Masters Theses

Date of Award

5-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

H. L. Dodds

Abstract

Nuclear Criticality Safety is a major field of interest in nuclear engineering today. The analyses of hypothetical criticality accident scenarios are an important part of this field. To safely mitigate the consequences of such an accident, the results of the accident must be known. This thesis presents a theoretical model for predicting the consequences of a hypothetical criticality accident involving dry highly-enriched uranium (HEU) powder. The results obtained with the model include power histories, integrated fission yields, temperature histories, and reactivity histories of the systems analyzed.

The materials of concern in this study are 93.2% U235 enriched dry uranium powders, UO3 and UF4 . To simulate a powder pile on a concrete floor, a finite slab geometry (1x1xh and 2x2xh meters) is used where the pile height, h, determines the system reactivity. The model employs neutronics with simple, lumped parameter thermal feedback. Feedback reactivity effects are caused by changes in temperature, density, and volume. Temperature is calculated using an energy balance equation. Density and volume changes are calculated from an empirical relationship which is a function of temperature.

Results of excursion calculations involving different feedback models, geometries, powders, etc. are presented. Peak temperatures for the excursions range from 1000K to 2000K and total fission yields are calculated to be around 1019 fissions.

Some validation work is performed for the neutronics portion of the computational model. Finally, some conclusions of the study and suggestions for future work are presented.

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