[en] The Spanish nuclear regulatory agency, Consejo de Seguridad Nuclear (CSN), like most nuclear regulatory agencies and utilities, regularly conducts and participates in emergency drills. These drills refine the procedures, methods, and communication pathways necessary to support an emergency situation. During the drills, the plant conditions that may exist, the systems available, and the evolving plant conditions are initially unknown to the participants. They must be able to analyze the (simulated) plant data and respond with the proper actions to recover from the accident state. Given the limited plant data transmitted, assimilation of the information and interpretation of the evolving accident state is difficult. The MAAP Accident Response System (MARS) provides the CSN emergency response team with a means of evaluating, interpreting, and tracking the integral plant response using only the standard information about the current plant conditions. Moreover, potential future plant states, including possible operator actions, can be examined using the near-term, faster than real time, MARS predictor function. This paper summarizes how MARS can be used to assist the CSN staff