A new model was developed for analyzing solvent extraction processes carried out in columns. Each column is treated as a series of well-defined equilibrium stages where the backmixing (other-phase carryover) between stages can be large. By including all mass transfer effects in the backmixing value, the same number of stages can be used for all extracted components no matter what their distribution coefficients. This greatly simplifies the calculations required when modeling multicomponent solvent extraction processes. Initial testing shows the new model to be better than either the Height of an Equivalent Theoretical Plate (HETP) or the Height of a Transfer Unit (HTU) method.

The Yucca Mountain Project, managed by the Nevada Operations Office of the US Department of Energy (DOE), is examining the feasibility of siting a repository for high-level nuclear waste at Yucca Mountain, on and adjacent to the Nevada Test Site. Excavation stability will be required during construction, waste emplacement, retrieval (if required), and closure, covering a period of approximately 100 years. In order to incorporate a means of evaluating excavation stability in the design process, a drift design methodology has been developed. This methodology uses both empirical and analytical methods in conjunction with detailed descriptions of site conditions to evaluate a proposed design. At present, the emphasis is on analytical numerical methods because of the limited experience, in tuff at elevated temperatures. This paper describes the proposed methods for analysis of systematically jointed, isotropically jointed, and widely spaced, discretely jointed rock masses. Loads resulting from in situ stress, thermal expansion, and seismic events are considered. Criteria for strength and failure of intact rock and the rock mass are applied to analysis results to assess the stability of proposed drift designs and to guide the design of the ground support system.