Room Temperature Oxidation/Corrosion

DOE-HDBK-3010-94

4.0 Solids; Metals

layer ... stage III is a similar linear process entered after a transition period, but origin of

this change is unknown.... observed increase in particle size with increasing reaction

temperature interpreted as combination of two factors ... metal hardness and malleability

with temperature ... hardness decreases with temperature ... increasing malleability reduces

stress generated at metal-oxide interface and promotes formation of thicker product layer

before spallation ... indicates formation of centimeter sized hydride particles if reaction

temperature equal or exceeds half the melting temperature of metal in degree centigrade ...

second factor that may alter particle size is kinetic in nature ... spallation involves nucleation

of crack at surface and propagation of those cracks through the stresses material with

ultimate coalescence and formation of free particles. Nucleation and propagation are both

time dependent ... growth rate of oxide layer is large compared to spallation rate at high

temperature and formation large particles are favored, at room temperature the oxide growth

rate is extremely slow and the longer time available for spallation favors extensive crack

formation and small particle size ... largest diameter observed for low-temperature oxide is

~ 5 m in geometric diameter ..."

Condit (October 1986) reviewed the airborne release of plutonium metal under fire and

explosion conditions. The effects of various factors on the airborne release of plutonium are

listed in Figure 4-1 from that document. Five configurations are covered below based upon

the temperature of oxidation and the airflow (i.e., turbulence) around the oxidizing material

or oxide. Other experimental data covering the airborne release of plutonium during highly

energetic accident situations involving assembled nuclear weapons (e.g., aircraft crashes and

rocket/jet fuel fires with potentially concurrent falling molten material) indicate larger release

fractions for the plutonium metal under these circumstances (ARF = 1E-2) and would

correspond to the configuration covered here of disturbed molten metal surface (e.g., flowing

molten metal where surface is renewed allowing greater surface turbulence), high surface

turbulence, and violent reactions.

4.2.1.1.1 R oom T em p eratu re O xid ation /C orrosion . Stewart (1963) observed no

detectible change in appearance of a plutonium metal surface in 7 days at room temperature

and dry air. In moist air, a loose coating of powder was evident. Only 10% of the airborne

particles formed in 100% relative humidity air were in the respirable size range. The oxide

removal rate (Ci/cm2-hr) as a function of metal phase and humidity is shown in Figure 4-2

reproduced from the reference document. The ordinate is expressed in terms of Ci of

activity/cm2-s. Assuming the specific activity (7.4E-2 Ci/g) quoted for weapons grade

plutonium by Raabe (November 1978) and Eidson and Kanapilly (February 1983), the author

calculates the maximum rates for unalloyed and delta-stabilized metal in dry air and 100%

humidity to be:

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