Initial Assessment of Ruthenium Removal Systems for Tritium Pretreatment Off-Gas
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
The processing of used nuclear fuel releases volatile and semivolatile radionuclides into the off-gas streams associated with the various processing steps. Ongoing efforts to develop methods to control the release of gaseous radionuclides to the environment have identified ruthenium (specifically 106Ru) as one of the semivolatile nuclides requiring a high degree of abatement. The tritium pretreatment process will release a fraction of the ruthenium as volatile ruthenium tetroxide (RuO4). Scoping tests were conducted to characterize the adsorption/deposition of RuO4 from dry gas streams by two different substrates: steel wool and silica gel. A simple test system was assembled to produce RuO4 through oxidation of powdered ruthenium metal, followed by a temperature-controlled sorption column. Tests were conducted with no sorbent present in the column to obtain baseline data on the evolution of RuO4 and deposition of ruthenium on the internal surfaces of the column. Silica gel and steel wool were tested as adsorbent media. Gaseous effluent from the column was scrubbed with caustic solution to remove any remaining ruthenium. Ultraviolet/visible spectroscopy (UV/Vis) and inductively coupled plasma–mass spectroscopy analyses were used to measure the amount of ruthenium in the scrub solutions. The UV/Vis analysis proved to be problematic because of precipitation of ruthenates, ruthenium oxides, and hydrated ruthenium oxides that occurred over time. An effective stabilization agent that does not adversely affect the desired spectra needs to be identified if this method is to be used in the future. There were indications that oxidation of powdered ruthenium metal did not generate a stream with steady concentration of RuO4, so improved techniques are needed for follow-on experiments designed to infer deposition rate. Both steel wool and silica gel are able to decrease the effluent Ru concentration by a factor of 10–100 during the 5-hour tests conducted. These tests were conducted using a dilute RuO4-bearing dry gas stream and the short test duration did not result in sorbent saturation or in an estimation of Ru breakthrough time. RuO4 desorbs from silica gel at room temperature. As interactions between RuO4 and silica gel are not irreversible, it cannot function as a disposal media without pretreatment to reduce RuO4 to a less mobile species. Silica gel may be useful as a RuO4 sorbent or delay media in some applications. Based on visual observations, steel wool was an effective deposition substrate with no evidence of RuO4 release. The deposition form should be identified and methods to assay the ruthenium content need to be developed.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1427631
- Report Number(s):
- ORNL/SPR-2017/576; NTRD-MRWFD-2018-000200
- Country of Publication:
- United States
- Language:
- English
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