Some facts and background information :
[1] In Chernobyl, the nuclear reaction was left to operate at 100% of capacity after a failure, relied on a graphite control rod design from 1942 which is not used any more, and did not house the reactor inside a containment vessel. In Fukushima, immediate steps were taken to bring the reaction under control. Sometime in between the earthquake and the tsunami (perhaps only 90 seconds after the earthquake), sensors automatically injected control rods filled with boron into the reactor vessel, immediately reducing the power of the nuclear reaction to roughly 3% of its original level. Furthermore, the Fukushima reactor vessels are housed inside concrete containment units.
[2] What remains is the challenge of bringing the residual 3% reaction under control. Given the power of nuclear energy, even at 3% of its original level, it needs to be cooled further. Japan appears to have suffered a considerable failure regarding back-up generators needed to both circulate cooling water through the containment units, and ventilate the buildings of hydrogen build-up. Where does the hydrogen come from? Vaporized water converts to very high volumes of steam, which at high temperatures can separate back into hydrogen and oxygen. Hydrogen is highly combustible, even at only 2% concentrations.
[3] The failure of the diesel generators, are primarily a result of the tsunami washing away their fuel storage tanks, rather than from flooding which disabled the generators themselves. At most US nuclear plants, diesel fuel storage tanks are either buried underground, or located within a structure designed to handle an earthquake or flood. In Japan this appears not to be the case; they were above ground, adjacent to the beach, and not well protected. It is amazing to think that inland US nuclear power plants are more flood-proof than their Japanese counterparts. With the failure of the electrical systems, hydrogen has not been venting, and appears to have resulted in the explosions at 3 buildings. In one building, an explosion/fire may have damaged the concrete containment unit, or the concrete “suppression chamber” which helps reduce pressure/heat from the reactor.
[4] The critical objective is to inject water inside the containment unit (which houses the reactor vessel). While exposure of uranium/plutonium rods to air inside the reactor vessel increases the risk that the rods melt, as long as the reactor vessel is not breached and sufficient water is available, the process can eventually be cooled. The next 72 hours are critical.
[5] As for nuclear power more broadly, when the book is written, the failure of the Fukushima systems design will play as prominent a role as the earthquake and tsunami itself. There is no question that one of the 5 most powerful earthquakes on record (which forced the North American tectonic plate eastward by 66 feet), combined with 6-meter tsunami waves, creates a terrifying and formidable obstacle for energy facilities. But considering how well facilities whose backup power did not fail are doing, design flaws regarding fuel storage tanks (and perhaps very basic ones) are likely to be part of the aftermath. The chart shows how Japan’s nuclear efficiency (measured by its capacity factor) is among the lowest in the world. This may be a partial indication of Japan’s design, maintenance and engineering inadequacies compared to other countries, which use different models, electrical system redundancies and protocols.
What now for Japan?
``What has so often excited wonder, is the great rapidity with which countries recover from a state of devastation, the disappearance in a short time, of all traces of mischief done by earthquakes, floods, hurricanes, and the ravages of war. An enemy lays waste a country by fire and sword, and destroys or carries away nearly all the moveable wealth existing in it: all the inhabitants are ruined, and yet in a few years after, everything is much as it was before.”
John Stuart Mill, Principles of Political Economy, 1848
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Topic: Serious earthquake in Japan (Read 10202 times)