(738e) Formic Acid Free Flowsheet Development to Eliminate Catalytic Hydrogen Generation in the Defense Waste Processing Facility

The Defense Waste Processing Facility (DWPF) processes legacy nuclear waste generated at the Savannah River Site (SRS) during production of plutonium and tritium demanded by the Cold War. The nuclear waste is first treated via a complex sequence of controlled chemical reactions and then vitrified into a borosilicate glass form and poured into stainless steel canisters. Converting the nuclear waste into borosilicate glass canisters is a safe, effective way to reduce the volume of the waste and stabilize the radionuclides.

Testing was initiated to determine whether the elimination of formic acid from the DWPF’s chemical processing flowsheet would eliminate catalytic hydrogen generation.  Historically, hydrogen is generated in chemical processing of alkaline High Level Waste sludge in DWPF.  In current processing, sludge is combined with nitric and formic acid to neutralize the waste, reduce mercury and manganese, destroy nitrite, and modify (thin) the slurry rheology.  The noble metal catalyzed formic acid decomposition produces hydrogen and carbon dioxide.  Elimination of formic acid by replacement with glycolic acid has the potential to eliminate the production of catalytic hydrogen.  

Flowsheet testing was performed to develop the nitric-glycolic acid flowsheet as an alternative to the nitric-formic flowsheet currently being processed at the DWPF.  This new flowsheet has shown that mercury can be reduced and removed by steam stripping in DWPF with no catalytic hydrogen generation.  All processing objectives were also met, including greatly reducing the Slurry Mix Evaporator (SME) product yield stress as compared to the baseline nitric/formic flowsheet.  Ten DWPF tests were performed with nonradioactive simulants designed to cover a broad compositional range.  No hydrogen was generated in testing without formic acid.