INFLUENCE OF SAMPLING FLOW RATE ON THORON EXHALATION RATE MEASUREMENTS BY THE CIRCULATION METHOD

Evaluation of accurate measurement methods for radon exhalation rate with advection effect and application in field

In decommissioning of a uranium tailings pond, radon exhalation rates on a beach surface should meet regulatory standards. Accurate measurements of the radon exhalation rate are demanded. However, current studies fail to consider the impact of advection under temperature variations or pressure gradients caused by gas movement on measurements using an accumulation chamber. Two proposed methods were therefore evaluated to accurately measure radon exhalation rates on the loose medium surface under advective conditions. Repeated experiments were conducted on a laboratory experimental platform filled with uranium tailings sand under advective flow rates of 0.03 and 0.3 L/min to validate the stability and reliability. Deviations between measured and true values were 0.1-6.1 % and 6.3-29.2 % for the two methods, respectively. Subsequently, numerical simulation was used to analyze defects of traditional methods and mechanisms of the new methods. In a field study, all methods were compared, and a predictive map of radon exhalation rates was created using interpolated data from 20 random sites using the new method. Results from the proposed methods, compared with traditional ones, were closer to true values under advective conditions, and accurate assessment of beach surface treatment was expected.

Improved data analysis techniques for calculating more accurate radon and thoron exhalation rates from building interior solid walls

The impacts of mathematical models and associated parameters on radon (222Rn) and thoron (220Rn) exhalation rates based on in-situ testing at building interior solid walls were demonstrated to improve data analysis techniques. The results showed that the heterogeneity of their activity concentrations within the measurement system was more significant for thoron than radon. The diurnal variation in indoor radon should be considered for better data quality. In conclusion, a model should be appropriately made and selected under the purposes and accuracy requirements of the exhalation test.

Novel approaches for accurately measuring radon exhalation rate and mechanism interpreted by numerical simulation

Measurements of radon exhalation rate using traditional methods can be affected by back-diffusion or differential pressure in the accumulation chamber, resulting in deviations between the measured and the true values. To obtain an accurate radon exhalation rate for evaluation of radon-risk regions, two novel approaches of measurements based on traditional methods were proposed. Repeated experiments were implemented on a self-designed stainless cylindrical vessel filled with uranium tailings sand. The measured radon exhalation rates on average were 0.51 ± 0.02 and 0.52 ± 0.02 Bq m-2 s-1 for the two proposed methods, with 0.02% and 0.04%, respectively, deviations from the theoretical value. In addition, numerical techniques were employed to interpret the defects of traditional methods and mechanisms of proposed approaches to measure accurate values. Two novel approaches have significantly reduced the impact of back diffusion and differential pressure inside the chamber and consumed less time.

Impact of humidity and flowrate on the thoron measurement sensitivity of electrostatic radon monitors

The accurate measurement of thoron activity concentration is an important issue in both thoron exposure evaluation and in reducing its influence on radon measurement. For radon monitors based on electrostatic collection technique and an alpha spectrometry analyser, air humidity and sampling flowrate are key factors influencing the sensitivity of thoron activity concentration measurement. For the purpose of improving thoron measurement sensitivity and stability, theoretical derivation and experimental studies were systemically performed in this study. The results show that thoron measurement sensitivity decreases as a negative exponential function with absolute humidity increasing, and the sensitivity of thoron is much lower than that of radon under the same conditions, which is mainly caused by the small value of the concentration ratio of thoron inside to outside of the chamber. When the air exchange rate of the measurement chamber (sampling flowrate/inner volume) increases, the measurement sensitivity of thoron gas first increases rapidly and then decreases slowly after reaching its maximum at the air exchange rate of 0.24 s^-1. In practice, in the normal air exchange rate range (for example <0.05 s^-1), increasing the sampling flowrate could greatly improve the thoron measurement sensitivity, which consequently suggests an effective way to update thoron measurement under the present conditions of the monitor.