Optimization of Sr-90 precipitation in nitric acid using design of experiments for radioactive waste characterization method

90 Sr radiochemical method using nitric acid for Sr and Ca separation was optimized using design of experiments methodology. Nitric acid concentration and total volume of solution were determined as influencing factors applying Plackett–Burman design. These parameters were then optimized using Box–Behnken experimental design. An optimal nitric acid concentration of 63% and a total solution volume of 26 mL were found to achieve a Sr recovery of 93% with only 5% of Ca for a single precipitation. The developed procedure was applied on real radwaste samples: effluent, sludge and concrete. By comparison of the recovery and the 90 Sr activity measurement with the results of the in-house standard method based on fuming nitric acid, the optimized method with concentrated nitric acid was validated. The fuming nitric acid can now be eliminated for 90 Sr radioactive waste characterization.