RE: Graphite Quiz: Re: Chapelcross -(2)

["Scott, Arthur (MOL)" <Arthur.Scott@MOL.GOV.ON.CA>]

-----Original Message-----

From: Emil Murat [mailto:kerrembaev@YAHOO.COM]



Here comes the quiz: Reactor Designers.





 Why did they/he/she choose those Magnesium/Graphite?  



A few suggestions:

These reactors use natural uranium fuel, so minimal neutron capture in the

core is a necessity.



Graphite had been used for the Pu production reactors (Hanford, Windscale)so

there was experience with it. 

Windscale used air as the coolant to avoid the positive void coefficient of

water cooled reactors, so they stuck with gas cooling but switched to

readily available CO2. There is no free oxygen in CO2, so there was no

chance of ignition of graphite or any other material in the core.Another

choice would have been Nitrogen, but the cross section of N is 1.9, much

higher than C 0.0034, O 0.00027 barn. Helium 0.007 barn was not readily

available.



The fuel had to be clad in something. 



Thermal Neutron capture cross sections

Iron	    2.55 barn

Aluminium 0.234 barn

Magnesium 0.063 barn

Zirconium 0.182 barn



Looks like Mg is the best choice.



Possibly when the design was carried out the separation of Zr from Hf (106

barn) was not fully developed, so Zr was not even plausible as fuel

sheathing.





 

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