SEMI-IMPLICIT THERMAL-HYDRAULIC COUPLING OF ADVANCED SUBCHANNEL AND SYSTEM CODES FOR PRESSURIZED WATER REACTOR TRANSIENT APPLICATIONS
Open Access
- Author:
- SOLER-MARTINEZ, MARIA DESAMPARADOS
- Graduate Program:
- Nuclear Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Maria Nikolova Avramova, Thesis Advisor/Co-Advisor
Maria Nikolova Avramova, Thesis Advisor/Co-Advisor - Keywords:
- RELAP5/COBRA-TF
semi-implicit coupling
coupling codes - Abstract:
- Being able to predict two-phase phenomena transients is a priority for the computer simulation programs used in nuclear safety assessments of Pressurized Water Reactors. System codes were developed for modeling the entire primary system, yet they use a relatively coarse nodalization that introduces some inaccuracies into the analysis. Sub-channel codes apply a finer discretization to the PWR core and therefore reduce some of these limitations, but at a higher computational cost. To achieve relatively accurate solutions while maintaining reasonable computational costs, one of the best options would be to couple codes in order to analyze the entire system. The coupling concept offers clear advantages for analysts because it permits a higher level of detailed modeling that avoids the limitations of certain computer programs. In the past few years, numerous coupled thermal-hydraulic system codes have been developed enabling the modeling of different portions of the integrated domain with programs that will include their own available features that users can fully employ. Furthermore, in order to get more realistic information about some transient phenomena, not only do the models need to improve, but the numerical robustness and stability satisfying the qualitative accuracy requirements must also be fulfilled. The numerical solution of nonlinear systems involves an iterative process. Picard iteration has been widely used for solving nonlinear systems because it is easy to codify, has a relatively low computational cost, involves a symmetric linear system, and has low continuity requirements. The main goal of this thesis is to describe the work carried out in the coupling of the COBRA-TF sub-channel code to the RELAP5-3D system code. Coupling both codes includes their current capabilities and incorporates features to extend the models’ analysis, especially for Loss-of-Coolant Accidents (LOCAs). Another focus of the thesis is to study a possible numerical improvement in COBRA-TF in order to achieve numerical robustness and more stable solutions while simulating transient phenomena. The main contribution of this study is the development of improved general coupling interfaces, which are designed to perform axial and lateral coupling between two codes while accounting for the differences in the code models as well as improving the stability and numerics of the coupled scheme.