British Columbia Mine Reclamation Symposium

The rationale for geologic disposal of high-level radioactive vaste in the United States Dlugosz, J. J.; Bedinger, Marion S.

Abstract

The program for disposal of high-level and transuranic radioactive waste in the United States calls for establishment of a mined repository in geologic formations that will provide for retreivability of the vaste for 50 years. The goal of radioactive waste isolation in mined repositories is to prevent unacceptable concentrations of radionuclides from migrating to the accessible environment. Early concepts of highlevel radioactive vaste disposal assumed that containment of the waste by the enclosing rock would be virtually complete. With the application of broader scientific and engineering disciplines, specifically geology and hydrology to the study of prospective environments for vaste disposal, the realization came that total isolation of the vaste in the immediate vicinity of the repository cannot be ensured. Furthermore, it vas realized that the geological and hydrological methods available today are not appropriate for predicting conditions or events that may prevail during the extremely long time required for waste isolation. Earth processes that are of major concern during the waste-isolation storage time include: (1) rates of radionuclide transport in the ground-water flow system which, in turn, reflect chemical reactions of radionuclides with ground water and earth materials; (2) climatic changes; and (3) tectonic and associated erosional events. To compensate for the limitations in our knowledge, the current rationale for waste isolation emphasizes the need for a series of independent barriers to vaste migrations. Multiplicity of these barriers, both engineered and natural, will compensate for uncertainties in predicting natural and man-induced conditions and events that may occur during the time required for waste isolation. The site selected for intense study for suitability of high level and transuranic radioactive waste isolation is Yucca Mountain in the desert of the southern part of the State of Nevada. The target buiial zone is in welded tuff at a depth below the surface of about 300 meters. The burial zone is in the unsaturated ?^np about inn me fers above the water table. The climate is arid; the average precipitation is about 150 mm/yr. Studies are currently ongoing to determine if the site vill provide long term isolation of radioactive waste.

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