Preparation of Surrogate Post-Detonation Debris Using a Plasma Torch

Preparation of Surrogate Post-detonation Debris Using a Plasma Torch

P. A. Taylor, A. D. Braatz and A. V. Giminaro

A commercial plasma spray system is being used to prepare powders that have been exposed to the extremely high temperatures present in a plasma torch (10,000–15,000°C). The feed powders represent materials present at the Trinity site in New Mexico and at selective urban sites¹. The goal of the project is to determine the impact of the high temperatures on particle dispersion and leaching rates. The primary constituents of the feed are silica (~60 wt%) and alumina (~14 wt%), with smaller amounts of calcium oxide (~9 wt%), potassium oxide (~6 wt%), sodium oxide (~2 wt%) and magnesium oxide (~2 wt%). The urban feed has an iron concentration similar to the calcium, plus trace amounts of many other metals. The powder feeder for the plasma gun can handle particle sizes ranging from 20–200 µm, but a narrow particle size distribution is needed to ensure that the particles are uniformly exposed to the plasma arc. A laser-based particle visualization system will be used to show the path of the particles into the plasma arc. The flow rate of the carrier gas can be adjusted to optimize the exposure of the particles to the arc. The average surface temperature of the particles inside the plasma arc will also be measured. A spray dryer will be used to produce composite particles of uniform size, using small amounts of an organic binder. Early tests of the system used a Clinoptilolite zeolite powder that had been sieved to a 106–150 µm particle size. The zeolite has a similar composition to the urban sites. Figure 1 shows the plasma torch in operation, and Fig. 2 shows representative zeolite particles before and after exposure to the torch.

 

Fig. 1.  Plasma torch viewed through a welding screen; plasma gas of 9% hydrogen in argon

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 2.  Scanning electron microscope photo of as-received zeolite particle (left) and a particle after exposure to the plasma torch

 

1.       A. V. Giminaro et al., “Compositional planning for development of synthetic urban nuclear melt glass,” J Radioanal Nucl Chem, 306:175–181, 2015.