Four former executives had in 2022 been ordered to collectively pay 13.3 trillion yen in a suit brought by shareholders over the nuclear disaster triggered by a massive tsunami in 2011.

But that verdict was thrown out Friday by the Tokyo High Court, a spokeswoman for the institution told AFP.

Shareholders argue the catastrophe could have been prevented if Tokyo Electric Power Company (TEPCO) bosses had listened to research and implemented preventative measures, like placing an emergency power source on higher ground.

But the defendants counter that the risks were unpredictable, and the studies in question are not credible.

"The defendants... cannot be found to have had this foreseeability at a point in time before the earthquake in question," Friday's court ruling said.

TEPCO declined to comment on the High Court verdict, but the shareholder plaintiffs reacted with anger.

"If I were to summarise today's ruling in one phrase: it is a ruling that will lead to future serious nuclear accidents," said Hiroyuki Kawai, head of their legal team.

"When nuclear operators read this ruling, I believe they'll become even more complacent," he later told AFP.

"No major earthquake has ever been accurately predicted in advance," Kawai added.

- 'Take responsibility' -

Three of the Fukushima Daiichi nuclear plant's six reactors were operating when a massive undersea quake triggered a massive tsunami on March 11, 2011.

They went into meltdown after their cooling systems failed when waves flooded backup generators, leading to the worst nuclear disaster since Chernobyl.

Overall the tsunami along Japan's northeast coast left around 18,500 people dead or missing.

The 13.3 trillion yen damages award was meant to cover TEPCO's costs for dismantling reactors, compensating affected residents and cleaning up contamination.

In 2015, British oil giant BP was ordered to pay $20.8 billion for the Gulf of Mexico oil spill in what was described at the time as the highest fine ever imposed on a company in the United States.

The High Court court spokeswoman said that an appeal by the shareholders for an even higher damages order of 22 trillion yen had been dismissed on Friday.

"Take responsibility for the Fukushima nuclear accident!" said a pink-and-white banner displayed by the plaintiffs after the ruling.

They said they would now appeal to the Supreme Court.

In March this year, Japan's top court said it had finalised the acquittal of two former TEPCO executives charged with professional negligence over the Fukushima meltdown.

The decision concluded the only criminal trial to arise from the plant's 2011 accident.

kh-cg-kaf/sco

TEPCO - TOKYO ELECTRIC POWER

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