Three former executives of Tokyo Electric Power Company Holdings Inc. pleaded not guilty Tuesday in an appeal trial for failing to prevent the 2011 Fukushima nuclear crisis, triggered by a devastating quake-tsunami disaster in northeastern Japan, according to their defense counsel.

The lawyers for former TEPCO Chairman Tsunehisa Katsumata, 81, and former vice presidents Ichiro Takekuro, 75, and Sakae Muto, 71, called for the Tokyo High Court to dismiss the appeal filed in 2019 by court-appointed lawyers acting as prosecutors on charges of professional negligence resulting in death and injury.

In September 2019, the Tokyo District Court acquitted the three former executives of the Fukushima plant operator on the charges, saying they could not have foreseen the massive tsunami that crippled the Fukushima Daiichi power plant and caused core meltdowns.

Combined photo shows former executives of Tokyo Electric Power Company Holdings Inc., (from L) Tsunehisa Katsumata, Ichiro Takekuro and Sakae Muto. (Kyodo)

The court-appointed lawyers maintained the district court ruling contained factual errors.

Those acting as prosecutors had sought five-year prison terms for the executives, arguing they could have prevented the nuclear disaster if they had fulfilled their responsibility to collect information and put in place safety measures.

The appeal trial, which began at the high court Tuesday, is expected to again focus on whether the former executives could have predicted the tsunami following a magnitude-9.0 earthquake that hit northeastern Japan on March 11, 2011.

Katsumata did not make a court appearance Tuesday due to ill health.

In 2016, Katsumata and the two former vice presidents were indicted for failing to implement tsunami countermeasures leading to the deaths of 44 people, including patients forced to evacuate from a nearby hospital, as well as for injuries sustained by 13 people in hydrogen explosions at the Fukushima Daiichi plant.

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TEPCO was informed in 2008 by one of its subsidiaries of the possibility that a tsunami as high as 15.7 meters could hit the Fukushima plant based on the government's long-term evaluation in 2002 of quake risks.

The district court ruled in 2019 that "it would be impossible to operate a nuclear plant if operators were obliged to predict every possibility related to tsunami and take necessary measures."

On March 11, 2011, the six-reactor plant on the Pacific coast was flooded by tsunami waves exceeding 10 meters triggered by the massive earthquake, causing the reactor cooling systems to lose their power supply.

The Nos. 1 to 3 reactors subsequently suffered core meltdowns, while hydrogen explosions damaged the buildings housing the Nos. 1, 3 and 4 units. Many people were forced to evacuate in what is known as the world's worst nuclear crisis since the 1986 Chernobyl disaster.

Katsumata and the two former vice presidents were indicted by court-appointed lawyers in 2016 after an independent panel of citizens mandated indictment.