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Tuesday, June 7, 2011

Fukushima Daiichi update: Tuesday June 7

A number of developments have occurred since our last report.

NISA has completed a first review of data demanded from TEPCO relative to plant indications and personnel actions in the early days of the accident and according to press reports has concluded that serious core damage began to occur at the Fukushima Daiichi site's No. 1 reactor only several hours after the tsunami. Specifically, the reporting indicates that fuel exposure (to a steam only environment I assume) began two hours after the tsunami and core melt began a total of five hours after the tsunami. Damage to the other two reactor cores (No. 2, No. 3 plants) did not begin until 79-80 hours after the tsunami. The estimate of the very early damage by NISA is in line with statements that, for whatever reason, the isolation cooling system was shut down very early into the accident; these statements were made by TEPCO within the last month.

Further indication of the serious damage at No. 1 plant is the fact that TEPCO's new, temporarily installed pressure gauge at No. 1 plant is reading essentially atmospheric pressure or slightly above. This means that -- IF the gauge is correct -- the reactor vessel is in much better communication with the outside environment than might previously have been assumed.

As continuously noted, TEPCO continues to struggle with the water exiting the reactor cores and at last total had what it felt was over 105,000 tons of contaminated water on site (contaminated to various degrees, and in total.)

In other reports, NISA has calculated that the core melt events at the three reactors likely produced from 800 to 1000 kilograms of hydrogen at each of the plants. As we've detailed here many times, this hydrogen came from both the metal-water reaction of the zirconium-alloy ("zircaloy" is the trade name) fuel rod clad and from some radiolytic dissociation of water. This is the hydrogen that exploded and caused the damage of the reactor buildings. For comparison purposes, if we convert to standard measure and find that the Fukushima plants developed from 1760 to 2200 pounds of hydrogen each and compare with the something over 700 pounds developed at Three Mile Island 2, it becomes obvious why the reactor buildings were so severely damaged at Fukushima. At TMI, the hydrogen burn caused a pressure pulse (of about 28 psig if I recall) but did no permanent damage; the hydrogen burn was contained entirely inside the reactor containment (which is of an entirely different and probably superior design.) The damage to No. 1 and No. 3 buildings is obvious; damage to No. 4 building was due to hydrogen leaking INTO that building from No. 3 plant's common vent. The hydrogen explosion at No. 2 plant was more contained but damaged the suppression pool or "toroid" below the plant.

Water injection to the reactor cores continues as noted in previous posts. Injection to spent fuel pools continues occasionally, with hydrazine added as TEPCO deems necessary (this is a corrosion inhibitor.) Temperature of No. 3 reactor is climbing slowly, and has been since May 28th.

TEPCO hopes to have its first water decontamination plant operating on or about June 15th at the site. (Pictures of this plant will be up on this site later today.)

As a result of the video of steam release in the No. 1 reactor building many people have commented or e-mailed asking just where this steam was spotted by the robot. The TEPCO map below shows clearly the location of the pipe penetration in the floor.

The date of the above illustration is June 4.

As noted previously TEPCO continues to bring a great deal of tank capacity on site, in order to get a leg up on the buildup of water from core injection; this has been occurring over roadways to the site since June 4, according to TEPCO press releases.

More details later.

7:45 AM Eastern Tuesday June 7, 2011
ATOMIC POWER REVIEW

13 comments:

  1. While the hydrogen management clearly has been entirely unsatisfactory, the performance of the reactors in the face of a complete core failure has been outstanding.
    Three cores were demolished and are presumed by the Japanese government to have melted through the RPV at least in part, yet there were no major steam explosions or mass ejections of core material. That indicates the design is pretty resilient far beyond design spec.
    That should be pointed out in the public debate.

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  2. @netudiant: You are perfectly correct. What we are apparently witnessing here is a better than would have been estimated mechanical performance of the equipment in the face of an actual worst-case DBA which may, at least in the case of No. 1 plant, have been exacerbated by the loss of the isolation condenser system very early (whether by failure, by personnel error or improper procedure.) A steam explosion might well have been expected at some point in this scenario for No. 1 which clearly did not happen -- unless of course it were concurrent with the hydrogen explosion, which is highly unlikely given the evidence on record of the emissions following the explosion.

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  3. Are people generally not convinced by the Gunderson and Busby argument that, based on isotopic ratios, it seems that the "hydrogen" explosion at #3 (March 14) was actually a criticality event in the #3 spent fuel pool? No one seems to be looking at this as the possible source of the high atmospheric discharge.

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  4. @magee: No, we are not -- largely because Gundersen is not really a reliable source. This is the last guy anyone would go to for real facts. Truthfully. No one in the nuclear industry finds anything this man has to say to be credible. I'll prove this to you, if you would like. Go to Rod Adams' site using the link below and read the entire post he made about Gundersen:

    http://atomicinsights.com/2011/02/arnie-gundersen-has-inflated-his-resume-yet-frequently-claims-that-entergy-cannot-be-trusted.html

    Now, we won't even get into how unlikely a spent fuel pool criticality is in reality. I also have personally not seen anything that indicates solid fuel material outside the site. This claim has been around a few weeks now and has been discredited in all the circles in which I travel. The reality of what is going on there is troubling to be sure, but this isn't what happened.

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  5. @magee: No doubt there are some people who are convinced by Gunderson or Busby, just like some people are convinced by Caldicott. But a criticality event in the spent fuel pool would have had far different characteristics than we have seen. It's not enough to take one or two puzzling measurements from the hydrogen explosion and force fit them to an entirely different event without subjecting that alternative to at least as critical (!) a treatment. And their hypothesis fails miserably on that count.

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  6. Will, did you have any more information on the two workers that picked up an internal dose? WNN story
    The early reports I saw didn't quite gel with the idea that they had been overexposed, since the quoted Bq intake (under 10kBq) assessed as I-131 for a 60g thyroid only came out (by my calculation) at an overestimate of 25mSv.

    Also, I'm not sure how widely acknowledged it is that I-131 doesn't cause thyroid cancer in adults.

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  7. @joffan: There are a number of reports out about these two, and it appears they were in No. 3 / No. 4 control room when the hydrogen explosion at No. 1 plant occurred and were not wearing any masks or breathing protection. That's about all the hard data I can glean at the moment that's newly released.

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  8. Isn't the assumption zero probability of containment leakage in worst case? Anyway, this is largely academic and of little value in the public debate. It's like boasting that the Titanic took two hours to sink instead of one hour. I agree that it could have been worse (just an observer's impression) but to credit the infrastructure prior to full insight of causes and effects seems more than a little premature. I doubt that the designers nor the operators have foreseen this course of events.

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  9. @ashen: What??!! "Isn't the assumption zero probability of containment leakage..." Who said zero containment leakage? I didn't. TEPCO didn't. NISA didn't. Who said that? Where did you see that? And what relevance does that have to the commentary? Further, how much experience do you actually have examining reactor accidents? This leads to the question: How can you determine what is premature and what is not?

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  10. Thanks Will.

    Is it true that an emergency coolant system driven by steam & independent of power availability exists on the Mark 1 reactor?

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  11. @barrywilliamsmb: Yes, if you mean the BWR/4 and BWR/5 reactors with the Mk I containment. The No. 1 plant at Fukushima Daiichi (which is a BWR/4 reactor) has the older isolation condenser system, while the others have the turbine driven high pressure injection and a separate low pressure injection system. The low pressure is also turbine driven; both use steam from the reactor itself, generated by decay heat.

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  12. Should these steam driven systems automatically have continued the cooling process even though the plant was dark or were they also disabled by the earthquake / tsunami?

    A researcher is saying that this system was disabled on purpose.

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  13. @barrywilliamsmb: The systems are designed to work when only the DC power from station batteries is available. However, there have been assertions which seem credible that the system at No. 1 plant (not the same as systems at the other plants mechanically, for whatever that is worth) was disabled early in the event, by operators attempting to avoid a cooldown limit on the plant. This has been reported semi-officially but has not been explained in full detail yet. We can be assured it will be.

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