ML11090A087
| ML11090A087 | |
| Person / Time | |
|---|---|
| Site: | Three Mile Island  |
| Issue date: | 04/05/2011 |
| From: | Shanley L Exelon Nuclear |
| To: | Office of Nuclear Reactor Regulation |
| Bowen, Jeremy | |
| Shared Package | |
| ML11090A079 | List: |
| References | |
| NUMARC 93-01, Rev 4 | |
| Download: ML11090A087 (18) | |
Text
Public Meeting Concerning Rev 4 to NUMARC 93-01 Rockville, MD March 29, 29 2011 TMI Fire (a)(4) Tabletop Pilot Method and Results Leo Shanley
TMI Fire (a)(4) Pilot - Overview 9 Methodology
- Use Fire PRA to identify important components based on table in 93-01 Rev. 4
- Fire PRA CDF top event quantified Determine equipment to consider in scope of Section 11 revisions Determine important scenarios when equipment is unavailable Obtain insights and help identify Risk Management Actions (RMA)
- Focus of Fire PRA use will be on development and application of insights 2
TMI Fire (a)(4) Pilot - Overview 9 Why not use CDF values directly (i.e.,
similar to internal events)?
- Fire PRAs are in various states of refinement at the 10 Exelon sites Fire PRA level of detail not yet comparable to that of Internal E
Events PRA
- General conservatisms in methodology, some of which are being addressed by industry initiatives
- Specific conservatisms revealed when removing equipment from service 3
TMI Fire (a)(4) Pilot - Overview 9 TMI Fire PRA Status
- Internally reviewed, reviewed but not peer reviewed
- Includes SSEL components
- Scenarios and cutsets have not yet been reviewed against specific maintenance configurations 4
TMI Fire (a)(4) Pilot - Methodology 9 Scope: identify equipment within the existing (a)(4) scope that is found to have appreciable impact on core damage mitigation for fire initiators.
- Looking g for components p that,, when removed from service, result in one or more scenarios where no success paths are available (i.e.,
CCDP = 1.0)
Per the table in NUMARC 93-01 (Draft) Rev. 4, these components require risk management actions if removed from service for 3 - 30 days
- Should be able to screen scenarios that already have CCDP = 1.0 in the base case 5
TMI Fire (a)(4) Pilot - Methodology 9 Table from NUMARC 93-01 (Draft) Rev. 4
[Section 11.3.7.3]
Number of Core Damage Avoidance Success Paths Available 1 or More Success Paths Available No Success Paths Available Duration of Unavailability Duration of Unavailability
<3d 3-30d >30d <3d 3-30d >30d Normal Controls RMA Normal RMA Avoid Controls Config.
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TMI Fire (a)(4) Pilot - Methodology 9 Risk Management Actions (RMA):
develop a process for implementing risk management actions related to fire risk impacts of equipment identified
- Review Fire CDF cutsets for cases with identified equipment out-of-service Identify the scenarios in which there are no success/mitigation paths Determine what is driving scenario The RMA must address the initiator or plant configuration that results in core damage 7
TMI Fire (a)(4) Pilot - Results 9 Scope
- Started with at-power internal events (a)(4) scope of equipment Approximately 160 components that affect the PRA are included in the TMI (a)(4) model.
Identified scenarios of interest by comparing CCDP for each scenario with base case CCDP for each scenario Used PARAGON software to help automate process of quantification and CCDP calculations 8
TMI Fire (a)(4) Pilot - Results 9 Scope
- Identified about 50 components that resulted in one or more scenarios that met the criteria Mostly electrical buses, buses ECCS pumps pumps, Service Water and EDGs Some asymmetry in trains (EFW, 120V Vital AC)
- Nothing unexpected - most potentially fire risk significant components are important for internal events 9
TMI Fire (a)(4) Pilot - Scope Results 9 Electrical Buses, MCCs, Distribution Panels (19)
DC Distribution (6) Panels, 120V Vital AC (1) 9 ECCS ((8))
- Make-up Pumps (3), Decay Heat Removal Pumps (2),
BWST Suction Valves (2), BWST 9 Service and Component Cooling Water (11)
- Service Water Pumps (3), Decay Heat Service Water Pumps and HX (2), Nuclear Services CCW HX (2),
Decay Heat CCW Pumps (2), Intermediate CCW Pumps (2) 10
TMI Fire (a)(4) Pilot - Scope Results 9 Emergency Feedwater (4)
CST (1) 9 Diesel Generators (3)
Atmospheric Dump Valve (1) 11
TMI Fire (a)(4) Pilot - Results 9 Risk Management Actions (RMA)
- Reviewed CCDP =1 cutsets to characterize the scenarios and develop RMAs With one train unavailable, a fire affecting the other train could result in core damage
- Affected Fire Areas and Scenarios Minimum of one scenario in one fire area (e.g.,
EDG-1A)
Some equipment important to fire (buses, ECCS pumps) have many scenarios (>15) in multiple fire areas (>5) 12
TMI Fire (a)(4) Pilot - Results 9 Risk Management Actions (RMA)
- Nearly all identified components require RMAs in current (a)(4) program (e.g., protect opposite train, minimize time in configuration)
Internal events CDF or LERF > 2x Baseline Reduced Defense-in-depth
- About 60% of the identified components have Tech Spec AOTs < 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
- Nearly half of the identified components are not normally removed from service while at-power Buses, MCCs, Batteries, BWST, CST 13
TMI Fire (a)(4) Pilot - Potential RMAs 9 Transients/Cable Fires
- Sensitivity to or control of hot work in fire zones or areas within fire zones
- Minimize transient combustibles
- Fire watches 9 High Hi h E Energy A Arcing i F Faultslt (HEAF)
- Minimize electrical switching 9 Incipient Detection
- Ensure its available for scenarios where its important 9 Suppression
- Ensure automatic suppression systems are available where important and/or brief Fire Brigade 14
TMI Fire (a)(4) Pilot - DHR Pump RMA Equip Fire Area Fire Area Detection/ Cause of Fire No. of Potential RMAs Equip ID Description ID Description Suppression Scenarios DH-P-1A DHR Pump AB-FZ-5 281 General None Cable fires in 2 (B01, B02) Avoid or minimize 1A Area various trays with hotwork in area.
potential to spread 1 (B06) Avoid or minimize to other trays hotwork in area.
CB-FA-2b 322 1S (Train Incipient Fire in Remote 1 (E01) a) Ensure detection B)) ESF 480V Detection Shutdown Transfer system y is available Switchgear Switch Panel with b) Brief operators failure of detection and fire brigade on or fire brigade significance of fire in response this room.
Cable fire with 1 (F04) Avoid or minimize potential to spread hotwork in area.
to other trays CB-FA-2c 322 Tech Incipient Fire in cabinet RS- 1 (J02) a) Ensure detection Support Detection SCC-B2 with failure system is available Center of detection or fire b) Brief operators brigade and fire brigade on significance of fire in this room.
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TMI Fire (a)(4) Pilot - EDG RMAs Equip ID Equip Fire Area Fire Area Detection/ Cause of Fire No. of Potential RMAs Description ID Description Suppression Scenarios EDG 1A CB-FA-3b 338 1E (Train B) Incipient HEAF in 1E 1 (B6) Avoid or EG-Y-1A Switchgear Room Detection switchgear minimize breaker manipulations on 1E switchgear EG-Y-1B EDG 1B CB-FA-3a 338 1D (Train A) Incipient HEAF in 1D 5 (B3, B4, Avoid or Switchgear Room Detection switchgear B5, B6, B7) minimize breaker manipulations on 1D switchgear EG-Y-4 SBO DG CB-FA-1 306' Rad Con No Cable fire in 2 (B01, Avoid or Office and Lab tray with B03) minimize Area propagation to hotwork in area other trays 16
TMI Fire (a)(4) Pilot - Conclusions 9 Fire PRA can be used to identify fire risk significant equipment
- No surprises in equipment identified - most equipment already risk significant for internal events
- Identified equipment list is manageable - nearly half off equipment i t is i nott normally ll removedd ffrom service i
while at-power 9 Fire PRA can be used to establish RMAs
- Review needed at the cutset level to evaluate the scenario and develop RMAs
- Some components have many scenarios that may require RMAs 17
TMI Fire (a)(4) Pilot - Conclusions 9 Lessons Learned
- Fire PRAs provide conservative results when equipment removed from service - some screening needs to be done during review
- Need to account for flags g and split p fractions -
best to set them to 1.0 to ensure nothing is missed
- More than 1 component removed from service Are there new scenarios beyond the union of the individual equipment scenarios?
Some cases were reviewed as part of tabletop Generally not found 18