Michele Kearney's Nuclear Wire

Major Energy and Environmental News and Commentary affecting the Nuclear Industry.

Thursday, October 1, 2015

Fukushima Daiichi Unit 2 Reactor Core

Unit 5 was checked first to prove the process.  We know the core is there because Units 5 and 6 did not lose power, and so had no core damage.

Unit 2 core obviously had a great deal of melting, if not totally melted.

The radioactive decay of the atom splitting pieces that produces that heat that causes melting, decreases continuously with time. (I guess this was why the name “decay” was chosen.  This relates what is happening to processes with which people are familiar.) 

Because the heat generation always decreases and never again increases, your words that a meltdown might occur again  are not right.  

In the terrible, gross, Chernobyl accident, the mixture of molten fuel and molten/burning graphite flowed for a while out broken pipes, then solidified.  The pictures are dramatic.  The formations were dubbed “elephants feet.”  You can find them on line. http://nautil.us/blog/chernobyls-hot-mess-the-elephants-foot-is-still-lethal

At Unit 2, based on the findings, I expect that molten core mass will have melted through the reactor vessel, and solidified somewhere below it.  In the MK I BWR design, the reactor vessel sits on a  tall collar, because the control rod drives stick out from the bottom of the vessel.  (I’ve stood under them)  The collar sits on the inside of the “upside down light bulb” shaped primary containment.  There is a flat concrete floor poured in the bottom of the bulb that provides a working surface.  The “bulb” sits on a large solid concrete pedestal  that is not quite as big around as the bulb.  The pedestal sits on the floor of the reactor building, which is the secondary containment.  Around the pedestal is the Suppression Pool-the torus – doughnut shaped.  It is about half filled with water and connected to the bulb.

I expect all the core to have cooled and solidified long ago – first days – and be in the bottom of the bulb and perhaps on the floor of the reactor building.  All the concrete and steel soaks up heat being generated from the molten core mass, and speeds up the cooling.

Howard Shaffer

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