ML042370849
| ML042370849 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 08/23/2004 |
| From: | Abney T Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML042370849 (11) | |
Text
August 23, 2004 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop: OWFN P1-35 Washington, D.C. 20555-0001 Gentlemen:
In the Matter of )
Docket No. 50-259 Tennessee Valley Authority )
BROWNS FERRY NUCLEAR PLANT (BFN) - UNIT 1-PROPOSED TECHNICAL SPECIFICATIONS (TS) CHANGE TS - 431 - REQUEST FOR LICENSE AMENDMENT - EXTENDED POWER UPRATE (EPU) OPERATION PROBABILISTIC SAFETY ASSESSMENT (PSA) UPDATE This letter provides updated Probabilistic Safety Assessment (PSA) information to support NRC Staff review of BFN Unit 1 Proposed Technical Specification Change TS-431 transmitted to the NRC by letter dated June 28, 2004 (Reference 1). This update reflects BFN Unit 1 PSA modeling changes made since submittal of Reference 1. These changes do not alter the conclusions reached in Reference 1 that BFN Unit 1 can be safely operated at Extended Power Uprate (EPU) conditions.
Reference 1, Enclosure 4, Section 10.5, Individual Plant Evaluation, provided the BFN Unit 1 Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) results for operation at EPU conditions. Section 10.5 also reported information relating to initiating event contributions to these quantities, and relative importance of specific operator actions. As a result of the PSA model update, many of these values have changed. The changes to the CDF and LERF are as follows:
Parameter Reference 1 Value Revised Value Total CDF (yr-1, mean value) 1.66 E-6 1.86 E-6 LERF (yr-1, mean value) 2.93 E-7 1.87 E-7
U.S. Nuclear Regulatory Commission Page 2 August 23, 2004 to this letter identifies the impact of these changes to Reference 1, Enclosure 4 resulting from the BFN Unit 1 PSA modeling changes. These changes do not alter the conclusions reached in Reference 1 that BFN Unit 1 can safely operate at the requested license power level of 3952 MWt.
If you have any questions about this submittal, please contact me at (256) 729-2636.
Sincerely, Original signed by T. E. Abney Manager of Licensing and Industry Affairs REFERENCE
- 1.
TVA letter to NRC, Browns Ferry Nuclear Plant (BFN) - Unit 1-Proposed Technical Specifications (TS) Change TS - 431 -
Request For License Amendment - Extended Power Uprate (EPU)
Operation, dated June 28, 2004.
U.S. Nuclear Regulatory Commission Page 3 August 23, 2004 (Via NRC Electronic Distribution)
U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-3415 Mr. Stephen J. Cahill, Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Senior Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, AL 35611-6970 Kahtan N. Jabbour, Senior Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)
One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739
U.S. Nuclear Regulatory Commission Page 4 August 23, 2004 MJB:BAB Enclosure cc (w/o Enclosure):
A. S. Bhatnagar, LP 6A-C M. J. Burzynski, BR 4X-C J. C. Fornicola, LP 6A-C D. F. Helms, BR 4T-C J. E. Maddox, LP 6A-C R. F. Marks, PAB 1C-BFN R. G. Jones, NAB 1A-BFN K. L. Krueger, POB 2C-BFN J. R. Rupert, NAB 1A-BFN K. W. Singer, LP 6A-C M. D. Skaggs, PAB 1E-BFN E. J. Vigluicci, ET 11A-K NSRB Support, LP 5M-C EDMS WT CA - K (with Enclosure)
S:\\Licensing\\Lic\\Submit\\Subs\\U1 EPU PSA Update Supplement 8-23-04.doc
E1-1 ENCLOSURE 1 UPDATE TO BFN UNIT 1 PROBABILISTIC SAFETY ASSESSMENT AT EXTENDED POWER UPRATE CONDITIONS INTRODUCTION By letter dated June 28, 2004 (Reference 1), TVA transmitted to the NRC TS-431 - Request For License Amendment - Extended Power Uprate (EPU) Operation. That amendment application requested NRC approval to increase the licensed maximum thermal power level from 3293 MWt to 3952 MWt. Enclosure 4 of that request contained NEDC-33101P, Browns Ferry Unit 1 Safety Analysis Report for Extended Power Uprate, Revision 0 (BFN Unit 1 PUSAR). Section 10.5 of the PUSAR, Individual Plant Evaluation, provided the results of the BFN Unit 1 specific Probabilistic Safety Assessment (PSA) performed at Extended Power Uprate (EPU) Conditions.
As a result of BFN Unit 1 PSA modeling changes made since submittal of Reference 1, the calculated values of the BFN Unit 1 Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) at EPU conditions has changed. These changes result from revisions to the initiator contributions to the BFN Unit 1 CDF and LERF (reported in the BFN Unit 1 PUSAR, Table 10-4) and the Frequency Weighted Fractional Importance to Core Damage of Operator Actions Used in Browns Ferry Unit 1 PRA (reported in the BFN Unit 1 PUSAR, Table 10-5). These changes are detailed below.
CHANGES RESULTING FROM BFN UNIT 1 PSA MODELING IMPROVEMENTS The specific changes to information previously reported to the NRC in Reference 1, Enclosure 4, are described below.
- 1.
PUSAR Section 10.5, Individual Plant Evaluation Paragraph 7 Text:
An uncertainty analysis was performed to more fully describe the core damage frequency. The mean core damage frequency is 1.66E-6. The fifth percentile is 5.13E-7 while the ninety-fifth percentile is 4.65E-6. The ratio of the ninety-fifth percentile to the median for this distribution is 3.9.
Paragraph 7 Impact Based on PSA Update:
An uncertainty analysis was performed to more fully describe the core damage frequency. The mean core damage frequency is 1.86E-6. The fifth percentile is 5.37E-7 while the
E1-2 ninety-fifth percentile is 4.80E-6. The ratio of the ninety-fifth percentile to the median for this distribution is 3.6.
- 2.
PUSAR Table 10-3, Browns Ferry Summary of CDF and LERF The values in BFN Unit 1 PUSAR Table 10-3 have changed as follows:
Table 10-3 Browns Ferry Summary of CDF and LERF Parameter Value Total CDF (yr-1, mean value) 1.86 E-6 LERF (yr-1, mean value) 1.87 E-7
- 3.
PUSAR Table 10-4, Summary of the Initiator Contributions to CDF and LERF for Browns Ferry Unit 1 The update to the BFN Unit 1 PSA has resulted in the values in BFN Unit 1 PUSAR Table 10-4 changing as follows:
Table 10-4 Summary of the Initiator Contributions to CDF and LERF for Browns Ferry Unit 1 Initiator Category Contribution to CDF and LERF Initiator Category Mean frequency (events per year)
CDF LERF Transient initiator categories Inadvertent Opening of One SRV 4.36E-2 1.42E-8 2.28E-11 Spurious Scram at Power 8.70E-2 2.98E-8 5.83E-11 Loss of 500kV Switchyard to Plant 9.73E-3 2.38E-8 1.70E-10
E1-3 Initiator Category Contribution to CDF and LERF Initiator Category Mean frequency (events per year)
CDF LERF Loss of 500kV Switchyard to Unit 2.30E-2 5.14E-8 4.48E-10 Loss of Instrumentation and Control Bus 1A 4.10E-3 9.73E-10
< 1E-12 Loss of Instrumentation and Control Bus 1B 4.10E-3 2.93E-8 6.79E-11 Total Loss of Condensate Flow 9.09E-3 3.76E-8 1.55E-10 Partial Loss of Condensate Flow 1.80E-2 5.55E-9 7.07E-12 MSIV Closure 5.70E-2 9.67E-8 1.21E-9 Turbine Bypass Unavailable 1.96E-3 3.10E-9 2.82E-11 Loss of Condenser Vacuum 9.72E-2 1.67E-7 2.16E-9 Total Loss of Feedwater 2.58E-2 5.59E-8 5.02E-10 Partial Loss of Feedwater 2.58E-2 7.94E-9 1.12E-11 Loss of Plant Control Air 1.20E-2 6.58E-8 2.23E-10 Loss of Offsite Power 6.43E-3 2.17E-7 9.32E-10 Loss of Raw Cooling Water 7.95E-3 1.21E-8 1.73E-10 Momentary Loss of Offsite Power 7.17E-3 1.88E-9 1.08E-12 Turbine Trip 5.09E-1 1.86E-7 4.88E-10 High Pressure Trip 4.30E-2 1.40E-8 2.25E-11 Excessive Feedwater Flow 2.60E-2 8.00E-9 1.13E-11 Other Transients 3.70E-1 1.38E-7 3.50E-10
E1-4 Initiator Category Contribution to CDF and LERF Initiator Category Mean frequency (events per year)
CDF LERF ATWS Categories Turbine Trip ATWS N/A 1.54E-7 8.18E-8 LOSP ATWS N/A 1.86E-9 9.73E-10 Loss of Condenser Heat Sink ATWS N/A 4.77E-8 2.52E-8 Inadvertent Opening of SRV ATWS N/A 1.21E-8 6.37E-9 Loss of Feedwater ATWS N/A 9.87E-8 5.23E-8 LOCA initiator categories Breaks Outside Containment 6.67E-4 3.12E-8 2.06E-10 Excessive LOCA (reactor vessel failure) 9.39E-9 9.09E-9 4.16E-11 Interfacing Systems LOCA 3.15E-5 5.00E-8 5.20E-9 Large LOCA - Core Spray Line Break Loop I 1.57E-6 4.37E-9 1.44E-10 Loop II 1.57E-6 4.36E-9 1.44E-10 Large LOCA -
Recirculation Discharge Line Break Loop A 1.10E-5 1.85E-8 1.13E-9 Loop B 1.10E-5 1.85E-8 1.13E-9 Large LOCA -
Recirculation Suction Line Break Loop A 7.85E-7 4.72E-9 6.80E-11 Loop B 7.85E-7 4.72E-9 6.80E-11 Other Large LOCA 1.57E-6 2.45E-9 1.42E-10
E1-5 Initiator Category Contribution to CDF and LERF Initiator Category Mean frequency (events per year)
CDF LERF Medium LOCA Inside Containment 4.00E-5 2.13E-8 4.21E-9 Small LOCA Inside Containment 5.00E-4 1.34E-10 1.08E-11 Very Small LOCA Inside Containment 3.38E-3 7.71E-10
< 1E-12 EECW Flood in Reactor Building -
shutdown units 1.20E-3 7.41E-11
< 1E-12 EECW Flood in Reactor Building -
operating unit 1.85E-6 1.19E-9 2.10E-12 Flood from the Condensate Storage Tank 1.22E-4 1.39E-9 4.95E-12 Flood from the Torus 1.22E-4 4.01E-8 8.55E-10 Large Turbine Building Flood 3.65E-3 5.51E-8 7.41E-11 Small Turbine Building Flood 1.65E-2 1.65E-8 3.38E-11
- 4.
PUSAR Table 10-5, Frequency Weighted Fractional Importance to Core Damage of Operator Actions Used in Browns Ferry Unit 1 PRA.
PUSAR Table 10-5 identifies and ranks the operator actions with the largest contributions to core damage. As a result of the BFN Unit 1 PSA Update, the importance of some actions has increased and some decreased. Since the table lists these actions in order of importance (from largest contribution to core damage to smallest), the order of some of the operator actions has changed, some operator actions previously listed in Table 10-5 have been removed, while others not previously listed have been added. The values in BFN Unit 1 PUSAR Table 10-5 have changed as follows:
E1-6 Table 10-5 Frequency Weighted Fractional Importance to Core Damage of Operator Actions Used in Browns Ferry Unit 1 PRA Database Variable Operator Action Description Frequency-Weighted Fractional Importance to Core Damage HPRVD1 OPERATOR FAILS TO INITIATE DEPRESSURIZATION 2.6734E-001 HPWWV1 OPERATOR FAILS TO OPEN WETWELL VENT 2.3142E-001 HRSPC1 OPERATOR FAILS TO LOCALLY RECOVER SP COOLING FAILURE 1.3861E-001 HOU11 OPERATOR FAILS TO ALIGN THE RHR UNIT 1/UNIT 2 CROSSTIE 4.0047E-002 HPHPE1 OPERATOR FAILS TO CONTROL LEVEL WITH HPCI/RCIC (EARLY - 6 HOURS) 1.9984E-002 HPHPR1 OPERATOR FAILS TO CONTROL LEVEL WITH HPCI/RCIC FOLLOWING LEVEL 8 TRIP 1.7241E-002 HOTAF1 OPERATOR FAILS TO CONTOL LEVEL AT TAF DURING ATWS - UNISOLATED VESSEL 1.5492E-002 HPSPC1 OPERATOR FAILS TO ALIGN SUPPRESSION POOL COOLING - THIS IS A NON ATWS SCENARIO 1.0550E-002 HODWS1 OPERATOR FAILS TO ALIGN FOR DRYWELL SPRAY. THIS IS A NON ATWS SCENARIO.
6.5391E-003 HPRVD2 OPERATOR FAILS TO INITIATE DEPRESSURIZATION GIVEN FAILURE TO CONTROL HIGH PRESSURE LEVEL CONTROL 6.1699E-003 HPTAF2 OPERATOR FAILS TO CONTOL LEVEL AT TAF DURING ATWS-ISOLATED VESSEL 3.3992E-003 HREEC1 OPERATOR FAILS TO RESPOND TO INADEQUATE EECW FLOW TO DG FOLLOWING LOSP 2.8482E-003 HPSLC1 OPERATOR FAILS TO INITIATE SLC GIVEN RPV ISOLATED 1.4401E-003 HPSPC2 OPERATORS FAIL TO ALIGN SUPPRESSION POOL COOLING DURING ATWS 1.4147E-003
E1-7 Database Variable Operator Action Description Frequency-Weighted Fractional Importance to Core Damage HOREE2 OPERATOR FAILS TO ALIGN SWING RHRSW PUMPS FOR EECW (SCENARIO REQUIRES 1 PUMP TO BE ALIGNED) 4.3626E-004 HPHPL1 OPERATOR FAILS TO CONTROL HPCI/RCIC LONG TERM (6-24 HOURS) 3.3985E-004 HOSL2 OPERATOR FAILS TO INITIATE STANDBY LIQUID CONTROL - VESSEL IS ISOLATED FROM CONDENSER 3.1950E-004 HOX2 OPERATOR FAILS TO CROSSTIE 4 KV SHUTDOWN BOARD 3.1177E-004 HOX1 OPERATOR FAILS TO ALIGN BATTERY CHARGER 2B TO 250V DC BATTERY BOARD 2.6481E-004 HOAD1 OPERATOR FAILS TO INHIBIT ADS 2.0260E-004 HODSB1 OPERATOR FAILS TO ALIGN DIESEL BOARD FOR DIESEL C 6.4999E-005 HOR480 OPERATOR FAILS TO RECOVER 480 SHUTDOWN BOARD 3.8890E-005 HOLPC1 OPERATOR FAILS TO CONTROL LPCI/CS INJECTION 1.7068E-005 HORTB1 OPERATOR FAILS TO PROVIDE BACKUP TRIP SIGNAL 4.6205E-006 REFERENCE
- 1.
TVA letter to NRC, Browns Ferry Nuclear Plant (BFN) - Unit 1-Proposed Technical Specifications (TS) Change TS - 431 -
Request For License Amendment - Extended Power Uprate (EPU)
Operation, dated June 28, 2004.