Kansai Electric Power Co.'s Takahama No. 4 reactor in Fukui Prefecture on Friday became the nation's fourth to be restarted since 2012 and the first to burn MOX, a mixed-oxide fuel that contains plutonium.

In a statement released Friday afternoon, Kepco President Makoto Yagi said safety would remain the top priority and that the utility would continue to promote safety standards beyond what was legally required.

The startup came nearly a week after a radioactive water leak was discovered at the reactor's auxiliary building on Feb. 20. Kepco halted restart preparations while it repaired the leak, saying it did not pose a danger to the environment.