A three-dimensional stochastic model of the behavior of radionuclides in forests I. Model structure

This paper develops a mechanistic approach to modeling the behavior of radionuclides in forests as a first step in assessing the long-term risks. The resultant three-dimensional stochastic model assumes that the behavior of radionuclides follows a Markov process and is driven by the bio-geo-chemical mechanisms affecting radionuclide transport through soils and uptake by forest vegetation. The potential states radionuclides can occupy and the transitions between these states are presented. A random walk approach is developed in which particles representing radionuclides are moved through the defined states. This random walk model is solved via a Monte Carlo simulation. The ensemble behavior of particles is then used to predict the long-term spatial and temporal distribution of radionuclides in the forest. To test this approach, a scenario is constructed in which Cs-137 is deposited into a coniferous forest. In Parts II and III to follow, this approach is then used to examine the behavior of Cs-137 in forest soil and vegetation subsequent to a deposition into the coniferous forest ecosystem.