Volatility of ruthenium-106, technetium-99, and iodine-129, and the evolution of nitrogen oxide compounds during the calcination of high-level, radioactive nitric acid waste
The nitrate anion is the predominant constituent in all high-level nuclear wastes. Formic acid reacts with the nitrate anion to yield noncondensable, inert gases (N/sub 2/ or N/sub 2/O), which can be scrubbed free of /sup 106/Ru, /sup 129/I, and /sup 99/Tc radioactivities prior to elimination from the plant by passing through HEPA filters. Treatment of a high-level authentic radioactive waste with two moles of formic acid per mole of nitrate anion leads to a low RuO/sub 4/ volatility of about 0.1%, which can be reduced to an even lower level of 0.007% on adding a 15% excess of formic acid. Without pretreatment of the nitrate waste with formic acid, a high RuO/sub 4/ volatility of approx. 35% is observed on calcining a 4.0 N HNO/sub 3/ solution in quartz equipment at 350/sup 0/C. The RuO/sub 4/ volatility falls to approx. 1.0% on decreasing the initial HNO/sub 3/ concentration to 1.0 N or lower. It is postulated that thermal denitration of a highly nitrated ruthenium complex leads to the formation of volatile RuO/sub 4/, while decarboxylation of a ruthenium-formate complex leads to the formation of nonvolatile RuO/sub 2/. Wet scrubbing with water is used to remove RuO/sub 4/ from the off-gas stream. In all glass equipment, small amounts of particulate RuO/sub 2/ are formed in the gas phase by decomposition of RuO/sub 4/. The /sup 99/Tc volatility was found to vary from 0.2 to 1.4% on calcining HNO/sub 3/ and HCOOH (formic acid) solutions over the temperature range of 250 to 600/sup 0/C. These unexpectedly low volatilities of /sup 99/Tc are correlated to the high thermal stability limits of various metal pertechnetates and technetates. Iodine volatilities were high, varying from a low of 30% at 350/sup 0/C to a high of 97% at 650/sup 0/C. It is concluded that with a proper selection of pretreatment and operating conditions the /sup 106/Ru and /sup 99/Tc activities can be retained in the calcined solid with recycle of the wet scrubbing solution.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- DOE Contract Number:
- W-7405-ENG-26
- OSTI ID:
- 5517210
- Report Number(s):
- ORNL-5562; TRN: 80-004947
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
IODINE 129
VOLATILITY
RADIOACTIVE WASTE PROCESSING
HIGH-LEVEL RADIOACTIVE WASTES
SOLIDIFICATION
RUTHENIUM 106
TECHNETIUM 99
CALCINATION
FORMIC ACID
NITRIC ACID
NITROGEN
NITROUS OXIDE
RUTHENIUM OXIDES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL REACTIONS
CRYOGENIC FLUIDS
DECOMPOSITION
ELEMENTS
EVEN-EVEN NUCLEI
FLUIDS
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
IODINE ISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MANAGEMENT
MONOCARBOXYLIC ACIDS
NITROGEN COMPOUNDS
NITROGEN OXIDES
NONMETALS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PROCESSING
PYROLYSIS
RADIOACTIVE MATERIALS
RADIOACTIVE WASTES
RADIOISOTOPES
RUTHENIUM COMPOUNDS
RUTHENIUM ISOTOPES
TECHNETIUM ISOTOPES
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
WASTE MANAGEMENT
WASTE PROCESSING
WASTES
YEARS LIVING RADIOISOTOPES
052001* - Nuclear Fuels- Waste Processing