Suggested by my relative…
It goes a bit more into depth about the actual process of a “meltdown” in the reactor vessel. It’s not materially different than anything I’ve said to this point.
It adds a new term to my vocabulary – concrete Ablation.
According to it (which I’m taking as reliable), during TMI about half of the fuel melted, and that fuel “ablated” about half way through the bottom of the reactor vessel – but keep in mind they never actually lost cooling. They were just confused over the water level.
Ablation means it has been “eaten away”
Studies were done to see what happens if you progress to the next step – and the bottom of the reactor vessel gives way (this is not the suppression pool) and the molten fuel drops to the concrete below.
Simulating the process using heated non-radioactive melted uranium and other materials that would be in the “corium” (the melted mess), if there was no water cooling things down, the concrete would ablate at “millimeters per minute”. MIT seems to be down playing that statement, which concerns me – how many millimeters per minute? (1 inch = 25 mm). Note that in this test, the uranium is just hot, it isn’t generating new heat and doesn’t contain plutonium.
Let’s assume they mean 2 mm per minute…. in an hour, that is 120 mm or 4 4/5 inches. As the concrete ablates, it would tend to create a narrow bottom (that’s me, not MIT) that would concentrate the corium as it eats its way down. In a day, that would eat through 9 feet. Pouring in water at that point slows down the ablation, but doesn’t stop it. As a bonus, the ablation of concrete generates gases – that if they aren’t vented will create yet more of a pressure problem for the containment structure.
Looking for info on concrete ablation
http://www.plinius.eu/home/liblocal/docs/PLINIUS-Papers/Oxide-metal_MCCI.pdf
http://www.eurosafe-forum.org/userfiles/1_04_MCCI%20Eurosafe%202010.pdf
The above link matches my ballpark calculation:
Melt-through in less than 1 day for a 4m thick siliceous basement and imposed stratification
“According to it (which I’m taking as reliable), during TMI about half of the fuel melted, and that fuel “ablated” about half way through the bottom of the reactor vessel”
That’s an important factoid I’d never heard before. I had always been under the impression from initial reports that the TMI-2 core had significant damage, but the the reactor vessel was okay. 50% ablation is definitely not “okay”. No wonder they never attempted plant restart.
Some of the new generation reactors have a “core catcher” that is specially designed to capture and spread the corium over a large area where it can be cooled before it starts eating into the concrete foundation.
http://en.wikipedia.org/wiki/European_Pressurized_Reactor