Simultaneous isotopic analysis of fission product Sr, Mo, and Ru in spent nuclear fuel particles by resonance ionization mass spectrometry

Abstract

Fission product Sr, Mo, and Ru isotopes in six 10-μm particles of spent fuel from a pressurized water reactor were analyzed by resonance ionization mass spectrometry (RIMS) and evaluated for utility in nuclear material characterization. Previous measurements on these same samples showed widely varying U, Pu, and Am isotopic compositions owing to the samples’ differing irradiation environments within the reactor. This is also seen in Mo and Ru isotopes, which have the added complication of exsolution from the UO2 fuel matrix. This variability is a hindrance to interpreting data from a collection of particles with incomplete provenance since it is not always possible to assign particles to the same batch of fuel based on isotopic analyses alone. In contrast, the measured 90Sr/88Sr ratios were indistinguishable across all samples. Strontium isotopic analysis can therefore be used to connect samples with otherwise disparate isotopic compositions, allowing them to be grouped appropriately for interpretation. Strontium isotopic analysis also provides a robust chronometer for determining the time since fuel irradiation. Because of the very high sensitivity of RIMS, only a small fraction of material in each of the 10 μm samples was consumed, leaving the vast majority still available for other analyses.

Zirconium analysis in microscopic spent nuclear fuel samples by resonance ionization mass spectrometry

“…However, previous work measured the 90 Sr/ 88 Sr ratio in this sample to be 0.566(7). 21 Together with the RIMS background-corrected 90 Zr/ 92 Zr ratio from this measurement of 0.63(3) and the reported pellet average concentrations of 88 Sr (435 ppm) and 92 Zr (769 ppm) from bulk measurements we expect a 90 Sr/ 90 Zr ratio of 0.51(2). Assuming all off-resonant ions on mass 90 are 90 Sr we measure a 90 Sr/ 90 Zr ratio of 0.09(1), which indicates a strontium suppression factor of 5.9(7).…”

“…Similar to U, Pu, Mo, and Ru, 11,21 the Zr isotopic composition is dependent on the sample's radial location within these fuel pellets. Fig.…”

“…Assuming all off-resonant ions on mass 90 are 90 Sr we measure a 90 Sr/ 90 Zr ratio of 0.09(1), which indicates a strontium suppression factor of 5.9(7). While the 90 Sr/ 88 Sr ratio does not vary significantly within a sample set of common origin and age, 21,39 this calculation does not account for differences between pellet average and sample-specific Zr composition. The given number can therefore only be taken as an estimate.…”

“…The isotopic compositions of actinides and other fission products in these samples were previously measured and are described in detail elsewhere. 11,21 In brief, the samples are 10 micrometer-sized cubes cut from two spent nuclear fuel pellets discharged from the Belgium pressurized water reactor No. 3 in September 1980.…”

“…For example, 90 Sr ( T 1/2 = 28.91 years) interferes with 90 Zr and 96 Mo interferes with 96 Zr. 20,21 In addition, while the isotopes of Mo and Nb are shielded and thus not significantly produced in reactors, their stable isotopes can be an Zr isobaric interferences if they are introduced during sample preparation and chemical pretreatment in traditional mass spectrometric approaches.…”