Exelon Corp., the largest U.S. utility holding company, restored offsite power to the Byron 2 reactor in Illinois that was knocked out two days ago by electrical equipment failure.
The plant, 85 miles (137 kilometers) west of Chicago, where Exelon is based, ended an “unusual event,” the lowest of four federal emergency classification levels, at 8 p.m. local time yesterday, Paul Dempsey, a company spokesman, said in a telephone interview today. Diesel generators used to power the site were switched off.
“We’re in the process of going through some systems and pieces of equipment, testing, to get ready for the unit start up,” Dempsey said. He said he didn’t know when it would start.
Crews replaced a line insulator yesterday that failed in the switchyard of the 1,136-megawatt Byron 2. The unit has been sent out for testing to determine why it failed and results have not returned, Dempsey said.
The plant vented steam containing tritium to relieve pressure in the reactor until 3 a.m. local time yesterday, he said. There was no impact on the safety of employees or the public, he said.
Another unit at the plant, the 1,164-megawatt Byron 1, is operating at full capacity.
Tritium is a naturally occurring radioactive form of hydrogen that is produced in the upper atmosphere and falls to the ground in rain water, according to the NRC. It is also a byproduct of nuclear plants, a weak type of radiation that doesn’t penetrate the skin, the federal agency said.