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Backup generator at Calvert Cliffs nuclear plant fails, triggering special federal review

The Calvert Cliffs Nuclear Power Plant Units 1 and 2 are located near Lusby. Photo by the Nuclear Regulatory Commission.

A massive backup diesel generator at the Calvert Cliffs nuclear power plant in Southern Maryland was recently out of service for at least week, triggering an ongoing special inspection by the Nuclear Regulatory Commission.

The backup generator is one of five at the nuclear plant in Lusby, which is operated by Constellation Energy and produces about 37% of all electric power in Maryland; two functioning generators are necessary to run the plant’s two nuclear towers if the regional electric power grid ever goes down.

While there was never any danger to the public, the Nuclear Regulatory Commission and Constellation say, the mechanical failure of the generator, which was discovered during a regular in-house inspection of the plant on April 24 and lasted until Monday, is leading to extra scrutiny of the plant by federal regulators.

“Because of redundant systems, this event did not directly impact plant safety,” NRC Region I Administrator Raymond Lorson said in a statement this week. “Nevertheless, our team has been tasked with learning more about why this problem occurred and what steps the company is taking to ensure it does not happen again.”

A three-member team from the NRC was dispatched to the plant on Monday to begin the special inspection process. The team will work with resident federal inspectors assigned to Calvert Cliffs, who have been following Constellation Energy’s actions on-site since the mechanical failure of the generator was discovered during a regular monthly inspection of the generator last week.

The NRC said its inspection team will gather information regarding the problems involving the generator and will seek to evaluate Constellation’s response. The team will document its findings in a report to be issued within 45 days following the conclusion of the review.

The temporary failure of the backup generator comes as policy debates in Maryland intensify over nuclear power and its role in producing carbon-free energy. According to several estimates, Calvert Cliffs, the state’s lone nuclear power plant, generates more than 80% of the state’s clean electricity.

Nuclear power plants are steadily being decommissioned in the U.S. because they are expensive to operate. But with policymakers scrambling to reduce greenhouse gas emissions across the country and new technology emerging that may enable nuclear power to be generated more efficiently and at smaller facilities, investors are rethinking the ethics and efficacy of nuclear generation — especially as the climate crisis grows.

Calvert Cliffs’ two federal operating licenses are up for renewal in the mid-2030’s, and there’s some sense among energy industry experts that companies like Constellation will not want to continue building and improving nuclear plants if they do not feel that federal and state policymakers are sufficiently supportive. The plant along the Chesapeake Bay has been open since 1975.

“There’s a serious concern that if the train is on the tracks for only doing solar and wind [energy], and they’re getting government subsidies, what’s the incentive to invest in nuclear?” said Del. Mark N. Fisher (R-Calvert), whose district includes Calvert Cliffs and who sits on the House Economic Matters Committee, which writes energy policy.

The state is conducting a study to look at the costs and benefits of expanding nuclear energy use in the state, both at Calvert Cliffs and, potentially, with small modular nuclear reactors. That report is expected out by the end of the year.

‘Special inspections are not unusual’

A power shutdown at a nuclear power plant has serious consequences.

Like all U.S. nuclear plants, Calvert Cliffs is hooked up to an electric power grid — in this case, PJM, which supplies power to 13 states on the East Coast and in the Midwest, plus the District of Columbia. If there’s a power failure on the grid, nuclear power plants have diesel generators, about 20 feet long and 8 feet wide, to keep the plant operating, and some also have battery storage facilities. But in the worst case scenario, if all the generators failed, the battery storage would power the plants for only four to eight hours, increasing the possibility of a deadly nuclear meltdown.

Nothing that happened at Calvert Cliffs over the past week came anywhere close to approaching such a nightmare scenario.

Calvert Cliffs has five emergency diesel generators. Two are dedicated to one of the nuclear reactors and two are dedicated to the other. A fifth can be used at either — and it just takes one generator to operate each of the towers if the electric grid goes down.

But this was not the first time the nuclear plant has experienced a problem with that particular emergency generator in the recent past.

Last September, the NRC finalized a report on a problem that it determined to be of low to moderate safety significance associated with a failure of the same generator. In that case, the NRC discovered that a “foreign material” found its way into the generator, resulting in its automatic shutdown and failure during routine testing.

Operators have determined that the plant’s other emergency diesel generators are unlikely to have similar problems, but NRC inspectors are reviewing that assessment as part of the newest review.

“Special inspections are not unusual,” Diane Screnci, an NRC spokesperson, told Maryland Matters. “We conduct special inspections to get a fuller understanding of a technical issue — to better understand what happened, why it happened and what actions the company is taking to fix the problem and prevent it from happening again.”

Fisher, the state lawmaker, said the Calvert Cliffs plant has a well-established system for notifying local officials in case of emergency at the power plant but it was not activated with the shutdown of the backup generator.

Mark Rodgers, a spokesperson for Constellation, said the generator was back in service on Monday, a week after the problem was discovered during the regular monthly inspection. The company in a statement said inspectors had “observed signs of degraded performance,” prompting the shutdown.

“We are working together constructively with the NRC inspection team,” Constellation added in its statement.


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Backup generator at Calvert Cliffs nuclear plant fails, triggering special federal review