FATE OF FISSILE MATERIAL BOUND TO MONOSODIUM TITANATE DURING COOPER CATALYZED PEROXIDE OXIDATION OF TANK 48H WASTE

Taylor-Pashow, K.

Savannah River Site (S.C.)

关键词: Copper;    Testing;    Hydroxides;    Peroxides;    Potassium;   

DOI  :  10.2172/1048223
RP-ID  :  SRNL-STI-2012-00391
RP-ID  :  DE-AC09-08SR22470
RP-ID  :  1048223

美国|英语

来源: UNT Digital Library

【 摘 要 】

At the Savannah River Site (SRS), Tank 48H currently holds approximately 240,000 gallons of slurry which contains potassium and cesium tetraphenylborate (TPB). A copper catalyzed peroxide oxidation (CCPO) reaction is currently being examined as a method for destroying the TPB present in Tank 48H. Part of the development of that process includes an examination of the fate of the Tank 48H fissile material which is adsorbed onto monosodium titanate (MST) particles. This report details results from experiments designed to examine the potential degradation of MST during CCPO processing and the subsequent fate of the adsorbed fissile material. Experiments were conducted to simulate the CCPO process on MST solids loaded with sorbates in a simplified Tank 48H simulant. Loaded MST solids were placed into the Tank 48H simplified simulant without TPB, and the experiments were then carried through acid addition (pH adjustment to 11), peroxide addition, holding at temperature (50 C) for one week, and finally NaOH addition to bring the free hydroxide concentration to a target concentration of 1 M. Testing was conducted without TPB to show the maximum possible impact on MST since the competing oxidation of TPB with peroxide was absent. In addition, the Cu catalyst was also omitted, which will maximize the interaction of H{sub 2}O{sub 2} with the MST; however, the results may be non-conservative assuming the Cu-peroxide active intermediate is more reactive than the peroxide radical itself. The study found that both U and Pu desorb from the MST when the peroxide addition begins, although to different extents. Virtually all of the U goes into solution at the beginning of the peroxide addition, whereas Pu reaches a maximum of {approx}34% leached during the peroxide addition. Ti from the MST was also found to come into solution during the peroxide addition. Therefore, Ti is present with the fissile in solution. After the peroxide addition is complete, the Pu and Ti are found to precipitate from solution, while the U remains in solution throughout the remaining processes, including pH adjustment to 1 M free hydroxide. The Ti is likely forming a peroxotitanate material, which can then resorb the leached Pu from solution, but has a low affinity for U. Since Pu was not detected in the SEMEDS studies, it cannot be conclusively determined in what form the Pu returns to the solids; however, the Pu likely resorbed onto the peroxotitanate material. Based on the results of this experiment, Savannah River National Laboratory (SRNL) recommends the following experiments to further examine the fate of fissile material in CCPO processing of Tank 48H: (1) Repeat with full simulant matrix (organic and Cu catalyst present along with simulated radioactive sludge); and (2) Repeat of the above test after selection of final conditions (i.e., pH, temperature) if they differ from conditions tested.