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temperatures above 750C, while the oxides fired at lower temperature are made up
of medium size grains. This work thus indicates that for oxalate derived plutonium
oxide, the number density of respirable particles may actually increase for
calcination temperatures above 750C.
2. The standard accepts two approaches to verification that materials have been
adequately stabilized: 1) testing essentially every container loading (each container
would have a moisture measurement applicable to it, even if the measurement was
of a batch sufficient to fill several containers) or 2) use of a "qualified process" for
stabilization and packaging that would reduce the requirements for materials testing.
1) Stabilization at 950C and appropriate handling prior to packaging ensure that
the only significant mechanism for container pressurization is decomposition of
readsorbed water into hydrogen gas. Thus, verification of adequate stabilization
requires only measurement to ensure that residual moisture in the packaged
material is below the threshold specified in Criterion
The LOI test is accomplished by heating the sample to at least 1000C for at
least one hour and determining the resulting weight loss. The LOI test has great
attractiveness for application to stabilized plutonium materials because it is
simple, inexpensive and highly practical in a glovebox environment. LOI has the
unfortunate characteristic of not directly measuring the parameter of greatest
interest hydrogenous material content. Decades of experience with pure
plutonium oxide and recent results in the MIS program with oxides obtained
from Hanford and Rocky Flats and tested at LANL indicate that LOI is an
adequate test for moisture for fairly pure oxides (plutonium content greater than
approximately 80-85 wt%) [Mason et al. 1999]. However, the MIS program also
shows that lower assay materials of interest to the 94-1 program almost always
fail the standard LOI test because of impurities other than water that become
volatile at LOI test temperatures. Salt impurities are particularly troublesome in
providing false negative indications. This Standard therefore encourages use of
LOI for fairly pure plutonium oxide materials and use of moisture-specific
alternative methods for lower grade materials.

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