05000313/LER-2018-003, Manual Trip Due to Turbine Bypass Valve Failing Open
| ML18222A240 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/10/2018 |
| From: | Pyle S Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 1CAN081805 LER 2018-003-00 | |
| Download: ML18222A240 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 3132018003R00 - NRC Website | |
text
10 CFR 50.73 1CAN081805 August 10, 2018 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Licensee Event Report 50-313/2018-003-00 Arkansas Nuclear One, Unit 1 Docket No. 50-313 License No. DPR-51
Dear Sir or Madam:
Pursuant to the reporting requirements of 10 CFR 50.73, attached is the subject Licensee Event Report concerning the manual trip due to a turbine bypass valve failing open at Arkansas Nuclear One, Unit 1.
There are no new commitments contained in this submittal.
Should you have any questions concerning this issue, please contact me at 479-858-4704.
Sincerely, ORIGINAL SIGNED BY DAVID B. BICE FOR STEPHENIE L. PYLE SLP/dkb Attachment: Licensee Event Report 50-313/2018-003-00 Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4704 Stephenie L. Pyle Manager - Regulatory Assurance Arkansas Nuclear One
1CAN081805 Page 2 of 2 cc:
Mr. Kriss Kennedy Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, GA 30339-5957 LEREvents@inpo.org A. Plant Status At the time this condition was identified, Arkansas Nuclear One, Unit 1 (ANO-1), was performing a reactor startup from a planned refueling outage and operating at approximately 2% power. No structures, systems or components were out of service at the time of this event that contributed to the event.
B. Background - System Design A set of four (4) Turbine Bypass Valves (TBVs) [FCV] with a combined capacity of 15% power (3.75% power each) are used to remove excess heat from the reactor at low power when the Main Turbine Generator is not in operation. Each Once Through Steam Generator (OTSG) has 2 TBVs, and the pair individually control the respective OTSG at the Steam Generator Header pressure designated-setpoint if in automatic, or at the Operator desired setpoint if being controlled in manual.
The Unit 1 Reactor, Feedwater, and Turbine Systems are controlled by an Integrated Control System (ICS) that allows for operation in an automatic or manual mode. ICS monitors several of its inputs via a Smart Automatic Signal Selector System and alerts the Operator if a mismatch in signals is detected, and has the ability to automatically transfer controlling functions to the good input if certain parameters are met.
During normal lower power operation prior to synchronizing the Main Turbine to the grid, the TBVs are operated in automatic and cycle as needed to maintain each OTSG pressure at a setpoint of approximately 895 psig. As power is raised, the TBVs open further until the Main Turbine is synchronized to the grid, at which time the TBVs will close and remain closed throughout power escalation.
C. Event Description
On June 16, 2018, at approximately 1122 CDT during ANO-1 reactor startup from a scheduled refueling outage (1R27), ANO-1 B OTSG to the A Main Condenser TBV CV-6687 failed to in the full open position with the reactor in Mode 2 and approximately 2% power. The TBV failed open due to failure of the valve positioners copper instrument air tubing. This created an additional steam demand which resulted in Reactor Coolant System temperature lowering and, subsequently, lowering pressurizer level.
Pressurizer level continued to lower to less than 100 inches which met the criterion for a manual reactor trip in accordance with Operating Procedure 1202.001, Reactor Trip.
At 1126 CDT, Operations manually tripped the reactor from approximately 4% power. Operations transitioned to Operating Procedure OP-1202.003, Overcooling, due to meeting entry criteria on lowering OTSG pressure and RCS temperature. The overcooling was terminated by Main Steam Line Isolation (MSLI) actuation when the B OTSG pressure reached 600 psig, resulting in closure of both Main Steam Isolation Valves. The plant was placed in a stable condition utilizing Emergency Feedwater and the Atmospheric Dump Valves.
The failed tubing and fittings on CV-6687 were replaced with stainless steel following the failure via Work Order 503935.
This event was reported to the Nuclear Regulatory Commission on June 16, 2018 via Event Notification 53459 based on meeting the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) due to Reactor Protection System (RPS) Actuation (scram) and 10 CFR 50.72(b)(3)(iv)(A) for specified system actuation.
D. Event Cause
The direct cause of this event was vibration induced high cycle fatigue failure in the TBV CV-6687 instrument copper tubing at the compression fitting. This cause is supported by the Failure Analysis.
The root cause of this event was determined to be the instrument air copper tubing had less than adequate robustness for the TBV system high vibration application.
A contributing cause of this event was insufficient controls over the rerouting of instrument air tubing with consideration of vibration induced fatigue failure.
E. Corrective Actions
Actions to address the direct cause included a walk down of the associated piping supports of all TBVs by Engineering and Maintenance personnel. The walk down did not identify a deficiency or degradation of influence related to piping vibration.
Actions to address the root cause include replacement of the tubing and fittings on CV-6687 with stainless steel and flexible hose. This corrective action is also being applied to all four (4) ANO-1 TBVs (CV-6687, CV-6888, CV-6689, and CV-6690) during the next scheduled refueling outage (1R28). These actions are included in the corrective action program.
Actions to address the aforementioned contributing cause include the generation of guidance documents for the installation/rerouting of non-safety related equipment such as instrument air piping, ventilation ducting, and electrical cabling.
The extent of condition review included tubing and fitting inspection for condition and tightness of the three other ANO-1 turbine bypass valves. Air leakage on one TBV was identified and the condition was corrected on June 18, 2018. No issues were identified on the other two turbine bypass valves.
F. Safety Significance Evaluation The actual safety consequences of this event included a manual reactor trip from approximately 4% power. Systems and components operated as designed following the reactor trip and the subsequent MSLI actuation. The impact of the manual trip on risk was evaluated and determined to be below the screening criterion for risk significance.
There were no actual consequences to the general safety of the public, nuclear safety, industrial safety and radiological safety for this event.
G. Basis for Reportability An eight-hour non-emergency notification was reported to the NRC via Event Notification 53459 on June 16, 2018. The basis for that notification was the requirements listed in 10 CFR 50.72(b)(2)(iv)(B)
(RPS actuation) and 10 CFR 50.72(b)(3)(iv)(A) (specified system actuation).
This event is reported pursuant to the following criteria:
10 CFR 50.73(a)(2)(iv)(A) states, in part:
Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section; 10 CFR 50.73(a)(2)(iv)(B) states, in part:
The systems to which the requirements of paragraph (a)(2)(iv)(A) of this section apply are:
(1) Reactor protection system (RPS) including: reactor scram or reactor trip.
H. Additional Information
A review of the ANO corrective action program and Licensee Event Reports for the previous three years was performed. One event was identified (CR-ANO-1-2016-0276). This was an ANO-1 event that occurred on January 21, 2016, which involved the A OTSG Turbine Bypass Valve failing full open when an instrument airline connection to the positioner separated. The ANO-1 Load Demand Hand/Auto Station was promptly placed in Manual and power was lowered to maintain heat balance power less than 100%. The direct cause of CV-6689 failing full open was the copper instrument air line breaking at the fitting due to improper installation.
Energy Industry Identification System (EIIS) codes and component codes are identified in the text of this report as [XX].