Tokyo (CNN) -- Worse-than-expected damage in one reactor is forcing a change of plans at Japan's Fukushima Daiichi nuclear power plant, but its owners say they still expect to end the 2-month-old crisis by January.
The Tokyo Electric Power Co. said it will have to change its plans for cooling reactor No. 1 after determining the unit's fuel rods melted almost completely in the early hours of the disaster and that the pressure vessel at the heart of the reactor may be leaking. That has forced the company to revise its plan to cool the reactors by flooding the surrounding space to draw heat away from the core, the company announced Tuesday.
The company says it will now step up efforts to set up a cooling system in which water is pumped through the reactor, chilled, decontaminated and pumped back into the crippled reactors -- similar to the system knocked out by the March 11 earthquake and tsunami that triggered the worst nuclear disaster since Chernobyl.
But Sakae Muto, Tokyo Electric's vice president for nuclear power, said the company still is planning on restoring normal cooling no later than October and bringing the reactors to a complete "cold shutdown" by January at the latest.
Tokyo Electric first laid out a six- to nine-month timetable for bringing an end to the crisis in mid-April, a month after the historic earthquake that struck northern Japan. But an assessment released over the weekend concluded that coolant levels in the No. 1 reactor at Fukushima Daiichi were much lower than previously believed.
That meant the fuel assembly at the reactor's core was fully exposed and melted, settling into the bottom of the surrounding pressure vessel and likely damaging the vessel.
"That would make this a very, very bad accident and extremely difficult to clean up," said Kenneth Bergeron, a physicist who used to work at the U.S. Department of Energy's Sandia National Laboratories in New Mexico. Bergeron said the molten core may have damaged some of the lines leading into the pressure vessel, such as the tubes that house the control rod drive mechanisms, leading to the leaks.
The company said that while it believes the unit is now leaking, temperature readings from inside the pressure vessel suggest the molten fuel is now being kept cool.
Unit 2 was already believed to be leaking, resulting in a massive buildup of highly radioactive water in the turbine plant behind the reactor. And in documents released Tuesday, the company warned that it faces "the same risk" in the No. 3 reactor.
All three overheated when cooling systems failed at Fukushima Daiichi, about 240 kilometers (150 miles) north of Tokyo. Hydrogen explosions blew apart the housings around the No. 1 and No. 3 reactors and another is suspected of damaging the No. 2 reactor.
Engineers have been forced to pump hundreds of tons of water a day into the reactors and the spent fuel pools of units 1, 3 and 4 to prevent them from overheating again. But the resulting release of radiation forced the evacuations of more than 100,000 people in towns surrounding the plant and has forced Japan to rethink its plans for future nuclear plants.
"The government must squarely face the Japanese people's sense of betrayal over the belief that nuclear power is safe," Banri Kaieda, Japan's minister of the economy, trade and industry, said Monday. "The government has been drawing up nuclear energy policy as a nation with scarce resources. We as a government take full responsibility. We shall finish this accident. We will do our utmost as a country for you all to go back to your home sweet home."
Over the weekend, residents began evacuating from two villages that had originally been outside the danger zone drawn around the plant. The towns of Iitate and Kawamata were downwind of the plant in the early days of the disaster, and radiation levels there are high enough to raise the long-term risk of cancer for those remaining, the government said.
"I know that they are having to endure great hardships, and their life in evacuation going forward will be a very harsh one," Chief Cabinet Secretary Yukio Edano told reporters Monday. "We truly regret that this had to happen."
Radiation levels in Iitate, about 40 kilometers (25 miles) northwest of the plant, were nearly 40 times normal background levels Monday, according to data released by the country's Science Ministry. Someone who spent eight hours a day outside would get the government's maximum allowable dose of 20 millisieverts in about six months at those levels.
Residents of those towns and all or part of three others were given orders to start packing in April. Five more areas have been put on notice to await evacuation orders, and the government says it will decide whether those residents will be allowed to return around the time the crisis is resolved.
CNN's Kyung Lah and Matt Smith contributed to this report.