The fate of xenon-131 from iodine-131 absorbed on the silver zeolite samplers

Wei-Hsung Wang, Purdue University

Abstract

The purpose of this study was to investigate whether xenon-131, the decay daughter of I-131, was retained in or escaped from the silver zeolite cartridge after iodine-131 had been adsorbed in the cartridge. Currently, silver zeolite cartridges are used in the nuclear power industry to adsorb the radioactive iodine gas in sampling lines because of their high retention efficiency for gaseous iodine but not for noble gases. If xenon-131 is desorbed and escapes from the silver zeolite cartridge, the surfaces originally occupied by iodine-131 in the silver zeolite cartridge may be vacant and thus available to adsorb other iodine gas molecules. The reusability of silver zeolite cartridges may reduce the sampling cost and radioactive waste volume and also preserve the silver resource. A silver zeolite cartridge containing only iodine-131 of known activity in a cartridge holder was connected with a blank charcoal cartridge in another cartridge holder. The end of each cartridge holder was sealed so the diffusion of xenon was contained in a closed system. Radioactive xenon-131 m, the daughter of iodine-131, was used as an indicator for stable xenon-131. The absence or presence of xenon-131m on the charcoal cartridge was used to determine if xenon-131 was desorbed from the silver zeolite cartridge. A NaI scintillator was used to detect iodine-131 and a HPGe detector was used to detect xenon-131 m. The desorption fraction of xenon-133 from the silver zeolite cartridge was found to be 0.66 ± 4.3% and the retention fraction of xenon-133 in the charcoal cartridge was found to be 0.61 ± 7.5%. Xenon-131m was frequently present in the charcoal cartridge. This showed that xenon131 was desorbed and escaped from the initial occupied sites in the silver zeolite cartridge after iodine-131 decayed. The amount of xenon-131m escaping from the silver zeolite cartridge fluctuated from day to day. This is thought to be due to what is known as the tunnel blocking effect. This effect has been described in the literature and involves the random location of xenon-131m atoms in the microscopic infrastructure of the silver zeolite.

Degree

Ph.D.

Advisors

Ziemer, Purdue University.

Subject Area

Occupational safety|Radiation|Nuclear physics

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