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Wiped-Film Evaporators for Evaporating Alkaline Light Water Reactor Radioactive Wastes

C. B. Goodlett

Nuclear Technology / Volume 43 / Number 2 / Pages 259-267

April 1979


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Evaporation tests with synthetic alkaline wastes typical of intermediate-level waste streams from the processing of spent reactor fuel were made at the Savannah River Laboratory (SRL) with two small wiped-film evaporators [0.93 and 0.46 m2 (10 and 5 ft2) heat transfer area]. Each feed (six total) was processed separately within the operating range of each evaporator. Feed flows varied from 0.026 to 0.24 ℓ/min (0.1 to 0.9 gal/min) in increments of 0.026 to 0.013 ℓ/min (0.1 or 0.05 gal/min). Steam chest temperatures were maintained at 130, 150, 170, or 182 C. Rotor-tip speed was maintained at 10.7 m/s (35 ft/s). Concentrate and process condensate from the evaporator were sampled at each set of operating conditions. The concentrate sample was analyzed for density (at exit temperature), volume percent of solids at room temperature, weight percent of water, and sodium concentration. Each evaporator condensate sample was analyzed for sodium to calculate entrainment from the evaporator based on sodium carryover. All concentrates from waste feeds high in NaOH and NaAlO2 flowed freely in liquid form out of the evaporator. Concentrates from waste feeds containing Na2SO4 and Na2CO3 included appreciable amounts of precipitated solids at high boildowns. The tests showed that all of the feeds could be converted in one pass to a free-flowing slurry that solidifies upon cooling to ambient temperature. Wiped-film evaporators with ∼3.72 m2 (40 ft2) of heat transfer surface are being installed at SRL to determine mechanical operability and processing characteristics with simulated alkaline defense waste. Both visual and instrument control systems will be tested during operability tests of the prototype evaporators.

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