A NaI(Tl)-based radioactive noble-gas monitoring system used for radiation monitoring.

Radioactive noble-gas monitoring is necessary in nuclear facilities. A NaI(Tl)-based radioactive noble-gas monitoring system was developed. In order to increase the amount of air to be measured, the sample vessel of this system was larger than that of other systems, and was pressurized to about 5 × 105 Pa. In a laboratory experiment, technical ways to reduce the memory effect were investigated. In field tests, a method of spectra analysis was established and calibration coefficients and minimum detectable concentrations of 133Xe, 135Xe and 41Ar were calculated. Finally, detection ability was compared with other online monitoring systems.

Radon removal trap design and coefficient testing for the development of an effective radioxenon sampling, separation and measurement system.

To monitor low-level radioxenon isotopes activity concentrations in the bulk gases, a radioxenon sampling, separation and measurement system has been developed. The xenon enrichment factor of this system is more than 105 after the separation of impurities, including N2, O2, CO2and H2O, as well as radon and its progenies, such as 214Pb and 214Bi. Since radon and its progenies interfere with radioxenon measurement, they have to be removed before radioxenon counting. To separate radon from xenon, different dynamic adsorption coefficients of xenon and radon are used to design small radon removal trap to retain radon after eluting xenon, and the ratio between radon and xenon dynamic adsorption coefficient gives the adsorbent weight relationship between the xenon adsorption trap and its related radon removal trap. To test the effectiveness of radon removal, the relative measuring method is used by measuring γ-rays energies of radon progenies in canister filling with either the measuring sample prepared by the system or the original gas. The results show that the radon removal coefficient and the stable xenon recovery, which are two important parameters in the radioxenon system, are at the order of 10-6 and >70% respectively. These meet the specifications proposed by the Comprehensive Nuclear-Test-Ban Treaty Organization.

The determination of trace amounts of natural 133Xe in gas under high radon activity concentration levels.

Radioxenon monitoring has become one of the major concerns in both international monitoring systems and on-site inspection. The most important technical specifications for radioxenon system are the radon removal coefficient and the minimum detectable activity concentration. We have developed one kind of on-site radioxenon sampling, separation and measurement system, and have tested it under high radon activity concentration levels. The result shows the natural (133)Xe background activity concentration, the (133)Xe/(222)Rn ratio and the radon removal coefficient to be in the ranges 0.73-1.6 mBq/m(3), (1.5-3.5) × 10(-8) and (2.3-57) × 10(-8), respectively.