05000250/LER-1917-001, Regarding Loss of 3A 4kV Vital Bus Results in Reactor Trip, Safety System Actuations, and Loss of Safety Injection Function
| ML17136A372 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 05/16/2017 |
| From: | Summers T Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2017-094 LER 17-001-00 | |
| Download: ML17136A372 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2501917001R00 - NRC Website | |
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U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555-0001 Re:
Turkey Point Unit 3 Docket No. 50-250 Reportable Event: 2017-001-00 Date of Event: March 18, 2017 L-2017-094 10 CFR § 50.73 May 16, 2017 Reactor Trip, Auxilia1y Feed Water and Emergency Diesel Generator 3A Actuations, Loss of Safety Injection Function, and Completion of Technical Specification Required Shutdown The attached Licensee Event Report 05000250/2017-001-00 is submitted pursuant to 10 CFR 50.73(a)(2)(i)(A), 10 CFR 50.73(a)(2)(iv)(A), and 10 CFR 50.73(a)(2)(v)(D),
If there are any questions, please call Mr. Mitch Guth, Licensing Manager, at 305-246-6698.
Sincerely, z lL Thomas Summers Regional Vice President - Southern Region Florida Power & Light Company Attachment cc:
Regional Administrator, USNRC, Region II Senior Resident Inspector, USNRC, Turkey Point Nuclear Plant Florida Power & Light Company 9760 SW 344'" St., Homestead, FL 33035
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (02-2014)
LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of digits/characters for each block)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMER
- 3. PAGE Turkey Point Unit 3 05000250 YEAR SEQUENTIAL NUMBER REV NO.
3 of 4
2017 001 00 prevention of FM intrusion when systems are opened. The Thermo-Lag installation did not require opening switchgear cubicles.
- 2. The design process does not prompt review of Safety Data Sheets for material being considered in a design to determine if there are any hazards being introduced during installation and use of the material.
ANALYSIS OF THE EVENT
Thermo-Lag 770-1 material was being installed over existing Thermo-Lag 330-1 to increase power cable protection fire ratings to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> in the 3A 4kV switchgear room. The process placed 770 material (hard panels) around the existing material. Sealant 770 is used on the seams to strengthen the enclosure. A black loosely-woven fabric (carbon fiber mesh) is placed onto the seam and covered with the 770 sealant.
The 3A 4kV switchgear room was classified as a foreign material exclusion (FME) area and was being maintained clean as you go by the insulators during the work activity. To control cleanliness in the room, the carbon fiber mesh was being cut outside the room. The material occasionally needed trimming, which was done inside the switchgear room on a scaffold covered in griffolyn to prevent materials from dropping below. To maintain the FME area, a supervisor inspected the area at completion of work to verify the area was clean and free of debris.
A CLR is a protective device used to limit fault current by introducing reactance between sections of a line or between line and ground. The CLR is centered in its cubicle. The bus bars in the CLR cubicle are uninsulated. The 3A 4kV switchgear bus grounded to the inside of the CLR cubicle when the air gap was bridged by the carbon fiber mesh material to the C phase bus bar. This resulted in an electrical arc flash which potentially damaged the adjacent CLR. The carbon fiber mesh material entered the CLR cubicle through gaps in the enclosure.
The internal bus fault caused the Unit 3 auxiliary transformer feeder breaker [EA, BKR] to open and a 3A 4 kV switchgear lockout. The Unit 3 reactor tripped on an undervoltage condition to vital power. The pressure from the arc flash damaged a fire door to the adjacent redundant 3B 4kV vital switchgear room.
All three RCPs tripped at the beginning of the event. In addition to the 3A RCP that is powered from the 3A 4kV bus, the 3B and 3C RCPs which are powered from the 3B 4kV bus tripped on underfrequency. The 3B RCP was started approximately 57 minutes after the event began to restore forced circulation.
ANALYSIS OF SAFETY SIGNIFICANCE When an arc flash occurs in a switchgear train, all equipment fed from it would be de-energized as a result of protection actuations creating a plant transient. The reactor shutdown and the opposite vital electrical train was relied on to maintain Unit 3 in a safe and stable shutdown condition.
The Turkey Point units have alternate methods to provide power to the equipment necessary to maintain shutdown. For this reason, the potential to reach a condition in which one or more barriers fail, increasing the likelihood of radioactive release is very low. U.S. NUCLEAR REGULATORY COMMISSION (02-2014)
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMER
- 3. PAGE Turkey Point Unit 3 05000250 YEAR SEQUENTIAL NUMBER REV NO.
4 of 4
2017 001 00 All safety systems actuated as required in response to the bus failure and operators maintained adequate decay heat removal for a controlled cool down to Mode 5 (cold shutdown).
The fire door that separates the 3A and 3B 4kV vital switchgear rooms was compromised during the event by a damaged latching mechanism. However, given the low combustible load in the CLR cubicle and proper operation of the auxiliary transformer feeder breaker, there was no fire scenario that required proper functioning of the fire door.
In conclusion, based on the unique susceptibility of the CLR cubicle to FM induced arcing, the low internal combustible loading of the cubicle, proper actuation of the fault protection devices, and operator recovery actions, the safety significance of the 3A 4kV bus failure is considered to be low and there was no effect on the health and safety of the public.
The Safety Injection function for both units was lost for approximately 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. There was low safety significance associated with the HHSI unavailability as the success criterion is one HHSI pump for small and medium loss of coolant accidents (LOCA). In addition, the control switches for the Unit 4 HHSI pumps had been placed in the pull-to-lock position and the pumps could have been started manually to mitigate a large break LOCA if needed.
CORRECTIVE ACTIONS
Corrective actions are in accordance with Condition Report 2192198 and include:
- 1. The CLR was removed from its cubicle, sent to a vendor for examination and testing, and then reinstalled and returned to service.
- 2. The Thermo-Lag installation procedure will be revised to incorporate additional precautions for handling Thermo-Lag materials.
- 3. A case study will be provided to targeted personnel concerning this event emphasizing that FME also applies to nearby equipment that is not opened and that can be affected by the work activity.
- 4. Procedures governing FM and material control will be revised to enhance personnel awareness of the potential to introduce FM into nearby equipment that is not opened and that can be affected by the work activity.
- 5. The Engineering product risk and consequence assessment process will be revised to ensure the Responsible Engineer includes a review of Safety Data Sheets for material being considered in the design.
ADDITIONAL INFORMATION
EIIS Codes are shown in the format [IEEE system identifier, component function identifier, second component function identifier (if appropriate)].
FAILED COMPONENTS IDENTIFIED: None
PREVIOUS SIMILAR EVENTS
None