Impact of Quaternary Climate on Seepage at Yucca Mountain, Nevada

Whelan, J.F. ; Paces, J.B. ; Neymark, L.A. ; Schmitt, A.K. ; Grove, M.

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

关键词: Oxygen 18;    Coatings;    Cavities;    Water;    Opals;   

DOI  :  10.2172/893805
RP-ID  :  NA
RP-ID  :  NA
RP-ID  :  893805

美国|英语

来源: UNT Digital Library

【 摘 要 】

Uranium-series ages, oxygen-isotopic compositions, and uranium contents were determined in outer growth layers of opal and calcite from 0.5- to 3-centimeter-thick mineral coatings hosted by lithophysal cavities in the unsaturated zone at Yucca Mountain, Nevada, the proposed site of a permanent repository for high-level radioactive waste. Micrometer-scale growth layering in the minerals was imaged using a cathodoluminescence detector on a scanning electron microscope. Determinations of the chemistry, ages, and delta oxygen-18 values of the growth layers were conducted by electron microprobe analysis and secondary ion mass spectrometry techniques at spatial resolutions of 1 to about 20 micrometers ({micro}m) and 25 to 40 micrometers, respectively. Growth rates for the last 300 thousand years (k.y.) calculated from about 300 new high-resolution uranium-series ages range from approximately 0.5 to 1.5 {micro}m/k.y. for 1- to 3-centimeter-thick coatings, whereas coatings less than about I-centimeter-thick have growth rates less than 0.5 {micro}m/k.y. At the depth of the proposed repository, correlations of uranium concentration and delta oxygen-18 values with regional climate records indicate that unsaturated zone percolation and seepage water chemistries have responded to changes in climate during the last several hundred thousand years.