05000390/LER-2014-001, Regarding Loss of Air to Train a Motor Driven Auxiliary Feedwater Pump Level Control Valves
| ML14080A075 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 03/21/2014 |
| From: | Church C Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 14-001-00 | |
| Download: ML14080A075 (9) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3902014001R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 March 21, 2014 10 cFR 50.73 ATTN: Document Contro! Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390
Subject:
Licensee Event Report 390/2014-001, Loss of Air to Train A Motor Driven Auxiliary Feedwater Pump Leve! ControlValves This submittal provides Licensee Event Report (LER) 39012014-001. This LER provides details concerning Motor Driven Auxiliary Feedwater Pump Level ControlValves failing open due to loss of air. This report is being submitted in accordance with 10 CFR 50.73(aX2)(iXB).
There are no regulatory commitments in this letter. Please direct any questions concerning this matter to Gordon Arent, WBN Licensing Director, at (423) 365-2004.
Respectfully,anh Christopher R. Church Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Page 2
U.S. Nuclear Regulatory Commission Page 2 March 21,2014 Enclosure cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident lnspector - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION lo2-2014) od*o'o iH#i
-"fT"tr LICENSEE EVENT REPoRT (LER)
_ +lt (See Page 2 for required number of digits/characters for each block)
APPROVED BY OMB: NO. 3150-0{04 EXPIRES: 0113112017 Estimated burden per response to comply with this mandatory collectbn request 80 houns.
Reported lessons leamed are incorporated into he licensing process and fed back to indusfy.
Send oomments regarding burden estimate to the FOIA, Privacy and Infurmation Collections Branch O-5 F53), U,S. Nudear Regulatory Commission, Washingbn, DC 205550001, or by intemete-mail to lnfooollects.Resouroe@nrc.gov, and to he Desk Offloer, ffice of lnfurmation and RegulatoryAfiairs, NE0B-10202, (315S0104), Ofibe of Management and Budget, Washingbn, DC 20503. !f a npans used to impose an information collection does not dbplay a arenty valid OMB contnol number, the NRC may not mnduct or sponsor, and a person is not required to respond to, the information collection.
. FACILITY NAME Watts Bar Nuclear Plant, Unit 1
- 2. DOCKET NUMBER 05000390
- 3. PAGE 1
OF 7
r. NTLE Loss of Air to Train A Motor Driven Auxiliary Feedwater Pump Level Control Valves
- 5. EVENT DATE
- 6. LER NUIIIBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI DAY I YEAR YEAR lt=^lr'fiHf'lnEo' MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 05000 01 24 I 2014 2014 - 001 - 00 03 20 2014 FACILITY NAME DOCKET NUMBER 05000
- 9. OPERANNG iiODE I l. THIS REPORT lS SUBIIITTED PURSUAI{T TO THE REQUIREilEilTS OF 10 CFR $: (Cher,k ail l/nat app$
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X 50.73(aX2Xi)(B) tr 50.73(aX2XvXD)
Specfi in Abstract belor or in
C. Dates and Approximate Times of Occurrences
Date Time (EDT)
Event October 20,2012 Unit 1 Refueling Outage Hold Orders 1-3-0730C and 1-3-0730D were issued to repair leaks associated with the installation of nitrogen backup supplies to Train A Motor Driven AFW Pump LCVs in accordance with DCN 58387.
October 22,20'12 N/A Hold Orders were released with the ACAS supply valves to the Train A Motor Driven AFW Pump LCVs (0-lSV-32-371and 0-ISV-32-373) in the CLOSED position, inadvertently isolating the ACAS supply to the AFW valves.
October 24,2012 0419 WBN Unit 1 entered Mode 3 and the three trains of AFW are required to be operable according to Technical Specification Limiting Condition for Operation (LCO) 3.7.5.
January 24,2014 1525 Operations personnel vented the nitrogen header that supplies backup nitrogen to AFW air operated valves forAppendix R backup motive force for the valves. Valve 1-LCV-3-156-A and valve 1-LCV-3-1&t-A failed open due to loss of control air.
TechnicalSpecification LCO 3.7.5 was entered.
January 24,2014 1612 Valves 0-lSV-32-371 and 0-lSV-32-373were opened, restoring control air to 1 -LCV-3-1 56-A and 1 -LCV-3-1 64-4. Technical Specification LCO 3.7.5 was exited.
D. Manufacturer and Model Number (or other identification) of each component that failed during the event None E. Other Systems or Secondary FunctionsAffected None
F. Method of Discovery of Each Component or System Failure or Procedural Error
Main Control Room personnel discovered 1-LCV-3-156-A and 1-LCV-3-1An-A failed open due to loss of control air. Valves failed open following removal of the backup nitrogen control system.
G. The Failure Mode, Mechanism, and Effect of Each Failed Component
\\Alith the safety related ACAS supply isolated to the Train A Motor Driven AFW Pump LCVs, '1-LCV-3-156-A and 1-LCV-3-164-A cannot be considered operable due to the fact that the Main LCVs fail in the open state and thus are incapable of modulating AFW flow to control steam generator level.
H. OperatorAc{ions Upon discovery Operators promptly opened valves 0-lSV-32-371 and 0-lSV-32-373, restoring controlairto 1-LCV-3-156-A, 1-LCV-3-16l+-A, 1-LCV-3-156A-A and 1-LCV-3-164A-A. The operators verified that ACAS was properly aligned to the other AFW Train LCVs.
l. Automatically and Manually Initiated Safety System Responses
There were no safety system responses and none were required.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known:
The direct cause of this event was that valves 0-lSV-32-371 and 0-lSV-32-373 were closed as part of work order activities and Operations personnel failed to restore the valves to their normal open position.
B, The cause(s) and circumstances for each human performance related cause:
The apparent cause of this event was Supervision has not effectively monitored personnel to ensure they properly value their signature.
Contributing cause was that contrary to management expectations, the drawing was not used during Pre Job Briefing.
IV. ANALYSIS OF THE EVENT
Each Motor Driven Auxiliary Feedwater pump is capable of supplying two steam generators and there are two Motor Driven AFW pumps. The Turbine Driven (TD) AFW pump is capable of supplying four SGs. One train of AFW (flow to two steam generators) is capable of removing decay heat and coolthe unit until residual heat removal (RHR) entry conditions. The flow from the Motor Driven AFW Pump is automatically controlled by a four inch LCV and a paralleltwo inch LCV. The LCVs are controlled to maintain the required level in their respective SG. The LCVs have split range control such that the two inch LCV is fully open before the four inch LCV begins to throttle open. The two inch LCV is used for low flow demand and the four inch LCV is utilized when flow demand increases beyond the capabilities of the two inch LCV. During cool down, as the pressure in the SG is reduced the LCVs willthrottle dorvn to maintain the required flow. A pressure switch (PS) dornstream of the LCVs closes the four inch LCV prior to low pressure conditions that could result in significant valve cavitation occurring. The main four inch LCVs fail open on loss of air while the two inch bypass LCVs fail closed on loss of air. DCN 58387 installed a backup, non-safety source of nitrogen to each AFW air operated valve (AOV) to help mitigate the effects of an Appendix R fire.
Absent the Appendix R Nitrogen supply, a loss of ACAS supply to the Motor Driven AFW Pump LCVs results in bypass valves 1-LCV-3-156A-A and 1-LCV-3-164A-A failing in the closed state, while main valves 1-LCV 156-A and 1-LCV-3-164-A fail in the open state. \\A/ith the safety related ACAS supply isolated to the Train A Motor Driven AFW Pump LCVs, 1-LCV-3-156-A, 1-LCV-3-164-A, 1-LCV-3-156A-A and 1-LCV-3-1A[A-A cannot be considered operable due to the fact that the main LCVs fail in the open state and thus be incapable modulating AFW flow to control SG level. Absent the Appendix R Nitrogen supply, the valves would be incapable of fulfilling their required safety function.
Surveillances were conducted during the period of time thatACAS was isolated. The Motor Driven AFW Pump LCVs performed within the ln Service Testing (lST) required stroke times in both the open and closed directions. While the nitrogen supply is not safety-related, TVA completed a seismic evaluation that demonstrates components of the nitrogen supply system located outside the Auxiliary Building (AB) are sufficiently seismically rugged to withstand a Safe Shutdown Earthquake (SSE). Calculations performed demonstrate that the minimum required nitrogen pressure to meet the pressure and flow requirements for the Motor Driven AFW Pump LCVs is 74 psig. A review of the nitrogen tank pressure taken during operator rounds each shift shows that 96 percent of the time the nitrogen available was at or above the required 74 psig when the valves were considered inoperable.
Additionally, in the case of SG overfill event the operator has the ability to secure the Train A Motor Driven Auxiliary Feedwater Pump to prevent overfill. ln this instance, the Train B Motor Driven Auxiliary Feedwater Pump and the Turbine Driven Auxiliary Feedwater Pump can be used to mitigate an accident, to remove decay heat and cool the unit to the point that RHR can be placed in service.
Furthermore, in the event of Main Steam Line Break, Main Feedwater Line Break, SG tube rupture, or a faulted SG, the Train A Motor Driven AFW Pump can be secured, or manual action can be taken to close the manual isolation valves upstream and downstream of the LCVs. This will allow forAFW isolation to the impacted SGs.
Specifically, procedure for Faulted Steam Generator lsolation, directs the operator to isolate AFW flow to the faulted SG. Additionally, the procedure for Steam Generator Tube Rupture, directs the operator to isolate AFW flow to the ruptured SG.
The Probabilistic Risk Assessment evaluation of risk documented demonstrates the isolation of essential air (for the period in question) from the ACAS to Train A Motor Driven AFW Pump LCVs 1-LCV-3-156-A and 1-LCV 164-A, as well as 1-LCV-3-156A-A, SG 2 Motor Driven AFW Pump Bypass Level ControlValve, and 1-LCV 1O4A-A, SG 1 Motor Driven AFW Pump Bypass LevelControlValve is not risk significant. Risk as determined by the internal events model remains very small, even if unavailability of control air throughout an entire year is assumed. Extemal events can be shown by qualitative reasoning to be minor risk contributors. Fire risk need not be considered for loss of control air. Therefore the risk associated with unavailability of control air to Train A Motor Driven AFW Pump LCVs is evaluated to be very small.
ASSESSMENT OF SAFETY CONSEQUENCES
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event:
Each Motor Driven AFW pump is capable of supplying two steam generators and there are two Motor Driven AFW pumps. The Turbine Driven AFW pump is capable of supplying four SGs. One train of AFW (flow to two steam generators) is capable of removing decay heat and coolthe unit until RHR entry conditions. Operator logs were reviewed during the time that Train A Motor Driven AFW Pump LCVs were considered inoperable. During this time period eitherthe Train B Motor Driven AFW Pump orthe Turbine Driven AFW Pump was operable or both of these trains were operable except for one day at O7O2 on January 10,2014. Because of an inoperable Diesel Generator (DG) and TS 3.8.1 Condition 8.2 required action (Declare required feature(s) supported by the inoperable DG inoperable when its required redundant feature(s) is inoperable), the three trains of AFW were declared inoperable when the A-A Auxiliary Air Compressor was declared inoperable. Technical Specification LCO 3.7.5 Condition D was entered at 0703 on January 10, 2014 and Technical Specification LCO 3.7.5 was exited at1022 on January 10,20'14 afterthe A-A Auxiliary Air Compressor was successfully operated for fifteen minutes and declared operable.
D. Scram with Complications Consideration This event did not include a scram.
VIII. COMMITMENTS
There are no commitments.