There are very few things not covered in the plant procedures, especially the “John Wayne” procedures, more commonly known as the Severe Accident Management Guidelines (SAMG). We have people who spend their careers coming up with worst case scenarios and how to handle them, and they have left very little unaccounted for in terms of what might happen and how to deal with it.
The problem here is the largeness of scale of the event. In the short term, the quake and the tsunami both resulted in all units continuing to work reasonably well and safely under the circumstances. What was difficult to account for was the enormous loss of infrastructure in the broader area, making it difficult to impossible to get new equipment of the right kind and quantity into the area.
But believe me, heavy duty poking around inside the plant under dangerous conditions is what they practice doing all the time, and I believe things could have been much worse had they not already been accustomed to doing the dang near impossible.
The Fukushima 50/180 have nothing but my respect and admiration. God bless them all.
I confess not having a BWR/3 SAMG handy at the moment.
However, I wonder what the unions say about drilling through concrete walls in the presence of large accumulations of H2 when they read the SAMG... if it the SAMG has anything like that as you infer.
Disclaimer, I am not here implying anything one way or another about TEPCO rank and file, just focused on the procedures reported used at fukushima dai-ichi.