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Wednesday, December 14, 2011

Update to core cooling information at Fukushima Daiichi

I have finally (thanks to A. David Rossin and some other new friends) finally seen an illustration from TEPCO indicating the cooling flow paths being used at the Fukushima Daiichi plants; it does appear now that TEPCO is using the core spray rings instead of the top spray as they had indicated before these second flow paths were added. Below, an illustration of the GE BWR3/BWR4 reactor pressure vessel and attached and internal fixtures, marked up for this update.

The blue stars indicate the location of the normal feedwater flow path; feedwater is introduced through a nozzle in the pressure vessel and is supplied to a ring ("sparger") which directs the feedwater flow downward, all around the outside of the core barrel.

The yellow star on the left side of this illustration shows the nozzle for connection of the core spray; that on the right shows the location of the core spray ring. This is the added flow path being used at at least one or all of the plants, as indicated in a November 30 TEPCO illustration I've just seen this morning.

On the top of the illustration we see a red star by the top spray connection; TEPCO had previously indicated that this would be the second flow path, but clearly the core spray ring is more logical.

It's important to note that the feedwater sparger is OUTSIDE the core barrel and that the core spray sparger is INSIDE the core barrel. This makes the core spray far more effective in directly cooling the core ... so long as the core is mostly in its original location.

One of the things that this author is still wondering about is the recirc pump seals. If the recirc pump seals are failed and leaking, then this will provide a leak path out of the reactor vessel essentially at the height of the jet pump standpipes. This would make it hard to keep water level higher than roughly 2/3 of the normal core height by feedwater flow alone.

There are some further developments regarding TEPCO press releases that I'm just now aware of and will update on those later on today.

8:45 AM Eastern Wednesday December 14, 2011

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