Nuclear Triage?

This is pretty grim news, if true.

Even still, in the context of the major catastrophe there, it’s small potatoes. It’s going to cost billions to reclaim much of the land just from the seawater inundation (perhaps including dikes, with some advice from the Dutch). This just may mean that there will be a small part of it that will never be reclaimable in the foreseeable future.

On the other hand, they can console themselves with the thought that this probably won’t happen again for a few hundred years.

37 thoughts on “Nuclear Triage?”

  1. Well, CNN also reported that an official misspoke, saying milliseivert when he meant microseivert. Makes a big difference, and that statement was the trigger of seriously grim speculation. The intel we are getting via the news is very, very poor quality.

    My bet, if there is anything at all to it, is that they are rotating the 50 out and replacing it with a new crew. Typical way to cut everyone’s dose. Frankly, I’m surprised they didn’t do that before now. My gut feeling is that people started panicking after the highly dramatic hydrogen explosions. Shoot, I freaked out a bit, assuming it was the containment vessel.

    Still very serious, but despite everything I will be surprised if they manage to kill anyone not directly involved in the operation.

  2. I don’t know *what* is going on in the #4 building.
    Those reactors have been shut down for months – there shouldn’t be any heat source sufficient to generate hydrogen.

    The NEI claims the spent fuel ponds should be fine, and it should take days for the water to boil off even if it reaches boiling temperatures.

    One (presumably) of the better informed agencies said that the fire in the building was due to oil leaking from damaged machinery.

    Of course then what blew a hole in the building?

    The biggest mystery to me is how you get any kind of hydrogen generation from water at atmospheric pressure. If it’s at atmospheric pressure, it’s either a gas, and vents, or it’s a liquid and is nowhere near the temperatures where hydrogen forming reactions take place.

    If the fuel completely dried out, there shouldn’t be any water to react with, even if it melts into a pile of slag. If there is water in the pool, the fuel should be at 100C or less.


  3. Hi Mr. Simberg,

    Thank you for the link. I’ve read many of your posts, and it’s an honor to be noticed.

    My analysis is bouncing all over the place as we get info. This one is definitely worst-case. But I completely agree with your long-term analysis. Japan has less real estate to give away than most, but there’s no breaking point here.

    I just don’t want real people sacrificing their lives for statistical models.

  4. ams, the cladding of the fuel rods is made mostly of zirconium — because it has a very low neutron cross section and is more resistant to corrosion than steel — and if the temperature rises high enough Zr will reduce water, thus:

    Zr(s) + 2 H2O(g) -> ZrO2(s) + 2 H2(g)

    This reaction is actually exothermic, so it’s thermodynamically favored, but it proceeds very slowly for solid chunks of Zr and at moderate temperatures, e.g. below the melting point of about 1800C. I’m not sure exactly why, but I think the ZrO2 forms a passivating layer, much as Al2O3 forms a passivating layer atop aluminum (by nature a very reactive metal) in air. The reaction is then limited by the diffusion rate of H2O across the oxide layer, which is slow at low temperatures, and gets slower and slower as the thickness of the ZrO2 layer grows.

    At high temperatures, however, the diffusion speeds up, and if the fuel rods melt you may get finely divided droplets, which tremendously increases the surface area exposed to H2O and greatly reduces the kinetic barrier to reaction. Under those circumstances, it is feared that the reaction could proceed quite vigorously and generate a lot of H2 relatively quickly.

    More active metals, like Na and K, will reduce water and generate H2 at room temperature.

  5. I read reports of 1 Sievert/hr in unit 1, which is why they had to pull out the remaining crew.

    Now many people are evacuating Tokyo

    The administration has boldly sent two nuclear experts, probably policy wonks. I guess they’ll have to multi-task across 4 reactors. The Japanese asked us for serious help, and the NRC initially said they’d take the request into consideration, but finally are sending a second team of 34 people with radiation monitoring equipment.

    I haven’t seen such a focused response since the crew of the Titanic went back for seconds at the salad bar a couple hours after striking an iceberg.

  6. Carl,

    I understand what you are saying about the reaction, but what is the catalyst for this event occurring in unit 4? I understand a machinery fire that is not fought due to insufficient resources to fight the fire in a shutdown reactor. But if unit 4 is having more problems than that, then I’m very concerned about units 1-3 that were operational the day of the earthquake. Unless what we are seeing is the discomforting site of triage, in which a significant fire in unit 4 was ignored for the more serious situation next to it.

  7. I’m still trying to figure out how close, exactly, the Ronald Reagan was. Both initially and when diverted away.

    The two crucial elements in this disaster were known the immediately upon having the tsunami wipe out the third power source – they need power and distilled water.

    The Ronald Reagan is an awesome source of both – and is supposed to both be “sealable” and have pretty amazing external NBC scrubbing capabilities.

  8. According to JAIF, radiation levels are back around 2000 uSv/hr – this isn’t healthy by any means, but it shouldn’t be *immediately* harmful.

    Judging by past performance, it’s probably going to stay between ~500-~2000 uSv/hr until they can stop venting steam a week or two from now.

    I think the supplies on those ships would have been a great help to getting cooling lines up and running – I hope this isn’t overreaction on the part of our government.

  9. I hope this isn’t overreaction on the part of our government.

    Ditto… for both governments. I’m actually ok for milking the heroism of the 50 workers to help boost morale, but the downside is invoking an irrationale level of fear. Governments tend to take risk adversion in an overly conservative manner for the first level reaction (e.g. radiation leak, run for the hills) and forget about the next consequence (e.g. the leak was minor, but now that everybody is gone, we can put out a simple diesel fire). Again, hope it isn’t an overreaction either by government or those covering the story for us viewers at home.

  10. Oops, sorry, Leland, I overlooked ams’s comment that the #4 reactor had been shut down for months. The short answer is I dunno — not enough data. What I’ve read suggests there was a fire in Unit #4 caused by a (chemical) fuel leak, not an H2 explosion. The explosions were at the active reactors, I think.

  11. Reports are now that the spent fuel in no. 4’s cooling pools is totally dry. Radiation levels from it must be very high.

  12. Why so, Paul? The cooling pool is not under pressure, nor confined, so if the temps are even moderately above 20 — I heard they were in the 80s — the water will evaporate just like a puddle on a hot day. But whether the water is there or not doesn’t seem to me to do squat as far as radiation levels are concerned. It just means the stuff may get quite hot and (1) melt and make a God-damned mess, or (2) cause something flammable to catch fire, which runs the risk of spreading the G.D. mess outside of where it’s supposed to be contained.

  13. The water in the pools is the primary shielding. No. 4 is now apparently a giant gamma source irradiating the whole site.

  14. Hmm. Did they really have that much water around the fuel? The decay length of gammas in water is pretty long, about 6 cm I think, of order 15 to 20 times more than concrete or common light metals. Wouldn’t they have lined the pool with 6 inches of concrete, rather than count on 6 feet of water on each side of the fuel assemblies?

  15. The walls of the pools of Mark I BWRs are 4 to 8 feet thick. However,upwards shielding is from 26 feet of water. Without that, gamma could be emitted upward then scattered back toward the ground (skyshine).

  16. According to the IAEA:

    The IAEA can confirm the following information regarding the temperatures of the spent nuclear fuel pools at Units 4, 5 and 6 at Fukushima Daiichi nuclear power plant:

    Unit 4

    14 March, 10:08 UTC: 84 ˚C

    15 March, 10:00 UTC: 84 ˚C

    16 March, 05:00 UTC: no data

    Unit 5

    14 March, 10:08 UTC: 59.7 ˚C

    15 March, 10:00 UTC: 60.4 ˚C

    16 March, 05:00 UTC: 62.7 ˚C

    Unit 6

    14 March, 10:08 UTC: 58.0 ˚C

    15 March, 10:00 UTC: 58.5 ˚C

    16 March, 05:00 UTC: 60.0 ˚C

    The IAEA is continuing to seek further information about the water levels, temperature and condition of all spent fuel pool facilities at the Fukushima Daiichi nuclear power plant.


    This doesn’t look anything like the scenario that has been talked about for the past day. If these readings are correct, I don’t see how the spent fuel could be the source of the fires. It could be a source of intense gamma radiation, but it doesn’t look like it is putting out enough heat to melt down.

    The only worrisome one is pool #4. Even so, zirconium is supposed to melt at 2000F, and zirconium fires aren’t supposed to be possible under acheivable temperatures and oxygen levels. The uranium is already oxidized.

  17. Sorry – zirconium melts at 1850C.

    I wonder if it is worth sending people up there to stop – if all that happens is the fuel gets hot and sits in an empty pool, then let it sit in the empty pool.

  18. ams – See this. Apparently, it would melt through to cool water below, which would cause an explosion blanketing the area with fallout.

    Hopefully, they will get things under control, but the worry appears to be more than media hype.

  19. Clarification: that guy is talking about a scenario in which they cannot continue to cool the reactor core. With all the focus on the spent fuel pools, I thought he was talking about that. I suppose this peril should be decreasing as the cores cool, but I have no idea how long that takes.

  20. Wait…they forgot to put on a roof?

    How thick is the roof going to be anyway? Its panels are designed to blow off in an explosion, so they can’t be too heavy. I believe the walls/roof of the superstructure are made of sheet steel.

  21. “ams – See this. Apparently, it would melt through to cool water below, which would cause an explosion blanketing the area with fallout.

    Hopefully, they will get things under control, but the worry appears to be more than media hype.”

    1) Right – but is it only steel? I thought concrete, being an oxide soup, would almost be refractory.

    2) The spent fuel should only have a fraction of the power density of the present core fuel directly after shutdown. We’re talking 0.2 W/cm^3 or less – the equilibrium temperatures shouldn’t be that bad, should they?

  22. “the equilibrium temperatures shouldn’t be that bad, should they?”

    As best I understand it, no. As soon as the moderating water was removed, it should have (mostly) stopped fissioning and started to cool, which is why this design is supposed to be so much better than Chernobyl which was graphite moderated, and graphite can’t be dumped out like water.

    The main gap in my knowledge here is I do not know how you can carry the heat away if putting water in slows the neutrons enough to start the chain reactions anew. Maybe it’s a matter of where the flows go, and there are separate pipes for cooling and for moderating. Or, maybe its a matter of cutting the coolant with boron – I really do not know.

    But, there is some time constant associated with the cooling down. The best I have been able to find says it could be anywhere from hours to days to months. I wish I could find info on this somewhere…

  23. “As best I understand it, no, it shouldn’t be.”

    Just wanted to clarify whether I was agreeing (yes) or disagreeing.

  24. The spent fuel pools are not at criticality.

    The reactors with the rods inserted (or the boric acid inserted) is also not at criticality. I don’t think the reactor has a chance of restarting the reaction. Even if it melts into a pile of slag, there should still be the rods sticking into it, and the boric acid around it to keep it from being critical.

    Where the power is coming from is decay heat from the leftover slow fission products in the fuel rods. That can still heat everything up, and the heat must be removed to prevent anything more exciting from happening (like the molten slag leaking anywhere).

    The power density in the rods should be something like 1% of what it was when the reactor was operating. The power density in the spent fuel rods should be much less than that, since they have been decaying for months.

    (Which is why I am wondering what the real worst case temperature for the dry spent fuel rods is – if it isn’t melting, we shouldn’t have people risking their lives to cool them off, they should be keeping their heads down in the control room and working the reactors)

  25. This guy says here that, as of 3/16/2011, “the reactor cores will need significant cooling for at least another 5 days before stability can be ensured.” But, he said here that “decay heat drops rapidly on reactor shut down (e.g a 3GW reactor will reduce to 200MW decay heat after 1s and 50MW after 1 hour… But takes long time (3-6months!) to reduce to negligible levels)”. So, 5 days or 5 months? Or, 1 second? I just do not know.

  26. I understand nothing is at critical reaction levels. But, apparently there is still tremendous heat to be removed from the core, and I do not know how long that takes.

    And, it’s all hot enough that, if exposed to air, it will cause volatile radioactive emissions. The spent fuel can do this if the water in the pools boils off. As far as I can tell, that is the main threat there. The core may still be hot enough that, if not actively cooled, it could detach, melt through the floor, come into contact with cold water, and cause a catastrophic event (I do not want to say “explosion” because that suggests a nuclear explosion, and it would not be that).

    At least, that is the best I have been able to surmise.

  27. Here is a chart showing core heat decay for a 3000 MWth reactor. I have read that the Fukushima reactors are less than 1000 MW each – does that scale directly to MWth? – so I guess the curve should scale accordingly. I still don’t know at what level it is “safe”, so there is a certain conservation of ignorance involved, i.e., I know as little as I did, but my unknowing-ness has changed form.

  28. A good WAG for heat engine efficiency is 33% – so 1000MW requires 3000MWth power. After shutdown, it should eventually fall to 30MWth over the short term, and exponentially decay from there.

  29. OK, you’ve remedied half my ignorance. Now, at what level is it safe from the catastrophic scenario where, without cooling, it can melt through the floor, hit the water below, and Whoosh!

    Not that I am particularly alarmed (ignorance is bliss), as I am assuming this is not a likely occurrence. Just curious…

  30. I saw a report saying the cooling pool at one of the reactors had concrete lost from a wall, but the steel liner still looks intact (but I don’t know if they could see small holes that would render the pool unfillable.)

    The concrete loss is troubling, since hydrogen explosion overpressure alone wouldn’t do it. I imagine steel structural elements collapsing after an explosion could rip some off. The pool is right next to the outer containment structure, so that concrete could be damaged as well.

    I suspect they’re going to have to erect shielded access tunnels to keep working on all the reactors.

Comments are closed.