Global(VI)integrating coupled THCinto PA model

2021 ◽  
Author(s):  
Dinara Ermakova ◽  
Haruko Wainwright ◽  
LianGe Zheng ◽  
Ian Shirley ◽  
Hannah Lu
Keyword(s):  
Global Sensitivity Analysis ◽  
Chemical Properties ◽  
Process Models ◽  
Order Model ◽  
Reduced Order ◽  
Geochemical Parameters ◽  
Complex Process ◽  
Bentonite Buffer ◽  
Aqueous Complexation

Abstract The bentonite buffer long-term integrity is of significant interest in the performance assessment (PA) of nuclear waste disposal. This study aims at understanding how the initial geochemical parameters affect long-term chemical properties within the buffer, which will subsequently affect the transport. Using coupled thermal-hydrological-chemical (THC) models for migration of U(VI) in a generic repository, we performed a global sensitivity analysis (GSA) to identify the influence of each parameter on the temporal evolution of a spatially averaged distribution coefficient for the entire buffer. Such an analysis can be used in a repository-scale PA. In this work, we used the TOUGHREACT software to model coupled THC processes in a generic clay repository with bentonite buffer. In this model, U(VI) is released from a canister via schoepite dissolution, which is assumed to occur 1000 years after closure. U(VI) migrates through the bentonite buffer affected by two-site protolysis non-electrostatic surface complexation and cation exchange. GSA results showed that adsorption density on smectite, pH, volume fractions of smectite, calcite, Ca2+ aqueous concentration all play a significant role in U(VI) transport, since roughly 80% of adsorbed U(VI) is absorbed by smectite, and Ca2+ affects the aqueous complexation with U(VI). This work demonstrates the complex process models potential usefulness that can be transferred to the PA model. It also provides information needed to proceed with the development of a reduced-order model, which has the potential to optimize repository designs, site characterization, performance confirmation.

Development of a reactive transport code MC-CEMENT ver. 2 and its verification using 15-year in situ concrete/clay interactions at the Tournemire URL

Clay Minerals ◽  
2013 ◽  
Vol 48 (2) ◽  
pp. 185-197 ◽  
Author(s):  
T. Yamaguchi ◽  
M. Kataoka ◽  
T. Sawaguchi ◽  
M. Mukai ◽  
S. Hoshino ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Chemical Properties ◽  
Bentonite Buffer ◽  
Alkaline Environments ◽  
Radioactive Waste Repositories ◽  
Long Term Performance ◽  
Term Performance ◽  
Waste Repositories

AbstractHighly alkaline environments induced by cement-based materials are likely to cause the physical and/or chemical properties of the bentonite buffer materials in radioactive waste repositories to deteriorate. Assessing long-term alteration of concrete/clay systems requires physicochemical models and a number of input parameters. In order to provide reliability in the assessment of the long-term performance of bentonite buffers under disposal conditions, it is necessary to develop and verify reactive transport codes for concrete/clay systems. In this study, a PHREEQC-based, reactive transport analysis code (MC-CEMENT ver. 2) was developed and was verified by comparing results of the calculations with in situ observations of the mineralogical evolution at the concrete/argillite interface. The calculation reproduced the observations such as the mineralogical changes in the argillite limited to within 1 cm in thickness from the interface, formation of CaCO3 and CSH, dissolution of quartz, decrease of porosity in the argillite and an increase in the concrete. These agreements indicate a possibility that models based on lab-scale (∼1 year) experiments can be applied to longer time scales although confidence in the models is necessary for much longer timescales. The fact that the calculations did not reproduce the dissolution of clays and the formation of gypsum indicates that there is still room for improvement in our model.

Model Order Reduction of Transmission Line Model

2020 ◽  
Vol 19 ◽  
Keyword(s):  
Transmission Line ◽  
Large Scale ◽  
Original System ◽  
Reduced Order Model ◽  
Benchmark Problems ◽  
Transmission Line Model ◽  
Order Model ◽  
Line Model ◽  
Reduced Order ◽  
Numerical Effort

Transmission Line model are an important role in the electrical power supply. Modeling of such system remains a challenge for simulations are necessary for designing and controlling modern power systems.In order to analyze the numerical approach for a benchmark collection Comprehensive of some needful real-world examples, which can be utilized to evaluate and compare mathematical approaches for model reduction. The approach is based on retaining the dominant modes of the system and truncation comparatively the less significant once.as the reduced order model has been derived from retaining the dominate modes of the large-scale stable system, the reduction preserves the stability. The strong demerit of the many MOR methods is that, the steady state values of the reduced order model does not match with the higher order systems. This drawback has been try to eliminated through the Different MOR method using sssMOR tools. This makes it possible for a new assessment of the error system Offered that the Observability Gramian of the original system has as soon as been thought about, an H∞ and H2 error bound can be calculated with minimal numerical effort for any minimized model attributable to The reduced order model (ROM) of a large-scale dynamical system is essential to effortlessness the study of the system utilizing approximation Algorithms. The response evaluation is considered in terms of response constraints and graphical assessments. the application of Approximation methods is offered for arising ROM of the large-scale LTI systems which consist of benchmark problems. The time response of approximated system, assessed by the proposed method, is also shown which is excellent matching of the response of original system when compared to the response of other existing approaches .

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