TOKYO (AP) - The operator of Japan's damaged nuclear power plant said Tuesday that it is highly likely that fuel rods at two more reactors at the facility had mostly melted in the hours and days immediately after the March 11 earthquake and tsunami.
The clearer picture of the extent of the damage comes as U.N. nuclear experts planned to meet with Japan's trade minister later Tuesday at the start of their fact-finding trip.
Tokyo Electric Power Co. had said last week that repaired water gauges showed that fuel rods in Unit 1 at the Fukushima Dai-ichi plant had mostly melted and fallen into a lump at the bottom of the pressure vessel - a state that TEPCO officials have described as a "meltdown" - after the complex's cooling system was knocked out by the tsunami.
Fresh data from Units 2 and 3 indicate that fuel rods in those reactors were in a similar state, said spokeswoman Aya Omura.
In all three reactors, the melted fuel is mostly covered with water and remain at temperatures that are far below dangerous levels, officials say.
"It is unlikely that the meltdowns could worsen the crisis because melted fuels are covered in water," said Takeo Iwamoto, a company spokesman.
The delegation from the International Atomic Energy Agency will focus on safety issues and include a visit to the Fukushima Dai-ichi plant, about 140 miles (230 kilometers) northeast of Tokyo. They will report its findings to a conference of IAEA member nation government ministers starting June 20.
The disaster at Fukushima plant, the world's worst nuclear crisis since Chernobyl, has raised questions about the lax oversight of Japan's nuclear industry.
TEPCO continues to face obstacles in bringing the radiation-leaking plant under control.
On Monday, officials said temporary containers holding radioactive water pumped from the reactors are almost full, raising concerns it could overflow and leak into the sea again. They said the water could fill the tanks in three days and a system to reprocess the water - now measuring more than 80,000 tons - for reuse in the reactors is not yet finished.
Fully ridding the plant of the contaminated water - which is pooling in reactor and turbine buildings, trenches and pits - could take through the end of December, TEPCO spokesman Junichi Matsumoto has said. The amount of the contaminated water could eventually swell to about 200,000 tons, as TEPCO continues to pump water into the reactors and their spent fuel storage pools to help control temperatures and radiation.
Matsumoto had initially said the storage area could last until the system is ready in mid-June. If the storage containers reach full capacity, the water would have to stay inside the turbine basement areas, where it is pooling.
TEPCO has been working with French nuclear engineering giant Areva on a system to reprocess the water, reducing radioactivity and removing salt, so it can then be pumped back into the reactors for cooling.
The operator has also been scrambling to get hold of additional containers for water that is less radioactive. A mega-float giant storage tank that can hold about 10,000 tons of water arrived at the shores of the plant over the weekend.