ML043450171
| ML043450171 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/06/2004 |
| From: | Duke Energy Corp |
| To: | Office of Nuclear Reactor Regulation |
| Olshan L N, NRR/DLPM, 415-1419 | |
| Shared Package | |
| ML043630033 | List: |
| References | |
| TAC MC4608, TAC MC4609, TAC MC4610 | |
| Download: ML043450171 (25) | |
Text
Duke Oconee Nuclear Site
[ Energysm NRC public meeting to discuss Oconee tornado mitigation strategy November 16, 2004 11/16/2004 1 Attachment 2
Duke Agenda
- Purpose of Meeting
- Oconee Tornado PRA Status Report
- Risk Reduction Team (RRT) - Charter
- RRT Findings
- Summary
- Schedule 11/16/2004 2
Duke Purpose of Meeting
[ Energysm
- Provide a tornado risk model status update.
- Present results from Oconee Tornado Risk reduction team whose mission is to evaluate modifications that would improve PRA, defense-in-depth, and equipment reliability/availability.
- At this point, leave the Staff with a better understanding of the Oconee direction with regard to those modifications being evaluated.
11/16/2004 3
.uke Oconee Tornado PRA Status EnergySM Report Major Tornado Analysis Updates Since 2002 LAR
- SSF Diesel Generator Reliability Data
- Human Error Dependency Analysis
- Updated Oconee Tornado Missile Analysis
- Steam Generator Replacement 11/16/2004 4
,Duke Energysm SSF D/G Reliability
- Conducted Detailed Review of
- Failure Data
- Start Demands & Loaded Run Hours
- Resulted in Lower Failure Estimated Rates
- 2 re-classified events
- Undercounted start demands and run hours 0
Conclusion:
Oconee SSF Diesel Generator Reliability is very comparable to average industry diesel reliability except for the maintenance unavailability caused by Unit 2 CCW outages.
11/16/2004 5
Duke Human Reliability Energysm Analysis
- The Oconee PRA Rev. 2 was criticized in its PRA Peer Review for not adequately addressing Human Error Dependencies when multiple human actions occur in the same accident sequence.
- Duke recently completed implementation of a new human error dependency model to address Oconee human error combinations.
- Results in an increase in the estimated CDF.
- This addresses an important PRA quality issue affecting the tornado analysis results.
11/1.6/2004 6
Duke Tornado Missile Analysis For Tornado Missile Damage:
@Duke seeks to justify U3 CR North Wall design based on low damage probability.
- Updated TORMIS model developed to evaluate tornado missile damage probability for
- U3 CR North Wall
- BWST
- Other Targets of Interest
- Unit 3 Control Room North Wall Found Acceptable 11/16/2004 7
EDnergy Tornado Missile Analysis BWST Modeling Changes
- Old TORMIS model used an arbitrary tank thickness (1/8 inch) instead of actual tank thickness.
- BWST constructed of 7 tiers of welded steel plates
- New model uses thickness 0.3125 (sides) and 0.25 (dome) e Correction results in significantly lower damage probabilities. (and still very conservative) 11/16/2004 8
Duke Energysm Updated BWST Results F-Scale Basic Event .. Freq Initiator Conditional Con a +;- Ol Value IdVles.' % Chang Change Prob.(
F-2 BF2BWSTDEX 5.37E-05 0.020 0.01i -72%
F-3 BF3BWSTDEX 4.12E-05 0.037 0 166 -78%
F-4 BF4BWSTDEX 3.59E-05 0.051 0 -84%
F-5 BF5BWSTDEX 1.71 E-06 0.073 0439 -83%
Total Frequency 4.56E-06 2s; '3E -80%
I i 11/16/2004 9
Duke Steam Generator Enera Replacement
- Replacement SG design improvements
- Higher Compressive Tube Stress Capacity
- Analysis Improvements
- Higher Initial SG Operating Level
- PRA Impact
- Increased Time Available for Feedwater Recovery
- Improved Human Reliability Estimates for TDEFWP Recovery and SSF ASW Alignment 11/16/2004 10
Dukey Tornado Risk Results
- Historical Estimates of 5.E-05 Tornado CDF have produced consistent results relative to 4.E-05 the uncertainty associated with tornado data and 3.E-05 modeling techlniques, and general PRA uncertainties Preliminary 2.E-05 -Rev. 3
- Current Oconee tornado risk remains consistent with historical estimates, but with 1E05 less modeling uncertainty.
O.E+00O NSAC/60 IPE IPEEE Rev. 2 LAR Final OR3
- Results based on WOG2000 Seal LOCA model. CEOG model is worth approximately 3E-06/yr reduction in overall CDF.
11/16/2004 11
Duke CDF Reduction Benefits
- "Public" Benefits estimated using methodology similar to SAMA methodology
(-'$40,000 to --$50,000 per 1E-06/yr CDF reduction)
)Major Plant Modifications are not cost justified based on PRA benefit alone.
11/16/2004 12
Duke Risk Reduction Team (RRT) -
ne@gySM Charter
- Gather subject matter experts from various plant organizations, from the general office, and outside consultants to serve on the RRT.
- Improve Mitigation Strategies for Risk Significant Design Basis Issues
- Consider current design basis initiatives and their impact to the overall risk profile.
- Consider, as appropriate, potential modifications that would significantly reduce risk, without creating additional operator burden.
11/16/2004 13
Duke PRA Insights Review of ONS PRA provided the following insights into current plant vulnerabilities:
- Reliance on the Standby Shutdown Facility (SSF) or Station Auxiliary Service Water (ASW) for event mitigation.
- Majority of top postulated equipment failures are related to the SSF.
- Majority of top postulated operator failures are related to actions associated with the SSF or Station ASW.
11/16/2004 14
Durke Risk Reduction Strategy Energy..
>Improve Availability and Reliability of the SSF
)>Provide a Reliable back-up to the SSF 11/16/2004 15
Duke Tornado Mitigation Risks
- Issues with Secondary Side Heat Removal (SSHR).
- Potential Loss of Station ASW Pump Flow Control.
- Ability to Operate the Atmospheric Dump Valves (ADVs).
- Steam Generator Compressive Tube Stresses.
- Pressurizer Safety Valve Reseating.
11/16/2004 16
,Duke Tornado Mitigation Risks Energysm (cont.)
- Issues with Primary Side Volume and Pressure Control.
- Potential missile damage to Borated Water Storage Tank (BWST).
- Ability to Access LP-28 (BWST Outlet Valve).
- Potential Failure of Main Steam Branch lines.
- Potential Loss of Spent Fuel Pool Suction for High Pressure Injection (HPI).
11/16/2004 17
i Duke Tornado Mitigation Risks Energysm (cont.)
- Structural Protection Issues
- Potential missile damage to BWST.
- Potential Structural Failure of Unit 3 Control Room Wall.
- Potential Structural Failure of West Penetration Room.
11/16/2004 18
,Duke Tornado Mitigation Risks Energysm (cont.)
- Potential Loss of 4kv Power and Control Power.
- Failure of 4kv Bus
- Loss of Control Power 11/16/2004 19
Duke Potential SSHR
[Energysm Modifications
- New High Head Station ASW pump with replacement of existing piping and addition of necessary flow control.
- Use existing Station ASW pump, with addition of motor operated valves (MOVs), flow control instrumentation, and replacement of current ADVs with MOVs.
- Provide alternateSSFASWpu7np suction source (Increase SSF availability).
11/16/2004 20
Duke Potential Primary Side EnEergySm Modifications
- Protect Sufficient BWST Volume.
- Ensure Letdown Storage Tank. (LDST) mak-e up from Bleed Holdup Tank and Concentrated Boric Acid Storage Tank
- Improve Power Supply to HPI Pumps.
11/16/2004 21
Duke Potential Structural 5Energy. AModifications
- Provide Missile Protection for BWST and Wind Protection for West Penetration Room and Cask Decontamination Room.
- Provide Wind Protection for West Penetration Room and Cask Decontamination Room (assumes that BWST absorbs missiles)
- Provide Wind and Missile Protection for Main Feeder Bus and associated switchgear in Turbine Building.
- Provide Wind (dp) Protectionfor Unit 3 Control Room Wall (This item previously committed).
11/16/2004 22
Duke Potential 4kv and Control n~ergySM Power Modifications
- Upgrade Protected Power Path from Standby Bus 1 to ASW Switchgear.
- New Onsite Power Source: Either New Combustion Turbine or Diesel, with all required support systems and protected power path to ASW switchgear.
- Provide Protected power path to battery chargers from ASW Switchgear.
- Provide Back Up Power to SSFfrom a Protected Power Source (Improve SSF Availability).
11/16/2004 23
DukeS Summary
- Updated PRA model shows significant tornado risk reduction
- Initiated Overall Risk Reduction Effort in order to identify modification alternatives that would improve Oconee's mitigation strategies, PRA, defense in depth, equipment reliability and availability
- Modification Alternative to be selected will effectively address issues discussed 11/16/2004 24
Dukes Energy5. Schedule
- Risk Reduction Team meeting
- Complete
- Present findings to plant management
- Mid-December 2004
- Plant Management approval
- January 2005
- Feasibility study completed
- July2005
- Detailed scoping and cost estimate completed
- July2006
- LAR submitted
- October 2006 11/16/2004 25