Oxidation at Elevated Temperatures

DOE-HDBK-3010-94

4.0 Solids; Metals

indicating that large pieces of uranium are very difficult to ignite as large amounts of

external heat must be supplied and serious heat loss prevented.

The particle size distributions of residual oxides produced under a variety of conditions have

also been measured and are shown in the reference document (see Figures 4.8, 4.10 and

4.11). The distribution becomes coarser and the solubility in simulated lung fluid decreases

as the temperature increases. Oxidation of the metal at <450 oC generated a fine, black

non-adherent powder. At temperatures around 535 oC, the oxide was a fine, black powder

sintered into lumps. At temperatures >700 oC, the oxide appeared to be a hard, black scale.

The ARF and RF for three potential accident configurations for thermal stress (airborne

release during the oxidation of uranium at elevated temperatures, airborne release from

disturbed molten uranium surfaces, and airborne release during explosive release of fine

molten metal drops) are covered below.

4.2.1.2.1 O xid ation at E levated T em p eratu res. Mishima et al. (March 1985)

characterized the oxide generated by the April 1983 burn test involving munitions containing

depleted uranium (DU) penetrators and reviewed the literature on airborne release.

Tests subjecting munitions to rigorous fire conditions are performed prior to deployment to

ascertain the thermal and blast hazards during transport and storage. Twelve 120-mm rounds

containing 48 kg of DU as rods ~ 1 in. in diameter by 30" long were subjected to a wood

and diesel fuel fire. The rounds cooked-off (i.e., the propellant used flared) and the DU

rods were retained in the burning mass at temperatures from 800 to 1100 oC range for

~ 3 hours. No detectible airborne DU was collected by air samplers surrounding the burn

at distances <100 m. Samples of the oxides generated were collected and the particle size

distribution, morphology and solubility in simulated interstitial lung fluid were measured.

The fraction of the oxide generated by the burn <10 m AED ranged from 0.2 to

0.65 wt/o. The fraction of the residual oxide <10 m AED were predominantly U3O8 and

all in the "Y" class (dissolution halftimes in simulated interstitial lung fluids of >100 days).

The ARF x RF values for uranium during oxidation at elevated temperatures found in the

literature were:

Elder and Tinkle (December 1980):

Air, up to 3.2 m/s, fire

5E-3

Air/Air-CO2, 3.2 m/s, 500 oC

1E-7

900 oC

4E-6

Carter and Stewart (September 1970)

Air, static, molten metal

4E-4

Free-fall molten drops

6E-3

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