[en] The manner in which equations of state of data for U0₂ fuel and sodium are used in whole core accident studies is considered. The phases involved in hypothetical fast fast reactor accidents involve the study of different phenomena. Contributions are presented from workers at three locations whose main interests lie in different accident phases. The first section deals with a mechanistic approach to the predisassembly and disassembly phases of the accident using a single computer code. The second concentrates principally on 'conventional' whole core disassembly phase studies but does also include some 'fine structure' work on the mechanics of fuel movement within individual pins. The last section deals principally with molten fuel/coolant thermal interaction phenomena which can influence practically all stages of accident development, and with the energy source term in containment loading calculations. Details of the data used are given in the appendices. (author)