APR: your source for nuclear news and analysis since April 16, 2010

Sunday, March 27, 2011

NISA having a meeting right now...

Chief Cabinet Secretary Yukio Edano has just revealed on live TV that, after briefing him on some details, NISA is having a closed door meeting at this time to discuss the possibility of a reactor pressure vessel and/or drywell failure at Fukushima Daiichi No. 2 plant. They're positive that the water in the turbine building is coolant that was in contact with melted fuel.

We're expecting further details on this important discussion later today.

DEVELOPING 10:41 PM Eastern Sunday 3/27


  1. Any comment on the video posted by NHK and others showing new views of the damaged reactors?


  2. I've seen the videos; what is bothering me is that there appear to be a number of people speculating on what these videos show, while what's really important at these plants right now are things that can't be seen from the air anyway. So while the videos do help provide a total picture they're not my focus. Surely however some of these images will become iconic views, and I do applaud the men who took the risk to fly right over the top of the plants.

  3. The more complete video of that overflight is 4:20 min and available under

  4. Thanks for the response. The reason I mentioned this particular one is that it shows some equipment inside unit 4 - perhaps the crane over the fuel storage pool (green) and another yellow structure. Also visible are the steam plumes emanating from most of the damaged units. I have been curious about the cause of the explosions that damaged unit 4 - source of the hydrogen and what could be inferred from this. The violent explosion that occurred in unit 3 destroyed the upper third of the structure - perhaps down to the level of the concrete plug and the fuel pool. How much do you know about the particular configuration of the units at Daiichi? Can you reasonably infer anything about the fuel storage areas from the damage visible?

    I understand that what cannot be seen - level of, and specific damage to the reactor containment systems and cooling mechanisms - is crucial for accurate evaluation and that for the moment these areas are inaccessible due to radiation levels. I would guess that the robots that were requested are to be used, at least in part, for damage assessment in such areas.

  5. I have a question for you : NISA regularly reports the temperature at the bottom of the pressure vessel, which means that the sensor there is operational. Could it be possible with a pressure vessel punctured at the bottom by the corium ? Intuitively, I would say no.

    Thanks for your blog, it is one of the best place for people who need accurate information and analysis about the Fukushima accidents.

  6. A follow on:
    Radiation levels spiked at surrounding monitoring stations early on the 21st to levels similar to those on the 15th associated with explosions and fires. The spike was followed by a series of smaller peaks and an elevated base level that has since been slowly declining but has not yet reached the levels recorded prior to the 21st. I believe that official sources noted a worrying increase in reactor pressure prior to this that then stabilized without any noted intervention. No releases were documented at this time, but it seems to me that something destabilized causing the spike and since has established some sort of new equilibrium. There was also a small, abrupt drop in the declining trend on Saturday around the time it was stated that borated water was being injected into unit 2. Any reasonable guess as to what occurred?


  7. Good comments by everyone...

    The explosion in Unit 4 was clearly radiolytic and/or metal-water evolved hydrogen.

    Very hard to infer anything about the fuel pools from the video, although it's going to serve as a good first recon for entry whether by robot or human.

    You might have a good temperature reading if only a couple of the penetrations (control rod, other measuring) failed and allowed a small release of core material before cooling allowed them to re-seal with formerly molten core material. This is a "never seen before" situation and MUCH will be learned about true reactor accidents from analysis of these cores and pressure vessels.

    @cbaisan: A very good summation of some of the events. It's very hard to say.. but it sure looks as if there is continuous core overheat with peaks and valleys in temperature, and as you hint at, occasions of pressure and/or material release and then re-sealing of whatever orifice allowed the release. As we know, now the NISA is looking very hard at what the mechanism is for this release.

  8. I have posted a video about German radiation hardened robotic intervention systems offered to Japan (they didn't accept any so far): http://www.youtube.com/watch?v=dbdwUnUvmFw
    Pretty good stuff to have in a situation like this.

    In the video linked in an earlier comment, the yellow structure in no 4 is the dome of the reactor vessel currently removed and set aside as the reactor was in maintenance.

    The spike of radiation release on march 21 may have the same reason as the hydrogen explosions in 1 and 3. The Mark I reactor vessel is prone to leak at the lid seals when under overpressure. When the overpressure is gone due to a release it will seal again.

    See the recent All Things Nuclear piece at http://allthingsnuclear.org/post/3940804083/possible-cause-of-reactor-building-explosions