Stabilizing the crisis at the Fukushima No. 1 power plant by the end of the year may be impossible, senior officials at Tokyo Electric Power Co. said Sunday, throwing a monkey wrench into plans to let evacuees return to their homes near the plant.

The confirmation of core meltdowns hitting reactors 1 through 3, accompanied by breaches to the critical pressure vessels that hold the nuclear fuel, has led officials to believe that "there will be a major delay to work" to contain the situation, one official said.

Tepco, the plant's operator, announced on April 17 its road map for bringing the troubled reactors into a cold shutdown within six to nine months.