Assessment of the Nuclide Inventory for Uranium-Contaminated HEPA Filter Wastes

Around 3,000 units of spent HEPA filter waste at KAERI have been dismantled into a filter frame and filter media part, where most radioisotopes are captured, for efficient management. The filter media generated from the same facility were then compacted into a 200- L drum, after taking the representative samples for the assessment of the nuclide inventory of them according to the sampling procedure. In general, uranium existing in the waste could be analyzed using radiochemical methods such as alpha spectrometry, a liquid scintillation counting (LSC) system, and mass spectrometry. Although these methods can be processed with low detection limits by using the chemical pre-treatment of samples and the specific detector, time and cost constrains compared with their accuracy dictates the use of a simpler method of application. High resolution gamma spectrometry can simply and easily provide a reasonable estimate of the uranium activity as a less time and cost consuming technique. In this study, a high purity germanium (HPGe) detector was employed to determine the activity of uranium-contaminated HEPA filter waste. The activity of U-235 and U-238 was identified by the analyses of a gamma ray peak of 143.76 keV belong to U-235 and of the daughters of U-238 such as Th-234 and Pa-234m with a secular equilibrium. To confirm their feasibility using gamma ray spectroscopy, the analysis results were compared with the gross alpha activity in the same sample