Origin determination of reactor produced plutonium by mass spectrometric techniques: application to nuclear forensic science and safeguards

The age and production type, i.e. origin, are highly important parameters to be revealed when seized Pu from illicit trafficking has to be analysed. In addition, in a view of pending Fissile Material Cut-off Treaty, the age determination of Pu enables to control the agreement. The ages of Pu bulk samples were determined from the Pu/U, Pu/U and Pu/U ratios by IDMS and the results were compared to the ages obtained from the Pu/Am ratio by gamma-spectrometry. The ages from three different Pu/U ratios were uniform showing that the Pu/U separation, when reprocessing the spent fuel, was complete. Small differences between ages from the Pu/U and Pu/Am ratios were observed, giving consistently higher ages of a few per cent from the Pu/Am ratio. This is most likely due to the Am traces remained in Pu after the reprocessing. Particle analyses were performed from the above mentioned Pu/U ratios by SIMS. Due to the different ionisation efficiencies of Pu and U, a relative sensitivity factor (RSF) had to be determined for the Pu/U ratio. The RSF was then applied to correct the measured ratios. The SIMS showed its strength when using the technique to determine the age of powder mixtures. The ages of different components are possible to reveal, which is a big advantage compared to the bulk analysis, where this is not possible. The production of the Pu material, i.e. the reactor type, was determined using the isotopic correlation technique. The Pu compositions for different spent fuels (Candu, LWR, graphitemoderated LWR, Magnox, fast reactor and typical research reactors) were calculated by ORIGEN2 and SCALE computer codes and they were plotted in the graph, which separates the reactor types depending on their characteristic neutron spectra and initial U enrichments. The reactor types were possible to reveal in most of the cases and when not, these reactor types could be excluded to be the origin. A new detector type TIMS, Multi-Micro-Channeltron-TIMS, was introduced. The MMCTIMS allows the reduction of the needed sample amount by a factor of 1000 compared to the conventional Faraday cup detector TIMS. This is very important because it is desired to manage as small samples as feasible when handling health hazardous materials like actinides.

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