An Analysis of Bias in Groundwater Modelling Due to the Interpretation of Site Characterization Data

1996 ◽  
Vol 465 ◽  
Author(s):  
K. J. Clark ◽  
T. Ikeda ◽  
M. D. Impey ◽  
T. McEwen ◽  
M. White
Keyword(s):  
Performance Assessment ◽  
Cross Section ◽  
Groundwater Modelling ◽  
Water Fluxes ◽  
Full Dataset ◽  
Site Characterisation ◽  
A Site ◽  
Parameter Values ◽  
Modelling Process ◽  
Varied Parameter

ABSTRACTBias is a difference between model and reality. Bias can be introduced at any stage of the modelling process during a site characterisation or performance assessment programme. It is desirable to understand such bias so as to be able to optimally design and interpret a site characterisation programme. The objective of this study was to examine the source and effect of bias due to the assumptions modellers have to make because reality cannot be fully characterised in the prediction of ground-water fluxes. A well-defined synthetic “reality” was therefore constructed for this study. A limited subset of these data were independently interpreted and used to compute groundwater fluxes across specified boundaries in a cross section. The modelling results were compared to the “true” solutions derived using the full dataset. This study clarified and identified the large number of assumptions and judgements which have to be made when modelling a limited site characterisation dataset. It is concluded that bias is introduced at each modelling stage, and that it is not necessarily detectable by the modellers even if multiple runs with varied parameter values are undertaken.

Site Characterization Strategy and Its Role in Post Closure Performance Assessment

1997 ◽  
Vol 506 ◽  
Author(s):  
A.K. Littleboy ◽  
P.J. Degnan ◽  
R.S. Mcleod ◽  
S. Norris
Keyword(s):  
Radioactive Waste ◽  
Groundwater Flow ◽  
Performance Assessment ◽  
Numerical Models ◽  
Radioactive Waste Disposal ◽  
Sufficient Information ◽  
Site Specific ◽  
Groundwater Flow Modelling ◽  
Site Characterisation ◽  
A Site

ABSTRACTCalculations of risk or dose from the groundwater flow pathway are a central part of the assessment of post closure performance for a deep repository system for radioactive waste. These calculations need to be supported by a knowledge of the various components of the disposal system. Site characterisation provides a site specific geological database which can be used to build, test and refine numerical models of the geosphere and, to some extent, the biosphere components of the disposal system in order to evaluate its future evolution.Site characterisation programmes, and groundwater flow modelling within the performance assessment need to progress in an interactive manner to ensure that both remain focused on the resolution of key uncertainties which impact the overall performance assessment. The data derived from site investigations can be classified in terms of their application within the performance assessment: establishing the framework for numerical models; enabling the parameterisation of numerical models; testing model output; refining models; and demonstrating their credibility. Site characterisation programmes need to be established to provide the appropriate level of information for each of these stages. It is therefore not particularly useful to classify information into the traditional disciplines of geology, hydrogeology and geochemistry.A key issue for developing a geological and hydrogeological database for performance assessment is determining when sufficient information has been obtained. Primarily, this is dictated by the needs and sensitivities of the performance assessment and any regulatory requirements. However, radioactive waste disposal agencies work in a political environment that is strongly influenced by public perception. In order to progress, any programme must attain a broad measure of credibility and acceptability to other key “stakeholders”.The paper draws on examples and experiences from the extensive programme of work which has been performed by Nirex to understand the characteristics of a site near Sellafield in Cumbria, and to develop groundwater flow models to support the assessment of the post closure performance of a potential repository located at that site. Uncertainties important in influencing calculated risk within an interim assessment, published as the “Nirex 95 assessment” were used to develop further site-specific investigations. The resulting site characterisation activities generated an enhanced and refined site-specific geological and hydrogeological database for a subsequent assessment - the “Nirex 97 assessment”.

scholarly journals Geotechnical Approach to Early-Stage Site Characterisation of Shallow Wave Energy Sites

2021 ◽  
Vol 9 (6) ◽  
pp. 605
Author(s):  
Craig Heatherington ◽  
Alistair Grinham ◽  
Irene Penesis ◽  
Scott Hunter ◽  
Remo Cossu
Keyword(s):  
Wave Energy ◽  
Early Stage ◽  
Breaking Waves ◽  
Time Frame ◽  
High Energy ◽  
Specific Information ◽  
Terrain Analysis ◽  
Site Suitability ◽  
Site Characterisation ◽  
A Site

Marine renewable energy is still in its infancy and poses serious challenges due to the harsh marine conditions encountered for wave or tidal installations and the survivability of devices. Geophysical and hydrodynamic initial site surveys need to be able to provide repeatable, reliable, and economical solutions. An oscillating water column wave energy converter is to be installed on the west coast of King Island, Tasmania. The location is in a high-energy nearshore environment to take advantage of sustained shoaling non-breaking waves of the Southern Ocean and required site-specific information for the deployment. We provide insight into scalable geophysical site surveys capable of capturing large amounts of data within a short time frame. This data was incorporated into a site suitability model, utilising seabed slope, sediment depth, and water depth to provide the terrain analysis needed to match deployment-specific characteristics. In addition, short-term hydrology and geotechnical work found a highly energetic seabed (near seafloor water velocities <1 m/s) with sufficient bearing capacity (6 MPa). In a highly energetic environment, care was taken to collect the relevant data needed for an assessment of critical information to an emerging technology companies primary project. This is in addition to the malleable methodology for a site suitability model that can incorporate various weighted parameters to prioritise the location for shallow wave energy sites in general.

scholarly journals The 7Be(p, ?)8B Cross Section at Low Energies

1980 ◽  
Vol 33 (2) ◽  
pp. 177 ◽  
Author(s):  
FC Barker
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Solar Neutrinos ◽  
Model Calculations ◽  
Spectroscopic Factors ◽  
Low Energies ◽  
Standard Values ◽  
Experimental Values ◽  
Parameter Values ◽  
Potential Parameters

The nonresonant part of the 7Be(p, )I)8B cross section at low energies is recalculated by means of a direct-capture potential model, using parameter values determined by fitting 7Li(n, n)7Li and 7Li(n, )I)8Li data. Standard values of the potential parameters and spectroscopic factors give values of the 7Li(n,)I) cross section that are too large. Modified values that fit the thermal-neutron capture cross section predict 7Be(p,)I) cross sections that are much less than the experimental values. Also, shell model calculations predict resonant 7Be(p,)I) cross sections that are smaller than the experimental values. It is suggested that the accepted experimental values of the 7Be(p, )I) cross section may be too large, perhaps due partly to an overlarge accepted value for the 7Li(d, p)8Li cross section, which has been used for normalization purposes. A decrease in the 7Be(p,)I) cross section would reduce the calculated detection rate of solar neutrinos and lessen the discrepancy with the measured value.

NNWSI Performance Assessment Considerations

1983 ◽  
Vol 26 ◽  
Author(s):  
L. D. Tyler ◽  
R. R. Peters ◽  
N. K. Hayden ◽  
J. K. Johnstone ◽  
S. Sinnock
Keyword(s):  
Performance Assessment ◽  
Nuclear Waste ◽  
Yucca Mountain ◽  
Department Of Energy ◽  
Nuclear Waste Repository ◽  
Nuclear Waste Storage ◽  
Human Environment ◽  
Assessment Task ◽  
Waste Storage ◽  
A Site

ABSTRACTThe Nevada Nuclear Waste Storage Investigations (NNWSI) project includes a Performance Assessment task to evaluate the containment and isolation potential for a nuclear waste repository at Yucca Mountain in southern Nevada. This task includes calculations of the rates and concentrations at which radionuclides might be released and transported from the repository and will predict their consequences if they enter the human environment. Among the major tasks required for these calculations will be the development of models for water flow and nuclide transport under unsaturated conditions and in fractured hard rock. The program must also quantify the uncertainties associated with the results of the calculations. The performance assessment will provide evaluations needed for making major decisions as the U. S. Department of Energy seeks a site for a repository. An evaluation will be part of the environmental assessments prepared to accompany the potential nomination of the site. If the Yucca mountain site is selected for characterization and development as a repository, the assessments will be required for an environmental impact statement, a safety analysis report, and other documents.This program has been divided into five tasks. Collectively they will provide the performance assessments needed for the NNWSI Project.

scholarly journals Groundwater Flow-Modeling and Sensitivity Analysis in a Hyper Arid Region

Water ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 2131
Author(s):  
Sameh W. H. Al-Muqdadi ◽  
Rudy Abo ◽  
Mohammed O. Khattab ◽  
Firas M. Abdulhussein
Keyword(s):  
Hydraulic Properties ◽  
Arid Regions ◽  
Groundwater Discharge ◽  
Groundwater Modelling ◽  
Western Desert ◽  
Flow Modeling ◽  
Significant Challenge ◽  
Water Recharge ◽  
Upstream Weighting ◽  
Modelling Process

Groundwater modelling is particularly challenging in arid regions where limited water recharge is available. A fault zone will add a significant challenge to the modelling process. The Western Desert in Iraq has been chosen to implement the modelling concept and calculate the model sensitivity to the changes in aquifer hydraulic properties and calibration by researching 102 observations and irrigation wells. MODFLOW-NWT, which is a Newtonian formulation for MODFLOW-2005 approaches, have been used in this study. Further, the simulation run has been implemented using the Upstream-Weighting package (UPW) to treat the dry cells. The results show sensitivity to the change of the Kx value for the major groundwater discharge flow. Only about 7% of the models from the region can be irrigated utilizing greenhouses supported by external recharge.

The Difficulties of Undertaking Site Characterisation on Operational Nuclear Licensed Sites

2003 ◽  
Author(s):  
Peter Booth ◽  
Robert Gordon
Keyword(s):  
Waste Disposal ◽  
Monitoring Network ◽  
Sampling Strategy ◽  
Site Investigation ◽  
Technical Requirements ◽  
Fit For Purpose ◽  
Safety Cases ◽  
Site Characterisation ◽  
A Site ◽  
Ground Contamination

Undertaking site investigation on nuclear licensed sites is very different to site investigation on other sites, even those which are heavily contaminated. This paper sets out to highlight some of the issues which need to be considered when formulating a fit for purpose, yet defensible site characterisation programme on such a site. The first and most important aspect of the work is to set out clearly your objectives. There may be a number of reasons why a site investigation is being undertaken. These could include purely fulfilling your site licence conditions as an operator or they could be more specific like supporting a defined de-licensing or decommissioning project, installing a monitoring network, or determining the extent of ground contamination. Ensuring that a conceptual model exists is the next step, even if only at a preliminary stage, as this coupled with the desk study will help formulate the site characterisation programme. Logistical issues as well as technical requirements need to be factored in, but in order to maintain transparency it is important to declare the latter first. Like other sites with ground contamination, issues like sampling and analysis need to be considered. Clearance procedures on nuclear licensed sites are extremely stringent and can lead to delays. These need to be considered, especially if sending samples offsite for organics analysis. The laboratories themselves need to be licensed to handle radioactive samples and the transport regulations also need to be adhered to. Other logistical issues requiring consideration include safety cases, plant modification proposals and waste disposal. The technical side itself sets its own challenges in that decisions need to be closely linked into the logistics. Will the samples and data be collected primarily through intrusive techniques or is there a requirement to utilise non-intrusive methodology? How do you defend the proposed site sampling strategy when you have access restrictions? Do you need to have permanent monitoring facilities? These are just some of the questions which need to be answered if a site operator is to have a transparent and defensive site investigation programme on a nuclear licensed site.

Focused Ion Beam Milling and Micromanipulation Lift-Out for Site Specific Cross-Section Tem Specimen Preparation

1997 ◽  
Vol 480 ◽  
Author(s):  
L. A. Giannuzzi ◽  
J. L. Drown ◽  
S. R. Brown ◽  
R. B. Irwin ◽  
F. A. Stevie
Keyword(s):  
Cross Section ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Specific Area ◽  
Specimen Preparation ◽  
Tem Analysis ◽  
Site Specific ◽  
Area Of Interest ◽  
Carbon Coated ◽  
A Site

AbstractA site specific technique for cross-section transmission electron microscopy specimen preparation of difficult materials is presented. Focused ion beams are used to slice an electron transparent sliver of the specimen from a specific area of interest. Micromanipulation lift-out procedures are then used to transport the electron transparent specimen to a carbon coated copper grid for subsequent TEM analysis. The experimental procedures are described in detail and an example of the lift-out technique is presented.

Performance Assessment of a Repository for Intermediate-Level Radioactive Waste Using the Probabilistic System Assessment Program Mascot

1994 ◽  
Vol 353 ◽  
Author(s):  
J. E. Sinclair ◽  
P.J. Agg
Keyword(s):  
Performance Assessment ◽  
North West ◽  
The North ◽  
Deep Geological Disposal ◽  
Safety Case ◽  
Recent Developments ◽  
Radiological Safety ◽  
System Assessment ◽  
Intermediate Level Radioactive Waste ◽  
A Site

AbstractUK Nirex Ltd is planning the deep geological disposal of intermediate- and low-level radioactive wastes. A site close to Sellafield in Cumbria in the north-west of England has been selected for evaluation, and an extensive programme of site characterization is underway. In support of this programme of characterization, and in preparation for presentation of a post-closure radiological safety case, performance assessment using mathematical modelling has been carried out by the Disposal Safety Assessment Team at AEA Technology, on behalf of UK Nirex Ltd. This paper describes recent developments of the assessment models relating to the groundwater pathway for return of radionuclides to the environment.

Conclusions from an Nea Workshop: The Role of Phenomenological Sorption Modelling in Performance Assessment of RadioactiveWaste Disposal Systems

1983 ◽  
Vol 26 ◽  
Author(s):  
A.B. Muller ◽  
D. Langmuir ◽  
I. Neretnieks
Keyword(s):  
Performance Analysis ◽  
Performance Assessment ◽  
Systems Design ◽  
Sorption Process ◽  
Surface Ionization ◽  
Natural Environments ◽  
Far Field ◽  
Degree Of Confidence ◽  
Site Characterisation

ABSTRACTTo give due credit to the barrier of the far field geologic environment in many host media it is necessary to account for sorption processes. The ultimate impact of sorption modelling will be in helping to define the degree of confidence that may be placed on geochemical retardation occurring in this barrier. For those involved in site characterisation, systems' design, design implementation and regulation, this confidence is best derived from a combination of a fundamental phenomenological understanding of the sorption process with empirical observations of sorption in natural environments. Neither alone is adequate. By performing a few additional measurements during classical Ko experiments, the data necessary for the more fundamental models, such as that of double-layer or surface ionization and complexation, may also be provided. The basis of these models and their integration into broader performance analysis are outlined in the context of how this maximises confidence in the geologic barrier of critically concerned groups.

scholarly journals A machine learning approach to emulation and biophysical parameter estimation with the Community Land Model, version 5

2020 ◽  
Vol 6 (2) ◽  
pp. 223-244
Author(s):  
Katherine Dagon ◽  
Benjamin M. Sanderson ◽  
Rosie A. Fisher ◽  
David M. Lawrence
Keyword(s):  
Machine Learning ◽  
Optimal Parameter ◽  
Learning Approach ◽  
Water Fluxes ◽  
Biophysical Parameters ◽  
Biophysical Parameter ◽  
Community Land Model ◽  
Model Version ◽  
Machine Learning Approach ◽  
Parameter Values

Abstract. Land models are essential tools for understanding and predicting terrestrial processes and climate–carbon feedbacks in the Earth system, but uncertainties in their future projections are poorly understood. Improvements in physical process realism and the representation of human influence arguably make models more comparable to reality but also increase the degrees of freedom in model configuration, leading to increased parametric uncertainty in projections. In this work we design and implement a machine learning approach to globally calibrate a subset of the parameters of the Community Land Model, version 5 (CLM5) to observations of carbon and water fluxes. We focus on parameters controlling biophysical features such as surface energy balance, hydrology, and carbon uptake. We first use parameter sensitivity simulations and a combination of objective metrics including ranked global mean sensitivity to multiple output variables and non-overlapping spatial pattern responses between parameters to narrow the parameter space and determine a subset of important CLM5 biophysical parameters for further analysis. Using a perturbed parameter ensemble, we then train a series of artificial feed-forward neural networks to emulate CLM5 output given parameter values as input. We use annual mean globally aggregated spatial variability in carbon and water fluxes as our emulation and calibration targets. Validation and out-of-sample tests are used to assess the predictive skill of the networks, and we utilize permutation feature importance and partial dependence methods to better interpret the results. The trained networks are then used to estimate global optimal parameter values with greater computational efficiency than achieved by hand tuning efforts and increased spatial scale relative to previous studies optimizing at a single site. By developing this methodology, our framework can help quantify the contribution of parameter uncertainty to overall uncertainty in land model projections.

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