PILOT PLANT DENITRATION OF PUREX WASTE WITH SUGAR. PDF Download

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Batch denitration of synthetic Purex waste was investigated in 12 batch runs in the pilot plant denitration unit. Sugar was continuously added to 25 liters of hot waste. After sugar addition was complete, the hot solution was digested for several hours. The reaction proceeded smoothly and was easily controlled. About 19 to 22 moles of nitric acid were destroyed per mole of sugar with a reaction pot temperature of 100 deg C and a digestion period of 12 hours. About 17 moles of nitric acid were destroyed per mole of sugar when the reaction pot temperature was reduced to 95 deg C.A possible plant flowsheet for batch denitration with sugar was developed. This ilowsheet presumes batch denitration of large 2,500-gallon batches of waste in a standard 5,000-gallon Purex Plant tank and incorporates 12 hours of sugar addition and 12 hours of digestion. The flowsheet was successfully demonstrated in the pilot plant equipment. A 1.4M sugar solution was added to 25 liters of hot (100 deg C) waste for 12 hours and the mixture was digested for 18 hours. The initial nitric acid concentration was 6.14M. The residual nitric acid concentration was 0.94 and 0.90M after 12 and 18 hours of digestion, respectively. A residual carbon content equivalent to 1.9 and 0.4% of the total carbon fed as sugar was present after 12 and 18 hours of digestion, respectively. About 19 moles of nitric acid were destroyed per mole of sugar fed. Foaming was produced during batch denitration with sugar by addition of 0.4 gram of dibutyl phosphate per liter of synthetic waste. The addition of 0.2 gram of Dow-Corning Antifoam B per liter of waste reduced foam levels by about a factor of two. An induction period of about six to nine minutes was observed before the reaction started. The length of the induction period increased as initial sugar addition rates were reduced. Gentle air sparging reduced the induction period by about a factor of two. Attempts to use sodium nitrite as a means of decreasing the induction period were not successful. Sugar solution was added to cold waste, and the mixture was heated to determine the pot pressures and tower pressure drops that could be developed under abnormal conditions. A decrease in pot vacuum of 30 in. of water and a tower pressure drop of 8 in. of water were observed when 20 liters of waste and 2.7 liters of 2.5M sugar solution were mixed together and rapidly heated to 100 deg C. (auth).