Japan’s Fukushima Daiichi nuclear complex suffered a second explosion today, destroying an outer building at unit 3. Unit 3, a third reactor at the six-reactor facility, lost its cooling capacity just as Unit 1 did on Saturday. Engineers are flooding both units with seawater and boron to prevent a meltdown.
The Center is concerned about the status of the spent fool pool, which contain used nuclear fuel. These explosions could have compromised that fuel and could have spewed it into the surrounding environment.
Just as with Unit 1, the explosion at unit 3 did not damage the core containment structure. These reactor vessel containment is quite robust, as is evident by remaining intact with a massive structural explosion right around it. Both explosions resulted from a hydrogen build-up. The hydrogen was produced by the exposure of the reactor’s fuel rods and their zirconium alloy casing to hot steam. In normal conditions, the fuel rods would be covered and cooled by water.
The blast injured 11 people, one seriously and Japan’s nuclear agency warned those within 12 miles to stay indoors. Trace amounts of radioactive elements cesium-137 and iodine-131 have been detected outside the plant.
The Fukushima Daiichi unit 3 was built by Toshiba, using a GE design. Last year, the unit began using some reprocessed fuel known as “mox,” a mixture of plutonium oxide and uranium oxide, produced from recycled material from nuclear weapons as part of a program known as “Megatons to Megawatts.” (Wash Post, 3/13/2011)