Transfer of radionuclides in the case of snow

Fig. 1: Radionuclide deposition and distribution paths in wintertime.

Snow has a very high efficiency for washout of aerosol bound radionuclides from the atmosphere. Thus, snowpacks as well as soils act as sinks for radioactive matter, even though typical filter capacities for contaminants are missing in snow compared to soils. Water saturation of the soils in spring, massif bedrock (e.g. in high altitude mountains), the existence of permafrost or urban soil sealing often inhibit ground infiltration. Subsequently, release of nuclides increases during snowmelt connected with increased surface runoff (Fig. 1). Radioactivity is continuously concentrated in the snowpack during the winters due to partial snowmelt and sublimation. Accordingly, huge amounts of radionuclides could be released to surface waters or sewage systems in relatively short time periods when snowmelt initiates in spring.

Snow-related radionuclide transfer processes have not been closely studied so far and many related aspects are not yet fully understood. In particular, transport and behaviour of radionuclides during the winter season are highly relevant because of:

  • potential direct contamination of winter grain and perennial plants;
  • in the case of continuous snow coverage radionuclides will be accumulated and their release delayed, but will then be rapidly discharged with snowmelt runoff;
  • indirect contamination by melting water that will contaminate plants, soil, water bodies and sewage systems;
  • the prolongation of the vegetation period due to climate change increases the probability that vegetation may directly be contaminated by sporadic onsets of winter.

Therefore, the research group “Preventative Radiation Protection” investigates the transport pathways of radionuclides from the atmosphere into the hydrosphere within different research projects. In specific, the deposition of radionuclides on snow will be studied as well as their behaviour in the snowpack and release into aquatic ecosystems (Fig. 2). The main research topics are:

Washout of aerosol-bound radionuclides with different types of precipitation

Balance of the radionuclide transport from snowpack to drainage systems

Laboratory column experiments with contaminated snow for the determination of migration rates and residence times

A prognosis of larger scale contamination and strategies for decontamination and mitigation will be developed. Suitable parameters related to the radionuclide transport to be used in atmospheric radionuclide distribution models have already been successively provided. The latter are currently implemented in decision support systems for nuclear emergency management to regionalise and improve the models, in which only rain was considered so far.

Fig. 2: Radionuclide distribution in snow, meltwater and surface waters.

Experimental investigations will be performed at the Environmental Research Station Schneefernerhaus (UFS) on Mount Zugspitze (Fig. 3). The Helmholtz Zentrum München operates a laboratory at the high altitude station (2,650 m a.s.l.) that provides excellent experimental conditions with high precipitation rates and low temperature due to its location at the northern ridge of the Alps.

The field studies will be complemented by laboratory experiments with snow columns that will be contaminated with artificial radionuclide tracers. For these experiments a snow laboratory with a cooling chamber is available at the Institute of Radiation Protection at Helmholtz Zentrum München.

Fig. 1: Environmental Research Station Schneefernerhaus, Mt. Zugspitze. (Photo: K. Hürkamp)