Photo/IllutrationThe 2011 tsunami damaged pumps at the Fukushima No. 1 nuclear plant. (Provided by Tokyo Electric Power Co.)

An employee of Tokyo Electric Power Co. testified in court that his boss abruptly ended preparations in 2008 to build a seawall to protect the Fukushima No. 1 nuclear plant from a towering tsunami.

“It was unexpected,” the employee said of former TEPCO Vice President Sakae Muto’s instructions during a hearing at the Tokyo District Court on April 10. “I was so disheartened that I have no recollection of what followed afterward at the meeting.”

Muto, 67, was deputy chief of the company’s nuclear power and plant siting division at the time.

He, along with Tsunehisa Katsumata, former TEPCO chairman, and Ichiro Takekuro, former TEPCO vice president, are now standing trial on charges of professional negligence resulting in death and injury over the 2011 nuclear disaster at the Fukushima No. 1 plant.

To prove negligence, prosecutors are trying to show that the top executives could have predicted the size of the tsunami that swamped the plant on March 11, 2011, resulting in the most serious nuclear accident since the 1986 Chernobyl disaster.

The employee was a member of a team tasked with compiling steps against tsunami at the earthquake countermeasures center that the utility set up in November 2007.

He reported directly to Muto.

According to the employee, TEPCO was considering additional safeguards on the instructions of the then Nuclear and Industrial Safety Agency for all nuclear plant operators to review their anti-earthquake measures.

The group weighed its options based on a long-term assessment of the probability of major earthquakes released by the science ministry’s Headquarters for Earthquake Research Promotion in 2002.

The assessment pointed out that Fukushima Prefecture could be hit by a major tsunami.

Some experts were skeptical about the assessment, given that there were no archives showing a towering tsunami ever striking the area.

But the employee told the court, “Members of the group reached a consensus that we should incorporate the long-term assessment” in devising countermeasures.

The group asked a TEPCO subsidiary to conduct a study on the maximum height of a tsunami on the basis of the assessment.

The subsidiary in March 2008 informed the group that a tsunami of “a maximum 15.7 meters” could hit the Fukushima plant.

The group reported that number to Muto in June that year.

Based on Muto’s instructions, the group studied procedures on obtaining a permit to build a seawall to protect the Fukushima No. 1 nuclear plant, according to the employee.

But in July, Muto, without giving an explanation, told the group at a meeting that TEPCO will not adopt the 15.7-meter estimate, the employee said.

He said Muto’s decision stunned group members who had believed the company was moving to reinforce the plant.

The tsunami that caused the triple meltdown at the Fukushima No. 1 nuclear plant reached 15.5 meters.

But Muto and the two others on trial have pleaded not guilty, arguing that the 15.7-meter prediction was “nothing more than one estimate.”

Why the TEPCO management dropped the tsunami prediction will be the focus of future hearings.

Prosecutors had initially declined to press charges against the three former executives, citing insufficient evidence. However, a committee for the inquest of prosecution twice concluded that the three should be indicted.

Their trial began in June last year. Lawyers are acting as prosecutors in the case.

(This story was compiled from reports by Mikiharu Sugiura, Takuya Kitazawa and Senior Staff Writer Eisuke Sasaki.)