13 March: Japanese reactor scare-mongering begins from anti-nuclear propaganda politicians

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http://nige.wordpress.com/ The Sendai earthquake moment magnitude of 9.0 is equivalent to a total energy of about 31,800 megatons of TNT, of which 1.5% or 477 megatons of TNT equivalent appeared as explosion-equivalent "surface waves" composed of ground shock motion and tsunami water waves, similar to the effects from ground-coupled shock energy in a surface burst explosion. See http://www.jclahr.com/alaska/aeic/magnitude/energy.txt

http://glasstone.blogspot.com The explosion on 12 March 2011 of the outer concrete containment building of Japan's Fukushima Dai-ichi nuclear reactor Number 1, the oldest of 11 reactors on the shoreline immediately exposed to the 9.0 moment magnitude earthquake and 7 metre tsunami which inundated emergency generators required for cooling the radioactive decay heat after shutdown. The reactor was designed in 1971 and is 170 miles northeast of Tokyo. Unlike the latest designs of nuclear reactors, this old reactor design does not allow natural convection cooling to dissipate the radioactive decay heat after shutdown, but requires a powered pump to keep the coolant flowing.

The decay heat in the steel pressure vessel converted the stagnant coolant water into high pressure steam and a mixture of hydrogen and oxygen gas, which had to be vented into the concrete containment building surrounding the 15 cm thick steel reactor core vessel. The hydrogen and steam mixture in the outer building then exploded, blowing the concrete roof off and allegedly venting a small quantity of gaseous fission products, mainly xenon-135, from damaged fuel rods (the zirconium casings of fuel rods melt at 1200 C), which had been released into the outer building along with the steam and hydrogen gas during the pressure venting. The strong steel reactor core remained intact.

After the explosion, the radioactivity level inside the concrete containment building reached 100 microSieverts per hour or 10 mR/hour (1000 times natural background radioactivity). Outside the building, it reached 0.8 microSieverts per hour or 0.08 mR/hr (8 times background). Chief Cabinet Secretary Yukio Edano said radiation around the plant had fallen after the time of the blast, confirming that the steel fuel vessel is intact. Sea water is now being used to cool down the reactor core, as is now being done at reactor number 3.

The episode proves the safety of nuclear power in the worst case scenario of an 9.0 moment magnitude earthquake followed by a massive tsunami which destroyed backup power for coolant circulation, was safe for 11 reactors and caused only a minor venting of short-lived volatile nuclides with a maximum radiation level outside the oldest reactor buildings of 8 times background, which rapidly decayed and dispersed. The volatile radioactive fission product gas xenon-135 has a 9.2 hours half life, so under 3% remains after 48 hours or 5.2 half lives, and in addition it is quickly dispersed and diluted to safe levels. The initial maximum dose rate outside the building of 8 times normal background would be down to just 0.2 times background just assuming xenon-135 decay, and neglecting the dispersion effect. This extreme proof test of the safety of nuclear power even under an immense earthquake and tsunami is one piece of good news to come from the natural devastation scene in Japan. Lucky they didn't have a wind farm in the devastated area, or the falling turbine blades would have caused a real additional danger, while solar cells would have been swept along as hazardous debris in the tsunami!

It's mainly gaseous xenon-135 with a half life of 9.2 hours that's escaped, less than 3% remains after 48 hours. Also, it mixes rapidly with the air and gets diluted, too. Notice that background is 0.01 mR/hour so the peak dose rate of 1000 times higher is 10 mR/hour. If this decays with 9.2 hours half life, the total dose with exponential decay is simply the initial peak dose rate times the mean life (for exponential decay the mean life is 1/ln 2 or 1.44 half lives). Hence total dose = 10 x 1.44 x 9.2 = 132 milliRoentgens. This is about the dose you get naturally over a year. No significant plutonium will have vented, because it's a solid, not a gas. You only need to take potassium iodine tablets if the total predicted dose exceeds 20 Roentgens to the thyroid. The amount of iodine-131 released will be far less than the xenon-135 because it's mass number is further from the peak on the M-shaped fission product abundance curve, and its longer half life (8 days) reduces its specific activity per atom. If they had wind turbines or solar cells in Japan with the same power output, they would have caused a serious hazard from flying panel debris, wind blades, etc., during the earthquake and tsunami.
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