Unit 3 MOX likely melted through

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MOX fuel that was believed to have been kept cool at the bottom of one of the reactors at the crippled Fukushima No. 1 nuclear plant after its core melted is believed to have breached the vessel after melting again, a study said Monday.

The study by Fumiya Tanabe, an expert in nuclear safety, said most of reactor 3’s mixed uranium-plutonium oxide fuel may have dribbled into the containment vessel underneath, and if so, the current method being used to cool the reactor will have to be rethought. This could force Tokyo Electric Power Co. to revise its schedule for containing the five-month-old disaster.

Tepco earlier said that the cores of reactors 1 to 3 are assumed to have suffered meltdowns, although the melted fuel was believed to have been kept at cool enough to solidify at the bottom of each pressure vessel after water was injected.

After analyzing data made public by Tepco, Tanabe argues it became difficult to inject coolant water into the pressure vessel after the pressure rose early March 21. He says the fuel at the bottom overheated and melted again over a four-day period.