Japan has restarted a reactor at the world’s largest nuclear plant nearly 15 years after a disaster at the Fukushima power plant forced the country to shut all its nuclear reactors.

Reactor no.6 at the Kashiwazaki-Kariwa plant located northwest of Tokyo was restarted on Wednesday.

It was delayed by one day because of an alarm malfunction and is expected to begin operating commercially next month.

This is the latest installment in Japan’s nuclear power reboot, which still has a long way to go. The seventh reactor is not expected to come back on until 2030, and the remaining five could be decommissioned.

That leaves the plant with far less capacity than it once had when all seven reactors were operational: 8.2 gigawatts.

Japan, which had always heavily relied on energy imports, was an early adopter of nuclear power. But these ambitions were scuppered in 2011 by what is now remembered as one of the worst nuclear disasters in history.

Triggered by the most powerful earthquake ever recorded in Japan, the meltdown in the reactors at Fukushima Daiichi led to radioactive leakage. It traumatised local communities that were evacuated, and many have not returned despite official assurances that it was safe to do so.

Still the fear and lack of trust fuelled public opposition to nuclear power and Japan suspended its entire fleet of 54 reactors shortly after the Fukushima disaster.

It has now spent the past decade trying to wake up those power plants, as it tries to expand its source of clean energy to reach net zero emissions by 2050.

Since 2015, it has restarted 15 out of its 33 operable reactors. The Kashiwazaki-Kariwa plant is the first of those owned by Tepco to be turned back on.

Before 2011, nuclear power accounted for nearly 30% of Japan’s electricity and the country planned to get that up to 50% by 2030. Its energy plan last year unveiled a tamer goal: it wants nuclear power to provide 20% of its electricity needs by 2040.

Global momentum is building around nuclear energy, with the International Atomic Energy Agency estimating that the world’s nuclear power capacity could more than double by 2050. In Japan, as of 2023, nuclear power accounted for just 8.5% of electricity.

Prime Minister Sanae Takaichi, who took office in October, has emphasised the importance of nuclear power for Japan’s energy self-sufficiency. Especially as it expects energy demand to surge because of data centres and semiconductor manufacturing.

Japan’s leaders and its energy companies have long pushed for nuclear power. They say it’s more reliable than renewable energy like solar and wind, and better suited for Japan’s mountainous terrain. But critics say the emphasis on nuclear energy has come at the cost of investing in renewables and cutting emissions.

Now, as Japan tries to revive its nuclear power ambitions, the costs of running the reactors have surged, partly because of new safety checks that require hefty investments from companies trying to restart plants.

The government could subsidise the costs, or pass them on to consumers – both unpalatable options for Japan’s leaders, who have for decades been hailing the affordability of nuclear power. An expensive energy bill could also hurt the government at a time when households are protesting about rising costs.

The government’s “hands are tied when it comes to financially supporting nuclear power, unless it’s willing to go back on one of the main selling points”, Koppenborg said.

Beyond the fear of another disaster like Fuksuhima, a series of scandals have also rattled public trust.

The Kashiwazaki-Kariwa plant in particular found itself embroiled in a couple of them. In 2023, one of its employees lost a stack of documents after placing it on top of their car and forgetting it there before driving away. In November, another was found to have mishandled confidential documents.

A TEPCO spokesperson said the company reported the incidents to the Nuclear Regulation Authority (NRA), adding that it aimed to continue improving security management.

These revelations are “a good sign” for transparency, says Koppenborg. But they also reveal that “Tepco is struggling to change its ways and the way it approaches safety”.

Hisanori Nei, a former senior nuclear safety official said he was “surprised” by the scandal at Hamaoka, he believed the harsh penalty dealt to its operator should deter other companies from doing the same.

What happened at Fukushima turned Japanese public opinion against what had been hailed as an affordable and sustainable form of energy.

Thousands of residents filed class action lawsuits against Tepco and the Japanese government, demanding compensation for property damage, emotional distress and health problems allegedly linked to radiation exposure.

In the weeks after the March 2011 disaster, 44% of Japanese thought the use of nuclear power should be reduced, according to a survey by Pew Research Center. That figure jumped to 70% by 2012. But then polls by the Japanese business publication Nikkei in 2022 showed that more than 50% of people supported nuclear power if safety was ensured.

But there is fear and mistrust. In 2023, the release of treated radioactive water from the Fukushima Daiichi nuclear plant sparked anxiety and anger both at home and abroad.

And many still remain opposed to restarting nuclear plants. In December, hundreds of protesters gathered outside the Niigata prefectural assembly where Kashiwazaki-Kariwa is located, voicing safety concerns.

Last week, ahead of Kashiwazaki-Kariwa’s restart, a small crowd gathered in front of Tepco’s headquarters to protest again.

Nuclear safety standards have been ramped up after Fukushima. The NRA, a cabinet body established in 2012, now oversees the restarting of the country’s nuclear plants.

At Kashiwazaki-Kariwa, 15-metre-high (49ft) seawalls have been built to guard against large tsunamis; watertight doors now protect critical equipment at the facility.

“Based on the new safety standards, [Japan’s nuclear plants] could survive even a similar earthquake and tsunami like the one we had in 2011,” says Nei, the former senior nuclear safety official.

But what worries Dr. Florentine Koppenborg, a senior researcher at the Technical University of Munich is, “They’re preparing for the worst they’ve seen in the past but not for what is to come.”

Some experts worry that these policies are not planning enough to account for rising sea levels due to climate change, or the once-in-a-century megaquake that Japan has been anticipating.

“If the past repeats itself, Japan is super well-prepared,” Koppenborg said. “If something really unexpected happens and a bigger than expected tsunami comes along, we don’t know.”