Tepco confirms extra partial fuel rod meltdown at plant
Tokyo Electric Power (Tepco) has confirmed the meltdown of extra fuel rods in reactors at its damaged Fukushima nuclear power plant.
The company said that the rods were in its Number 2 and Number 3 reactors.
Tepco has been trying to contain radiation from the plant, crippled by the 11 March earthquake and tsunami.
The company said that it planned to stick to its timetable of getting the radiation under control by January.
Tepco's announcement came on the same day that a team from the United Nations' atomic watchdog, the International Atomic Energy Agency (IAEA), kicked off a visit in Japan.
Earlier this month, Tepco had revealed that rods at its Number 1 reactor melted down. It was thought that a similar problem had occurred in the other reactors but it was difficult to confirm.
"Based on our analysis, we have reached the conclusion that a certain amount of nuclear fuel has melted down," Ken Matsuda, a Tepco spokesman told the BBC.
He said the analysis came from a report that Tepco was required to submit to Japan's Nuclear and Industrial Safety Agency (Nisa).
The spokesman added that most of the fuel from the Number 2 reactor had melted approximately 100 hours after the earthquake, which measured 9 on the Richter scale, struck Japan.
The meltdown in the Number 3 reactor took place about 60 hours after the quake.
Mr Matsuda said the new discovery would not alter Tepco's plans.
The company has said that it wants to reach a "cold shutdown" of the power plant by January, and has been trying to cool the reactors and get the unstable fuel rods back under control.
"This result does not change our work," he said.
Earlier in May, Tepco revealed that the damage sustained by the Number 1 reactor immediately after the earthquake and tsunami was far more severe than initially thought.
Professor Nobumasa Akiyama of Hitotsubashi University in Tokyo said Tepco's new revelation reinforces that idea.
In an effort to better understand the current situation in Japan specialists from the IAEA are joining other international experts in Tokyo for a fact-finding mission.
They are expected to submit a report on Japan's handling of the nuclear crisis to present to the IAEA's member states.
The group is expected to visit the Fukushima nuclear plant, though details have not been finalised.
Professor Akiyama said that the IAEA had come under criticism for its reaction to the Fukushima crisis.
"First of all, it has not been able to provide the information on what's going on on the ground," he said. "Secondly, it hasn't been able to provide a prescription for the solution of the crisis."
Mr Akiyama said the nuclear agency would be expected to provide more guidelines for nuclear safety after the visit to Japan this week.
He added that it may need to be beef up its funding and staff if it was going to be able to fulfil its mandate.