Dive Summary:

• Workers at the Perry Nuclear Power Plant in Ohio found elevated carbon monoxide levels, prompting them to classify the situation as an "usual event."
• First Energy, who operates the plant, said that the carbon monoxide levels were slightly elevated, but still within safe limits; a leaking bottle of acetylene - used in welding - is the most likely cause of the alarm.
• The plant's operation was not affected by the incident and occurred in a completely different building from the nuclear reactor.

From the article:

An “unusual event” was declared at the Perry Nuclear Power Plant on Wednesday morning after workers found elevated carbon monoxide levels.

At about 10:20 a.m. a group of workers were at the plant preparing to do some welding work when a high carbon monoxide reading was detected, said Jennifer Young, spokesperson for First Energy. ...