Wednesday, April 6, 2011

New Worries at Fukushima

The New York Times reported today on a March 26th Nuclear Regulatory Commission assessment of the problems at the Fukushima Daiichi nuclear power plant.  New information includes:
  • Filling the containment structures with thousands of tons of water makes them vulnerable to rupture during aftershocks -- especially since their integrity is already questionable after the main quake and the ensuing hydrogen explosions.  After the cooling systems failed and the normal cooling pipes either melted or plugged up, the Japanese simply pumped in sea water to immerse the reactor vessel.
  • "The assessment provides graphic new detail on the conditions of the damaged cores in reactors 1, 2 and 3. Because slumping fuel and salt from seawater that had been used as a coolant is probably blocking circulation pathways, the water flow in No. 1 'is severely restricted and likely blocked.' Inside the core itself, 'there is likely no water level,' the assessment says, adding that as a result, 'it is difficult to determine how much cooling is getting to the fuel.' Similar problems exist in No. 2 and No. 3, although the blockage is probably less severe, the assessment says."
  • The reactors need to be cooled for many months before they will be able to be decommissioned.  Without the closed-loop cooling capability (which has perhaps been lost forever because of the melting of the cores), this must be done by flooding the units with water.  But that solution has a large number of problems associated with it, including ground water contamination, storage of the water (or discharge to the ocean), erosion of footings and foundations, etc.
  • Fragments of radioactive fuel may have been expelled up to a mile away by the hydrogen explosions.   A large amount of fuel landed between two reactor buildings, and had to be bulldozed over, presumably to enable workers to be in the area.
Read more here.

It appears that exceptionally radioactive water is escaping from the No. 2 reactor, probably from the toroidal suppression pool that sustained an explosion early in the crisis.  This is the water that was flowing from under the ground, through a crack in a concrete-lined pit, and then into the ocean.  It has been measured at 7.5 million times the legal limit for ocean dumping.  That high of a level would imply that the water is coming directly from the core.  Containment has failed.

I also noticed that the measurements of radioactivity at the plant are being hampered by the fact that their rate dosimeters cannot measure greater than 1000 millisieverts per hour (100 rem/hour)-- and the levels are apparently well above that.  At 1000 millisieverts per hour, you would have an increased cancer risk in 6 minutes, and would have full radiation sickness symptoms with an hour of exposure.  If you stay four hours in that environment, you would likely die from radiation sickness.  If you stayed six hours, you would almost certainly die.

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