Looking pale and worn and sitting with his head bowed, the president of JCO Co. on Tuesday appeared before Diet members and repeatedly apologized for the nuclear accident 19 days earlier that was Japan's worst.

"I am terribly sorry for causing such a serious accident. It should never have happened," Hiroharu Kitani said before the Lower House's Standing Committee on Science and Technology.

His apologies for the accident in Tokai, Ibaraki Prefecture, were followed by explanations from Kenzo Koshijima, director of the plant, on how workers triggered a self-sustaining nuclear fission chain reaction by pouring an excessive amount of uranium from a bucket into a processing tank.