The Yomiuri Shimbun
The Nuclear and Industrial Safety Agency has reported to a Cabinet Office safety panel that nuclear fuel pellets in the Nos. 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 Monday 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 percent “damaged.”
According to 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 the Nos. 2 and 3 reactors. Melting fuel pellets also likely led to a hydrogen explosion at the No. 1 reactor, Nishiyama said.
Tokyo Electric Power Co., the operator of the crippled plant, has said the cores of the Nos. 1 to 3 reactors have been damaged by 25 percent to 70 percent. But the agency emphasized that these figures are only estimates.
“We can’t say for sure about how much has melted until the rods are actually taken out,” Nishiyama said.
(Apr. 20, 2011)
Source: The Daily Yomiuri