The Chernobyl nuclear accident 137Cs cumulative depositions simulated by means of the CALMET/CALPUFF modelling system

Özet

The widely used dispersion modelling system CALMET/CALPUFF has been applied in order to evaluate its abilityto simulate dry and wet depositions at regional scales (up to 1000 km from a source) in the specific case ofradionuclides released in the atmosphere, during the 1986 Chernobyl Nuclear Power Plant accident. The 137Cscumulative deposition data sampled at 410 sites on the entire territory of Ukraine after the accident have beenused for model verification. As meteorological input for feeding the CALMET pre-processor, we used a dataset oftime series recorded in 211 surface stations, 194 precipitation stations and 14 upper air stations. Two differentschemes for the emissions source have been adopted both available from scientific literature on pollutants releaseduring the Chernobyl accident. This work shows that the CALMET/CALPUFF system is able to reproducethe large-scale features of the measured 137Cs deposition pattern, which are the main traces on the territory ofUkraine. However, the fine structure of depositions, which are mainly due to precipitations, are poorly caught.The simulated deposition pattern appears excessively smoothed and an explanation for that is provided. Besides,we have found that the resistant model for dry deposition velocity of 137Cs aerosol particles significantly underestimatesdepositions and the closest agreement with measurements is achieved with constant depositionvelocity of 0.005 m/s. Finally, the strong dependence of the simulated contamination pattern on the emissionsource parameterization is confirmed.