Self-sustained Oxidation Above th e Ignition Temperature cont'd

DOE-HDBK-3010-94

4.0 Solids; Metals

Carter and Stewart (1970) reported the results of experiments to determine the ARF and RF

for plutonium under fast reactor processing conditions. Two types of experiments to

measure airborne release and particle characteristics were performed: free fall of ignited

metal droplets and exploding wires. The ignited metal drop experiments were conducted in a

0.14-m diameter by 0.75-m tall vertical cylinder with a resistance furnace on top. Taller

tubes were used for the U experiments conducted. The metal was heated in the resistance

furnace to the predetermined temperature. An upflow of air adequate to entrain particles

<30 m AED was passed through the cylinder. For static experiments (air velocities

<1.0 m/s), the Pu was heated in air and the residue crumbled/disintegrated into the cylinder.

For the 660 oC experiments, the Pu was heated in argon to the desired temperature and fell

through the upflow of air in the cylinder (ignited and may have attained temperature

equivalent to the 2000 oC case discussed next). For the 2000 oC (estimated from the

temperature of ignited Pu in previous experiments) experiments, Pu metal was heated in air

until ignited and allowed to fall through the upflow of air in the cylinder.

The morphology of the airborne particle from the free-fall drop of ignited metal appear to be

very similar to that from the exploding wire experiments (see Table A.22, Comparison

Between Exploding Wire Aerosol and Droplet Fume in Liquid Suspension, in Appendix A).

Both show a wide size range of spherical particles with a significant number >1 m AED.

Sparking (incandescent airborne material) of the metal during the fall or on impact indicated

the presence of large (0.1 to 1.0-mm) spherical particles in the residual powder and the

presence of airborne vapor.

The total metal dispersed as particles or aggregates 10 m unit density spheres (AED) or less

was determined for each experiment. Figure 4-6 reproduced from Carter and Stewart (1970)

shows representative distribution for the three major experimental regimes. The geometric

mean and 95% confidence total Pu airborne dispersion as a function of accident stress are

reproduced as Table A.23 in Appendix A. The ARF and RF values for the various

conditions are:

geometric mean

ARF 3.5E-3/RF 1.0

ARF 1E-2/RF 1.0.

Both Mishima (August 1964) and Kanapilly (March 1982) reported on the measured ARF

from Pu metal suspended over a gasoline fire. Two 100-gram Pu rods were suspended in a

metal basket over a ignited pool of gasoline in a 4-ft square by 11-ft tall chimney. Estimates

of the airborne release based on weight loss gave the highest values but difficulties in

recovery of the residual materials created substantial uncertainty in the estimates. The

authors quote 5E-4 as a bounding ARF value. Luna (February 1994) reevaluated the data for

airborne release from the Vixen A trials (outdoor burning of Pu metal suspended above a

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