ABSTRACT

ABSTRACT

The thermal and thermomechanical response in the vicinity of the nuclear waste emplacement was evaluated for two potential nuclear waste repository sites located in bedded salt formations. The numerical analyses were performed using the finite element method and considered site-specific conceptual repository designs for underground vertical borehole emplacement of commercial high-level waste (CHLW) and spent fuel (SF) at the proposed Davis Canyon site in the Paradox Basin in southeastern Utah and in the proposed Palo Duro Basin site in the Permian Basin in northwestern Texas. The thermal and thermomechanical environments were determined for the emplacement of CHLW and SF at each site, with the determination of the resulting radial salt pressure on the waste package being the parameter of primary interest.

INTRODUCTION

Background

The development of nuclear energy has created a need for the safe disposal of radioactive wastes. The National Waste Terminal Storage (NWTS) Program has been established to investigate several concepts for isolating radioactive wastes from mankind and the environment. Among these concepts, geologic disposal (isolation in deep underground structures in stable geologic formations) appears to be the most practical method. Salt formations are among the candidate geologic formations because salt is easy to mine, has a relatively high thermal conductivity, is relatively free of water, and is a ductile material that can undergo large deformations without failing. Four salt formations are being considered as potential sites for a nuclear waste repository. Two of these sites are located in bedded salt stratigraphies: the Paradox Basin in southeastern Utah and the Permian Basin in northwestern Texas. The other two sites are salt domes: the Richton Dome in southeastern Mississippi and the Vacherie Dome in northwestern Louisiana. In the evaluation of potential geological formations to host a nuclear waste repository, the expected thermal and thermomechanical environments to which the nuclear waste packages will be subjected must be quantified. This study addresses the thermomechanical responses of the current conceptual repository designs proposed for two bedded salt repository sites located at Davis Canyon in the Paradox Basin, Utah, and in Palo Duro Basin in the Permian Basin, Texas.

Objectives

  • To evaluate the canister region thermal and thermomechanical responses of the Davis Canyon and Palo Duro Basin repository sites for their respective conceptual repository and waste package designs.

  • To determine the required adjustment to the repository design parameters (primarily thermal loading) to satisfy a set of prescribed canister region performance constraints.

The objectives of this study were two fold, viz:The first and primary objective pertains to the determination of expected canister region thermomechanical responses (e.g., temperatures, displacements, and stresses) for the waste package designs provided by Westinghouse [1982] and the conceptual repository designs provided by Stearns-Roger Services, Inc. The results obtained from the analysis of each design were compared with a set of proposed performance constraints for the canister region. The secondary objective of the study provided an opportunity to examine possible adjustments that can be made to several repository design parameters to satisfy any canister region performance constraints that were violated.

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