As a non-nuclear person, I need to make some assumptions:
1: Even with the control rods in place, the fuel generates some heat.=20
That quantity of heat needs cooling to prevent boiling the very clean=20
water inside the reactor, this may take some time (days??) without=20
outside cooling. The water slowly heats, and there is insufficient heat=20
radiation/conduction to dissipate the heat.
2: Normally the reactor water is cooled by a second water cooling=20
system, using a heat exchanger to move the heat between the 2 waters. =20
The 2nd cooling system could be dissipating the heat with a cooling=20
tower (didn't see any here), taking sea water, adding heat to it, and=20
sending back to the sea, or some other method.
4: Without cooling, thing of a pot of water on the stove. With enough=20
heat at the bottom, bubbles of steam rise to the surface, even though=20
the biggest part of the water is not near boiling.
4: If sea water is used for the 2nd cooling system (to cool the reactor=20
water), it would seem good engineering practice to place that equipment=20
between the reactor and sea, in a straight line.
5: There WERE several smaller buildings located between the reactor and=20
sea that before and after satellite photos, that are now gone from the=20
Tsunami. Were these in fact the cooling pumps??
6: There was reports that the reactor facility was short of electric=20
power. As strange as it sounds, it is possible that the voltages=20
produced at the nuclear site need to go off site, to a=20
transformer/switchgear yard, reduced in voltage, and then return to the=20
nuclear site to power controls, pumps, etc. Several years ago, in=20
Western, Ohio, USA, at the Davis Besse nuclear generating plant. A small=20
tornado took out a single moderate voltage electric line going to the=20
plant. The plant was shut down for several weeks, until the electric=20
wires could be replaced, and the unit brought back on line properly.

As I said, this is some educated guessing base on the little (true??)=20
information known, and there are lots of other scenarios that can be=20
supposed. :~(



On 3/14/2011 3:43 PM, Bob Blick wrote:
>
> On Mon, 14 Mar 2011 14:35 -0500, "Olin Lathrop" wrote:
>   =20
>> Bob Blick wrote:
>>     =20
>>> How much cooling do those reactors need if the fuel rods were OK and
>>> the control rods are fully inserted? More than passive water cooling
>>> with whatever flow can be achieved through convection?
>>>       =20
>> Apparently yes.  The article said the pressure was building, and they di=
d
>> several steam releases to cool it down.  Eventually they ran out of wate=
r
>> such that the top of the rods became exposed.
>>     =20
> I know the rods were very hot and needed to cool down from operational
> temperature, but that shouldn't take more than a few days. So it does
> seem that passive cooling will never be enough.
>
> Bob
>
>   =20
--=20
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