Within the framework of safety analysis for the Next European Torus, a decay heat hazards assessment is under way at the Joint Research Centre at Ispra. Undercooling accidents [loss-of-coolant and loss-of-flow accidents (LOCAs and LOFAs)] due to pump failure have been investigated assuming an automatic plasma shutdown in both cases. The passive heat removal mechanisms considered include radiation between components and residual cooling by the thermosyphon effect in the main cooling circuits. Conservative thermohydraulic calculations have been made to determine coolant velocity and temperature transients to avoid water boiling in the circuits. Temperature transients in the whole reactor, coupling radiation and water cooling effects, have been assessed, taking into account the reciprocal influence of the different cooling circuits. Sensitivity studies have been performed to analyze some thermohydraulic parameters. Results show that during a LOFA, water boiling can be avoided provided that the water inertia is large enough, and material melting temperatures are not reached during a LOCA.