The No.2 reactor at the Ikata nuclear plant in Ehime Prefecture, western Japan, is to be decommissioned.
Board members of Shikoku Electric Power Company made the decision on Tuesday. The reactor went into operation 36 years ago.
Government guidelines introduced after the 2011 Fukushima nuclear accident limit the operation of reactors to 40 years in principle, but allow for extensions of up to 20 years.
Shikoku Electric decided not to apply for the extension. It said the massive cost of new safety measures required for a restart does not make financial sense.
The utility has already decided to scrap the plant's No.1 reactor. The No.3 reactor was restarted in 2016. But a high court issued an injunction to halt it last December.
The Ikata No.2 reactor is the 9th in Japan now slated for decommission, excluding those at the Fukushima Daiichi power plant.