Zhou W.,Rensselaer Polytechnic Institute |
Apted M.J.,Intera Inc. |
Nuclear Technology | Year: 2010
This paper describes the recent work to evaluate the technical storage capacity for spent fuel in the Yucca Mountain repository. To increase the capacity from the current statutory limit of 63000 tonnes HM commercial spent nuclear fuel (CSNF), two alternative repository designs are proposed and analyzed, which add two additional emplacement drifts adjacent to each currentdesign drift. All designs assume the same waste package inventory, or heat generation rate, and drift ventilation as the current design. As both alternative designs would fit the well-characterized repository footprint, no additional site characterization at Yucca Mountain would be necessary. The work also examines extended ventilation and phased waste-loading assumptions in anticipation of an expanded role for nuclear power in electricity generation. The key parameter to the storage capacity in the Yucca Mountain site is water movement. To study the thermal and hydrological responses to increased storage capacity, series of two-dimensional models were used to simulate coupled heat and mass (water and air) transfer within the repository system and the near-field subsurface environment, including all geological formations above and below the repository horizon from the surface to the water table. A three-dimensional model was applied to investigate the effect of axial heat transfer and fluid flow. The results show that the current repository footprint can accommodate three times the currently legislated 63000 tonnes HM of CSNF without compromising repository performance.
Singh A.,Intera Inc. |
Minsker B.S.,University of Illinois at Urbana - Champaign |
Bajcsy P.,University of Illinois at Urbana - Champaign
Journal of Computing in Civil Engineering | Year: 2010
The interactive multiobjective genetic algorithm (IMOGA) is a promising new approach to calibrate models. The IMOGA combines traditional optimization with an interactive framework, thus allowing both quantitative calibration criteria as well as the subjective knowledge of experts to drive the search for model parameters. One of the major challenges in using such interactive systems is the burden they impose on the experts that interact with the system. This paper proposes the use of a novel image-based machine-learning (IBML) approach to reduce the number of user interactions required to identify promising calibration solutions involving spatially distributed parameter fields (e.g., hydraulic conductivity parameters in a groundwater model). The first step in the IBML approach involves selecting a few highly representative solutions for expert ranking. The selection is performed using unsupervised clustering approaches from the field of image processing, which group potential parameter fields based on their spatial similarities. The expert then ranks these representative solutions, after which a machine-learning model (augmented with the spatial information of the selected fields) is trained to learn user preferences and predict rankings for solutions not ranked by the expert. To better mimic the "visual" information processing of human experts, algorithms from the field of image processing are used to mine information about the spatial characteristics of parameter fields, thus improving the performance of the clustering and machine-learning algorithms. The IBML approach is tested and demonstrated on a groundwater calibration problem and is shown to lead to significant improvements, reducing the amount of user interaction by as much as half without compromising the solution quality of the IMOGA. © 2010 ASCE.
Smith G.,GMS Abingdon Ltd. |
Kozak M.W.,Intera Inc.
Health Physics | Year: 2011
This paper describes the development and evolution of the Electric Power Research Institute's (EPRI) post-closure dose assessment for potential releases of radionuclides from the proposed High Level Waste repository at Yucca Mountain. The starting point for this work was the 1995 publication of Technical Bases for Yucca Mountain Standards by the Commission on Geosciences, Environment and Resources of the National Research Council. This report proposed the development and application of an individual risk-based standard for releases from the repository to replace the existing one, which was based on radionuclide release limits. This in turn implied the development and application of methods to assess radiation doses to humans. Accordingly, EPRI produced a methodology for such dose assessment as part of its Total System Performance Assessment program for the proposed Yucca Mountain repository site. The methodology initially addressed releases via groundwater and then releases associated with extrusive igneous events. The methodology was updated and applied over the following years to take account of regulatory developments, changes in estimates of the source term to the biosphere, peer review through international model comparison exercises, new site generic data, and new data concerning conditions at the point of compliance in Amargosa Valley. The main outputs were Biosphere Dose Conversion Factors, which relate radionuclide levels in environmental media to the annual individual doses to a member of a hypothetical critical group and to the regulator-defined Reasonably Maximally Exposed Individual. Most recently, consideration has been given to uncertainty in the dose estimates based on a probabilistic analysis. The paper provides a perspective on the evolution of the dose assessments in response to the developments listed above. Copyright © by the Health Physics Society.
Hodges B.R.,University of Texas at Austin |
Furnans J.E.,Intera Inc. |
Kulis P.S.,University of Texas at Austin
Journal of Hydraulic Engineering | Year: 2011
Measurements of stratification and dissolved oxygen (DO) illustrate a hypersaline gravity current with salt loads similar to a desalination plant brine discharge. Over a 48-h sampling period in August 2005, alternating cycles of high- and low-temperature hypersaline water were observed along the bottom of Corpus Christi Bay in Texas, coincident with low benthic DO and tidal flushing from an adjacent smaller bay. The gravity current underflow was typically less than 10% of the overall water depth. Strong salinity gradients prevented wind-mixing of the entire water column. Hypoxic and near-hypoxic conditions were associated with limited DO replenishment from the ambient water. High DO levels in the underflow source water did not deter the development of offshore benthic hypoxia. A quasi-Lagrangian analysis is used to evaluate the relationship between ambient mixing and lateral mixing within the underflow. The analysis is further applied to estimating DO demand rates in the hypersaline plume. Mixing between the ambient water and the underflow predominately occurs over the sloping bay boundary. Once the gravity current reaches the flatter section of the bay, mixing is substantially reduced and DO is progressively depleted at the bottom. The transit time of the underflow (i.e., residence time or isolation time for water near the bottom) and wind-mixing energy appear to be key factors governing stratification persistence and potential hypoxia development. The observations and analyses provide insight into possible fate, impacts, and open questions associated with similarly scaled salt loadings from a desalination plant into a shallow bay. © 2011 American Society of Civil Engineers.
Singh A.,Intera Inc. |
Mishra S.,Intera Inc. |
Ruskauff G.,Intera Inc.
Ground Water | Year: 2010
In recent years a growing understanding has emerged regarding the need to expand the modeling paradigm to include conceptual model uncertainty for groundwater models. Conceptual model uncertainty is typically addressed by formulating alternative model conceptualizations and assessing their relative likelihoods using statistical model averaging approaches. Several model averaging techniques and likelihood measures have been proposed in the recent literature for this purpose with two broad categories-Monte Carlo-based techniques such as Generalized Likelihood Uncertainty Estimation or GLUE (Beven and Binley 1992) and criterion-based techniques that use metrics such as the Bayesian and Kashyap Information Criteria (e.g., the Maximum Likelihood Bayesian Model Averaging or MLBMA approach proposed by Neuman 2003) and Akaike Information Criterion-based model averaging (AICMA) (Poeter and Anderson 2005). These different techniques can often lead to significantly different relative model weights and ranks because of differences in the underlying statistical assumptions about the nature of model uncertainty. This paper provides a comparative assessment of the four model averaging techniques (GLUE, MLBMA with KIC, MLBMA with BIC, and AIC-based model averaging) mentioned above for the purpose of quantifying the impacts of model uncertainty on groundwater model predictions. Pros and cons of each model averaging technique are examined from a practitioner's perspective using two groundwater modeling case studies. Recommendations are provided regarding the use of these techniques in groundwater modeling practice. Copyright © 2009 The Author(s). Journal compilation © 2009 National Ground Water Association.
Clemo T.,Boise State University |
Clemo T.,Intera Inc.
Ground Water | Year: 2010
A model coupling fluid hydraulics in a borehole with fluid flow in an aquifer is developed in this paper. Conservation of momentum is used to create a one-dimensional steady-state model of vertical flow in an open borehole combined with radially symmetric flow in an aquifer and with inflow to the well through the wellbore screen. Both laminar and turbulent wellbore conditions are treated. The influence of inflow through the wellbore screen on vertical flow in the wellbore is included, using a relation developed by Siwoń (1987). The influence of inflow reduces the predicted vertical variation in head up to 15% compared to a calculation of head losses due to fluid acceleration and the conventional Colebrook-White formulation of friction losses in a circular pipe. The wellbore flow model is embedded into the MODFLOW-2000 ground water flow code. The nonlinear conservation of momentum equations are iteratively linearized to calculate the conductance terms for vertical flow in the wellbore. The resulting simulations agree favorably with previously published results when the model is adjusted to meet the assumptions of the previous coupled models. © 2009 National Ground Water Association.
Furnans J.,Intera Inc.
World Environmental and Water Resources Congress 2015: Floods, Droughts, and Ecosystems - Proceedings of the 2015 World Environmental and Water Resources Congress | Year: 2015
Since 2010, the Lower Colorado River Authority (LCRA) has been modifying its water management plan (WMP) based on stakeholder complaints and initiatives. The WMP development process unites the LCRA with irrigators, firm customers (like the City of Austin), environmental interests, lakeside communities, and Texas regulators in allocating limited water supplies while attempting to meet the growing needs of all parties. To develop the WMP, the LCRA performed water availability modeling (WAM) using past naturalized-hydrology to examine the impact of proposed management scenarios. This approach has proven useful in illustrating what "would have happened" previously given current diversion and storage needs, and maximizes water availability through the basin's drought of record. Managing water resources in this "backward-looking" manner is now the accepted procedure for such activities in Texas. As illustrated in this WMP development process, the backward-looking modeling procedure can be effective, yet can be hampered by limitations in the WAM models. These limitations include: (1) naturalized flow usage (limiting real-time utility); (2) utilizing monthly timesteps (when Texas streamflows are more often "flashy"); and (3) minimizing conservation incentives of water users (whose efforts provide water for other non-conserving users). To counteract these deficiencies, an alternative model has been developed which simplifies the water accounting process so that water users can clearly understand their water availability. This paper includes the first description of the "Water Banking" approach to water management in the Lower Colorado River Basin, and provides a comparison with WAM results from the WMP process. © 2015 ASCE.
Martinez G.F.,University of Arizona |
Martinez G.F.,Intera Inc. |
Gupta H.V.,University of Arizona
Water Resources Research | Year: 2011
Methods to select parsimonious and hydrologically consistent model structures are useful for evaluating dominance of hydrologic processes and representativeness of data. While information criteria (appropriately constrained to obey underlying statistical assumptions) can provide a basis for evaluating appropriate model complexity, it is not sufficient to rely upon the principle of maximum likelihood (ML) alone. We suggest that one must also call upon a "principle of hydrologic consistency," meaning that selected ML structures and parameter estimates must be constrained (as well as possible) to reproduce desired hydrological characteristics of the processes under investigation. This argument is demonstrated in the context of evaluating the suitability of candidate model structures for lumped water balance modeling across the continental United States, using data from 307 snow-free catchments. The models are constrained to satisfy several tests of hydrologic consistency, a flow space transformation is used to ensure better consistency with underlying statistical assumptions, and information criteria are used to evaluate model complexity relative to the data. The results clearly demonstrate that the principle of consistency provides a sensible basis for guiding selection of model structures and indicate strong spatial persistence of certain model structures across the continental United States. Further work to untangle reasons for model structure predominance can help to relate conceptual model structures to physical characteristics of the catchments, facilitating the task of prediction in ungaged basins. Copyright 2011 by the American Geophysical Union.
Apted M.,Intera Inc.
13th International High-Level Radioactive Waste Management Conference 2011, IHLRWMC 2011 | Year: 2011
Interest in possible reprocessing of spent nuclear fuel and advances in materials science have raised the prospect of developing new, 'advanced' waste forms to aid in cleanup and disposal for high-level waste (HLW). In deciding if and how new waste forms might aid final disposal, however, it is vital to understand that the performance of waste forms can only be properly understood and evaluated within the context of long-term health-risk (dose-rate) performance of multiple barrier disposal systems. A risk-informed, system approach is distinct from previous sub-system testing and evaluations that measure waste-form dissolution rate ("durability") without full consideration of a disposal-system context. A simple mass-transfer model is first used to illustrate the linkage and functional relationship between waste-form dissolution and radionuclide transport with respect to the performance of disposal systems. In addition, a series of sensitivity calculations are made with the COMPASS/IMARC code in order to determine the fractional dissolution rate of a HLW waste form that would be necessary to control the release of specific radionuclides from a representative EBS. It is shown that hypothetical 'advanced HLW waste forms' would need to be 100 to 10,000 times more durable (i.e., lower dissolution rate) than current HLW borosilicate glass to reduce the release of key, long-lived radionuclides from disposal systems.