We have developed a system to optimize BWR fuel reloads using the 3D neutron core simulator CM-PRESTO code; in this code the combinatorial technique tabu search along with the heuristic rules of Control Cell Core (CCC) and Low Leakage (LL) have been incorporated. The objective of this work is to maximize the cycle length while satisfying the operational thermal limits and cold shutdown constraints. To test our optimization system an actual BWR operating cycle was used, corresponding this cycle to an 18-months cycle with a length of 9,281 MWD/TU which used 112 fresh fuel assemblies of 3.53 w/o of U -235, the corresponding loading pattern was generated using engineer expertise. We used a modified tabu search technique to seek for a loading pattern of maximum energy without violating the operational and safety limits. Numerical experiments show a maximum cycle length of 9,788 MWD/TU which does not violate the operational thermal limits and has a cold shutdown margin of 1.06% Δk/k, which is greater than the 1% Δk/k minimal limit value. If we want to increase the cold shutdown margin up to 1.5% Δk/k the energy is penalized obtaining only a maximum of 9,381.6 MWD/TU. However, we have in both cases an increase of energy produced i with the energy produced by the actual operating cycle achieving the goal of this task.