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Preliminary description of small block mineralogical features, data report

Description: The large block heater test, to be conducted at Fran Ridge (Lin et al., 1994), is designed to provide a database with which to test codes that simulate hydrological, geochemical, and geomechanical processes that may occur within the repository block. The geochemical processes that may occur include rock-water interaction within the matrix of fracture bounded blocks, and with the minerals that line fractures (see, for example, Buscheck and Nitao, 1992,1993ab, 1994; Glassley, 1993). As a first step in evaluating these interactions, characterization of the fractures, and of the matrix that is adjacent to those fractures, must be completed Characterization of the fractures and matrix before the large block test is started will allow a `baseline` set of data to be collected that will describe the properties of the large block prior to the test. After the test is completed, the block will be dismembered and characterization of the matrix and fractures will be repeated. Changes in matrix and fracture mineralogies will allow documentation of the mineralogical consequences of rock-water interaction resulting from heating of tuff under the conditions of the test.
Date: February 3, 1998
Creator: Glassley, W., LLNL
Partner: UNT Libraries Government Documents Department

Predicting mineral alteration at the potential nuclear waste repository at Yucca Mountain, NV with reactive transport modeling

Description: We present the results of a reactive transport modeling study that examines the sensitivity of mineral evolution to temperature, condensate properties and water flow conditions anticipated to occur in the potential Yucca Mountain nuclear waste repository site. We have investigated a key aspect of the thermal-hydrological repository system, the interaction of condensate water flowing through fractures at the site. Future simulations will include mineral changes at the boiling front, a process not considered in this study. Our simulations show that the principal mineral changes that occur are dissolution of the initial phases (mainly calcite, but also feldspars and clay) and formation of zeolites and hydrated aluminous phases. Major differences in mineral alteration occur over very short distances. Fracture mineral alteration is clearly coupled with the thermal hydrological environment. Fracture porosity is enhanced in those areas where condensate forms, an upper, lower temperature condensate zone and a lower, high temperature condensate zone. The locations where mineral precipitation occur and porosity decreases depend on the integrated residence time of the solution on the fracture surface. In general, mineral precipitation is expected to occur in the region -150 m above the water table. Whether the changes in porosity are significant enough to modify thermo-hydrological behavior remains to be evaluated.
Date: April 1, 1998
Creator: Glassley, W., LLNL
Partner: UNT Libraries Government Documents Department

Review of existing reactive transport software

Description: Simulations of thermal and hydrological evolution following the potential emplacement of a subterranean nuclear waste repository at Yucca Mountain, NV provide data that suggest the inevitability of dependent, simultaneous chemical evolution in this system. These chemical changes will modify significantly both the magnitude and structure of local porosity and permeability; hence, they will have a dynamic feedback effect on the evolving thermal and hydrological regime. Yet, despite this intimate interdependence of transport and chemical processes, a rigorous quantitative analysis of the post- emplacement environment that incorporates this critical feedback mechanism has not been completed to date. As an initial step in this direction, the present document outlines the fundamental chemical and transport processes that must be accounted for in such an analysis, and reviews the inventory of existing software that encodes these processed in explicitly coupled form. A companion report describes the prioritization of specific capabilities that are needed for modeling post-emplacement reactive transport at Yucca Mountain.
Date: February 3, 1998
Creator: Glassley, W., LLNL
Partner: UNT Libraries Government Documents Department