ML17207A067
| 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: |
| References | |
| NEI 17-02, Rev 0 | |
| Download: ML17207A067 (65) | |
Text
NEI 17-02 Bruce Montgomery TORNADO Director, Strategic Planning NEI MISSILE RISK EVALUATOR July 6, 2017 (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.
3
Overview TMRE Methodology
- 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.
4
Overview of TMRE Pilot Plants
- Three plants volunteered to pilot the TMRE risk-informed methodology o Shearon Harris Nuclear Power Plant - Duke Energy
- Single Unit 3-loop W PWR - CP 1978; OL 1987 o Vogtle Electric Generating Plant- Southern Nuclear Operating Company
- Two additional W AP1000 reactors under construction o Grand Gulf Nuclear Station - Entergy Nuclear
TMRE Technical Advisory Group
- NEI established the industry TMRE Technical Advisory Group (TAG) o Membership - 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 o TAG meets weekly 6
TMRE Pilot Timeline
- Harris and Vogtle TMRE Pilot LAR Target Schedules o Pre-Submittal Meetings - August 1 o TMRE Pilot LAR submittal - August 31
- Grand Gulf TMRE Pilot LAR Target Schedule o Pre-Submittal Meeting - October 6 o TMRE Pilot LAR submittal - October 20
- Following issuance of any necessary RAIs regarding the third pilot LAR review o Incorporate pilot LAR lessons learned into NEI 17-02 o Updated NEI 17-02 will be submitted for NRC review and approval - Anticipated 2nd Quarter 2018 7
Bruce Montgomery Director, Strategic Planning NEI 17-02 NEI 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 9 Frequency
Table of Contents (cont.)
- Section 7: Evaluate Target and Missile Characteristics
- Section 9: Quantify Risk, Perform Sensitivity Studies, and Compare to Thresholds
- Section 10: License Amendment Request 10
Alex Gilbreath PRA Engineer, Southern Nuclear TMRE Tornado Hazard Frequency
=
Background===
- 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.
12
Hazard Frequency Calculation
- 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 range 13
Example Hazard Frequency Calculation
- The end result is a plant-specific initiating event frequency for each F-scale tornado.
Intensity Initiating Event Frequency F2 8.56E-05 F3 2.16E-05 F4 5.63E-06 F5 1.08E-06 F6 5.95E-08 14
Leo Shanley Manager, JENSEN HUGHES TMRE Missile Impact Parameter (MIP) and Missile Characteristics
Topics Covered
- Exposed Equipment Failure Probability (EEFP)
- Missile Impact Parameter (MIP) o Definition of MIP o MIP Values for Use in the EEFP
- Discuss TMRE Missile Inventories o Classifying Missiles o Missile Confirmatory Walkdowns 16 o Outage Impacts and Temporary Missiles
Exposed Equipment Failure Probability
- 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 magnitude EEFP =
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) 17
Missile Impact Parameter (MIP)
- MIP can be thought of as a missile flux MIP = Probability of Missile Hit / ft2 / missile / tornado 18
Missile Impact Parameter (MIP)
- MIP values were derived using published TORMIS data (EPRI NP-768) o NEI 17-02, Appendix B provides the basis for the MIP values to use in the TMRE o NEI 17-02 MIP values apply generically to all sites
- Separate MIP values are provided for each F-Scale tornado from F2 to F6
- Separate MIP values are provided for Near Ground and Elevated targets 19
MIP Values from NEI 17-02 Tornado Elevated Near Ground Intensity Targets (>30) Targets (<30)
F2 5.8E-11 1.1E-10 F3 2.0E-10 3.6E-10 F4 3.4E-10 6.3E-10 F5 8.7E-10 1.6E-09 F6 1.3E-09 2.4E-09 20
Number of Missiles
- 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 17-02 Tornado # of Missiles Intensity F2 155,000 F3 155,000 F4 205,000 F5 240,000 F6 240,000 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:
o Pipes, 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 o Additional structures evaluated to confirm TMRE missile inventory remains bounding o Sensitivity study to account for construction-related missiles 24
Leo Shanley Manager, JENSEN HUGHES TMRE Targets
Overview
- Describe Target Characteristics
- Target Area Calculations 26
- 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 o The list of vulnerable SSCs determined as part of the discovery activities o A list of potentially unprotected SSCs from the TMRE PRA
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 o The 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 o Examples: Pipe or cable tray mounted on wall, tank in a corner 36
Leo Shanley Manager, JENSEN HUGHES TMRE Targets and Exposed Equipment Failure Probability
Overview
- Describe how robust targets are addressed in the EEFP
- Describe EEFP calculations and provide examples 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 o Analyses 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 39 type/failure mode
Robust Target Types and Failure Modes
- Several robust target types:
o Exposed Pipes o Exposed Tanks o SSCs below Concrete Roofs o SSCs 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 Calculation Torna MIP # of Target Fragil EEFP do (Near Missiles Expos ity Intens Groun (non- ed ity d robust) Area Target (ft2)
)
F2 1.1E-10 155,000 12 1.0 2.0E-04 F3 3.6E-10 155,000 12 1.0 6.7E-04 F4 6.3E-10 205,000 12 1.0 1.5E-03 F5 1.6E-09 240,000 12 1.0 4.6E-03 41 F6 2.4E-09 240,000 12 1.0 6.9E-03
Alex Gilbreath PRA Engineer, Southern Nuclear TMRE PRA Modeling
Overview
o Calculate risk associated with non-conforming SSCs.
o Starting point is the plant-specific peer-reviewed internal events model.
43
Event Tree/Fault Tree Selection
- The TMRE assumes LOOP/RX Trip will occur o LOOP and SBO event trees typically represent the tornado accident sequence.
o Other trees should be reviewed for tornado impact as well.
Compliant/Degraded Case
- The purpose of the TMRE is to calculate the difference in risk between plant configurations.
o Compliant case o Degraded case - Nonconforming SSCs 45
Other Modeling Considerations
- Operator actions in the PRA must be examined for feasibility.
o Structure Considerations o Timing Considerations
- Non-feasible operator actions are not credited (i.e.
set to 1 or TRUE) in both cases
46
Target Impact Basic Events 47
PRA Technical Adequacy
- Internal Events o Peer-reviewed o As-built, as-designed o Address open findings
- TMRE specific supporting requirements 48
Leo Shanley Manager, JENSEN HUGHES TMRE Quantify Risk and Sensitivity Analyses
Topics Covered
- TMRE Sensitivity Analyses o Zonal vs. Uniform Missile Distribution o MIP for Highly Exposed Targets o Base Case Conservatisms o Open F&Os
- Risk Metrics and Thresholds 50
Compliant vs. Degraded Cases
- Compliant Case o Configuration where the plant is built per the required design/licensing bases o All SSCs required to be protected against missiles are assumed to be so protected, even if they are not
- Degraded Case o This is the current configuration of the plant (i.e.,
with potential non-conformances for tornado 51 missile protection)
Quantify Risk
- Need to quantify the compliant case and the degraded case for CDF and LERF o Increase 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 o Zonal vs. Uniform Missile Distribution o Missile Impact Parameter for Highly Exposed Targets o Compliant 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 o Realistic missile distribution is variable (i.e., zonal) o Large 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:
o CDF > 10-7/yr or LERF 10-8/yr
- Increase EEFP for targets with Risk Achievement Worth (RAW) > 2.0 o Only affects basic events for F4 - F6 tornadoes o Increase EEFP by 2.75x
Highly Exposed Targets
- SSCs for which all the following apply:
o Not located inside a Category I structure (i.e., either outside or in a non-Category I structure) o Not protected against horizontal missiles o Has an elevation less than 30 above grade 56
Sensitivity for Highly Exposed Targets
- Threshold to perform sensitivity:
o CDF > 10-7/yr or LERF 10-8/yr
- Increase EEFP for highly exposed targets with Risk Achievement Worth (RAW) > 2.0 o Only affects basic events for F4 - F6 tornadoes o Increase EEFP by 2.5x
Sensitivity for Conservative Assumptions
- Conservative assumptions in the compliant case may not be conservative for CDF and LERF calculations o Review cutsets in the top 90% of the TMRE compliant case to identify conservatisms related to SSC failures o Perform a sensitivity study to determine the potential impact of conservative equipment failures 58
Comparison to Risk Thresholds
- Address defense-in-depth and safety margins 59
Ken Lowery Senior Licensing Engineer TMRE Southern Nuclear License Amendment Request
LAR Process
- Preparation
- Pre-Submittal Meeting
- Submittal
- SER 61
- Summary Description
- Detailed Description o Background information o Current Licensing Basis requirements for tornado missile protection o Reason for the proposed change 62
- Defense-in-Depth
- Safety Margins o Risk Assessment (RG 1.174) 63
- Regulatory Evaluation o Applicable Regulatory Requirements/Criteria o No Significant Hazards Consideration Analysis
- Environmental Consideration 64
Summary 65