ML033370684
| ML033370684 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 11/25/2003 |
| From: | Nuclear Management Co |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| Download: ML033370684 (1) | |
Text
1 Committed to Nuclear Excellence Palisades Regulatory Conference November 25, 2003
2 Committed to Nuclear Excellence Committed to Nuclear Excellence Agenda Agenda Introduction Douglas Cooper Objectives Daniel J. Malone
Background
Michael Carlson Risk Discussion Jeb Kingseed Corrective Actions Michael Carlson Conclusion Daniel J. Malone
3 Committed to Nuclear Excellence Objectives Objectives
- NMC will present
- Agreement with finding
- Facts and assumptions used to determine safety significance
- Corrective actions
- Conclusion of Green safety significance
4 Committed to Nuclear Excellence
Background
Background
- March 25, 2003, with plant in Mode 6
- Signpost driven into buried conduit in parking lot
- Conductors within conduit damaged, affecting breaker protective relaying
- Protective relaying tripped breakers open, disconnecting offsite power circuits
5 Committed to Nuclear Excellence Background (cont)
Background (cont)
- Systems responded as expected
- NRC finding identified
- Failure to have administrative controls in place for digging or excavating
- NMC agrees with the finding
- NMC has determined the finding significance to be Green
6 Committed to Nuclear Excellence Risk Discussion Risk Discussion
- Background
- Completed qualitative assessment of 3/25/03 loss of offsite power (LOOP) for the shutdown condition
- Completed quantitative analysis of the LOOP for the at-power condition
- Used Phase III probabilistic safety assessment (PSA) model
7 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
- Methodology
- Identified dominant PSA sequences
- Re-examined basis for recovery actions
- Re-assessed the time available for recovery actions using modular accident analysis program (MAAP)
- Determined the time for operators to complete recovery actions
- Calculated new human error probabilities (HEPs)
8 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
- Dominant PSA sequences
- LOOP, failure of both diesel generators (DGs), successful auxiliary feedwater (AFW) injection, failure to restore safety related bus within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />
- LOOP, failure of both DGs, failure of AFW, failure to restore safety related bus within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />
9 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
Time Available For Recovery Actions Sequence Baseline PSA Time to Core Damage (hrs)
MAAP Analysis Time to Core Damage (hrs)
LOOP, Loss of DGs, AFW available 4
8.5 LOOP, Loss of DGs, Loss of AFW 2
2.5
10 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
Time for Operators to Complete Recovery Actions Time used in the analysis 115 min and 57 min Crew 1 Crew 2 Diagnosis and manual actions 114 min 91 min Manual actions 54 min 57 min Time to Recover Offsite Power and Open the First PORV (includes both diagnosis and manual actions)
11 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
Diagnosis Time Used in Analysis LOOP (both circuits) and Loss of DGs MAAP Calculated Available Time Available Time for Diagnosis Diagnosis Time used in the HEP Analysis With AFW
~8.5 hrs
(~510 min) 453 min (510 min - 57 min) 183 min (240 min - 57 min)
Without AFW
~2.5 hrs
(~150 min) 93 min (150 min - 57 min) 90 min
12 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
New Human Error Probabilities New Human Error Probabilities The change is the result of credit for recovery actions specific to the LOOP scenario of 3/25/03 Sequence Baseline Recovery Factor Updated Recovery Factor LOOP, Loss of DGs, AFW available 6.0E-01 5.6E-03 LOOP, Loss of DGs, Loss of AFW 7.4E-01 2.3E-02
13 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
- Model and analyses conservatisms
- Assumed no AFW flow after 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />
- DG recovery not credited
- Used 1 in 32 years as initiating event likelihood (IEL)
- Used degraded high pressure safety injection pump curve
- Assumed core damage at 1600 degrees F
14 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
- NRCs IEL is 1 in 32 years (3.11E-02/year)
- Regardless of which IEL is used in the Palisades PSA model, the change in risk is <1E-06/year : Green
15 Committed to Nuclear Excellence
- Palisades analyses validated by industry experts
- Initiating Event Likelihood
- Modular Accident Analysis Program
- Probabilistic Safety Assessment Risk Discussion (cont)
Risk Discussion (cont)
16 Committed to Nuclear Excellence Risk Discussion (cont)
Risk Discussion (cont)
- Summary
- Identified dominant PSA sequences
- Re-examined basis for recovery actions
- Re-assessed the time available for recovery actions using MAAP
- Determined the time for operators to complete recovery actions
- Calculated new HEPs
- Calculated risk using revised HEPs
17 Committed to Nuclear Excellence Corrective Actions Corrective Actions
- Issued stop work order
- Repaired damaged conductors
- Rerouted protective relaying
- Protected conduit
- Created new controls
18 Committed to Nuclear Excellence Conclusion Conclusion
- Evaluated the performance deficiency
- Implemented corrective actions
- Determined safety significance to be Green