Abstract: Subway has become one of the most important traffic tools for the public in nearly all the provincial capital cities in China. To confirm the radiation safety in this special underground spaces, a one-year survey of radon activity concentration measurement was carried out in all metro stations at Line-one. Totally 25 stations were involved. Passive integrated radon cup monitor with CR-39 as a detector was adopted for radon integrated measurement. For measurement quality control, the background track density of CR-39 was strictly defined and controlled during operation of the survey. The annual average radon activity concentration of all the 25 stations is (13.9±3.7) Bq/m³ range from 6.4 to 32.9 Bq/m³. For seasonal variation, radon activity concentration in winter was obviously higher than the other three seasons. It was (18.1±2.2) Bq/m³. For Spring, Summer and Autumn, they were (12.7±1.9), (12.9±3.5) and (12.4±4.4) Bq/m³ respectively. Comparisons of different stations and different floors were also performed and no statistically significant difference was observed.

Key words: Nanning city, metro station, radon activity concentration, CR-39, quality control