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This is a link to a series of comments posted by Micheal Goad a retired nuclear accident management instructor in answer to some questions I had about the nature of a nuclear meltdown. I'm passing this on because his comments were similar to some comments made  here to some of my recent diaries about Fukushima. I am not an expert on this subject. Though I still have questions, I feel it's important to demure to the experts, some of whom may have spoken here.

http://www.wired.com/...

These are the relevant comments at the link above:

Micheal Goad
Very interesting post. For several years, I taught severe accident management classes for nuclear plant operators. It included discussion on corium, eutectic formation and core concrete interaction (CCI). I'm now retired, but, on occasion do contract work as an ops instructor.
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R Crosby Lyles  Michael Goad • 5 days ago
This is an idea I had about stopping a meltdown. Nuclear Engineering is not my particular field though I have studied some Chemistry, Electrical Engineering and Thermodynamics. I'm not necessarily promoting the idea but I am curious about its feasibility. Any feedback is greatly appreciated.
https://www.youtube.com/....
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Michael Goad  R Crosby Lyles • 4 days ago
The "meltdown" is not a result of fission, but, rather, is due to the inability to remove heat produced by the decay products from an already shutdown reactor. The key is to remove the heat that is being produced. The simplest way to stop the melt process is to add borated water to the reactor vessel if the core is still in the vessel or to the building if the core has gone ex-vessel (vessel breached). The boron is to prevent any potential recriticality once the mass is covered by water. If borated water is not available, the melt process can be significantly slowed or even stopped by adding unborated water in quantities less than or equal to the amount that will be totally boiled off by the heat being generated.
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R Crosby Lyles  Michael Goad • 2 days ago
This is the second time I have heard that the generated heat is not do to fission but to the heat given off by the decay products. Is this a matter of semantics? If a "meltdown" occurs doesn't that imply "criticality?" What is a criticality but a runaway fissile chain reaction? Will not dispersal of a mass of decay products into a particle absorbent substrate cause this material to not generate as much heat? The heat generated is not a function of the concentration of radioactive matter?
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Michael Goad  R Crosby Lyles • a day ago −
Is this a matter of semantics? No.

If a "meltdown" occurs doesn't that imply "criticality?" No. A meltdown is a result of the failure to remove decay heat.

What is a criticality but a runaway fissile chain reaction? Criticality is the point during reactor operations where the nuclear chain reaction is exactly self-sustaining. Every fission causes an average of one more fission.

Will not dispersal of a mass of decay products into a particle
absorbent substrate cause this material to not generate as much heat? No -- the same amount of heat will be generated. It would just be spread out. The heat is generated by the nuclear decay of products that were produced during the period the fuel was critical and their daughter products.

The heat generated is not a function of the concentration of radioactive matter? No. The heat generated is a function of the original power history of the fuel prior to shutdown and how long it's been shutdown. "Quantitatively, at the moment of reactor shutdown, decay heat from these radioactive sources is still 6.5% of the previous core power, if the reactor has had a long and steady power history. About 1 hour after shutdown, the decay heat will be about 1.5% of the previous core power. After a day, the decay heat falls to 0.4%, and after a week it will be only 0.2%."
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R Crosby Lyles  Michael Goad • an hour ago
Thanks for taking the time for a point by point explanation. Seeing your qualifications, I'm sure you know what you are talking about. The discussion is a worthwhile endeavor because not many people understand what is going on(apparently myself included) at Fukushima in particular and there is a lot of misinformation out there.

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Comment Preferences

  •  Tip Jar (13+ / 0-)

    Peace, Love, and Prosperity. See more on the R. Crosby Lyles channel on YouTube.

    by Rich Lyles on Sat Dec 28, 2013 at 03:37:41 PM PST

  •  This is informative (7+ / 0-)

    I think it's very helpful to know the facts when discussing Fukushima and and the use of nuclear energy. A lot of comments and "reporting" seems to come more from fear and not understanding what is going on and those who want to believe the worst no matter what. Or it's having a little bit of knowledge, just enough to make a person assume they know all when they don't have a total picture of the situation.

    Of course the blocking of information has not helped either.

    Sadly the misinformation is not helping with trying to stop the use of nuclear power. As one who was in Tokyo for two weeks starting 3/11 I know the damage that happens from both misinformation and the blocking of information. While a diary like this won't get many comments or tips I for one appreciate real information when it is posted on-line.

    Thank you

  •  While the formatting... (9+ / 0-)

    ...could use some love, and I think you want "defer" for "demure" (I can be demure for experts, but I'm not proud of it lol)...T&R for the honesty.  Most things I read about Fukishima are rich with commentary by people who haven't a clue about the technology or science, and it doesn't help.  This was very good of you to post.

    ...j'ai découvert que tout le malheur des hommes vient d'une seule chose, qui est de ne savoir pas demeurer en repos dans une chambre.

    by jessical on Sat Dec 28, 2013 at 04:35:17 PM PST

  •  Good of you to go looking (13+ / 0-)

    for explanation you can understand. But I think you're still missing some pertinent detail.

    The term "decay heat" refers to the heat (thermal radiation) generated when a 'radioactive' atom decays and turns into a different elemental atom. This isn't fission even though some uranium and transuranic atoms do decay by means of spontaneous fission. It's just the heat of disintegrating atoms. This is why spent fuel can melt if it's not kept cooled long enough for the decay to stop producing enough heat to melt the metals.

    Fission of course makes the heat quotient a whole heckuva lot worse, but not that many reactor cores have melted while fission was still going on. All the excess heat does is throw the timetable into overdrive.

    Borated water won't stop a meltdown, it'll just absorb excess neutrons in a still-fissioning reactor. Boron doesn't cool multi-thousand degree molten metal any better than plain old water does. It simply absorbs neutrons, and gums up the works with deposits.

    The problem with adding "less than" amounts of coolant water to a melting core is the multi-thousand degree molten metal. Which not only 'flashes' water to steam before it can get close to the surface of the mass, but does it with such an abundance of energy that it separates oxygen and hydrogen atoms that comprise water molecules via the well known process of radiolysis. Hydrogen and oxygen gases don't mix very safely in a hot environment.

    'Flash' criticalities can occur whenever the moderator (water) is present, but a sustained fission chain reaction can't happen in a reactor core unless it retains the open geometric configuration that allows water to circulate around the fuel rods and assemblies. Reactor fuel can't go critical as in "critical mass" like a bomb because it isn't enriched with fissile isotopes nearly enough to do so. Reactor fuel is usually 3-5% enriched with fissiles, while a bomb is more than 95% pure fissiles.

    Bottom line is that once these things get 'turned on' - irradiated by fission - they cannot be 'turned off' without residual heat removal in operation. Because if they don't have that, they melt down.

    •  radiolysis (6+ / 0-)

      So is that how we ended up with those hydrogen explosions at Fukushima?

      •  Some of the gases (8+ / 0-)

        probably came from radiolysis, but for those units that blew due to loss of coolant water in the spent fuel pools [1, 2 and probably 4], the hydrogen got there via oxidation of the zircalloy cladding on the fuel rods when they overheated.

        Only one of the explosions was 'suspicious' per its origin (reactor/containment vs. SFP), that of the #3 unit which blew straight up in a detonation, rather than roiling out (widely) via conflagration. TEPCO still insists it was the #3 SFP, but nobody really knows since no one's been able to get in there to find out. The entire #3 area is far too radioactive for human approach. I did hear they sent some clean-up robots in there a couple of weeks ago, but I'm jaded by all their ridiculous self-serving lies. I'll believe it when I see it in a medium they can't stage.

        Rad levels at the vent stack for units 1 and 2 are still quite lethal as well - to the tune of at least 10 Sieverts per hour (1,000 Rem). It's also broken at about 100 feet above the ground. It'll probably topple in the next good shake (or the next), at which point maybe their remote control bulldozers and cranes can shuffle it into the lagoon for "safekeeping." Because they now have silt fencing over the outlets.... [oy].

        •  is there a site with all the pics (0+ / 0-)

          organized spatially and temporally?

          I don't think anything has been inside Unit 1 or 3 on the top decks.

          they bagged up Unit 1, and it's been a mystery for a year now.

          Tepco and Mystery, usually a bad thing.

    •  Thank you. That's very helpful. (3+ / 0-)
      Recommended by:
      LakeSuperior, Joieau, kaliope

      Part of my confusion comes from stories about how radio active materials are often placed on a grid on the floor to ensure they are not place too closely together. This is why I assumed that the concentration of material was in anyway related to heat output. As always the Devil is in the details.

      Peace, Love, and Prosperity. See more on the R. Crosby Lyles channel on YouTube.

      by Rich Lyles on Sat Dec 28, 2013 at 08:03:00 PM PST

      [ Parent ]

      •  Concentration is related in several ways. (0+ / 0-)

        The more concentrated the spontaneously fission pile, the less surface are for cooling.

        Two, Assuming some melted moderator is in there too, the rate of neutron generated fission also goes up.  

        http://www.nrc.gov/...

        Also if the absorbing material separate out, neutron fission goes up.  

        I'm sorry, the nuke industry has institutionalized it's lies to the point where all the nuke pros sing from the same hymnal.  

    •  don't forget thermolysis Joieua (0+ / 0-)

      heat water hot enough, and it disassociates.

      but yeah a little bit of hydrogen and the damn thing
      blows, just look at Unit 4.

  •  small quibble (5+ / 0-)
    I feel it's important to demure (sic) to the experts...
    Always question any assertions by so-called experts. Especially in this particular industry. The coverups and lies go back decades.
    •  Right. I thought about that for quite a while. (3+ / 0-)
      Recommended by:
      freshwater dan, kaliope, Joieau

      I used "demure" because in my previous comments I didn't give enough credit where credit was apparently due as the comments of a few kossacks have been verified by other sources. Where I was once "sure" that I knew what I was talking about, now I am not. So until I do enough research to make a more credible argument, I will demure to those who have.

      Great comment. Thanks.

      Peace, Love, and Prosperity. See more on the R. Crosby Lyles channel on YouTube.

      by Rich Lyles on Sat Dec 28, 2013 at 08:20:32 PM PST

      [ Parent ]

  •  Is there a difference (2+ / 0-)
    Recommended by:
    kaliope, Joieau

    ...between a melt down and a melt through?  The core can melt down and remain contained in the reactor vessel.  Or it can melt through the bottom of the vessel into the soil.

    •  it is re-enforced concrete under the reactor (1+ / 0-)
      Recommended by:
      kaliope

      vessel...not soil.

      •  Core catcher (1+ / 0-)
        Recommended by:
        LakeSuperior

        The apron of reinforced concrete under a reactor containment is dubbed the "core catcher". Typically it's about 1.5 metres or more thick and it's designed to spread any melted core material over a large area to help dissipate the heat of radioactive decay and prevent further penetration.

         To get there the molten core material has to melt its way through the reactor vessel bottom (30 or 40 cms of high-grade steel) and then drop into the containment structure and then melt its way through that (usually a metre-plus thick reinforced concrete structure) and thence drop onto the core catcher.

         In the case of the RMBK-4 reactor at Chernobyl the core melt also included moderating material in the form of solid graphite, a well-known problem with that reactor design where it suffers positive feedback as the graphite gets hotter. There was no core catcher under the reactor, just work spaces and rooms. Even then the molten core materials stopped there and didn't penetrate into the ground.

        •  at chernobyl (0+ / 0-)

          the soviets used every chopper in the country to air drop
          lead, boron and cadmium to shut in the core.

          At Fukushima, the japanese screwed around for months.

          All that core catcher does is buy some time.

          Really, it's not much help if it worked,  water is
          flowing across the basement and carrying isotopes
          out to sea.

          if it didn't work it burned into the ground is headed to africa :-(

  •  Be carefull, institutional lying is what the nuke (0+ / 0-)

    industry does.

    They love to refine terms and then make you feel stupid and ignorant for not knowing their arcane nit picking.  

    This is how physicists lie.  

    For instance, a reactor that melts down is still fission, it's may or may not be above the critical point, but heat is being generated by fission.

    So if the pile is just below critical, or the corium is, then you add the spontaneous radioactive decay, which is large, you can have more energy generated than a new reactor just going critical.  

    When it melts into a coruim pile, the reactants to indeed get closer, and fission increases.

    The borated water cannot get into the melted pile.

    Note that spent fuel rods must be separated to prevent criticality.  

    •  what decay heat (spontaneous ) vs Criticality. (0+ / 0-)

      means

      Decay heat is spontaneous random break down of
      unstable isotopes to more stable forms, they toss
      a proton or a neutron or a couple of eletrons and photons
      and it's a little bit of heat, and it's not self sustaining.

      if you take a piece of brand new nuclear fuel, it's a little warmer then room temp, it's how things like a RTG (Radio thermal Generator) work. They produce heat, and that's
      useful in it's own way just to keep a key piece of hardware
      from freezing or to power a thermocouple on a deep space probe.

      then there is criticality.  If you can manage the neutron flux,
      a self sustaining chain reaction or a runaway chain reaction
      happens.  the runaway chain reaction we call an atomic bomb.  the self sustaining one is a nuclear reactor.
      a neutron from one split, knocks another atom apart.

      if you manage it, it's a lot of heat, Gigawatts, and you can make steam.

      but it's managing a knife edge.  If you lose the reaction,
      lots of products poison the reactions, if you go to far it goes critical and explodes as a dirty bomb.

      but that decay heat is a real bear.

      6.5%?  seems like nothing, till you realize we are talking Gigawatts.

      Can you cool 65 MW of heat? with a busted set of pumps?

      for a month?

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