[ RadSafe ] Fwd: [New post] Fukushima Nuclear Accident – 17 March update]]
Maury Siskel
maurysis at peoplepc.com
Thu Mar 17 09:13:02 CDT 2011
A bit of sanity in chaos ........
Best,
Maury&Dog [MaurySiskel maurysis at peoplepc.com]
============================
http://bravenewclimate.com/2011/03/17/fukushima-17-march-summary/
-------- Original Message --------
Subject: [New post] Fukushima Nuclear Accident – 17 March update
Date: Thu, 17 Mar 2011 08:01:27 +0000
From: BraveNewClimate <no-reply at wordpress.com>
To: maurysis at peoplepc.com
<http://bravenewclimate.com/author/bravenewclimate/>
Fukushima Nuclear Accident – 17 March update
<http://bravenewclimate.com/?p=4112>
Barry Brook <http://bravenewclimate.com/author/bravenewclimate/> | 17
March 2011 at 6:30 PM | Categories: Hot News
<http://bravenewclimate.com/?category_name=hot-news>, Nuclear
<http://bravenewclimate.com/?category_name=nuclear> | URL:
http://wp.me/piCIJ-14k
The crisis at the Fukushima Daiichi nuclear power station is approaching
a weeks' duration. The on-site situation remains extremely serious, with
glimmers of hope being shrouded by a shadow of deep uncertainty.
If you've not been following the situation on BraveNewClimate
<http://bravenewclimate.com/>, and want to recap, please read these
recent updates:
Japan Nuclear Situation – 14 March updates
<http://bravenewclimate.com/2011/03/14/japan-nuclear-updates/>
Further technical information on Fukushima reactors
<http://bravenewclimate.com/2011/03/14/fukushima-more-technical-info/>
Fukushima Nuclear Accident – 15 March summary of situation
<http://bravenewclimate.com/2011/03/15/fukushima-15-march-summary/>
Fukushima Nuclear Accident – 16 March update
<http://bravenewclimate.com/2011/03/16/fukushima-16-march-summary/>
These are assumed knowledge for understanding the rest of this post. The
preparation of the material below was aided greatly by the private
advice of my acquaintances in the nuclear engineering field.
As predicted yesterday, attention over the last 24 hours has focused on
the critical situation with the ponds used for temporary storage of
spent nuclear fuel at the individual reactor units, before it is moved
to a centralised facility on site. Although this old fuel has lost much
of its original radioactivity, the decline is exponential (see this
figure) which means that thermal energy must continue to
be dissipated for months.
This figure shows the location of the spent fuel ponds:
<http://bravenewclimate.files.wordpress.com/2011/03/gereactor_snfpond.jpg>The
problem, as is explained in this updated fact sheet by the NEI
<http://resources.nei.org/documents/japan/Used_Fuel_Pools_Key_Facts_March_16_Update.pdf>,
is that as these ponds heat, their deep covering of water (which acts as
a radiation shield and a cooling mechanism), starts to evaporate. If
they reach boiling point, because of lack of operational maintenance
systems, the evaporation rate will accelerate. If exposed, the there is
a potential for these old fuel rods and their zirconium cladding to
melt, and radiation levels will rise considerably. The heat generated in
spent fuel depends on a number of parameters, including: (1) level of
build-up of fission products (burn-up) and (2) length of time after
having been taken out of the reactor.
The spent fuel pool temperature has been rising gradually since last
Friday due to the loss of cooling pump (presumably no power source). As
we know from previous updates, the side of the Reactor 4 building has
been lost (it's the left-most of the 4 buildings in the following image):
<http://news.bbcimg.co.uk/media/images/51702000/jpg/_51702369_japan_earthquaketsu_fukushima_daiichi3_march16_2011_dg.jpg>
The Unit 4 reactor was already shut off for periodic maintenance when
the earthquake struck. IF the fire was caused by hydrogen, its only
plausible source would be spent fuel degrading in steam. Under this
scenario, initial inventory was probably reduced by sloshing during the
earthquake, and heat generation and resulting evaporation/boiling would
thereafter be more than double that in other pools due to it containing
freshly off loaded fuel. Temperature indications in the absence of water
would be that of the mixture of steam and air in the location of the
thermowell.
Nothing can be confirmed at this stage. As has been the case throughout
this crisis, information is hard to come by and must be pieced together.
Are the spent fuel in the pools in Units 3 and 4 are now uncovered?
TEPCO claims that NRC Chief Jaczko was wrong
<http://nextbigfuture.com/2011/03/us-says-plants-spent-fuel-rods-dry.html>
in claiming this, that the spent fuel pools in both Units 3 and 4 need
some refilling but are NOT dry. (The Japanese authorities are apparently
saying they've seen water still in the Unit 4 pool.) The big concern
here is that unlike the releases from damaged fuel in the reactor cores
of Units 1, 2, and 3, which were largely filtered by scrubbing in the
containment suppression pools (wetwell torus), releases of volatile
fission products (e.g., cesium and iodine) from these spent fuel pools
have direct pathways to the environment, if they remain dry for an
extended period.
Efforts to deliver water to these pools have proven to be very
difficult, and fuel damage may be occurring. If they are exposed, then
the use of the evaporation of salt water as a heat sink over periods of
more than a few days is not viable because the quantities of salt
deposited as the water evaporates becomes large in volume and plugs the
flow paths through the fuel, degrading heat removal. Everything that is
cooled becomes a heat sink to condense anything volatilised.
Unfortunately, a fresh water supply seems difficult to come by.
One option is to bring fresh water by helicopter, but the amounts needed
imply a large number of flights and gamma radiation levels are high
above the pools making overflights hazardous. NHK has reported a number
of successful water dumps using helicopters
<http://news.xinhuanet.com/english2010/world/2011-03/17/c_13783526.htm>
today. If radiation levels on the ground increase further, personnel
access will become more challenging. Additional spent fuel is stored in
pools in Units 5 and 6 and in a large centralized storage pool. A key
issue is how to continue to make up water to these pools in the longer
term, particularly if site access becomes more difficult.
<http://news.xinhuanet.com/english2010/world/2011-03/17/13783526_21n.jpg>
<http://news.xinhuanet.com/english2010/world/2011-03/17/13783526_21n.jpg>
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