Keep in mind we also have better modeling tools available to us than even those from five years ago. Some of the more detailed modeling shows stress distribution is more efficient than originally calculated. Also, we are better able to model the small-scale wind flows around the containment shell which leads to complex but understandable pressure distributions over the entire structural surface.
Bottom line is, I don't think containment integrity is going to be the driving factor in any post-Fukushima regulatory ratcheting. It is most likely going to focus on remediation of unexpected loss of emergency AC.
You are absolutely correct. They've already made strides in this area since TMI and 9/11. I 'think' that each unit at Browns Ferry has two diesels, plus there are two additional diesels added more recently (I think it was in response to 9/11). In all, there are 8 at Browns Ferry, of which 7 were available at the time of the tornado. 7 easily handled all the loads for the few minutes that off-site power was unavailable, and the 8th one was to be restored to service ASAP (down for maintenance).
Oh, I never thought TVA would ever have a containment problem. The containment portion of nuke plant designs is wildly over-engineered.
Where Fukushima has opened our eyes is the support infrastructure design issue. The tsunami exposed cascading, multiple system failures. Outside power failed, then the gensets failed, then the battery systems failed. With no power, they had no way to vent H2 out of the building containment, which is a large part of what has complicated their situation.
I think that two things come out of Fukushima for those of us who aren’t henny-penny anti-nuke types:
1. We really have to get away from the uranium/plutonium fuel cycle for power reactors. The only reason why we’re actually using u/Pu as fuel is an artifact of the Cold War and the nuclear weapons fuel processing.
2. Nuke plants need to think more about the SHTF scenarios and start modeling some really big crapstorms that include such things as “OK, you’re going to be cut off from the outside world of resupply for 30 days. How do you use what is on-site to get back to a stable state?”