Leakage Rate Assessment for Cracked Reinforced Concrete Panels in Nuclear Power Plants = 원자력발전소의 균열 발생 철근 콘크리트 패널에 대한 누설률 평가

다국어 초록 (Multilingual Abstract)

This dissertation investigates the mechanisms and prediction of gas transport through cracked reinforced concrete (RC) members, with emphasis on structural integrity and leak-tightness of nuclear containment systems. The study integrates experimental, empirical, and numerical approaches to elucidate the relationship between mechanical cracking behavior and resulting air permeability.
A series of laboratory tests were conducted on RC beam specimens subjected to flexural loading conditions. Airflow tests were performed under various differential pressures to quantify the leakage rate corresponding to different crack widths, reinforcement ratios, and plate thickness. The results revealed strong dependencies of flowrate on crack geometry, as well as on rebar ratio and plate thickness.
From these results, semi-empirical equations were formulated to predict the leakage rate through cracked RC, combining theoretical flow models with experimentally derived reduction factors that capture the effect of crack morphology. The proposed models improved the prediction accuracy compared to conventional leakage rate prediction formulas mostly developed for plain concrete.
Complementary numerical analyses were performed using a finite element framework coupling mechanical damage and flow behavior. An isotropic damage model was employed to represent crack formation and propagation, while the flow field was solved based on Darcy’s law. The model was validated against experimental data, demonstrating its ability to reproduce both the structural response and the leakage characteristics.
The dissertation establishes a unified methodology for assessing gas transport in cracked RC, providing insights applicable to the design and safety evaluation of containment structures. Future extensions include three-dimensional and strongly coupled analyses under high pressure, adoption of the Forchheimer equation for non-Darcy flow, and expanded experimental studies covering broader material and loading parameters.

국문 초록 (Abstract)

본 논문은 균열이 발생한 철근 콘크리트 부재를 통한 가스 이동 메커니즘과 예측을 연구하며, 특히 원자력 발전소 격납건물의 구조적 건전성과 누설 저항 성능에 중점을 둔다. 본 연구는 실험적, 경험적, 수치적 접근법을 통합하여 기계적 균열 발생 거동과 그에 따른 공기 투과성 간의 관계를 규명하였다.
휨-인장 하중을 받는 중공 철근 콘크리트 보 시편에 대해 일련의 실험을 수행하였다. 다양한 차압 수준 하에서 누설 실험을 실시하여 서로 다른 균열 폭 수준, 철근비, 판 두께에 따른 누설율을 비교하였다. 그 결과 유량이 균열 형상뿐만 아니라 철근비와 판 두께에 강하게 의존함을 확인하였다.
이러한 결과를 바탕으로 균열이 발생한 철근 콘크리트를 통한 누설율을 예측하기 위해 이론적 유량 모델과 균열 형상의 영향을 반영한 실험적으로 도출된 감소 계수를 결합한 반경험적 예측식을 제시하였다. 제안된 모델은 주로 무근 콘크리트를 대상으로 개발된 기존 누설율 예측식에 비해 높은 정확도와 낮은 분산을 보였다.
한편, 기계적 손상과 유체 거동을 결합한 유한 요소 해석 프레임워크를 활용한 수치 해석이 수행되었다. 균질 손상 모델을 콘크리트의 구성 방정식으로 사용했으며, 유동장은 Darcy 법칙에 기반하여 해석되었다. 본 모델은 실험 데이터와의 대조를 통해 검증되었으며, 구조적 응답과 누설 특성을 모두 재현할 수 있음을 보였다.
본 논문은 균열이 발생한 철근 콘크리트의 가스 이동 평가를 위한 통합적 방법론을 확립하여, 격납건물 안전성 평가에 적용 가능한 기초를 제안한다. 향후 확장 연구로는 고압 하에서의 3차원 및 강결합 해석, 그리고 더 광범위한 재료 및 하중 조건을 포괄하는 실험 연구 확대를 포함한다.

목차 (Table of Contents)

• Abstract i
• Table of Contents iv
• List of Acronyms viii
• List of Tables x
• List of Figures xi
• Chapter 1. Introduction 17
• 1.1 Background 17
• 1.2 Scope and Objectives 21
• 1.3 Outline of Dissertation 24
• Chapter 2. Literature Review 26
• 2.1 Leakage Tests 27
• 2.1.1 Material-level Tests 27
• 2.1.2 Structural Element-level Tests 31
• 2.1.3 Large-scale and Structural-system Tests 37
• 2.2 Leakage Rate Prediction Equations 41
• 2.3 Numerical Methods to Predict Leakage Rate 47
• Chapter 3. Proposal of Air Leakage Test Method 52
• 3.1 Introduction 52
• 3.2 Experimental Plan 53
• 3.2.1 Test Variables 53
• 3.2.2 Specimens 54
• 3.2.3 Test Setup and Instrumentation 62
• 3.2.4 Test Procedure 64
• 3.3 Test Results 67
• 3.3.1 Structural Response 67
• 3.3.2 Airflow Test Results 76
• 3.4 Effect of Test Variables on the Leakage Rate 84
• 3.4.1 Effect of Reinforcement Ratio 84
• 3.4.2 Effect of Plate Thickness 85
• 3.5 Leakage Rate Predictions 88
• 3.5.1 Leakage Rate Prediction Formulae 88
• 3.5.2 Calibration of Flexural Crack Width 91
• 3.5.3 Discussions on the Prediction Results 95
• 3.6 Future Study 97
• 3.7 Summary 98
• Chapter 4. Experiments for Air Leakage through Flexural Tension Crack 101
• 4.1 Introduction 101
• 4.2 Experimental Plan 102
• 4.2.1 Specimens and Setup 102
• 4.2.2 Instrumentation 109
• 4.2.3 Test Procedure 111
• 4.3 Test Results 115
• 4.3.1 Structural Response 115
• 4.3.2 Airflow Test Results 123
• 4.4 Discussion 135
• 4.4.1 Effect of Reinforcement Ratio 135
• 4.4.2 Effect of Plate Thickness 137
• 4.4.3 Effect of Transverse Reinforcement 138
• 4.5 Summary 139
• Chapter 5. Empirical Model for Air Leakage through Flexural Tension Cracks 141
• 5.1 Introduction 141
• 5.2 Depth-wise Crack Width Profile 143
• 5.2.1 Test Plan 143
• 5.2.2 Test Results of Crack Width 151
• 5.2.3 Estimation of Crack Width Profile 155
• 5.2.4 Test Results of Airflow 158
• 5.3 Governing Equations and Model Development for Airflow 160
• 5.3.1 Derivation of Governing Equations 160
• 5.3.2 Simplified Equations 163
• 5.4 Model Calibration 167
• 5.4.1 Reduction Factor 167
• 5.4.2 Reduction Factor Model Reflecting Reinforcement and Cover Thickness 170
• 5.5 Validation 175
• 5.6 Future Study 180
• 5.7 Summary 181
• Chapter 6. Finite Element Model for Air Leakage Prediction 183
• 6.1 Introduction 183
• 6.2 Poroelasticity Model for Reinforced Concrete 185
• 6.2.1 Governing Equations 185
• 6.2.2 Scalar Damage Model 187
• 6.2.3 Permeability Model 192
• 6.3 Simulation Setup 199
• 6.4 Numerical Results 203
• 6.4.1 Structural Responses 203
• 6.4.2 Fluid Response 213
• 6.5 Future Study 224
• 6.6 Summary 225
• Chapter 7. An Investigation of Leakage-Based Criteria for Containment in PSA 227
• 7.1 Introduction 227
• 7.2 Regulatory and Design Context 228
• 7.2.1 Design Criteria 228
• 7.2.2 Evaluation Criteria 233
• 7.3 Proposed Application in PSA Framework 238
• Chapter 8. Conclusions 251
• 8.1 Summary 251
• 8.2 Future Study 255
• Bibliography 258
• 초 록 278