An experimental study on natural weathering of radionuclides from urban surfaces for aerosols deposited in wet and dry conditions

Abstract

-The European Model for Inhabited Areas (ERMIN) predicts long-term doses and other consequences following contamination of built-up areas by airborne radioactivity. Central to ERMIN are empirical models of the longterm behaviour of radionuclides on building and other surfaces in the environment. Experiments in which building materials were contaminated, and weathered outdoors for up to 1 year following contamination have enhanced the data on weathering from surfaces that can be used in ERMIN. New data have been obtained for the elements americium, cadmium, caesium, cobalt, iodine, ruthenium and strontium and for the surfaces brick, concrete and clay roof tiles, concrete slabs, glass, sandstone, tarmac and wood cladding. The results have highlighted some differences between the retention of aerosols on surfaces, particularly for glass. This paper presents a summary of the results and identifies the main differences in retention observed.

European decision support modelling of long-term external doses received in inhabited areas contaminated by a nuclear power plant accident – 2: Post deposition contaminant mobility on outdoor surfaces

“…Strontium deposited in water solution has for example been found to weather off a clay roof with a half-life of only ca. 2.5 months (Brown et al, 2016), whereas most of the caesium deposited in solution on a clay roof would remain over decades (Andersson, 2009). Thus modelling retention of all ionic contaminants using parameters derived for caesium would be expected to make the dose estimates somewhat conservative.…”

“…Common to these materials is that they generally contain minerals, which selectively and strongly fix and retain caesium cations (De Preter, 1990;Andersson, 1991). Other radionuclide ions would be expected to be less strongly held (Andersson, 2009;Brown, 2016), although it has been demonstrated that ruthenium in representative ionic forms is not very easily removed from a roof clay or concrete tile surface (Andersson, 1991). ERMIN uses weathering data based on the Chernobyl time series caesium measurements (Andersson, 2009) for all radionuclides in ionic form for these types of roof materials.…”

“…The exception regarding radionuclide ions concerns very smooth (non-porous) surfaces, where experimentation suggests that the weathering of cationic caesium (and very likely also other ions) on a glass roof would occur with a half-life of the order of 95 days (Brown et al, 2016), and investigations from the European ECP-4 project (Mamaev et al, 1993) suggest a similar value for smooth (uncorroded) metal roof covers.…”

Enhancement of the ERMIN urban dose and remediation model to account for physicochemical properties of contamination

“…Another modification suggested by the experimental results is that an initial reduction in contamination at the "time of first rain" might better represent weathering from some surfaces; this could be added and would not be too onerous for users to provide. Other factors that may influence weathering in specific weather conditions are discussed in Brown et al (2016).…”

“…The surface retention experiments performed under the PREPARE project (Brown et al, 2016) correspond to the soluble aerosols group. Undertaking experiments in real weather conditions has meant that interpretation of the results has not been straightforward.…”