Speakers
Description
According to the regulatory guidelines of the Nuclear Safety and Security Commission of South Korea, the activity concentrations of fourteen key radionuclides, including Nb-94, must be determined for the acceptance of radioactive waste, and analytical laboratories are required to demonstrate the capability to evaluate activity levels down to 1% of the disposal limit.
Although Nb-94 can be directly measured by gamma spectrometry without chemical separation, elevated background caused by Compton scattering from coexisting Co-60 often leads to increased minimum detectable activity (MDA), making it difficult to satisfy regulatory requirements. In addition, accurate determination of Nb-94 is essential for deriving scaling factors for heterogeneous radioactive waste such as DAW(dry active waste), sludge, spent resins, and concentrated powders.
In this study, a separation method was developed for the determination of Nb-94 radionuclide without employing anion exchange chromatography for Nb separation. A selective Fe(OH)3 precipitation step using Fe carrier at pH 4.5–5.0 was applied. Inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed that more than 99.5% of Fe and Nb were retained in the precipitate, while over 85% of Co remained in the supernatant. If the gamma results do not satisfy the MDA of Nb-94, the solution is evaporated to be dried and dissolved in 0.5 M nitric acid. The insoluble residue containing Nb was dissolved using NH₄Cl/HF and directly analyzed by gamma spectrometry.
The proposed pretreatment procedure enables efficient removal of Co interference and reliable recovery of Nb-94 without dedicated chromatographic separation. As a result, the MDA of Nb-94 was successfully reduced below 1% of the disposal limit, thereby improving analytical sensitivity of Nb-94 and operational efficiency for routine radioactive waste characterization