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I have been watching all the major news shows this morning reporting on the nuclear disaster at Fukushima plant and decided to stop and Tivo CNN.  Every once-in-a- while CNN gives a pair of two-minute segments on what is going that has at least a degree of depth and coherency. Otherwise, the news shows mostly have casually knowledgeable anchors talking between themselves in completely lay terms, or interviewing reporters (who the anchors always congratulate as doing a “great job of explaining things”) or rushing experts through complex ideas into vague conclusions so they can get to their next segment. The anchors discuss gibberish amongst themselves debating questions like “Would you evacuate your family from Tokyo?” and cut off experts in mid-sentence to ask vague, innocuous questions like “Are the Japanese doing enough?”, or “Bottom-line, are things getting better or worse?”

Both the news media and the Obama administration seem absolutely unwilling to give a worst-case scenario.  Below is my assessment of the situation only as a layman who has some background on how these plants work and who has have learned from reports on television and the web of the current situation.

What is clear is that the industry never planned for handling a multiple-reactor unit plant failure while protecting the workers needed to limit damage in the worst case scenario.  And that scenario is far worse than Chernobyl.

Anyone with expertise that can straighten me out, please help me to understand what's going on.

The Fukushima I plant has four reactor units. Units 1, 2 and 3 face similar problems. Unit 4 was shut down for maintenance before the earthquake/tsunami and has a unique problem which is the current one that is causing the greater release of radioactivity Fukushima Radioactivity Increases.

Each of Units 1, 2 and 3 have exposed radioactive rods which can now only be cooled down by pumping seawater over them. Whether this process will work or not is not is uncertain, but they are having some problems with it because the seawater vaporizes. If the rods are not cooled down gradually, which will take days or weeks to accomplish, the rods will melt, partially or completely, to the bottom of their containment structure (CS). Each CS is designed to contain a complete meltdown, but each appears to be vulnerable to explosions.

Unit 1 was hit by the first explosion but the explosion only harmed the outer building. Reports are that the CS is intact.

Unit 2 was recently hit by an explosion (reported as the third explosion) which caused a short-term spike in radioactivity. Reports are that the CS was damaged and is cracked or punctured in some way, although there is no significant release going on now.

Unit 3 was hit by an explosion (reported as the second explosion) which apparently, like Unit 1 only damaged the outer building and not the CS.

It is not clear if Unit 4 has a problem of exposed fuel rods in the CS.  Unit 4 however, was hit by a fire yesterday and radiation temporarily spiked. Spent fuel rods that were sitting in a pool outside the containment vessel are in danger. The water pool is boiling and threatening to expose these rods in which case radioactivity would be emitted since they are not in the CS.

The unanswered questions are:

1)  Can the rods be cooled successfully with seawater? 2) If not, and a meltdown occurs, will it be partial or complete?  3) If a meltdown occurs, will the residual radioactive material be contained by the unit’s CS?

The current process of cooling the rods by seawater has shown problems already and a partially meltdown has apparently begun at least one unit. A partially meltdown will occur if it continues for a while but the rod cools sufficiently before complete meltdown.  A full meltdown will occur if the meltdown goes unchecked. The containment vessels will hold if they do what they are designed to do and are not damaged by exterior explosions (as Unit 2 has apparently been damaged).
If the all CS structures withstand a meltdown, we will have a “Three Mile island” incident. There, the one affected CS held a relatively small partial meltdown (1/3 of one rod) and released relatively low levels of radiation and no proven deaths resulted.  If a meltdown occurs and the CS fails, we will have a “Chernobyl” incident.

What is concerning is that due to increased dangers, 750 of the 800 workers that were at the plant yesterday, have been evacuated. This leaves only 50 people to deal with the problems at all four units. All four units need people at the site to makes assessments, to open and close valves, and do the other manual work to keep the recovery efforts going.

Simple questions experts have not been able to answer are: 1) Do units 1, 2 and 3 also have spent fuel rods outside their CS which are subject to the same problem as Unit 4?; and 2) Does Unit 4 also have the problem of needing seawater to cool exposed fuel rods?

The chilling reality as pointed out by one expert, is that the nuclear industry does not have a plan for what to do when only one problem causes a deadly rise of radioactivity at the plant (perhaps the Tepco executives should be required to help out on-site now). How can you deal with trying to limit the damage posed by other problems with people working at the site when those workers would be exposing themselves to deadly levels of radiation?

Thus, if a meltdown occurs at any one unit and the CS does not hold, or any pool containing spent fuel rods evaporates and the result is deadly radiation, can the rest of the units still be worked on?  Any continuing recovery efforts would have to be undertaken by those willing to be exposed to deadly radiation. Since it requires continued maintenance to keep the seawater cooling going, and perhaps the spent fuel rods to cool in the water they are in, abandonment by workers of all units would lead to complete meltdown at each unit and perhaps the exposure of all the spent fuel rods. Each CS would either hold or not based on its own ability to maintain structural integrity in response to a complete meltdown (which they are designed to do) and any explosions (perhaps not designed to do since reports are that the Japanese believe that the CS at Unit 2 is already damaged by an explosion).

The Chernobyl plant had no CS, so once a meltdown started and could not be stopped, massive radiation leakage was inevitable. Chernobyl exploded.  I have not been able to determine if there were any spent fuel rods at Chernobyl.  But Chernobyl only had one unit affected as opposed to four. And of course Chernobyl was located in an area not nearly as densely populated as the eastern coast of Japan.  Accordingly, this disaster would seem to have at least the potential of being greater than Chernobyl, with the release of radiation from any breached CS or spent fuel rod pool going into the ground, water and/or atmosphere.      

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Comment Preferences

  •  T&R, excellent and sobering analysis n/t (0+ / 0-)
  •  The questions are starting to be answered (3+ / 0-)
    Recommended by:
    Catte Nappe, ginja, chimene

    And we now have a tentative timeline...

    Workers Strain to Retake Control After Blast and Fire at Japan Plant
    By KEITH BRADSHER and HIROKO TABUCHI

    TOKYO — A small crew of technicians braved radiation and fire through the day on Tuesday as they fought to prevent three nuclear reactors in northeastern Japan from melting down and stop storage ponds loaded with spent uranium fuel pods from bursting into flames.

    Tokyo Electric Power Company officials announced on Tuesday evening that they would consider using helicopters in an attempt to douse with cold water a boiling rooftop storage pond for spent uranium fuel rods. The rods are still radioactive and potentially as hot and dangerous as the fuel rods inside the reactors if not kept submerged in water.

    “The only ideas we have right now are using a helicopter to spray water from above, or inject water from below,” a power company official said at a news conference. “We believe action must be taken by tomorrow or the day after.”

    Hydrogen gas bubbling up from chemical reactions set off by the hot fuel rods produced a powerful explosion on Tuesday morning that blew a 26-foot-wide hole in the side of reactor No. 4 at the Fukushima Daiichi nuclear power plant. A fire there may have been caused by machine oil in a nearby facility, inspectors from the United States Nuclear Regulatory Commission said, according to an American official.

    timeline...
    Workers Strain to Retake Control After Blast and Fire at Japan Plant
    By KEITH BRADSHER and HIROKO TABUCHI

    TOKYO — A small crew of technicians braved radiation and fire through the day on Tuesday as they fought to prevent three nuclear reactors in northeastern Japan from melting down and stop storage ponds loaded with spent uranium fuel pods from bursting into flames.

    Tokyo Electric Power Company officials announced on Tuesday evening that they would consider using helicopters in an attempt to douse with cold water a boiling rooftop storage pond for spent uranium fuel rods. The rods are still radioactive and potentially as hot and dangerous as the fuel rods inside the reactors if not kept submerged in water.

    “The only ideas we have right now are using a helicopter to spray water from above, or inject water from below,” a power company official said at a news conference. “We believe action must be taken by tomorrow or the day after.”

    Hydrogen gas bubbling up from chemical reactions set off by the hot fuel rods produced a powerful explosion on Tuesday morning that blew a 26-foot-wide hole in the side of reactor No. 4 at the Fukushima Daiichi nuclear power plant. A fire there may have been caused by machine oil in a nearby facility, inspectors from the United States Nuclear Regulatory Commission said, according to an American official.

    "Senator McCain offered up the oldest Washington stunt in the book - you pass the buck to a commission to study the problem." - Senator Obama, 9-16-2008

    by justmy2 on Tue Mar 15, 2011 at 12:31:46 PM PDT

  •  Chernobyl had 4 units (3+ / 0-)
    Recommended by:
    Catte Nappe, ginja, Cassandra Waites

    But yes, the accident was confined to one unit - the other 3 continued to operate until the last one was decommissioned in 1999 (file that under "jobs could you never pay me enough to take").

    There was/is spent fuel at Chernobyl, but once the reactor exploded, that kind of became a minimal contributor to the problem.

    O povo unido jamais será vencido

    by SLKRR on Tue Mar 15, 2011 at 01:18:36 PM PDT

  •  SIX reactors at Fuku 1..... (0+ / 0-)

    http://en.wikipedia.org/...

    Unit 4 was supposed to be shutdown then there another WTF? moment....we watch?

  •  it's the water (4+ / 0-)
    Recommended by:
    skillet, ginja, Cassandra Waites, SLKRR

    There is one and only one way for Hydrogen to be produced in large enough quantities to produce an explosion.  Namely, H is produced as a result of a chemical reaction with the zirconium in the Zircalloy cladding of the fuel rods.  And this chemical reaction takes place when the fuel rods reach a temperature of 1200 C (2200 F).  Hence the presence of H means the rod temp has reached at least 1200 C.  For at least the top parts of the fuel rods.  

    And this means that the water is boiling away (or leaking) faster than it can be replaced. Because no parts of the fuel rods would reach that temperature if they were completely surrounded by water.  

    The reaction is similar, but not identical, to these from highschool chemistry.

        Na (metal) + H2O ---> NaOH + H

        Mg (metal) + HCl ---> MgCl + H    [leaving out the 2's]

     With zirconium, it is

        Zr + H20 ---> ZrO + H              [Zr + 2H20 ---> ZrO2 + 2H2]

    That is, Zr metal is converted to Zr-oxide, releasing hydrogen in the process.  This does not occur at low temperatures.  However, once started the reaction is exothermic, that is, it releases heat.  Hence, it tends to get hotter, thus boiling away more water, and speeding up the release of more hydrogen.  If nothing happens to get things cool, the process feeds on itself in a runaway fashion.

    The problem is made worse by what is known as the "two phase problem."  That is, at the surface of the Zircalloy there is a mixture of liquid water, water vapor (steam), and hydrogen gas.  The gases carry heat away poorly, and in effect they provide an insulating layer that hinders the liquid from effective cooling.  And zirconium oxide is a much poorer conductor of heat than the metal, so the growing amount of ZrO2 further hinders heat transfer from the fuel rods.  Hence, as time goes on, things get hotter.

    The rods are about 3 meters long (10 ft), and the water bath normally covers them completely.  In this loss of cooling scenario, they are not uncovered all at once.  The water level slowly drops, exposing the upper parts of the rods, and the above applies basically to the circa 10-cm region around the water level; above is hot, below is cool. But at this level, all is turbulent.  And as the water level drops, this region keeps revealing new sections of the rods to the H-producing reaction.  (The region above the turbulent interface is filled with very hot steam and previously released hydrogen, keeping the ZrO reaction going.)

    Worser problems: The Zircalloy tubes (filled with uranium oxide pellets or some mix with plutonium) do not like this situation at all.  They are much hotter than they can stand, they experience huge localized hot spots, a thermal gradient, the Zircalloy becomes soft, and the cladding is rapidly being converted to zirconium oxide (there are some other chemical reactions, too). They then begin to swell, bend, balloon, buckle, get wart-like bubbles, and eventually develop holes.  (The rods always have a fairly high internal pressure owing to the Xenon generated by the radioactive decay).  The swelling and buckling may reduce the space between the rods, which then impairs the water circulation, leading to more super-hot spots.  At an advanced stage, this becomes a runaway process with a total meltdown unstoppable and inevitable.  The whole Pacific Ocean could not stop it.

    The holes are what cause isotopes of cesium, xenon, iodine and other unsavory nucleotides to get released.  

    So far, it seems that only a few upper centimeters of the fuel rods have undergone this process, and only maybe a two or three rods have developed holes (out of perhaps 50 rods--not sure of the total number).  The concern is, if they have not been able to pump enough water in to prevent this level of Zr-hydrogen reaction, why won't it get worse?  The plant operators know everything--and more--than I have described, but they have not been able to get enough water into the reactor vessels.  

    The hydrogen problem, again, is that the water level is falling faster than they can pump it in (pump out hot water, replace with cool water).  Water, water everywhere but not enough to cool.  

    Why can't they get enough water in?  Electricity, valves, pipes are involved.  Another topic.

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