Yamanote said:
The results of today's survey is no surprise to me. Apparently this kind of containment isn't able to do it's job in case of a core melt-down accident.
If I recall correctly, the weak spot of the MKI containment was supposed to be the joints between PCV and SC. So all the water poured into the RPV escapes rather quickly through either damaged joints or a damaged torus and ends up in the torus room. And perhaps some corium has already taken the same path one year ago.
Well speaking more broadly I think what Fukushima taught us is that containment doesn't actually do a job of containing everything, which is how it tended to be described in the past. Either temperature or pressure or both will cause it to fail under severe core melt conditions.
Rather, at least at these type of reactors & containment facilities, containment still contains a lot of stuff and keeps radiation levels down to the extent that people can at least work on site. But in the event of a core melt the containment will not keep everything inside.
If we discover that reactor 2 did release the majority of the substances that contaminated land, then I think the lesson here is one that was already known, that you have to release some of the nasties from containment via wet-venting. You release some substances but at least a lot of stuff is scrubbed or otherwise remains inside containment. Containment may then leak but at least a lot of the stuff that came out of the fuel at the height on the accident got scrubbed before release. But if you fail to wet-vent at all, like happened with reactor 2, then you risk these substances coming straight out from the drywell when it fails.
So on one level containment seems like a misnomer if you have to release stuff from containment via venting in an accident to save containment, what sort of containment is that? But in fact its much better to do that than not wet-vent at all.
And even the much discussed known flaws with containment due to heat or pressure have a silver lining. If we look at the worst fears over Fukushima, they involved the containment itself exploding or otherwise breaking in a rather dramatic way. But the sorts of leaks due to heat or pressure that seem likely to have occurred at Fukushima probably helped prevent this from happening. Not much consolation since a leaking containment vessel is still bad news for the environment, but I guess its not as bad as a more explosive loss of containment.
And no I don't think you can describe the MK-I containment weak spot as being the joints between S/C and D/W, simply because there are lots of weak spots and I don't think it would be fair to single one out in particular as being the weakest. All manner of seals etc will degrade at certain temperatures, as well as the containment cap, personnel & equipment access hatches and other pipework penetrations.
