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

The combined use of nitric and formic acids, in lieu of formic acid alone, to reduce H₂ emissions during the treatment of high-level radioactive waste sludge was investigated. The H₂ 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 H₂ generation rate was reduced by more than a factor of 2, and a more gradual rise in the H₂ evolution resulted. However, the addition of mercury to the sludge increased the evolution of H₂ 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 H₂ from high-level waste sludge and a means of mitigating it.