abstract
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Various models of the nuclear reactor system are developed and evaluated in order to provide insight on the fundamental phenomena involved in the coolant void effect as a guide to future simulation studies and experimental design.
The mathematical description of the fundamental phenomena and consideration of the macroscopic physical characteristics define models for the neutron flux density and the coolant void fraction for the case of boiling-light-water nuclear reactors. Experimental comparisons are made whenever possible to evaluate the effectiveness of those models. The two-group neutron diffusion model and Hancox's void model were found necessary to describe the steady state behaviour of the nuclear reactor cell. The errors and limitations of present day models and techniques are delineated; the directions for improvement are also indicated. In general, it was found that independent experimental estimates of the fundamental parameters are needed to replace the current reliance on extensive experimental model correlations. In this way the need for expensive prototypes can be eliminated.
A temporal transformation of the general space-time neutron equations is developed to facilitate their solution by standard numerical techniques. It was found that the computation time can be reduced over threefold for transient control problems.
The coupling of the fluid model and the neutron flux model proves most interesting and shows that coolant voiding can have a profound effect on both the steady state and the transient behaviour of nuclear reactors. It is also shown that errors in present day techniques for investigating the coupling effect can lead to errors in reactivity estimates of more than the prompt critical limitation.