Cesium chloride, even if it is deposited as a dry particle, will eventually become a liquid when exposed to relative humidity (RH) above 67% or to rain. Cesium-containing liquid droplets can easily be transported through porous materials or through surface cracks. Once Cesium ions (Cs hereafter) have migrated into these materials, Cs can be difficult to efficiently extract without removal of the affected surface. The adsorption of the Cs to the porous materials also makes it difficult to remove using existing chemically-based decontamination technologies.

The ability to remove Cs from surfaces depends on the ability to reach the contamination. This ability is partially governed by the penetration depth of the Cs contamination. EPA experimentally assessed the migration of Cs into urban materials, including asphalt, brick, concrete, limestone, and granite. Based on limited experimental studies, penetration depth of Cs into the building materials was in the following order, from greatest to least: limestone > brick > concrete = asphalt = granite. 

Weathering can reduce the contamination on surfaces, although it may be impacted by the depth of penetration of the Cs into the surface. To assess the impacts of the weathering process on Cs contamination, researchers determined the amount of Cs removed from urban surfaces (asphalt, brick, concrete, limestone, and granite) and the amount of Cs that penetrated the building materials after a simulated rain event. These results suggest that it would make it even more difficult to remove Cs from the materials that had greatest penetration depth of Cs, such as limestone, brick and concrete, after a rain event than prior to the event due to greater subsurface penetration.

Cs (a soluble ion in water) primarily follows the flow of water in water and wastewater infrastructure. However, the spread of Cs is also related to the ability of the Cs ion to interact with construction materials and other substances found in the urban environment, including water and wastewater systems. EPA has studied these interactions at the bench and pilot-scale.

Related Research Products

• Summary: Fate and Transport of Cesium RDD Contamination – Implications for Cleanup Operations
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• Report: Fate of Radiological Dispersal Device (RDD) Material on Urban Surfaces: Impact of Rain on Removal of Cesium
• Journal Article: Review of technologies for preventing secondary transport of soluble and particulate radiological contamination from roadways, roadside vegetation, and adjacent soils