The corrosion or oxidation of plutonium does not always occur in a
linear or predictable manner. The oxidation rate is a complex
function of the surrounding atmosphere, the moisture content, and
the alloys or impurities present in the metallic plutonium.4
Ignition Temperatures and Pyrophoricity of Plutonium, Its
Alloys, and Its Compounds
Plutonium and some of its alloys and compounds are pyrophoric.
Pyrophoric material is a liquid or solid that, even in small
quantities and without an external ignition source, can ignite within
5 minutes after coming in contact with air (NFPA Fire Protection
Handbook). Pyrophoric plutonium metal has been defined as "that
metal which will ignite spontaneously in air at a temperature of
150°C (320°F) or below in the absence of external heat, shock, or
friction" (Stakebake, 1992).5 Finely divided plutonium metal would
be considered pyrophoric while massive plutonium would be
nonpyrophoric. Martz et al. (1994) has proposed a mechanism for
plutonium pyrophoricity that predicts the ignition temperature as a
function of surface mass ratio and particle size. The most
numerous forms of pyrophoric plutonium are chips, lathe turnings,
and casting crucible skulls. Plutonium hydride and sesquioxide
(Pu2O3) are probably the most commonly occurring pyrophoric
compounds. Plutonium carbide, oxycarbide, nitride, and oxide
phases with compositions between the sesquioxide and dioxide are
potentially pyrophoric. Known pyrophoric alloys include Pu-U and
Pu-Ce, Waber (1967) summarized much of the early work on
plutonium corrosion and oxidation and is a good source for
identifying other pryophoric alloys.
See Wick (1967), Coffinberry and Miner (1961), and Kay and Waldron (1966) for details on the oxidation of unalloyed plutonium
and the stabilized alloy of plutonium.
Also in DOE/DP-0123T, Assessment of Plutonium Storage Safety Issues at Department of Energy Facilities (DOE, 1994a).