Non-linear time-dependent modelling of heterogeneous nuclear reactors

Abstract

This thesis is about time-dependent core-level neutronic simulations of nuclear re actors. In such systems, the neutron flux may oscillate in space and time due to the production and consumption of given fission products, in particular Xenon-135. This phenomenon is known as Xenon oscillations. A numerical simulator was devel oped to model such a phenomenon. The simulator numerically solves large systems of non-linear equations, which in this case requires the use of implicit methods. The way this has been accomplished uses techniques that are different from standard practice. The tool capitalizes on a static solver earlier developed and uses the same approximations in terms of spatial discretization and boundary conditions. The simulator was demonstrated to produce physically-correct results when applied to a realistic model of a pressurized water reactor. The simulator allows for time dependent perturbations defined in terms of insertions of control rod banks, and the realistic PWR model includes realistic control rod insertions. Xenon oscillations were predicted by the tool in some specific situations.