RADSEARCH MEASUREMENTS FOR THE QUANTIFICATION OF CESIUM AND COBALT IN LEGACY SODIUM LOOP SECTION WASTE

摘要

Sodium loop sections were irradiated in several nuclear reactors at the Idaho National Laboratory (INL) in the 1970's and 1980's in order to study the effects of high temperature and off normal conditions. The remaining waste was packaged for disposal in dual layer steel waste containers at INL. These containers have recently been retrieved by CH2M-WG Idaho, LLC. (CWI) for processing to separate the reactive metals from the matrix and then package the waste for final disposal. Historical data on the waste containers indicated a significant quantity of cesium-137 in the various containers and this information has been used to calculate the expected dose-rate and current Cs-137 content. The expectation was that other nuclides would have decayed away in the roughly 40 years since the packages were loaded. The ANTECH RadSearch G3050 Gamma Camera was used to take measurements of the waste containers in a number of configurations in order to establish how the canisters could be assayed prior to processing. Two canisters were selected for measurement, which are currently stored in concrete shielded containers. Three measurement configurations were employed including: indirect measurement through the concrete shield, indirect measurement through a carbon steel shield bell used to transfer such containers, and direct measurement of the container in open air. The first two measurements showed roughly the location of the container within the shield; however, the spectra were degraded so nuclide identification was not possible. Measurement of the container in open air provided data on the dose-rates and the nuclides present. Contact dose-rates on the measured containers were typically about 2 Sv/h (200 rem/h) and in one case the dose-rate was roughly a factor of 100 higher than expected from the recorded Cs-137 content. A goal of the measurement campaign was to investigate which radionuclides were contributing to the high dose-rate and to gain information on the spatial distribution of the radionuclides. Results of the measurements showed that the Cs-137 content was as expected but that in some cases, a significant quantity of Co-60 was also present. The measurements also showed that the Cs-137 spatial distribution was not uniform.