In September, 2 reactors at the plant in Satsuma Sendai City in Kagoshima Prefecture became the first in Japan to meet new, tougher government regulations introduced after the 2011 nuclear disaster in Fukushima. Later, the governor of Kagoshima gave consent to Kyushu Electric Power Company to restart them.
The utility still needs approval from the Nuclear Regulation Authority for technical documents. It told the authority on Thursday that preparing them will take 2 or 3 months longer than expected because the authority says many revisions are needed.
One of the documents explains in detail facility designs for the plant's Number 1 reactor. The company originally planned to submit it in December. It now says it will take until the end of February, due to the need to provide more detailed data and explanations on earthquake resistance.
The utility says it will submit by the end of March a separate document describing designs for facilities that are shared with the Number 2 reactor.
The restart may not come until May or later, possibly the summer, pending the regulator's approval of the documents and onsite inspections.
All of Japan's commercial nuclear reactors remain offline.