Background
Se-79 is a beta emitting fission product of U-235 in nuclear reactors. It is a radionuclide of interest for decommissioning nuclear reactors due to its long half-life (105 years). Se-79 exists in trace level concentrations with low activity in nuclear waste; however, it is one of the nuclides that are requested to monitor in waste packages before their final disposal. Despite its relevance, a clear gap exists in literature regarding this fission product and its analysis.
Objectives
This thesis project aims to:
- Optimization of separation procedures for Se-79 from various matrices (metals, graphite, concrete, ion exchange resin).
- Comparative evaluation of analytical methods.
- Identify the matrix-specific limitations in routine monitoring.
Proposed approaches
Separation approaches:
- Distillation of Se from HCl solution – rapid method, limitations need to be identified for each sample matrix. [1]
- Cation-exchange resin with AgNO3 precipitation – effective but time-consuming. [2]
Measurement techniques:
- Liquid Scintillation Counting (LSC) – sensitive but requires removal of interfering beta-emitting radionuclides.
- ICP-MS/MS: good for trace-level detection but interfering isobaric interferences in each sample type needs to be identified (e.g., Br-79). Potential for using different reaction/collision gases (H2, O2, CH4, NH3) to further separate Se.
Se-75 can be used as radioactive tracer for method development, yield corrections, and validation.
Expected outcomes
- Overview of Se chemistry and existing methods for Se-79.
- Reliable workflow for Se-79 separation and measurement useful for routine monitoring of decommissioning waste materials.
- Quantitative evaluation of methos, including detection limits and recoveries.
Location
Institute for Energy Technology, Environmental Protection and Radiation Safety department.
Kontaktperson
Dep. Head Ingrid Helen Hauge