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RE: C-14
Surprisingly, at least to me, n irradiation of nitrogen produces more
C-14 than n irradiation of carbon.
Future
nitride and carbonitride fuels will produce so much C-14 that exhaustive
scrubbing of all gaseous effluents will be required.
I thought that was not considered a mayor concern with carbide fuel
processing.
This
issue with nitrides is not a bug, it is a feature: nitride fuels will be
more proliferation resistant, and processing plants more
expensive.
marco
Here is more about C-14 related to nuclear
systems. The highly touted pebble bed reactors now proposed will use
graphite coated and carbide coated fuel pellets. Some carbon-14 is formed in
these. Any recovery operations involving burning the graphite and
carbide coatings to retrieve and recycle uranium-233 (from thorium) and -235
and plutonium-238 and -239 will presumably release radioactive carbon dioxide
to the atmosphere. This will probably be deemed unacceptable because of
the increase in long lived atmospheric carbon-14, so some capture may well be
required. One of the early proposals for the HTGR system was to capture
the carbon as carbonate such as calcium carbonate which is generally very
insoluble (clamshell, limestone, etc.). I have been away from the HTGR systems
for so long that I am not up to date on current spent fuel handling thoughts.
Also, large-scale processes that produce such materials as an
agricultural byproduct would also tend to reduce the carbon dioxide load in
the atmosphere.
Of course, we could just bury pebble bed spent fuel in
Yucca Mt. and be done with it. It won't go anywhere. Ever. (Unless we
need to retreive it in 150 years to reprocess it to get the materials for
fueling the breeders that will be required then.)
Just some thoughts.
John Andrews
Knoxville, Tennessee