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Nuclear reactors in the news - accurate reporting? - Page 14

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Posted by hubops on March 24, 2011, 1:23 am
 
    < huge snippage >


Thanks for your posts,  daestrom.
  Are you familar with the Candu design -
and is it  - in any way - superior / inferior ?
Our Canadian pundits have described the boiling water
reactor as a big reactor with a little water -
- Candu - as a little reactor with a lot of water.
  ( heavy water moderator ? )

Also  -  in the Japan scenario - or others -
would a large, raised reservoir -  ie man-made-lake -
with gravity-feed fresh water - ... be useful ?
.. it seems like that could have been the answer
to last-ditch emergency cooling issues.
 ... and for normal times  -  a little lake is a
wonderful recreation spot.
  John T.


Posted by daestrom on March 25, 2011, 11:31 pm
 
On 3/23/2011 21:23 PM, hubops@cccanoemail.com wrote:

The Candu can be fueled with simple uranium without any enrichment.
This makes its fuel cheaper.  It thus requires heavy water for moderator
but it still uses light water for the coolant.  This water has to be
kept circulating after shutdown to remove decay heat, much like LWRs.

As far as the BWR having 'little water', I'd disagree somewhat.  Typical
BWR has 200 inches (~17 feet or 5 m) of water above the top of fuel
inside the reactor vessel when operating.  As such, after a
trip/isolation, they can survive for a short while with *no* water
addition (the steam formed from decay heat is released via steam relief
valves as you boil some of that water).  It's not a long-term solution
obviously, but if there isn't a leak, it doesn't boil dry in seconds.
And one of the safety systems, RCIC, doesn't need AC power to inject
water back into the reactor.

IIRC, Candu use coolant in small tubes spread across the reactor so I'm
not sure just how long one could be left without cooling.


Funny you should ask...

Several of the 'advanced' reactor designs are striving for completely
passive safety systems.  The AP1000 for example puts a *large* storage
tank of water inside the containment, raised up higher than the reactor.
  In some scenarios, explosive valves can be opened to depressurize the
reactor and allow gravity draining of this water into the core.  The
safety systems are designed that if all AC power is lost and not
restored, these valves will automatically fire before the batteries die.

The ESBWR design has similar features.

daestrom

Posted by Morris Dovey on March 25, 2011, 7:47 pm
 On one of the web sites I visit from time to time I found a radiation
chart and some additional (related) links.

    http://blog.xkcd.com/2011/03/19/radiation-chart/
    (Click on the chart to see the full-size version.)

xkcd.com is a bit geeky - but so am I. One of my all-time favorite
cartoon images is at http://xkcd.com/162/

Before browsing the cartoons, you should carefully read the warning at
the bottom of the page...

--
Morris Dovey
DeSoto Solar
http://www.iedu.com/DeSoto/

Posted by z on March 27, 2011, 6:22 pm
 @speranza.aioe.org:


That site made my morning.  Thanks

-Zachary in ORegon

Posted by vaughn on March 28, 2011, 10:58 pm
 

So we ignore the experts in favor of some guy on the Internet?

Vaughn



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