Manganese-stabilized steels have been proposed as candidate structural materials for fusion reactors, because they have been perceived as “low-activation” materials. Depending on the neutron spectra and the neutron fluence, the decay heat in Mn-stabilized steels is about 3–7 times larger than that in the Ni-stabilized steels. This large amount of decay heat could have serious impact in the case of the loss of coolant accident (LOCA). A two-dimensional LOCA model has been used to examine the LOCA temperature response of the manganese steel when utilized in an earlier U.S. design of ITER. The results show that the Mn-steel has approached its melting temperature by less than 100°C after about 7 hours from the onset of LOCA. On the other hand, the results for the nickel stabilized steel alloy 316SS show that the maximum temperature reached is 532°C in about the same time.