The man was carrying out maintenance work on reactor, which is temporarily out of service when a jack broke loose and crashed into the man’s chest.
The man was rushed to hospital in Oskarshamn but was declared dead on arrival, the Local reported.
The accident occurred shortly before 5am in the reactor’s turbine hall. The police have conducted a technical investigation of the scene and a report has been submitted to the Swedish Work Environment Authority.
The owner of the plant, OKG, immediately suspended all work on the reactor and has appointed a crisis group to help staff cope with the shock.
"We are all very deeply distressed," OKG’s head of information, Anders Österberg said, as quoted by the Local.
The man was resident in Östergötland and worked for a sub-contractor. His name has not been released by authorities.