About 20 people gathered outside the building in Tokyo where the Nuclear Regulation Authority met on Wednesday to protest its decision to allow the Tokai No.2 plant to resume operations.
The protesters carried banners saying they disagree with a 20-year extension of operations and shouted, "No restart!" and "Protect people's lives."
The group handed a petition with about 15,000 signatures from across Japan to an authority official. This brings the total number of anti-restart signatures submitted to the nuclear regulator to nearly 30,000.
Makoto Yanagida, who heads a citizens' group, said it's a very sad day. He said because the Tokai No.2 plant is close to Tokyo, many people will no longer be able to live in the city in the event of a major accident.