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Re: Graphite Quiz: Re: Chapelcross -(2)
Dear Emil:
I believe that:
1) Graphite was chosen as the moderator since the
original reactors were graphite moderated and it
easier to work with than heavy water. Graphite is
really not that flammable (try burning it). Without
going into all of the physics involved it requires
very high graphite internal heat to produce the
reaction
C + 02 ------- CO. Graphite would also allow for
gas cooling (900 degrees C), which is much more
efficient than water (300 degrees C) when it comes to
producing power for electicity. (going back here and
I quote from a 1949 AEC document, "The original plans
for the 1000 kW Oak Ridge Reactor, made in 1942,
called for the eventual use of Helium gas in order to
cool the production reactors or piles...because of
insufficient helium, the Oak Ridge Reactor was
graphite moderated, air cooled with uranium metal clad
in aluminum tubes.....This was to serve as the pilot
plant for large scale Pu production plants and make Pu
for experimental purposes since there was little
available.....because of difficulties with air as a
coolant in a large scale reactor, the designs were
changed to water as the coolant with graphite as the
moderator........") So, the UK and later France chose
rather brillantly to use CO2 as the coolant for their
earliest reactors. And it has worked quite well for
50 years.
2) Magnesium alloy makes sense since it has a higher
thermal conductivity(0.4 cal/sec-cm) and specific heat
(0.32 cal/gm) and lower density (1.5 gm/cc) than
aluminum (0.25 cal/sec-cm, 0.26 cal/gm, 2.4 gm/cc). In
an alloy form Mg is quite strong, less brittle and has
less characteristic heat warping problems than
aluminum and other metals....(Just look at all of the
expensive Mg alloy bicycles that replaced Al and Fe
ones).
3) Magnesium does react with O2 in the air. However,
since it is an alkaline earth metal, it is much slower
than Na, K or Li. The Mg alloy with Al etc. is much
slower yet. As as a precaution, CO2, N2 or Helium
would kept over the Mg alloy to prevent this oxidation
from occuring. Bear in mind that Zr at high
temperatures can also react with O2 in the air so we
might keep CO2 over it too.
I could keep going on here, but MAGNOX in UK and
France was a logical progression toward a highly
advanced and very efficient and extremely safe
inert gas cooled, carbon moderated nuclear power
plant.
Therefore, as a teacher, the answer to your quiz
question is obviously h) None of the above is true.
Paul W. Shafer---Physics Teacher and former Nuclear
Radiation Protection Engineer LaCrosse BWR and
Pathfinder SBWR.
--- Emil Murat <kerrembaev@YAHOO.COM> wrote:
> Greetings,
>
> 1.1 If I were them, I would be keeping my eye on
> moderator as well.
>
> 1.2 Even, during this particular event, there was NO
> air-oxygen introduced into the moderator.
>
> However,
>
> 2.1 Isn't it this a strange combination?
> 2.1.1 Magnesium-Graphite.
>
>
> 3.1
>
> Here comes the quiz: Reactor Designers.
>
>
> Why did they/he/she choose those materials?
>
> a) Magnesium has a pretty look :-)
> b) It is slim = has light weight. :-)
> c) Both graphite and magnesium are flammables =
> temperature + free oxygen.
> d) In Great Britain: Zirconium is an import product,
>
> Magnesium is an export product.
> e) The reactor designer wanted to be a plane
> engineer
> rather than a nuclear.
> f) A, B and E
> g) C and D
>
>
> Good luck, fellas!
>
>
> Emil.
>
>
> >>>>>>>>>>
> From the original message:
>
> > > Emergency workers were called in and carbon
> > dioxide was sprayed
> > > over the basket to ensure it did not catch fire.
>
>
> >>>>>>>>>>>>
> From: Paul William Shafer
> Subject: Chapelcross
> >>
> It seems to me that Chapelcross is a MAGNOX graphite
> CO2 cooled reactor like the ones
> ...
> ...
> Magnesium canned oxide fuel may explain why
> CO2 was sprayed over the spent fuel to prevent a
> fire
> from occuring.
>
>
>
>
>
>
>
> > > -----Original Message-----
> > > From: Susan Gawarecki [SMTP:loc@ICX.NET]
> > >
> > > Britain Nuclear Accident Probed
> > >
> > > LONDON (AP) via NewsEdge Corporation -
> > > Spent fuel rods were accidentally dropped onto
> the
> > reactor floor of a
> > > nuclear power plant in Scotland last week, its
> > operator said Sunday.
> > >
> .........
> .........
> > >
> > > Emergency workers were called in and carbon
> > dioxide was sprayed
> > > over the basket to ensure it did not catch fire.
> > >
>
>
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