Effect of a Random Variation of Rock Salt Creep on Calculations of Storage Room Closure for the WIPP Project

摘要

Heterogeneity is characteristic of many geologic media. In particular, naturally occurring rock salt in southeastern New Mexico shows a wide variation of secondary creep rates between tested samples. It is important to know how this scatter in properties affects room closure predictions. This report presents the results of a study designed to quantify this effect for a particular isothermal storage room model. A series of calculations of room closure are made with both homogeneous and randomly distributioned creep properties. Calculations involving random property variations were divided into two sets: those in which variations occurred only in the vertical direction, and those in which both horizontal and vertical variations were present. The introduction of randomly distributed creep properties is shown to yield room closure predictions which, when averaged among several calculations, are reduced from the single prediction of an analogous homogeneous calculation. The analysis finds an average creep property value which could be used to achieve the same closure result as the average of several random calculations. Some statements concerning confidence intervals on room closure predictions are made. (ERA citation 08:014121)