A notably desirable result of 950oC calcination is that metal impurities are
expected to be converted largely or entirely to binary oxides (e.g., Fe2O3, Cr2O3,
and Ga2O3) and complex oxides containing more than one metal cation.
Thermodynamics strongly favors reduction of high valent oxides such as Fe2O3
and U3O8 by hydrogen, thereby providing a large potential chemical sink for
elemental hydrogen generated by chemical or radiolytic means. To illustrate the
potential magnitude of this effect, consider that 3 wt% of Fe in a maximum 5 Kg
charge or impure oxide corresponds to about 214 grams (about 1.3 moles) of
Fe2O3. This amount of ferric oxide theoretically is capable of converting about 45
atmospheres (about 660 psi) of hydrogen at 150oC to water in a typical storage
package, assuming about one liter of gas void space.
In this Standard, the maximum allowable package heat generation rate (19
watts) is reduced substantially from the 30 watts permitted by DOE-STD-3013-
96. As a result, bounding container and material temperatures will be
substantially lower. Recent calculations of thermal profiles for one bounding
scenario (exposure of a 19 watt 9975 shipping container to diurnal insulation)
indicates maximum container and oxide temperatures of 147oC (297oF) and
275oC (527oF) respectively [Hensel 1999a,b] (see Table A-1, Section A.220.127.116.11).
From these and related analyses, a solar influence of about 46oC (83oF ) on oxide
temperature can be deduced. Using a straight line extrapolation from the 30 and
19 watt cases, peak oxide temperatures near 150oC (302oF) and 205oC (401oF )
can be estimated for 6 and 12 watt oxide packages, respectively. When the solar
factor is subtracted, the resulting temperatures for "normal" storage in 9975
packages (near 105oC at 6 w and 160oC at 12 w) are seen to be within or close
to the range experienced during typical vault storage of plutonium oxides.
Significantly, the heat generation rates for 5 kg of the 30-50 wt% plutonium
materials studied to date in the MIS program are less than 6 watts. All MIS
materials studied to date in the 50-80 wt% range have wattage under 12 watts
for 5 kg, as should be expected since the wattage of 4.4 kg of typical weapons
grade plutonium metal is about 12.5 watts (see Section B.4 in Appendix B).
Therefore, impure materials packaged under this Standard with weapons grade
isotopic compositions will never experience the bounding temperatures calculated
for the 19-watt solar scenario. The vast preponderance of higher specific wattage
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