APro, a modularized process-based total system performance assessment framework, was developed at the Korea Atomic Energy Research Institute (KAERI) to simulate radionuclide transport considering coupled thermal-hydraulic-mechanicalchemical processes occurring in a geological disposal system. For reactive transport simulation considering geochemical reactions, COMSOL and PHREEQC are coupled with MATLAB in APro using an operator splitting scheme. Conventionally, coupling is performed within a MATLAB interface so that COMSOL stops the calculation to deliver the solution to PHREEQC and restarts to continue the simulation after receiving the solution from PHREEQC at every time step. This is inefficient when the solution is frequently interchanged because restarting the simulation in COMSOL requires an unnecessary setup process. To overcome this issue, a coupling scheme that calls PHREEQC inside COMSOL was developed. In this technique, PHREEQC is called through the “MATLAB function” feature, and PHREEQC results are updated using the COMSOL “Pointwise Constraint” feature. For the one-dimensional advection-reaction-dispersion problem, the proposed coupling technique was verified by comparison with the conventional coupling technique, and it improved the computation time for all test cases. Specifically, the more frequent the link between COMSOL and PHREEQC, the more pronounced was the performance improvement using the proposed technique.

1. Introduction
2. METHODOLOGY
    2.1 Operator Splitting Method
    2.2 Conventional Coupling Technique Implementedin APro Using MATLAB
    2.3 New Coupling Technique Calling PHREEQCas MATLAB Function Inside COMSOL
3. Numerical Results
    3.1 Verification With the 1D ARD BenchmarkProblem
    3.2 Performance Analysis for the ProposedTechnique
4. Conclusion
Acknowledgements
REFERENCES

• Dong Hyuk Lee(Korea Atomic Energy Research Institute)
• Hong Jang(Korea Atomic Energy Research Institute)
• Hyun Ho Cho(Korea Atomic Energy Research Institute)
• Jeonghwan Hwang(Korea Atomic Energy Research Institute)
• Jung-Woo Kim(Korea Atomic Energy Research Institute) Corresponding author