ML17320A200

Insights from Implementing FLEX in the Peach Bottom Seismic PRA Model

ML17320A200
Person / Time
Site:	Peach Bottom
Issue date:	11/15/2017
From:	Tarpinian P, Vanover D Exelon Generation Co
To:	Office of Nuclear Reactor Regulation
Schwab A
Shared Package
ml17312a356	List: ML17320A146 ML17320A193 ML17320A200 ML17320A201
References
Download: ML17320A200 (13)

Text

Public Meeting on FLEX and RIDM Insights from Implementing FLEX in the Peach Bottom Seismic PRA Model November 15, 2017 Don Vanover Phil Tarpinian

Overview Purpose - Determine the benefit of crediting FLEX in the PBAPS internal events and seismic PRA models Discussion points FLEX Related Procedure Changes FLEX Alternatives Modeled Preliminary Full Power Internal Events Results and Insights Preliminary Seismic PRA Model Results and Insights Conclusions and Recommendations 2

FLEX Related Procedures SE-11 provides direction in all LOOP scenarios at PBAPS Extended Loss of Offsite Power (ELAP) declaration at 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> if power not restored to any 4 kV bus (Sheet 5)

Key Actions Identified from ELAP Sheet 6 from SE-11 3

FLEX Alternatives Modeled DC load shed commences early in SE-11 prior to declaration of ELAP Battery calculation review indicated that performance of these initial steps would be sufficient to avoid LERF potential if HPCI or RCIC is available ELAP declaration results in additional load shedding steps to further extend battery life for deployment of FLEX generators Bundled execution steps by impacted DC panels Alignment of FLEX Generators to Div I 480 VAC Allows for RPV depressurization capabilities via SRVs Allows for continued RCIC operation with DC available FLEX pump alignment Allows for RPV injection or Makeup to torus With RCIC initially available, either leads to long term success state 4

FLEX Related Human Failure Events

• NEI 16-06 Attributes HEP Description Feasible Available Time Command Environ-in and Reliable Margin and mental Scenario Control Conditions Operators Fail DC Load SBO Yes Yes SE-11, Varies Shed (SBO, Div I Only) Att. T Operators Fail DC Load ELAP Yes Yes FSG-012 Varies Shed (ELAP)

Operators Fail to Align Flex ELAP Yes Yes FSG-010 Varies Generator to Div I FSG-011 Operator Fails to Partially SBO Yes Yes T-101 Varies Depressurize RPV and T-102 Vent Cont. to Prolong RCIC Operators Fail to Align Flex ELAP Yes Yes FSG-040 Varies Flow Path to RPV FSG-041 5

FLEX Related Human Error Probabilities

• Values Obtained Using EPRI HRA Approach HEP Description FPIE Value SPRA Value Operators Fail DC Load Shed (SBO, 2.5E-02 5.2E-02 Div I Only)

Operators Fail DC Load Shed 3.8E-02 9.8E-02 (ELAP)

Operators Fail to Align Flex 3.6E-02 3.7E-02 Generator to Div I Operator Fails to Partially (<7.2E-02) 7.2E-02 Depressurize RPV and Vent Cont.

to Prolong RCIC Operators Fail to Align Flex Flow 2.5E-02 2.5E-02 Path to RPV 6

FLEX Related Human Error Probabilities Deep load shed action more significantly impacted for seismic since Only one EO is available Action needs to be completed as soon as possible - little margin normally available for success High workload assumed for seismic vs. moderate for FPIE Leveraged availability of the FLEX procedures, training, and timing validation for Peach Bottom Allowed detail to first be developed for the FPIE FLEX actions Required little change/enhancement for seismic 7

FLEX Related Human Error Probabilities FLEX actions are considered to apply across all HRA damage state bins because the SSCs that drive the individual bin adjustments become irrelevant for FLEX Operators would proceed to FLEX actions on the ELAP basis of no 4kV bus being able to be repowered within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> regardless of the seismic bin-related SSC failures Since the whole idea of FLEX is for this type of catastrophic event, applying the individual seismic bin adjustments is not necessary 8

SBO SEQUENCE LOGIC Extended RPV Depressurization Continued RCIC or FLEX Injection DC load shed required for alignment of generators Alignment of generators required for extended RPV depressurization and continued RCIC operation 9

FPIE RESULTS Full Power Internal Events Results Case Description CDF Value LERF Value Unit 2 w/ No Credit for FLEX 3.4E-06 / yr 4.9E-07 / yr Unit 2 w/ Credit for FLEX in 3.0E-06 / yr 4.4E-07 / yr ELAP scenarios Benefit consistent with SBO contribution w/ HPCI or RCIC Available

~10% CDF reduction from SBO and SBO-like conditions (i.e., LOOP and CCF of EDGs, or Trip and CCF of 4 kV buses)

~10% LERF reduction from similar scenarios Additional credit could be obtained if credit for FLEX generators was not limited to ELAP scenarios 10

SPRA RESULTS Seismic PRA Model Results Case Description CDF Value LERF Value Base Case w/ No Credit for FLEX 2.0E-5 / yr 3.9E-6 / yr Base Case w/ Credit for FLEX 1.9E-5 / yr 3.7E-6 / yr Site considering many options for finalization Currently limited by relatively flat hazard curve at high g levels 1E-2 Annual Freq. of Exceedance 1E-3 1E-4 1E-5 1E-6 1E-7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 SSE IPEEE Peak Ground Acceleration, g RLE 11

SUMMARY

Conclusions Reduction in CDF and LERF values can be obtained in internal events and seismic results with nominal credit for FLEX systems when procedurally directed HRA benefited from strong inputs; specifically validation, procedures, and training Seismic benefit limited by unique site hazard curve (that is relatively flat at high g levels)

Recommendations Work with site to help optimize path forward for SPRA model completion As FPRA update is completed, identify when alignment of FLEX generators may be beneficial to include in the Fire Area Safe Shutdown Guides 12

Additional Questions?

dvanover@jensenhughes.com Philip.Tarpinian@Exloncorp.com 13