The man blocking the world’s largest nuclear plant says he grew opposed to atomic energy the same way some people fall in love.

Previously an advocate for nuclear power, Ryuichi Yoneyama campaigned against the restart of the facility as part of his successful gubernatorial race last year in Niigata Prefecture.

He attributes his political U-turn to the “unresolved” 2011 disaster at the Fukushima No. 1 nuclear power plant and the lack of preparedness at the larger facility in his own prefecture, both owned by Tokyo Electric Power Company Holdings Inc.

“Changing my opinion wasn’t an instant realization,” Yoneyama said in an interview. “It was gradual. As people say, you don’t know the exact moment you’ve fallen in love.”

Yoneyama won’t support the restart of the Kashiwazaki-Kariwa plant in Niigata Prefecture until an investigation is complete into the chain of events that resulted in the triple meltdown at Fukushima No. 1, which he visited Wednesday. While utilities don’t need approval from local authorities to restart plants, power companies are tradition-bound not to move ahead until they get their consent.

Yoneyama, a 49-year-old doctor and native of Niigata, is one of the highest-profile local opponents pitted against a political establishment led by Prime Minister Shinzo Abe. The establishment sees nuclear power as crucial for the country’s long-term energy security and environmental goals.

Regulations and public opinion are keeping nearly all of Japan’s atomic stations shut almost six years after the meltdowns at Fukushima, where the search has barely begun for fuel that burned through to the bottom of the reactors.

“If the local governor remains firmly opposed to the restart, it will be very difficult for the reactors to come back online,” said James Taverner, an analyst at IHS Markit Ltd. “In addition to the local government, building the support and trust of local residents is key.”

A Kyodo News poll on the day of Yoneyama’s October election showed about 64 percent of Niigata voters opposed the restart of Kashiwazaki-Kariwa, known popularly as KK. The restart of the facility was one of the key issues in the race to replace Gov. Hirohiko Izumida, who was famous for his tough stance against Tepco. He unexpectedly announced in August that he wouldn’t seek a fourth term.

To the residents of the prefecture, Yoneyama was the candidate who would make nuclear safety a priority, while his main opponent gave off the vibe that he was a member of the reactor restarts camp, the former governor said by email.

In last year’s gubernatorial race in Kagoshima Prefecture, where Kyushu Electric Power Co. operates the Sendai nuclear plant, a three-term incumbent was defeated by an opponent campaigning to temporarily close the reactors. A district court last year barred Kansai Electric Power Co. from running two reactors at its Takahama station in Fukui Prefecture only weeks after they’d been turned back on.

Yoneyama supported bringing back online Japan’s reactors during his unsuccessful bid in 2012 for a seat in the Lower House. The country was being forced to spend more on fossil fuel imports after the disaster, so restarting the plants was needed to help the economy recover, he said at the time.

Though Yoneyama’s position switch helped secure his first electoral victory after four failed campaigns for the Diet, nuclear opponents see him driven by more than political opportunism.

“I had my reservations about Yoneyama,” said Takehiko Igarashi, an official at the Niigata division of the anti-nuclear group Nakusou Genpatsu. “But after he was vetted and endorsed by the Japanese Communist Party and other smaller parties that have an anti-nuclear slant, I knew that I could trust him.”

Tepco and Abe’s government see restarting KK as one way for Japan’s biggest utility to boost profits and help manage its nearly ¥16 trillion ($139 billion) share of the Fukushima cleanup. Resuming reactors 6 and 7 will boost annual profits by as much as ¥240 billion, the utility has said.

The economic argument, however, is beginning to hold less sway, with Yoneyama saying the benefits to the local economy are “overstated.” While the prefecture risks missing out on ¥1.1 billion a year in government support without the restarts, that represents a small slice of the prefecture’s budget, which tops ¥1 trillion, according to Yoneyama.

Abe, a strong backer of nuclear power, leads a government aiming for nuclear to account for as much as 22 percent of the energy mix by 2030, compared with a little more than 1 percent now.

While restart opponents like Yoneyama demand the government guarantee the safety of the reactors, they’ve also criticized the evacuation and emergency response plans as inadequate.

In his first meeting with Tepco executives since taking office, Yoneyama earlier this month told Chairman Fumio Sudo and President Naomi Hirose that he won’t support KK’s restart until a new evacuation plan is drawn up using the results of a Fukushima investigation. Tepco will fully cooperate with the probe and stay in communication with the governor, the company said in response to a request for comment.

“Once I realized that the Fukushima disaster couldn’t be easily resolved, of course my opinion changed,” Yoneyama said. “If another accident occurs, overseas tourism will become a distant dream. Even Japanese may flee the country.”