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

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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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