A reactor at FPL's St. Lucie Nuclear Plant was down for over a day after 'manual reactor trip'

ST. LUCIE COUNTY — One of two reactors at the St. Lucie Nuclear Plant on Hutchinson Island was manually shutdown the morning of Dec. 10 after operators noticed lowering water levels entering its steam generator.

The Unit 1 reactor was shut down by a "manual reactor trip" — meaning it was a staff decision to power down — at approximately 10:24 a.m. last Friday, according to an announcement by the Nuclear Regulatory Commission.

The pressurized water reactor remained offline through Sunday, when it started to regain power, according to Florida Power & Light Co. spokesperson Peter Robbins. Unit 1 has been operating at 100% power since Monday.

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What caused the shut down?

An investigation is underway to determine why the water entering the generator — which is then converted into steam to create electricity — started to decrease, according to the NRC. It's classified by the commission as a "non-emergency" event.

"We believe it was a valve that was inadvertently closed," Robbins told TCPalm. That led to the staff decision to shut down the reactor, he said. "Everything responded exactly the way it should and the unit was shut down in a matter of just a couple of minutes."

It's "infrequent" that staff manually shut down a reactor, Robbins said, though he could not immediately provide a list of manual shutdowns over the unit's history. The action is "something we don’t hesitate to do if the situation requires it," he said in an email.

The shutdown doesn't appear to have created a problem requiring significant repairs, said Edwin Lyman, director of nuclear power safety with the Union of Concerned Scientists.

"We know it wasn't severe because the plant compensated, shut down safely and was able to be stabilized. And then they returned to the service," Lyman said.

"Every time a plant has an unplanned or unexpected shutdown, that could potentially trigger a more serious event. Even though they're usually benign, that doesn't increase additional risks," Lyman said. "Every time you have a (shutdown) like this, it just takes one other thing to go wrong and then you have a problem."

That's why nuclear power plants need to take measures to prevent these unplanned shutdowns from occurring, Lyman told TCPalm. The NRC calls reactor shutdowns "an important way to protect the components in a nuclear power plant from failing or becoming damaged."

St. Lucie Unit 2 — the reactor adjacent to Unit 1 — was not affected by the shutdown and remained at full power, according to the NRC. There were no power outages because of the shutdown, Robbins said.

Construction began on Unit 1 in 1970 and the reactor was commissioned in 1976. Construction began on Unit 2 in 1977 and was commissioned in 1983. The facility cost $4.6 billion to construct. The facility sits on 1,300 acres of land on Hutchinson Island and employs more than 700 people.

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Max Chesnes is a TCPalm environment reporter focusing on issues facing the Indian River Lagoon, St. Lucie River and Lake Okeechobee. You can keep up with Max on Twitter @MaxChesnes, email him at max.chesnes@tcpalm.com and give him a call at 772-978-2224.

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This article originally appeared on Treasure Coast Newspapers: A St. Lucie Nuclear Plant reactor was down for over a day after manual shutdown