Bench-Scale Study of Direct Calcination of Raffinate Waste

摘要

Bench-scale tests of the direct calcination process for Portsmouth were conducted using batch pot calcination of simulated and actual raffinate wastes. These studies included investigation of the evaporation step needed to concentrate the raffinate before calcination. Tests were conducted at calcination temperatures of 600, 700, 1000, and 1200 sup 0 F with two levels of evaporative concentration before calcination at 1000 sup 0 F. Evaporation only tests were also made. Performance of the bench-scale system was excellent. A calcination temperature of 715 sup 0 F indicated that 80 to 100% of the Tc was retained in the calcined solids, while all of the nitrates were decomposed to oxides. With calcination temperatures of greater than or equal to 1000 sup 0 F, part of the Tc escaped from the calcination pot to the scrubber. Below 700 sup 0 F, not all of the nitrates were decomposed to oxides. Most of the U remained in the calcined solids for calcination temperatures of less than or equal to 1000 sup 0 F. The mass of solids remaining after calcination was 4 to 5% of the original raffinate for calcination temperatures from 700 to 1000 sup 0 F. Flow rate through the off-gas treatment system was variable. The water scrubber had a good removal efficiency for nitrate and most metals, but not for uranium. The trapping efficiency of the limestone trap for nitrate was low. Flowsheet studies indicate that enough U would pass through the scrubber and chemical traps to cause an unacceptably high release of radioactivity if the assay of the uranium exceeded 33%. A small HEPA filter after the limestone chemical traps is recommended to reduce U emissions. A flowsheet was developed for a full-scale process for the direct calcination of raffinate waste. (ERA citation 13:003120)