Stabilize any other potential gas-producing constituents

DOE-STD-3013-2000

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