[en] Vapor explosions sometimes occur when molten metal falls in a volatile cool liquid. This phenomenon is complex and difficult to observe accurately because of the rapid and violent motions. Its importance is derived from an assumed sequence in nuclear reactors. This report gives a model for the initiation phase, which occurs after the liquid metal has broken up into droplets, but before the actual explosion. During this time, the liquid metal droplets heat the coolant liquid by radiation across a vapor layer. The droplets cool and the vapor layer decreases in thickness until either direct contact is made or until the dynamics of the vapor film result in instabilities which in turn lead to almost instantaneous boiling