Characterization of Permeability/Porosity Relationships as a Function of Rubble Pile Polydispersity during Room Closure at the Waste Isolation Pilot Plant

Abstract:

Room closure is an important aspect of the safety concept and waste isolation strategy at the Waste Isolation Pilot Plant, located in southeastern New Mexico, USA. Isolation of waste constituents is achieved as disposal rooms converge upon the waste packages, and over long timescales, entomb the waste packages in an extremely low permeability mass of reconsolidated salt. If roof fall occurs, the safety case needs to take into account the evolution of permeability within the disposal room over time. This would include predictions for permeability/transport at relatively early times when the rubble pile will contain an extremely poorly-sorted mixture of large, meter-scale evaporite fragments and much smaller-sized fragments of salt at the millimeter scale.

Roof collapse at WIPP is also of interest in that resulting rubble piles likely consolidate in a manner differently from typical experimental salt consolidation tests. As a result, fluid transport during room consolidation under roof collapse scenarios has not been well characterized. Here we discuss progress toward characterizing initial rubble piles using micro-computed tomography and computational fluid dynamics modeling of fluid transport in pore spaces within rubble. We detail methods used to separate segmented binary (solid and fluid) images and determine preliminary particle size distributions of rubble piles using image analysis software. In an initial trial, we show how particle separates are applied in a numerical scheme for particle consolidation. We use image analysis methods to extract a finite element mesh for the pore spaces within initial fractures from the disturbed rock zone and run-of-mine salt and perform example computational fluid dynamics (CFD) simulations of gas transport within representative sub-samples. We discuss paths forward in developing a methodology for modeling empty room rubble pile consolidation and gas transport at WIPP.

SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2019-14112A