Hydrogen Generation During Treatment of Simulated High-Level Radioactive Waste with Formic Acid

Abstract

The Integrated Defense Waste Processing Facility (DWPF) Melter System (IDMS), operated by the Savannah River Technology Center, is a one-fifth scale pilot facility used in support of the startup and operation of the U.S. Department of Energy’s DWPF. Seven IDMS runs examined the effect of noble metals in simulated high-level radioactive waste (HLW) and important process variables on the generation of H2 during the preparation of melter feed with formic acid. The results showed that due to the noble metals in actual HLW, the lower flammable limit of H2 in air (4 vol%) could be exceeded in D WPF vessels, depending on such factors as off gas generation and air inleakage. A small but detectable quantity of H2 was generated even in the absence of noble metals. The results also verified that the most important process variable that affected the H2 generation rate was the amount of formic acid added to the system.Forced air purge systems with H2 monitoring instruments were installed in the DWPF to control the concentration of H2 in the offgas by fuel dilution during melter feed preparation. The design-basis forced air purge flow rate required in the DWPF during radioactive operations was based on the peak H2 generation rate observed during an IDMS run operated with 25% excess formic acid. This amount of excess formic acid was deemed a credible deviation from nominal operating conditions; therefore, a margin of safety was included in the design basis.