by this Standard [Eller et al. 1999]. It is also notable that no plutonium storage
package failures have resulted to date at the United Kingdom's Atomic Weapons
Establishment since a good quality-control regime for stabilizing and packaging in
food-pack cans was instituted several years ago for interim (10 year) storage
[Freestone et al. 1998]. The AWE procedure involves calcination at 400C and an
LOI criterion of 2 wt% [Freestone 1998].
A key conclusion from all the work described above is that plutonium container
environments have inherent self-limiting mechanisms that prevent accumulation
of significant pressures of oxygen and hydrogen over calcined oxides. These
mechanisms are very likely to limit buildup of unacceptable pressures of either
hydrogen or oxygen alone. Known mechanisms limiting oxygen buildup include
recombination with hydrogen and formation of PuO2+x from adsorbed water.
Mechanisms that limit hydrogen buildup include recombination with oxygen to
produce water and probably reduction of PuO2+x and other high valent materials
by hydrogen. It is therefore very likely that the bounding gas assumption made
in this Standard (and in DOE-STD-3013-96) is highly conservative.
4) Minimize potential for water readsorption above the 0.5 wt% threshold
MIS measurements on 33 items from Rocky Flats and Hanford which will be
stabilized according to this Standard, show that pure and impure oxide material
surface areas below 5 m2/gram generally result from calcination at 950oC for two
hours. [Haschke/Ricketts 1995; Haschke/Ricketts 1997; Haschke/Martz 1998;
Mason et al. 1999; Manchuron-Mandard/Madic 1996]. This work also shows that
post-calcination water readsorption on oxide particles should not pose a practical
problem with respect to the 0.5 wt% criterion of this Standard (readsorption onto
salt is discussed in the preceding section).
5) Stabilize any other potential gas-producing constituents
This Standard's calcination criterion (2 hrs at 950C) is intended to ensure that in
addition to moisture, all other potential gas-producing impurities in plutonium-
bearing oxide materials are eliminated. The technical literature shows that
nitrates, sulfates and carbonates of plutonium are effectively converted to oxides
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