05000443/LER-2021-002, Condition Prohibited by Technical Specifications Entered Due to Service Water Cooling Tower Fan Inoperable
| ML21320A354 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 11/16/2021 |
| From: | Levander M NextEra Energy Seabrook |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SBK-L-21119 LER 2021-002-00 | |
| Download: ML21320A354 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4432021002R00 - NRC Website | |
text
U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Seabrook Station Docket No. 50-443 Seabrook Station NEXTeraM EN~~~~
November 16, 2021 10 CFR 50.73 SBK-L-21119 Licensee Event Report (LER) 2021-002-00 Condition Prohibited by Technical Specifications Entered due to Service Water Cooling Tower Fan Inoperable Enclosed is Licensee Event Report (LER) 2021-002-00. This LER reports an event that occurred at Seabrook Station on September 17, 2021. This event is being reported pursuant to the requirements of 10 CFR 50.73(a)(2)(i)(B).
Should you require further information regarding this matter, please contact me at (603) 773-7631.
Sincerely, NextEra Energy Seabrook, LLC Matthew Levander Licensing Manager cc:
D. Lew, NRC Region I Administrator J. Poole, NRC Project Manager C. Newport, NRC Senior Resident Inspector NextEra Energy Seabrook, LLC P.O. Box 300, Seabrook, NH 03874
Enclosure to SBK-L-21119
NRG FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)
- 3. Page Seabrook Station 443 1 OF 3
05000
- 4. Title Condition Prohibited by Technical Specifications Entered due to Service Water Cooling Tower Fan Inoperable
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Month Day Year Year Sequential Revision Month Day Year Facility Name Docket Number Number No.
05000 09 17 2021 2021 -
002 -
00 11 16 2021 Facility Name Docket Number 05000
- 9. Operating Mode 110. Power Level 1
100
)
Abstract
On September 17, 2021 at 04:56, with Seabrook Station at 100% power, the Unit 1 Service Water Cooling Tower Fan "B" was declared inoperable due to failure of the associated gear box. The Technical Specifications (TS) Allowed Outage Time (AOT) was 7 days for this condition. On September 23, 2021 at 1930 EST, prior to the expiration of the 7-day AOT, the NRC verbally approved NextEra's request for enforcement discretion to allow 5 additional days to process an Emergency License Amendment Request (LAR). The Emergency LAR would have then allowed continued operation to complete final preparations and necessary repairs that would have taken place during a planned refueling outage, which began in early October, 2021. Seabrook Station operation continued at 100% power for the duration that the Service Water Cooling Tower Fan "B" was inoperable. Operability was restored on September 26, 2021 at 04:47 following the completion of a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post maintenance Operability run. The cause of the event was due to a failed fan reduction gearbox due to inadequate lubrication. An April 28, 2021 gearbox oil analyses was the first indication that an elevated particulate count existed. However, the condition that caused the failure was traced back to maintenance performed in January 2021. Immediate corrective actions were to replace the gear box and drive shaft, perform necessary gear alignments, and perform post maintenance testing that demonstrated Operability.
Event Description
In January 2021, after receiving two consecutive cooling tower fan Service Water Cooling Tower Fan "B" gearbox oil samples analysis reports indicating low viscosity and elevated particulate count, an oil change on the fan gearbox oil was performed. As part of post maintenance testing from the oil change, the fan was started and was quickly secured due to visible oil coming out of the fan air path. Visual examination of the unit identified that the pressure switch on the side of the gearbox had a cracked housing and was leaking oil. As a result, the pressure switch was replaced. When the fan was restarted, oil leakage from the fan air path was again identified. Troubleshooting efforts included removing the oil system internal spray nozzle and relief valve. The internal spray nozzle was found plugged and was subsequently cleared and the relief valve successfully bench tested. As part of these maintenance activities, the oil system was cleaned and flushed several times. Post maintenance testing revealed no abnormal indications, and the fan was declared Operable on January 10, 2021. An April 28, 2021 gearbox oil analyses was the first indication since the fan maintenance performed in January 2021 that the elevated particulate count had not been resolved, and could potentially cause a similar lube oil blockage condition.
On September 17, 2021 at 04: 17 Operations started the "B" train Service Water Cooling Tower fans in preparations for gearbox lube oil sampling. The control room received Service Water Cooling Tower Fan 'B' Oil Pressure Low Alarm at approximately 04:55. In response to the alarm, Operations secured the 'B' cooling tower fan and an operator was sent to locally walk down the fan. The Operator identified the fan's drive shaft was broken and oil was leaking out of its gearbox [BS,RGR]. The 'B' Train SW Cooling Tower Loop was declared inoperable and the station entered Technical Specification (TS) 3.7.4, Action B. TS 3.7.4, Action B, states that with one cooling tower service water loop or one cooling tower cell inoperable, return the affected loop or cell to OPERABLE status within 7 days, or be in at least HOT STANDBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. After the failed gear box (Western Gear Corporation, Model 2593) and drive shaft were replaced, Operability was restored on September 26, 2021 at 04:47 following the completion of a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> post maintenance run.
Since the gearbox failure mechanism existed prior to the September 17, 2021 failure, dating back to a gearbox oil analyses that showed a high particulate count with large steel bearing wear, it is concluded that this condition existed for a duration longer than the Technical Specifications action allowed outage time. This event is being reported in accordance with 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications." There were no out of service SSCs that were inoperable and contributed to the initiation or limited the mitigation of the event.
Safety Consequences
The Atlantic Ocean serves as the normal Ultimate Heat Sink for Seabrook Station. However, in the unlikely event that the normal supply of cooling water from the Atlantic Ocean is unavailable, the atmosphere serves as the ultimate heat sink using the mechanical draft evaporative cooling tower. The normal ultimate heat sink of the Atlantic Ocean was fully capable of performing its design function. The remaining "A" train Service Water Cooling Tower Fan continued to be able to provide it's safety function. There were no actual safety consequences for this event, and no safety system responses occurred.
Cause of Event
The cause of the fan failure was determined to be excessive debris in the Service Water Cooling Tower Fan "B" gearbox oil reservoir. This was due to the increased heat density output of the heating elements in the oil reservoir, carbon steel drain lines subject to debris formation, and this debris was released from a static resting place in the drain line through the process of performing the oil refill from the drain line using a pump during January, 2021 maintenance. An oil spray nozzle meant to disperse oil onto the high speed pinion bearing was impaired by this debris. The blockage in the oil nozzle caused the bearing to operate non-lubricated and eventually fail; subsequently leading to a drive shaft failure as well.
Corrective Actions
Immediate corrective actions after the September 17, 2021 failure were to replace the gear box and drive shaft, perform necessary gear alignments, remove gearbox oil heaters from service, and perform sufficient post maintenance testing.
The planned Corrective Actions are to (1) replace installed heaters with heaters of the correct wattage density. (2)
Replace the carbon steel drain lines with stainless steel on the remaining fan units. (3) Revise the Machinery Oil Sampling procedure to direct the refill of oil reservoirs, pumps, or other oil containment systems through the installed fill location and direct the practice of not using drain lines or sample lines for refilling without specific work instruction that considers the introduction of debris into the system.
Previous Similar Events
Service Water Cooling Tower fan shaft failures have previously occurred in the past, but these failures were attributed to vibration issues with the original two piece shaft with intermediate pillow block bearings. The design was changed to a one piece composite shaft, which resolved those specific issues. No Licensee Event Reports were submitted due to these failures.
Additional Information
The Energy Industry Identification System (EllS) codes are included in this LER in the following format: [EllS system identifier, EllS component identifier]. Page 3
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