green, which is of least concern, to red, which is of most concern. A yellow finding is the second most serious. White findings are less serious than yellow, but greater than green.

Cracks and leaks involving the diesel generator system occurred on at least five occasions from 2003 to 2022, according to the NRC.

Each time, Dominion — or its predecessor, SCE&G — fixed the problems. But the utilities never resolved to the NRC’s satisfaction why the cracks and leaks continued to occur. The full reason for the problems remains unclear, but previous NRC reports suggested that vibrations and maintenance of the pipes that later cracked may have contributed.

The problems were found during testing at the plant, so they did not occur during an actual emergency.

Despite lowering the safety rating from yellow to white, the NRC will conduct an additional inspection at the V.C. Summer plant, according to a Dec. 21 letter from the agency’s regional administrator, Laura Dudes, to Dominion nuclear chief Eric Carr.

The agency will make sure the cause of the problems are fully understood and that changes made by Dominion are sufficient to ensure problems at the plant don’t happen again, the letter said.

“This inspection aims to ensure Dominion Energy has thoroughly analyzed the root cause and implemented effective measures to prevent recurrence,’’ according to the NRC’s email.

Dominion, in a statement this week, said it is replacing piping in the diesel generator system and has improved the design of the fuel delivery system. “More resilient piping’’ will be installed in the first quarter of 2024, the company said.

“Dominion Energy’s commitment to safety, along with the NRC’s process for regulating nuclear power stations, ensure we continue to operate to the highest safety standards,’’ the company’s statement said.

The company also noticed that one of the problems, found in November 2022, marked the first time in 40 years that a fuel oil leak had made an emergency diesel generator inoperable.

Problems with cracks in the diesel generator system were uncovered at about the same time electrical problems with the system were noted last year.

In that case, an electrical problem was found in the plant’s “B” diesel generator system. That made the system inoperable for several weeks in 2022. In that case, the NRC also said the company failed to correct the problem and issued a white finding against Dominion.

The history of problems with the generator system prompted one nuclear power watchdog to express reservations about the NRC’s recent decision to drop the safety designation from yellow to white.

Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, said Dominion’s assurances appear to be “pencil-sharpening exercises that make a bad situation look better on paper.’’ Most of the risk from the cracks and leaks comes from the possibility of fires that could break out, he said.

“I think that given the length of time that this problem was ignored, since at least 2003, despite warning signs, ... the more serious finding was warranted,’’ Lyman said in an email.

Dominion Energy’s V.C. Summer plant is located about 25 miles northwest of Columbia in Fairfield County. Its former owner, SCE&G, attempted to build two additional reactors, but the project was beset by cost overruns and delays and was ultimately abandoned in 2017.