Penetration factor and indoor deposition rate of elementary and particulate iodine in a Japanese house for assessing the effectiveness of sheltering for radiation exposures

Abstract

Sheltering is one of the countermeasures for protection against radiation exposures in nuclear accidents. The effectiveness of sheltering is often expressed by the reduction factor, that is the ratio of the indoor to the outdoor cumulative radioactivity concentrations or doses. The indoor concentration is mainly controlled by the air exchange rate, penetration factor, and indoor deposition rate. The penetration factor and indoor deposition rate depend on the surface and the materials and structure of windows and doors as it is these openings in the building envelope that control penetration. We investigated experimentally these parameters of I2 and particles. The experiment was performed in two apartment houses, three single-family houses, and chambers. The obtained penetration factor ranged from 0.3 to 1 for particles of 0.3–1 μm and 0.15–0.7 for I2 depending on the air exchange rate. The indoor deposition rate for a house room ranged from 0.007 to 0.2 h−1 for particles of 0.3–1 μm and 0.2–1.5 h−1 for I2.

Uncertainty and sensitivity analyses for the reduction factor of sheltering for radiation exposures

“…Conversely, there are few studies on indoor deposition for I 2 . Our previous study (Hirouchi et al 2021) found that the indoor deposition rate for I 2 increased with the air exchange rate, although that for particles was independent of the air exchange rate. The relationship between the indoor deposition rate for I 2 (h −1 ), λ d.I , and the air exchange rate (h −1 ), λ e , is expressed as follows (Hirouchi et al 2021):…”

“…In this study, the size of particulate iodine discharged during nuclear power plant accidents was assumed to be the same as in the Chernobyl accident, and the particle size of 0.1-1 µm was targeted. According to our literature surveys, the indoor deposition rate for 0.1 to 1 µm particles ranged from 0.01 to 1 h −1 (Thatcher and Layton 1995, Fogh et al 1997, Thornburg et al 2001, Allen et al 2003, Chao et al 2003, Thatcher et al 2003, Ferro et al 2004, Rim et al 2010, Chen et al 2012, El Orch et al 2014, Tran et al 2017, Xiao et al 2020, Xie et al 2020, Hirouchi et al 2021. Based on the mean and standard deviation of the indoor deposition rates obtained by these studies, the mean and standard deviation of the indoor deposition rate in this study were assumed to be 0.28 h −1 and 0.23, respectively.…”

“…Here, the leakage area is defined as the total area of gaps in a house, and the gross building coverage ratio is defined by the ratio of the building area to the land area, including roads, within 30 m of a target house. The indoor deposition rate depends on the particle size, interior surface material, surface-to-volume ratio in a room, and chemical forms such as particulate and gaseous forms (Fogh et al 1997, Liu and Nazaroff 2001, Thatcher et al 2003, Hussein et al 2009, Tran et al 2017, Lai et al 2020, Hirouchi et al 2021. The penetration factor depends on the air exchange rate, chemical form, and gap characteristics such as shape, length, and size (Liu and Nazaroff 2003, Thatcher et al 2003, Chen and Zhao 2011, Chen et al 2012, Stephens and Siegel 2012, Li et al 2017, Hirouchi et al 2021.…”

Special issues and computational techniques: the Bernard Wheatley Award for 2021

“…The above emphasis on computer models and techniques should not be allowed to eclipse the useful practical studies that were reported during 2021. Hirouchi et al (2021) addressed an important issue in emergency preparedness, which is the degree to which radioactive aerosols will be present in indoor air following an accident. This requires consideration of their penetration into houses and subsequent deposition and has a bearing on decisions regarding whether evacuation or sheltering is the preferred option in different circumstances.…”

“…This requires consideration of their penetration into houses and subsequent deposition and has a bearing on decisions regarding whether evacuation or sheltering is the preferred option in different circumstances. Hirouchi et al (2021) studied this issue for elemental and particulate iodine, because 131 I is an important radionuclide that is readily released to air in severe accidents at nuclear reactors. The studies were performed in a stainless-steel chamber in the laboratory, and both in apartments and single-family houses.…”