Modeling burnup-induced fuel rod deformations and their effect on transient behavior of a VVER-440 reactor core

This paper describes the simplified model for burnup-induced fuel rod deformations occurring during base irradiation period, from manufacturing to the beginning of the transient. Model is intended to be used together with a codes that are used for analysis of whole core and plant transients. Model consist of thermal and mechanical parts. Due to the high conductance approximation for the gap conductance, the thermal part of the model can be solved independently from the mechanical model. In this way the use of iterative solvers is avoided and model is simple to implement. Model is verified against FRAPCON simulations and has been integrated to the reactor dynamics code HEXTRAN, in which it provides initial data for fuel behavior module FINIX for transient simulation. Effect of burnup initialization on simulation of reactor transients has been demonstrated with the reactor dynamics code HEXTRAN that uses FINIX as a fuel behavior module.