The reactor crews returned to the earthquake stricken Fukushima Daiichi nuclear power plant in northern Japan Wednesday after a plume of radioactive steam forced them away Tuesday.
The number of workers was increased from 50 to 100, and the radiation dose they can legally experience was doubled from 100 millisieverts to 250 millisieverts. Authorities said raising the exposure limit was “unavoidable due to the circumstances.”
The power plant was hit by the earthquake and tsunami Friday. The tsunami damaged the emergency generators that run the cooling pumps.
The earthquake emergency system immediately shut down the operating reactors, as planned, but the fuel rods continue to produce “decay heat.” That heat is great enough to cause the fuel rods to burn if they are not cooled.
When the radioactive fuel burns, the radioactivity is carried away in the smoke and soot, which is now falling on the inhabited areas around the plant.
The cooling systems failed and the rods boiled off the remaining water.
The oxygen in the cooling water attached to the cladding on the fuel rods, and freed the water’s hydrogen gas. The hydrogen gas then exploded, blowing the concrete roofs off three of the reactors.
The emergency crews have to clear the rubble from the explosions in order to get water cannons close enough to the reactor buildings.
The environment around the plant is covered with radioactive soot from the burning fuel rods, and the reactors are still producing very high levels of radiation.
The workers are all wearing full protective suits to keep the dust off of their bodies, especially from inhaling it, but the suits cannot protect from the deadly rays given off by the dust, or more importantly, given off by the reactors. All the workers who have chosen to stay at the plant are receiving very significant levels of radiation. Imagine getting a sunburn all the way to your bones.
The greatest danger is that the fuel rods will melt and begin to flow away from the control rods. The control rods keep the fuel bundle from having enough neutron radiation in common to form a chain reaction. The chain reaction produces enormous heat, and if the fuel flows past the control rods, there is no mechanism to stop the chain reaction, which will produce tons of radioactive smoke and airborne soot.
The only good news is that decay heat subsides over a period of weeks. If the fuel can be kept cool, the situation will gradually improve. That’s still a big “if.”
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