1. Idaho National Engineering and Environmental Laboratory Assessment of Margin for In-Vessel Retention in Higher Power Reactors 2004 RELAP5 International Users Seminar Sun Valley, Idaho, USA August 25-27, 2004 D. L. Knudson and J. L. Rempe

2. Idaho National Engineering and Environmental Laboratory 204-GA50005-30 Outline Background Approach Initial Results Remaining Evaluations Summary

3. Idaho National Engineering and Environmental Laboratory 304-GA50005-30 K-INERI Program Objective Use systematic approach to develop specific recommendations to improve the margin for in-vessel retention of relocated materials during a severe accident in high-power reactors (up to 1500 MWe). –Combine state-of-the-art analytical tools and key U.S. and Korean experimental facilities –Focus on modifications to enhance external reactor vessel cooling and in-vessel core catcher performance –Focus on APR1400, but methodologies developed so that they can easily be applied to other reactor designs Background

4. Idaho National Engineering and Environmental Laboratory 404-GA50005-30 K-INERI Applies State-of-the-Art Analytical Tools and Key Experimental Facilities Background

5. Idaho National Engineering and Environmental Laboratory 504-GA50005-30 SBLB Used to Evaluate Proposed Coatings and Insulation/Vessel Configuration Background Subscale Boundary Layer Boiling Facility Proposed coatings and enhanced insulation/vessel configuration significantly increase CHF Insulation modified to enhance ERVC flow

6. Idaho National Engineering and Environmental Laboratory 604-GA50005-30 Unique In-Vessel Layered Design Proposed and Evaluated Background

7. Idaho National Engineering and Environmental Laboratory 704-GA50005-30 KAERI and INEEL Facilities Provide Integral Data for Assessing Core Catcher Performance Using Simulant and Prototypic Materials Background KAERI LAVA-GAP results suggest IVCC reduces vessel heat loads INEEL HTTL prototypic tests suggest that proposed coatings protect substrate from molten core materials

8. Idaho National Engineering and Environmental Laboratory 804-GA50005-30 SCDAP/RELAP5-3D © Represents All Major Processes Affecting IVR of Corium Reactor pressure vessel Metallic layer ERVC Oxide crust Oxide pool Convection Heat transfer to overlying coolant Corium/vessel gap or corium/vessel contact resistance Stratified Configuration Reactor pressure vessel ERVC Oxide crust Oxide pool Convection Heat transfer to overlying coolant Corium/vessel gap or corium/vessel contact resistance Homogeneous Configuration Approach Narrow gap cooling

9. Idaho National Engineering and Environmental Laboratory 904-GA50005-30 SCDAP/RELAP5-3D © Approach Select bounding transient from full-plant analysis results Develop APR1400 lower head model Calculate base case response (without core catcher and ERVC enhancements) Modify SCDAP/RELAP5-3D © for core catcher and ERVC simulation based on experimental results Calculate response with core catcher and ERVC Compare results with and without core catcher and ERVC Approach

10. Idaho National Engineering and Environmental Laboratory 1004-GA50005-30 SCDAP/RELAP5-3D © Model Includes Latest RELAP5 Nodalization with Refined SCDAP Core and COUPLE Lower Head RELAP5 (250 volumes, 316 junctions, 284 heat structures) SCDAP (3 channels, 15 axial nodes, with radial crossflows) Approach

11. Idaho National Engineering and Environmental Laboratory 1104-GA50005-30 Simplified RELAP5 Lower Head Model Lower head dimensions consistent with plant model Time-dependent downcomer and core TH boundary and initial conditions from plant analysis Simplified downcomer / lower head connection Suitable for base case calculations Approach

12. Idaho National Engineering and Environmental Laboratory 1204-GA50005-30 SCDAP/RELAP5-3D © Ideal Tool for Evaluating Impact of IVCC and ERVC Adjustment of external boundary conditions consistent with ERVC Flow paths for engineered (vessel-to-catcher) gap Approach

13. Idaho National Engineering and Environmental Laboratory 1304-GA50005-30 COUPLE 2D Mesh Represents Lower Head Without core catcher External convective boundary (h = 70 W/m 2 -°C; T ∞ = 391 K) Constant contact conductance (500 W/m 2 - °C) Homogeneous corium bed Overlying 3 RELAP5 volumes (190, 200, and 210) Hemisphere-to-cylindrical vessel transition ignored 588 nodes 540 elements Approach

14. Idaho National Engineering and Environmental Laboratory 1404-GA50005-30 LOCA-1 Selected as Bounding Lower Head Transient Transient Time of relocation (s) Relocated constituents (kg)Corium characteristics at relocation UO 2 ZrO 2 ZrTotal Temp (K) Power Density (MW/m 3 ) Est avg vessel heat flux (MW/m 2 ) a SBO-111,100111,00024,2006,440145,0003,3002.490.147 to 1.32 SBO-28,63099,60018,5006,940125,0003,0103.280.170 to 1.53 SBO-310,600111,00021,2008,300144,0003,3902.720.161 to 1.45 LOCA-14,990108,0005,1803,520119,0003,4603.480.182 to 1.64 a. Assuming hemispherical configuration, without sensible heat effects, for quasi-steady conditions, with estimated heat loss from upper corium surface at 10 and 90% of total. Approach

15. Idaho National Engineering and Environmental Laboratory 1504-GA50005-30 Relocation History Extracted for Bounding Transient Time (s) Relocated mass (kg)Relocated material UO 2 ZrO 2 ZrSteelAbsorberTemperature (K)Decay power (MW) 3280 3620 3700 3820 4030 4990108,0005180 93 38 145 3244 32 13 50 157 2033 80 1480 1100 1620 1560 1420 3460 0 51.2 108,00051803520952350Relocated mass totals Lower head structural steel ignored, but will be treated as a sensitivity in COUPLE analyses Approach

16. Idaho National Engineering and Environmental Laboratory 1604-GA50005-30 Planned Calculations Evaluate Individual and Combined Impact of Proposed IVR Strategies CalculationDescription Base caseWithout in-vessel core catcher and ERVC CC + ERVC-c Effects of in-vessel core catcher and combined effects of external micro-porous coating and insulation enhancement CCEffects of in-vessel core catcher ERVC-c Combined effects of external micro-porous coating and insulation enhancement ERVC-mEffects of external micro-porous coating ERVC-iEffects of external insulation enhancement Approach

17. Idaho National Engineering and Environmental Laboratory 1704-GA50005-30 Lower Head Fails by Melting Within 15 min in Base Case Analysis Without IVCC or ERVC Initial Results

18. Idaho National Engineering and Environmental Laboratory 1804-GA50005-30 Lower Head Melting Quick and Extensive in Base Case Analysis Initial Results

19. Idaho National Engineering and Environmental Laboratory 1904-GA50005-30 Remaining Evaluations Core catcher –Heat transfer correlations for a narrow gap –Countercurrent flow limiting correlations ERVC –Heat transfer correlations for a submerged hemisphere with coatings and enhanced insulation structure Planned Calculations Require Experimental Data from K-INERI Program

20. Idaho National Engineering and Environmental Laboratory 2004-GA50005-30 Summary SCDAP/RELAP5-3D © APR1400 lower head model developed LOCA-1 selected as a bounding transient Base case calculations –indicate early failure of lower head due to melting –demonstrate SCDAP/RELAP5-3D © ideal analysis tool for evaluating IVR strategies proposed in K-INERI program. Heat transfer correlations (from experimental efforts) needed for simulating core catcher and ERVC.