March 15, 2021: PhD public defense – Nancy Wanna – Method development for spent nuclear fuel characterization using isotope dilution HPIC-SF-ICP-MS - UGent

Name: Nancy Wanna

Date: March 15, 2021 - 16h-18h00 CET

This is an online event.

Method development for spent nuclear fuel characterization using isotope dilution HPIC-SF-ICP-MS

Characterization of spent nuclear fuel (SNF) is performed for criticality safety and nuclear safeguards at the back-end of the nuclear fuel cycle, i.e. SNF management. For the experimental determination of SNF burn-up, the concentrations of uranium (U), plutonium (Pu) and neodymium (Nd) (which is a fission product monitor) are determined by using radiometric and mass spectrometric methods. SNF components must be separated into individual fractions using chromatography prior to mass spectrometric analysis using thermal ionization mass spectrometry (TIMS) and inductively coupled plasma - mass spectrometry (ICP-MS), to avoid isobaric overlaps (e.g. 238U and 238Pu). TIMS and ICP-MS are based on accurate and precise isotope ratio measurements, to determine the elemental concentrations and nuclide-specific compositions of U, Pu and Nd in SNF. The determination of the elemental concentration and nuclide-specific composition of gadolinium (Gd) can also be of interest in the case of experimental fuels such as “Gd fuel”, where Gd is included in the fuel assembly as a burnable neutron absorber to improve reactor performance.

During this PhD a method based on isotope dilution sector field (SF) ICP-MS coupled with high pressure ion chromatography (HPIC), was developed to determine the concentrations and isotopic compositions of U, Pu, Nd and Gd in SNF. This project stems from SCK CEN’s efforts to minimize the radiation risk to the operator and to increase sample throughput for SNF characterization, which is currently accomplished by separating SNF components using gravitational ion chromatography (which can take up to two weeks) followed by their analyses using TIMS and alpha spectrometry (an ISO 17025 accredited method). Firstly, a method requiring less than 60 minutes for the separation of the elements of interest using HPIC-SF-ICP-MS was developed and validated. Secondly, the SF-ICP-MS parameters and different calculation methods were investigated to obtain the most precise isotope ratios from transient signals. Thirdly, the concentrations of U, Pu and Nd in a UOx SNF and those of U, Pu, Nd and Gd in a “Gd fuel” were determined by using isotope dilution HPIC-SF-ICP-MS. Finally, an overall uncertainty budget for isotope dilution HPIC-SF-ICP-MS was derived using the bottom-up approach, which was used to compare this isotope dilution HPIC-SF-ICP-MS method with the existing isotope dilution TIMS and alpha-spectrometry method. The amount fractions obtained using isotope dilution HPIC-SF-ICP-MS for U, Pu, Nd and Gd in both fuel types were similar (± 1.5 %) to those obtained using isotope dilution TIMS and alpha spectrometry. The expanded uncertainties on the mass fractions of Nd in UOx fuel and Gd in “Gd fuel”, obtained using isotope dilution HPIC-SF-ICP-MS were smaller than those obtained with isotope dilution TIMS. On the other hand, the developed method was limited by its background signals (blank and instrumental background) in the case of fuels with low levels of fission. Overall, the isotope dilution HPIC-SF-ICP-MS was found to be a fast, safe and accurate method to characterize SNF samples in just two days.

Promotor:

  • Frank Vanhaecke (UGent)

SCK CEN mentors:
  • Karen Van Hoecke (SCK CEN)

  • Andrew Dobney (SCK CEN)

  • Mirela Vasile (SCK CEN)

Click here for a list of obtained PhD degrees.