LABORATORY PROGRESS ON THE DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTE BY DEEP- WELL INJECTION

Abstract

Results of laboratory studies on the neutralization of Purex-type wastes are reported, including the radiochemical distribution of the fission products in the precipitate and supernate and the effect of sodium and calcium neutralizations on fission-produet separation. The problem of interstitial precipitation encountered when a second incompatible liquid is injected into a formation is discussed. Results indicate a piston-iike displacement of the interstitial liquid by the injected waste with only a small zone of precipitation formed along the contacting edge. Slurry tests were performed to determine the eapacity of various geologic materials for sorption of cesium and strontium from a synthetic Purex-type waste containing carriers and tracers. The materials studied include sands, feldspars, shales, clays, and limestone. The amount of cesium sorbed was found to be a function of several variables, among which are concentration of cesium in the waste, concentration of other cations, amount and nature of the clay material, and composition and amounts of other minerals in the disposal formation. Several types of shales and clay minerals, including illite, bentonite, montmorillonite, kaolinite, halloysite, and Conasauga shale, were slurried with simulated neutralized 6 M Purex waste. Sorption of cesium ranged from 0.6 to 6.0 mg/20 g, respectively, for the variousmore » materials tested. Results of slurry tests indicated that if the Purex-type waste were diluted 30 to 1 with concentrated brine, the amount of cesium sorbed per cubic foot would be about 2.7 curies. This is within the 2 to 8 curries/ft/sup 3/ estimated to be safe from thermal considerations. Core tests on a Berea sandstone showed similar sorptive capacities. Sequestering or complexing agents, that is, versenes, did not materially affect the cesium removal, but did result in a decreased sorption of strontium hy clays. Strontium sorption in systems studied ranged from less than 0.2 to 2.0 mg of strontium sorbed per 20 g of clay. Slurry results indicated increased H ion concentration decreases sorption; sorption of cesium is a function of the Na/Ca ratio; the Na/Sr ratio is not as important to strontium removal as pH of the solution; and limestone slightly decreases the amount of cesium sorbed per gram of illite. The results of the sorption studies suggest that undue localized heat production, due to sorption of radioactive materials near the well, can be controlled so that it will not be a serious problem. (auth)« less