Radioactive analysis of a spent HEPA filter using the distribution characteristics of the captured radionuclide

To investigate the species and the distribution of the captured nuclides in a HEPA filter, it was dismantled into a metal part and a filter medium part to obtain a filter medium. From the nuclide analysis results for a filter medium part through pre-treatment of it, it was possible to obtain three kinds of typical distributions in view of the distribution of the captured nuclides in the filter medium. When considering these distribution characteristics of the captured radionuclide, the region showing the high concentration of the captured nuclides was the intake or the outlet part of the HEPA filter. On the other side, the middle part generally represented a uniform distribution below the average concentration of the captured nuclides. Therefore, in the event of taking a representative sample of a HEPA filter at the intake and the outlet part, the results of a nuclide analysis for that sample could be estimated as existing in the range from 1.0 to 1.5 times the real concentration of the nuclides captured by a filter medium. As a result, to conduct a radionuclide assessment of a spent HEPA filter without a dismantlement of it, the analysis results for a representative sample taken from both the intake and the outlet part of a spent HEPA filter could be regarded as an average value for the corresponding HEPA filter. (author)