Session: FSI-03-01 Structures Under Extreme Loading Conditions-1

Paper Number: 155659

155659 - A Study on Structural Analysis Methodologies to Account for the Hydraulic Loads on Reactor Vessel Internals 

Abstract: 

Introduction

For reactor vessel internals, vibration and stress analysis under hydraulic loads is regulated to ensure safety margins through a comprehensive vibration evaluation program [1]. Previous studies employed computational models of the coolant and fluid dynamics to generate frequency-domain loads for structural analysis. However, these models have limitations in capturing certain dynamic effects, such as eigenvalue shifts caused by the coolant [2]. To overcome these limitations, this study performs a modal analysis that incorporates the internal coolant, applying mode-based structural analysis to account for the system’s dynamic characteristics. Focusing on individual internal structures, the proposed methodology enables more detailed evaluations while reducing computational effort. The primary objective of this research is to develop a structural analysis methodology for reactor vessel internals that integrates the dynamic response of the full vessel assembly, incorporating fluid-structure interactions.

Methodology for structural analysis

A time history load on the fluid-structure surface was generated using transient analysis within a reactor vessel assembly, which includes the coolant, reactor, and internal structures [3,4]. The processed load was then applied to the surface of a reconstructed single internal structure through interpolation and extrapolation. In this study, the sub-modeling method was adopted to efficiently apply dynamic loads to internal structures, enabling detailed analysis while minimizing computational demands [5].

The stress analysis results for the internal structures under different load application methodologies were compared. When the fluid-structure interaction is not considered, the internal structures experience a significantly lower stress response. This could lead to a non-conservative analysis, as the actual stress is likely higher than what is observed without the coupling effects. On the other hand, when the coupling load at the fluid-structure interface is incorporated, the stress results match those of the reference case. This demonstrates that even when analyzing only the internal structures, incorporating the fluid-structure interaction load, as derived from reference dynamic analysis, ensures reliable stress response predictions.

References

[1] United States Nuclear Regulatory Commission, Comprehensive Vibration Assessment Program for Reactor Internals during Preoperational and Initial Startup Testing, Regulatory Guide 1.20, Rev.4, (2017).

[2] Kim, Kyu-Hyung; Ko, Do-Young. An Analysis on Comprehensive Vibration Assessment Program for APR1400 Reactor Vessel Internals. Transactions of the Korean Society for Noise and Vibration Engineering, (2020), 30.3: 229-238.

[3] KIM, Kyu Hyung; KO, Do Young; KIM, Tae Soon. Hydraulic and Structural Analysis for APR1400 Reactor Vessel Internals against Hydraulic Load Induced by Turbulence. International Journal of Safety, (2011), 10.2: 1-5.

[4] PARK, Jong-beom, et al. Seismic Responses of Nuclear Reactor Vessel Internals considering Coolant Flow under Operating Conditions. Nuclear Engineering and Technology, (2019), 51.6: 1658-1668.

[5] The Japan Society of Mechanical Engineers, An Alternative Rules on Seismic Design of Seismic S Class Piping by Elastic-Plastic Response Analysis, Standard No. JSME NC-CC-008 (in Japanese), (2019). Nonmandatory Appendix SEGP-B.

Presenting Author: Chiwoong Ra Yonsei University, Department of Mechanical Engineering

Presenting Author Biography: Graduate student in Mechanical Engineering at Yonsei University. Received a Bachelor’s and Master’s degree in Mechanical Engineering from Yonsei University. Research interests include structural vibration and non-linear finite element analysis, particularly in NPP components.

Authors:

Chiwoong Ra Yonsei University, Department of Mechanical Engineering
No-Cheol Park Yonsei University, Department of Mechanical Engineering
Hyungyu Roh Yonsei University, Department of Mechanical Engineering
Jeonghyun Kim Yonsei University, Department of Mechanical Engineering