Japanese nuclear reactor update: Amid signs of progress, new problems
Scientists warn of risks from spent-fuel cooling pools and plutonium-rich, mixed-oxide fuel inside one nuclear reactor, even as the No. 1 and No. 3 reactors appear to be coming under control.
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A particular feature of the 40-year old General Electric Mark 1 Boiling Water Reactor model – such as the six reactors at the Fukushima site – is that each reactor has a separate spent-fuel pool. These sit near the top of each reactor and adjacent to it, so that cranes can remove spent fuel from the reactor and deposit it in a swimming-pool-like concrete structure near the top of the reactor vessel, inside each reactor building.Skip to next paragraph
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If the hydrogen explosions damaged those pools – or systems needed to keep them cool – they could become a big problem. Keeping spent-fuel pools cool is critical and could potentially be an even more severe problem than a reactor meltdown, some experts say. If water drains out, the spent fuel could produce a fire that would release vast amounts of radioactivity, nuclear experts and anti-nuclear activists warn.
"There should be much more attention paid to the spent-fuel pools," says Arjun Makhijani, a nuclear engineer and president of the anti-nuclear power Institute for Energy and Environmental Research. "If there's a complete loss of containment [and thus the water inside], it can catch fire. There's a huge amount of radioactivity inside – far more than is inside the reactors. The damaged reactors are less likely to spread the same vast amounts of radiation that Chernobyl did, but a spent-fuel pool fire could very well produce damage similar to or even greater than Chernobyl."
But another scientist said while the spent-fuel pools have capacity for high volumes of radioactive material, the amount of fuel currently in the spent-fuel pool might be less than widely believed, based on data he has seen showing only about as much spent fuel in the vulnerable pool as contained in the reactor.
"The inventory numbers I've seen for the spent-fuel pool [that was losing coolant] is well below capacity," said Edwin Lyman, a physicist with UCS, which describes itself as neither pro- nor anti-nuclear power, but which says nuclear safeguards today are not adequate. "That could limit the damage."
The US Seventh Fleet, which patrols the seas near Japan but does not publish its precise whereabouts, reportedly detected small amounts of radiation drifting in the vicinity of its ships, so moved the fleet to a different location.
The threat from plutonium-rich MOX
Another little-reported concern is a small but potentially dangerous amount of plutonium-based "MOX" – mixed-oxide fuel – inside the No. 3 reactor, says Dr. Lyman, who notes that plutonium particles are more dangerous to the human body than other particles that might be emitted.
Tokyo Electric said some three yards of a MOX fuel rod was above the water line, suggesting that plutonium and other elements could be in the gases vented to the atmosphere, reported the Kyodo News Agency.
"If the core of that No. 3 reactor melts and venting occurs, some of that plutonium and other nasty elements present in that fuel could end up on the winds," Lyman says.