05000259/LER-1917-004, Regarding Safety System Functional Failures Due to the Lnoperability of Both Unit 1 and 2 Control Bay Chillers
| ML17313A848 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 11/09/2017 |
| From: | Bono S Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 17-004-00 | |
| Download: ML17313A848 (12) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 2591917004R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 November 9, 2017 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Units 1, 2, and 3 10 CFR 50.73 Renewed Facility Operating License Nos. DPR-33, DPR-52, and DPR-68 NRC Docket Nos. 50-259, 50-260, and 50-296
Subject:
Licensee Event Report 50-259/2017-004-00 The enclosed Licensee Event Report provides details of the concurrent inoperability of both trains of the Unit 1 and 2 Control Bay Chillers, and the safety systems which they supported. The Tennessee Valley Authority is submitting this report in accordance with 10 CFR 50. 73(a)(2)(v)(A)/(B)/(C)/(D), as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact J. L. Paul, Nuclear Site Licensing Manager, at (256) 729-2636.
Enclosure:
Licensee Event Report 50-259/2017-004 Safety System Functional Failures Due to the lnoperability of Both Unit 1 and 2 Control Bay Chillers cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant
ENCLOSURE Browns Ferry Nuclear Plant Units 1, 2, and 3 Licensee Event Report 50-259/2017-004-00 Safety System Functional Failures Due to the lnoperability of Both Unit 1 and 2 Control Bay Chillers See Enclosed
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017) the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 13. PAGE Browns Ferry Nuclear Plant, Unit 1 05000259 1 OF1 0
- 4. TITLE Safety System Functional Failures Due to the lnoperability of Both Unit 1 and 2 Control Bay Chillers
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR REV MONTH DAY YEAR
- Browns Ferry Nuclear, Unit 2 NUMBER NO.
05000260 09 10 2017 2017
- - 004
- - 00 11 09 2017 FACILITY NAME DOCKET NUMBER Browns Ferrv Nuclear Unit 3 05000296
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §:'Check all that apply)
D 20.2201 (b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) 1 D 20.2201(d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
D 50. 73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A) 1:81 50. 73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2) 1:81 50.73(a)(2)(v)(B)
D 73.71(a)(5) 100 D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii) 1:81 50.73(a)(2)(v)(C)
D 73.77(a)(1 )
D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A) 1:81 50. 73(a)(2)(v)(D)
D 73.77(a)(2)(i) 0 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT
~ELEPHONE NUMBER (Include Area Code)
Ryan Coons, Licensing Engineer 56-729-2070 CAUSE SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TOEPIX B
- 14. SUPPLEMENTAL REPORT EXPECTED
~NO SUBMISSION N/A N/A N/A DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On September 9, 2017, at 1520 Central Daylight Time (CDT), Operations personnel declared Unit 1/2 Control Bay (CB) Chiller (CHLR) A inoperable after observing that its outlet water temperature exceeded its specified limits. On September 10, 2017, at 1151 CDT, the Unit 1 /2 CB CHLR B was declared inoperable after failing to start and providing a flashing error code to an operator in the field. The concurrent inoperability of both Unit 1 /2 CB CHLRs required Browns Ferry Nuclear Plant (BFN) to declare the immediate inoperability of the electrical equipment in the affected electric board rooms, including all four Unit 1 /2 4160 V Shutdown Boards, resulting in a Safety System Functional Failure, and entry into Technical Specifications (TS) Limiting Conditions for Operation (LCO) 3.0.3 for BFN, Units 1, 2, and 3. On September 10, 2017, at 2110 CDT, the Unit 1/2 CB CHLR B was restored to operable status following a capacitor replacement, and LCO 3.0.3 was exited.
The Unit 1/2 CB CHLR A failure was caused by a thermistor failure, likely due to a break in the cable system.
The Unit 1/2 CB CHLR B failure was due to a capacitor failing to hold its charge. Corrective actions include changing the preventive maintenance frequency interval for CB CHLR capacitor replacement from 10 years to 4 years. In addition, the concurrent Unit 1/2 CB CHLR failures were caused by a design which lacked defense-in-depth, where removing one Unit 1/2 CB CHLR from service for unplanned corrective maintenance created a single-point failure risk. A design change has been proposed to install a cross-tie between the Unit 3 Chillers and the Unit 1/2 Chillers to provide cooling in the event that Unit 1/2 CB CHLR A and B were to both become inoperable.
NRC FORM 366 (04-2017)
I.
Plant Operating Conditions Before the Event
At the time of discovery, Browns Ferry Nuclear Plant (BFN), Units 1, 2, and 3, were in Mode 1 at 100 percent power.
II.
Description of Event
A. Event Summary On September 9, 2017, at 1520 Central Daylight Time (CDT), Operations personnel observed that the outlet water temperature on Unit 1/2 Control Bay (CB) Chiller (CHLR) [CHU] A exceeded its specified limits. Unit 1 /2 CB CHLR A was then declared inoperable for troubleshooting on September 9, 2017. The inoperability of Unit 1/2 CB CHLR A required BFN, Units 1 and 2, to enter Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.4, Control Room Air Conditioning (AC) System, Condition A.
On September 10, 2017, at 1151 CDT, Unit 1/2 CB CHLR B failed to start, and an operator in the field noted a flashing error code. Operations personnel noted that the A Compressor on Unit 1 /2 CB CHLR B was not running, and was not warm to the touch. Operations personnel declared Unit 1 /2 CB CHLR B inoperable at this time.
The concurrent inoperability of both Unit 1/2 CB CHLRs required Browns Ferry Nuclear Plant (BFN) to declare the immediate inoperability of the electrical equipment in the affected electric board rooms, including all four Unit 1/2 4160 V (4kV) Shutdown Boards (SD BDs) [ECBD]. This resulted in multiple TS LCO and Technical Requirements Manual (TRM) LCO entries and a Safety System Functional Failure for safety systems on all three Units.
The concurrent inoperability of Unit 1/2 CB CHLRs A and B also required BFN, Units 1 and 2, to enter TRM LCO 3.7.6, Electric Board Room Air Conditioning (AC) System, Condition B. This LCO requires the unit, with two Unit 1/2 electric board room AC subsystems inoperable, to declare the electrical equipment in the electric board rooms inoperable immediately.
In particular, this event resulted in the loss of two trains of Standby Gas Treatment (SGT) [BH],
which required entry into TS LCO 3.0.3 for BFN, Units 1, 2, and 3. As a result of the unplanned entry into TS LCO 3.0.3, all three BFN Units were required to be in Mode 2 by 2151 CDT on September 10, 2017. The NRC Headquarters Office granted BFN an Enforcement Discretion from complying with TS LCO 3.0.3, Condition A, which extended the time to shutdown by 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and 9 minutes, such that all three Units were now required to either exit TS LCO 3.0.3 or be in Mode 2 by 1000 CDT on September 11, 2017.
On September 10, 2017 at 1945 CDT, the Tennessee Valley Authority (TVA) submitted an 8-hour event notification (EN) to the NRC in accordance with 10 CFR 50.72(b)(3)(v)(A)/(B)/(C)/(D), as any event or condition that could have prevented the fulfillment of the safety function of structures or Page 2of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017) *..,,,-*-... \\
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LICENSEE EVENT REPORT (LER)
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- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
Browns Ferry Nuclear Plant, Unit 1 05000-259 2017
- - 004
- - 00 systems that are needed to shut down the reactor and maintain it in a safe shutdown condition, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
On September 10, 2017, at 2110 CDT, Unit 1/2 CB CHLR B was declared operable, and BFN, Units 1, 2, and 3 exited all applicable TS LCOs and the Notice of Enforcement Discretion (NOED).
Unit 1/2 CB CHLR A was declared operable on September 13, 2017 at 1445 CDT following the completion of repairs and post-maintenance testing.
B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event At the start of this event, Unit 1/2 CB CHLR A was inoperable for unplanned corrective maintenance due to a failed thermistor. This resulted in the concurrent inoperability of Unit 1/2 CB CHLR A and B.
C. Dates and approximate times of occurrences
Dates and Times Occurrence September 9, 2017 The Control Bay Auxiliary Unit Operator (AUO) noted Unit 1/2 CB at 1520 CDT CHLR A alarms for "Chiller A Trouble" and "Chilled Water High Temp". An additional AUO also reported a flashing error code.
Operations personnel declared CB CHLR A inoperable, and Units 1 and 2 entered TS LCO 3. 7.4, Condition A. The chiller remained in-service pending troubleshooting.
September 9, 2017 at 1715 CDT September 10, 2017 at 1130 CDT September 10, 2017 at 1151 CDT The CB CHLR system engineer notified Operations personnel that the B circuit for the Unit 1/2 CB CHLR A failed, potentially due to a failed thermistor [TE]. The Unit 1/2CB CHLR A continued running at half load.
Operations personnel alternated the Unit 1/2 CB CHLRs from A to B, in accordance with the applicable operating instruction.
Unit 1/2 CB CHLR B was declared inoperable after an operator
- noticed it gave a flashing error code on its A Compressor, which did not appear to be running and was not warm to the touch. Since Unit 1/2 CB CHLR A was also inoperable, and TS LCO 3.7.4 Condition A was previously entered on Unit 1/2 for this condition, Operations personnel entered all applicable TRM LCO and TS LCOs at this time Page 3of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017)
LICENSEE EVENT REPORT (LER)
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- 3. LER NUMBER Browns Ferry Nuclear Plant, Unit 1 Dates and Times September 10, 2017 at 1746 CDT September 10, 2017 at 1945 CDT September 10, 2017 at 2110 CDT September 13, 2017 at 1445 CDT YEAR 05000-259 2017 Occurrence SEQUENTIAL NUMBER
- - 004 NRC Headquarters Office granted BFN Enforcement Discretion from complying with the TS LCO 3.8. 7 required action to enter TS LCO 3.0.3 Condition A, which would have required all Units to be in Mode 2 by 2151 CDT on September 10, 2017. The Enforcement Discretion extended this time by 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and 9 minutes, such that all three Units were now required to either exit TS 3.0.3 or be in Mode 2 by 1000 CDT on September 11, 2017.
Operations personnel issued an 8-hour EN 52959 to the NRC.
Unit 1 /2 CB CHLR B was declared operable after being placed back in service with one new capacitor [CAP] and one degraded capacitor. Unit 1/2 CB CHLR B started and all parameters were monitored and verified to be correct.
All applicable Units 1, 2, and 3 TS and TRM LCOs were exited, including TS LCO 3.0.3, therefore, exiting the NOED.
Unit 1/2 CB CHLR A was declared operable after the completion of repairs and post-maintenance testing.
D. Manufacturer and model number of each component that failed during the event
REV NO.
- - 00 The thermistor temperature element was manufactured by Trane Air Conditioning, with vendor part number SEN00307.
The failed capacitor was a metalized polypropylene quick-connect 15 microFarad capacitor, manufactured by Renken Industries, Inc. and qualified by Nuclear Logistics, Inc. with manufacturer part number P91 C23156H05.
E. Other systems or secondary functions affected
Loss of the Unit 1/2 CB CHLRs resulted in a loss of the Unit 1 and 2 Control Room AC System.
Additionally, the inoperability of all BFN, Unit 1 and 2, 4kV SD BDs rendered the following systems inoperable: Page 4of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017) /,...,:.\\_
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- 3. LER NUMBER Browns Ferry Nuclear Plant, Unit 1 4kV SD BD A Emergency Diesel Generator (EOG) A [DG]
Residual Heat Removal (RHR)[BO] Pump [P] 1A RHR Pump 2A Core Spray (CS) [BM]
Pump 1A CS Pump 2A RHR Service Water (RHRSW) [CC] Pump A 1 RHRSW Pump A2 Standby Liquid Control (SLC) [BR] Pump 1A SGTA Control Room Emergency Ventilation System (CREVS) A [UF]
05000-259 4kV SD BD B EOG B RHR Pump 1C RHR Pump 2C CS Pump 1C CS Pump 2C RHRSW Pump C1 RHRSW Pump C2 SLC Pump 2A CB CHLR 3A YEAR SEQUENTIAL NUMBER 2017
- - 004 4kV SD BD C EDGC RHR Pump 1B RHR Pump 2B CS Pump 1B CS Pump 2B RHRSW Pump B2 RHRSW Pump B3 (EECW) [Bl]
SLC Pump 1B 4kV SD BD D EOG D RHR Pump 10 RHR Pump 20 CS Pump 10 CS Pump 20 RHRSW Pump 02 RHRSW Pump 03 (EECW)
SLC Pump 2B SGTB
F. Method of discovery of each component or system failure or procedural error
REV NO.
- - 00 An AUO noted Unit 1/2 CB CHLR A alarms for "Chiller A Trouble" and "Chilled Water High Temp",
and an additional AUO also reported a flashing error code.
Unit 1/2 CB CHLR B was declared inoperable after an operator noticed it gave a flashing error code on it's A Compressor, which did not appear to be running and was not warm to the touch.
G. The failure mode, mechanism, and effect of each failed component
For Unit 1/2 CB CHLR B, the capacitor failed to hold its charge.
For Unit 1/2 CB CHLR A, post-event testing indicated no failure mode for the thermistor, which continued to operate as-designed with no deviations from the manufacturer's tolerance specifications. As such, this failure is attributed to a loose or open cable connection between the system and the thermistor. Page 5of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017)
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- 3. LER NUMBER YEAR Browns Ferry Nuclear Plant, Unit 1 05000-259 2017
H. Operator actions
SEQUENTIAL NUMBER
- - 004 REV NO.
- - 00 In response to identified error codes on Unit 1/2 CB CHLR A and B, Operations personnel declared Unit 1/2 CB CHLR A and B inoperable. Additionally, Operations personnel declared CREVS A, SGT A and B, and EOG A, B, C, and D inoperable and entered TS LCO 3.0.3.
I. Automatically and manually initiated safety system responses
There were no automatic or manual safety system responses associated with this condition.
Ill.
Cause of the event
A. Cause of each component or system failure or personnel error The cause of the concurrent Unit 1 /2 CB CHLR failures was a design which lacked defense-in-depth. Specifically, removing one Unit 1/2 CB CHLR from service for unplanned corrective maintenance creates a single-point failure risk in the event that the second Unit 1/2 CB CHLR becomes inoperable.
The most likely cause of the Unit 1/2 CB CHLR A thermistor failure was a loose or open connection in the cable system on the system side of the thermistor. This cable was cut, removed, and replaced during maintenance as part of the corrective maintenance to replace the failed thermistor for the current event. The open connection was likely due to a broken cable, but since the cable was not preserved for testing, this cannot be confirmed or denied. Given the age of this cable, the likely failure mode was infant mortality.
The cause of the Unit 1/2 CB CHLR B failure was that its capacitors in line with the stepdown transformer had lost their ability to hold a high enough voltage during chiller startup to maintain power to its controller. This was first evidenced by improper controller operation and the multiple error codes observed by maintenance personnel during troubleshooting and restart attempts. This was verified by measuring stepped down line voltage, which was found to be below specifications, indicating either a capacitor issue or a transformer problem.
There were no human performance related root causes associated with this event.
IV.
Analysis of the event
This event resulted from a capacitor failure on the Unit 1/2 CB CHLR B train when the redundant.
Unit 1 /2 CB CHLR A train was already inoperable for maintenance. Equipment in electric board rooms rely on chilled water from this system for proper functioning in all conditions, including accident conditions. Therefore, all Unit 1 and 2 4kV SD BDs and associated EDGs were declared inoperable along with the chiller. Page 6of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017) l,o"""' *'*".i.,~
tC LICENSEE EVENT REPORT (LER)
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, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
\\.....i YEAR Browns Ferry Nuclear Plant, Unit 1 05000-259 2017
- 3. LER NUMBER SEQUENTIAL NUMBER
- - 004 REV NO.
- - 00 The safety function of the 4kV SD BDs, as part of the Standby AC Power System, is to provide a self-contained, highly reliable source of power, as required for the Engineered Safeguards System, so that no single credible event can disable the core standby cooling functions or their supporting auxiliaries. lnoperability of the Unit 1 and 2 4kV SD BDs and EDGs caused the loss of several safety systems and the unplanned entry into a shutdown LCO for BFN Units 1 and 2. The loss of two trains of SGT also caused the unplanned entry into a Unit 3 shutdown.
The inoperability of Unit 1/2 CB CHLR A required BFN, Units 1 and 2, to enter TS LCO 3.7.4, Control Room Air Conditioning (AC) System, Condition A, which, when the Units are in Modes 1, 2, or 3, requires the affected Units 1 and 2 control room AC subsystem to be restored to operable status within 30 days.
On September 10, 2017, at 1151 CDT, Unit 1/2 CB CHLR B failed to start, and an operator in the field noted a flashing error code. Operations personnel noted that the A Compressor on Unit 1 /2 CB CHLR B was not running, and was not warm to the touch. Operations personnel declared Unit 1/2 CB CHLR B inoperable at this time.
The concurrent inoperability of Unit 1/2 CB CHLRs A and B required BFN, Units 1 and 2, to enter TS LCO 3.7.4, Control Room Air Conditioning (AC) System, Condition B, which requires an immediate action to restore one Unit 1 and 2 control room AC subsystem to operable status; placing an alternate cooling method in operation within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />; and restoring operability to one control room AC subsystem within 7 days.
The concurrent inoperability of Unit 1/2 CB CHLRs A and B also required BFN, Units 1 and 2, to enter Technical Requirements Manual (TRM) LCO 3.7.6, Electric Board Room Air Conditioning (AC)
System, Condition B. This LCO requires the unit, with two Unit 1/2 electric board room AC subsystems inoperable, to declare the electrical equipment in the electric board rooms inoperable immediately.
For BFN, Units 1 and 2, all four (4kV) SD BDs were declared inoperable.
With 4kV SD BDs A, B, C, and D inoperable, BFN, Units 1 and 2, entered TS LCO 3.8.7, Distribution Systems - Operating, Condition A, which requires that, with one Unit 1 and 2 4kV SD BO inoperable, the Unit 1 and 2 4kV SD BO be restored to operable status within five days, and that the associated EOG be declared inoperable immediately. BFN, Units 1 and 2, declared EOG A, EOG B, EOG C, and EOG D inoperable.
With 4kV SD BDs A, B, C, and D inoperable, BFN, Units 1, 2, and 3 entered TS LCO 3.8.7, Conditions F (Unit 1) and G (Units 2 and 3). These LCOs require, with one or more required other units AC boards inoperable, that the affected SGT or CREVS subsystems be declared inoperable immediately. BFN, Units 1 and 2, declared SGT A, SGT B, and CREVS A inoperable and entered TS LCO 3.8.7, Conditions H (Unit 1) and I (Unit 2). These LCOs require, with two or more electrical power distribution subsystems inoperable that result in a loss of function, that the unit enter TS LCO 3.0.3 immediately. Page 7of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017)
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
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- 3. LER NUMBER YEAR Browns Ferry Nuclear Plant, Unit 1 05000-259 2017 SEQUENTIAL NUMBER
- - 004 REV NO.
- - 00 With SGT A and B inoperable, BFN, Units 1, 2, and 3, entered TS LCO 3.6.4.3, SGT System, Condition D. This LCO requires immediate TS LCO 3.0.3 entry when two or three SGT subsystems are inoperable in Mode 1, 2, or 3.
With EOG A, EOG B, EOG C, and EOG D inoperable, BFN, Units 1 and 2, entered TS LCO 3.8.1, AC Sources - Operating, Condition B, for each inoperable EOG. Failure to meet any of the TS LCO 3.8.1, Condition B completion times requires entry into TS LCO 3.8.1, Condition I, which requires Units 1 and 2 to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
Additionally, with EOG A, EOG B, EOG C, and EOG D inoperable, BFN, Unit 3 entered TS LCO 3.8.1, Condition K, for each inoperable EOG. This LCO requires declaring the required feature(s) supported by the inoperable Unit 1 and 2 EOG inoperable when the redundant required feature(s) are inoperable, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> from the discovery of Condition K concurrent with inoperability of redundant required feature(s); and declaring the affected SGT and CREVs subsystem(s) inoperable within 30 days.
With CREVS A inoperable, BFN, Units 1, 2, and 3, entered TS LCO 3.7.3, Control Room Emergency Ventilation (CREV) System, Condition A. This LCO requires an inoperable CREV subsystem to be restored to operable status within 7 days, when the unit is in Modes 1, 2, or 3, and during operations with a potential for draining the reactor vessel (OPDRVs).
V.
Assessment of Safety Consequences
This event resulted in inoperability of all four Unit 1 and 2 4kV SD BDs and their associated EDGs; however, the equipment remained available during the event. This equipment was declared inoperable because it was unable to perform its safety function under all design basis conditions for supplying reliable power to safety-related equipment in order to shut down the reactor and maintain it in a safe shutdown condition, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
The 4kV SD BDs are located in the Unit 1 and 2 Electric Board Rooms (EBR). System failure could result if the equipment operating temperature in the EBRs exceeded the 104 degrees Fahrenheit (F) operability limit. During this event, non-qualified temporary cooling was available to ensure the temperature in the EBR would not exceed the 104 degrees F operability limit of the associated safety-related components. Therefore, there was no significant risk to the health and safety of the public or plant personnel for this event.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event Non-qualified temporary cooling was available to ensure that the EBR room temperatures would not exceed the 104 degrees F operability limit of the associated safety-related components. Page 8of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017)
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LICENSEE EVENT REPORT (LER)
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- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
Browns Ferry Nuclear Plant, Unit 1 05000-259 2017
- - 004
- - 00 B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident This condition did not occur during a shutdown.
C. For failure that rendered a train of a safety system inoperable, estimate of the elapsed time from discovery of the failure until the train was returned to service This event resulted in inoperability of multiple plant safety systems, from September 10, 2017 at 1151 CDT, when the Unit 1/2 CB CHLR B was declared inoperable after a flashing error code was discovered on the A Compressor, until September 10, 2017 at 2110 CDT when the Unit 1/2 CB CHLR B was declared operable after verification that a capacitor replacement corrected the error.
VI.
Corrective Actions
Corrective Actions are being managed by TV/\\s corrective action program under Condition Reports (CRs) 1336821 and 1340251.
A. Immediate Corrective Actions
Maintenance crews worked in parallel to restore both Unit 1/2 CB CHLR trains to operable status.
Unit 1/2 CB CHLR B was returned to service first, after replacing a 15 microFarad capacitor and reinstalling a degraded 20 microFarad capacitor that tested at 14 microFarads. The chiller was started and all parameters were monitored and verified as satisfactory. Unit 1/2 CB CHLR A was later declared operable after replacement of the thermistor and completion of its associated post-maintenance testing.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future On September 13, 2017 the CB CHLR A capacitors were replaced as a precautionary measure.
The degraded CB CHLR B capacitor was replaced with a new capacitor on September 14, 2017.
The following corrective actions to prevent recurrence are currently are in progress:
- 1. An action was initiated to ensure that outstanding CB CHRL work orders are scheduled.
Another action is in place to ensure the completion of these work orders.
- 2. The preventive maintenance frequency interval for CB CHLR capacitor replacement will be changed from 10 years to 4 years.
- 3. A design change has been planned to prevent future recurrence by installing a cross-tie between the Unit 3 Chillers and the Unit 1/2 Chillers. This cross-tie of chilled water between Unit 3 and Units 1/2 would provide cooling in the event that both Unit 1/2 CB CHLRs A and B were to become inoperable. Page 9of10 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2017)
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUMBER YEAR Browns Ferry Nuclear Plant, Unit 1 05000-259 2017 VII.
Previous Similar Events at the Same Site
SEQUENTIAL NUMBER
- - 004 REV NO.
- - 00 A similar event occurred at BFN on July 14, 2015, when the Unit 1 and 2 CB CHLR A was rendered inoperable when its condenser coils became fouled with dirt and insects while Unit 1/2 CB CHLR B was rendered inoperable for scheduled maintenance. This event was recorded in Licensee Event Report 05000259/2015-003-00.
The corrective actions to prevent the recurrence of the July 2015 event were focused on inspecting the condition of equipment for the effects of dirt, insects, and other natural phenomena, and would not have prevented this event.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments. Page 10of10