Small Molten Metal Drops Hurled Through Air or Explosion of Entire Metal Mass 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

14-cm diameter by 75-cm tall vertical cylinder with a resistance furnace on top. The

dimensions were limited by the size of the glovebox for delta-alloy Pu experiments. Taller

tubes were used for the U experiments. 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, 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.

For the exploding wire experiments, 50 to 400 mg of metal were violently dispersed by a

large electrical charge discharge (4000 J) through the metal in a 3.5-liter chamber. The

aerosol within the chamber was discharged ~ 1 min after formation via a cascade impactor

(size distribution of airborne particles) and a membrane filter (transmission electron

microscopy for morphology). Based on these results, bounding ARF and RF values (at a

95% confidence limit) for vapor formation from droplets (exploding wire, violent ejection

molten droplets) are assessed to be 5E-1 and 1.0.

Raabe, et al. (November 1978) reported the ARF and size distribution of the fume made

airborne during the free-fall of ignited drops of delta-phase plutonium metal. Small discs

were cut from 50-m-thick foil in the size range believed representative of fragments that

could result from explosive damage. The discs were positioned on a very thin film of

combustible material on top of a 0.15-m wide by 0.18-m deep by 3-m tall stainless steel

chamber with a glass viewing window down the front panel. The discs were ignited by a

laser (500 oC, adequate to ignite but not to vaporize metal) and formed drops 50 to 500 m

in diameter. The ignited material fell down the chamber. Air was drawn through a

perforated plate down through the chamber. Large particles were collected in a aluminum

foil lined cup at the bottom of the chamber with airborne materials carried to aerosol

samplers (seven-stage cascade impactor, spiral centrifuge, point-to-plane precipitator + glass

fiber filters). The experimental apparatus is shown in Figure A.21

Essentially all of the plutonium available was driven airborne with ~ 40% of the source in

the respirable size range. The airborne material was primarily a web-like chain of

crystalline, cubic particles 0.004 to 0.1 m on a side with a few discrete spherical particles

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