05000382/LER-2023-002, Plant Shutdown Required by Technical Specifications for Unidentified Reactor Coolant System Leakage in Containment
| ML23129A791 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 05/09/2023 |
| From: | Milster L Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| W3F1-2023-0031 LER 2023-002-00 | |
| Download: ML23129A791 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 3822023002R00 - NRC Website | |
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~ entergy W3F 1-2023-0031 May 9, 2023 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Lela Milster Manager Regulatory Assurance 504-739-6250 10 CFR 50.73
Subject:
Licensee Event Report 50-382/2023-002-00, Plant Shutdown Required by Technical Specifications for Unidentified Reactor Coolant System Leakage in Containment Waterford Steam Electric Station, Unit 3 NRC Docket No. 50-382 Renewed Facility Operating License No. NPF-38 Entergy Operations, Inc. (Entergy) submits the enclosed Licensee Event Report (LER) 50-382/2023-002-00 for Waterford Steam Electric Station, Unit 3 (Waterford 3). The event reported herein is reportable in accordance with 10 CFR 50. 73(a)(2)(i)(A) - The completion of any nuclear plant shutdown required by the plant's Technical Specifications.
The LER describes the Unidentified Reactor Coolant System Leakage in Containment and subsequent Plant Shutdown.
This letter contains no new commitments.
Should you have any questions concerning this issue, please contact Leia Milster, Manager, Regulatory Assurance, at 504-739-6250.
Respectfully, Leia Milster LEM/mrp Entergy Operations, Inc., 17265 River Road, Killona, LA 70057
W3F 1-2023-0031 Page 2 of 2 Enclosure: Licensee Event Report 50-382/2023-002-00 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Waterford Steam Electric Station, Unit 3 NRC Project Manager - Waterford Steam Electric Station, Unit 3 Louisiana Department of Environmental Quality
Enclosure W3F1-2023-0031 Licensee Event Report 50-382/2023-002-00
Abstract
On March 9, 2023, while operating in Mode 1 at 100% power, Waterford Steam Electric Station, Unit 3 (WF3) operators identified elevated activity and unidentified leakage in containment from the reactor coolant system (RCS). On March 10, 2023, at 0030 CST Operations entered Technical Specification 3.4.5.2 action (c) due to Unidentified Leakage exceeding 1 gpm. Technical Specification (TS) 3.4.5.2 action (c) requires reducing the leakage rate to within limits within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or be in at least HOT ST AND BY within the next 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 />.
Operators located the leak source near the Reactor Coolant Pump (RCP) 1 B but were unable to access the leak source while the plant was at po~er. On March 10, 2023, at 0257, WF3 operators commenced a manual reactor shutdown in accordance with TS. The required safety systems and shutdown equipment performed as expected, resulting in an uncomplicated shutdown. The condition was reported on March 10, 2023 (Event Number 56403).
The source of the through wall leak was near a weld on RCP 1 B instrument tubing likely caused by high cycle fatigue in conjunction with vibrational stress from missing tube supports that were previously corrected in 2016. The cracked tubing was replaced, and operability was restored. WF3 returned to Mode 1 and commenced power ascension on March 14, 2023. This event is reportable under 10 CFR 50.73(a)(2)
(i)(A) "The completion of any nuclear plant shutdown required by the plant's Technical Specifications."
PLANT STATUS On March 9, 2023, Waterford Steam Electric Station, Unit 3 (WF3) was operating at 100% power in Mode 1. There were no other structures, systems, or components that were inoperable at the time that contributed to the event.
EVENT DESCRIPTION
On March 9, 2023, at 2200 CST, WF3 entered OP-901-111, "Reactor Coolant System Leakage," and OP-901-403, "High Activity In Containment," due to elevated Reactor Coolant System (RCS) leakage in Containment. On March 10, 2023, at 0030, unidentified leakage exceeded 1 gpm and WF3 entered Technical Specification (TS) 3.4.5.2 action (c) due to Unidentified Leakage exceeding 1 gpm. Technical Specification 3.4.5.2 action (c) requires reducing the leakage rate to within limits within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or be in at least HOT STANDBY within the next 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 />.
Operators entered containment to locate the leak source. The leak was identified inside the D-ring, near reactor coolant pump (RCP) 1B [P]. The leak was inaccessible while the plant remained at power. On March 10, 2023, at 0257, WF3 operators commenced a manual reactor shutdown in accordance with TS. The required safety systems and shutdown equipment performed as expected, resulting in an uncomplicated reactor shutdown.
Once the plant was offline, the RCS leak was confirmed to be due to a through wall leak near a weld on the 0.5 inch instrument tubing line [TBG] of RCP 1 B. The cause is attributed to high cycle fatigue due to vibrational stress in conjunction with missing tube supports [SPT] previously corrected in 2016. The cracked tubing was replaced, and operability was restored. The removed tubing was sent to a vendor for additional failure analysis. WF3 returned to Mode 1 and commenced power ascension on March 14, 2023.
This event is reportable under 10 CFR 50.73(a)(2)(i)(A) "The completion of any nuclear plant shutdown required by the plant's Technical Specifications."
TIMELINE
- March 9, 2023, 22:00: Entered OP-901-111, Reactor Coolant System Leak, and OP-901-403, High Activity in Containment, due to elevated RCS Unidentified Leakage in containment
- March 10, 2023, 00:30: RCS Unidentified Leakage has exceeded 1 gpm. T.S. 3.4.5.2 was entered
- March 10, 2023, 02:30: Personnel entered Containment to search for the source of RCS Unidentified Leakage.
Containment team reported water falling from inside of the RCP 1 B D ring cell. Leak source was not accessible while at power
- March 10, 2023, 02:57: Plant down power commenced
- March 10, 2023, 05:21: Operations manually tripped the reactor [RCT] in accordance with OP-10-005 "Plant Shutdown". The main turbine [TRB] tripped and the station entered Mode 3
- March 10, 2023, 14:06: Closed RCP 1B instrument line valve to isolate RCS leak. Field Operators confirmed that the RCS leak stopped
- March 12, 2023, 23:19: During the extent of condition investigation, engineering determined there was a bent and damaged section of tubing downstream of RCP Valve 115B (RC MVAAA 115 B). The condition was evaluated and determined to be acceptable for the remainder of the cycle
- March 13, 2023, 04:15: Post Maintenance Testing was completed satisfactory
- March 14, 2023, 13:29: WF3 entered Mode 1 and began power ascension EXTENT OF CONDITION
- 2. DOCKET NUMBER
- 3. LER NUMBER I
00382 NUMBER NO.
I YEAR SEQUENTIAL REV
- - 1 002 1-G Engineering completed a walkdown of RCP 1A, 2A, and 2B to determine if any additional RCS leaks, excessive vibration, missing supports, or deformed tubing were present. During this extent of condition investigation, engineering identified a bent and damaged section of tubing downstream of reactor vessel loop 1 B high pressure root valve [RTV]
(RC MV AAA 115 B) and a potential similar stressed condition on a tubing weld for RCP 2A. The conditions were evaluated in accordance with EN-FAP-OM-030 "Operational Decision Making" process, entered in the corrective action program, and evaluated the conditions as acceptable for the remainder of this cycle
SAFETY ASSESSMENT
The actual consequence to this condition resulted in a forced shutdown, which was a low risk evolution. This event leakage was greater than 1 gpm and was significantly less than the capacity of two charging pumps at approximately 82 gpm. The leakage associated with this RCS instrument tubing line was lower than the threshold to be considered a small break loss of coolant accident due to the capacity of the charging pumps. There were no consequences regarding the safety of the public, nuclear safety, industrial safety or radiological safety for this event.
EVENT CAUSES The cause of the event on March 10, 2023 is attributed to high cycle fatigue due to vibrational stress in conjunction with missing tube supports that were previously corrected in 2016. WF3 has sent the removed tubing section to a vendor for additional failure analysis. A previous WF3 event in 2016 documents elevated RCS leakage from RCP 1 B in a different section, downstream of this event. The 2016 event was caused by fretting from two missing supports on the same 0.05 inch high pressure instrument tubing line. It is unknown how long the supports were missing prior to 2016. This allowed for the tubing to vibrate for an unknown amount of time and is likely a contributor to the failure in 2023.
CORRECTIVE ACTIONS
The cracked tubing line was replaced, and operability was restored on March 13, 2023 at 0415 CST.
PREVIOUS SIMILAR EVENTS
On October 10, 2016 at 2200, RCS leak rate unidentified leakage increased from 0.04 gpm to 0.44 gpm. Additional containment sump inflow increased was observed. A containment walk down identified water at the bottom of the RCP 1 B cell. On October 24, 2016, the leakage investigation team identified a probable leak location was from the RCP 1 B pump differential pressure instrumentation line. Two tubing supports directly downstream from the leak location were identified missing. On October 25, 2016, after isolating the 0.5 inch tubing leak, the location of the leak was found to be in contact with a structural steel support member. Prior removal of the tubing supports allowed the instrument line to come in contact with a support beam, causing a longitudinal crack in the instrument tubing. The tubing appeared to have been fretting on the structural steel support member for an unknown duration. Page 3
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