The three-dimensional site-scale model of Yucca Mountain has been under development by Lawrence B... more The three-dimensional site-scale model of Yucca Mountain has been under development by Lawrence Berkeley Laboratory and U.S. Geological Survey (LBL/USGS) over the last four years. The model has been used to evaluate moisture flow within Yucca Mountain for different assumed infiltration patterns and for various assumed hydrological conditions and properties of faults. This model is under constant development as new data may require grid modifications or extensions as new wells are drilled and information from the Exploratory Studies Facility (ESF) become available. Recent development of the model include calibrations against observed gas and temperature data, incorporation of the ESF into the numerical grid, and the areal extension of the model in all directions to include data from nearby wells and for studies of water infiltration into nearby faults such as the Solitario Canyon fault. This paper summarizes these recent developments of the LBL/USGS site-scale model.
Groundwater flow patterns and chemical evolution in the Yucca Mountain area were inferred using g... more Groundwater flow patterns and chemical evolution in the Yucca Mountain area were inferred using groundwater geochemical and isotopic data taken from several databases available for the region. The interpreted flow patterns are based on areal distributions and cross-correlations of relatively nonreactive chemical (Cl and SO4) and isotopic (delta 18O, delta 2H, delta 34S) species, as well as on inverse groundwater mixing and water/rock reaction models simulated with the USGS geochemical code PHREEQC that considered the evolution of reactive species. The use of multiple chemical and isotopic species within a general modeling framework that considers both mixing and water/rock interactions provides a better understanding of groundwater compositional variations for the Yucca Mountain area than has previously been available. The PHREEQC groundwater mixing and reaction models were also used to understand carbon isotope evolution along the flow paths and provide more confidence in calculations of groundwater velocities using groundwater carbon-14 activities.
ABSTRACT The Nevada Test Site (NTS), located 105 km northwest of Las Vegas, Nevada, hosted 828 un... more ABSTRACT The Nevada Test Site (NTS), located 105 km northwest of Las Vegas, Nevada, hosted 828 underground nuclear explosions between 1951 and 1992, leaving an estimated 1.3e+08 curies of tritium, fission products, activation products and unspent fuel in the subsurface when the nuclear test moratorium was adopted in September, 1992. In two former testing areas of the NTS - Yucca Flat and Rainier Mesa- a significant fraction of the initial radionuclide inventory was introduced from nuclear tests with working points in the unsaturated zone. In Yucca Flat, an arid, low-elevation alluvium-filled basin where most tests were conducted in vertical shafts, unsaturated flow and transport models indicate that radionuclide migration to the water table is most likely where overlying subsidence craters receive significant infiltration from overland flow during infrequent runoff events. At Rainier Mesa, a wetter, high-elevation remnant of a once more extensive volcanic plateau, most tests were conducted at the ends of horizontal drifts in the vicinity of local perched water zones. Unsaturated flow and transport models of one of the larger tunnel complexes (N-tunnel) indicate that despite relatively high infiltration rates on the mesa, radionuclide diffusion from the flowing fractures to the porous matrix may significantly attenuate radionuclide movement to the water table.
ABSTRACT The former Nevada Test Site (now the Nevada National Security Site) hosted 828 undergrou... more ABSTRACT The former Nevada Test Site (now the Nevada National Security Site) hosted 828 underground nuclear explosions between 1951 and 1992, leaving an estimated 1.3e+08 curies of tritium, fission products, activation products and unspent fuel in the subsurface when the nuclear test moratorium was adopted in September, 1992. In two former testing areas of the Nevada National Security Site - Yucca Flat and Rainier Mesa- a significant fraction of the initial radionuclide inventory was introduced from nuclear tests with working points in the unsaturated zone. In Yucca Flat, an arid, low-elevation alluvium-filled basin where most tests were conducted in vertical shafts, unsaturated flow and transport models indicate that radionuclide migration to the water table is most likely where overlying subsidence craters receive significant infiltration from overland flow during infrequent runoff events. These craters tend to be located along the perimeter of the basin and have large contributing watersheds in the surrounding hills. At Rainier Mesa, a wetter, high-elevation remnant of a once more extensive volcanic plateau, most tests were conducted at the ends of horizontal drifts in the vicinity of local perched water zones. Unsaturated flow and transport models of one of the larger tunnel complexes (N-tunnel) indicate that despite relatively high infiltration rates on the mesa, radionuclide diffusion from the flowing fractures to the porous matrix may significantly attenuate radionuclide movement to the water table, depending on the assumed fracture attributes. Simulations show that the tunnel itself may be an important hydraulic feature that connects radionuclide sources to sub-vertical faults that are assumed to extend to the water table.
Core Ideas Gas transport modeling can estimate ground surface breakthrough after an underground n... more Core Ideas Gas transport modeling can estimate ground surface breakthrough after an underground nuclear explosion. Comparison tracer‐injection experimental and model results reveals parameter sensitivity. Barometric pumping may explain gas breakthrough following an underground nuclear explosion. Amplitude and period of barometric pressure signal are key in controlling breakthrough. An underground nuclear explosion (UNE) generates and distributes radioactive gases that can be transported to the ground surface though preexisting and explosion‐induced fractures over timescales of hours to months. If detected, the presence of short‐lived radionuclides in gas is evidence of a recent UNE. Numerical modeling can provide estimates of surface arrival times that can help inform gas monitoring strategies at suspected foreign test sites. Efforts are underway at historic US UNE sites to better understand subsurface gas‐transport processes following a UNE by geologic characterization of the near‐...
The three-dimensional site-scale model of Yucca Mountain has been under development by Lawrence B... more The three-dimensional site-scale model of Yucca Mountain has been under development by Lawrence Berkeley Laboratory and U.S. Geological Survey (LBL/USGS) over the last four years. The model has been used to evaluate moisture flow within Yucca Mountain for different assumed infiltration patterns and for various assumed hydrological conditions and properties of faults. This model is under constant development as new data may require grid modifications or extensions as new wells are drilled and information from the Exploratory Studies Facility (ESF) become available. Recent development of the model include calibrations against observed gas and temperature data, incorporation of the ESF into the numerical grid, and the areal extension of the model in all directions to include data from nearby wells and for studies of water infiltration into nearby faults such as the Solitario Canyon fault. This paper summarizes these recent developments of the LBL/USGS site-scale model.
Groundwater flow patterns and chemical evolution in the Yucca Mountain area were inferred using g... more Groundwater flow patterns and chemical evolution in the Yucca Mountain area were inferred using groundwater geochemical and isotopic data taken from several databases available for the region. The interpreted flow patterns are based on areal distributions and cross-correlations of relatively nonreactive chemical (Cl and SO4) and isotopic (delta 18O, delta 2H, delta 34S) species, as well as on inverse groundwater mixing and water/rock reaction models simulated with the USGS geochemical code PHREEQC that considered the evolution of reactive species. The use of multiple chemical and isotopic species within a general modeling framework that considers both mixing and water/rock interactions provides a better understanding of groundwater compositional variations for the Yucca Mountain area than has previously been available. The PHREEQC groundwater mixing and reaction models were also used to understand carbon isotope evolution along the flow paths and provide more confidence in calculations of groundwater velocities using groundwater carbon-14 activities.
ABSTRACT The Nevada Test Site (NTS), located 105 km northwest of Las Vegas, Nevada, hosted 828 un... more ABSTRACT The Nevada Test Site (NTS), located 105 km northwest of Las Vegas, Nevada, hosted 828 underground nuclear explosions between 1951 and 1992, leaving an estimated 1.3e+08 curies of tritium, fission products, activation products and unspent fuel in the subsurface when the nuclear test moratorium was adopted in September, 1992. In two former testing areas of the NTS - Yucca Flat and Rainier Mesa- a significant fraction of the initial radionuclide inventory was introduced from nuclear tests with working points in the unsaturated zone. In Yucca Flat, an arid, low-elevation alluvium-filled basin where most tests were conducted in vertical shafts, unsaturated flow and transport models indicate that radionuclide migration to the water table is most likely where overlying subsidence craters receive significant infiltration from overland flow during infrequent runoff events. At Rainier Mesa, a wetter, high-elevation remnant of a once more extensive volcanic plateau, most tests were conducted at the ends of horizontal drifts in the vicinity of local perched water zones. Unsaturated flow and transport models of one of the larger tunnel complexes (N-tunnel) indicate that despite relatively high infiltration rates on the mesa, radionuclide diffusion from the flowing fractures to the porous matrix may significantly attenuate radionuclide movement to the water table.
ABSTRACT The former Nevada Test Site (now the Nevada National Security Site) hosted 828 undergrou... more ABSTRACT The former Nevada Test Site (now the Nevada National Security Site) hosted 828 underground nuclear explosions between 1951 and 1992, leaving an estimated 1.3e+08 curies of tritium, fission products, activation products and unspent fuel in the subsurface when the nuclear test moratorium was adopted in September, 1992. In two former testing areas of the Nevada National Security Site - Yucca Flat and Rainier Mesa- a significant fraction of the initial radionuclide inventory was introduced from nuclear tests with working points in the unsaturated zone. In Yucca Flat, an arid, low-elevation alluvium-filled basin where most tests were conducted in vertical shafts, unsaturated flow and transport models indicate that radionuclide migration to the water table is most likely where overlying subsidence craters receive significant infiltration from overland flow during infrequent runoff events. These craters tend to be located along the perimeter of the basin and have large contributing watersheds in the surrounding hills. At Rainier Mesa, a wetter, high-elevation remnant of a once more extensive volcanic plateau, most tests were conducted at the ends of horizontal drifts in the vicinity of local perched water zones. Unsaturated flow and transport models of one of the larger tunnel complexes (N-tunnel) indicate that despite relatively high infiltration rates on the mesa, radionuclide diffusion from the flowing fractures to the porous matrix may significantly attenuate radionuclide movement to the water table, depending on the assumed fracture attributes. Simulations show that the tunnel itself may be an important hydraulic feature that connects radionuclide sources to sub-vertical faults that are assumed to extend to the water table.
Core Ideas Gas transport modeling can estimate ground surface breakthrough after an underground n... more Core Ideas Gas transport modeling can estimate ground surface breakthrough after an underground nuclear explosion. Comparison tracer‐injection experimental and model results reveals parameter sensitivity. Barometric pumping may explain gas breakthrough following an underground nuclear explosion. Amplitude and period of barometric pressure signal are key in controlling breakthrough. An underground nuclear explosion (UNE) generates and distributes radioactive gases that can be transported to the ground surface though preexisting and explosion‐induced fractures over timescales of hours to months. If detected, the presence of short‐lived radionuclides in gas is evidence of a recent UNE. Numerical modeling can provide estimates of surface arrival times that can help inform gas monitoring strategies at suspected foreign test sites. Efforts are underway at historic US UNE sites to better understand subsurface gas‐transport processes following a UNE by geologic characterization of the near‐...
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Papers by Edward Kwicklis