[ 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 ........
Maury&Dog [MaurySiskel maurysis at peoplepc.com]


-------- 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


    Fukushima Nuclear Accident – 17 March update

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: 

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 

Further technical information on Fukushima reactors 

Fukushima Nuclear Accident – 15 March summary of situation 

Fukushima Nuclear Accident – 16 March update 

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:

problem, as is explained in this updated fact sheet by the NEI 
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):


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 

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 
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 
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.


Read more of this post <http://bravenewclimate.com/?p=4112#more-4112>

Add a comment to this post <http://bravenewclimate.com/?p=4112#respond>



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