ML11090A087
| ML11090A087 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| 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 2011 March 29, 2011 TMI Fire (a)(4) Tabletop Pilot Method and Results Leo Shanley
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 TMI Fire (a)(4) Pilot - Overview 2
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
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
PRA TMI Fire (a)(4) Pilot - Overview 3
Events PRA General conservatisms in methodology, some of which are being addressed by industry initiatives Specific conservatisms revealed when removing equipment from service
9 TMI Fire PRA Status Fire PRA databases updated in 2007, underlying PRA model updated in 2009 Internally reviewed but not peer reviewed TMI Fire (a)(4) Pilot - Overview 4
Internally reviewed, but not peer reviewed Includes SSEL components Scenarios and cutsets have not yet been reviewed against specific maintenance configurations
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 for components that, when removed TMI Fire (a)(4) Pilot - Methodology 5
g p
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
9 Table from NUMARC 93-01 (Draft) Rev. 4
[Section 11.3.7.3]
TMI Fire (a)(4) Pilot - Methodology Number of Core Damage Avoidance Success Paths Available 1 or More Success Paths Available No Success Paths Available 6
Duration of Unavailability Duration of Unavailability
<3d 3-30d
>30d
<3d 3-30d
>30d Normal Controls RMA Normal Controls RMA Avoid Config.
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 TMI Fire (a)(4) Pilot - Methodology 7
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
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.
TMI Fire (a)(4) Pilot - Results 8
Quantified Fire PRA CDF with (a)(4) components unavailable one at a time.
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
9 Scope Identified about 50 components that resulted in one or more scenarios that met the criteria
Mostly electrical buses ECCS pumps Service TMI Fire (a)(4) Pilot - Results 9
Mostly electrical buses, ECCS 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
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) 10
( )
- 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)
TMI Fire (a)(4) Pilot - Scope Results 9 Emergency Feedwater (4)
CST (1) 11 9 Diesel Generators (3)
Atmospheric Dump Valve (1)
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 TMI Fire (a)(4) Pilot - Results 12 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)
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 TMI Fire (a)(4) Pilot - Results 13
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
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 Hi h E A
i F
lt (HEAF)
TMI Fire (a)(4) Pilot - Potential RMAs 14 9 High Energy Arcing Faults (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
TMI Fire (a)(4) Pilot - DHR Pump RMA Equip ID Equip Description Fire Area ID Fire Area Description Detection/
Suppression Cause of Fire No. of Scenarios Potential RMAs DH-P-1A DHR Pump 1A AB-FZ-5 281 General Area None Cable fires in various trays with potential to spread to other trays 2 (B01, B02)
Avoid or minimize hotwork in area.
1 (B06)
Avoid or minimize hotwork in area.
CB-FA-2b 322 1S (Train B) ESF 480V Incipient Detection Fire in Remote Shutdown Transfer 1 (E01) a) Ensure detection system is available 15
)
Switchgear Switch Panel with failure of detection or fire brigade response y
b) Brief operators and fire brigade on significance of fire in this room.
Cable fire with potential to spread to other trays 1 (F04)
Avoid or minimize hotwork in area.
CB-FA-2c 322 Tech Support Center Incipient Detection Fire in cabinet RS-SCC-B2 with failure of detection or fire brigade 1 (J02) a) Ensure detection system is available b) Brief operators and fire brigade on significance of fire in this room.
TMI Fire (a)(4) Pilot - EDG RMAs Equip ID Equip Description Fire Area ID Fire Area Description Detection/
Suppression Cause of Fire No. of Scenarios Potential RMAs EG-Y-1A EDG 1A CB-FA-3b 338 1E (Train B)
Switchgear Room Incipient Detection HEAF in 1E switchgear 1 (B6)
Avoid or minimize breaker manipulations on 1E switchgear 16 EG-Y-1B EDG 1B CB-FA-3a 338 1D (Train A)
Switchgear Room Incipient Detection HEAF in 1D switchgear 5 (B3, B4, B5, B6, B7)
Avoid or minimize breaker manipulations on 1D switchgear EG-Y-4 SBO DG CB-FA-1 306' Rad Con Office and Lab Area No Cable fire in tray with propagation to other trays 2 (B01, B03)
Avoid or minimize hotwork in area
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 f
i t i t
ll d f i
TMI Fire (a)(4) Pilot - Conclusions 17 of equipment is not normally removed from service 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
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 and split fractions -
TMI Fire (a)(4) Pilot - Conclusions 18 g
p 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