Thanks Jim. The documents detail is new to me but its conclusions are old news, having been used to come up with the official release estimates and that graph of release rates over time which we have sometimes referred to when talking about reactor 2. Incidentally that graph was updated slightly at some later point, refining in particular events around the 15th, so somewhere there is likely to be an update of that paper I would think, or a different but related study.
It was good to learn a bit more about the data they used. It matches pretty well with what we had gleaned from less wordy sources, that a lack of certain kinds of sampling at various points in time made some of the estimates rather uncertain. For example they mention that certain data was only available when the march 15th plume met wet weather in the north west , giving them a much better look at a narrow range of time than the 15th as a whole.
And for example their focus on the suppression chamber is very understandable given the explosion report, but since the report was written they have become less certain as to what exactly happened in the region of the suppression chamber, backing away from the explosion theory somewhat whilst not denying the possibility that the suppression chamber was damaged.
These are also some of the reasons why we have only recently had this discussion about the possibility that reactor 2 did actually manage to dry vent for a few minutes around midnight. We can find data that shows radiation levels rising at locations south of the plant in the hours after midnight, but they aren't of the type most used in the report, which gets its best glimpse of reality much later on the 15th when things have gone to the north west and fallen to the ground with the wet weather.
Given the stuff that fell to Earth later on the 15th, and the radiation levels on site during the daytime on the 15th, I don't think anybody is trying to suggest that the possible midnight dry vent was more significant than what came out of the reactor for hours during the day. But the vent is of interest because it has largely been discounted in the past, many of us thought that it was reasonably certain there had been no vent due to the wording used in various reports, lack of pressure drop, etc. But if it did happen then its of interest both in terms of demonstrating the differences in what came out of reactor 2 compared to the other reactors, and in possibly explaining the story of the contamination that went towards Tokyo as opposed to the stuff which affected the ground in the north west so much which is better understood. Mind you even though its better understood I am sure reactor 2 still manages not to get star billing when discussing the north west contamination in most reports, which often focus more on the weather and previous emissions from reactor 1 than the bad story of reactor 2 on the 15th.
When looking at what happened during the daytime of the 15th I no longer make the assumption that the stuff came mostly from the suppression chamber, since we don't actually know how much came out of the drywell as it depressurised that morning. Much later we saw signs of stuff emerging from refuelling floor level in the area of the drywell top, but that may have been responsible for relatively little emissions compared to, for example, the drywall depressurising via the suppression chamber failure point. I probably need to look at those graphs again that showed estimates for where substances may have gone, the one that mentions the FHB, but I don't expect to learn much and that stuff was based on modelling anyway. If we don't learn much more about reactor 2 from the next endoscope mission, then I am prepared for a very long wait before getting more detail that could shed light on nature of suppression chamber failure and its role in the emissions of the 15th.
Another reason why I try not to assume too much that the suppression chamber damage was the main release pathway, is that it was about the only form of containment damage that they have wanted to mention much, especially at the time, so it provided a very simple bit of narrative at that moment, 'here is the event that has taken things to another level'. Even later we only got vague comments that the possibility of containment damage at the other reactors could not be denied. We've seen them taking air samples from above likely failure points of refuelling floor level containment top areas, and sometimes steam emerging from such areas on videos, primarily at reactor 3 but occasional glimpses from others.
So for me right now, if I am looking for a shorthand way to describe why reactor 2s emissions were so bad, I'll look more broadly than the suppression chamber. The possible dry vent didn't change the pressure in a notable way, and so I can still speculate that reactor 2 was different from the others because one or more parts of containment failed and released substances whilst the containment was under rather high pressure, unrelieved by scrubbed venting. Whereas at the other 2 reactors, for all we know containment failures may not have had such an opportunity to release substances, due to venting or the damage to containment happening due to heat or explosions at a time when the pressure wasn't at such a peak. However as I write this I have forgotten some key data trends from other reactors so that last statement may be easy to disprove.