Assessing field-scale migration of mobile radionuclides at the Nevada Test Site

Journal Article · Tue Sep 26 04:00:00 UTC 2006 · Journal of Environmental Radioactivity

OSTI ID:983640

Hu, Q; Rose, T P; Smith, D K; Moran, J E; Zavarin, M

Numerous long-lived radionuclides, including {sup 99}Tc (technetium) and {sup 129}I (iodine), are present in groundwater at the Nevada Test Site (NTS) as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. We synthesize a body of groundwater data collected on the distribution of a number of radionuclides ({sup 3}H, {sup 14}C, {sup 36}Cl, {sup 99}Tc and {sup 129}I), which are presumably mobile in the subsurface and potentially toxic to down-gradient receptors, to assess their migration at NTS, at field scales over distances of hundreds of meters and for durations of more than thirty years. Qualitative evaluation of field-scale migration of these radionuclides in the saturated zone provides an independent approach to validating their presumably conservative transport in the performance assessment of the proposed geological repository at Yucca Mountain, which is located on the western edge of NTS. The analyses show that the interaction of {sup 3}H with a solid surface via an isotopic exchange with clay lattice hydroxyls may cause a slight delay in the transport of {sup 3}H. The transport of {sup 14}C could be retarded by its isotopic exchange with carbonate minerals, and the exchange may be more pronounced in the alluvial aquifer. In particular, {sup 99}Tc may not necessarily exist as a mobile and conservative species {sup 99}TcO{sub 4}{sup -}, as commonly assumed for NTS groundwater. This is corroborated with recent in situ redox potential measurements, both across and near Yucca Mountain, showing that groundwater at multiple locations is not oxidizing. Speciation of iodine and its associated reactivity and mobility is also complex in the groundwater at the NTS and deserves further attention. The assumption of no retardation for the transport of {sup 99}Tc (especially) and {sup 129}I, used at the performance assessment of Yucca Mountain repository, is probably overly conservative and results in unrealistically high estimated doses for down-gradient receptors.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 983640
• Report Number(s): UCRL-JRNL-224902
• Journal Information: Journal of Environmental Radioactivity, Journal Name: Journal of Environmental Radioactivity Vol. 99; ISSN 0265-931X; ISSN JERAEE
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
CARBONATE MINERALS
CLAYS
DISTRIBUTION
EVALUATION
IODINE
ISOTOPIC EXCHANGE
NEVADA TEST SITE
NUCLEAR WEAPONS
PERFORMANCE
RADIOISOTOPES
REDOX POTENTIAL
TECHNETIUM
TRANSPORT
YUCCA MOUNTAIN