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Transcription

1 KAERI/RR-2738/2006

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5 - ii -

6 - iii -

7 - v -

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9 - vii -

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11 Chapter 1 Introduction 1 Section 1 Evaluation of Steam Explosion Risks and Establishment of Engineered Safety Features 1 Section 2 Development of a Quenching Mesh for Protection of Instruments 4 Section 3 Establishment of Evaluation Technology for Cooling Behavior of Molten Corium 5 Chapter 2 State of Art 9 Section 1 Evaluation of Steam Explosion Risks and Establishment of Engineered Safety Features 9 Section 2 Development of a Quenching Mesh for Protection of Instruments 10 Section 3 Establishment of Evaluation Technology for Cooling Behavior of Molten Corium 11 Chapter 3 Contents and Results of Research 13 Section 1 Evaluation of Steam Explosion Risks and Establishment of Engineered Safety Features Improvement and Application of Experimental Measurement Methodology 14 가. Installation of Intermediate Catcher and Quick-Acting Valve 14 나. Improvement of Measurement Methodology for Temperature, Static Pressure, Void Fraction and Melt Velocity 16 다. Improvement of Measurement Methodology for Dynamic Pressure and Dynamic Load 30 라. Development of Axial Tomography 31 마. Improvement of Measurement Methodology for High Temperature Melt 39 - ix -

12 2. Experiments for Evaluation of Material Characteristics and Steam Explosion Mitigation Principle 54 가. Experiments for Evaluation of Material Characteristics 54 나. Physical and Chemical Analysis on Debris 91 다. Observation of Miscibility Gap and Analysis of Thermodynamical Phase Diagram Evaluation of Steam Explosion Risks 119 가. Preparation of Integrated Report on Steam Explosion Experiments 119 나. Preparation of Evaluation Report on Steam Explosion Risks 128 다. Promotion of OECD/SERENA Phase 2 International Collaborative Research Program Evaluation of Feasibility of Core Catcher 138 가. Development of Concepts and Application of Patents 138 나. Experimental Facility Design and Experimental Results Results and Discussions 165 Section 2 Development of a Quenching Mesh for Protection of Instruments Development of a Quenching Mesh 166 가. Experiments with 5 Combustion Chambers and Extended Vessel 166 나. Experiments with 7 Combustion Chambers and Extended Vessel Specifications of a Prototypic Quenching Mesh Development of Evaluation Model for Function of a Quenching Mesh Results and Discussions x -

13 Section 3 Establishment of Evaluation Technology for Cooling Behavior of Molten Corium Improvement and Application of Analysis Methodology of Steam Explosions 187 가. Improvement and Verification of Breakup Model 187 나. Improvement of Lagrangian Model 191 다. Evaluation of Material Effects and Application of Integrated Model to a Reactor Case (TEXAS-V) 200 라. Evaluation of Multi-Dimensional Model and Application of Integrated Model to a Reactor Case (MC3D) Improvement and Application of MCCI Analysis Methodology 219 가. Examination and Evaluation of MCCI-1 Test Results 219 나. Development and Evaluation of Separate Effect Model 229 다. Application to a Reactor Case Results and Discussions 249 Chapter 4 Degree of Research Achievement and Contribution to Related Fields 253 Section 1 Evaluation of Steam Explosion Risks and Establishment of Engineered Safety Features 253 Section 2 Development of a Quenching Mesh for Protection of Instruments 255 Section 3 Establishment of Evaluation Technology for Cooling Behavior of Molten Corium 255 Chapter 5 Proposal for Applications 257 Section 1 Evaluation of Steam Explosion Risks and Establishment of Engineered Safety Features 257 Section 2 Development of a Quenching Mesh for Protection of Instruments xi -

14 Section 3 Establishment of Evaluation Technology for Cooling Behavior of Molten Corium 259 Chapter 6 Technical Informations Collected from Abroad during Research 261 References 265 Appendix A Proposal for OECD/SERENA Phase 2 - xii -

15 제 1 장연구개발과제의개요 1 제 1 절증기폭발위해도평가및대처방안수립 1 제 2 절계측기보호용소염망개발 4 제 3 절노심용융물냉각거동평가기술구축 5 제 2 장국내 외기술개발현황 9 제 1 절증기폭발위해도평가및대처방안수립 9 제 2 절계측기보호용소염망개발 10 제 3 절노심용융물장기냉각거동평가기술구축 11 제 3 장연구개발수행내용및결과 13 제 1 절증기폭발위해도평가및대처방안수립 실험계측방법론개선 / 적용 14 가. 중간저장조및고속격리밸브설치 14 나. 온도 / 정압 / 기포율 / 용융물전달속도측정방법개선 16 다. 동압 / 동하중측정방법개선 30 라. 축방향토모그래피개발적용 31 마. 초고온용융물온도측정방법개선 물질특성평가 / 완화방안원리입증실험 54 가. 물질특성평가실험 54 나. 데브리물리화학분석 91 다. Miscibiliy Gap 관찰및열역학적상태도해석 증기폭발위해도평가 119 가. 증기폭발실험종합보고서작성 119 나. 증기폭발위해도평가보고서작성 128 다. SERENA 2단계국제공동연구추진 Core Catcher 타당성평가 138 가. 개념개발및특허출원 xiii -

16 나. 실험장치설계및실험결과 결과및토의 165 제 2 절계측기보호용소염망개발 계측기보호용소염망개발 166 가. 연소격실 5개와확장용기에서의실험 166 나. 연소격실 7개와확장용기에서실험 기기보호용소염망시작품명세서 소염망성능평가모델개발 결과및토의 186 제 3 절노심용융물장기냉각거동평가기술구축 증기폭발해석방법론개선 / 적용 187 가. 분쇄모델개선검증 187 나. Lagrangian 모델개선 191 다. 물질효과평가및통합모델원자로경우적용 (TEXAS-V) 200 라. 다차원모델평가및통합모델원자로경우적용 (MC3D) MCCI 해석방법론개선 / 적용 219 가. MCCI-1 실험결과검토및평가 219 나. 개별효과모델개발및평가 229 다. 원자로경우적용 결과및토의 249 제 4 장연구개발목표달성도및관련분야에의기여도 253 제 1 절증기폭발위해도평가및대처방안수립 253 제 2 절계측기보호용소염망개발 255 제 3 절노심용융물장기냉각거동평가기술구축 xiv -

17 제 5 장연구개발결과의활용계획 257 제 1 절증기폭발위해도평가및대처방안수립 257 제 2 절계측기보호용소염망개발 258 제 3 절노심용융물장기냉각거동평가기술구축 259 제 6 장연구개발과정에서수집한해외과학기술정보 261 참고문헌 265 부록 A OECD/SERENA Phase 2 제안서 - xv -

18 표 고속카메라위치에따른측정조건 23 표 고속카메라에의한실험부속도측정결과 (TROI-48, 상부 ) 28 표 고속카메라에의한실험부속도측정결과 (TROI-48, 하부 ) 28 표 고속카메라와열전대에의한용융물속도측정결과 (TROI-48) 29 표 투시창및방사율비조정에따른이색복사온도계의온도측정값 46 표 투시창에따른이색복사온도계의보정식 46 표 Measurement parameters and their descriptions 63 표 TROI 실험의개요 (TROI-45 ~ TROI-48) 64 표 TROI 실험의개요 (TROI-49 ~ TROI-52) 65 표 TROI 실험의개요 (TROI-53 ~ TROI-56) 66 표 TROI 실험의개요 (TROI-57 ~ TROI-60) 67 표 체번호에따른 debris 크기 91 표 Debris 분석결과 ( 실험년도 2005 ~ 2006년 ) 92 표 금속충전물의분석결과 ( 철및 stainless steel) 93 표 배기되는기체에포함된원소 94 표 TROI-49번용융고화물의시료채취위치및특성 99 표 TROI-49번의시료에따른화학분석결과 (ICP-AES) 99 표 층분리된시료의 ICP-AES 화학분석결과 (w/o) 115 표 물질효과규명을위한대상실험 123 표 Core catcher 실험계측인자 148 표 번의 Core catcher 실험개요 148 표 상온에서실험경우및화염속도 169 표 가속및온도증가에따른격실간소염망성능실험경우 176 표 가속및온도증가에따른모델기기에대한소염망성능실험경우 177 표 기기보호용소염망시작품명세서 182 표 Model I과 II 의소염거리 183 표 TROI-13 의주요입력조건및 TEXAS-V 코드의주요인자 xvii -

19 표 Initial condition and model constant for sensitivity study of TROI 표 Ex-vessel steam explosion conditions and model parameter for TEXAS-V code 212 표 SSWICS 실험 matrix 220 표 MET-1 test specification 223 표 CCI 콘크리트의주요물성치 224 표 Specification for CCI test 225 표 LCS 콘크리트침식계산의주요입력자료 232 표 냉각수주입시점 232 표 D 콘크리트침식계산결과요약 (0 % LCS) 235 표 D 콘크리트침식계산결과요약 (5 % LCS) 236 표 D 콘크리트침식계산결과요약 (10 % LCS) 236 표 D 콘크리트침식계산결과요약 (15 % LCS) 237 표 D 콘크리트침식계산결과요약 (20 % LCS) 237 표 해석에사용된주요입력자료 242 표 해석에사용된용융물조성및질량 243 표 APR1400 MCCI 해석주요입력자료 xviii -

20 그림 중간저장조와고속격리밸브개략도 15 그림 용융물제트낙하모습 (25cm x 25cm) 16 그림 열강화유리를통과한온도교정곡선 17 그림 용융로속의용융물온도 19 그림 입수직전의용융물의온도 19 그림 정압계교체후정압거동 20 그림 차압계로측정한기포율 (TROI-59) 21 그림 희생열전대의온도변화 22 그림 용융물가시화용고속카메라위치 (B1 and B2) 24 그림 고속카메라의측정위치 25 그림 고속카메라로측정한용융물형태 (TROI-48, 상부 ) 26 그림 고속카메라로측정한용융물형태 (TROI-48, 하부 ) 27 그림 고속카메라와열전대에의한용융물속도측정결과 (TROI-48) 30 그림 전기장을이용한축방향토모그래피의종류 33 그림 축방향토모그래피를위한하드웨어및경계조건 34 그림 축방향토모그래피의민감도행렬구성 34 그림 역전사알고리듬에따른복원이미지 35 그림 축방향토모그래피를위한하드웨어시스템 35 그림 축방향토모그래피모의실험장치 37 그림 축방향토모그래피실험을위한소프트웨어 38 그림 기포가없는경우축방향토모그래피실험을통하여복원된이미지 38 그림 TROI 실험장치에서이색온도계측정위치 40 그림 텅스텐 thermowell을이용한온도측정법 41 그림 공동을이용한온도측정법 42 그림 온도측정을위한아르곤기체공급관 43 그림 아르곤기체공급에따른온도변화 (UO2/ZrO2=70/30, TROI-54) 44 그림 강화유리투시창에대한온도보정곡선 45 그림 TROI-27 실험에서온도측정보정결과 47 - xix -

21 그림 IRCON 이색복사온도계방사율비의정의 49 그림 복사온도계의방사율비 (k) 에따른온도보정곡선 50 그림 방사율비에따른교정실험및이론보정온도비교 51 그림 TROI-57 실험에서의용융물배출과정의온도변화 53 그림 이색복사온도계의응답속도 (rt) 에따른온도계측오차 53 그림 고속밸브장착후 TROI 실험장치의개략도 68 그림 TROI-45에서의동압 69 그림 TROI-45에서증기폭발에의한동압 69 그림 TROI-45에서외부기폭에의한동압 70 그림 TROI-45에서증기폭발에의한동하중 70 그림 TROI-45에서의파편층크기분포 71 그림 TROI-46에서의동압 71 그림 TROI-46에서의동하중 72 그림 TROI-46에서의파편층크기분포 72 그림 TROI-47에서의용융물온도 73 그림 TROI-47에서의파편층크기분포 73 그림 TROI-48에서의동하중 74 그림 TROI-48에서의파편층크기분포 74 그림 TROI-51에서의동압 75 그림 TROI-51에서의동하중 75 그림 TROI-51에서의파편층크기분포 76 그림 TROI-52에서의용융물온도 76 그림 TROI-52에서의동압 77 그림 TROI-52에서의파편층크기분포 77 그림 TROI-53에서외부기폭에의한동압 78 그림 TROI-53에서증기폭발에의한동압 78 그림 TROI-53에서증기폭발에의한동하중 79 그림 TROI-53에서의파편층크기분포 79 그림 TROI-54에서의동압 80 그림 TROI-54에서의동하중 80 그림 TROI-54에서의파편층크기분포 81 그림 TROI-55에서의동압 81 그림 TROI-55에서의동하중 82 - xx -

22 그림 TROI-55에서의파편층크기분포 82 그림 TROI-56에서의동압 83 그림 TROI-56에서자발적인증기폭발에의한동압 83 그림 TROI-56에서의파편층크기분포 84 그림 TROI-57에서의동압 84 그림 TROI-57에서의동하중 85 그림 TROI-57에서의파편층크기분포 85 그림 TROI-58에서의동압 86 그림 TROI-58에서의동하중 86 그림 TROI-58에서의파편층크기분포 87 그림 TROI-59에서의동압 87 그림 TROI-59에서 steam spike에의한동압 88 그림 TROI-59에서 steam spike에의한동하중 88 그림 TROI-59에서의파편층크기분포 89 그림 TROI-60에서입수직전용융물의온도 89 그림 TROI-60에서의동압 90 그림 TROI-60에서의파편층크기분포 90 그림 사이클론형에어로졸채집장치도면 95 그림 사이클론형에어로졸채집장치 96 그림 용융물의고화후의모습 (TROI-49) 97 그림 용융고화물의상분리 (TROI-50) 98 그림 XRD 분석결과 ( 하부고화층 ; TROI-49); 적색수직선 기준피크 100 그림 % debris의 XRD(TROI-57-7) 102 그림 UO 2 /ZrO 2 =70/30 충전된 debris의 XRD(TROI-13-7) 103 그림 표면연마된시료의형태 (TROI-13, 40X) 104 그림 위치에따른분석결과 (TROI-13a, 270X) 105 그림 위치에따른분석결과 (TROI-13b, 270X) 106 그림 위치에따른분석결과 (TROI-13C, 300X) 107 그림 위치에따른 EPMA 분석결과 (TROI-13, 시료 a, b, c) 108 그림 TROI-47-7 debris, 40X 110 그림 TROI-47-7b particle b, 120X 110 그림 EPMA 분석결과 (TROI-47-7b) xxi -

23 그림 Debris의입자 (TROI-51-5, 40X) 112 그림 Debris 입자 b에대한 EPMA 분석결과 (TROI-51-5b 85X) 112 그림 Debris의 EPMA 분석결과 (TROI-51-5b) 113 그림 금속을포함한코륨용융물의상분리 116 그림 XRD 분석결과 ( 하부고화층, CL) 117 그림 용융물층의상태도 (TROI-49) 117 그림 금속층의원소비율 (TROI-49) 118 그림 산화물층의원소비율 (TROI-49) 118 그림 용융물성분에따른증기폭발의에너지변환율 121 그림 TROI-13 입자의단면도 123 그림 TROI-13 입자의단면에따른조성분포 124 그림 TROI-17 입자의단면도 124 그림 TROI-17 입자의단면에따른조성분포 125 그림 지르코니아실험에서의미세입자 125 그림 지르코니아실험에서의거대입자 126 그림 TROI-47 입자의단면도 126 그림 TROI-47 입자의단면에따른조성분포 127 그림 TROI-51 입자의단면도 127 그림 TROI-51 입자의단면에따른조성분포 128 그림 In-vessel and Ex-vessel steam explosion situation for SERENA Phase 그림 Calculated In-vessel impulse at vessel bottom 131 그림 Calculated Ex-vessel impulse at cavity wall 131 그림 Sensitivity study on composition by using TEXAS-V 133 그림 Calculated volume fraction of each phase at triggering time in 70:30 corium/water interaction 133 그림 Calculated volume fraction of each phase at triggering time in 80:20 corium/water interaction 134 그림 Calculated volume fraction of each phase at triggering time in 0:100 corium/water interaction 134 그림 Calculated fuel diameter at given location for each material right before triggering event xxii -

24 그림 Schematic view and main characteristics of the KROTOS and TROI facilities 138 그림 노심용융물피동냉각및가둠장치 139 그림 원자로용기를관통한노심용융물냉각장치및그방법 140 그림 울진 3,4호기원자로공동단면도 141 그림 Core catcher 실험용 P&ID 144 그림 TROI 장치를개선한 Core catcher 실험장치 145 그림 코륨용융물의하부에서냉각수주입용시험부 149 그림 시험부 150 그림 TROI 장치에설치된수냉도가니및코일 ( 실험 1) 151 그림 냉각수주입에따른증기폭발및용융물분출에의한배선연소기체 152 그림 실험중배출된용융물에의하여손상된장치 ( 실험 1) 154 그림 증기폭발로분출된용융물에의한손상및크러스트모습 155 그림 용융물크러스트주위로냉각수의주입및증기분출과정 ( 실험 #1) 156 그림 실험부 (#2) 158 그림 실험후 Injector의모습 (#4) 160 그림 주입되는냉각수유량 161 그림 냉각수주입부온도 162 그림 보호용기압력 162 그림 증기관의압력 163 그림 증기온도 163 그림 증기유량 164 그림 실험장치구성도 167 그림 연소실및주요계측위치 167 그림 모델기기 168 그림 Mesh Type 1, 2, 3, 그림 기기주위소염망설치모습 169 그림 소염망이없을때기기주위온도 170 그림 소염망이없을때기기주위화염전파모습 170 그림 표 의 Test No.2에대한압력및온도 171 그림 표 의 Test No.9에대한압력및온도 xxiii -

25 그림 화염전파모습 172 그림 화염전파모습 172 그림 두장겹쳤을때소염망사진 173 그림 소염망두장사용시격실거동 173 그림 실험장치 174 그림 장애물사진 175 그림 화염이미지 176 그림 화염이미지 177 그림 모델기기표면온도 178 그림 Pressure Transmitter 179 그림 압력계보호용소염망 179 그림 소염망전면도 179 그림 소염망좌측면도 179 그림 소염망우측면도 180 그림 보호용소염망하면도 180 그림 소염망걸쇄 181 그림 소염망조인트 181 그림 팽창비, 압력, 화염속도와소염거리 184 그림 팽창비, 압력, 화염속도와소염거리 184 그림 Model I의 d/b 185 그림 Model II의 d/b 185 그림 Particle size distribution of TROI 그림 Particle size distribution by old breakup 193 그림 Particle size distribution by new breakup 194 그림 Particle size distribution by modified new breakup 194 그림 L-33 Explosion pressures Old breakup 195 그림 L-33 Explosion Modified new breakup 196 그림 노외증기폭발 TEXAS-V 입력 197 그림 Explosion pressure comparison 198 그림 Explosion impulse comparison 198 그림 TROI-13의 TEXAS-V 입력조건 201 그림 C(47) 에대한민감도분석 xxiv -

26 그림 Calculated explosion pressure of TROI-13 during explosion 203 그림 Sensitivity study on TROI-13 test 204 그림 Sensitivity study on composition by using TEXAS-V 205 그림 Calculated volume fractions for each composition 206 그림 Calculated fuel diameter at given location for each composition 206 그림 Sensitivity study on water depth by using TEXAS-V 207 그림 Calculated volume fractions for each composition 208 그림 Calculated vapor fraction at 130 cm water pool test 208 그림 Calculated fuel fraction at 130 cm water pool 209 그림 Sensitivity study on water cross-sectional area by using TEXAS-V 210 그림 Calculated volume fractions for each composition 210 그림 Initial and geometrical condition for Ex-vessel explosion 211 그림 Calculated explosion pressure for Ex-vessel explosion, C(47)=100e 그림 Calculated volume fraction for Ex-vessel mixing, C(47)=100e 그림 Calculated volume fraction for Ex-Vessel mixing, C(47)=10e 그림 Calculated explosion pressure for Ex-vessel explosion, C(47)=10e 그림 Geometry and typical mesh size of calculation 216 그림 Calculated flow maps for TROI Mixing at t= 0.64 s 216 그림 Pressures on the axis on bottom, middle, top of water tank 217 그림 Calculated explosion pressure on various position for TROI test 217 그림 Geometry and typical mesh size of calculation 218 그림 절단된 SSWICS ingot 모양 221 그림 SSWICS 실험에서측정된열유속 xxv -

27 그림 고화층파쇄강도 222 그림 Span 6 m 원자로의파쇄강도 222 그림 Debris/water 열유속 226 그림 콘크리트침식형상 (CCI-1 test) 227 그림 콘크리트침식형상 (CCI-2 test) 227 그림 콘크리트침식형상 (CCI-3 test) 228 그림 콘크리트침식경계면사진 (CCI-1 test) 228 그림 콘크리트침식경계면사진 (CCI-2 test) 229 그림 콘크리트침식경계면사진 (CCI-3 test) 229 그림 시간에따른노심용융물온도 233 그림 시간에따른열평형관계 234 그림 시간에따른 debris 분포 234 그림 콘크리트침식이완료된시점의총침식깊이 238 그림 콘크리트침식이완료된시점까지걸리는시간 239 그림 콘크리트침식이완료된시점의 bed와 crust 질량 239 그림 냉각수주입이시작될때까지침식된콘크리트깊이 240 그림 실험 ( 좌 ) 및해석 ( 우 ) 의 test section 241 그림 용융물온도비교 243 그림 콘크리트침식깊이비교 244 그림 열평형비교 (heat release) 244 그림 열평형비교 (heat addition) 245 그림 Melt height 비교 245 그림 콘크리트침식깊이 (MELCOR 계산 ) 248 그림 콘크리트침식형상 (MELCOR 계산 ) xxvi -

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35

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42 ` φ ` 105 `

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44 Tcal (Calibrated Temperature) Tm (Measured temperature) Temperature (K) Reference Temperature (K)

45 - 18 -

46 MELTTEMP seconds 2800 Temperature(K) Time(sec) MELTTEMP Temperature(K) Time(sec)

47 PVSP004 PVSP005 FVSP001 Pressure(MPa) Time(sec)

48 VFDP101 (20-40cm) VFDP102 (40-60cm) VFDP103 (60-80cm) Void Fraction Time(sec)

49 340 Temperature(K) IVT201 (0cm) IVT202 (20cm) IVT203 (40cm) IVT204 (60cm) IVT209 (0cm) Time(sec)

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52

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57 HS C Thermocouple melt velocity, m/s height from bottom, mm

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60 ε ε

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77 Signal Output Ratio k=1.30 k=1.15 k=1.00 k=0.85 k= Temperature (K)

78 3000 Measured temperature (K) Glass, k = 1.00, measured Glass, k = 1.15, measured Glass, k = 1.15, Theoretical Real Temperature (K)

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80 Temperature (K) True Measured(0.001 sec) Measured(0.01 sec) Measured(0.05 sec) Time (sec)

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95 Pyrometer Pyrometer-2 Argon supply to prevent oxidation PVSP004 PVT004 PVDP004 GAS004 plug top cold crucible Argon supply for aerosol removal Melt Catcher and Discharge Valve FVSP001 PVSP005 PVT005 PVDP005 GAS PVT003 PVDP003 IVT201~209 (every 20cm) pool depth :100cm window PVT002 PVDP002 PVT001 PVDP001 VFDP 102 IVT104 IVDP104 IVT103 IVDP103 IVT102 UWDP101 IVT101 IVDP102 IVDP101 IVT201 IVT209 IVDL VFDP 103 VFDP 101 manway 150 ET :Explosive (PETN 1g) Unit : cm water drain valve

96 Pressure(MPa) IVDP101 IVDP102 IVDP103 UWDP101 UWDP102 IVDP Time(sec)

97 Pressure(MPa) IVDP101 IVDP102 IVDP103 UWDP101 UWDP102 IVDP Time(sec) 800 IVDL Force(kN) Time(sec)

98 100 (%) Total Mass of Debris : 5.479kg % 34.0% 8.8% % 8.3% 6.7% 13.0% 0% 0% 0.1% 0.6% 1.4% (mm) Pressure(MPa) IVDP101 IVDP102 IVDP103 UWDP101 UWDP102 IVDP Time(sec)

99 IVDL Force(kN) Time(sec) 100 (%) Total Mass of Debris : kg % % 20 0% 0.3% 0.3% 1.5% 2.6% 7.7% 9.6% 7.5% 2.1% 1.8% (mm)

100 4000 MELTTEMP seconds Temperature(K) Time(sec) 100 (%) Total Mass of Debris : kg % % 7.8% 7.0% 4.1% 0% 0% 0% 0.3% 1.0% % 7.3% (mm)

101 30 25 IVDL Force(kN) Time(sec) 100 (%) Total Mass of Debris : kg % % 7.9% 6.8% 4.4% 0% 0% 0% 0.2% 1.1% % 7.6% (mm)

102 Pressure(MPa) IVDP101 IVDP102 IVDP103 IVDP104 IVDP105 IVDP106 UWDP101 UWDP Time(sec) IVDL Force(kN) Time(sec)

103 100 (%) Total Mass of Debris (Test Section 내 + 외부 ) : 6.309kg % 12.7% 11.1% 8.1% 7.1% 4.3% 0.1% 1.1% 1.1% % 6.3% 9.4% (mm) 3000 MELTTEMP seconds Temperature(K) Time(sec)

104 UWDP101 UWDP102 Pressure(MPa) Time(sec) 100 (%) Total Mass of Debris : 8.604kg % % 6.5% 4.5% 6.0% 0% 0.1% 0.1% 0.4% 1.2% % 5.9% (mm)

105 Pressure(MPa) IVDP101 IVDP102 IVDP103 IVDP Time(sec) 6 Pressure(MPa) IVDP101 IVDP102 IVDP103 IVDP Time(sec)

106 100 IVDL Force(kN) Time(sec) 100 (%) Total Mass of Debris : kg % 9.1% 8.6% 4.9% 0% 0.1% 1.4% 0.1% 0.4% % 12.6% 6.6% (mm)

107 Pressure(MPa) IVDP101 IVDP102 IVDP103 IVDP Time(sec) IVDL Force(kN) Time(sec)

108 100 (%) Total Mass of Debris : kg % 18.9% 15.0% 15.4% 8.7% 8.9% 0.4% 2.4% 1.5% % 0.6% 2.2% (mm)

109 100 (%) Total Mass of Debris : 7.940kg % 15.9% 19.6% 15.6% 14.2% 6.7% 6.5% 0.0% 0.9% 1.5% % 1.2% (mm)

110 Pressure(MPa) IVDP101 IVDP102 IVDP103 IVDP104 UWDP Time(sec)

111 100 (%) Total Mass of Debris : kg % 7.9% 8.9% 10.5% 7.2% 4.5% 0.2% 1.3% 1.1% % 6.6% 7.3% (mm) Pressure(MPa) PIVDP101 (20cm) PIVDP102 (40cm) PIVDP103 (60cm) PIVDP104 (80cm) Time(sec)

112 IVDL Force(kN) Time(sec) 100 (%) Total Mass of Debris : 9.437kg % 11.5% 9.1% 6.5% 6.7% 2.8% 0.0% 0.6% 0.7% % 3.8% 1.4% (mm)

113 IVDL Force(kN) Time(sec)

114 100 (%) Total Mass of Debris : kg % 23.7% 8.6% 10.2% 13.2% 9.7% 5.5% 0.2% 1.4% 1.0% % 1.1% (mm)

115 IVDL Force(kN) Time(sec)

116 100 (%) Total Mass of Debris : 9.306kg % 37.4% % 8.2% 2.7% 4.4% 5.4% 0.1% 0.5% 0.4% % 0.6% (mm) 2800 MELTTEMP Temperature(K) Time(sec)

117 Pressure(MPa) PIVDP101 (20cm) PIVDP102 (40cm) PIVDP103 (60cm) PIVDP104 (80cm) Time(sec) 100 (%) Total Mass of Debris : 8.595kg % % 2.5% 2.7% 4.5% 5.8% 5.1% 0.1% 0.7% 0.5% % 10.1% (mm)

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119 UO 2 ZrO 2 UO 2 ZrO 2 UO 2 ZrO 2 UO 2 ZrO 2 UO 2 ZrO 2 UO 2 ZrO 2 UO 2 ZrO 2 UO2 ZrO 2 ZrO 2 UO 2 ZrO 2 ZrO 2 UO 2 ZrO 2 UO 2 ZrO 2 UO 2 ZrO

120 UO 2 ZrO 2 UO 2 ZrO

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122 Pipe, 1" φ φ φ 25 Sampling Pot, 3ea φ

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127 Lin (Counts) Theta - Scale

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129 UO 2 ZrO Lin (counts) TROI 57-7 UO2 ZrO theta

130 TROI 13-7 U3O8 UO2 Lin (counts) theta UO 2 ZrO

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135 UO2/ZrO2, % 50 UO2; 13a UO2; 13b UO2; 13c ZrO2; 13a ZrO2; 13b ZrO2; 13c Disntance, μm UO 2 ZrO

136

137 a b c

138 U, Zr, O % U O Cr Zr Fe Ni Fe, Cr, Ni % Distance TROI-47-7b -0.5 TROI-47-7b, 120X, W x D = x μm

139 a b c

140 60 U Zr O Cr Fe Ni U, Zr, O % Fe, Cr, Ni % Distance TROI-51-5b, Metal and Oxygen TROI-51-5b, 85X

141 UO 2 ZrO 2 UO 2 ZrO

142

143 Upper Oxide Part Lower Metal Part

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147

148 Conversion ratio (%) Untriggered(0.6m) Triggered(0.6m) Triggered(0.3m) Untriggered(0.3m) UO2/ZrO2/Fe = 63/27/10 UO2/ZrO2/Zr/SS = 63/13.5/12.5/ , 21-23, UO2 Content

149

150

151 UO2 % UO2 ZrO Distance (micron), TROI

152 84 82 UO2 content, % Distance, μm TROI-17b

153

154 60 U O Cr Zr Fe Ni 2 U, Zr, O % Fe, Cr, Ni % Dis tance -0.5 b a c

155 U, Zr, Fe % U Fe Zr Distance TROI-51-7c, Metal Contents

156

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159

160 Pressure at Bottom during Explosion(MPa) base comp-8:2 Comp-0: Time (msec) Volume Fraction at Trigger Time Base-13 B:GasFrac C:LiqFrac D:FuelFrac Height From Bottom(m)

161 Volume Fraction at Trigger Time Corium8:2 B:GasFrac C:LiqFrac D:FuelFrac Height From Bottom(m) Volume Fraction at Trigger Time ZrO2 B:GasFrac C:LiqFrac D:FuelFrac Height From Bottom(m)

162 Mean Fuel Diameter per Cell(m) :3Corium 8:2Corium ZrO Height from Bottom(m)

163

164

165 5 kg of melt 1-D geometry New release device X-ray radioscopy External trigger UO2-ZrO2-Steel-Zr-FP KROTOS test section 20 kg of melt 2-D geometry Intermediate catcher Tomography External trigger TROI test assembly

166 Gas Tank Steam Condensed water Filter Coolant Storage Tank Intermediate Storage Tank Melt

167 (6) Reactor Vessel Molten Pool (5) (1) (4) (2) (3)

168 4'-0" EL 116' - 1' ICI chase Reactor Cavity EL 93'- 6" EL 86' EL 80' - 7 5/8" 4'-0" 3'-0" 5'-0" EL 69' 3'-0" EL 55' Carbon Steel Liner EL 52' EL 41'

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188 WFLOW Water Flow Rate (L/min) Time (sec)

189 Injector Temperature (K) CT201 CT202 CT Time (sec) FVSP001 Vessel Pressure (MPa) Time (sec)

190 PSF Pressure (MPa) Time (sec) 293 TSFLOW Steam Temperature (K) Time (sec)

191 SFLOW Steam Flow Rate (m 3 /s) Time (sec)

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197 Pressure Rise[Bar] P at COMP 2 P at Expan T at COMP 2 T at Right T at Upper T at Front T at Left Temperature[ o C] Time[msec]

198 Pressure Rise[Bar] P at COMP 2 P at Expan T at COMP 2 T at Right T at Upper T at Front T at Left Temperature[ o C] Time[msec]

199 Pressure Rise[Bar] P at COMP 2 P at Expan T at COMP 2 T at Right T at Upper T at Front T at Left Temperature[ o C] Time[msec]

200 Pressure Rise[Bar] P2 P1 T Temperature[ o C] 0.1 T Time[msec]

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209

210 ρu /(ρb P Vf) d= 5.4 eβα SL d = 4α SL d = 4.88α S L d = 5.34α S L d = 4 eβ α SL d= 4.9 eβα S L d= 5.4 eβα S L

211 Quenched Propagation 2.0 (d/b) ρ b /(ρ u PxV f ) 2.0 Quenched Propagation 1.5 (d/b) Expansion Ratio/(PxV f )

212 7.0x x10-5 H2:Air=10:90 H2:Air=30:70 d/b 5.0x x x x x10-5 Model I-1 Model I-2 Model I-3 2.0x x10-5 H2:Air=10:90 Single H2:Air=10:90 Multiple H2:Air=30:70 Single H2:Air=30:70 Multiple d/b 1.0x x Model II-1 Model II-2 Model II

213 ρu /(ρb P Vf) d= 5.4 eβα SL

214

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219 λ

220 Mass Ratio per Particle Size (% Total Mass of Debris = kg Particle Size(mm)

221 Mass Ratio per Particle Size (%) Total Mass of Debris = kg Particle Size(mm) Mass Ratio per Particle Size (%) Total Mass of Debris = kg Particle Size(mm)

222 Pressure at Bottom during Explosion(MPa) DP01 DP02 DP03 DP04 DP Time (msec)

223 Pressure at Bottom during Explosion(MPa) DP01 DP02 DP03 DP04 DP Time (msec)

224 5.5m = m2 Free board volum e = 100m 3 Air, 0.2M P a,- > Steam, 0.2M Pa, 393.4K(saturated) +0.22*#1 4.22m=0.5*#8 M elt free fall=1m 0.5m, 2950K, gravity pour=1m/s 80/20, 8000kg/m3, 100K superheat 1m=0.2m*#5 9.22m 4m w ater pool 0.2MPa 50K subcooled 343.4K 4 m =0.2m * #20 5m Trigger cell at m elt bottom contact

225 Pressure at Bottom during Explosion(MPa) OB-Pressure NB-Pressure MNB-Pressure Time (msec) Impuse at Bottom(kPa sec) OB-Impulse NB-Impulse MNB-Impulse Time (msec)

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230 Explosion Pressure(MPa) BDP01 CDP02 DDP03 EDP04 FDP Time(msec)

231 Pressure at Bottom during Explosion(MPa) base comp-8:2 Comp-0:10 fall-2.6 pres-0.2 pres-0.4 warea warea wdep-0.95 wdep-1.30 Ftemp-3300 Ftemp Time (msec)

232 Pressure at Bottom during Explosion(MPa) base comp-8:2 Comp-0: Time (msec)

233 Void Fraction at Trigger Time :30 Corium 80:20 Corium 100 ZrO Height From Bottom(m) Mean Fuel Diameter per Cell(m) :3Corium 8:2Corium ZrO Height from Bottom(m)

234 Pressure at Bottom during Explosion(MPa) base wdep-0.95 wdep Time (msec)

235 Void Fraction at Trigger Time cm 95cm 130cm Height From Bottom(m) Vapor Fraction s 1.0s 1.2s 1.4s 1.6s Height From Bottom(m)

236 Fuel Fraction s 1.0s 1.2s 1.4s 1.6s Height From Bottom(m)

237 Pressure at Bottom during Explosion(MPa) Base Warea Warea Time (msec) Void Fraction at Trigger Time m m m Height From Bottom(m)

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240 Explosion Pressure(MPa) B:DP01 C:DP02 D:DP03 E:DP04 F:DP Time(msec) Volume Fraction at Trigger Time B:GasFrac C:LiqFrac D:FuelFrac Height From Bottom(m)

241 Volume Fraction at Trigger Time B:GasFrac C:LiqFrac D:FuelFrac Height From Bottom(m) Explosion Pressure(MPa) B:DP01 C:DP02 D:DP03 E:DP04 F:DP Time(msec)

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244 Mixing Pressure(Pa) 2.5x x x x x10 6 P(14,1,23) P(1,1,1) P(11,1,1) P(1,1,17) P(11,1,17) Time(sec) Explosion Pressure(Pa) 3.0x x x x x x10 6 P(1,1,12) P(1,1,24) P(18,1,1) P(18,1,12) P(18,1,24) Time(sec)

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248 00 00 Time by which most structures have achieved thermal equilibrium TEST # vertical line 1 1 bar 8% LCS 2 1 bar 8% SIL 3 4 bar 8% LCS 4 4 bar 23 % LCS 5 4 bar 15% LCS 6 1 bar 15% SIL 7 4 bar 4% LCS conduction-limited Elapsed time after ignition ( sec )

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253 CCI-1 Power Off Crust Breach Test CCI-1 (SIL Concrete) Test CCI-2 (LCS Concrete) Test CCI-3 (SIL Concrete) Heat flux (kw/m 2 ) CCI-2 Power Off at 122 Minutes CCI-3 Crust Breach CCI-3 Power Off Elapsed time from cavity flooding (minutes)

254 cm PARTICULATE AND LAVA FROM WET CAVITY ERUPTIONS FOLLOWING BREACH 15.6 kg SIDEWALL CRUST MATERIAL 44.6 kg IN ITIAL PO WD ER H EIG H T +55 LOOSE CRUST MATERIAL +50 FRO M D RY CAVITY CONCEALED VOID ERUPTIONS 23.3 kg CORIUM TOP CRUST ~ 5 cm THICK SWK SWI 3 4 SWL SWJ IN ITIAL M ELT H EIG H T 25 cm ORIGINAL CAVITY BOUNDARY +5 WN WS 0 SWG SWH DENSE BLACK SWE OXIDE PHASE SWC 2 5 BASEMAT 1 SWF SWD POSTTEST CAVITY ABLATION PROFILE. TOTAL VOLUM E OF ERODED CONCRETE = 79 l (181 kg) -30 SWA 55 cm SWB LIGHT OXIDE PHASE - CONCRETE SIDEWALLS -45 PREDOMINATELY -50 SiO 2-55 D RAWIN G : CC I1 DEBRIS SAM PLE LOCATIONS (WEST VIEW) ELECTRODE CLAMP DRAWING NO.: MCCI460 DRAWN BY: D. KILSDONK DATE: 11/9/04 IBEAM FILE: CCI1_DSL.DWG(AC97) NORTH VIEW FORM WEST AT CENTER LINE SOUTH MIDDLE SECTION SIDEWALL CRUST 88.5 kg TOP CRUST 5-10 cm TH ICK IN CENTER cm +85 LARGE VOID REGION 49.2 kg POSTTEST CAVITY ABLATION PROFILE BASED ON MEASUREMENTS +80 REGION IN ITIAL PO WDER HEIG HT IN ITIAL M ELT H EIGHT (25 cm ) INITIAL CONCRETE SURFACE +30 VOLCANIC MOUND (~ 22 l) SWK 8 SWL SWI WN 3 4 SWJ WS LAYER OF CALCINED CONCRETE POWDER (~ 3 cm THICK) 0 SWG SWH SWE SWF POSTTEST CAVITY ABLATION PROFILE. TOTAL VOLUME OF ERODED SWC SWD CONCRETE = 220 l (513 kg) SWA 6 5 BASEMAT 7 SWB POROUS, SOLIDIFIED MELT OVER BASEMAT DRAWING: CCI2 BOTTOM SECTION (WEST VIEW) POSTTEST ABLATION ELECTRODE CLAMP DRAWING NO.: MCCI462 DRAWN BY: D. KILSDONK DATE: 11/9/05 IBEAM FILE: CCI2_BSWVPTA1.DWG(AC100) NORTH VIEW FORM WEST AT CENTER LINE SOUTH

255 cm LOWER SECTION SIDEWALL CRUST 47.7 kg FIRE BRICK ERUPTION MOUND 8.5 kg MIDDLE SECTION SIDEWALL CRUST 14.4 kg IN ITIAL PO WD ER H EIG H T IN ITIAL CO N CRETE SURFACE TOP CRUST 85.4 kg INITIAL M ELT H EIG H T (25 cm ) SWM VOID REGIONS 5 SWN POROUS SOLIDIFIED MELT SWK SWI WN SWG SWL SWJ WS SWH POSTTEST CAVITY ABLATION PROFILE. TOTAL VOLUME OF ERODED CONCRETE = 116 l (263 kg) SWE SWC SWA SWF SWD SWB MONOLITHIC OXIDE LAYER PARTIALLY DECOMPOSED CONCRETE WITH AGGREGATE EMBEDDED IN OXIDE BASEMAT ELECTRODE CLAMP IBEAM DRAWING: CCI3 BOTTOM SECTION (WEST VIEW) POSTTEST SAMPLES DRAWING NO.: MCCI655 DRAWN BY: D. KILSDONK DATE: 11/9/05 FILE: CCI3_BSWVPTA1.DWG(AC112) NORTH VIEW FORM WEST AT CENTER LINE SOUTH

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257 j g, crit = δ crit ρ e cr cr 0.445Rhm ( Tm T f ), kcr ( T f Tsat ) 1 ln 1 δ ( ) 1 crithm Tm T f ξ q " hlv ( l v ) = dry C ν v ρ ρ g 5 /13 Nk c 2 cr cr ( e ) e sat crack 2 4 /13 α exp T sol T sat σ y + α E exp cr 15 /13 d ρ c e ls dt = k (T f T I ) X c UO 2 ρ c q dec 2 h m (T m T f )

258 q " dry m ( T f Tsat ) χuo ρcrqdecδ P, χ con ) kcr + + ρvh δ 2 ( 2 lv j nc T sat e sat d dt = q d X UO2 ρ c q dec ρ v h lv j nc ] T sat h m (T m T f ) ρg K e = E ρm 1 / 2 j m = Ke jg

259

260 3500 TMELT TOXSOL TOXLIQ TFRZ Temperature (K) Elapsed time (minutes)

261 3000 Top Heat Concr. Heat Oxidation Decay Q (kw) Elapsed time (minutes) 60 Bot. Abl. Void Melt Bot. Crust Top Crust Top Bed Elevation (cm) Elapsed time (minutes)

262 δ 0 δ total ts mbed m crust m melt 15 cm 20 cm 25 cm 30 cm 35 cm 40 cm δ 0 (cm) Time to δ 0 (min.) δ total (cm) m bed (kg) m crust (kg) m melt (kg) t s (min.)

263 15 cm 20 cm 25 cm 30 cm 35 cm 40 cm δ 0 (cm) Time to δ 0 (min.) δ total (cm) m bed (kg) m crust (kg) m melt (kg) t s (min.) cm 20 cm 25 cm 30 cm 35 cm 40 cm δ 0 (cm) Time to δ 0 (min.) δ total (cm) m bed (kg) m crust (kg) m melt (kg) t s (min.)

264 15 cm 20 cm 25 cm 30 cm 35 cm 40 cm δ 0 (cm) Time to δ 0 (min.) δ total (cm) m bed (kg) m crust (kg) m melt (kg) t s (min.) cm 20 cm 25 cm 30 cm 35 cm 40 cm δ 0 (cm) Time to δ 0 (min.) δ total (cm) m bed (kg) m crust (kg) m melt (kg) t s (min.)

265 mass % 5.0 mass % 10.0 mass % 15.0 mass % 20.0 mass % Total ablation depth at stabilization (cm) Initial collapsed melt depth (cm)

266 0.0 mass % 5.0 mass % 10.0 mass % 15.0 mass % 20.0 mass % 700 Incremental time to stabilization (min.) Initial collapsed melt depth (cm) mass % 5.0 mass % 10.0 mass % 15.0 mass % 20.0 mass % Mass % stabilized as crust vs. total (crust + bed) (%) Initial collapsed melt depth (cm)

267 mass % 5.0 mass % 10.0 mass % 15.0 mass % 20.0 mass % Ablation depth at a given concrete content (cm) Initial collapsed melt depth (cm)

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270 Melt Temperature (K) MELCOR_Melt Temp. Test_Melt Temp. CORQUENCH_Melt Temp Time (min.)

271 Ablation Depth (cm) MELCOR_Radial MELCOR_Axial Test_Axial Test_Radial 1 Test_Radial 2 CORQUENCH_Radial CORQUENCH_Axial Time (min.) 1200 Q (kw) MELCOR_Concrete MELCOR_Top CORQUENCH_Concrete CORQUENCH_Top Time (min.)

272 Q (kw) MELCOR_Decay Heat MELCOR_Chemical Reaction CORQUENCH_Decay Heat CORQUENCH_Chemical Reaction Time (min.) Height (cm) MELCOR_Melt height CORQUENCH_Void melt CORQUENCH_Bot. crust CORQUENCH_Top crust CORQUENCH_Top bed Time (min.)

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275 Ablation Depth (Max. Radial)_MELCOR Ablation Depth (Max. Axial)_MELCOR Ablation Depth (m) Time (min.) 8 Z direction (m) sec sec sec sec sec R direction (m)

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296 Revision 3, 28 August 2006 OECD RESEARCH PROGRAMME ON FUEL-COOLANT INTERACTION SERENA Proposal for a Phase 2 programme prepared by D. Magallon (CEA) J.H. Song (KAERI) R. Meignen (IRSN) N. D. Suh (KINS) with contributions by M. Bürger and M. Buck (IKE) for the analytical part

297 Revision 3, 28 August 2006 Content 1 Summary conclusions of Phase Scope of Phase Generic situations considered Code calculations of the selected experiments Code applications to reactor situations Phase 2 proposal Objectives of Phase Short presentation of KROTOS and TROI facilities Advantages of using the two facilities Experimental programme Basic test conditions Fuel material Melt release Test matrix Analytical activities Deliverables Cost estimate and schedule Cost breakdown table for experimental activities Concluding remarks APPENDIX: Analytical programme.18 2

298 Revision 3, 28 August Summary conclusions of Phase Scope of Phase 1 Phase 1 of OECD/SERENA programme brought together most international experts in the area of Fuel Coolant Interaction (FCI) with the objective of evaluating the capabilities of the current generation of FCI computer codes in predicting steam explosion induced loads, reaching consensus on the understanding of important FCI phenomena relevant to the reactor situations, and propose confirmatory research to bring predictability of FCI energetics to required levels for risk management. The objective of Phase 1 was reached through comparative calculations of existing experiments and reactor cases by using available tools. It was divided into five tasks: 1. Identification of relevant conditions for FCI in reactor 2. Comparison of various approaches for calculating jet break-up and pre-mixing, 3. Comparison of various approaches for calculating the explosion phase, 4. Reactor applications, 5. Synthesis and proposal for Phase 2. Next sections summarise the findings. 1.2 Generic situations considered Task 1 had the objective of determining the most relevant situations for energetic FCI in reactors. Energetic FCI occurring ex-vessel during melt discharge through a large breach in the lower head into a flooded cavity was considered of most concern, and a side pour the most challenging case for the structures. In-vessel, multiple jets through the core support plate were considered as potentially the most challenging for the primary circuit in case of energetic FCI. Therefore, SERENA aimed at verifying the capabilities of the codes to predict these situations with a sufficient level of confidence. The status of the predictive capabilities of the codes and associated uncertainties were verified and compared first on relevant experiments for the two main phases of a steam explosion, i.e., pre-mixing and explosion. Pre-mixing was analysed first separately because the strength of the explosion strongly depends on pre-mixing conditions at the time the explosion triggers. It is therefore important to verify that this phase is calculated adequately for the purpose. Noting that no relevant multi-pour experiment exists, 3

299 Revision 3, 28 August 2006 the best we could extract today from existing experimental data base in relation with these reactor situations was found in the FARO, KROTOS and TROI programmes. Calculations were performed for FARO L-28 and FARO L-31 for pre-mixing, and KROTOS 44, TROI-13 and FARO L-33 for explosion, respectively. 1.3 Code calculations of the selected experiments Analyses of the premixing experiment calculations (Task-2) and explosion experiment calculations (Task-3 ) indicated that most computer codes were not able to successfully predict important parameters of the experiments, such as mixture properties, pressure and temperature histories, and dynamic pressure propagation during explosion. Also, large scatter in modelling and predictions was noticed between the participating computer codes. For the simulation of premixing experiments, most of the calculations significantly overestimated void fraction with respect to the experimental data deduced from water level swell measurement. Knowing the importance of void in pre-mixing for steam explosion behaviour, attention was largely focused on this issue. Several sensitivity calculations were done in addition to the base cases to identify the reasons for such differences. The break-up mechanisms, particularly in the first phase of the premixing, i.e., up to melt-bottom contact (in the experiments, spontaneous steam explosions often trigger when the melt front contacts the bottom), were also investigated. However, resolution of this issue was not possible, since none of the existing corium experimental data have spatial distribution of fuel fraction and void. For the simulation of explosion experiments, it was observed that FCI codes tend to noticeably overestimate the energetics for the tests with corium, while they predict reasonable behaviour for the tests with alumina, such as KROTOS-44. It was noted that the computer codes were tuned to the KROTOS data in their developmental stage. So, expert's discussions largely focused on the material influence on the energetics, in view of the recent observations in TROI complementing those already obtained with KROTOS. This aspect was judged to be one of the major uncertainties for predictions. 1.4 Code applications to reactor situations In Task 4, two standard problems reflecting the generic situations referred to in Section 1.1 were selected for analysis by the computer codes, one for in-vessel steam explosion and one 4

300 Revision 3, 28 August 2006 for ex-vessel steam explosion, respectively. Each computer code was used with the most appropriate parameters and model options as deduced from Task 2 and Task 3 analyses. The ex-vessel results show noticeable differences in the predictions. The calculated maximum pressure loads at the cavity lateral wall vary from a few MPa to ~40 MPa and the impulses from a few kpa.s to ~100 kpa.s (except in one case, where the impulse is significantly higher). It was recognized that a level of loads of the order of some tens of kpa.s might be prejudicial to the integrity of the cavity. For the in-vessel case, the level of the impulses was relatively low. The reason for such reduced values of the loads stands essentially in the high voiding of the pre-mixing region as calculated. The analyses of the reactor situations highlighted the differences in models and representation of the scenarios in the calculations. Evaluation of the significance of these differences in view of the reactor safety margins was performed by expert judgment. It was generally agreed that the margins in the in-vessel case might be considered as sufficient. For the ex-vessel case, it was recognized that the internal structures, such as the reactor pit, could be damaged by the loads due to a steam explosion. If we increase the knowledge level for the nature of corium resulting in mild steam explosions, we might be able to quantify the safety margin for ex-vessel steam explosion. This information will be very helpful both for the design of containment structures and for setting up an appropriate severe accident management strategy. Lastly, the impact on the results of the different ways used to represent the 3-D geometry of a reactor situation by 1-D and 2-D approximations could not be resolved in the absence of data in reactor-like situations. Actually, the codes extrapolate from the level of simplifications adopted for experiments performed in axi-symmetrical configurations and it has never been verified whether this is adequate for the purpose. Experimental simulation of full-scale real reactor conditions is not possible, but experiments in non-conventional geometries would be helpful to assess the functionality of the codes in terms of extrapolation capabilities to reactorlike configurations. Partners in Phase 1 agreed that uncertainties on the pre-mixing flow patterns, especially on void and melt distribution, and on material influence on steam explosion energetics can be adequately reduced by performing a limited number of well-designed tests in the KROTOS and TROI experimental facilities in Phase 2 of SERENA, complemented by analytical activities as described in the next sections. 5