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Materials Interactions and Temperatures in the Three Mile Island Unit 2 Core

Charles S. Olsen, Steven M. Jensen, Eric R. Carlson, Beverly A. Cook

Nuclear Technology

Volume 87 / Number 1 / August 1989 / Pages 57-94


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Core debris samples obtained from different regions of the Three Mile Island Unit 2 (TMI-2) core were examined to characterize the interaction among core components and the coolant, to determine the peak temperatures at which the interactions occurred, and to evaluate core melt progression in TMI-2. Estimates of peak temperatures were needed from these samples because of the strong influence that temperature has on core damage progression and fission product behavior. The peak temperatures can be bounded by comparing the observed microstructure and compositions with established phase diagrams. The microstructures were determined by optical metallography and scanning electron microscopy, and compositions were determined by energy and wavelength dispersive X-ray spectroscopy and scanning Auger spectroscopy. The material interactions among the core components are very complex and involve not only the interaction between the Zircaloy cladding and the UO2 fuel, but interactions with control rod materials (Ag-In-Cd) and Inconel spacer grids as well. Phase diagrams do not exist for some of the complex combinations of materials, and the models may have to be simplified and concentrated on the more significant interactions that involve material transport. The present models for core melt progression need to incorporate these more complex interactions in order to more closely predict the behavior of a core during a severe accident such as temperatures for material relocation.

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