Abstract: A radioactive methyl iodine method is adopted to carry out the efficiency test of iodine adsorbers of ventilation systems for a nuclear power plant. Radioactive iodine source (Na¹³¹I) solution is used in the tests. During the operation and storage of the iodine source solution, an event that a small amount of ¹³¹I released into the ventilation system occurred and ¹³¹I was detected in periodic sampling of the exhaust stack. In order to prevent the problem before their occurring and to ensure safety, the cause analysis of this event was carried out and the results show that the main reason is the volatilization of ¹³¹I into the iodine source room when a small amount of Na¹³¹I solution attached to the inner wall of the syringe and the surface of the needle during the preparation of Na¹³¹I solution using a syringe in a glove box. The poor sealing of the bottle of Na¹³¹I solution stored in the iodine source cabinet is also a main reason for the volatilization of ¹³¹I. Therefore, some improvement measures are implemented with a good results in this nuclear power plant.

Key words: nuclear power plant, iodine adsorber, Na¹³¹I solution