One of the reactors at Japan's crippled nuclear power plant has been damaged more severely than originally thought, officials say.
Repairs to monitoring equipment revealed that the water level in the core of Unit 1 at the Fukushima Dai-ichi plant is much lower than previously thought, leaving the portion of the fuel rods still intact fully exposed.
Other fuel has slumped to the bottom of the pressure vessel and is thought to be covered in water.
The findings also indicate a greater-than-expected leak in that vessel. Radioactive water pouring from troubled reactors has pooled around the complex, hindering work to bring the plant under control.
However, temperatures in the unit are still far below dangerous levels because the plant's operator, Tokyo Electric Power Co, continues to inject new water to keep the rods cool. That radioactive water is apparently then leaking into and through the larger, beaker-shaped drywell, or containment vessel.
"The situation (in the core) hasn't changed since (early in the crisis), and the fuel rods are being cooled by water continuously being injected into the core," nuclear official Takashi Sakurai said.
Nuclear Industrial and Safety Agency officials said the new data indicates that it is likely that partially melted fuel had fallen to the bottom of the pressurised vessel that holds the reactor core together and possibly leached down into the drywell soon after the March 11 quake and tsunami that struck Japan's north-eastern coast.
While officials said it was unlikely that the chunks of fuel were still dangerously hot or that they could melt through the concrete base of containment vessel, they acknowledged that the level of damage could complicate plans detailed in April to bring the plant to a cold shutdown within nine months.
Further examination was needed to ascertain the full extent of damage, they said.