Abstract
This report documents studies undertaken by Quintessa during 2010 in preparation for the SR-Site review that will be initiated by SSM in 2011. The studies relate to consequence analysis calculations, that is to the calculation of radionuclide release and transport if a canister is breached. A sister report documents modelling work undertaken to investigate the coupled processes relevant to copper corrosion and buffer erosion. The Q{sub eq} concept is an important part of SKB's current methodology for radionuclide transport using one-dimensional transport modelling; it is used in particular to model transport at the buffer/fracture interface. Quintessa's QPAC code has been used to investigate the Q{sub eq} approach and to explore the importance of heterogeneity in the fracture and spalling on the deposition hole surface. The key conclusions are that: - The basic approach to calculating Q{sub eq} values is sound and can be reproduced in QPAC. - The fracture resistance dominates over the diffusive resistance in the buffer except for the highest velocity cases. - Heterogeneity in the fracture, in terms of uncorrelated random variations in the fracture aperture, tends to reduce releases, so the use of a constant average aperture approach is conservative. - Narrow channels could lead to
More>>
Citation Formats
Robinson, Peter, and Watson, Claire.
Handling Interfaces and Time-varying Properties in Radionuclide Transport Models.
Sweden: N. p.,
2010.
Web.
Robinson, Peter, & Watson, Claire.
Handling Interfaces and Time-varying Properties in Radionuclide Transport Models.
Sweden.
Robinson, Peter, and Watson, Claire.
2010.
"Handling Interfaces and Time-varying Properties in Radionuclide Transport Models."
Sweden.
@misc{etde_1013168,
title = {Handling Interfaces and Time-varying Properties in Radionuclide Transport Models}
author = {Robinson, Peter, and Watson, Claire}
abstractNote = {This report documents studies undertaken by Quintessa during 2010 in preparation for the SR-Site review that will be initiated by SSM in 2011. The studies relate to consequence analysis calculations, that is to the calculation of radionuclide release and transport if a canister is breached. A sister report documents modelling work undertaken to investigate the coupled processes relevant to copper corrosion and buffer erosion. The Q{sub eq} concept is an important part of SKB's current methodology for radionuclide transport using one-dimensional transport modelling; it is used in particular to model transport at the buffer/fracture interface. Quintessa's QPAC code has been used to investigate the Q{sub eq} approach and to explore the importance of heterogeneity in the fracture and spalling on the deposition hole surface. The key conclusions are that: - The basic approach to calculating Q{sub eq} values is sound and can be reproduced in QPAC. - The fracture resistance dominates over the diffusive resistance in the buffer except for the highest velocity cases. - Heterogeneity in the fracture, in terms of uncorrelated random variations in the fracture aperture, tends to reduce releases, so the use of a constant average aperture approach is conservative. - Narrow channels could lead to the same release as larger fractures with the same pore velocity, so a channel enhancement factor of sq root10 should be considered. - A spalling zone that increases the area of contact between flowing water and the buffer has the potential to increase the release significantly and changes the functional dependence of Q{sub eq}frac on the flowing velocity. Quintessa's AMBER software has previously been used to reproduce SKB's one-dimensional transport calculations and AMBER allows the use of time varying properties. This capability has been used to investigate the effects of glacial episodes on radionuclide transport. The main parameters that could be affected are sorption coefficients and flow rates. For both single and multiple glacial episodes the time-dependency of model parameters did not result in much change to the calculated peak fluxes to the biosphere. This is because fluxes are calculated to be dominated by the poorly-sorbed radionuclides 129I and 36Cl. However, a small increase (less than an order of magnitude) in the overall flux contributed from the radium decay chain, which is important for long timescales, was calculated during the phase when the multiple glacial episodes are occurring. These conclusions are preliminary and could be changed if different radionuclides are important in the SR-Site assessment. The known shortcomings of its one-dimensional radionuclide transport modelling capability has led SKB to fund the development of the MARFA code, which it is understood will be used in addition to the existing methodology in SR-Site. A detailed review of this code and the associated documentation has been undertaken. New semi-analytic methods have been developed in order to provide a means of checking the accuracy of MARFA calculations. The key conclusions are that: - MARFA can handle large networks in practicable run times, generally works well for single radionuclides or short chains and accurately handles advective systems where matrix diffusion effects are dominant. - The code has, however, a number of important limitations. In particular, it is unable to handle long decay chains with short-lived radionuclides and calculations immediately after flow rate changes can be inaccurate. - The documentation and Quality Assurance are poor. A large number of errors have been found in the User Guide and the associated test cases do not adequately test the use of the code for the anticipated applications. - These limitations bring into question the code's suitability (in its present form) for performance assessment calculations for a deep radioactive waste repository}
place = {Sweden}
year = {2010}
month = {Dec}
}
title = {Handling Interfaces and Time-varying Properties in Radionuclide Transport Models}
author = {Robinson, Peter, and Watson, Claire}
abstractNote = {This report documents studies undertaken by Quintessa during 2010 in preparation for the SR-Site review that will be initiated by SSM in 2011. The studies relate to consequence analysis calculations, that is to the calculation of radionuclide release and transport if a canister is breached. A sister report documents modelling work undertaken to investigate the coupled processes relevant to copper corrosion and buffer erosion. The Q{sub eq} concept is an important part of SKB's current methodology for radionuclide transport using one-dimensional transport modelling; it is used in particular to model transport at the buffer/fracture interface. Quintessa's QPAC code has been used to investigate the Q{sub eq} approach and to explore the importance of heterogeneity in the fracture and spalling on the deposition hole surface. The key conclusions are that: - The basic approach to calculating Q{sub eq} values is sound and can be reproduced in QPAC. - The fracture resistance dominates over the diffusive resistance in the buffer except for the highest velocity cases. - Heterogeneity in the fracture, in terms of uncorrelated random variations in the fracture aperture, tends to reduce releases, so the use of a constant average aperture approach is conservative. - Narrow channels could lead to the same release as larger fractures with the same pore velocity, so a channel enhancement factor of sq root10 should be considered. - A spalling zone that increases the area of contact between flowing water and the buffer has the potential to increase the release significantly and changes the functional dependence of Q{sub eq}frac on the flowing velocity. Quintessa's AMBER software has previously been used to reproduce SKB's one-dimensional transport calculations and AMBER allows the use of time varying properties. This capability has been used to investigate the effects of glacial episodes on radionuclide transport. The main parameters that could be affected are sorption coefficients and flow rates. For both single and multiple glacial episodes the time-dependency of model parameters did not result in much change to the calculated peak fluxes to the biosphere. This is because fluxes are calculated to be dominated by the poorly-sorbed radionuclides 129I and 36Cl. However, a small increase (less than an order of magnitude) in the overall flux contributed from the radium decay chain, which is important for long timescales, was calculated during the phase when the multiple glacial episodes are occurring. These conclusions are preliminary and could be changed if different radionuclides are important in the SR-Site assessment. The known shortcomings of its one-dimensional radionuclide transport modelling capability has led SKB to fund the development of the MARFA code, which it is understood will be used in addition to the existing methodology in SR-Site. A detailed review of this code and the associated documentation has been undertaken. New semi-analytic methods have been developed in order to provide a means of checking the accuracy of MARFA calculations. The key conclusions are that: - MARFA can handle large networks in practicable run times, generally works well for single radionuclides or short chains and accurately handles advective systems where matrix diffusion effects are dominant. - The code has, however, a number of important limitations. In particular, it is unable to handle long decay chains with short-lived radionuclides and calculations immediately after flow rate changes can be inaccurate. - The documentation and Quality Assurance are poor. A large number of errors have been found in the User Guide and the associated test cases do not adequately test the use of the code for the anticipated applications. - These limitations bring into question the code's suitability (in its present form) for performance assessment calculations for a deep radioactive waste repository}
place = {Sweden}
year = {2010}
month = {Dec}
}