A few days after the tidal waves destroyed the generators providing back-up electrical power to Fukushima Daiichi’s cooling system, the protective water bath boiled away from the spent fuel pond for reactor no. 4, leaving the stored spent fuel rods partially exposed to the air. Had it not been for heroic efforts on the part of Japan’s nuclear workers to replenish water in this spent fuel pool, these spent rods would have melted down and their zirconium cladding would have ignited, which most likely would have released far more radioactive contamination than what came from the three reactor core meltdowns.
Japanese officials estimate that, to date, the Fukushima Daiichi nuclear disaster has released just over half of the total radioactive contamination released from Chernobyl, but other sources suggest that the radiation released could be significantly more. In the event of an extreme GMD-induced long-term grid collapse covering much of the globe, if just half of the world’s spent fuel ponds boil off their water and become radioactive zirconium-fed infernos, the ensuing contamination will far exceed the cumulative effect of 400 Chernobyls.
Most of us tend to believe that a nuclear reactor is something that can be shut down in short order, like some massive piece of machinery that can be turned off by simply flipping a switch, or by performing a series of operations in a prescribed manner over a relatively short time, such as a few hours or perhaps a day or two. In spite of my MIT education (BSME, MIT, 1978), until recently I too was under the spell of this comforting delusion, which is far from the truth. You see, the trillions of chain reactions going on inside a nuclear reactor’s core continuously produce such incredible amounts of energy that a single nuclear power plant can generate more electricity than is required to power a good sized city. Unfortunately, these reactions do not simply “cease fire” at the flip of a switch. In general, it takes 5 to 7 days to slow down a reactor core’s nuclear chain reactions to the point where the core may be removed from the reactor.
After removal, the fuel rods are quite “hot”, both from the perspective of temperature and radioactivity. For the next 3 to 5 years these fuel rods must be immersed under roughly 20 feet of continuously cooled water, both to shield the surrounding area from radioactivity, as well as to prevent catastrophic melt-down from occurring. According to Gundersen, after slowing down the chain reactions inside the reactor cores at Fukushima for a full eight months, the fuel rods would start melting down again if coolant flow was suspended for just 38 hours.
Gundersen explained that, essentially all modern nuclear reactors are designed with banks of “fuel rods”, which contain highly radioactive materials, combined with banks of “control rods”, which mesh between the fuel rods like the interwoven fingers of your right and left hands. It is the degree of interweave that moderates and controls the rate of nuclear chain reactions. He further explained that in the event of a significant loss of reactor control, reactors are designed for a “fail-safe” process to occur, where the control rods automatically fall into the fully meshed position with respect to the fuel rods, resulting in maximal slowing of the core’s nuclear reactions and beginning the process of shutting down the reactor.
Typically, this action rapidly reduces the power produced by these chain reactions by a factor of 20:1 (to 5.0 per cent of full power), but that still leaves thousands of horsepower worth of waste heat that must be removed if the reactor core is not to rapidly overheat and fail catastrophically. After a day of leaving the control rods in the fully interwoven position, this reaction slows to 1.0 per cent, and after a week it will be about 0.1 per cent of full power. Once the reactions in the fuel rods slow to the point where the rods may be removed from the reactor, the spent fuel rods must be cooled inside containment ponds for 3–5 more years before the nuclear reactions decay to a point where the rods can be moved to specially designed air-cooled storage banks.
As mentioned previously, nuclear power plants are only required to store enough backup fuel reserves on-site to keep their backup diesel generators running for a period of one week. The NRC has always operated from the assumption that extended grid “blackouts” would not last for periods of more than a few days. The government has promised that, in the event of a major catastrophe such as a Hurricane Katrina, diesel trucks will show up like clockwork at all troubled nuclear facilities until local grid-supplied electrical power services have been re-established. Unfortunately, governments and regulators have not considered the possibility that the next extreme GMD which Mother Nature unleashes upon Earth will quite likely disrupt grid services over much of the industrial world for a period of years, not just days. The chances that the world’s nuclear reactors will receive weekly deliveries of diesel fuel under such chaotic circumstances are practically zero. In a world suffering from loss of fuel and electric power, if any such deliveries were attempted those fuel tankers would be prime targets for armed hijackers.
Had it not been for heroic efforts on the part of Japan’s nuclear workers to replenish waters in the spent fuel pool at Fukushima, those spent fuel rods would have melted down and ignited their zirconium cladding, which most likely would have released far more radioactive contamination than what came from the three reactor core melt-downs. Japanese officials have estimate that the Fukushima Daiichi nuclear disaster has already released into the local environment just over half the total radioactive contamination as was released by Chernobyl, but other sources estimate it could be significantly more than was released by the accident at Chernobyl. In the event that an extreme GMD induced long-term grid collapse covering much of the globe, if just half of the world’s spent fuel ponds were to boil off their water and become radioactive zirconium fed infernos, the ensuing contamination could far exceed the cumulative effect of 400 Chernobyls.
