I posted this on another thread but will dare to post it again here. Seems to explain very clearly why things can go to hell even without a reactor core meltdown. The authorm, “B.Z.” explains at the Survivalblog link his credentials and he knows what he’s talking about.
Found this on the Ticker Forum thread, it’s from Survivalblog. Note that the article (below is an excerpt) was written and posted by Rawles in September; it is in connection with loss of grid power from an EMP or severe solar storm. But the situation is the same, whatever the loss of power is from. He explains very clearly why there is no need of a core meltdown to have a very bad radiation leak. From everything I have read (and it has been obsessive for 2 days at least), it looks as though this is exactly what is happening at the Fukushima nuke plant.
TF link:
http://tickerforum.org/akcs-www?post=182121&page=16
Survivalblog link:
http://www.survivalblog.com/2010/09/effects_of_an_emp_attack_or_se.html
Effects of an EMP Attack or Severe Solar Storm on Nuclear Power Plants, by B.Z.
You might ask, “well, if the containment structure can contain the melted reactor core, is there a real danger to the public?” The answer is, “yes,” but not from where you think. The reactor core may well be the focus of most people, but the real concern is somewhere else.
What many people don’t know about nuclear power plants is that when spent fuel is off-loaded from the reactor core, the fuel is then placed into what is essentially a large, very deep swimming pool called the “spent fuel pool.” Fuel that has been removed from an operating reactor core is still very hot (both in the sense of temperature and radiation level). In fact, if you were to stand within even 50 feet of a spent fuel assembly with no shielding, you would receive a lethal dose of radiation in just seconds. The water in the spent fuel pool, in addition to cooling the fuel assemblies, acts as a biological shield. In fact, water is an excellent shielding material. You can stand at the top of the spent fuel pool in virtually any nuclear power plant in the US and receive virtually no dose of radiation, so long as the fuel assemblies are covered by about 25 feet of water.
The building that houses the spent fuel pools at nuclear power plants in this country is usually a simple building, with concrete sides and floors but usually with nothing but a thin, corrugated steel roof. This is the root of the problem. Just like the fuel in the reactor, the fuel assemblies in the spent fuel in pool must also be cooled. These pools have their own independent, multiply redundant systems for cooling, separate from the systems that cool the reactor core. However, these pool cooling systems can be cross-tied with the reactor cooling systems in an emergency. The water in the spent fuel pool must be continuously circulated through heat exchangers (again, like your car radiator) to reject heat. Loss of off-site power will also cause a loss of spent fuel cooling. Normally, the temperature in these spent fuel pools is somewhere around 100 to 110 degrees F or so (similar to a typical suburban “hot tub”). When the spent fuel cooling system pumps stop operating, the fuel assemblies in the spent fuel pool will immediately begin to heat up. These fuel assemblies will continue to heat the water in the spent fuel pool until it boils. The best case scenario of “time to boil” for these spent fuel pools is perhaps 90 hours. The worst case, such as just after a core offload, would be much shorter, perhaps as little as four hours or even less. At that point, once the fuel assemblies in the spent fuel pool become uncovered because the water has boiled off, the effects mirror what would happen in the reactor core. The spent fuel assemblies will heat up until the fuel cladding starts to melt. As bits of the melting fuel fall into what is left of the water in the pool, the process will just accelerate as the heat source is now more concentrated since it has fallen back into the water and the water may flash to steam and this may cause the pressure in the building to increase, and radioactive steam, carrying radioactive particles, will now begin to exit the building through the non-sealed penetrations, portals or doors in the building.
Of course, there are usually multiple sources of water than can be called upon to re-fill the spent fuel pool before the water all boils off. But virtually all of these systems are dependent upon working, electrically operated pumps to move this water. If control systems have failed due to the EMP and there is no power to operate the pumps (either to add additional water or to pump water through the heat exchangers), then the fuel will ultimately become uncovered. Exposing the hot zirconium fuel cladding to air and steam causes an exothermic reaction, and the cladding will actually catch fire at about 1,000 degrees C. Even the NRC concedes that this type of fire cannot be extinguished, and could rage for days (Source: Bulletin of the Atomic Scientists, Vol. 58, No. 1, Jan./Feb. 2002).
The bottom-line is that if the spent fuel cooling pumps cannot be operated or the system cannot be cross-tied with the reactor shutdown cooling system, then the fuel assemblies in the spent fuel pool will melt, catch fire, and radioactive fission products will be released into the atmosphere and much of the countryside downwind of the nuclear power plant will be contaminated for many years.
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That’s very clearly written—and yes, worrisome, despite the “everything’s under control” posts from some FReepers here.