ANALYSIS OF PROMPT EXCURSIONS IN SIMPLE SYSTEMS AND IDEALIZED FAST REACTORS

To analyze conceptual fast reactor accidents, two spherical models are used. These are (1) a homogensous core in which all core material is assumed to be molten and at a relatively low density, and (2) a heterogeneous system in which the uraaium is assumed to be in the form ef spherical shells each ef which is separated by low density material or void. in case (1), a nonlinear equation ef state is approprinte, and the concept of threshold'' is important. In case (2), a normal equation of state is applicable. The analytic theory is applied to the first model. This theory shows a strong dependence of the explosive energy release on the free'' energy, Q, which can be produced without causing disassembling accelerations. For Q = O, the total energy release varies as the cube of the excess reactivity. In the limit ef large Q, the explosive energy varies as the 1/2 power of the excess reactivity and is generally much larger than the total energy for a comparable system with Q = 0. The differential calculation is applied to both spherical models. in this case thn motion ef various portions ef the core and reflector is followed in detail.more » A general survey is described in which the various parameters ef impontance to conceptual accidents are isolated and described. Comparison to the analytic theory in made for a few special cases. (auth)« less