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Radioactive elements released in coal ash and exhaust produced by coal
combustion contain fissionable fuels and much larger quantities of fertile
materials that can be bred into fuels by absorption of neutrons, including
those generated in the air by bombardment of oxygen, nitrogen, and other
nuclei with cosmic rays; such fissionable and fertile materials can be
recovered from coal ash using known technologies. These nuclear materials
have growing value to private concerns and governments that may want to
market them for fueling nuclear power plants. However, they are also available
to those interested in accumulating material for nuclear weapons. A solution
to this potential problem may be to encourage electric utilities to process
coal ash and use new trapping technologies on coal combustion exhaust to
isolate and collect valuable metals, such as iron and aluminum, and available
nuclear fuels.
In response to your inquiry about natural production of Pu-239 from
airborne
U-238:
I did the calculations several years ago that showed
the following: Given the relatively constant flux of neutrons in the atmosphere
(as reported in the literature), I wondered if the increased combustion
of coal around the world that injects increasing quantities of exhausts
(that is known to contain U-238 as a component) might breed Pu-239 in the
atmosphere. Handbook and literature data for neutron absorption cross-sections
were consulted, and rather straight-forward calculations indicated that
a very small reaction rate does exist for the assumptions I made, but so
small in my view that any real effects are negligible.
One reason is that any radiotoxic
effects from this process are overwhelmed by the combined radiotoxicity
of some 40 radioisotopes in the parent coal (exceeding 100 gm/year Pu-239
equivalent, perhaps over 300 gm/year, for each 1000 MWe of coal combustion,
given average concentration data). And, whatever effects coal-source radiotoxicity
may have was ruled as
insignificant by EPA in its 1984 "final ruling" document.
I believe this to be the
first time that airborne production of Pu-239 has been predicted, but in
any real sense, it is nothing more than a curiosity. Any concern about
Pu-239 most likely addresses its supposed radiotoxicity, which is well
over-stated in view of real world data, and given that each 1000 MWe of
coal combustion disperses some 27 metric tons/year of radiological material
in the biosphere (based on average composition data), any natural production
of Pu-239 is clearly of very minor proportions.
What I find curious is that
every coal-fired steam plant has throughput of non-trivial quantities of
radiological material (given average concentration data for U and Th),
but they are subject to no regulations. Meanwhile, the nuclear industry
is heavily constrained by regulations to
track trivial, or even supposed, radiological material - at enormous
cost.
What would happen if a nuclear
site was reported to be freely exhausting ~27 metric tons (~60 Curies)
of radiological material into the biosphere annually? Meanwhile, a strong
case can be made that every 1000 MWe coal-fired steam plant does it year
after year, and no one cares.
If you need any more data,
I can likely provide whatever you might need.
Alex Gabbard
ORNL
Metals and Ceramics Division
wga@ornl.gov (gabbardwa)
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