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the long-term storage conditions anticipated for stabilized materials [Tandon et
al. 1999a, Tandon et al. 1999b and references therein].
The preceding discussion addresses stabilization issues for plutonium oxide materials
that are rooted in safety concerns. An additional issue for these materials, which is
based more in operational than safety concerns, is the behavior of salt impurities in
plutonium oxides that have resulted from pyrochemical operations. The common
impurities NaCl and KCl, which can achieve levels of tens of percent in unstabilized
impure oxides being addressed by this Standard, have moderate volatilities above
800C. The practical impact of moderate volatilities is that materials with these
characteristics have difficulty meeting the 0.5 wt% LOI criterion with reasonable
calcination times. (Corrosion implications of chlorides during storage are addressed
in Section A.6.3 of this Appendix.) A second concern is the maintenance impact of
volatilized salts on furnace and off-gas systems. Salt volatilization is much more
problematic at 950C than at 800C because the vapor pressures of NaCl and KCl
are roughly an order of magnitude greater at the higher temperature. This Standard
retains the 950C calcination criterion of Standard 3013-96 but recommends that
operational complications regarding salt evolution be carefully monitored.
Although not suggested in this Standard, one perceived benefit of calcining
plutonium oxide is reducing the respirable fraction of the powder [USDOE 1994a].
Haschke and Ricketts reported particle size distributions for plutonium oxide
prepared from oxalate precipitation and hydride-catalyzed oxidation of metal after a
calcination cycle that included treatment at 950C for two hours [Haschke/Ricketts
1995]. The authors' measurements indicated that about 2% of the mass fraction for
hydride-derived oxide was below ten microns in size, compared to about 0.05% for
oxalate derived oxide, implying that the method of oxide preparation can be a
strong determinant of the particle size distribution. This work also indicated that the
frequently assumed correlation of specific surface area with particle size is not
always valid, due to porosity effects. In other words, the decrease in surface area
observed in calcination is not necessarily accompanied by a decrease in the number
of smaller particles. Subsequent work by Machuron-Mandard and Madic [Machuron-
Mandard/Madic 1996] examined particle size behavior for oxalate-derived plutonium
oxide calcined at 100C intervals between 450C and 1050C. The studies showed
that the number of very small particles increases as the oxide is calcined at

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