Thermohydraulic Analysis of Coolant Entry Patterns in a High-Temperature Pebble Bed Reactor: Insights and Characterization

Abstract

Conducting three-dimensional thermohydraulic analysis of an entire nuclear reactor poses significant challenges due to the considerable geometric volume and complex internal structures involved. The top reflector is one of the internal structures found in high-temperature pebble bed Small Modular Reactors (SMR). This structure serves several critical functions, including neutron reflection, control and distribution of helium inlet into the core, neutron and thermal shielding, among others. In this kind of system, the detailed representation of the top reflector includes the representation of more than 460 channels of 2.5cm of diameter. Considering that the reactor has almost a ten of meters then dimension scales of various orders must be represented, which is a challenge. In this sense, a three-dimensional Computational Fluid Dynamics (CFD) thermohydraulic analysis of the entry pattern to the core of a High Temperature SMR using ANSYS CFX has been done. This study presents a comparison between five coolant entry patterns into the core. Initially, two prototype models of 460x2.5cm, one with vertical channels and another with inclined channels, are modeled. Additionally, two prototype models of 20x12cm of equivalent area, with vertical and inclined channels are also included. Finally, a simplified porous media model with the same equivalent area is considered. The thermohydraulic behavior of the coolant before and after passing through the top reflector was then analyzed for these five patterns. An analysis of fuel elements temperature in the core was conducted. It is important to highlight that this study is qualitative and has the goal of identifying and characterizing the impact that the coolant entry pattern into the reactor core has on the main thermohydraulic parameters in this region. The study exposes a strong correlation between the porous media model and all prototype models in terms of the maximum fuel temperature, average fuel temperature, and helium velocity. In this study, the potential applicability of the porous media models for an integral full-scale reactor simulation in the future was demonstrated. As a benefit, the porous media model reduces the mesh quantity compared to a prototypic model.

Keywords

• ; top reflector detailed representation
• ; thermohydraulic analysis
• porous media
• HTR
• CFD

Supporting Institution

Research Support Foundation of the State of Pernambuco (FACEPE)

Project Number

BFP-0093-3.09/21 and BFP-0146-3.09/23

References

1. OECD/NEA, “Advanced Nuclear Reactor Systems and Future Energy Market Needs,” 2021.
2. IEA, “World Energy Outlook 2021,” Paris, 2021.
3. OECD/NEA, “Generation IV International Forum, Technology Roadmap Update for Generation IV Nuclear Energy Systems,” Paris, 2014.
4. IAEA, “Guidance on Nuclear Energy Cogeneration,” Vienna, 2019.
5. GIF, “GIF R&D Outlook for Generation IV Nuclear Energy Systems: 2018 Update,” 2018.
6. B. Zohuri, “Generation IV nuclear reactors,” in Nuclear Reactor Technology Development and Utilization, A. N. Salah Ud-Din Khan, Ed., Elsevier, 2020, pp. 213–246. doi: 10.1016/B978-0-12-818483-7.00006-8.
7. IAEA, “Nuclear Power Reactors in the World,” 2021.
8. GIF, “Generation IV International Forum 2020 Annual Report,” 2020.

9. GIF/RSWG, “Basis for the Safety Approach for Design & Assessment of Generation IV Nuclear Systems,” Vienna, 2021.
10. D. E. Shropshire, A. Foss, and E. Kurt, “Advanced Nuclear Technology Cost Reduction Strategies and Systematic Economic Review,” 2021.
11. Y. A. Hassan and H. Students, “Theoretical Foundations and Applications of Computational Fluid Dynamics in Nuclear Engineering,” Trieste, 2022.
12. A. Gámez Rodríguez, L. Y. Rojas Mazaira, C. R. García Hernández, D. Dominguez Sanchez, and C. A. Brayner Oliveira Lira, “An integral 3D full-scale steady-state thermohydraulic calculation of the high temperature pebble bed gas-cooled reactor HTR-10,” Nucl. Eng. Des., vol. 373, no. December 2020, 2021, doi: 10.1016/j.nucengdes.2020.111011.
13. C. Wang, Y. Liu, X. Sun, and P. Sabharwall, “A hybrid porous model for full reactor core scale CFD investigation of a prismatic HTGR,” Ann. Nucl. Energy, vol. 151, p. 107916, 2021, doi: 10.1016/j.anucene.2020.107916.
14. IAEA, “Evaluation of High Temperature Gas Cooled Reactor Performance: Benchmark Analysis Related to the PBMR-400, PBMM, GT-MHR, HTR-10 and the ASTRA Critical Facility,” IAEA, Vienna, 2013.
15. Z. Zhang, J. Liu, S. He, Z. Zhang, and S. Yu, “Structural design of ceramic internals of HTR-10,” Nucl. Eng. Des., vol. 218, no. 1–3, pp. 123–136, 2002, doi: 10.1016/S0029-5493(02)00205-4.
16. Y. M. Ferng and C. T. Chen, “CFD investigating thermal-hydraulic characteristics and hydrogen generation from graphite-water reaction after SG tube rupture in HTR-10 reactor,” Appl. Therm. Eng., vol. 31, no. 14–15, pp. 2430–2438, 2011, doi: 10.1016/j.applthermaleng.2011.04.007.
17. Y. M. Ferng and C. W. Chi, “CFD investigating the air ingress accident for a HTGR simulation of graphite corrosion oxidation,” Nucl. Eng. Des., vol. 248, pp. 55–65, 2012, doi: 10.1016/j.nucengdes.2012.03.041.
18. I. ANSYS, ANSYS CFX Solver Modeling Guide, 19.0. Canonsburg, PA, 2018.
19. D. Milian Pérez, A. Gámez Rodríguez, L. Hernández Pardo, M. L. Daniel Evelio, and B. de O. L. Carlos Albrto, “Implementation of a Multi-cell Approach in the Multi-Physics Calculations of an Aqueous Homogeneous Reactor,” Int. J. Thermodyn., vol. 24, no. 4, pp. 125–133, 2021, doi: 10.5541/ijot.895287.
20. I. ANSYS, ANSYS CFX-Solver Theory Guide, 19.0. Canonsburg, PA, 2018.
21. KTA, “Reactor Core Design of High-Temperature Gas-Cooled Reactors Part 2: Heat Transfer in Spherical Fuel Elements,” KTA, 1983.
22. KTA, “Reactor Core Design for High-Temperature Gas-Cooled Reactor Part 1: Calculation of the Material Properties of Helium,” KTA, 1978.
23. Z. Gao and L. Shi, “Thermal hydraulic calculation of the HTR-10 for the initial and equilibrium core,” Nucl. Eng. Des., vol. 218, no. 1–3, pp. 51–64, 2002, doi: 10.1016/S0029-5493(02)00198-X.
24. J. C. L. Pritchard, J. Philip, Introduction to Fluid Mechanics, 8th ed. John Wiley & Sons, Inc, 2011.
25. H. Wang and Z. J. Zhai, “Analyzing grid independency and numerical viscosity of computational fluid dynamics for indoor environment applications,” Build. Environ., vol. 52, pp. 107–118, 2012, doi: 10.1016/j.buildenv.2011.12.019.
26. P. J. Roache, Verification and validation in computational science and engineering. Albuquerque, N.M: Hermosa Publishers, 1998.
27. S. Hu, R. Wang, and Z. Gao, “Safety demonstration tests on HTR-10,” 2nd Int. Top. Meet. High Temp. React. Technol., pp. 22–24, 2004.