Characterization and treatment of gaseous effluents from in situ vitrification

In situ vitrification (ISV) is the in-place melting of buried wastes and the surrounding soil to produce a durable glass and crystalline waste form. Effluents released during in situ vitrification of buried simulated radioactive wastes have been characterized. Because ISV may be a prime candidate for waste stabilization, gaseous effluents must be well characterized and efficiently treated in order to minimize occupational and public exposure during operation. Volatilization and entrainment behavior has been determined for simulated fission products, simulated transuranics, and heavy metals in the off gas of three pilot-scale field tests. Losses of rare earth elements (Ce, La and Nd) used to simulate transuranic species and nonvolatile simulated fission products (Co, Mo and Sr) were very low, with soil-to-off-gas decontamination factors ranging from approximately 102 to over 105. Cesium losses were also quite low, with decontamination factors from 3 X 101 to 2 X 103. Heavy metal losses were highest, with Pb decontamination factors ranging from 7 to 30 and Cd decontamination factors of 3 to 4. Element losses decreased with increasing burial depth and increased when the surface cold cap was lost and during gas release periods. Off-gas particulate loadings were highest during startup and combustible gas releases and lowest during normal operation. Aerodynamic mass mean diameters of particulates in the untreated off gas ranged from < 0.1 to 1.4 μm, indicating the need for an off-gas system capable of efficiently removing submicron particles. (Auth.)