OST&I Natural Barriers Targeted Thrust FY 2005 New Start Projects

United States. Department of Energy. Yucca Mountain Project Office.

关键词: Corrosion;    Radioactive Waste Disposal;    Heating;    Halides;    12 Management Of Radioactive Wastes, And Non-Radioactive Wastes From Nuclear Facilities;   

DOI  :  10.2172/859054
RP-ID  :  NA
RP-ID  :  NA
RP-ID  :  859054

美国|英语

来源: UNT Digital Library

【 摘 要 】

The in-drift chemical environment plays a key role in determining the potential extent of waste package corrosion. Although the Alloy 22 proposed for use in the waste packages has been shown to resist corrosion in most environments, some concentrated solutions that could contact the waste packages can accelerate corrosion, especially those containing the halides Cl{sup -}, F{sup -}, and Br{sup -}. It is therefore critical to establish whether such concentrated solutions or brines will contact the waste package, and if so, in what volumes, for how long, and at what temperatures. Processes that could cause brines to contact the waste package include seepage of water into the drift from above, wicking of water into the invert below the waste package, and deliquescence of salts accumulated on the waste package. Also of concern is the possibility that heating of salt brines in the drift could generate acid gases that might have a corrosive effect on the engineered barrier system (the waste package and the drip shield). In addition, it is necessary to predict how such brines will evolve over time inside the drifts, whether as a result of ongoing transformations within the aqueous phase, exchange with the gas phase, or as a result of liquid or gas transport. All of these questions are addressed currently with a decoupled numerical approach. First, a thermal-hydrological-chemical (THC) model for coupled processes taking place in the rock surrounding the drift provides the seepage water chemistry and gas composition as a function of location around the drift over time. The output of this model provides the boundary conditions for an in-drift thermochemical reaction-path model with no explicit treatment of either liquid or gas transport. Although the current in-drift chemistry approach incorporates a Pitzer-type database for calculation of solute activities at high ionic strength, the lack of treatment of transport limits its ability to address questions concerning the in-drift chemical environment and its potential impact on engineered barrier system corrosion. Hence the current project approach is fit for its intended purpose of obtaining a license for repository construction, but can be improved upon by adding several capabilities to the modeling, such as: explicit consideration of masses of water and dissolved chemical species that can seep into the drift and contact the waste package, treatment of water vapor and gas transport within the drift, and consideration of how this might be affected by near-field conditions in the rock. This project involves the development of a fully coupled THC model, in which heat, water, and solute transport are combined with a rigorous thermodynamic approach applicable to highly concentrated brines at variable water activities. This approach will significantly increase the transparency and defensibility of the treatment of in-drift chemical processes. This, in turn, will greatly increase the confidence with which the range of chemical conditions likely to be encountered in the drift can be described, and the corrosive potential of the engineered barrier system can be assessed.