TOKYO — Three former executives of Tokyo Electric Power Co. apologized in court Friday for the 2011 Fukushima nuclear disaster, but pleaded not guilty to charges of professional negligence.

Tsunehisa Katsumata, the 77-year-old ex-chairman of TEPCO, and two former vice presidents said they don’t think they bear criminal responsibility because they couldn’t predict the enormous tsunami that flooded the plant.

That issue is expected to be the crux of their trial, the first to consider whether officials of the utility can be held criminally responsible. TEPCO itself has not been charged. The trial at Tokyo District Court is likely to take more than a year.

A prosecutor told the court that the three defendants had access to data and studies that anticipated the risk of a tsunami exceeding 30 feet that could trigger a loss of power and severe accidents.

“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.”

The lawyers in a Japanese trial are generally not identified by name.

Three reactors had meltdowns, and radiation spread into surrounding communities after the nuclear plant north of Tokyo was hit by a powerful earthquake and tsunami on March 11, 2011. Tens of thousands of residents were forced to evacuate, and some areas remain uninhabitable more than six years later.

Defense attorneys said in court that the tsunami projection was not well-established and divided experts.