Utredning av FOI:s metod för bestämning av totaldeponering av radionuklider

Authors:

  • Petra Lagerkvist
  • Catharina Söderström
  • Sofia Jonsson
  • Johan Kastlander
  • Peter Lundsten

Publish date: 2018-07-11

Report number: FOI-R--4607--SE

Pages: 32

Written in: Swedish

Keywords:

  • Total deposition
  • radionuclides
  • ion exchange resin
  • column
  • precipitation

Abstract

Collection and measurement of deposition of radionuclides is a part of the Swedish surveillance system for radiation protection. Collection of deposition is performed at four of the six air filter stations. The deposition is collected via a funnel placed at the roof of the station, the precipitation is passed through an ion exchange column, containing both anion and cation exchange resins. The contents of the column are ashed followed by measurement with gamma spectrometry to determine the deposited radionuclide activity. The current method used at FOI does not separate the anion and the cation resins before measurement and therefore a replacement consisting of a combined anion and cation exchange resin could be of interest. The collection efficiency of two different types of ion exchange columns have been investigated, the first being the one currently used, and the second type a column with an ion exchange resin of combination type. Laboratory tests, adjusted to correspond to common precipitation volumes, have been performed and the two types of column have also been used in parallel at the station in Kista. The column material have been measured before and after ashing to determine possible losses of collected activity during ashing. To investigate the temperature dependence of possible losses, column material spiked with only radioactive iodine have been ashed at different temperatures. Results from the efficiency and temperature tests are presented in this report. The results from the measurements show that both types of columns have a high collection efficiency for most of the tested radionuclides, >85 % for the anion/cation type and somewhat lower for the combination type, especially for ruthenium and tellurium. Nuclides present in an oxide form can pass through the column, and to collect these species another material might need to be added to the column. More than 30 % of the absorbed iodine are lost during ashing at 240ºC for both column types, already at 60ºC significant losses are detected. To be able to quantify the amount of radioactive iodine in deposition, the column material should preferably be measured before ashing, and calibration for this new geometry is necessary. For a complete investigation of the method the tests performed should be followed up with tests of the robustness, using larger amounts of precipitation. Expected species of the radionuclides in the precipitation need to be investigated. A prototype for rinsing of the precipitation funnel is presented in Appendix 1.

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