(446c) Nitric-Glycolic Acid Flowsheet Implementation in the Defense Waste Processing Facility to Reduce Generation of Hydrogen

The Defense Waste Processing Facility (DWPF) at the Savannah River Site (SRS) near Aiken, South Carolina, processes and immobilizes the legacy waste from the production of nuclear weapons materials. Although great progress has been made in processing and vitrifying high level waste (HLW) at SRS, approximately 100 million gallons of radioactive waste remains to be processed.

In this paper, we discuss the new flowsheet that has been developed for use in processing high level radioactive waste to virtually eliminate the generation of hydrogen, the facility’s primary flammability risk. The replacement of formic acid with glycolic acid along with optimizing HLW processing will allow DWPF to complete the mission of immobilizing the remaining waste sooner and safer.

Formic acid is an excellent reductant for transition metals, especially mercury. However, noble metals, primarily rhodium and ruthenium, catalyze the destruction of formic acid to produce hydrogen and carbon dioxide. Over 20 potential replacements for formic acid were evaluated, and glycolic acid was chosen as the best reductant to replace formic acid. Over 100 tests with simulants and actual waste have demonstrated that the chemical generation of hydrogen is almost eliminated using glycolic acid as the reducing acid.

DWPF plans to begin processing using the nitric-glycolic acid flowsheet in July 2022. This is a simple change as facility modifications are minimal. However, the use of glycolic acid also leads to significant changes in anion destruction and dissolution of transition metals. It will also require the destruction of residual glycolate in the recycle stream using sodium permanganate. The new flowsheet is arguably the most significant processing change since the radioactive startup of DWPF in 1996. Switching to glycolic acid will allow the facility to lower the air purge used to prevent a flammable atmosphere in addition to other processing changes designed to increase throughput. This paper will discuss the implementation of the new flowsheet in DWPF.