Let us start shall we?
The ‘cover all’ roof of Number One Reactor, cannot, and did not ‘Filtrate, contain, suppress or limit’ radioactive releases for the highly radioactive debris left from the explosion and melt through of Unit Number One.
What Did It Do?
It was to limit coverage of the seriousness of the damage, and any attempt at cooling by water and other means ie: Hiding the evidence and the ongoing illegal practice of removing far more radioactive waste into the oceans and otherwise, that TEPCO would fell far more comfortable knowing the YOU didn’t know.
What is Happening Now?
Well, they have to do SOMETHING.
They say it is to permit the removal of rubble over an ‘estimated’ [they love that word] 12-24 months of debris, which will then lead to the later removal of highly radioactive fuel, or what is left of it…
The 2020 Olympics should be entertaining if not lethal.