1. Perspective on Thermal Hydraulic Researches in the Nuclear Field

2. Contents Introduction Status of the Nuclear Power
Domestic & international status
Thermal hydraulic researches
Active T-H Research Areas
Computational tools
Development & application
Experimental study
Facility & instrumentation
Concluding Remarks

3. Introduction
Background
Objectives
Scope & Depth

4. Status of the Nuclear Power
Korean Status
Stable Phase
Gyeongju disposal facility
CP for APR1400
6th Generating Capacity
Electricity Generation
39% of total (’06.12)
Enhancing the Use of Nuclear Energy
Problems

5. Status of the Nuclear Power (Cont’d)
International Status
435 commercial NPPs operating in 30 countries
370,000 Mwe
16% of the world's electricity
Enhancing the Use of Nuclear Energy
Energy demand, global warming, pollution, etc
Problems

6. Status of T-H Researches
Researches on Existing NPPs (to GEN-III+)
Focused on safety
To resolve safety issues
To ensure NPP safety due to power uprates and continued operation for operating NPPs
To ensure NPP safety due to new safety features for new NPP designs
Researches on Next Generation NPPs
Developmental researches to makeup technology gap
Safety researches to ensure NPP safety

7. Status of T-H Researches (Cont’d)
NPP Generation
GEN-III
OPR1000
GEN-III+
APR1400
GEN-IV
Water-Cooled Reactor Systems
Gas-Cooled Reactor Systems
Liquid-Metal-Cooled Reactor Systems
Nonclassical Reactor Systems

8. Status of T-H Researches (Cont’d)
T-H Research Categories
System code application and development
Computer simulation is the only way of knowing how the plant will respond to normal and accidental conditions.
Experiment
To investigate real phenomena and/or prove system performance
To provide technical basis for the development of models and correlations
Computational Fluid Dynamics (CFD) code application and development
CFD has now been recognized as an important tool.
Widely used for single phase problems, but for multi-phase ones

9. Status of T-H Researches (Cont’d)
Relationship among Research Categories
System
Code
Models & Correlations,
Validation
Scailability,
Facility & test design
Experiment
Models & Correlations,
Complement
Problem Definition
IC & BC
Mechanistic models,
Validation
Facility & test design
CFD

10. System Code Application
Wide Use of Realistic System Codes
WCOBRA/TRAC, CATHARE, CATHENA, RELAP5/MOD3, TRACE
Problems
What is the uncertainty?
Application of realistic evaluation model (REM)
What is the safety margin?
Application to safety and license issues 
Is a design feasible?
Application to test applicability of codes and issue finding
Uncertainty evaluation and methodology development for existing reactors and issue finding for new reactors

11. System Code Application (Cont’d)
Activities in Korea (원자력안전해석심포지움, CAMP/MUG Meeting)
ECCS realistic evaluation model (KINS, KAERI, KNF, KOPEC)
Application of KINS-REM to APR1400

12. System Code Application (Cont’d)
Activities in Korea (Cont’d)
Safety issue resolution (KINS, NETEC, KNF, KOPEC)
Mixing Volume Calculation (RELAP5)
Boron Concentration after LOCA (BORON)
Application of RELAP5 to Long-term Cooling Issue

13. System Code Application (Cont’d)
Activities in Korea (Cont’d)
Safety margin evaluation (KINS)
Event Tree
Safety Margin
Changes in PCT PDF
Application of RELAP5 to Safety Margin Evaluation

14. System Code Application (Cont’d)
Activities in Korea (Cont’d)
Application to new reactors (KAERI)
MARS Code V/V for LBE (Liquid lead-bismuth eutectic) Properties
Application of MARS to KALIMER

15. System Code Application (Cont’d)
Activities in Korea (Cont’d)
Application to experiment for new reactors (SNU)
SNU RCCS Facility for VHTR
Bulk Temperature in the Water Tank
Application of MARS to SNU RCCS Experiment

16. System Code Application (Cont’d)
International Activities (International CAMP Meeting)
Very similar to Korean activities
Code application to evaluate safety issues
Code application to check the existing code applicability for new reactors
Fuel Cladding Temperatures during Blowdown for a Feedwater Line Break
Application of RELAP5 to HPLWR (European Supercritical Reactor

17. System Code Development
Background
Accumulation of T-H research results
Drastic increase in machine performance
Need to efficient NPP operation
Problems
How to reduce the uncertainty?
Develop more sophisticated modeling (code & nodalization)
Develop more mechanistic models 
How to makeup technology gaps?
Improve the existing code capability or develop new codes
Develop new physical models
Uncertainty reduction for existing reactors and development of a system code for new reactors

18. System Code Development (Cont’d)
Korean Activities for the Existing Reactors
MARS code consolidation (KINS)
DVI model for APR1400
Validation of 3-D capabilities
Code coupling
Development of numerical technique with a high precision (KAERI)
Multi-dimensional models for 2-Ф flow and interfacial transport phenomenon
Numerical scheme
Multi-dimensional component modules (RCS, SG, etc)
Development of domestic design code system (KHNP)
Secure his own property

19. System Code Development (Cont’d)
International Activities for the Existing Reactors
TRACE code development (USNRC)
Spacer grid models
Droplet field & entrainment modeling
Interfacial drag models
NEPTUNE project (France IRSN)
Multi-scale and multi-disciplinary calculations (CATHARE + CFD)
To prepare the new generation of industrial two-phase flow codes
To structure and coordinate the R&D works around two-phase flow

20. System Code Development (Cont’d)
Analysis Needs for New Reactor Systems
Design tools for the reactor and associated components and processes
Predictive capabilities for ensuring safety of future reactor designs
Evaluation tools for design certification and licensing processes
Analysis results must present a strong safety case with a high level of proof for reactor licensing.

21. System Code Development (Cont’d)
Current Status and Challenges
A current focus is to modify LWR safety codes.
Challenges
New fuels
Different coolants
Higher temperature operating conditions
Events relevant to high-temperature gas-cooled reactors differ from those in LWR’s
New severe accident models are needed for phenomena peculiar to the future reactors

22. System Code Development (Cont’d)
Activities in Korea for New Reactors
Extension of MARS code to new reactors (KAERI)
MARS-SMART
MARS-GCR
MARS-LBE

23. System Code Development (Cont’d)
Activities in the States for New Reactors
Gas-cooled reactor codes
GRSAC
LWR codes
ATHENA + FLUENT + CONTAIN
MAAP4
MANTRA
MELCOR
RELAP5-3D
Major problem is lack of data for development of models & correlations and code validation

24. CFD Code Application Background Problems
CFD codes commonly used in many industrial sectors are now applied for nuclear reactor safety of for design purposes.
CFD codes are mainly capable of obtaining at a lower cost, valuable information on some physical phenomena.
Enable to test virtually any configuration, from both qualitative and quantitative points of view
Problems
How to validate CFD code and make results reliable?
How to apply multi-component and multi-Ф problems?
Quality assurance for CFD codes, and identification of the weakness of CFD techniques

25. CFD Code Application (Cont’d)
Direct Numerical Simulation (DNS)
“Costly” Fluid Dynamics used exceptionally
100% accurate with NO modeling hypothesis
Large Eddy Simulation (LES)
“Colorful” Fluid Dynamics with great detail
Applicable to eng. problems but at some cost
Almost as reliable as DNS, know-how required and not well established
Reynolds Averaged (RANS)
Conventional Fluid Dynamics widely used in eng
Economical, and full reactor or sub-component design problems
Needs improvement & validation for new range of applications

26. CFD Code Application (Cont’d)
Journal of Fluids Engineering Editorial Policy
The Journal of Fluids Engineering will not consider any paper reporting the numerical solution of a fluids engineering problem that fails to address the task of systematic truncation error testing and accuracy estimation. Authors should address the following criteria for assessing numerical uncertainty.
The basic features of the method including formal truncation error of individual terms in the governing numerical equations must be described.
Methods must be at least second order accurate in space.
Inherent or explicit artificial viscosity (or diffusivity) must be assessed and minimized.
Grid independence or convergence must be established.
When appropriate, iterative convergence must be addressed.
In transient calculations, phase error must be assessed and minimized.
The accuracy and implementation of boundary and initial conditions must be fully explained.
An existing code must be fully cited in easily available references.
Benchmark solutions may be used for validation for a specific class of problems.
Reliable experimental results may be used to validate a solution.

27. CFD Code Application (Cont’d)
USNRC ACRS Position on CFD Application
Anticipate increasingly use of CFD codes
To resolve multidimensional effects important to safety
Very little effort on CFD work in NRC
CFD codes are validated to a much less rigorous standard than codes for nuclear use, and the source codes are not available.
CFD codes appear to include a number of ad hoc fixes to improve stability and robustness
Comments on NRC plan for CFD model development
NPHASE for regulatory applications
Feasibility of the plan within the resource constraints of the agency.
Standards of reliability and accuracy required for CFD codes

28. CFD Code Application (Cont’d)
1-Ф Problems for the Existing Reactors
Boron dilution
Mixing of cold and hot water in Steam Line Break event
Hot-leg temperature heterogeneity
PTS (pressurised thermal shock)
Counter-current flow of hot steam in hot leg for severe accident investigations of a possible “Induced Break”
Thermal fatigue (e.g. T-junction)
Hydrogen distribution and combustion in containment

29. CFD Code Application (Cont’d)
1-Φ Problems for New Reactors
Natural circulation in LMFBRs
Coolability & Flow induced vibration of APWR radial reflector
Flow in lower plenum of ABWR
Depressurization of a GCR
Decay heat removal in a GCR
Thermal loading on structures
Containment integrity (peak pressure) during the long-term cooling of innovative reactors with passive safety systems

30. CFD Code Application (Cont’d)
2-Φ Problems Where CFD Is Recommended
2-Φ CFD tools are far less mature than single phase tools.
Identification of the relevant basic phenomena which need to be modeled for a given application
Assessment of the model including verification, validation and demonstration tests
Definition of new R&D work for a more detailed validation, for a better numerical efficiency, and a better accuracy and reliability of predictions

31. CFD Code Application (Cont’d)
CFD Application to Boron Dilution Issue

32. CFD Code Application (Cont’d)
CFD Application to 2-Φ Problems

33. CFD Code Development Immature Field with Many Challenges
Multi-component and multi-phase flow
Turbulent models
Numerical techniques
Verification & validation
Highlighted by technology development, enhanced machine performance, and relative low costs compared to experiments

34. CFD Code Development (Cont’d)
New T-H Many Challenges for VHTR

35. CFD Code Development (Cont’d)
INL 10-Year Plan for CFD

36. CFD Code Development (Cont’d)
Limited Scope CFD Analysis

37. Experimental Study
Mostly Accompanied by Code Development and Validation
Code development
Experiments to capture physics
Experiments to develop models & correlation
Component level experiments to develop component models in a code
Code validation
System or component level experiments (SETs & IETs)
Proof Experiments with Real Scale Facility

38. 원자력 열수력 실험의 국내 기관별 역할 열수력 실증실험 기술 개발(계측, 고온고압 실험, 척도해석 등) 원자력
전력 연구원
학 계
산업계
안전 기술원
원자력
연구소
열수력 실증실험 기술 개발(계측, 고온고압 실험, 척도해석 등)
중대형 열수력 실증실험체계 구축 및 실험 수행
중장기적 열수력 실증실험 연구 방향 도출
열수력 실증실험 기반 기술 개발
중소형 열수력 실험체계 구축 및 실험 수행
산업체 응용 실험 수행
실증실험 결과 활용
성능/안전성 향상 및 코드 검증을 위한 실증실험 필요 분야 도출
안전규제 현안/관심사 관련 실증실험 필요 분야 도출

39. 주요 대학의 핵심 연구 분야 KAIST 서울대 포항공대 경희대 제주대 기 타 CHF, Post-CHF 열전달 및 관련 메커니즘
비등 및 응축 열전달
신형원자로 계통 및 기기의 열수력 특성 (DVI 관련 현상, 피동 노심 냉각, 피동 격납 용기 냉각, 가스냉각로 등)
서울대
2상유동 및 Subcooled Boiling 특성 규명 (계측기 개발 포함)
신형원자로 계통 및 기기의 열수력 특성 (DVI 관련 현상, 피동 피동 격납 용기 냉각, 가스냉각로 등)
소형 열수력 종합효과실험
포항공대
비등 및 응축 열전달 특성 (다양한 열전달 증진 메커니즘 연구 포함)
계측 기술 개발: 전자기 유량계, Heat Flux Meter 등
비원자력 분야 산업체 응용 연구
경희대
Thermal Mixing & Stratification
Fluid-Structure Interaction
제주대
Electrical Impedance Imaging
기 타
Fundamental Research in Various Topics

40. 국내 실험 기술 및 인프라 수준 개별효과실험 체계 종합효과실험 체계 고온/고압 실험 및 측정기술은 세계적 수준에 접근
원자력 중장기 연구개발사업 등을 통해 열수력 핵심 모델 관련 실험시설을 확보하고 연구 진행 중
코드 모델 평가를 위한 상세 측정 데이터 생산 본격화
국내 개발 원자로 특성을 반영한 고유 모델 일부 개발
국내 실험에 기반한 고유 모델 개발 성과는 크게 미흡
종합효과실험 체계
ATLAS 구축으로 국내 원전 산업/규제에 필수적인 최소한의 종합효과실험체계 확보
국외 실험 데이터만으로는 미흡한 APR1400 및 OPR1000 관련 대부분의 사고 시나리오 모의 가능  산업체 및 규제검증 코드의 경쟁력에 필수
SMART 등 설계 특성이 크게 다른 원자로의 경우 새로운 종합효과실험시설 필요

41. Experimental Study for Advanced Reactor Systems
APEX Facility
Advanced Plant Experiment
Complete 2x4 Loop Primary System:
Length scale 1/4
Volume Scale 1/192
Core Power ~ 1 MW
Passive Safety Systems:
2 Core Makeup Tanks (CMTs) , 2 Accumulators, a Passive Residual Heat Removal (PRHR) Heat Exchanger, IRWST, and a 4-Stage ADS System.
Hot & Cold Leg SBLOCAs, MSLB, Inadvertent ADS, Double-Ended DVI Line Break, Station Blackout and Long Term Recirculation.

42. Experimental Study for Advanced Reactors Systems (Cont’d)
PUMA Facility
Purdue University Multi-Dimensional Integral Test Assembly
Design a well-scaled integral test facility having proper and sufficient instrumentation
Pressure ratio 1/1
Area ratio 1/100
Length (height) ratio 1/4
Power ratio 1/200
Maximum heater rods power 650 kW
Assess important SBWR phenomena for LOCA and other transients

43. Experimental Study for New Reactor Systems
Experiments for CFD Model Assessment

44. Experimental Study for New Reactor Systems (Cont’d)
Experiments for CFD Model Assessment (Cont’d)

45. Concluding Remarks Importance of T-H Researches Lots of T-H Researches
Safety issue resolution for the operating NPPs
Advanced and future reactor systems
Increased needs for CFD technology development
Keep your eyes on TREND
Integrate information gathered and extract points
Not predicting the future would be like driving a car without looking through the windshield.