Modelling of indoor external and internal exposure due to different building materials containing NORMs in the vicinity of a HNBRA in Mahallat, Iran

In this study, by considering the Naturally Occurring Radioactive Materials (NORMs) contained in the building materials used in Mahallat, Iran - an area exposed to a high level of natural background radiation - residential scenarios were simulated by applying the computer code RESRAD-BUILD to estimate the long-term Effective Dose rate of three different cases of basic building materials utilized in walls, floors and ceilings. Maximum effective dose rates of between 504 and 1433 mu Sv yr(-1) were calculated in the second case study, tiled cement floor. The highest external and radon doses were also calculated to be 369 and 1064 mu Sv, respectively. The simulation results revealed that Th-232 and K-40 contribute the most and least to the indoor dose, respectively. As a result of a sensitivity analysis, it was found that the air exchange rate is a key variable to easily reduce the radiological impacts of building materials. It was also shown that due to the presence of Ra-226, the sensitivity of effective dose to changes in wall thickness was higher than other radionuclides found in the building materials.