Aerolization of Plutonium - STD-1128-98master0056

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

(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.

The health physics aspects of an accidental plutonium fire can be serious. A fire

can burn through containment structures, resulting in the dispersal of PuO2 over a

wide area, with the potential for inhalation exposure during the fire or during

subsequent decontamination efforts. The conditions under which a plutonium

fire can occur in a dry glovebox have been studied. With only 5% oxygen in

nitrogen, the metal will burn easily. At the 1% level, however, a fire will not

continue to burn unless heat is supplied (Rhude, 1962). Turnings must be

generated in a dry atmosphere and should be converted to the oxide as soon as

convenient, preferably on the same day they are made. Some solvents and

organic compounds form flammable mixtures with plutonium. In one incident,

tetrachloroethane was inadvertently substituted for another lathe coolant in a

metal-turning operation. Chips of plutonium aluminum alloys were ignited,

resulting in the blowout of a glove-box panel. In a separate event, burning

plutonium chips dropped into carbon tetrachloride resulted in an explosion (AEC,

1965).

2.6.3.3 Aerolization of Plutonium

The ignition of plutonium metal becomes a major hazard when enough

plutonium has burned to produce a significant amount of dispersable material and

a serious enough fire to damage the pertinent containment structures. The

particle size of PuO1.9 fired at a low temperature varies from 3% at <1 m to 97%

at 1-5 m (Stakebake and Dringman, 1967). Sintered PuO2.0 has a particle size

<2 m. Haschke (1992) made an effort to define the maximum value of the

source term for plutonium aerosolization during a fuel fire. He found the rate to

be constant (0.2-g PuO2/cm2 of metal surface per minute) above 500C. The

mass distribution for products of all metal gas distributions are approximately

0.07 mass% of the oxide particles having geometric diameters #10 m.

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