A court official told AFP the trio's appeal had been dismissed in the only criminal trial to arise from the world's worst nuclear accident since Chernobyl.

Activists supporting the prosecution of the men, including Etsuko Kudo, a former resident of the Fukushima region, gathered outside the court to express their anger.

"How should I explain this ruling to kids in Fukushima who have been through so much pain?" Kudo, 68, told AFP.

"It's unbelievable that people who are responsible for such a major disaster can get away without being held criminally liable."

A massive tsunami swamped the Fukushima Daiichi plant on Japan's northeastern coast in March 2011 after a 9.0-magnitude undersea earthquake, the strongest in the country's recorded history.

The tsunami left 18,500 people dead or missing, but no one was recorded as having been directly killed by the nuclear accident, which forced evacuations and left parts of the surrounding area uninhabitable.

Wednesday's verdict affirmed a non-guilty ruling in September 2019 for the ex-bosses from the Tokyo Electric Power Company (TEPCO).

The men -- former TEPCO chairman Tsunehisa Katsumata, and former vice-presidents Sakae Muto and Ichiro Takekuro -- had faced up to five years in prison if convicted.

They were accused of liability for the deaths of more than 40 hospitalised patients who had to be evacuated following the nuclear disaster.

But the Tokyo District Court said in 2019 that they could not have predicted the scale of the tsunami that triggered the disaster.

The criminal case has been in the spotlight after a separate landmark verdict in July in a civil case involving the same three men and one other former executive.

The four were ordered to pay a whopping 13.32 trillion yen ($101 billion at today's rates) for failing to prevent the disaster.

Lawyers have said the enormous compensation sum is believed to be the largest amount ever awarded in a civil lawsuit in Japan -- although they admit that is symbolic, as it is well beyond the defendants' capacity to pay.

tmo/kaf/aha

TEPCO - TOKYO ELECTRIC POWER