05000259/LER-2009-002
| Browns Ferry Nuclear Plant (Bfn), Unit 1 | |
| Event date: | 03-21-2009 |
|---|---|
| Report date: | 09-27-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2592009002R01 - NRC Website | |
I. PLANT CONDITION(S)
Prior to the event, Units 1, 2, and 3 were operating in Mode 1 at 100 percent thermal power (approximately 3458 megawatts thermal). Unit 1 continued to operate at full power throughout the event and Units 2 and 3 were unaffected by the event.
II. DESCRIPTION OF EVENT
A. Event:
On March 20, 2009, at 2055 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.819275e-4 months <br /> Central Daylight Time (CDT), BFN Operations prepared to perform scheduled surveillance 1-SR-3.3.5.1.6(BI), Functional Testing of Residual Heat Removal (RHR) Loop l Pump And Minimum Flow Valve Logic. Operations declared RHR [BO] pumps 1A and 1C inoperable, entering Technical Specification (TS) LCO 3.5.1 Condition A and Required Action A.1: With one low pressure Emergency Core Cooling System (ECCS) injection/spray subsystem inoperable, within 7 days, restore the low pressure ECCS injection/spray subsystem to Operable status. On March 21, 2009, at approximately 0406 hours0.0047 days <br />0.113 hours <br />6.712963e-4 weeks <br />1.54483e-4 months <br /> CDT, while placing a jumper in accordance with the surveillance, Unit 1 received RHR Pump Initiate Lockout signal for Loop II RHR Pumps 1B and 10. With the lockout signal in place, the automatic start function of RHR Pumps 1B and 1D is inhibited. Operations immediately recognized the placement of the jumper per the instruction as an incorrect action.
At approximately 0406 hours0.0047 days <br />0.113 hours <br />6.712963e-4 weeks <br />1.54483e-4 months <br /> CDT, Unit 1 entered TS 3.5.1 Required Action H.1, with two or more low pressure ECCS injection/spray subsystems inoperable for reasons other than Condition A, and immediately entered TS LCO 3.0.3. After approximately one minute, Operations restored the automatic start function of RHR Pumps 1B and 1D, and exited TS LCO 3.5.1 Condition H and TS LCO 3.0.3.
I Unknown at the time of this event, RHR Loop 11 was inoperable due to the RHR Loop II Low Pressure Injection (LPCI) flow control valve 1-FCV-074-0066 being inoperable (LER 50-259/2010-003-02) and the Loop I RHR 1C pump was also inoperable (LER 50-259/2010-004-01) due to a rotor/shaft bow in the RHR pump 1C motor. The period of concurrent inoperability existed from approximately November, 2008 until November, 2010.
The Tennessee Valley Authority (TVA) is submitting this report in accordance with 10 CFR 50.73(a)(2)(v)(D), as any event or condition that could have prevented the fulfillment of the safety function needed to mitigate the consequences of an accident and 1 10CFR50.73(a)(2)(i)(B), any operation or condition which is prohibited by the plants Technical Specifications.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Major Occurrences:
March 21, 2009, at 1050 hours0.0122 days <br />0.292 hours <br />0.00174 weeks <br />3.99525e-4 months <br /> CDT TVA made an eight hour report to the NRC in accordance with 10 CFR 50.72(b)(3)(v)(D) as any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures of systems that are needed to mitigate the consequences of an accident.
D. Other Systems or Secondary Functions Affected
None.
E. Method of Discovery
Operations received main control room indication that the automatic start function of RHR Pumps 1B and 1D was inhibited.
F. Operator Actions
Operations personnel suspended performance of surveillance 1-SR-3.3.5.1.6(BI). They entered the appropriate TS LCO Actions and took immediate actions to restore the automatic start function of RHR Pumps 1B and 1D.
G. Safety System Responses
None.
III. CAUSE OF THE EVENT
A. Immediate Cause
The immediate cause for the event was an inadequate procedure step.
B. Root Cause
The functional test, 1-SR-3.3.5.1.6(BI) contained an error previously identified and not corrected. A pre-performance walkdown of the surveillance recognized that the jumper was being installed in panel 1-9-33 and removed from panel 1-9-32. However, when the revision was made to rectify the panel location, the wrong surveillance step was revised. Instead of revising the surveillance to install the jumper in the correct panel, 1-9-32, the revision removed the jumper from the wrong panel, 1-9-33. Consequently, the action to place and remove a jumper took place in the incorrect panel.
C. Contributing Factors
restart in September of 2006. The March 20, 2009, performance of this surveillance was the second performance since restart of Unit 1. The initial performance on September 10, 2006, during Unit 1 restart activities did not note any discrepancies in the effected section.
IV. ANALYSIS OF THE EVENT
At the time the event occurred on March 21, 2009, Operations installed a jumper that simulated an accident signal from the Unit 1 RHR Channel A logic system. As soon as the jumper installation was completed, the amber lights illuminated, indicating the 1B and 1D RHR pumps auto start function was inhibited. Operations immediately realized the 1B and 1D auto start function was inhibited and they took actions to restore the auto-start function. The auto-start function remained inhibited for approximately one minute.
I Unknown at the time of this event, RHR Loop II was inoperable due to the RHR Loop II Low Pressure Injection (LPCI) flow control valve 1-FCV-074-0066 being inoperable (LER 50-259/2010-003-02) and the Loop I RHR 1C pump was also inoperable (LER 50-259/2010-004-01) due to a rotor/shaft bow in the RHR pump 1C motor. The period of concurrent inoperability existed from approximately November, 2008 until November, 2010.
Unit 1 TS 3.5.1, ECCS — Operating, requires, in part, that each ECCS injection/spray subsystem and the Automatic Depressurization System (ADS) function of six safety/relief valves be OPERABLE in MODES 1, 2, and 3. With two or more low pressure ECCS injection/spray subsystems inoperable, TS 3.5.1 Condition H requires entry into TS LCO 3.0.3 until such time as the required Loop I LPCI is restored.
Because the concurrent condition of RHR Loop II LPCI and Loop I RHR pump 1C were unknown at the time, Unit 1 was not placed into LCO 3.0.3 as required by TS 3.5.1 Required Action H.1.
As a result of the above described inoperabilities, the TVA is also submitting this report in accordance with 10 CFR 50.73(a)(2)(i)(B) as any operation or condition which was prohibited by the plant's Technical Specifications.
V. ASSESSMENT OF SAFETY CONSEQUENCES
The RHR System is a multipurpose system designed to remove stored and decayed heat from the reactor and containment during both normal, shutdown and accident conditions. Its primary purpose is to serve as a Low Pressure Coolant Injection (LPCI) system which will restore and maintain, if necessary, the water level in the reactor vessel after a Loss of Coolant Accident once the reactor is depressurized. By maintaining the core flooded, sufficient cooling of the fuel is provided to preclude fuel clad melting and subsequent energy release due to a metal-water reaction.
A Probabilistic Risk Assessment (PRA) was performed for the past concurrent inoperability of the RHR Loops I and II for the time period that the RHR pumps 1A and 1C (Loop I LPCI) were inoperable for the performance of surveillance 1-SR-3.3.5.1.6(BI) considering the following:
Loop I RHR Pumps 1A and 1C inoperable from March 20, 2009, at 2055 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.819275e-4 months <br /> to March 22,2009, at 1414 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.38027e-4 months <br /> (Available) Loop II RHR Pumps 1B and 1D inoperable for approximately 1 minute on March 21, 2009, at 0406 hours0.0047 days <br />0.113 hours <br />6.712963e-4 weeks <br />1.54483e-4 months <br /> (Unavailable) LPCI Loop II (Flow Control Valve 1-FCV-074-0066) inoperable from March 20, 2009, at 2055 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.819275e-4 months <br /> to March 22, 2009, at 1414 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.38027e-4 months <br /> (Unavailable) Risk significant systems (or portions of risk significant systems) unavailable for extended periods of time reduces the margin of safety in the plant. A PRA was performed which calculated the Incremental Core Damage Probability Deficit (ICDPD) and Incremental Large Early Release Probability Deficit (ILERPD). The ICDPD was determined to be 3.13E-7 and the ILERPD was determined to be 1.93E-8.
Based on the PRA, this event posed minimal reduction to public health and safety.
VI. CORRECTIVE ACTIONS - The corrective actions are being managed by TVA's corrective action program.
A. Immediate Corrective Actions
Unit 1 operations suspended the performance of surveillance 1-SR-3.3.5.1.6(BI).
Operations revised the affected step in 1-SR-3.3.5.1.6(BI), and then successfully completed the surveillance.
B. Corrective Actions to Prevent Recurrence
Procedures which had not been satisfactorily performed (24 Month ECCS logic surveillances) were placed on administrative hold until a technical review was completed. I Operations Procedures Group procedure writers were re-indoctrinated on adequate independent qualified review techniques.
VII. ADDITIONAL INFORMATION
A. Failed Components
None.
B. Previous LERs on Similar Events None.
C. Additional Information
Corrective action document PER 166487.
D. Safety System Functional Failure Consideration:
This event is a safety system functional failure in accordance with NEI 99-02 because it meets the reporting criteria of 10 CFR 50.73(a)(2)(v)(B) and 50.73(a)(2)(v)(D). I E. Loss of Normal Heat Removal Consideration:
This event was not a complicated scram according to NEI 99-02.
VIII. COMMITMENTS
None.