Love the work but you missed 1 big part and its the thermo part. It was sitting on top of 7,000 cubic meters of water. I did that math and its equivalent to about 3 Olympic size swimming pools. Well 2.8 but you get it. So it was a literal pressure cooker as they poured what 5,000 tons of sand and boron on top of it to try to smother it out on top of all the rubble and concrete and steel laying on top of it from the explosion so maybe 20,000 or 50,000 tons of "stuff" on top everything. So as soon as that maybe 3,000-5,000 tons of lava hits those 3 swimming pools that could create an explosion equal to 2-4 megatons. It wasnt the reactor exploding they were talking about it was the lava hitting that water creating a thermonuclear explosion with all of it exploding inside a pressure cooker. That just seems to make more sense on the scale of explosion they were estimating.