05000260/LER-2017-001

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LER-2017-001, High Pressure Coolant Injection Safety System Functional Failure Due to a Blown Fuse
Browns Ferry Nuclear Plant, Unit 2
Event date: 02-16-2017
Report date: 04-14-2017
Initial Reporting
2602017001R00 - NRC Website
LER 17-001-00 for Browns Ferry, Unit 2, Regarding High Pressure Coolant Injection Safety System Functional Failure Due to a Blown Fuse
ML17104A238
Person / Time
Site: Browns Ferry Tennessee Valley Authority icon.png
Issue date: 04/14/2017
From: Bono S M
Tennessee Valley Authority
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML17104A238 (8)


comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Browns Ferry Nuclear Plant, Unit 2 05000-260 2017

NO

- 00

I. Plant Operating Conditions Before the Event

At the time of discovery, Browns Ferry Nuclear Plant (BFN), Unit 2, was in Mode 1 at approximately 76 percent power.

II. Description of Event

A. Event Summary On February 16, 2017, at 1052 Central Standard Time (CST), while the BFN Unit 2 High Pressure Coolant Injection (HPCI) system [BJ] was in standby readiness, Operations received the HPCI 120VAC POWER FAILURE alarm on Panel 2-9-3F. The crew responded per the Alarm Response Procedure and identified that fuse [FU] 2-FU2-073-0033C in the Auxiliary Instrument Room had cleared. This fuse protected the HPCI system flow controller (2-FIC-77-33), power supplies to the governor controls, and power supplies to various pressure transmitters from overcurrent events.

Since the HPCI system is a single-train safety system, any period of unplanned inoperability constitutes a safety-system functional failure affecting accident mitigation, and is a reportable event.

Operators replaced both the line and neutral fuses, and HPCI system availability was restored on February 16, 2017 at 1145 CST. Following a period of monitoring the current flow through the fuse and HPCI system operation tests, Operations declared the Unit 2 HPCI system Operable on February 17, 2017 at 1730 CST.

B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event There were no structures, systems, or components whose inoperability contributed to this event.

- 001 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Browns Ferry Nuclear Plant, Unit 2 05000-260 2017 - 00

C. Dates and approximate times of occurrences

- 001 Dates & Approximate Times February 16, 2017, at 1052 CST February 16, 2017, at 1145 CST Occurrence Operations received a HPCI 120VAC POWER FAILURE alarm.

HPCI system is declared inoperable due to the loss of 120 VAC power to the HPCI Flow Controller, 2-FIC-73-33.

The Unit Supervisor immediately verified Reactor Core Isolation Cooling (RCIC) system [BN] operability by administrative means, in accordance with the Required Actions for Technical Specification (TS) Limiting Condition for Operation 3.5.1, Condition C.

Operations declared the Unit 2 HPCI system available following fuse replacement for the HPCI system flow controller power supply. The Unit 2 HPCI system still remained inoperable pending further investigation.

February 17, 2017, Operations declared the Unit 2 HPCI system Operable at 1730 CST following fuse replacement and post-maintenance testing.

D. Manufacturer and model number of each component that failed during the event The failed component was a Shawmut Company fuse, model number AJT-3.

E. Other systems or secondary functions affected

No other systems or secondary functions were affected by this event.

F. Method of discovery of each component or system failure or procedural error Failure was discovered on February 16, 2017, at 1052 CST when the 120 VAC power supply circuit for HPCI system flow controller fuse cleared, triggering the HPCI 120VAC POWER FAILURE alarm on Control Room Panel 2-9-3F.

G. The failure mode, mechanism, and effect of each failed component The fuse failed when its internal resistor lead and its tension/retraction spring became uncoupled at their soldered junction. Analysis by the Tennessee Valley Authority (TVA) Central Laboratories Services determined that this was a spontaneous failure which was not due to an overcurrent event.

The presumed failure mechanism is solder creep, which is a time-dependent failure mechanism.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

The exact age and installation date of the failed fuse was unable to be determined. Based on the history of the name brand, the failed fuse was manufactured sometime between 1976 and 1999.

H. Operator actions

There were no operator actions associated with this event.

I. Automatically and manually initiated safety system responses

There were no automatic or manual safety system responses associated with this event.

III. Cause of the event

A. Cause of each component or system failure or personnel error The fuse failed when its internal resistor lead and its tension/retraction spring became uncoupled at their soldered junction, which was presumably weakened by solder creep.

B. Cause(s) and circumstances for each human performance related root cause No human performance related root causes were identified.

IV. Analysis of the event

TVA is submitting this report in accordance with Title 10 of the Code of Federal Regulations 50.73(a)(2)(v)(D), as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The condition was discovered on February 16, 2017, when the spurious failure of the fuse protecting the HPCI system flow controller signaled an alarm [FA] in the Control Room [NA]. This loss of power rendered Unit 2 HPCI system inoperable. Since HPCI system is a single-train safety system, the unplanned inoperability caused by the fuse failure constitutes a reportable event, which is considered a safety system functional failure, and a reportable event.

V. Assessment of Safety Consequences

This event resulted in inoperability and unavailability of the single train of the BFN Unit 2 HPCI system resulting in the inability of the HPCI system to perform its safety function. In the event of an emergency, the RCIC system remained operable, and all other Emergency Core Cooling Systems (ECCS) and Automatic Depressurization System (ADS) were available during this event to facilitate core cooling.

Based on the discussion above, during the time period that the HPCI system was inoperable, sufficient systems were available to provide the required safety functions to protect the health and safety of the public.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resource©nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Browns Ferry Nuclear Plant, Unit 2 05000-260 2017

NO

- 00 A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event The TS Required Actions and Completion Times for HPCI system inoperability is to immediately verify that RCIC system is operable by administrative means, and restore HPCI system operability within 14 days. If these actions do not meet their Completion Times, then TS requires Unit 2 to enter Mode 3 in

12 hours
1.388889e-4 days
0.00333 hours
1.984127e-5 weeks
4.566e-6 months

. Operations personnel immediately verified that RCIC was operable by administrative means on February 16, 2017 at1052 CST. During this event, all other ECCS, including the ADS, were available to mitigate abnormal and accident conditions.

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 event did not occur when the reactor was 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 The HPCI system was determined to be inoperable when a blown fuse resulted in a HPCI 120VAC POWER FAILURE alarm actuation on February 16, 2017 at 1052 CST. The HPCI system was declared operable on February 17, 2017 at 1730 CST following post-maintenance testing.

Approximately

31 hours
3.587963e-4 days
0.00861 hours
5.125661e-5 weeks
1.17955e-5 months

elapsed between the time of discovery and restoring operability.

VI. Corrective Actions

Corrective Actions are being managed by TVA's corrective action program under Condition Report (CR) 1263268.

A. Immediate Corrective Actions

The Operations crew responded in accordance with the Alarm Response Procedure, and identified that fuse 2-FU2-073-0033C in the Auxiliary Instrument Room had cleared. Operators promptly replaced both the line and neutral fuses to restore HPCI functionality. The Unit 2 HPCI system was declared available by Operations within

1 hour
1.157407e-5 days
2.777778e-4 hours
1.653439e-6 weeks
3.805e-7 months

of fuse failure.

B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future Corrective Actions included the prompt replacement of the failed fuses, a determination of the population of HPCI system and RCIC system fuses that should be replaced on a one-time basis, and the replacement of those fuses.

- 001 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Browns Ferry Nuclear Plant, Unit 2 05000-260 2017 - 00 VII. Previous Similar Events at the Same Site In May 2002, the NRC published NUREG-1760, an aging assessment of safety-related fuses. This study found that fusible link degradation accounts for approximately 80% of fuse failure events occurring below the fuse's rated current.

A search of the BFN Corrective Action Program identified 12 fuses which spuriously opened since 2010.

The search did not identify a fuse failure at the location described in this LER.

A review of BFN LERs for the last five years identified one event where a blown fuse resulted in an actual safety system functional failure: LER 50-260/2016-001-01, High Pressure Coolant Injection Safety System Functional Failure due to a Blown Fuse and a Failed Relay. For this event, the fuse failure was due to test equipment, not aging effects. Therefore, the corrective actions for this previous event would not have prevented the current event.

VIII. Additional Information

There is no additional information.

IX. Commitments There are no new commitments.

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