All nuclear power plants are subjected to a maintenance programme to guarantee the good condition of the equipment. The maintenance involves repairing faults that may arise during the operation of the facility and also preventive maintenance, consisting of conducting systematic reviews and periodic tests to avoid the occurrence of faults that can be avoided with maintenance, and to check that the equipment continues in suitable functional conditions.

In the limits and conditions of the nuclear power plant operating permits, the Spanish Nuclear Safety Council (CSN) requires the licensees of these facilities to implement a process for measuring the effectiveness of their maintenance practices. These requirements were transferred into a Council instruction that requires the licensees of nuclear power plants to monitor the effectiveness of their maintenance practices. These requirements apply to all the plant’s operating conditions. The CSN has developed a specific safety guide to facilitate compliance with this instruction and to set an acceptable method for this compliance.