ML17207A067

07/06/2017 - TMRE Public Meeting Slides

ML17207A067
Person / Time
Site:	Nuclear Energy Institute
Issue date:	07/06/2017
From:	Montgomery B Nuclear Energy Institute
To:	Office of Nuclear Reactor Regulation
Schwab A
Shared Package
ML17207A063	List: ML17181A307 ML17207A067
References
NEI 17-02, Rev 0
Download: ML17207A067 (65)

Text

Bruce MontgomeryDirector, Strategic Planning

NEI July 6, 2017 NEI 17-02TORNADO MISSILE RISK EVALUATOR (TMRE)

GUIDANCE DOCUMENT Agenda *Overview of TMRE Development

• Overview of TMRE Pilot Plants, Plans, and Schedules*TMRE Guidance Document Presentation 2

Overview TMRE Development

• TMRE development began Fall 2015.

• Since October 2015 NRC and industry held 6 public meetings to discuss methodology.

• November 2016 NEI began development of industry guidance on TMRE application.

• NEI 17-02, Revision 0, provided to NRC June 23, 2017.*Three plants will pilot the TMRE methodology prior to broader implementation.

• NEI 17-02 will be included in/attached to each pilot LAR.3

• Risk-informed methodology.

• Calculates SSC failure likelihood due to missile impact.

• Examines impact of failure using existing plant internal events PRA.

• Internal events PRA modified to account for effects from a tornado.

• Results compared to thresholds defined as delta-CDF and delta-LERF.

• License amendments pursuant to R.G 1.174.

Overview TMRE Methodology 4

Overview of TMRE Pilot Plants

• Three plants volunteered to pilot the TMRE risk-informed methodology oShearon Harris Nuclear Power Plant -Duke Energy

• Single Unit 3-loop WPWR -CP 1978; OL 1987 oVogtle Electric Generating Plant-Southern Nuclear Operating Company

• Dual Unit 4-loop WPWRs -CPs 1976; OL 1987/89

-Two additional WAP1000 reactors under construction oGrand Gulf Nuclear Station -Entergy Nuclear

• Single Unit BWR 6 -CP 1974; OL 1984 5

TMRE Technical Advisory Group

• NEI established the industry TMRE Technical Advisory Group (TAG) oMembership -Utility, Contractor, EPRI, Pilot Plant and NEI Representatives o Purpose*Oversees content of NEI 17-02

• Ensure each pilot applies the TMRE model to address site specific considerations

• Ensure consistency of TMRE model application across the pilots oTAG meets weekly 6

TMRE Pilot Timeline

• Harris and Vogtle TMRE Pilot LAR Target Schedules oPre-Submittal Meetings -August 1 oTMRE Pilot LAR submittal -August 31

• Grand Gulf TMRE Pilot LAR Target Schedule oPre-Submittal Meeting -October 6 oTMRE Pilot LAR submittal -October 20

• Following issuance of any necessary RAIs regarding the third pilot LAR review oIncorporate pilot LAR lessons learned into NEI 17-02 oUpdated NEI 17-02 will be submitted for NRC review and approval -Anticipated 2 ndQuarter 2018 7

Bruce MontgomeryDirector, Strategic Planning

NEI NEI 17-02 Overview Table of Contents

• Section 1:

Introduction

• Section 2: Compliance with Tornado-generated Missile Design and Licensing Basis

• Section 3: Overview of TMRE Methodology

• Section 4: Identify Nonconforming and Vulnerable SSCs*Section 5: Perform Plant TMRE Walkdown

• Section 6: Determine Site Tornado Hazard Frequency 9 Table of Contents (cont.)

• Section 7: Evaluate Target and Missile Characteristics

• Section 8: Develop TMRE PRA Model

• Section 9:

Quantify Risk, Perform Sensitivity Studies, and Compare to Thresholds

• Section 10: License Amendment Request 10 Alex GilbreathPRA Engineer, Southern Nuclear TMRETornado Hazard

Frequency

• The initiating event for the TMRE is a tornado strike.

• Initiating event frequencies are site-specific.

• In general, higher intensity means lower frequency.

• Multiple intensity scales

• Climatology data is readily available in NUREG/CR-4461, Rev. 2.

Background

12

• Develop the site-specific hazard curve.

• Use Fujita (F-Scale) wind speed data from the NUREG to plot a hazard curve.

• Determine the site-specific frequency that corresponds to the beginning and end of

each range.

• Calculate the initiating event frequency for each tornado intensity rangeHazard Frequency Calculation 13

• The end result is a plant-specific initiating event frequency for each F'-scale tornado.Example Hazard Frequency CalculationIntensityInitiating Event FrequencyF'28.56E-05 F'32.16E-05 F'45.63E-06F'51.08E-06F'65.95E-08 14 Leo ShanleyManager, JENSEN HUGHES TMRE Missile Impact Parameter (MIP)

and Missile

Characteristics Topics Covered

• Exposed Equipment Failure Probability (EEFP)

• Missile Impact Parameter (MIP) oDefinition of MIP oMIP Values for Use in the EEFP

• Discuss TMRE Missile Inventories oClassifying Missiles oMissile Confirmatory Walkdowns oOutage Impacts and Temporary Missiles 16

• The Exposed Equipment Failure Probability (EEFP) is used to determine the conditional probability that an exposed SSC is hit and failed by a tornado missile, given a tornado of a certain magnitudeEEFP = MIP x # of Missiles x Target Exposed Area x Fragility*The EEFP serves as the basic event failure probability for the tornado missile strike failure mode of exposed equipment (or targets)Exposed Equipment Failure Probability 17 Missile Impact Parameter (MIP) MIP = Probability of Missile Hit / ft2 / missile / tornado

• MIP can be thought of as a missile flux 18 Missile Impact Parameter (MIP)

• MIP values were derived using published TORMIS data (EPRI NP-768) oNEI 17-02, Appendix B provides the basis for the MIP values to use in the TMRE oNEI 17-02 MIP values apply generically to all sites

• Separate MIP values are provided for each F'-Scale tornado from F'2 to F'6

• Separate MIP values are provided for 'Near Ground' and 'Elevated' targets 19 MIP Values from NEI 17-02 TornadoIntensityElevatedTargets (>30')Near GroundTargets (<30')F'25.8E-111.1E-10F'32.0E-103.6E-10 F'43.4E-106.3E-10F'58.7E-101.6E-09F'61.3E-092.4E-09 20 Number of Missiles

• The number of missiles used in the EEFP calculation are provided in NEI 17-02

• Site verifies that the number of missiles is bounding*Missile inventory is based on potential missiles within ~2500' of targets

• NEI 17-02 Section 5 provides details on missile inventory walkdowns 21 Number of Missiles from NEI 17-02TornadoIntensity# of MissilesF'2155,000F'3155,000F'4205,000F'5240,000 F'6240,000 22 Missile Inventory Walkdowns

• The missile inventory walkdown is a separate walkdown*Guidance and examples are provided in Section 5 of NEI 17-02

• NEI 17-02 Table 5-2 provides list of 23 types of missiles (structural and nonstructural).

• Examples: oPipes, rebar, utility pole, wood beams and planks, pavers, concrete blocks, drums, gas cylinders, vehicles 23 Temporary Missiles

• Missile inventories will vary over time -do not need to be recalculated due to nominal changes.*Construction oAdditional structures evaluated to confirm TMRE missile inventory remains bounding oSensitivity study to account for construction-related

missiles 24 Leo ShanleyManager, JENSEN HUGHES TMRETargets

• Describe the TMRE Vulnerable SSC Walkdown

• Describe Target Characteristics

• Target Area Calculations Overview 26 TMRE Vulnerable SSC Walkdown

• Collect data to inform modifications to the PRA to develop the TMRE model

• Confirm vulnerability of SSCs from Discovery Walkdowns*Identify additional vulnerabilities and targets

• Review PRA operator action access pathways

• Document details of targets (dimensions, elevation, shielding, robustness, and correlation) 27 High Wind Equipment List (HWEL)

• The HWEL is a list of SSCs that need to be considered vulnerable to tornado missiles (and/or tornado wind pressure) in the TMRE PRA

• The initial HWEL should contain oThe list of vulnerable SSCs determined as part of the discovery activities oA list of potentially unprotected SSCs from the

TMRE PRA*The HWEL will be updated based on information and observations from the Vulnerable SSC

walkdowns 28 Operator Actions Outside Cat I Structures

• Identify PRA operator actions that are performed outside Category I structures or require transit outside Category I structures

• Review actions with an operator prior to the walkdown 29 Non-missile Related SSC Failure Modes

• Located inside non-Category I structures due to structural collapse from tornado winds

• Located inside non-Category I structures, such as the Turbine Building, due to tornado missiles

• Located outside, but near, non-Category I structures due to structural failure of the non-Category I structure 30 Example Targets Turbine-driven AFW pump steam exhaust stack 31 Example Targets Steam relief exhaust stacks 32 Example Targets Exposed Service Water piping 33 Missile Barriers Wall behind door limits exposure of SSCs to missiles going through the door 34 Missile Barriers

• Missile protection on the side of the EDG room*Shielding should have been evaluated as part of the discovery walkdown 35 Target Areas

• Exposed area of each target must be determined for EEFP*Targets inside Category I structures may be vulnerable to a non-rated opening oThe effective area is the smaller of the opening or the target itself

• Target may be partially shielded, so that entire area of target is not exposed to missiles oExamples: Pipe or cable tray mounted on wall, tank in a corner 36 Leo ShanleyManager, JENSEN HUGHES TMRETargets and Exposed Equipment Failure

Probability

• Describe how robust targets are addressed in the EEFP*Describe EEFP calculations and provide examples Overview 38 Robust Targets

• EEFP calculations assume that fragility of the target is 1.0 (when struck by a missile, that target will fail to perform its function)

• Some targets are very robust/sturdy and are not damaged by all missile types oAnalyses done to estimate what missile types can damage certain robust targets, to reduce the

number of missiles (# of Missiles) used in the EEFP calculation

• NEI 17-02 provides missile ratios for target type/failure mode 39 Robust Target Types and Failure Modes

• Several robust target types:

o Exposed Pipes oExposed Tanks oSSCs below Concrete Roofs oSSCs behind Steel Doors

• Pipes, tanks and roofs are further divided based on thickness and pipe diameter

• Failure modes are perforation and crushing/crimping 40 Example EEFP CalculationTorna doIntens ity MIP (Near Groun dTarget)# of Missiles (non-robust)Target Expos ed Area (ft 2)Fragil ity EEFP F'2 1.1E-10155,000121.0 2.0E-04 F'3 3.6E-10155,000121.0 6.7E-04 F'4 6.3E-10205,000121.0 1.5E-03 F'5 1.6E-09240,000121.0 4.6E-03 F'6 2.4E-09240,000121.0 6.9E-03 41 Alex GilbreathPRA Engineer, Southern Nuclear TMREPRA Modeling Overview*The TMRE PRA model is the basis for the risk-informed license amendment.

oCalculate risk associated with non-conforming SSCs.

oStarting point is the plant-specific peer-reviewed internal events model.

43 Event Tree/Fault Tree Selection

• The TMRE assumes LOOP/RX Trip will occur oLOOP and SBO event trees typically represent the tornado accident sequence.

oOther trees should be reviewed for tornado impact as well.*The TMRE assumes LOOP is non-recoverable 44 Compliant/Degraded Case

• The purpose of the TMRE is to calculate the difference in risk between plant configurations.

oCompliant case oDegraded case -Nonconforming SSCs 45 Other Modeling Considerations

• Operator actions in the PRA must be examined for feasibility.

oStructure Considerations oTiming Considerations

• Non-feasible operator actions are not credited (i.e. set to 1 or TRUE) in both cases

• TMRE model accounts for failure of non-Category I structures and exposed non-safety related SSCs.

46 Target Impact Basic Events 47 PRA Technical Adequacy

• Internal Events oPeer-reviewed o As-built, as-designed oAddress open findings

• TMRE specific supporting requirements 48 Leo ShanleyManager, JENSEN HUGHES TMRE Quantify Risk

and Sensitivity

Analyses Topics Covered

• Overview of CDF and LERF Quantification

• TMRE Sensitivity Analyses oZonal vs. Uniform Missile Distribution oMIP for Highly Exposed Targets oBase Case Conservatisms o Open F&Os*Risk Metrics and Thresholds 50 Compliant vs. Degraded Cases

• RG 1.174 requires an evaluation of the change in risk (CDF and LERF)*Compliant Case oConfiguration where the plant is built per the required design/licensing bases oAll SSCs required to be protected against missiles are assumed to be so protected, even if they are not

• Degraded Case oThis is the current configuration of the plant (i.e., with potential non-conformances for tornado missile protection) 51 Quantify Risk

• Need to quantify the compliant case and the degraded case for CDF and LERF oIncrease in CDF/LERF (i.e., the delta) is simply:CDF = CDFDegraded-CDFCompliant LERF = LERFDegraded-LERFCompliant 52 Sensitivity Analyses

• TMRE-specific sensitivity calculations are discussed in NEI 17-02 oZonal vs. Uniform Missile Distribution oMissile Impact Parameter for Highly Exposed Targets oCompliant Case Conservatisms

• Address open findings in the internal events PRA model 53 Zonal vs. Uniform Missile Distribution

• MIP was derived from simulation results for a plant with a 'uniform' missile distribution oRealistic missile distribution is variable (i.e., 'zonal')

oLarge local missile inventory may lead to higher missile fluxes and thus higher target hit probabilities

• Sensitivity studies done to determine potential magnitude of missile hit probability 54 Zonal vs. Uniform Missile Distribution

• Threshold to perform sensitivity:

oCDF > 10-7/yr or LERF 10-8/yr *Increase EEFP for targets with Risk Achievement Worth (RAW) >2.0 oOnly affects basic events for F'4 -F'6 tornadoes oIncrease EEFP by 2.75x

• Quantify CDF and LERF 55 Highly Exposed Targets

• SSCs for which all the following apply:

oNot located inside a Category I structure (i.e., either outside or in a non-Category I structure) oNot protected against horizontal missiles oHas an elevation less than 30' above grade 56 Sensitivity for Highly Exposed Targets

• Threshold to perform sensitivity:

oCDF > 10-7/yr or LERF 10-8/yr *Increase EEFP for 'highly exposed' targets with Risk Achievement Worth (RAW) >2.0 oOnly affects basic events for F'4 -F'6 tornadoes oIncrease EEFP by 2.5x

• Quantify CDF and LERF 57 Sensitivity for Conservative Assumptions

• Conservative assumptions in the compliant case may not be conservative for CDF and LERF calculations oReview cutsets in the top 90% of the TMRE compliant case to identify conservatisms related to SSC failures oPerform a sensitivity study to determine the potential impact of conservative equipment failures 58 Comparison to Risk Thresholds

• Evaluate against risk thresholds in RG 1.174 oCDF < 10-6/yr and LERF < 10-7/yr*Address defense-in-depth and safety margins 59 Ken Lowery Senior Licensing Engineer

Southern Nuclear TMRE License Amendment

Request LAR Process

• Preparation

• Pre-Submittal Meeting

• Submittal*Acceptance Review

• RAIs*SER 61 TMRE LAR Development

• Overall Objective of a TMRE LAR

• Summary Description

• Detailed Description oBackground information oCurrent Licensing Basis requirements for tornado missile protection oReason for the proposed change 62 TMRE LAR Development (cont.)

• Technical Evaluation oTMRE Methodology oTraditional Engineering Considerations (RG 1.174)

• Defense-in-Depth

• Safety Margins oRisk Assessment (RG 1.174) 63 TMRE LAR Development (cont.)

• Regulatory Evaluation oApplicable Regulatory Requirements/Criteria oNo Significant Hazards Consideration Analysis

• Environmental Consideration 64 Summary 65