Factors influencing temporal variations of radon concentration in high-rise buildings

Ra-226 in building materials as a source of indoor radon in high-rise residential buildings in Russian cities

The problem of indoor radon in high-rise buildings is mostly associated with exhalation from building materials. Characterization of the radon entry from building materials by diffusion is required to provide a proper control of the population indoor radon exposure. To analyze the relationship between the content of Ra-226 in building materials and the indoor radon concentration the results of the following surveys in high-rise buildings in Russian cities were used: 1) indoor radon (>1000 apartments), 2) natural radionuclides in the building materials in existing buildings by means of non-destructive field gamma spectrometry (100 apartments). The surveys were carried out in nine large cities in different climatic zones. The radon entry rate due to diffusion from building materials, D, normalized to Ra-226 activity concentration, Ra, is in the range of 0.2-0.6 (Bq/m3/h)/(Bq/kg), depending on the type of building materials and building construction. In new multi-story buildings, the typical D/Ra ratio can be assumed to be 0.4 (Bq/m3/h)/(Bq/kg). In new energy-efficient buildings, the ratio of the radon concentration to Ra-226 activity concentration is on average 2.1 times higher than in multi-story buildings of lower energy efficiency built before 2000. The average radon exhalation rate from the building materials, normalized to Ra-226 activity concentration, is estimated to be 0.25 Bq/m2/h.

Relationship between Ra-226 activity concentration in building materials and indoor radon concentration: An example of Russian high-rise residential buildings

The worldwide trend toward the construction of high-rise buildings with high energy efficiency highlights the role of building materials as a source of indoor radon in the modern urban environment. The aim of the study is to analyze the relationship between the Ra-226 activity concentration in building materials and indoor radon concentration using the example of multi-story buildings in Ekaterinburg. Measurements of the activity concentration of natural radionuclides in building materials were carried out using a new non-destructive method. A radon survey conducted early provided the data on indoor radon concentrations in the same apartments. The obtained Ra-226 activity concentrations in building materials in high-rise buildings were found to be relatively low, ranging from 9.1 to 51 Bq/kg. The typical radon entry rate by diffusion from building materials for modern Russian multi-story buildings can be accepted as equal to 0.5 Bq/(m3∙h) per 1 Bq/kg of Ra-226 activity concentration. Ra-226 in building materials has been shown to be a primary source of indoor radon in modern high-rise buildings, where this factor can cause indoor radon concentrations above the reference level of 100 Bq/m3 at low air exchange rates. The activity concentration of Ra-226 in building materials should be considered a separate parameter for regulation within the national radiation protection systems.

Development of a "222Rn incremented method" for the rapid determination of air exchange rate using soil gas

The air exchange rate (AER) is a critical parameter that governs the levels of exposure to indoor pollutants impacting occupants' health. It has been recognized as a crucial metric in spreading COVID-19 disease through airborne routes in shared indoor spaces. Assessing the AER in various human habitations is essential to combat such detrimental exposures. In this context, the development of techniques for the rapid determination of the AER has assumed importance. AER is generally determined using CO₂ concentration decay data or other trace gas injection methods. We have developed a new method, referred to as the "²²²Rn incremented method", in which ²²²Rn from naturally available soil gas was injected into the workplace for a short duration (∼30 min), homogenized and the profile of decrease of ²²²Rn concentration was monitored for about 2 h to evaluate AER. The method was validated against the established ²²²Rn time-series method. After ascertaining the suitability of the method, several experiments were performed to measure the AER under different indoor conditions. The AER values, thus determined, varied in a wide range of 0.36-4.8 h^-1 depending upon the ventilation rate. The potential advantages of the technique developed in this study over conventional methods are discussed.

Delimiting radiation protection distance of underground uranium mining and metallurgy facilities: A case study in China

Delimiting radiation protection distance of uranium mining and metallurgy facilities is an important radiation protection approach to control the effective public dose caused by radon and radon progeny. Ventilation shafts are the main radon release paths of underground uranium mines. It is of great importance to research the diffusion regularities and influence range of the radon around the ventilation shaft. In this study, long-term and short-term radon accumulation monitoring approaches were adapted for onsite investigation. More than 520 sets of radon concentration were acquired. The survey results effectively revealed the distribution regularities of the radon concentration around the ventilation shaft with time, space, and working conditions. These results provide data for radiation protection in uranium mines. In addition, a radiation protection distance delimiting way was proposed for the investigated facility through effective public dose assessment.

The influence of building material structure on radon emanation

In this work, the radon emanation coefficients for selected building materials that are most often used in Serbia for covering floor surfaces (concrete, concrete screed, granite, glazed ceramic tiles, marble, roofing tile, and terrazzo tile) were determined, and the influence of the material structure on their values. The concentration of²²⁶Ra activity in the samples was determined using the gamma spectrometry method. Radon emanation was measured with the RAD7 device. The porosity of the samples was tested using mercury intrusion porosimetry and water absorption methods, and the structural analysis was performed using x-ray diffraction analysis and x-ray fluorescence analysis. The measured values of²²⁶Ra activity concentrations were in the range (4.93-298) Bq kg^-1, and the estimated values of the radon emanation coefficients were in the range (0.55-6.05) %. The obtained results indicate that the chemical and mineralogical composition, method of production, and the²²⁶Ra activity concentration have an influence on the emanation of radon from the material. No significant correlation was found between the radon emanation coefficient and the open porosity of the material, most likely due to the inhomogeneous presence of pores of different dimensions in the materials. It was established that the total value of the emanation coefficient depends on the emanation coefficient for pores ⩽100μm in size.

Design on intermittent ventilation strategy for radon removal in underground space

Ventilation to reduce radon was one of the most widely used, important, and effective means to reduce radon concentration in underground engineering. The largest energy consumption of underground buildings was the building ventilation system. Taking the radon migration process in a room as an example, this paper built a numerical model that accounted for the mechanism of radon production, exhalation, and diffusion process, by proposing a novel intermittent ventilation strategy to mitigate radon concentration in underground space. Three ventilation strategies (no ventilation, continuous ventilation, and intermittent ventilation) were compared under various wind speeds and fresh air ratios. Under the same safe duration of radon concentration, when intermittent ventilation was operated with the same wind speed, the startup time was reduced by 79.4%, 86.0%, 90.8%, 92.8%, 91.25%, with compared with continuous ventilation. The higher the fresh air ratio, the lower the radon concentration limit, and the faster the dynamic equilibrium state of radon concentration will be reached. During intermittent ventilation, reducing the fresh air ratio can greatly increase the recovery and utilization of the return air heat, thereby reducing the power of the air conditioning unit. Considering the comprehensive energy-saving benefits of the ventilation system, the appropriate intermittent ventilation plan should be made to meet radon reduction requirements in the range of low wind speed. If low wind speed was selected, there existed advantages of low ventilation noise and more comfortable, as well.

Seasonal Variation of Radon Concentrations in Russian Residential High-Rise Buildings

Assessment of the annual radon concentration is often required in indoor radon surveys of territories and individual dwellings for comparison with reference levels, studying factors affecting radon accumulation in dwellings, assessment of exposure in epidemiological studies, etc. The indoor radon surveys were carried out in multistorey buildings in eight Russian cities using solid state nuclear track detectors with an exposure period of three months. For these surveys, the estimation of annual indoor radon concentration was required to compare radon levels in buildings of high- and low-energy-efficiency classes located in different cities. To develop approaches to seasonal normalization in high-rise buildings, long-term one-hour radon concentration series obtained applying radon-monitors in 20 flats were analyzed. The dependency of indoor radon concentration on the indoor–outdoor temperature difference was studied taking into account the known natural, technogenic and anthropogenic factors affecting radon levels. The developed model of seasonal variations in multistorey buildings includes winter, summer, and demi-season periods, which differ both in ventilation intensity and dependency of radon concentration on the temperature difference. The developed model allows to estimate annual radon concentration taking into account the actual distribution of outdoor temperatures during the exposure of the track detectors.