Criticality analysis for a uranium storage facility

Correia, Michelle
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Protection against accidental criticality is of utmost importance due to the potential of extremely high doses (such as the 17 Sv in the case of the Toikamura accident) to personnel involved in a criticality accident. In this study a criticality study is performed on a storage facility for uranium-containing residue. A criticality safety evaluation is the method used to determine the criticality safety of a system. Various internationally accepted methods exist which can be used during a criticality safety evaluation, including the use of a validated calculational technique. The three-dimensional Monte Carlo code, MCNP, was used in this study to determine multiplication factors, keff, for several different theoretical storage configurations. The internationally accepted subcritical limit of keff = 0.95 was used to determine whether a specific configuration is safe in terms of criticality. This study determines whether the theoretical storage configurations will be safe in terms of criticality, and it also evaluates the influence of various moderators on the multiplication factor, as well as the effect of distance between individual canisters on the multiplication factor. This criticality safety evaluation aims to show that the proposed theoretical storage configurations are safe in terms of criticality. It also provides recommendations of how the storage capacity can be increased, based on the results of the study.
research report submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science. School of Physics. Johannesburg, 2015.