This work presents the analysis of a slurry polymerization stirred tank reactor for the production of high-density polyethylene. A coordination mechanism is adopted including initiation, propagation, first order deactivation, hydrogen transfer, ethylene transfer, transfer to co-catalyst and beta-hydride elimination. Two site types are considered each one with its own kinetic constants. A non-uniform solid phase is considered and in the particle there is a radial distribution of chemical species such as the living and dead polymer chains. In this sense, a general local balance is proposed, providing state equations for the moments of chain length distribution and for the active site concentrations that are treated together with all others modeling scales. The multigrain model approach was adopted. combined with a simulation strategy applying orthogonal collocation. The simulation procedure handles all the equations simultaneously and the model is capable of predicting the behavior of operation variables and variables associated with the polymer properties. (c) 2005 Elsevier Ltd. All rights reserved.