Tom Buck on mon 31 may 99
Excuse me, Clayarters, for touching on this topic again. But the request
for data on Uranium as a glaze material requires that this detailed
information be presented.
No, Ivor Lewis, depleted uranium is NOT nuclear reactor waste
fuel, that hellishly radioactive stuff that comes out of nuclear reactor
as spent (more correctly, "equilibrium") fuel.
Uranium, Atomic Number 92, Atomic Weight 238 (mostly) is usually
recovered from its ores as "yellow cake" or sodium diuranate
(Na2U2O7.6H2O).
The "light water" nuclear reactor (US designs, others) requires a
uranium oxide fuel containing more than nature's amount of 0.741% U-235
isotope, so the yellow cake is converted to UF6 (uranium hexafluoride), a
gas at ordinary temperatures. This gas then goes through a "gaseous
diffusion plant" (in USA chiefly) and two products are made: enriched
uranium IV oxide, and depleted uranium IV oxide which means it contains
substantially less of the U-235 isotope, the one that fissions readily in
H2O under suitable conditions. The fissioning of U-235 (some U-238) atoms
releases the energy that turns water into steam.
As you will gather, if we make a lot of reactor fuel enriched
with U-235, we will also produce a lot of depleted uranium, and most of it
goes into regulated storage looking for a market.
When an atom of U-238 or U-235, both longterm stable isotopes,
does undergo change, it does so in one of two ways:
1) It gives off an alpha particle (two protons, two neutrons, aka
a "stripped helium atom") and becomes a different element; or
2) The same atom fissions, splits in roughly equal halves,
releasing gamma-ray energy, a form of electro-magnetic energy that can
zoom into our cells and cause damage.
The U-238 isotope is prone to decay via emitting an alpha
particle whereas the U-235 isotope has a stronger tendency to fission. So,
depleted uranium oxide, with 60+% of its U-235 removed, will be much less
radioactive than natural uranium oxide.
If therefore a potter were to use UO2 (depleted) to achieve yellow
hued glazes, the risk of harmful radiation is reduced: alpha particles are
big and soon lose their kinetic energy through collisions with air
molecules. But the chemical toxicity remains. If the UO2-containing glaze
were to release U-ions to food being ingested, then the "patient" suffers
twofold, from uranium poisoning and from localized release of alpha
particles inside the body.
If yellow is that important, then spend the money to obtain the
rare earth element Praseodymium (AN 59, AW 141) as oxide and use it. This
element behaves like Titanium and Zirconium, both common in glazes judged
to be safe for foodware.
Tom Buck )
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
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