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Uranium (U) and plutonium (Pu) contents in nuclear materials must be maintained to a definite level in order to get the desired performance of the fuel inside the reactor. Therefore, high accuracy and precision is an essential criterion for the determination of U and Pu. We already reported the voltammetric determination of Pu in the presence of U in fast-breeder-test-reactor (FBTR) fuel samples, but interfacial, coupled chemical reactions between U(IV) and Pu(IV) enhance the peak-current density of U(VI) reduction and thus make voltammetry unsuitable for the quantitative determination of U in the presence of Pu. Thus, developing a voltammetric method for the simultaneous determination of U and Pu is highly challenging. Herein, we report the simultaneous voltammetric determination of U and Pu in 1 M sulfuric acid (HSO) on a poly(3,4-ethylenedioxythiophene) (PEDOT)-poly(styrenesulfonate) (PSS)-modified glassy-carbon (GC) electrode (PEDOT-PSS/GC). The modified electrode shows enhanced performance compared with bare GC electrodes. The peak-current density for U(VI) reduction is enhanced in the presence of Pu(IV), but it attains saturation when [Pu]/[U] in solution is maintained ≥2. Hence, under these circumstances, the variation of Pu concentration no longer influences the U(VI)-reduction peak, and thus the quantitative determination of U in the presence of Pu is possible. No interference is observed from commonly encountered impurities present in FBTR fuel samples. This method shows accuracy and precision comparable to those of the biamperometry method. High robustness, fast analysis, simultaneous determination, reduced radiation exposure to the analyst, and ease of recovery of U and Pu from analytical waste makes it a suitable candidate to substitute the presently applied biamperometry method.

Plutonium(VI) / Pyrazolone / Synergism / Thermodynamics / DPSO / TBP / TOPO SummarySynergistic extraction of hexavalent plutonium was studied from HNO3 medium (0.05 M) with 1-phenyl, 3-methyl, 4-benzoyl, pyrazolone-5 (HPMBP) and different monodentate neutral donors viz. diphenyl sulphoxide (DPSO), tri-n-butyl phosphate (TBP) and tri-n-octyl phosphine oxide (TOPO) using benzene as a diluent. Thermodynamic parameters (AG, AH, AS) evaluated by performing the experiments at various fixed temperatures (288 Κ to 318 K) were compared with those reported previously for the bidentate neutral donors (DBDECMP, DHDECMP and CMPO). The net enthalpy changes were negative and comparable. The monodentate neutral donors, however, showed a larger decrease in the entropy values. Further, the negative values of enthalpy and entropy changes indicated that the organic adduct formation is an addition reaction as reported earlier for the bidentate donors. entropy changes counteracted the reaction. The negative entropy changes suggested the adduct formation reaction to be of addition type and not of substitution. It was considered worthwhile to evaluate these thermodynamic parameters by using different monodentate neutral donors of varying basicities with an objective of comparing the previously obtained data for Pu(VI) with HPMBP and various bidentate neutral donors. A comparison of the entropy changes in the two systems (monodentate and bidentate neutral donors) was considered to be important from the point of view of our earlier interpretation of the bidentates behaving as monodentates. Further, it was thought interesting to compare the behaviour of Pu(VI) vs. that of U(VI) with HPMBP and monodentate neutral donors reported earlier from our laboratory [7].

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Extraction / Third-phase formation / DHDECMP / HNO 3 / SANS / Deuterated dodecane Summary. The third-phase formation in the DHDECMPdodecane-HNO 3 system during the actinides extraction was investigated based on the densities of the phases formed and the acid uptake by the DHDECMP phase. The effects of various parameters like nature of acids, diluents, temperature of extraction, acid molarity, and concentration of DHDECMP on the Third-phase formation were studied. The third-phase formation was also explained on the basis of results of smallangle neutron scattering studies (SANS).

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