Estimation of consequences following an atmospheric radioactive emission in a forest ecosystem

Institute of Protection and Nuclear Safety, Division of Environmental Protection, Laboratory of Environmental Modelling, 13108 Saint-Paul-lez-Durance cedex, France

Abstract

Forests represent very efficient filters of atmospheric aerosols. Radionuclides that are fixed on those aerosols fall on the aerial part of trees and understorey (leaves, branches and trunks) and on the soil (litter, mosses and first soil layers). Due to the high content of organic matters in the forest soils and the existence of a nutrition cycle by the humification process, radionuclides show a higher biodisponibility than in agricultural soils. IPSN developed, in collaboration with a finnish team from STUK (Finnish Nuclear Safety Authority), a model to assess the consequences of an atmospheric radioactive emission in a forest ecosystem. This dynamic compartment model has been developed with a simple and operational objective of crisis management. This model needs data relative to dry and wet depositions that are distributed in the ecosystem to trees, understorey and soil. Calculation of transfers between the different compartments of the ecosystem are used to calculate concentrations in forest products and external exposure. Then, ingestion dose and external exposure are calculated for several population groups : six age groups for the population, forest workers, hunters and mushroom and berry pickers. Calculations are made for iodine, caesium, strontium and plutonium isotopes and for three generic forest types : coniferous, deciduous and mixed forests. Forest structures vary in Europe with climate and soil type and also due to forest management. Many parameters in the model database are regional and should be adapted in order to substantially improve the estimations.