AbstractThis work studies the stability of the Be-steam reactions on the plasma-facing surface of the ITER first wall. This reaction is strongly exothermic and its rate is heavily dependent on temperature. Therefore, it is feared that, under certain conditions, it may become unstable. An initial monodimensional analysis investigated the dynamics of the phenomena and the relative magnitude of the quantities involved. Thermal radiation from the reacting surface is not enough to dissipate the heat produced. This is, however, feasible with only a gradient of 13 °C across the Be layer of the first wall. Subsequently, an axisymmetric model of the whole reactor vacuum chamber has been set up. A 20 cm large “hot band” was assumed in which the surface temperature had reached the melting point of beryllium (1283 °C). Three separate simulations of the short-term (up to 10 min.) transient were performed, corresponding to different thermal energy loads on the first wall. Decay heat has been taken into account and LOCA conditions have been assumed. The results of these analyses are given and their safety implications are discussed.