Conceptual model for regional radionuclide transport from a salt dome repository: a technical memorandum

Abstract

LIST OF FIGURES fisaa mie j££ 1 Path of radionuclides from the repository to the biosphere.. xii 2 Salt basins, salt domes, and uplifts, Northern Gulf Coast Region 4 LIST OF FIGURES (Continued) True-scale cross section of Vacherie Salt Dome showing selected horizons 32 Schematic history of salt dome growth 35 Index map showing location of Gulf Coast salt domes in which salt has been mined and salt structures can be observed. . 41 Pattern of layering in salt on 758-ft. level of Morton Salt Company mine at Weeks Island, Louisiana.. 43 Exaggerated effect of salt dome on regional flow path 58 Three barriers to radionuclide transport from a salt dome repository 61 Other repository media as part of the regional geonydrologic system vs. a salt dome as disturbance in the regional geohydrologic system 73 Structural section, Keechi Dome 101 Isochore map, Top of Pecan Gap Chalk to base of Austin Chalk, Keechi Dome 102 Groundwater-salinity distribution in Wilcox Aquifer around Keechi Dome ... 103 Northwest-southeast structure section through Oakwood Dome, Freestone and Leon Counties, Texas ... 106 Southwest-northeast structure section through Oakwood Dome, Freestone and Leon Counties, Texas ... 107 Groundwater salinity distribution around Oakwood Dome in Wilcox Aquifer 108 Map showing flow paths in the Sparta Sand from Vacherie Dome in North Louisiana 113 v LIST OF TABLES Follows Table Title pa 1 Range of Growth Rates (mm/yr) of Salt Domes of the North Louisiana Basin. . 38 Typical Chemical Composition of Doraal Salt 40 3 Status of Geologic Mapping in Subsurface Salt Mines of the Gulf Coast of the United States 42 vii ABSTRACT Disposal of high-level radioactive wastes is a major environmental problem influencing further development of nuclear energy in this country. Salt domes in the Gulf Coast Basin are being investigated as repository sites. A major concern is geologic and hydrologic stability of candidate domes and potential transport of radionuclides by groundwater to' the biosphere prior to their degradation to harmless levels of activity. This report conceptualizes a regional geohydrologfc model for transport of radionuclides from a salt dome repository. The model considers transport pathways and the physical and chemi cal changes that would occur through time prior to the radionuclides reaching the biosphere. Necessary, but unknown inputs to the regional model involve entry and movement of fluids through the repository dome and across the domecountry rock interface and the effect on the dome and surrounding strata of heat generated by the radioactive wastes. viii SUMMARV m RECOMMENDATIONS SUMMARY Future use of nuclear energy is highly dependent on capability to dispose of high-level wastes for a sufficiently long period of time to allow the wastes to decay to innocuous levels of radioactivity. Presently, these wastes are being stored in temporary facilities. Because of the time length involved (250,000 years), potential repositories must be geologically secure. Several geologic media are being considered including sal...