TOKYO (AFP) – The operator of Japan's tsunami-hit Fukushima nuclear power plant on Tuesday said it believed fuel had partially melted inside three reactors, as long suspected by experts.
Tokyo Electric Power Company (TEPCO) said new readings on water gauges indicated that the fuel had dropped to the bottom of the containment vessels of units two and three, matching its earlier assessment of unit one.
In all three reactors, relatively low temperatures indicated that the fuel was now mostly covered by water that has been pumped into the vessels, meaning there was no immediate threat of an uncontrolled full meltdown.
"It is highly possible that (partial) meltdowns have occurred at reactors two and three," a TEPCO spokesman said as the firm released its latest analysis of data from the plant after the March 11 quake and tsunami.
"Most of the fuel is believed to have fallen to the bottom (of pressure vessels that contain fuel rods) as has happened in reactor one," he said. "They are now being cooled and are in stable conditions."
Japan's March 11 disaster, which left nearly 25,000 people dead or missing, knocked out cooling systems at the Fukushima plant. This led reactors to overheat, triggering the worst nuclear crisis since Chernobyl 25 years ago.
Reactors four, five and six were under maintenance when the quake hit.
TEPCO estimates it will bring all six reactors to safe "cold shutdown", with low pressure and low temperatures, by some time between October and January, although it will take far longer to dismantle the plant.
Emergency crew have sprayed water into the facility since the quake to cool down the reactors and keep fuel rods in containment pools submerged under water, creating tonnes of toxic runoff that has leaked into the Pacific.
This week TEPCO warned that containment vessels for the radioactive water were almost full.
The company is building a new water treatment facility and has also docked a storage tank called the "megafloat" off the site to hold more low-level contaminated water.
An international panel of nuclear experts arrived in Japan this week to assess the accident and is due to report back to the UN's International Atomic Energy Agency in Vienna in late June.
The IAEA announced last week the mission, headed by Mike Weightman, chief inspector of nuclear installations in Britain, would comprise 20 experts from 12 different countries.
Japan has also decided to set up a panel independent of the nuclear industry and bureaucracy, and mostly made up of academics, to look into the causes of the crisis. It is expected to compile a mid-term report in December and a final report by mid-2012.
