Chlorine-36 alidation Study at Yucca Mountain, Nevada
The amount, spatial distribution, and velocity of water percolating through the unsaturated zone (UZ) at Yucca Mountain, Nevada, are important issues for assessing the performance of the proposed deep geologic repository for spent nuclear fuel and high-level radioactive waste. To help characterize the nature and history of UZ flow, isotopic studies were initiated in 1995, using rock samples collected from the Miocene ash-flow tuffs in the Exploratory Studies Facility (ESF), an 8-km-long tunnel constructed along the north-south extent of the repository block, and the Enhanced Characterization of the Repository Block (ECRB) Cross Drift, a 2.5-km-long tunnel constructed across the repository block (Figure 1-1, Sources: Modified from DOE 2002 [Figure 1-14] and USBR 1996). Scientists from Los Alamos National Laboratory (LANL) analyzed for chlorine-36 ({sup 36}Cl) in salts leached from whole-rock samples collected from tunnel walls and subsurface boreholes, and scientists from the U.S. Geological Survey (USGS) analyzed for isotopes of oxygen, carbon, uranium, lead, thorium, and strontium in secondary minerals collected from subsurface fractures and lithophysal cavities. Elevated values for ratios of {sup 36}Cl to total chloride ({sup 36}Cl/CL) at the level of the proposed repository indicated that small amounts of water carrying bomb-pulse {sup 36}Cl (i.e., {sup 36}Cl/Cl ratios greater than 1250 x 10{sup -15} resulting from {sup 36}Cl produced by atmospheric testing of nuclear devices during the 1950s and early 1960s) had percolated through welded and nonwelded tuffs to depths of 200 to 300 meters (m) beneath the land surface over the past 50 years. Because of the implications of short travel times to the performance of the proposed repository, the U.S. Department of Energy (DOE)/Office of Civilian Radioactive Waste Management (OCRWM), Office of Repository Development (ORD), decided to verify the {sup 36}Cl/Cl data with an independent validation study. DOE asked the USGS to design and implement a validation study that would include {sup 36}Cl and tritium ({sup 3}H) analyses. Core samples were taken from 50 new boreholes drilled across two zones in the ESF where a substantial number of samples with elevated {sup 36}Cl/Cl ratios had been identified previously. Also, core intervals from the Sample Management Facility (SMF) were acquired for water extraction and {sup 3H} analyses. This report documents the background and history of the validation study and presents the results of the {sup 36}Cl to total chloride ({sup 36}Cl/Cl) and {sup 3}H analyses.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- NA
- OSTI ID:
- 894191
- Report Number(s):
- TDR-NBS-HS-0000017, Rev. 00; DOC.20060829.0002, DC# 35641; TRN: US0700124
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
BOREHOLES
CARBON
CAVITIES
CHLORIDES
CHLORINE 36
GEOLOGIC SURVEYS
HIGH-LEVEL RADIOACTIVE WASTES
NUCLEAR FUELS
OXYGEN
RADIOACTIVE WASTE MANAGEMENT
SPATIAL DISTRIBUTION
STRONTIUM
TESTING
THORIUM
TRITIUM
URANIUM
VALIDATION
WATER
YUCCA MOUNTAIN
SPENT FUELS