Characterization of radiolytically generated degradation products in the strip section of a TRUEX flowsheet

Abstract

SUMMARYThis report presents a summary of the work performed to meet the FCRD level 2 milestone M3FT-13IN0302053, "Identification of TRUEX Strip Degradation." The effects of gamma radiolysis upon the efficacy of the strip section of a TRUEX flowsheet for the recovery of trivalent actinides and lanthanides from acidic solution were determined by a combination of static and test loop irradiations. Compositions of the irradiated aqueous and organic solutions were determined using a suite of analytical techniques. In addition, ESI-MS was used to identify some of the products of the radiolytic degradation of lactic acid, DTPA, CMPO, and TBP.For lactic acid, the major degradation products detected by ESI-MS were pyruvic acid and a species corresponding to a lactic acid-pyruvic acid cluster. The major product of DTPA degradation was determined by ESI-MS to be a DTPA lactam resulting from the radiolytic loss of glycolic acid. Acetate and several other unknown degradation products of both lactic acid and DTPA were detected by HPLC analysis. Several species arising from the degradation of CMPO ([(iBu) 2 NPrH] + , [(iBu) 2 PrH 2 ] + and CMPO-carboxylic acids) were determined by ESI-MS; which is consistent products identified in previous studies.The generally lower G-values determined for test loop irradiation compared to static irradiation experiments clearly points out the importance of performing radiolytic degradation studies using oxygenated, mixed aqueous and organic solutions. The actual mechanism by which dissolved oxygen present in the test loop ameliorates the radiolytic degradation is not known. However, the rapid reaction of oxygen with carbon centered radicals would produce less reactive peroxyl radicals. Further studies are necessary in order to develop a complete understanding of the role played by dissolved oxygen in the inhibition of radiolytic degradation of solvent extraction process solvents.Gamma radiolysis results in a small increase the distribution ratios in the strip section of the TRUEX flowsheet (D Am = <0.001 at 0 kGy absorbed dose to D Am = 0.015 at 1300 kGy absorbed). Even the distribution ratio determined for the highest absorbed dose is not expected to adversely impact operation of the stripping section of the TRUEX flowsheet. However, the generation of degradation products in the aqueous phase and the radiolytic destruction of lactic acid and DTPA may have serious impacts on a subsequent TALSPEAK process. Close coupling of the TRUEX and TALSPEAK operations may help to mitigate these effects by limiting the gamma dose to the strip product solution.