Combined Use of Nitric and Formic Acids to Reduce Hydrogen Emissions During the Treatment of High-Level Radioactive Waste

Abstract

At the Savannah River Site (SRS), the Defense Waste Processing Facility (DWPF) is being constructed to immobilize high-level radioactive liquid waste (HLW) into borosilicate glass using a slurry-fed melter. The combined use of nitric and formic acids, in lieu of formic acid alone, to reduce H{sub 2} emissions during the treatment of high-level radioactive waste sludge was investigated. The H{sub 2} generation can be mitigated substantially by substituting a fraction of formic acid with nitric acid as the required acid source, and then using formic acid as the required reductant source. The peak H{sub 2} generation rate was reduced by more than a factor of 2, and a more gradual rise in the H{sub 2} evolution resulted. However, the addition of mercury to the sludge increased the evolution of H{sub 2} as did increasing the amount of nitric acid used and the rate of addition of the formic acid source. Overall, these results provided clear insight into what controlled the evolution of HG{sub 2} from high-level waste sludge and a means of mitigating it.