[EN] The control rods are one of the fundamental components of the core of a nuclear reactor, these functions are control the power generated in the reactor thanks to its insertion and extraction of the core. Consisting of boron carbide, they function as a neutron absorber, thus reducing the fission reactions and, consequently, the energy produced. In addition, they work as an element of safety in case of emergency, when SCRAM happens (sudden stop of the reactor) they are inserted totally in the core. The life of the control rods is limited by the neutron fluence that they are subjected and by the general exposure to the aggressive chemical environment of the reactor coolant. This causes the deterioration of the bars and as a consequence the substitution, according to the methodology described in this project. This project includes the analysis of substitution of the control rods that will be done in Refueling 22 of the Cofrentes Nuclear Power Plant, reactor BWR-6. The replacement of these will be carried out following the acceptance standards by General ElectricHitachi, manufacturer, and the operating experience of the Cofrentes Nuclear Power Plant. Being essential for the elaboration of the project, the lifetime of the control rods and the monitoring of the emission of unwanted products in the moderator (water) of the reactor. Depending on the lifetime of the bars, residence time and boron and tritium content in the circuit water, the study will proceed. These computations were made with the software Capricore, provided by Iberdrola, is a simulator that allows to make predictions of burning as well as to know the status of the reactor in real time. Capricore calculates the burn through a model implanted in the nodal simulator Thermohydraulic-Neutronic 3D of the SIMULATE-3 core. After the computation of the lifetime of each control bar, we proceeded to the subsequent analysis of the results and several substitution strategies were elaborated, that were proposed to the direction of the Nuclear Engineering department of C. N. Cofrentes. All of them carried out the requirements of manufacturer General Electric-Hitachi (GE-H) and installer (C. N. Cofrentes) After the analysis of the substitution strategy will proceed to the accomplishment of Option 7. This option replaces 22 Reactor control rods, of which fifteen will be Marathon type, five Duralife where the most burned rod by rod handle (TIP) and two Ultra MD are included. Refueling 22 of the C. N. Cofrentes is scheduled to take place in November of the year 2019. TFGM