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[en] Current limitations of CANDU reactors to reliably locate defective >fuel< bundles have sparked interest into new identification techniques. Noble gas tagging, which would involve the addition of specific combinations of Kr and Xe isotopes to the fuel-to-sheath gap during manufacturing, has the potential to offer a means of locating failed-fuel bundles. The released tag with a given isotopic signature could be measured in the primary heat transport system by mass spectrometry. This technique would allow on-power failure location. Moreover, the technique could be of particular interest for demonstration irradiations with new fuel bundle designs. The viability of applying noble gas tagging to the CANDU reactor environment was examined by focusing on three critical aspects: the isotopically-appropriate choice of tag gas, the effects of the tag on fuel thermal performance, and the tag-detection ability of a typical mass spectrometer. Evaluations on the suitability of potential gas tags accounted for natural abundance, overlap with fission products, and neutron absorption cross-section, and yielded one krypton and several xenon isotopes. The impact of krypton and xenon gas additions to fuel-to-sheath heat transfer was modelled using a modified 2-D finite-element solver based on the COMSOL Multiphysics platform. The extent of fuel surface and centreline temperature increase was investigated over a typical fuel lifetime of 200 MWh kgU-1 by varying the fraction of backfilled helium replaced by krypton or xenon gas. The detection limits of two ICP-MS instruments (Thermo Elemental X7 and Varian 820-MS) were determined through measurements of aqueous krypton prepared by purging de-ionized H2O with specific concentrations of krypton gas. The prepared samples represented reactor conditions by spanning a concentration range of 10-12 to 10-9 (molKr/moH2O), inclusive of the expected tag concentration in a coolant grab-sample. Extrapolation techniques were applied to calculate the minimum aqueous concentration required for confident detection of Kr-78.