A core burnup simulation method for reload BWR fuel optimization

In order to improve uranium utilization, axial enrichment and gadolinia distributions have been optimized for boiling water reactor (BWR) fuel. These studies were made with reference to the initial fuel for simplicity of calculation. However, it is more practical to optimize the reload fuel, which accounts for the majority of nuclear fuel used. The axial one-dimensional (1-D) core model used to simulate the burnup performance of the initial fuel is no longer suitable for the reload core. On the other hand, the use of a three-dimensional (3-D) core model would make the computing time prohibitive, because the optimization calculation involves a large number of core burnup simulations. The authors have therefore developed a rapid and reasonably accurate core model, which is presented here. In addition, a method is given for calculating the equilibrium core performance in a single-cycle burnup.