Abstract: The applicability of several tracer gases for performance tests of iodine adsorbers were studied. Tracer gases investigated are trichlorofluoromethane (R-11), 1,1,1,2,2,3,4,5,5,5-decafluoro-pentane (Vertrel-XF), perfluoromethycylcopentane (PMCP), perfluoromethycyclohexane (PMCH), and perfluorodimethylcyclohexane (PDCH). Desorption behaviors of tracer gases from activated carbon affected by molecular weight, boiling point, temperatures, air velocity, moisture, water content of activated carbon were studied. R-11 was used in measuring mechanical leakage rates of iodine adsorbers at different levels of moisture loading. Meanwhile desorption efficiency of activated charcoal bed were measured after R-11 injection. Results show that the above alternative substitute gases (tracers) all meet the six criteria in Non-Mandatory Appendix TA-C of AG-1: Substitute Gas and Aerosol Substitute Selection Criteria. R-11 exhibited minimal desorption from activated carbon at less than 20% relative humidity of gas stream and 15% water content of activated carbon.Its result was more accurate.R-11 is now generally used in domestic nuclear power plants to measure mechanical leakage rates of iodine adsorbers.

Key words: tracer gas, leakage rate, desorption