[LINK] Nuclear power stations. Decay heat = there is no quick "shutdown"

Robin Whittle rw at firstpr.com.au
Sat Mar 19 16:00:17 AEDT 2011

Hi Kim,

You wrote, in part:

> You only need to keep the system up until you can shut the reactors down.

Please read up on reactors and nuclear fuel, in particular Decay Heat:


The fuel needs to be cooled after the fission reaction has been stopped.
 I understand the three operational reactors had their fission reaction
shut down in 4 seconds or so due to the control "rods" being fully
raised at the start of the earthquake.

Please take a look at the curves in the MIT page listed above.  The fuel
in these reactors is producing about 6MW (unit 1) and 10MW (units 2 and
3 right now.  It will take a couple of months for this decay heat to half.

Its not good enough to fill the reactor vessels with water, since the
water boils and the heat needs to be removed by some means.  (Still, I
wonder at what point the decay heat would be low enough that the reactor
could be filled with water - or at least to the top of the rods and then
- cooled by water being poured on the outside of the vessel.)  So at
present, to the extent they have water in the reactor vessels (I think
they had not been pumping any in for the last few days) they are relying
largely on evaporative cooling of this water to cool the reactor cores.
 This means steam is being emitted, which carries with it some of the
radioactive material which comes from the fuel into the water.

The Wikipedia articles and the MIT site are good sources of information:


I try to link to significant pages such as this from my page:
http://www.firstpr.com.au/jncrisis/ . This page has diagrams, photos and
videos which I think are pertinent.

 - Robin

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