MINNEAPOLIS (AP) — Authorities say a reported decrease in coolant level for one of the Prairie Island nuclear plant’s reactors came from a faulty reading.

The Nuclear Regulatory Commission on Tuesday declared an “unusual event,” the lowest level of its emergency classification system, because of the apparent coolant leak.

But the NRC later said tests found that no leakage had occurred.

The reactor had been shut down for refueling. The NRC says Prairie Island operators determined that maintenance and refueling activities appeared to have caused the false reading.

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