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View Diary: Everything You Never Wanted to Know about Nuclear Containments (214 comments)

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  •  Any comments on how they hydrogen got there? (3+ / 0-)
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    kbman, erratic, kurt

    The Union of Concerned Scientists seems to think that if you go even slightly above design pressure on the secondary containment, hydrogen starts to escape:

    But as workers increased the containment pressure they encountered a problem. The pressure stopped increasing and remained constant at 70 psi. The pumps continued to push air into the containment, but its pressure just stopped increasing. This unexpected plateau started a hunt for air leaking from the containment somewhere.

    A hissing sound attracted workers to the top of the containment structure. They identified air leaking through the drywell flange area (see Figure 1). The metal drywell head (see Figure 2) is bolted to the metal drywell with a rubber O-ring between the surfaces to provide a good seal fit.

    Any thoughts on how plausible this scenario is?
    •  According to one of the speakers at the MIT (9+ / 0-)

      conference on Tuesday, the plant operators were venting the hydrogen from the primary containment into the large space of the refuel level.  Here is a link for the video, unfortunately, it was in response to the next to last question and is at about the 1:10 minute mark.  I believe you can jump ahead on the streaming video.

      I suspect that Dave Lochbaum may have made the same assumption that Stan made when I asked him about this last Monday.  At US BWRs the venting path is strictly up the stack.  This would be consistent with what is presented at the link.  But according to the engineer at MIT who was apparently familiar with the actual process at Fukushima, they did not vent out the stack but rather to the refuel floor.  The purpose for this was likely to minimize exposure to the public.

      Also, the part you have blockquoted actually refers to something that happened during an integrated leak rate test at Brunswick, NC.  This is just conjecture on his part and it is not needed because the cause is known.  Also, there is no way that the plant operators would have allowed the drywell pressure to rise anywhere near that high prior to venting.

      Free: The Authoritarians - all about those who follow strong leaders.

      by kbman on Fri Mar 18, 2011 at 07:44:16 PM PDT

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      •  Explosion at unit 4 can not be explained that way (1+ / 0-)
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        All the fuel was in the spent fuel pool. Hydrolytic cladding oxidation generates hydrogen.

        That's clearly another potential source of hydrogen.

        look for my eSci diary series Thursday evening. "It's the planet, stupid."

        by FishOutofWater on Fri Mar 18, 2011 at 08:56:15 PM PDT

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        •  Yes, but that is already on the refuel level (4+ / 0-)

          and there is no mystery how the hydrogen got there, it just stayed in the space in which it was generated.   Here is how I put it in the diary ...

          The hydrogen explosion at unit 4 was due to hydrogen produced in the fuel pool itself.  This was only possible due to the water in the fuel pool dropping below the level of the top of the fuel rods.  Also, as can be concluded from the photos of unit 4, the explosion was much less energetic than that at units 1 or 3.

          Your comment does raise a very interesting point I hadn't considered.  It may be possible that the explosion at unit 3 was from a combination of the two sources.  If the fuel pool was leaking already due to the earthquake and uncovered fuel was generating hydrogen then that could have added significantly to the energy of the explosion.  I'm not saying this definitely happened, just that it might be a possibility to consider in putting all of the pieces of this incident together.

          Free: The Authoritarians - all about those who follow strong leaders.

          by kbman on Fri Mar 18, 2011 at 09:29:29 PM PDT

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      •  speculation (0+ / 0-)

        I think your referring to Mike Golay, who, after explaining basically the same pressure release into the torus process as Dave Lochbaum, says (at 01:16:08):

        In order to avoid overpressurizing the containment, what I've been told is that the operators vented the containment and let the hydrogen out of the secondary portion of the containment into the spaces of the reactor building that led to the explosion. That venting can also be done with our reactors, but my understanding is that the ducting takes them outside of the reactor building, and so it's a difference in design and practice.

        Golay's qualifiers (what I've been told, my understanding) indicate that this is secondhand information, possibly the same speculation that we have read here. It doesn't make a lot of sense that Japanese design and practice with Mark 1 reactors is to vent hydrogen into the outer containment building where it can collect and explode. Lochbaum's explanation has the advantage of not assuming the Japanese are stupid, but it does suggest that explosion risk exists with American reactors.

        •  Lochbaum's speculation fails on a few points (5+ / 0-)

          The venting of the primary containment was a step being actively taken to keep the drywell at manageable pressures.  They mentioned starting venting when pressure reached 1.5 times normal.  I presume this would be in the range of 22 psi.  The level that Lochbaum mentions is several times normal pressure.  Also, the situation in Bruswick was a hissing leak through a tiny opening created at this overpressure.  It would take quite a long time for sufficient hydrogen to build up from this kind of leak to produce the kind of explosion that we saw at either plant.  There is no evidence at all to support the idea that they maintained a dangerous level of overpressurization for any period of time, much less the time it would have required to build up this volume of hydrogen.

          I think I have more confidence in Golay's qualifiers than in Lochbaum's conjectures.  Given that the folks at MIT are working in partnership with people at TEPCO I see it as quite likely that they are getting information from those sources.  The qualifiers sound more like he is being explicitly accurate.  He has not seen the plant himself, but is going by what he has been told and the understanding he has of the circumstances on that basis.

          It does make sense that the Japanese government might tell TEPCO that they couldn't vent releases to the environment.  It also makes sense that people at the UCS want to make US citizens believe that Fukushima could easily happen here.  It is part of their agenda.

          Free: The Authoritarians - all about those who follow strong leaders.

          by kbman on Fri Mar 18, 2011 at 10:14:42 PM PDT

          [ Parent ]

          •  tx (4+ / 0-)
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            worldlotus, kbman, erush1345, BachFan

            Thanks, and great diary. I disagree with some of your conclusions but I appreciate your clarity.

            I had read speculation that TEPCO vented into the outer containment building to avoid bureaucratic hassle over radiation releases, but I doubt that anyone at TEPCO knows precisely who did what and when while responding to a crisis after a tsunami, certainly not anyone who has time to talk to academics in the US. Blaming the bureaucrats is the kind of tactic I would expect to see from people who are not directly involved in the crisis, but who do have time to talk to academics.

            I seriously doubt that it is "design and practice" in Japan, as Golay claims, to vent hydrogen into the outer containment building. I take it from your response that the design at Fukushima is to vent the steam to the environment, which is Lochbaum's claim.

            Lochbaum cites 70 psi as the pressure that lifted the drywell head, if I've got my math right that would be five times normal. The pressure reports were erratic when the crisis started (and possibly downplayed, since TEPCO has admitted it downplayed many reports early on), but we do know that they used fire engine pumps which had trouble overcoming the pressure in the containment vessel. Fire engine pumps generate pressure in the range of 150 psi. That adds a little more evidence to Lochbaum's theory.

            I'm neither mechanical engineer nor nuclear scientist, so again I really appreciate the time you've put into clarifying the situation. While I oppose the expansion of nuclear power I'm not committed to Lochbaum or anyone else's guesses as to what happened. I've just been reading as much as I can and trying to fit various people's theories and predictions to the facts, and so far Lochbaum's have fit the facts best.

            •  My understanding of the problem with the fire (2+ / 0-)
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              erush1345, BachFan

              pumps fighting back pressure was that it was while they were trying to inject seawater into the reactor vessel, not the primary containment.  Furthermore, if the primary containment was at 150 psi then that would be twice the pressure at which Lochbaum claimed that Bruswick stopped increasing in pressure due to the "head gasket" leak.  It would also be two and a half times the rated pressure of the containment and suggest that those guys should have stayed at GE because the containment was far stronger than the design specs ...

              Also, it would not have been a noteworthy issue if they had to stop pumping into the primary containment.  It WAS an issue that they had to stop pumping into the reactor because the core was still uncovered.  This was what led them to vent to the primary containment in the first place, the need to relieve pressure so more water could be added.

              I have seen several of your comments here and elsewhere and fully get where you are coming from.  You have been polite and have stayed focused on the issues.  The points you've raised have contributed to the conversation.  I thank you.

              Free: The Authoritarians - all about those who follow strong leaders.

              by kbman on Sat Mar 19, 2011 at 12:09:07 AM PDT

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          •  more evidence from IAEA (0+ / 0-)

            From IAEA's latest update:

            Workers have opened holes in the roofs of both buildings to prevent the possible accumulation of hydrogen, which is suspected of causing explosions at other units.

            Since whatever bureaucratic hassles prevented workers from venting steam to the environment no longer apply, why bother cutting holes? Cooling systems are working on the spent fuel pools in #5 & #6, and the hydrogen wouldn't come from venting into the building because they'll vent into the environment.

            Not conclusive for Lochbaum's theory, but this gives it more support than it gives Golay's theory.

            •  This doesn't add up (1+ / 0-)
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              Units 5 and 6 were in cold shutdown already.  If they have cooling systems working in the spent fuel pools then they should also be working in the reactors.  There were also no reports of problems at the reactors and no reports of seawater being pumped in.  The only reason they would have concern for hydrogen from the core would be if the fuel were significantly uncovered for a number of hours.  And if that were the case they would have been pumping seawater to cool them.

              This sounds more like a preventative related to the spent fuel pools.  More information is needed to evaluate this.

              Free: The Authoritarians - all about those who follow strong leaders.

              by kbman on Sat Mar 19, 2011 at 12:20:40 AM PDT

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              •  I read confirmation of this on the IAEA site (1+ / 0-)
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                They cut the holes as they were approaching the one week point which is how long they had before getting close to uncovering fuel.  Cutting the holes ahead of time made sense because if they waited until they needed the openings, it would have been unsafe to do the job.  And given their experiences of needing to add water to units 3 and 4 by air, I would bet that the openings they made were above the fuel pool to make that job easier if it became necessary.

                Free: The Authoritarians - all about those who follow strong leaders.

                by kbman on Sun Mar 20, 2011 at 10:55:56 AM PDT

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