A nuclear reactor includes an internal steam generator and a nuclear core disposed in a containment structure. A condenser is disposed outside the containment structure, and includes a condenser inlet line tapping off a steam line connected to the steam generator outside the containment structure, and a condensate injection line conveying condensate from the condenser to the integral steam generator. Isolation valves are located outside the containment structure on a feedwater line, the steam line, and the condensate injection line. The valves have an operating configuration in which the isolation valves on the feedwater and steam lines are open and the isolation valve on the condensate injection line is closed, and a heat removal configuration in which the isolation valves on the feedwater and steam lines are closed and the isolation valve on the condensate injection line is open.