Simulation of the Concentrations and Distributions of Indoor Radon and Thoron

Abstract

The technique of computational fluid dynamics (CFD) was used to study the concentrations and distributions of indoor radon (222Rn) and thoron (220Rn) as well as their progeny in three dimensions. According to the simulation results, in a naturally ventilated room, the activity distribution of 222Rn is homogeneous except for the places near air diffuser (supply and exhaust) locations. The concentration of 220Rn exponentially decreases with the distance from the source wall which is considered independently. However, as the ventilation rate increased, the concentrations of both 222Rn and 220Rn decreased and their activity distributions become complicated due to the effect of turbulent flow. It suggests that the impact factors of monitoring conditions (sampling site, airflow characteristics, etc.) should be taken into account in obtaining representative concentrations of 222Rn/220Rn for dose assessment. Both the simulation results of activities and their distributions agreed well with the experimental results in a laboratory room. It suggests that the CFD models may be applicable for the estimation of indoor 222Rn and 220Rn as well as their progeny.

Measurements and CFD modeling of indoor thoron distribution

“…The construction material for the floor and roof was same, so the thoron flux was assumed same for floor and roof. The measurement results for thoron flux were found to be comparable with the reported values elsewhere (Zhuo et al, 2001). The surface area of walls, floor and ceiling for the model room was 30.9 m 2 , 9.1 m 2 and 9.1 m 2 .…”

“…Table 1 shows input parameters used for CFD simulations. We used experimentally measured ventilation rate as input for closed room conditions while ventilation rate used for open room conditions (Zhuo et al, 2001) was taken as a representative input for such conditions.…”

“…However some studies have discussed scenarios where such assumptions may not remain valid (Katase et al, 1988;Yamasaki et al, 1995). The shorter half-life of thoron results in rapid exponential decrease of activity concentration away from the wall which may affect exposure-dose calculations (Zhuo et al, 2001). The internal radiation exposure due to inhalation of thoron decay products may be considerable near to the concrete wall (Katase et al, 1988).…”

CFD modelling of radioactive pollutants in a radiological laboratory

“…In addition attachment of nuclear particles with aerosols and deposition of particles and aerosols are included. The algorithms for dispersion and nuclear decay of particles and gas are based on the work by Zhuo et al [2]. The attachment of particles with aerosols and its deposition on the walls is based on the work by Porstendörfer [3] and Lai and Nazaroff [4].…”

Reference fields and calibration techniques for Rn-220 measuring instruments

“…The major concern of any developer of a thoron reference chamber is to create a uniform and homogeneous atmosphere. The use of air circulation systems, however, produces turbulent flows in the chamber, which can generate undesired non-uniformities in the gas distribution [10]. Moreover, a turbulent air circulation can affect the response of passive detectors, which work on the principle of gas diffusion and, due to the high air velocity, are often calibrated in conditions not found in practice.…”