Equipe de Géomagnétisme, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1, rue Jussieu, F-75005 Paris, France.
Sci Total Environ. 2012 Sep 1;433:247-63. doi: 10.1016/j.scitotenv.2012.06.034. Epub 2012 Jul 13.
Radiation hazard in dwellings is dominated by the contribution of radon-222 released from soil and bedrock, but the contribution of building materials can also be important. Using a simple air mixing model in a 2-story house with an attic and a basement, it is estimated that a significant risk arises when the Wall Radon exhalation Flux (WRF) exceeds 10×10(-3) Bq·m(-2)·s(-1). WRF is studied using a multiphase advection-diffusion 3-layer analytical model with advective flow, possibly induced by a pressure deficit inside the house compared with the outside atmosphere. To first order, in most circumstances, the WRF is proportional to the wall thickness and to the radon source term, the effective radium concentration EC(Ra), which is the product of the radium-226 concentration by the emanation coefficient E. The WRF decreases with increasing material porosity and exhibits a maximum for water saturation of about 50%. For EC(Ra)=10 Bq·kg(-1), in many instances, WRF is larger than 10×10(-3) Bq·m(-2)·s(-1) and, therefore, EC(Ra)=10 Bq·kg(-1) can be considered as the typical limit not to be exceeded by building materials. An upper limit of the WRF is obtained in the purely advective regime, independent of porosity or moisture content, which can thus be used as a robust safety guideline. The sensitivity of WRF to temperature, due to the temperature sensitivity of EC(Ra) or the temperature sensitivity of radon Henry constant can be larger than 5% for the seasonal variation in the presence of slight pressure deficit. The temperature sensitivity of EC(Ra) is the dominant effect, except for moist walls. Temperature and moisture variation effects on the WRF potentially can account for most observed seasonal variations of radon concentration in houses, in addition to seasonal changes of air exchange, suggesting that the contribution of walls should be considered when designing remediation strategies and studied with dedicated experiments.
住宅内的辐射危害主要来自土壤和基岩释放的氡-222，但建筑材料的贡献也可能很重要。在一座两层楼的房屋中使用一个简单的空气混合模型，该房屋有阁楼和地下室，当墙壁氡逸出通量（WRF）超过 10×10(-3) Bq·m(-2)·s(-1) 时，就会产生显著的风险。WRF 是使用多相平流扩散三层分析模型研究的，该模型具有平流，可能是由房屋内部与外部大气之间的压力差引起的。在大多数情况下，WRF 与墙壁厚度成正比，与氡源项（有效镭浓度 EC(Ra)）成正比，EC(Ra) 是镭-226 浓度与发射系数 E 的乘积。WRF 随材料孔隙率的增加而减小，并在约 50%的水饱和度下达到最大值。对于 EC(Ra)=10 Bq·kg(-1)，在许多情况下，WRF 大于 10×10(-3) Bq·m(-2)·s(-1)，因此，EC(Ra)=10 Bq·kg(-1) 可以被认为是建筑材料不应超过的典型限值。在纯平流区获得了 WRF 的上限，与孔隙率或含水量无关，因此可以用作可靠的安全指南。由于 EC(Ra)或氡亨利常数的温度敏感性，WRF 对温度的敏感性在存在轻微压力差的情况下，季节性变化的温度敏感性可能大于 5%。除了潮湿的墙壁外，EC(Ra)的温度敏感性是主要影响因素。WRF 对温度和湿度的变化的影响可能除了空气交换的季节性变化外，还可以解释房屋内氡浓度的大部分观测到的季节性变化，这表明在设计修复策略时应考虑墙壁的贡献，并通过专门的实验进行研究。
