Oxides - std3028

DOE-STD-3028-2000

area should not exceed 0.005 m2/g (24.4 ft2/lbm), based on a study of ignition

temperature versus surface area of uranium powder [Baker 1960]. The lowest

ignition temperature measured in the study was 255C (491F) for powder having a

specific surface area of 0.00512 m2/g (25 ft2/lbm). For foils and wires, experimental

ignition temperatures were somewhat higher than for powders having the same

surface area [Leibowitz and Bingle 1959]. Thus, the most readily ignitable form is

powder making the powder limits the most appropriate baseline. The 0.005 m2/g

(24.4 ft2/lbm) limit was chosen since this was the smallest surface area found to ignite

and the corresponding ignition temperature of about 255C (491F) is far above

temperatures expected to be achieved during storage [Thein 1999].

Uranium metal pieces larger than sieve mesh size 8 (0.00238 m or 0.00781 ft) are

assured of having a specific surface of less than 0.005 m2/g (24.4 ft2/lbm) and may be

stored in tube vaults. Thus, uranium metal of less than sieve mesh size 8

(0.00238 m or 0.00781 ft), powders, thin foils, and turnings of uranium are potentially

pyrophoric and must be converted to stabilized oxide prior to storage or must be

stored in a sealed container with an inert atmosphere.

2. Loose removable oxide associated with uranium metal also may be pyrophoric. An

adherent oxide layer on stored metal is generally beneficial because it tends to retard

further oxidation. However, as UO2 (the first oxide produced), this coating may be

pyrophoric. Therefore, prior to repackaging 233U metal, readily removable loose oxide

must be removed from outer metal surfaces. The pyrophoricity hazard from easily

removable oxide is mitigated by light brushing with a soft bristle or wiping, but not a

wire brushing, prior to packaging the metal. The loose oxide generated by brushing

should be treated and stored according to this Standard. Oxide removal should not

be so aggressive that the adherent oxide layer on the metal surface is removed.

Since 233U metal allowed by this Standard has low specific surface area (see

Criterion 6.1.1.1 for details) and is therefore easily examined, visual inspection for

free water and organic materials with the unaided eye during packaging is sufficient

to assure that unsafe quantities are not present in the storage environment.

A.6.1.2

Oxides

The uranium-oxygen system is one of the most complex systems known. These

oxides generally are reported as one of three formulae: UO2, U3O8, or UO3. The