Table 8.3 (cont'd)
Impure oxide from sources other than metal should be thermally stabilized at
1000±100°C for at least an hour, or placed in a combination of a slightly lower
temperature (-850°C) for longer heating time to result in the lowest loss on
ignition (LOI) practicable with existing equipment. This ensures complete
conversion of substoichiometric material and aids small-particle
coalescence, which diminishes dispersal risk.
Because plutonium oxide has greater potential for dispersion in severe accidents,
it should have priority over metal for storage in structurally robust vaults. Metal
should be characterized to ensure that it has not converted to oxide while in
storage. Stored plutonium will have an increasing radiation level because of the
build-up of 241Am. Therefore, characterization of metal should be done as soon
as possible and should make full use of small-sample statistical methods to
minimize worker exposure. The results of characterization should be integrated
with a site's surveillance plan, as well.
Quality assurance measures, labeling, and material characterization are essential.
Material and storage packaging specifics should be thoroughly documented.
(a) A higher oxidation rate may occur if the contained metal exhibits a high surface-area configuration, such as
sheet or foil. The maximum annual increase for normal (uncatalyzed) oxidation of a given metal geometry can
be calculated using a reaction rate of 3 x 10-7 g oxygen/cm2-minute measured for alpha-phase plutonium under
moist conditions at 50°C.