A labor standards office has determined the April suicide of a Kansai Electric Power Co. employee who logged hundreds of extra hours to extend the operating life of two nuclear reactors was another case of karoshi (death by overwork), sources close to the matter said.

The section chief in his 40s was trying to get the Nuclear Regulation Authority's approval to extend the operating life of reactor Nos. 1 and 2 at Kansai Electric's Takahama plant in Fukui Prefecture, the sources said Wednesday. Both were approaching their operating limit of 40 years.

The man, who has not yet been publicly named, is estimated to have worked over 200 hours of overtime in February and around 100 hours in both March and April. He committed suicide at a hotel in mid-April during a business trip to Tokyo.