Catalytic Effects of Silver in Iodine Reactors for Dissolved Used Nuclear Fuel

Description

The dissolution of used nuclear fuel generates a variety of off-gasses including flammable hydrogen and other species that are a concern for environmental release. The H-Canyon facility at the Savannah River Site is currently dissolving aluminum-clad research reactor fuel from material test reactors and the High Flux Isotope Reactor (HFIR) using a mercury-catalyzed nitric acid flowsheet. Savannah River National Laboratory recently developed and deployed a Raman spectrometer to monitor the off-gas stream from the dissolution process. Results from these measurements indicated a lack of the expected hydrogen, nitrous oxide, and nitric oxide in the off-gas stream. It was proposed that the silver on the silver nitrate–coated berl saddles present in the reactors for iodine capture were acting as a catalytic hydrogen recombiner. Nitric oxide is readily oxidized to nitrogen dioxide under normal conditions, but it was unclear what happened to the nitrous oxide. A laboratory-scale iodine reactor was assembled and filled with silver nitrate–coated berl saddles to help ascertain the fate of nitrous oxide and hydrogen. Testing with this laboratory-scale reactor observed the recombination of hydrogen when a simulated dissolver off-gas was passed through the reactor containing silver nitrate–coated berl saddles at the approximate temperatures seen in H-Canyon. However, the nitrous oxide concentration was unchanged, suggesting a more complex process occurring within the off-gas stream before it reaches the iodine reactors at H-Canyon.

Resources

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0 The Savannah River National Laboratory is implementing a separation flowsheet to recover rare isotopes and transplutonium elements from irradiated 242Pu targets known as Mark-18A targets. The Mark-18A targets contain the United States’ supply of nonseparated 244Pu, which has a wide range of applications from nuclear forensics to production of superheavy elements such as flerovium. The targets also contain hundreds of grams of heavy curium (246–248Cm), which is used as a target material for 252Cf production. This work investigates the use of diglycolomide resin (DGA Resin) to recover valuable trivalent actinides from the Mark-18A targets. Batch contact experiments were performed on a representative simulant to determine mass loadings. The resin showed an overall capacity of 11 mg/mL for a mixed metal matrix (Zr and La–Gd). Column experiments showed chromatographic separation with transition-metal breakthroughs occurring first followed by the lanthanide series La–Gd. The experiments showed that lanthanide breakthrough occurred after 11 mg/mL mass loading was reached on the column with the mixed metal matrix. A radiological column experiment with an in-line UV/vis cell was able to detect Nd breakthrough just prior to 241Am breakthrough. Implementing an in-line UV/vis cell into full-scale Mark-18A target processing will be used to limit breakthrough of trivalent actinides recovered from the targets. https://figshare.com/articles/journal_contribution/Scaling_Trivalent_Actinide_and_Lanthanide_Recovery_by_Diglycolamide_Resin_from_Savannah_River_Site_s_Mark-18A_Targets/13483425?file=25878177

Tags

  • iodine-reaction
  • hydrogen-recombination
  • nox-gases

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