Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

L.F. Miller

Abstract

This thesis contains an analysis of the Yucca Mountain Repository for high level nuclear wastes. A list of all the proposed waste materials was compiled. This list indicates that at the reference emplacement density of 57 kW/acre, the planned repository has insufficient capacity. Thus, incentives exist to increase the capacity by increasing the emplacement density. An alternative emplacement methodology utilizing a combination of actinide recycle, optimized geometry, and ventilated emplacement over an extended operation period promises to increase the capacity drastically.

Using previously calculated values of the decay heat in spent fuel (SF) and high level wastes (HLW) from which the actinides have been removed, one and three dimensional heat transfer calculations were performed to quantify the capacity increases for several combinations of burnup, geometry changes, and repository operating schedules. These calculations indicate that the reference emplacement density of 57 kW/acre, which corresponds to 120 fuel assemblies per acre, is overly conservative. According to these calculations, the actual limit for SF emplaced in the reference geometry is 75 kW/acre, which corresponds to 159 fuel assemblies per acre. By removing the actinides, this maximum increases to 211 assemblies per acre.

Calculations were performed for SF and HLW (SF From which the actinides have been removed via reprocessing) in optimized geometry. By spacing the radioactive material closer together, the maximum densities increase to 184 and 310 assemblies/acre for SF and HLW respectively. Similar calculations were performed for higher burnup materials, with no noticeable change in the relative results. Finally, staggered emplacement was analyzed. The maximum emplacement densities increase to 219 and 315 assemblies/acre for SF and HLW in standard geometry. In optimized geometry, the maximum densities are 222 and 590 assemblies/acre for SF and HLW.

The results reported above correspond to the reference hot repository in which the waste packages reach temperatures greater than 200o C. Licensing difficulties associated with this hot repository content have created interest in a cold repository in which the emplacement horizon does not exceed the boiling point of water. Results for the cold repository in the standard emplacement geometry indicate the expected decrease in the allowable loadings: 68 and 91 assemblies/acre for SF and HLW respectively. For optimized geometry, the loadings increase to 93 and 133 assemblies/acre for SF and HLW. The results for staggered emplacement, however, do not show such a great decrease. In standard geometry, the loadings are 94 and 135 assemblies/acre for SF and HLW, and in optimized geometry, they are 142 and 253 assemblies/acre. This last result indicates that a cold repository which should prove easier to license, can contain all the identified wastes if one combines actinide removal with optimized emplacement geometry and ventilated operation over an extended operating period.

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