Everyone is rightfully concerned about Japan and what is to become of the region around the Fukushima Dai’ichi generating station. The quality of information by the various broadcast outlets is improving somewhat in my estimation. What the rest of the world should take note of is the stoic and highly admirable manner in which the Japanese have responded to the earthquake*tsunami*nuclear-disaster trifecta that has fallen upon them. In a US city there’d be looting and widespread felonious mischief as local criminal entrepreneurs rose to the occasion.

Another thing that I hope is noticed is the manner in which the failures initiated and propagated at the power station.  The unfortunate low elevation of the emergency generators is the obvious one.  But there is something else that is dramatically affecting how the incident propagates.  If you look at the cutaway diagrams of the plant you will see the highly compact nature of the facility.  The footprint of the buildings are quite small given the amount of equipment and processing that occurs there. In particular, the location of the cooling pools for the spent fuel assemblies is at the upper level of the structure, above the reactor spaces. 

The upper level with the cooling pools has an overhead crane that can move along the length of the facility. The fuel elements can be pulled up and out of the reactor and moved laterally into the pool.   The General Electric design is quite efficient in the use of acreage. But in the event of a major upset with fire, explosions, major radioactive material release, and structural damage, the compactness of the facility and the elevation of the spent fuel cooling pools works for prolonged incident propagation and against termination. 

The very altitude of the cooling pool spaces presents a major hurdle to taking control of the situation.  Having this problem at ground level where you could directly apply resources to the event would be bad enough. But to have it many stories above ground places huge constraints on the responders.  Designers of power plants should be thinking about where hazardous energy can be released and how responders will deal with it. Problem- all facilities design projects are constrained by severe cost considerations. Designers prefer to think about the most efficient designs, not how their brain child is going to fail.

It is difficult to find truly informed opinion on the Fukushima reactor disaster in Japan.  The Daily Kos Community site by Richard Blair seems very credible from what I can discern.  The writer claims to be a Nuclear Power Operations-certified systems engineer in GE Boiling Water Reactors (BWRs). I have no reason to disbelieve it.

Actually, Rachel Maddow (and writers) did a very even handed presentation this evening of the basics of reactors, radiation, and nuclear power generation on her show. 

Blair (writing under the pseudonym Richard Cranium) shares some interesting insights on the Fukushima boiling water reactors. It’s worth a look.  It is part of a larger effort at information aggregation called the Japan Nuclear Disaster: Mothership.

The China Syndrome is a fanciful “theory” that postulates that when a nuclear reactor undergoes a meltdown, the hot core material melts through the pressure vessel and through the concrete containment flooring below into the ground. All the way to China. 

Well, this really can”t happen because the core, hot as it is and dense as it is, could only go to whatever depth matches it’s density. I don’t think many people really understand what happens to core material when it breaches the containment and encounters the subsurface. Further, it’s hard to say if the core material will remain intact as a single unit long enough to retain a critical condition as it spills outside of the reactor vessel assembly. 

The fuel elements are, I believe, ceramic in nature, making them refractory. Refractory materials have quite high melting points. A reaction mass that has some fluidity might well split off isolated blebs which could then take the whole mass away from a critical condition.  This would tend to dampen the reaction rate and allow the reaction mass to cool below the melting point of the mass.  

Quite apart from the dispersion of the core material is the loss of moderator around the reaction mass.  This would occur as the primary coolant water flashes to steam as the pressure vessel is breached. Loss of moderator reduces the number of neutrons in the resonant range and the power should drop accordingly.  The decay heat from the fission products should be fierce.

As a molten parcel of reactor core heats up the surface material below it, the molten flooring, soil, or bedrock must be fluid enough to allow the core to displace it downward. It could be that the blob gets elongated and increases the surface to volume ratio enough to allow the loss of neutron flux to cause the blob to cool below the melting point of the ground.   How a self-heating blob of core material behaves under the pull of gravity in a variable and possibly refractory rocky matrix is not an easy problem.

Ground water would be problematic for the neighborhood because eruptions of contaminated steam would be expected to issue from the crater.

I hope these poor fellows are able to get their reactors under control before the area gets too hot.  If the reactor spaces and control rooms get too hot it is going to complicate the remediation.

It is worth reading the updates from NISA.