Sunday, April 24, 2011

The Night's Plutonian Shore

When I was an undergrad at Berkeley, I was nervous about seeing my professors in office hours, as many students (including mine today) are.  I had good reason to be nervous since my Berkeley Physics profs. were all hot-shots in their field; indeed one (O. Chamberlin) was a Nobel Prize winner.  I remember one time while trying to find a professor's office, (and trying to distract myself from getting there), I discovered and read a plaque on the wall.  It was a historical marker stating that this was the location where the element Plutonium was discovered. (Unlike other elements Plutonium, Pu, must be synthesized, since its too radioactive to occur naturally) At the time I had no idea about Berkeley's role in the Manhattan Project, or what Plutonium really was.  Plutonium was named by its discoverers, McMillan and Seaborg, for the god of the underworld, Pluto.  On the periodic table it follows Uranium, and Neptunium.  (See a pattern there?)

There's been concern about reactor #3 at Fukushima Da-ichi because it contains MOX, or mixed oxide nuclear fuel.  "Mixed" means that Uranium is mixed with Plutonium.   Where did that Plutonium come from if it doesn't occur naturally?  It came from Japan's nuclear reactors, which, in the process of causing Uranium to fission (split in two) also produce plutonium as a by-product.  In Japan and other nuclear countries (but not the U.S.) this Plutonium by-product is "re-processed" by sorting out extraneous isotopes which inhibit fission (so called "neutron poisons") then re-using the Uranium/Plutonium mixture.  It was at one of these re-processing plants that a criticality event killed two Japanese workers.  Because Plutonium is a by-product of all Uranium fission, it can be found in all six of the reactors at Fukushima, not just #3.  In particular, when the explosions & fires at reactors #1,2 &3 destroyed the buildings they were housed in, its likely that the Plutonium & Uranium in the spent fuel pools could have been dislodged or scattered.  This would explain the story I blogged about earlier that "neutron beams" had been discovered around the plant, and the later admission that Plutonium had been found some distance away from the reactors.

Last night my wife and I watched the 1983 movie Silkwood, in which Meryl Streep's character, Karen Silkwood, a worker in a plant fabricating MOX for the Hanford Breeder reactor, somehow gets Plutonium in her lungs.  (Its a true story, the real Silkwood died under suspicious circumstances after whistleblowing serious safety violations at her workplace).   But how dangerous is Pu?  Ralph Nader claimed a small amount could kill everyone on Earth if spread out, but  one pro-nuclear power/weapons scientist bet that he would eat as much Pu as Nader would drink caffeine.   (This bet never happened.)  Because it decays slowly (half-life 24,200 years) Pu-239 doesn't emit as much radiation in a given minute than other radionuclides.  But this long half life implies that it takes 800 centuries for any quantity of Pu-239 to decay until it is 90% gone.   Pu-239 breaks down via Alpha decay, which makes it less dangerous.  Alpha particles are stopped by a piece of paper or skin so they are not harmful when an external exposure occurs.  However internal ingestion of Alpha emitters can be deadly.  My research has not been able to determine how deadly Plutonium is (some Manhattan Project workers actually ingested it by mistake and survived to old age!).  Its may depend a lot on how long it stays in your body.    The primary concern is the long half life and the threat that contamination may affect an area for generations.

These factors came up when a blog which has been covering the Fukushima meltdowns announced "Radioactive Fukushima Plutonium Bombarding US West Coast since March 18".  The site run by one Alexander Higgens is attempting to provide alternative media to complement information not covered in main stream media.  This is a worthwhile goal.   I learned from the site that one can visit the EPA's radiation monitoring website and get data on the isotopes they are searching for.  Higgins has done so, and this prompted his announcement above.   However, when I searched the EPA site for Plutonium in the SF area, I found that the levels detected were less than the uncertainty in the measurement.  Scientifically this means that zero Plutonium was detected in the US (at least in SF area).   Overall I've been somewhat disappointed that a blog/media site(s) which attempts to serve the important role of providing an alternative to the mainstream media has produced such headlines with shock value but not thoroughly researched.

One claim which I have not been able to investigate is that the initial forecasts for the spread of the radioactive plume where doctored to minimize the apparent threat.   This could easily be done by changing the color scale on the maps showing radiation flowing across the Pacific and beyond.  However the video linked above is too small to read the numbers on the scale.   It is clear that some serious downplaying has occurred, however.  For example, initially TEPCO said "its only a level 5 disaster...nothing to worry about".  Then, when they upgraded it to Level Seven, they said "Its OK now because most of the radiation was released back when we said it was Level Five" !!  

At our presentation on the quake/tsunami/meltdowns on Monday, Prof DeWitt pointed out that Plutonium is not volatile and unlikely to become airborne.   So it seems that now plutonium is not one of our main concerns, while keeping an eye on the levels of Cesium-137 and Iodine-131 in local milk and vegetables seems warranted as a precaution, especially for parents.  These levels have shown a rise in recent days.   Any increase in I-131 concentrations is troubling, due to its short half-life.  To me this constitutes further evidence for ongoing nuclear reactions at Fukushima.

     `Be that word our sign of parting, bird or fiend!' I shrieked upstarting -
     `Get thee back into the tempest and the Night's Plutonian shore!
      Leave no black plume as a token of that lie thy soul hath spoken!
      Leave my loneliness unbroken! - quit the bust above my door!
      Take thy beak from out my heart, and take thy form from off my door!'
      Quoth the raven, `Nevermore.'


Post a Comment

Subscribe to Post Comments [Atom]

<< Home