Thermomechanical response of WIPP repositories

Coarsely zoned STEALTH 2D calculations were used to investigate two candidate WIPP repositories. The grid was designed for one hundred thousand years of response with modest computing costs. As a result, the early time mechanical response was compromised by non-real oscillations that could not be damped completely before a few thousand years. In spite of these oscillations, it was possible to see that the dominant effects of stress and strain peaked between one and two thousand years, at the time of maximum heat in the site. This time corresponded to the condition that the surface heat loss rate balanced the heat generation rate. Though the creep strains were quite small, a large volume of salt was involved and the effects were significant. The peak surface uplift of 75HLW was increased by about 25% due to creep. However, the deviatoric stress relaxation due to creep produced large changes in the stress fields. The Rustler layer survived reasonable failure criterion for the 75HLW case with creep, and failed both in tension and shear, according to these same criterion, when the calculation was repeated without creep. The deviatoric stress fields, with and without salt creep, concentrated near the repository as expected and also in the Rustler layer due to its relatively high Young's modulus compared to the neighboring layers. Since the time of interest is so much smaller than the 100,000 years this calculation was designed to examine, it is possible to model the WIPP stratigraphy in much more detail and still be able to calculate the response for the time of interest. A finer zoned calculation of the response of the WIPP stratigraphy to a repository similar to the 75 K watt/acre repository is modeled in this report. In this calculation the Rustler formation is modeled as a five layered formation using material properties derived from data taken at the Nome site

Simulation of the thermomechanical response of Project Salt Vault. Final report

The feasibility of economically and accurately applying Lagrangian explicit finite-difference (EFD) techniques to the analysis of the thermomechanical response of radioactive wastes placed in salt repositories is demonstrated. Three numerical simulations of the Project Salt Vault (PSV) experiment were carried out, using STEALTH 2D, a two-dimensional EFD code. One calculation did not include a model for creep, while the other two calculations used a general model in which creep was included. As expected, when creep was included, it resulted in significantly more pillar shortening and room convergence than when it was not included. The first of the creep simulations (as well as the non-creep simulation) was designed to demonstrate the applicability of the EFD method.The second creep simulation was performed to evaluate the sensitivity of certain numerical parameters, such as zone size and boundary nearness. Numerical data are presented that compare the results of the three simulations to the results of the Project Salt Vault experiment. In the simulations which included creep, the room closure data are in excellent agreement with the shape and magnitude of the experimentally measured floor and roof closures. Temperature histories were also compared at several locations and these data were also in agreement with the experimental values