BYRON, Ill. (CBS) — Authorities continue to investigate why a reactor went down at a nuclear power plant near Rockford.

As CBS 2’s Susanna Song reports, Exelon Nuclear officials believe a failed piece of equipment at a switchyard caused the shutdown, but they are still investigating the exact cause.

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The switchyard delivers power between the plant and the electrical grid.

Exelon spokeswoman Krista Lopykinski said the problem started at 10:18 a.m. Monday in reactor Unit No. 2 at The Exelon Byron Nuclear Generating Station, located in Ogle County, about 100 miles west of Chicago, near Rockford.

While officials say everything was under control as of early Tuesday morning, the plant shutdown rattled some nerves on Monday.

“Well, I kind of panicked. And the first thing I did was go get those pills they’d given us,” said Patricia Carter, who lives in the neighboring town of Byron, Ill.

Carter grabbed the potassium iodide pills when she heard about the power plant emergency.

“My niece called and she told me to stay in the house. So that’s what I did,” she said.

Teresa works at the nearly Sunrise II Family Restaurant. She tells WBBM Newsradio everyone is on edge.

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“A couple came in and told us that they saw steam, and so they went up there to see, and they’re like, ‘Oh my God, is everything OK?’ and they were a nervous wreck,” she said.

Teresa said she hasn’t seen any steam coming from the plant Tuesday morning.

After the shutdown, operators released steam from the non-nuclear side of the plant to cool everything down. The steam contained low levels of a radioactive isotope of hydrogen called tritium.

The reactor is now running on backup power, and a plant spokesman said no one was ever in danger.

“No worry for our employees here onsite or the communities around. We have many highly-trained people onsite who are going to look into the issue,” said Exelon spokesman Paul Dempsey.

Another reactor at the plant is operating normally.

Four years ago, a similar situation occurred involving electrical transformers at the plant after power to one of the reactors was interrupted.

“I never worried about it,” Carter said. “But it was always in the back of my mind – if it did blow, what would I do.”

Officials say the situation Monday is not a huge concern. They claim it was the lowest of four levels of emergency.

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Still, the plant has been the focus of controversy ever since it was built. Area residents are worried about the potential for groundwater to be contaminated with radioactive material.