A study on thermal explosion as applied to molten fuel-coolant interaction

A brief review of the theory of the thermal explosion phenomenon is presented, with its particular application to liquid-cooled nuclear reactors. Consideration is given to the current understanding of this complex process, together with the uncertainties in the chain of events leading up to an effective thermal explosion. The example of an MFCI (molten fuel liquid coolant interaction) involving uranium dioxide and liquid sodium is chosen to present some novel general methods of calculation, referring to different stages of this phenomenon. The details of these new models are presented in appendices. The new approach is applied to the main concern of vapour explosion theory. This involves the occurrence of self-triggered and pressure pulse induced collapse of film boiling during the crucial coarse mixing stage. It is based on an analysis in which thickness of the vapour layer surrounding a hot particle plays a predominant role. The main features of this approach comprise theoretical calculations and a new experimental method for measuring this thickness, for two different types of film boiling. These features are presented in this paper and in earlier publications. 26 refs., 20 figs. (author)