Internal Flooding PRA For APR 1400 2015. 09 Dongwook Kim, Pyungtark Park and Myungro Kim KEPCO Engineering & Construction Safety Assessment Engineering Group

Contents Overview of IFPRA for APR 1400 EPRI Methodology Quantitative Summary Sensitivity Analysis for Design Improvement Summary of IFPRA

Overview of IFPRA for APR 1400 ASME Standard Category Capability II and Reg. Guide 1.200 Methodology EPRI TR-1019194 Guidelines for Performance of Internal Flooding Probabilistic Risk Assessment Pipe Failure Data Pipe Failure Data : EPRI 3002000079, Rev. 3

Task 1~4 Qualitative Analysis IDENTIFY FLOOD AREAS AND SSCs 2 SOURCES 3 PERFORM PLANT WALKDOWN AREA FLOOD CAUSES INITIATING EVENT OR SHUTDOWN ? AREA HAS FLOOD FLOOD OR PROP PATH IMPACTS SAFETY CRITICAL SSCS RETAIN FOR QUANTITATIVE ANALYSIS MAY SCREEN OUT FLOOD Quantitative Analysis , IMPACTS AND PRO - PAGATION PATHS 4 QUALITATIVE SCREENING EVALUATION YES NO Collecting the Plant information

Task 1 : The flood areas and SSCs Identify the flood areas Identify the Screened Building No SSC & Flood Source(Not cause the Initiating Event) No Impact to other Building by Propagation Identify the SSCs SSCs Mapped in the Internal Event PRA Model Subcomponent of SSCs which are identified to be located in the different flood area Terminal box, Local panel, Instrument cabinets SSCs related to HFE

Task 2 : Flood Source & Mitigation Feature Identify the flood source for each flood area Collect the information, such as system volume, flow rate Flood Mitigation System Door : Propagation / Mitigation Drain : Propagation(Drain Plugged)/Mitigation Curb : Mitigation Penetration : Propagation / Mitigation Louver / Plug / Window : Propagation Define Potential Propagation Pathway

Task 3 : Walkdown Purpose to verify information used in the above tasks Spatial Information needed for the development of flood areas Plant design features credited in defining flood areas SSCs located within each defined flood area Flood/Spray/other applicable mitigation features designed to protect the SSCs located in each defined flood area (e.g, drains, spray shields) Pathways that could lead to transport to the flood area Potential flood sources within each flood area

Task 4 : Qualitative Screening Qualitative Screening Criteria ASME Std. Screening Criteria IFSO-A3 No Flood Source in the Flood Area IFSN-A12 Not Cause an Initiating Event or immediate plant shutdown 1. No accident initiating/mitigation equipment 2. No Sufficient Flood source to cause failure of initiating/mitigation equipment IFSN-A13 Contain the Flood mitigation system capable of preventing unacceptable flood levels IFSN-A14 Potential human mitigation actions 1. Flood indication : Available in MCR 2. Flood Source : Isolable 3. Flood Mitigation action : Performed with high reliability

Task 5~9 Quantitative Analysis Qualitative Analysis (T1 ~ T4) BEGIN QUANTITATIVE EVALUATION PHASE TASK 6 FLOOD INITIATING EVENTS ANALYSIS 7 FLOOD CONSEQUENCE ANALYSIS 8 EVALUATION OF MITIGATION STRATEGIES 9 PRA MODELING OF FLOOD SCENARIOS 10 PRA QUANTIFICATION OF FLOOD SCENARIOS 11 DOCUMENTATION OF INTERNAL FLOODING COMPLETE IFPRA TASKS 5 CHARACTERIZATION INFORMATION NEEDED FOR PRA MODELING OF EACH SCENARIO Tasks 5, 6, 7, 8, and 9 are performed in an iterative process

Task 5 : Define the Scenarios Initial Evaluation (Screening Analysis) Detailed Evaluation Flood Source - All Flood Source in Flood area - Unlimited Volume / Max. Flow rate Each flood source for each Scenario System Volume/System flow rate (system operating flow) Assessment of Flood Effect Failure of All SSC in Flood Area(Including Propagation) - Failure of the SSCs based on the Flood Height Calculation Isolation/Mitigation Not Considered Considered Propagation Path Conservative Approach - Aux. Building Quad A or B or D (All floors) Identify the Inter-Quadrant Propagation Path - Perform the Flood Height Calculation

Task 6 : Flood Initiator & Frequencies Initial Evaluation (Screening Analysis) Detailed Evaluation Initiating Event Assumed failed any SSC by Flood will cause the “Reactor Trip” Selected based on the loss of system or SSC Frequency Quantification Total Pipe Break Frequency in Flood area - Quantifying by the Initiating Event - Quantifying by pipe size

Task 7 : Flood Consequences Analysis Propagation Path : General Access Area (2nd Floor) General Access Area Electrical Eq. Room HVAC Chase Stair/Elevator (Basement) Floor Drain Sump Area (Basement) Corridor Door (2nd floor) Drain EOF* Opening * : EOF : Emergency Overflow Drainage

Task 7 : Flood Consequences Analysis Spray FP break M. Flood spill rate = 6,000 gpm Flood spill rate = 2,000 gpm General Access Area Quad. C, 55 ft: 3.4ft Quad. C, 78 ft : 0.4ft CC break Isolated within 30 min Fail to isolate Quad. C, Basement : 10 ft Quad. C, 78ft : 1ft Quad. C/D, Basement: 10 ft Quad. C, 2nd Floor : 1ft D<10” D>10” Quad. C, Basement: 0.6 ft Quad. C, 2nd Floor : 0.1ft Quad. C, Basement: : 0.6 ft Quad. C, 2nd Floor : 0.3ft Flood Type System Pipe Size Isolated ? Scenarios (Damaged Area) AX break Spill rate = 2,000 gpm Spill rate = 7,000 gpm Quad. C, Basement: : 3.4ft Quad. C, 2nd Floor : 0.5ft Quad. C, Basement: : 7.2ft Quad. C, 2nd Floor : 0.4ft

Task 8 : Evaluation of Flood Mitigation Strateges Post Initiator HFE (based on Internal Event PRA Model) Screening Analysis Multiplier factor Applying Conservative value Considering Location of action Time of action Feasibility of action Detailed Analysis Re-evaluate Dominant HFEs Considering the Stress level/Workload

Task 8 : Evaluation of Flood Mitigation Strateges Flood Mitigation HFE Indication is available in the control room Potential Isolation Flood can be isolated, Isolation equipment is not affected by the flood The area is accessible Action is procedurally directed There is sufficient time available to perform action, including time needed to detect the break location

Task 10 : Quantitative Summary CDF Profile for Building Most Risk comes from next 3 Building at almost 95% of the CDF Auxiliary Building (85%) Turbine Building CCW Heat Exchange Building

Summary of IFPRA Aux. Building Quadrant Separation Minimize the Inter-quadrant Propagation Flood Door : inter-quadrant in 55’ High Density Seal Penetration : inter-quadrant in 55’, 78’, 100’ Design of the Flood Mitigation System : Minimize the Flood Accumulation Drain to Sump in Each Sump EOF to Corridor and Lowest level Each quadrant of lowest level in Auxiliary Building : Emergency Sump