Warm Water Oxidation Verification - Scoping and Stirred Reactor Tests

Abstract

3. Conditions of the stirred reactor tests were more oxidizing for the KW simulant stirred reactor test. In the bench-scale tests a 15% increase in U(VI) was observed. For the laboratory-scale tests, only a v 10% increase in U(VI) was observed. This may be attributed to more aggressive mixing of the stirred reactor test introducing more oxygen and that the stirred test was continuously open to the atmosphere. 4. Conditions of the stirred reactor tests were less oxidizing for the bench-scale test with 50:50 U oxide slurry, which increased in U(VI) by 1%, compared to the laboratory-scale tests that increased in U(VI) by 10%. All U(IV):U(VI) ratios evaluated indicated that test conditions were oxidizing. After considering potential measurement uncertainties, the uranium metal rate enhancement factor for the two matrices is between 1 and 2. The data generated support the use of a rate enhancement factor of 1 for the preconceptual flowsheet. Overall Observations/Conclusions The testing showed that the sludge solids that formed in 96 hours of ~95°C heating were generally weak, regardless of agitation and pH adjustment. However, in the bench-scale test with KW simulant, a zone of high strength agglomerated material was observed. The simulant representative of settler tank sludge prepared from ~50:50 uraninite:metaschoepite exhibited greater strength in the laboratory-scale scoping tests than the multi-component simulant prepared to emulate KW containerized sludge from SCS-CON-210 and 220). However, neither simulant presented an overwhelming challenge to re-suspension. Agitation did not increase the uranium metal corrosion rate. Of all test conditions evaluated, the greatest corrosion rates were observed for non-agitated KW simulant in the laboratory-scale scoping tests (about 1.7 times the rate predicted by the Databook). The lowest corrosion rate observed occurred in tests conducted with the 50:50 U oxide slurry under agitated conditions in the laboratory-scale scoping tests (0.9 times the Databook rate equation). Oxidation rates for all experiments are well within the uncertainty on the Databook rate (± a factor of 3). The rates observed for the larger scale tests with overhead stirring were similar to those observed in the laboratory-scale scoping tests. Further study of this system is encouraged to:  investigate the conditions associated with agglomerate formation,  evaluate the possible role of ferrihydrite and actual sludge matrices on uranium metal oxidation,  evaluate reactor vessels that may include jacketed sidewall heating and close-clearance mixing, and  evaluate longer runs analogous to the full length of time anticipated per sludge batch (~130 days).