KEPCO, which is responsible for operating the NPP, said the unit was reactivated at 15:00 local time (06:00 GMT). The Takahama NPP was shut down after a tragedy at the Fukushima-1 NPP in 2011.
The unit is expected to start producing energy on August 2 and, if all tests are successful, will reach full capacity around August 28, the statement read.
The Takahama NPP, located in Fukui Prefecture on Japan's largest island of Honshu, was commissioned in 1974, making it the country's oldest plant. The NPP became the second plant older than 40 years to be reactivated after the tragedy at Fukushima-1 NPP in 2011.
The first NPP to be reactivated was Mihama, also located in Fukui Prefecture. Its third reactor was reactivated on August 20, 2022, moving to a commercial load by September 26.
Japanese law limits the maximum operating time of NPP reactors to 40 years. It can be extended for another 20 years if all requirements are met and all inspections are passed.