Three men plead not guilty to professional negligence in the only criminal action targeting officials since the triple meltdown

Three former executives with the operator of the destroyed Fukushima Daiichi nuclear power plant have pleaded not guilty to charges of professional negligence, in the only criminal action targeting officials since the triple meltdown more than six years ago.

In the first hearing of the trial at Tokyo district court on Friday, Tsunehisa Katsumata, who was chairman of Tokyo Electric Power (Tepco) at the time of the disaster, and two other former executives argued they could not have foreseen a tsunami of the size that knocked out the plant’s backup cooling system, triggering a meltdown in three reactors.

“I apologise for the tremendous trouble to the residents in the area and around the country because of the serious accident that caused the release of radioactive materials,” Katsumata said, bowing slightly.

Prosecutors alleged that the 77-year-old, along with his co-defendants, Sakae Muto, 67, and Ichiro Takekuro, 71 – both former Tepco vice-presidents – had been shown data that anticipated a tsunami of more than 10 metres in height that could cause a power outage and other serious consequences.

Facebook Twitter Pinterest Activists protest against Tepco on Friday. Photograph: Toru Yamanaka/AFP/Getty Images

A report by a government panel said Tepco simulated the impact of a tsunami on the plant in 2008 and concluded that a wave of up to 15.7 metres (52 feet) could hit the plant if a magnitude-8.3 quake occurred off the coast of Fukushima. Executives at the company allegedly ignored the internal study.

The three men – charged with professional negligence resulting in death and injury – have since retired from Tepco.

The company, which faces a multibillion-dollar bill for decommissioning Fukushima Daiichi, is not a defendant in the trial. If convicted, the men face up to five years in prison or a penalty of up to 1m yen (£7,000).

Although there are no records of anyone dying as a result of exposure to radiation from the plant, prosecutors alleged the executives were responsible for the deaths of 40 elderly people who were evacuated from a hospital near the plant.

The Fukushima plant had a meltdown after the tsunami, triggered by a magnitude-9 earthquake, hit the plant on the afternoon of 11 March 2011.

The tsunami killed almost 19,000 people along the north-east coast of Japan and forced more than 150,000 others living near the plant to flee radiation. Some of the evacuated neighbourhoods are still deemed too dangerous for former residents to return to.

“They continued running the reactors without taking any measures whatsoever,” the prosecutor said. “If they had fulfilled their safety responsibilities, the accident would never have occurred.”

Facebook Twitter Pinterest A file picture shows a tsunami-hit district in Miyagi prefecture, Japan. Photograph: Kimimasa Mayama/EPA

Muto challenged the allegation by the prosecution that he and the other defendants failed to take sufficient preventative measures despite being aware of the risk of a powerful tsunami more than two years before the disaster.

“When I recall that time, I still think it was impossible to anticipate an accident like that,” he said. “I believe I have no criminal responsibility over the accident.”

Investigations into the accident have been highly critical of the lax safety culture at Tepco and poor oversight by industry regulators. Prosecutors considered the case twice, and dropped it both times, but a citizens’ judicial panel overrode their decision and indicted the former executives.

Outside the court, Ruiko Muto, a Fukushima resident and head of the group of plaintiffs, said: “Since the accident, nobody has been held responsible nor has it been made clear why it happened. Many people have suffered badly in ways that changed their lives. We want these men to realise how many people are feeling sadness and anger.”