JRP CALL information
Supported By

European Commission

Short description of the work
A. Puranen1, O. Roth1, D. Jädernäs1 and E. Curti2
1 Studsvik Nuclear AB, SE-61 182 Nyköping (S)
2 Nuclear Energy and Safety Department (NES), Paul Scherrer Institut, 5232 Villigen (CH)

Talisman grant TALI_C03-10 (Selenium redox speciation in high burn-up fuel)
In this study, we investigated oxidation state and coordination environment of Se in high-burnup UO2 spent nuclear fuel (SNF) samples from the Oskarshamn-3 boiling water reactor by means of micro X-ray absorption near-edge spectroscopy (m-XANES) and micro X-ray fluorescence (m-XRF). In spite of the low Se concentrations (about 100 ppm), the heavy UO2 matrix and the extremely small sample size, we were able to collect good quality XANES spectra, both from the core and rim region of the probed fuel pellet.
Two spent fuel microsamples of ~ (30 x 15 x 5) mm3 size were prepared by Focused Ion Beam (FIB) milling at Studsvik Nuclear AB, using a Zeiss® equipment with a Ga ion source. Both samples originate from a “matchstick”-sized strip of the same pellet (average burn-up 62.9 GWd/tU) encompassing the entire diameter of the pellet (from clad to clad) and passing through the center. The first sample (CEN) was cut from the central part of the pellet; the second chip (RIM) was prepared from the periphery and reached the fuel/gap interface.

All measurements of absorption and emission spectra were carried out in fluorescence mode, using a micro-focused monochromatic X-ray beam of about 2-3 mm (vertical) x 5 mm (horizontal) size in the energy ranges 12.6-13.2 keV (Se-K edge and Se-Ka fluorescence regions) and 17.2-17.3 keV (U-La fluorescence). The absorption spectra of Se reference compounds where measured simultaneously in fluorescence and transmission. A Ketek® single element Si detector was used to measure energy-dependent fluorescence intensities, while the transmitted signal was detected with a photodiode. Energy calibration was carried out using a Se(0) reference.
Several elements (U, Nd, Se) were mapped by micro-XRF over the limited available surface of both FIB samples. Within the precision of the method, the element distributions (including Se) were found to be uniform. Fourteen Se K- XANES spectra were collected on the two chips, including two approaching EXAFS quality. All XANES spectra proved to be strikingly similar to those previously measured on similar SNF from the Leibstadt reactor. Nevertheless, very small systematic differences were observed between the spectra of the two samples from Oskarshamn-3: Compared to those from the rim region, the normalized spectra from the center of the pellet are shifted by 0.5 eV to lower edge energies and have significantly larger edge crest heights. These differences are minor and lie within the standard deviation envelope defined by the spectra recorded on Leibstadt SNF. At the current status of data analysis, we cannot exclude that such differences might be due to instrumental bias.

Main visitor contact data
Name: Dr Anders Puranen
Organisation: Studsvik Nuclear AB

JRP Identification
JRP nr: TALI-C03-10
JRP title: Selenium redox speciation in high burn-up fuel
JRP scope: Scope 3: Actinide materials

Visited Associated Pooled Facility
Visited APF during the stay: PSI - MicroXAS Beamline
Name of the APF Contact Person: Daniel Grolimund

Other APF and organisation involved in the JRP
Other organisations involved:
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 6/2/2014
End date of the stay: 6/6/2014
Quantity of access: 15
Access Unit: Shifts
Misc.:

Other APF visitors of the JRP during the stay
Visitor 2: Enzo Curti (Paul Scherrer Institut)
Visitor 3:
Visitor 4:
Visitor 5: