Disposal of bituminized and other low- and medium-level wastes: Waste characterization and the retention of migrating radionuclides by steel corrosion products.

摘要

The validity of using scaling factors with the reference nuclide, {dollar}sp{lcub}137{rcub}{dollar}Cs, for activity determinations of {dollar}sp{lcub}238{rcub}{dollar}Pu, {dollar}sp{lcub}239, 240{rcub}{dollar}Pu, and {dollar}sp{lcub}241{rcub}{dollar}Am in low- and medium-level bituminized and unconditioned evaporator concentrates (ECs) produced at Riso National Laboratory (RNL), Denmark was investigated. The presence of constant activity ratios between {dollar}sp{lcub}137{rcub}{dollar}Cs and the Pu isotopes above was predicted because a large part of this waste stream originated from research on irradiated light water reactor fuel. Activity ratios were measured in different waste samples by comparison of gamma-measurements to results from destructive analyses using alpha-spectrometry. Results were verified using activity ratios of spent low-enriched fuel from the literature.; Continuation studies on the mechanisms influencing releases from bituminized low- and medium-level wastes were performed by leach tests on samples of various compositions and exposed to diverse environments. Four compositions of bituminized materials were studied including (1) bitumen with NaNO{dollar}sb3{dollar} and BaSO{dollar}sb4,{dollar} (2) bitumen with NaNO{dollar}sb3,{dollar} BaSO{dollar}sb4,{dollar} and Ni{dollar}sb2{dollar}Fe(CN){dollar}sb6,{dollar} (3) bitumen with NaNO{dollar}sb3,{dollar} BaSO{dollar}sb4,{dollar} Ni{dollar}sb2{dollar}Fe(CN){dollar}sb6,{dollar} and K-soap, and (4) bituminized RNL ECs. Leachant solutions used included (1) filtered deionized water, (2) 0.001-N KOH, (3) 0.01-N KOH, and (4) 0.001-N Ca(OH){dollar}sb2.{dollar} One trial was exposed to high-humidity air while two others had a cement disk suspended in the leachant. Some of the resulting data was used for the on-going validation of the SWL (Swelling, Water uptake, and Leaching) code created at RNL.; To improve the accuracy of projected releases from radioactive waste disposal systems, the sorption characteristics of steel corrosion products were investigated with a special emphasis on competitive sorption between Sr and Na. The corrosion rate of steel exposed to various environments was studied qualitatively and, with some systems, quantitatively. Traditional and non-traditional adsorption/desorption experiments on steel corrosion products using 0.01-M NaCl and 0.001-M NaCl solutions with two different concentrations of Sr were performed including one system with slow flow. Langmuir and Freundlich adsorption isotherms were used to analyze the data and to characterize the ion exchange capacity of the sorbate.