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1 2015 안전해석심포지움 대천, 핵연료연소도현안을반영한 안전해석방법론 한전원자력연료 이걸우

2 핵연료고연소도현안을반영한안전해석 One of Nuclear Safety Goals is to Maintain the Fuel Rod Integrity 핵연료 고연소도안전현안 안전해석 Nuclear Fuel Design HBU Safety Issues DBA LOCA analysis 2

3 Nuclear Fuel Design related to HBU FA Manufacturing Fuel Assembly Design Nuclear Design Thermal-Hydraulic Analysis Fuel Rod Performance Analysis COLSS/CPC Thermal Margin Analysis Transient Analysis LOCA Analysis Computer Code and Methodology Development 3

4 Nuclear Fuel Nuclear fuel generates the fission heat Nuclear fuel contains the fission products during heat generation Nuclear fuel experiences the irradiation 4

Typical High Burnup Fuel Fuel pellet cracking

temperature gradient The fuel fragments are

Power : few cracks Power decrease as a burnup

Fuel rod Pellet Burn-up Pellet densification

5 Typical High Burnup Fuel Fuel pellet cracking due to thermal stresses induced by the temperature gradient The fuel fragments are relocated slightly, gap size decreases Low Power : few cracks Power decrease as a burnup Ramped to high Power : many cracks Diameter Fuel rod Pellet Burn-up Pellet densification due to pore Swell due to fission gas in grain boundary 5

6 Typical High Burnup Fuel [Ref.] Wiesenack, Physical Principles and Computational Codes for Fuel Behaviour Modelling (Lecture 9.3), Nov , 2008 [Ref.] Wiesenack, Introduction to Fuel Behaviour Modelling, April 12-23,

7 Safety Analysis Safety Analysis is performed using the Plant and Nuclear design data For example, LBLOCA analysis is performed according to licensed evaluation methodology. 7

Typical Fuel Rod Behavior during LBLOCA LBLOCA ~300 s (5 min.) SBLOCA ~3600 s (1 hr.) 14OFA, 16/17ACE7,PLUS7 HIPER16/17 - ZIRLO, M5, HANA 1-Cycle : 18 month ~18000 MWd/MTU Maximum FA Avg.

8 Typical Fuel Rod Behavior during LBLOCA LBLOCA ~300 s (5 min.) SBLOCA ~3600 s (1 hr.) 14OFA, 16/17ACE7,PLUS7 HIPER16/17 - ZIRLO, M5, HANA 1-Cycle : 18 month ~18000 MWd/MTU Maximum FA Avg. BU < 55,000 MWd/MTU Peak Fuel Rod BU < 60,000 MWd/MTU Figure 1: Fuel rod cladding load in a double-ended Cold Leg Break LOCA [Ref.] KfK-3973, A Review of Zircaloy Fuel Cladding Behavior in a Loss-of-Coolant Accident, September 1985 [Ref.] KfK-4781, Cladding deformation and Emergency Core cooling of a Pressurized Water Reactor in a LOCA summary description of the REBEKA program, August

Typical Fuel Rod Behavior during LOCA Oxidation and phase change Rapid Diffusion

b < 750 O C > 950 O C (1400 F) (1750) 1.

Fuel Adiabatic Heat up (nearly stagnation flow) 3.

ECCS delivery and Reflood Quenching Steam Cooling General Cladding Behavior 800

9 Typical Fuel Rod Behavior during LOCA Oxidation and phase change Rapid Diffusion of Oxygen in Metal and Oxide Formation on Metal begin Typical Zircaloy Cladding a b < 750 O C > 950 O C (1400 F) (1750) 1. Power Rapid Decrease (Void Negative Reactivity) 2. Fuel Adiabatic Heat up (nearly stagnation flow) 3. Blowdown Cooling (and/or Burst) 4. High Temperature Oxidation 5. Steam Cooling 6. ECCS delivery and Reflood Quenching Steam Cooling General Cladding Behavior Clad. Temp. (C)1200 Power PCT 1204 O C ECR 17% Ballooning, Rupture, and Phase Change Quenching and Phase Change PQD 135 O C/275 O F [Ref.] R.Meyer (ACRS) NRC, Sep 8, 2005 time (minutes) 9

10 고연소도 (HBU) 안전현안 One of Nuclear Safety Goals is to Maintain the Fuel Rod Integrity 반응도인가사고 소결체열전도도저하 ECCS 허용기준변경 Reactivity Initiated Accident (RIA) Pellet Thermal Conductivity Degradation (TCD) 10 CFR 50.46c Revision Based on HBU fuel rod Tests (Experiments) - High Burnup Phenomena Related on Fuel rod performance Nuclear design and Safety Analysis 10

11 고연소도 (HBU) 현상 Peak Rod Burnup 60 GWd/t Power Peaking Factor Burndown Credit Pellet Pellet Conductivity Degradation Void volume changes (crack, open porosity, geometry) Densification Swelling Pellet Radial Power Distribution to the rim region Gap Open gap He Closed gap Fission Gas Release increase (Xe/Kr) Rod Internal Pressure increases Clad Oxidation increases Embrittlement High Temperature Deformation Burst 11

12 Burnup Effect during LOCA Global Transient Hydraulics is insensitive to fuel burnup during LOCA Initial Conditions of Fuel rod at High Burnup for LOCA All Fuel Rod data depends on the BURNUP All Physics parameters depends on the BURNUP Initial Core and Equilibrium Core Peaking Factor Axial Power Shape Reactivity Feedback 성능자료조건연소도증가에따른경향 소결체열전도도 Modified NFI ( 국부온도 ) 감소 소결체평균온도 Fuel Rod Data ( 국부출력조건 ) 증가 고온간극크기 Fuel Rod Data ( 국부출력조건 ) 감소 간극열전도도 Fuel Rod Data ( 국부출력조건 ) 증가 / 감소 봉내압 Fuel Rod Data ( 봉평균출력 ) 증가 산화막두께 Fuel Rod Data (CZP) 증가 간극기체조성 Fuel Rod Data (CZP) 핵분열기체분율증가 반경방향출력분포 Nuclear Data (TURBRN) 중심출력분율감소 f( 연소도, 농축도 ) 12

13 PIRT for HBU fuel Review of LOCA Regulatory Guide Review of HBU fuel NUREG-1230 (1988), Compendium of ECCS Research for Realistic LOCA Analysis, Chapter 6.14 Stored energy and internal heat transfer Fission product release Rod swelling, ballooning and rupture Oxidation-induced embrittlement NUREG/CR-5249 (1989), CSAU NUREG/CR-6744 (2001) MATPRO Uncertainty Parameters for Steady State and Transient 13

14 Requirements (KINS/GT-N007-2 or RG 1.157) 초기및경계조건과설비유용성 (KINS/GT-N007-2, 2 장 II 절 2. 가.(1) 항 ) 민감도분석결과를기초로발전소수명기간중가장극단적인초기조건. 단복합적으로발생할수없는초기조건을 가정할필요는없다. 파단면적스펙트럼, 기타초기및경계조건 초기저장에너지 Initial stored energy (KINS/GT-N007-2, 2 장 II 절 2. 나.(1) 항 ) ( 가 ) ( 나 ) ( 다 ) ( 라 ) KINS/GT-N007-2, 초기저장에너지 가상사고이전의정상운전상태에서핵연료내온도분포와초기저장에너지는가정한초기조건, 핵연료상태및운전이력에대해최적방법으로계산되어야한다. 이를위해핵연료소결체의열전도도와핵연료소결체와피복재사이의간극열전도능이평가되어야한다. 크랙공간기체의열전도도를고려한핵연료내온도분포에대한노내실험결과를근거로열전도도계산모델이개발되어야한다. 고온간극의크기와핵연료내부기체의성분및압력의함수로간극열전도능이결정되어야한다. 고온간극의크기를계산할때이산화우라늄혹은산화우라늄연료의팽창, 조밀화, 크리이프, 열팽창, 핵연료단편의전이, 피복재의크리이프등이고려되어야한다. 모델들이위에서기술한기본현상을포함하고기술적근거가적절한실험자료와해석에의해그타당성이입증될경우최적핵연료모델로사용될수있다. 적용 소결체열전도도반영최적열전도능반영 - 불확실도변수 Modified-NFI (IFA CLT Assessment) 간극열전도도모델 (NUREG/CR-5535, V1 Section 4) Fuel Rod Model (IFA Assessment) ( 마 ) 핵연료내부의열전달계산에사용되는모델은여러가지적합한실험자료와의비교를통해타당성이입증되어야하고핵연료연소, 핵연료소결체의균열및전이, 피복재크리이프, 기체혼합물의전도도를고려할수있어야한다. 참고문헌 [2, 3] 의모델및상관식은최적모델로사용될수있으며, 기술적근거가적절한실험자료와해석에의해타당성이입증된타모델도사용될수있다. NUREG/CR-5535, V1, Section 4 [2] Lanning, 1982 [3] MATPRO11(R2),

15 Requirements (KINS/GT-N007-2 or RG 1.157) 금속 - 물반응율 (KINS/GT-N007-2, 2 장.II 절 2. 나.(5) 항 ) KINS/GT-N007-2, II.2. 나초기저장에너지 (5) 항적용지르칼로이피복재와증기의반응으로부터발생하는에너지방출율, 수소생성율및피복재산화율은최적방법으로계산되어야한다. 기술적근거가적절한자료와해석에의해타당성이 Metal-Water Reaction ( 가 ) 입증된최적모델이사용되어야한다. 냉각재상실사고동안피복재의파열이발생한것으로예 - 불확실도변수측된핵연료봉에대해서피복재내부의산화반응도최적방법으로계산되어야한다. 피복재온도가 C (1900F) 이하에서의금속-물반응을계산하는상관식들은적절한자료와비교화여그타당성이입증되어야한다. 이상관식에는증기압, 피복재의예비산화, 산화과 [5] Cathcart, ORNL/NUREG- ( 나 ) 정중의변형, 증기와핵연료의내부산화등의효과가포함되어야한다. 피복재온도가 C 17 (1977) (1900F) 이상에서는참고문헌 [5] 의자료를사용하여에너지방출율, 수소생성율및피복재산화율이계산될수있다. 원자로노심열 / 물리적변수 (KINS/GT-N007-2, 2 장 II 절 2. 다.(1)(2) 항 ) ( 가 ) ( 나 ) ( 다 ) ( 라 ) (1) 피복재 / 핵연료봉의팽창과파열에대한열적변수적용 피복재내의온도분포와피복재내. 외부의압력차이로부터야기되는피복재의팽창과파열은시간에따라최적방법으로계산되어야한다. 기술적근거가적절한자료와해석에의해타당성이입증된모델이사용되어야한다. 간극의열전도능, 피복재의산화및취화, 수소발생, 피복재외부의열전달과유체유동을계산할때피복재의팽창및파열의정도가고려되어야한다. 핵연료와피복재온도를시간의함수로계산하기위해서는온도와시간의함수로기술된간극열전도능과기타열적변수가사용되어야한다. 피복재의팽창을계산하기위한최적방법에서는피복재온도의공간적분포, 가열량, 재료물성치비등방성의비대칭피복재변형및핵연료보의열. 재료변수들이고려되어야한다. (2) 기타노심열적변수원자로심의열적해석을수행할때, 노심내재료의물리적및화학적변화 ( 용융합금의형성, 상변화, 또는재료상화작용에의해야기되는기타현상들 ) 은필요에따라적절하게고려되어야한다. 기술적근거가적절한자료와해석에의해타당성이입증된모델이사용되어야한다. Swell and Rupture - 불확실도변수 Deformation Gap conductance Hot Gap size High Temperature Creep Plastic deformation MATPRO (FRAPCON/FRAPTRAN) 15

16 Comparison of Fuel Rod Model RELAP FRAPCON FRAPTRAN Parameter Coolant conditions 6-Eq simple input (HTC, P, T) or (H, P, T, G) Power Point input input Radial Power Profile input TUBRNP FRAPCON (BU, Enrich) Axial Power Profile input input input BU Oxidation Exothermal O X O T Decay Heat O O Time Thermal conduction equation SS/TR SS TR ρ*c p For transient (fuel+gap+clad) (Conduction)-crud X O X Input (SS crud effect) (Conduction)-ZrO 2 X O O Input (SS oxide effect) Gap conductance Dynamic Dynamic Dynamic Dynamic Uncertainty Gas O O O Radiation O O O Contact X O O Contact Convection Plenum Gas Temperature Model X O O Fuel Rod Mechanical Response O O O Pellet / Clad deformation Fuel Rod Internal Pressure Response O/X O O Clad deformation and burst High-Temperature Oxidation O X O BJ, CP, ZIRLO Cladding Failure Model Rupture X O PCMI, Ballooning 16

17 Fuel Rod Model Fuel RELAP User input RELAP FRAPCON FRAPTRAN MATPRO Parameter Melting Temperature X O O O BU TCD Volumetric Heat Capacity madata O O O O O T Thermal conductivity madata O O O O O (T, BU) TCD Emissivity gapcon O O O O T Thermal Expansion gapcon O O O O T Fuel densification O X O O O Sintering, BU initial condition Fuel Swell O X O O O (T, BU) initial condition Gas Conductance Gas Conductivity madata->gasthc O O O O T Clad Volumetric Heat Capacity madata O O O O O T ZIRLO Thermal conductivity madata O O O O O T Emissivity gapcon O O O O T Thermal Expansion gapcon->cthxpr O O O O T Elastic Modulus gapcon->celmdr O O O O T Axial Growth X O O O SS Creep * X O O O (T,stress) initial condition High temperature Creep cplexp->plstrn O X O X (T,stress) ZIRLO Meyer Hardness * X O O O contact Chemical Properties Oxide Thermal conductivity X O O O T Equivalent or Explicit SS Oxidation O X O X O T BJ or CP (ZIRLO) High Temperature Oxidation ht1tdp->qmwr * O O O X T BJ or CP (ZIRLO) Mechanical Properties Busrt Temperature cplexp->ruplas O X O X (T,stress) ZIRLO Busrt Blockage cplexp->plstrn O X O X (T,stress) ZIRLO 17

18 PIRT for HBU fuel NUREG/CR-6744 Steady State Fuel Rod Performance Uncertainty Parameters (for example) Steady State Fission Gas Release Transient Fission Gas Release Clad Corrosion Rod Growth Clad Creep Pellet Densification Clad Inside Diameter Clad Outside Diameter Pellet Diameter Fill Gas Plenum Length Pellet Density Fast Neutron Flux Initial Local Power at Transient Oxide Crud Pellet Swelling Rate Pellet Thermal Expansion Pellet Thermal Conductivity Categroty A Plant Transient Analysis PIRT Importance, H Uncertainty HBU Analysis Initial conditions gap size O I gap pressure 7 50 O I gas composition 1 50 O I Pellet and cladding dimension < O I burnup distribution O fixed cladding oxidation (ID & OD) < 1 50 O I coolant conditions rod free volume 7 50 O X gas communication (full) < 1 50 gadolinium distribution < initial stored energy-fuel O FAT initial stored energy-structure initial core pressure drop (grids) < pellet radial power distribution < O I rod axial power distribution <7 100 O I fuel assemble peaking factors O I pin peaking factors (pin power within FA) < fuel cycle design O ND transient power distribution moderator feedback O decay heat power fuel temperature feeback < O delayed neutron fraction < O Energy deposition in moderator and structures < O I SS and TR cladding to coolant HT Single phase convection Sub.NB,FC Critical heat flux/dryout film boiling 7 50 radiation heat transfer < rewet (liquid contact after dryout) 7 50 space grid TH interaction 6 50 Space grid rewetting and droplet breakup 7 0 Transient coolant condition (coolant) temperature 7 50 flow rate and direction (CCFL) 7 50 quality 7 50 void fraction 7 50 Pressure cross flow effects due to flow blockage 7 50 Fuel rod response Plastic deformation of cladding (Irreversible) 5 100? Direct gas pressure loading Thermal deformation of pellet and cladding (reversible) < Elastic deformation of cladding (reversible) < Heat resistances in fuel, gap and cladding 5 92 O contact Axial and radial temperature distribution 5 92 O Metal-water reaction heat addition < O Cladding oxidation magnitude < 1 90 O Cladding temperature 5 80 Cladding phase changes < burst criteria 5 50 time of burst 1 50 O location of burst and blockage 5 83 O relocation < 1 0 O time-dependent gap-size HT 5 58 O contact thermal and mechanical properties of pellet and cladding O18 MATPRO Multiple rod mechanical effects Rod bow < 1 0 Multiple rod thermal effects rod-to-rod radiation HT <

19 BELOCA (for example) Phenomenon/Process Model/Uncertainty Stored energy release 5 2 Pellet heat transfer pellet conductivity Gap conductance gap conductance Clad Oxidation reaction, heat source Cathcart-Powel Clad Ballooning (RIP) Flow Blocakge NUREG-0630 Fuel (axial) Relocation into clad-balloned region X Clad Burst NUREG-0630 Double-sided oxidation Cathcart-Powel Fuel rod radiation heat transfer (Guide tube) X Additional Parameters for HBU fuel Gap Pressure (related to Clad ballooning) Rod Free Void Volume Pellet Radial Power Distribution (related to FAT) Heat Resistance in fuel, gap and cladding Contact conductance Time-dependent Gap-size Heat Transfer (Gap conductance) Material Properties (Modified NFI) 19

20 Thermal Conductivity, W/m-K Thermal Conductivity, W/m-K Pellet Thermal Conductivity Degradation Modified NFI model (used in ROPER and FRAPCON/FRAPTRAN) Kfuel (W/m - K) K95 K 95 A a gad BT d/ (1 d/100) 1 f ( Bu) (1 0.9exp( 0.04Bu)) g( Bu) h( T) E exp( F / T) 2 T UO2 Thermal Conductivity (95%TD, 0 GWD/MTU) UO2 Thermal Conductivity (95%TD, 60 GWD/MTU) Temperature, K Temperature, K FATES PAD ROPER (m NFI) FATES PAD ROPER (m NFI) 20

mnfi Predicted Thermal Conductivity, W/m-K Pellet thermal conductivity (Modified NFI) UO2 thermal Conductivity HALDEN IFA Centerline temperature Temperature (350-2000 O C) Uncertainty 7.0 6.0 5.

21 mnfi Predicted Thermal Conductivity, W/m-K Pellet thermal conductivity (Modified NFI) UO2 thermal Conductivity HALDEN IFA Centerline temperature Temperature ( O C) Uncertainty Measured Thermal Conductivity, W/m-K Christensen [1] Godfrey [2] Bates [3] Gibby [4] Weilbacher [5] Goldsmith [6] Hobson [7] Ronchi [8] irradiated 21

22 Pellet Thermal conductivity Heat Generation Rate and Temperature Distribution in a fuel Assumed the uniform heat generation, W/m 3 Temperature independent thermal conductivity, W/(m-K) Actually, fuel conductivity is function of fuel temperature LHR (Linear Heat Rate) is restricted by Technical Specification Typical Maximum LHR is less than 15.0 kw/ft T T center surf Kdt LHR(W/m) 4π (T center T surf )K GWd/MTU and ERF Fuel Average Temperature 1500 K, and conductivity is 2.1 W/(m-K) for Modified-NFI Temperature difference ~ 1800 K: W/m divided by (4 x pi x dt) Fuel centerline temperature is less than K = 2400 K (~2100 C) Fuel melting temperature ~ 2800 C During the LOCA, the fuel temperature decrease because of power decreases. 22

23 Typical Fuel Rod Temperature 23 V V S p p dv t r q ds T t r k dv t T t r c t r q T t r k t T t r c ), ( ) ), ( ( ), ( ), ( ) ), ( ( ), ( ''' '''

24 Typical Fuel Parameters Fuel Temperature Fuel Temperature increases as the power (LHR) increases Fuel Temperature increases as the burnup increases After pellet and clad contact (at High burnup condition) Contact conductance increases Fuel temperature mainly depends on fuel conductivity 24

25 Typical Fuel Parameters Fuel Temperature System code (RELAP) is initialized to fit the fuel rod data RELAP steady state over-predicts the Initial stored energy (Fuel average temperature). Model Difference between the RELAP and fuel rod performance code data data data 25

26 Technical Issues to evaluate the High burnup (RELAP) Required calculation method and model for High Burnup Study 1. Peaking Factor Burndown Credit 2. Pellet Radial Power Distribution (RPD) model (from flat assumption) 3. Initialization of Fuel rod in RELAP5 computer code 4. Dynamic Gap conductance model with contact conductance (0.2) (0.4) (0.6) (0.8) (1.0) radial power Pellet 5. Transient (dynamic) Fuel Rod Internal Pressure model Additional Uncertainty Parameters and Evaluation P gap = Mole R V plenum N T + j=1 plenum V T i 1. Fuel Pellet conductivity (physical uncertainty): Consider the maximum FAT 2. Gap conductance (thermal uncertainty): rod model and manufacturing uncertainty 3. Rod internal Pressure (mechanical uncertainty): rod model and transient fission gas Limiting Break size/type and Limting Burnup Study 1. Limiting Burnup depends on the Break Size and other uncertainty parameters 2. Limiting Break size depends on the Burnup and other uncertainty parameters Additional change 1. Axial Shape and Radial peaking factor uncertainty 26

27 Technical Issues to evaluate the BELOCA Uncertainty Parameters and Evaluation 1. It is not possible and practical to implement all fuel rod data as uncertainty Fuel rod code can provide the BE condition and uncertainty range for the BELOCA. 2. Fuel Pellet conductivity (physical uncertainty) For LOCA uncertainty evaluation, Pellet thermal conductivity is the Physical material properties 3. Gap conductance (thermal uncertainty) Fuel rod model has the various model to calculate the temperature; creep and others Also, there is the tolerance in rod geometry introduced during manufacturing (rod dimension) 4. Rod internal Pressure (mechanical uncertainty) At the high-burnup condition, the RIP (fission gas release) plays the important role. Burst is affected by the initial and transient RIP. 5. Others affected by burnup Limiting Break Size and Type can be changed and/or uncertain in Burnup study Limiting Peaking Factor and Axial power shape depend on burnup 27

28 Summary Current HBU(High Burnup) issues in LOCA analysis TCD: Pellet Thermal Conductivity Degradation due to Burnup increase 10CFR50.46c Revision: HBU Experiments on ECCS Acceptance Criteria Fuel Behavior during LOCA is Swell, (ballooning), Rupture, and Oxidation Heat transfer in Pellet and Clad gap HBU Effects Hydraulic Responses are insensitive to burnup. Fuel Parameters are changed due to fuel rod burnup. (Point-kinetics) Nuclear Parameters are changed due to Cycle burnup. LOCA method must treat the HBU effects, such as burnup-dependent Fuel property and response during steady state and transient 28

슬라이드 1

슬라이드 1 APR1400 KNF/ / 2008. 4. 11 13 Table of Contents 1. APR1400 LBLOCA (Now vs. Before) 2. 3. 4. 13 2 1. APR1400 LBLOCA (Now vs. Before) Now Before 13 3 1. APR1400 LBLOCA (Now vs. Before) PCT Before Now SIT