Chernobyl was a graphite reactor that stopped radiation like little soldid walls..
3 Mile Island was a water reactor like the ones at Fukashima.
Uranium inside control cylinders of a metal designed to stop most radiation, is cooled by water. Water reactors do not use walls of graphite. Liquid sodium is used instead of water in some reactors but while it is more efficient in and accident if it leakds sodium burns a bit like Magnesium if it gets wet.


Could 3 Mile Island have gone critical and have had a huge explosion?
yes yes and yes.o

Did it?
no

It was amazingly close. It is said to have ben within a few degrees and perhaps only 50 pounds of additional melted uranium to obtain a chain reaction criticality.

One reason it did not blow up was that the specially coated floor of the reactor sloped away with the center poking up like a cone. The melted fuel flowed away from a central catching point and dispersed in a ring rather than a clump. Engineering prevented a full blwon atomic blast.






Yes gnu is right.

Cesium is a sign that some or all of the fuel has melted. How it flows and distributes on the floor is important for the reasons stated above.

Everything I have written here is from memory past and my current source3 is CNN IN - special earthquake tsunami edition.

If no Cesium was reported found in the air I too would have taken hope.

IF the pumps had worked I too would have taken hope.

I will take any valid hope. I welcome it.

Boric acid and seawater is at this moment flowing into one or more reactors. I called this procedure a band aid but ti is more like giving heroin to a terminal patient. It will settle the patient down but is not liekly of offering a cure. from contamination.

It is a last ditch effort to avoid criticality.


Can melted Uranium melt through concrete? r3einforced with rebar?

yes, unfortunetly this is one of those pesky design flaws in nuclear power plants.

Will it certainly melt through concrete?

no.






By the way Saturday Night Live did a sketch on 3 Mile Island.
They gave the job of cleaning up the water and melted fuel to an old black women Garret Morris and Jimmy Carter played by Akroyd was there to determine the cause of the melt down.
Carter discovered it was a Pepsi syndrome of a drink being spilled on the control panel.


At Fukashima once the other reactors were dwon for maintnence and water flooded the back up generators they no loner had a back up for the back up.

Its just one of those things that was sold as being impossible.