A leaky valve caused Three Mile Island to take a safety system offline for more than four days, said officials at the Nuclear Regulatory Commission (NRC).
The timeline reads on July 10 at 5:30 p.m. staff noticed the leak, which was about one drop of water every two minutes coming from a valve on a system designed to inject water at high pressure into the reactor during emergency situations, the NRC reported.
The water was not radioactive, and by design would only come in contact with radioactive fuel during an emergency.
This system would be essential in cooling the reactor if something were to go wrong, said Neil Sheehan, a NRC public affairs officer.
“This is one of the very important systems, and therefore it’s vital they get it back online,” Sheehan said.
Ralph DeSantis, spokesman for Three Mile Island, said the public safety risk posed by the offline water system was minimal because of redundancies built into the plant’s infrastructure.
“There’s actually two backup systems that put water in the reactor in the case of an emergency,” he said. “We had to take one out of service the whole time. We always had a backup system available in case we ever needed it.”
NRC standards required Exelon Nuclear, the company that owns and operates Three Mile Island, to repair the leak within 72 hours or else shut down the reactor.
After an initial failure to weld the leak, Exelon determined that it could fix the valve using a technique called “freeze sealing.” However, the job would put them past the 72-hour deadline, the NRC report said.
Exelon applied for an extension to fix the leak, and the NRC granted an additional 46.5 hours.
“They were able to make the argument that they didn’t have to shut down the plant,” Sheehan said. “We looked at the risk evaluation done by Exelon as well as our own risk evaluation, and we concluded that this would not affect health and public safety.”
The high pressure system went back online Tuesday morning, hours before the second deadline.