Objective:
Zeolite which is made of a special crystalline structure is a naturally occurring mineral group and can be used in radioactive waste management for site remediation /decontamination. There are a wide variety of naturally occurring and synthetic zeolites, each with a unique structure. The cations in zeolite are highly mobile and can be exchanged for other cationic species. On the other hand, bentonite forms from weathering of volcanic ash. This material may be used as an engineering barrier to enclose nuclear waste. In this study, radon reducing properties of zeolite and bentonite have been investigated. Methods: Using radioactive lantern mantle, a radon prone area with radon levels reaching the EPA’s action level (200 Bq/m3) was designed. Two sets of identical chambers (cylindrical chambers, diameter 10 cm, height 16 cm) were used in this study. No zeolite/bentonite was used in the 1st set of the chambers. A thin layer of either zeolite or bentonite powder was applied to the base of the first set of chambers. An unburned radioactive lantern mantle (activity 800 Bq) was placed in all chambers (both sets) to artificially increase the radon level inside the chamber and simulate the condition of a radon prone area. Radon level monitoring was performed by using a PRASSI portable radon gas survey meter.
Results: After placing the cap on its place, the radon levels inside the 1st set of the chambers were 871.9, 770.3, 769.2 and 635.7 Bq/m3 after 15, 30, 45 and 60 minutes respectively.
Zeolite significantly decreased the radon concentration inside the chambers and radon levels were 367.9, 435.4, 399.0 and 435.4 Bq/m3 after 15, 30, 45 and 60 minutes. The observed reduction in the radon level was statistically significant. As the radon concentrations in identical chambers with
Bentonite were 550.7, 526.5, 536.2 and 479.8 Bq/m3 after 15, 30, 45 and 60 minutes respectively, it is evident that zeolite is more efficient in reducing indoor radon levels.
Conclusions:
Zeolite and bentonite significantly decrease the indoor radon level. The efficiency of zeolite in radon reduction is significantly higher than that of bentonite. As both zeolite and bentonite can be found in many parts of IR Iran, these mineral sorbents can be used in national remedial action programs.