Highly Efficient and Selective Dissolution Separation of Fission Products by an Ionic Liquid [Hbet][Tf2N]: A New Approach to Spent Nuclear Fuel Recycling.

Here, we propose the use of carboxyl-functionalized ionic liquid, [Hbet][Tf2N], to separate the fission products from spent nuclear fuels. This innovative method allows the selective dissolution of neutron poisons, lanthanides oxide, as well as some fission products with high yield, leaving most of the UO2 matrix and minor actinides behind in the spent nuclear fuel and accomplishing the actinides recovery as a group. Water-saturated [Hbet][Tf2N] can dissolve lanthanides oxide from simulated spent nuclear fuel with a dissolution ratio of 100% at 40 °C. However, the dissolution of uranium is almost negligible (<1%) under the same conditions. This big difference in dissolution provides a novel separation approach to spent nuclear fuel recycling and may open new perspectives for spent nuclear fuel reprocessing. The recovery of Nd and U from metal-loaded ionic liquids and the recyclability of the ionic liquid [Hbet][Tf2N] have also been investigated. Furthermore, a U/ x value related to the lattice energy U of metal compound M xO y is used to elaborate the solubility. This work represents the first case for efficient fission products removal by selective dissolution, avoiding the complete dissolution of spent nuclear fuel, the producing of the large high-level radioactive waste, and reducing environmental hazards.

The effect of sample stability on the determination of radioactivity for various radionuclides by liquid scintillation counting.

For measuring a sample stored for a long period of time using liquid scintillation counting (LSC), it is necessary to study the long-term stability of the sample. The effect of sample stability on the determination of radioactivity for (241)Am, (90)Sr/(90)Y, (137)Cs, (147)Pm, (237)Np/(233)Pa, and (3)H by LSC has been investigated. The variation of quench level over time can be an indication of sample stability. If the variation in a sample is little, the effect of sample stability on the determination of the above radionuclides can be neglected. Otherwise, the sample stability will have impact not only on the counting efficiency (especially for low energy ß emitters), but also on the results of α/ß discrimination. For studying the stability of a sample, special attention should be paid to the radionuclides with chemical form apt to be adsorbed, because the quench level of a sample cannot be reflected by the quench index SQP(E) alone when significant physical quench exists. Shaking a sample stored for a long period of time and checking the LSC spectra can give the information on physical quench in the sample. In the range of this study, OptiPhase Hisafe 3 has much better quench resistance than Ultima Gold AB.

A method for optimum PSA setting in the absence of a pure α or ß emitter and its application in the determination of (237)Np/(233)Pa.

In the application of liquid scintillation counting (LSC), the α/ß discrimination is carried out with the function of pulse shape analysis (PSA), which requires the setting of the optimum PSA level. The optimum PSA are usually determined by the generation of cross-over plots, whereby a pair of vials, one containing a pure α emitter and the other a pure ß emitter, is counted. However, in some cases such as the determination of (237)Np/(233)Pa, a pure α emitter or a pure ß emitter is not available. Therefore, we have developed a new approach to set the optimum PSA by measuring the sample itself of mixed α/ß emitters. The count rate of the sample in the α-multi-channel analyzer changes monotonically with the increase of the PSA, and there is always an inflection point which is related to the optimum PSA. By fitting the data near the inflection point with the function y=ax(3)+bx(2)+cx+d, we can obtain the optimum PSA as -b/(3a), which can be used to determine the radioactivity of (237)Np/(233)Pa. The results obtained with this new approach were in good agreement with those obtained by HPGe γ spectrometry that was calibrated with an LSC sample of (237)Np/(233)Pa under a radioactive secular equilibrium. The new approach is promising to be used in simultaneous determination of gross α and ß emitters, especially in the absence of a pure α or ß emitter.

The long-term stability on basic performances of a diisopropylnaphthalene-based liquid scintillation cocktail.

The long-term stability of a cocktail is very important for liquid scintillation counting. The expiry date of a cocktail labeled on the container is usually one to three years later than the manufacture date, which is fairly short for the convenience of purchase, storage and use. Three batches of a diisopropylnaphthalene-based aqueous-miscible cocktail, Ultima Gold AB, with a span of 18 years of storage, have been compared on their basic performances, i.e. background count rate, counting efficiency, quench resistance, and α/ß discrimination. We found that the 18-year storage has less impact on the basic performances than batch-to-batch variability in cocktail compositions, which means Ultima Gold AB has very good long-term stability. Therefore, in practice Ultima Gold AB can be used even beyond its expiry date, if it is properly stored for less than 18 years. This result will bring much convenience to plan the purchase, storage and use of the cocktail. In addition, the influence of statistical fluctuations on the quench parameter SQP(E) has been studied.