Yuanzineng kexue jishu (Feb 2024)
Development of Rapid and Highly Sensitive On-site Automatic Monitoring System for Radioxenon Isotopes
Abstract
For the purpose of the peaceful, safe and reliable application of nuclear technology, the monitoring of radioactive gas is one of the most important items for on-site inspection of CTBTO and safety monitoring of nuclear installations, which could rapidly and correctly discriminate nuclear activity of violation treaty of CTBT (Comprehensive Nuclear-Test-Ban Treaty) and identify the leakage of nuclear installations. Since radio-xenon isotopes (mainly 131m,133,133m,135Xe) have distinguished features including high fission yields, leaking easily and spreading worldwide, notable decay properties and low ambient concentrations, which are seen as important monitoring objects. Based on the proposed principle combined with these techniques including dynamic adsorption at -110 ℃ ultra low temperature, impurity removal with hollow fiber membranes, and gamma spectrum monitoring with low background, a rapid and highly sensitive on-site automatic monitoring system for radioxenon was developed, which could sample, separate and measure radioxenon on-site with a rapid and efficient way. During the development process, the technological flow diagram for whole system was established, and the critical hardware components including impurity removal column, adsorption column, lead shield chamber, and sample container were designed. And then these elements were assembled as four modules about sampling, preprocessing, refrigeration and measurement units combined with other components such as three hollow fiber membranes, four flowmeters, two pressure sensors and a HPGe detector and so on. Meanwhile, two control softwares including upper computer and off-line control versions were designed. And the methods of efficiency calibration, recovery test, calculation of activity concentration and MDC (minimum detectable activity) of xenon, and uncertainty evaluation were studied. Then these parameters were tested including detection efficiency, recovery of stable xenon, MDCs of 133Xe and 135Xe, and uncertainties of measuring results. The experimental results show that the recovery of stable xenon is 79.9%, the MDC of 133Xe is less than 0.26 Bq/m3 within a 120 min cycle including sampling, enrichment and measurement, when the activity concentration of 222Rn and sampling volume are 20 Bq/m3 and 2 m3, respectively. Compared with technical specifications of other systems, the elapsed time of a cycle of the system developed in this paper decreases larger than 10 times of SAUNA-OSI and XESPM-Ⅲ systems, while the MDC of the systems is smaller than other rapid systems. Because this developed system has following features about high sensitivity, shorter monitoring period, automation during total process, it will provide a dominant and straightforward contribution to the on-site inspection (OSI) of CTBT, safety monitoring of the gaseous effluents and emergency monitoring for nuclear facilities, and will be a powerful supplement for current monitoring technique and systems.
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