There were a lot of qualifiers used, but TEPCO officials seemed to admit at a press conference yesterday the possibility that fuel is still melting at Unit 1. As the Mainichi Daily News reported:
An official at Tokyo Electric Power Co., the operator of the crippled Fukushima Daiichi nuclear power plant, admitted Wednesday that fuel of the plant’s No. 1 reactor could be melting.
At a press conference, TEPCO official Junichi Matsumoto said, ”I’m not saying with certainty that (the fuel) has never melted,” while noting that the utility has not been able to confirm the condition of the reactor’s core.
Describing the possible meltdown, Matsumoto said it can be compared to a state in which molten fuel accumulates like lava, or a state in which fuel rods get exposed after their tubes were broken. TEPCO considers such states as a meltdown, he said.
Asked whether the fuel at the No. 1 reactor is ”melting” or ”being damaged,” Matsumoto said TEPCO does not plan to define such conditions in haste.
The Straits Times included a summary prepared by NISA on the extent of damage to the fuel rods:
The Nuclear and Industrial Safety Agency of Japan has reported to a Cabinet Office safety panel that nuclear fuel pellets in the No. 1 to 3 reactors at the quake-hit Fukushima power station are believed to have partially melted.
The report was the first time the agency, an organ of the economy, trade and industry ministry, has acknowledged that nuclear fuel has melted at the Fukushima No. 1 nuclear plant.
Hidehiko Nishiyama, a spokesman for the agency, told a press conference about the agency’s report to the Nuclear Safety Commission. The agency had previously only described the nuclear fuel as having been at least 3 per cent ‘damaged’.
According to Mr Nishiyama, damage to reactors can be described in three phases of increasing severity. In the first phase of initial damage to a reactor’s core, the metallic casing surrounding the fuel pellets are damaged but the pellets remain intact. The second phase involves some melting of nuclear fuel. In the third phase, what is known as a meltdown, all the fuel pellets melt and accumulate at the bottom of the containment vessel.
The agency said it now believes the fuel pallets have melted because of the high levels of radiation detected at No. 2 and 3 reactors. Melting fuel pellets also likely led to a hydrogen explosion at the No. 1 reactor, Mr Nishiyama said.
Tokyo Electric Power Company (Tepco), the operator of the crippled plant, has said the cores of No. 1 to 3 reactors have been damaged by 25 per cent to 70 per cent. But the agency emphasised that these figures are only estimates. ‘We can’t say for sure about how much has melted until the rods are actually taken out,’ Mr Nishiyama said.