05000390/LER-2018-002-01, Shield Building Inoperability Due to Annulus Vacuum Transient
| ML18177A332 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 06/26/2018 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2018-002-01 | |
| Download: ML18177A332 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3902018002R01 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 June 26,2018 10 cFR 50.73 ATTN: Document Control 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 390/2018-002-01, Shield Building tnoperability Due to Annulus Vacuum Transient This submittal provides Licensee Event Report (LER) 390/2018-002-01. This LER supplement provides details concerning a condition where spurious equipment operation resulted in the shield building pressure limits exceeding Technical Specification allowed values. This condition is being reported as an event that could have prevented fulfillment of a safety function in accordance with 10 CFR 50.73(a)(2)(v).
There are no new regulatory commitments contained in this letter. Please direct any questions concerning this matter to Kim Hulvey, WBN Licensing Manager, at (423) 365-7720.
Respectfully, Site Vice President Watts Bar Nuclear Plant Enclosure cc: see Page 2
U.S. Nuclear Regulatory Commission Page 2 June 26,2018 cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident lnspector - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (02-2418)
. clf,
""t' LICENSEE EVENT REPORT (LER}
APPROVED BY OMB: NO.3150-0104 explnffi Estimated burden per response to comply with this mandatory collection request: B0 hours.
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the lnformation Services Branch (T-2 F43), U,S, Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to lnfocollects, Rglource@nrc.gov, and to the Desk 0fficer, Office of lnformation and Regulatory Affairs, NE0B-10202, (3150-0104), ffice of Management and Budget, Washington, DC 20503 lf a means used to impose an information collection does not display a currently vatiO QfUg control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection,
- 1. Facility Name Watts Bar Nuclear Plant, Unit 1
- 2. Docket Number 05000390
- 3. Page 10F6
- 4. Title Shield Building Inoperability Due to Annulus Vacuum Transient
- 5. Event Date
- 6. LER Number I
t. Report Date
- 8. Other Facilities lnvolved Month Day I Year year I S"Ouential I
t*lumber Rev No.
Monthl Day I year nifi'n'Name 01 17 l 2018 2019 -002
- - 01 06 26 I 2018 Facility Name
- 9. Operating Mode 1 1. This Report is Submitted Pursuant to the Requirements of 10 GFR g: (Check alt that apply) 1 tr zo.zzot(b) tr zo zzo3(aXsXi) tr 50 73(aX2)(i.XA) n so 73(aX2)(viii)(A) tr zo zzol (d) tr 20 zzoi(aX3Xii) n 50 73(aX2XiiXB) fl 50 73(aX2XviiiXB) tr zo 2zo3(aX1) tr za z2o3(aX4) n 50 73(ax2)(.ii)
I 50 73(a)(2)(ix)(A) tr 20 zzo3(aX2Xi) tr so 36(c)(r XIXA)
I 50 73(a)(2XivXA) tr 50 73(aX2Xx)
- 10. Power Level 100 tr zo 22o3(a)(2Xii)
I so 36(cxl XiixA)
I 50.73(aX2XvXA) tr 13 11 (aX4) tr zo.z2o3(a)(2Xiii) tr 50 36(c)(2) tr 50 73(aX2)(vXB)
I rc 71 (aXs) t] 20 2za3(aX2Xiv) f 50 46(ax3xii)
X 50.73(aX2)(vXC) n rczr(a)(1)
I zo.22o3(aX2Xv) 50 73(aX2X.)(A)
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f, 50 73(aX2)(iXB) n 50 73(ax2xvi.)
I B Tl(ax2)(ii) tr 50 73(ax2xi)(c) tr orHER specify in Abstract betow or in NRC Form 3664
- 12. Licensee Contact for this LER Licensee Contact Dean Baker, Licensing Engineer Telephone Number (lnclude Area Code) 423-452-4589cause I svstem I component lrvranutacturerl *:I?J;!'"
Cause
System I Component Manuracturer I
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x I vc I nly lanlLEYl v X
VC I PMC BAILEY I Y
- 14. Supplemental Report Expected I ves (lf yes, complete 15. Expected submission Date) X No
- 15. Expected Submission Date MonthlD"yfVear Abstract(Limitto14oospaceS,i.e.,approximately14single-spacedtypewrittenlines)
At 2002 Eastern Standard Time (EST) on January 17, 2018, Watts Bar Nuclear Plant Unit 1 annulus differential pressure went outside its pressure limit. At that time, the Shield Building was declared inoperable requiring entry into Technical Specification 3.6.15 Limiting Condition for Operation (LCO), Conditions A and B. Action was taken by field operators to swap annulus vacuum control dampers due to slow system response to restore annulus differential pressure. nt ZbZ+ ESf, annulus differential pressure was restored to required limits, the shield Building was declared operable, and TS 3.6.15 LCo, Conditions A and B were exited. This is being reported as an event or condition that could have prevented fulfillment of a safety function.
lnvestigation revealed that an Emergency Gas Treatment System (EGTS) operational test on January 12,201g, resulted in an abnormal damper configuration which contributed to this event. Following the event, tuning was plrfoimeO on the actuator for control damper 1-Pco-65-49, however an equipment cause could not be confirm6d. nrier a pressure transient on April 3, 2018 additional corrective actions were completed for 1-PCO-65-49 which included replacem"nt of tn",JrIi-'
pneumatic relay and controller. The procedure for performance of the EGTS operational test will be revised to incluAe-'-' ]
restoration steps. Lessons learned from this event will be addressed in licensed operator training.
I NRC FORM 366 (02-2018)
I.
PLANT OPERATING CONDITIONS BEFORE THE EVENT
Watts BarNuclear P,l]l! WBN) Unit 1 was at 100 percent rated thermal power (RTp). WBN Unit 2 was also at 100 percent RTP and was unaffected by this event.
II.
DESCRIPTION OF EVENT
A. Event Summary Ait2002 Eastern Standard Time (EST) on January 17,2018,WBN Unit 1 annulus differential pressure went outside its pressure limit. At that time, the Shield Building {EllS:NH} was declared ino_perable requiring entry_ into Technical Specification (TS) 3.6.15, Limlting Condi[ion for Operation (LCO) Conditions A and B. Action was taken by field operators to swap annulus vacuum control system {ElIS:VC} dampers {ElIS:CDMP} due to slow system response to restore annulus differential pressure. At2024 EST, annulus differential pressure was restored to required limits, the Shield Building was declared operable, and TS LCO 3.6.15, Conditions A and Ei were exited.
This event igbeing reported to the Nuclear Regulatory Commission (NRC) under 10 C-FR 50'73(aX2Xv)(C) and (D) as an event or condition that could. have prevented fulfiilment of a safety function needed to control the release of radioactive material and mitigate the consequences of an accident.
B. lnoperable Structures, Components, or Systems that Contributed to the Event Debris found in a subcomponent of the damper positioner likely contributed to this event.
C. Dates and Approximate Times of Occurences Date Time Event 1t12t18 1t12t18 1t12t18 1t17 t18 1t17 t18 1t17t18 EST 1405 1 406 1 500 2002 2017 2024 Commenced 0-5l-65-6-A, Operational Test Emergency Gas Treatment System Train A Received alarms for annulus differential pressure low (less than -5.s inches (in.) water gauge (w.9.)). The pressure transient resulted in one of two differential pressure setpoints required to auto swap from the normal annulus control dampers to the backup. This resulted in both dampers 1-PCO-65-93 and 1-PCO-65-94 left in the open position and both control dampers in service (not a normal configuration) 0-5l-65-6-A completed, Train A Emergency Gas Treatment System (EGTS) restored to operable status TS LCO 3.6.15 entry due to Annulus Ditferential Pressure (DP) less than the TS required of -S.5 in. w.g.
Operations placed backup annulus control damper in service (time is approximate)
Exited TS LCO 3.6.15 Condition A and B due to Annulus DP being restored to greater than -5.5 in. w.g.
on April 3, 2018, annulus vacuum was found lowering, and operations personneltransfened vacuum controlto the backup controldamper. subsequent troubleshooting of t-pcoos+g required the replacement of the positioner pneumatic-relay and the actuator controller.
D. Manufacturer and Model Number of Components that Failed During the Event No equipment failures were found following the January 17,201g event. Following a pressure transient on April 3, 2018, two components were replaied.
'The pneumatic relay $lrs,nwj*itnin the positioner was found to contain foreign material. The pneumatic relay is manuractrr"o 'uy Bailey, Part number AP21100. The Bailey actuator controiler {EllS:pMciwas atsoiepi4"J,'p"rt n umber 54921 SJ AKL 1 pAF.
E. Other Systems or Secondary Functions Affected
No other systems or secondary functions were affected.
F' Method of discovery of each Component or System Failure or procedural Error Plant alarms indicated that shield building vacuum was less than required.
G. Failure Mode and Effect of Each Failed Component No equipment failure was found following the January 1l,2O1g event.
H. Operator Actions
Upon receipt of the alarms, operations personnel responded in accordance with operating procedures.
L Automatically and Manually lnitiated safety system Responses Not applicable. While operators swapped the annulus vacuum controldampers, this is not a safety related system.
I1I. CAUSE OF THE EVENT A. The cause of each component or system failure or personnel error, if known.
No equipment failures were found following the January 17, 2O1a event, so an equipment cause cannot be confirmed. Following an annulus vacuum trinsient on April d,2o1g,tne lctuator '
positioner pneumatic relay and the actuator controller were found fiieO.'
B' The cause(s) and circumstiances for each human performance related root cause.
No human performance root causes are attributable to this event.
IV. ANALYSIS OF THE EVENT
The WBN containment de,sign includes a free standing steel pressure vessel surrounded by a reinforced concrete shield building. The shield building is maintained at a negative pressure of greater than -5 inches w.g. as required by TS during normal operation by the annulus vaCuum controt systeir, which is not safety-related' To address instrument uncertainty, the operations alarm for the shield blilding is set at -5.5 in.
w'9. The annulus vacuum control system consists, in part of redundant paths for presiure control, each of which include_an isolation damper (1-PCO65-93 and 1-PCO5-94) ancia controidamper (1-pCO-654g and 1-PCo-6549) to maintain the shield building vacuum at a setpointot -6.2 in. w.g. liee limptiReO 91e1cQ: ln the event of an accidenl, the safety-related Emergency Gas Treatment Sisiem leCiSy
{EllS:BH} would filter the exhaust from the shield building, reoucing the offsite dose io members of the public and to control room operators from postulated leakage of the containment pressure vessel.
The design of the EGTS is that it is capable of achieving an acceptable negative pressure in the shield building annulus assuming the annulus is not at a negaiive pressure. Wnit-e tne annulus is normally expected to be at a negative pressure relative to atmospheric, the dose analysis conservatively assumes the annulus is..at atmospheric pressure at event initiation. After blowdown, the annulus pressure will increase rapidly due to expansion of the containment vessel as a result of primary containment atmosphere temperature and pressure increases. The annulus pressure will continue to rise due to heating of the annulus atmosphere by conduction through the containment vessel. After a delay, the EGTS operates to maintain the annulus pressure below atmospheric pressure. Review of daia traces for this event indica.te that the annulus pressure went as low as approximately -4.6 inches w.g which bounds the analysis limit of atmospheric pressure.
Accordingly, while the shield building was outside its normal pressure limits, the safety function of the shield building to limit dose to the public and to control room operations personnel wai not lost.
On January 12,2018, a surveillance test was performed on Train A EGTS. During this test, a pressure transient occurred that was allowed by the test which resulted in opening the isolaiion Oamferi of both annulus vacuum control paths, which is an abnormal configuration. miJ atso resulted in both associated modulating dampers controlling annulus vacuum in a near fully closed position. An alarm was received during the pressure transient, but was not treated as valid Oy fhe operating staff and the related alarm response procedure was not entered.
On January 17,2018, a plant assistant unit operator recognized that both annulus vacuum control dampers were in service and closed isolation damper 1-PCO5-94 to restore the annulus vacuum system to the normal operating alignment. The control room was not notified of this configuration change.
Because both trains of modulating dampers were fully closed at this time to maintiin setpoint C6.z in.
w.g.), annulus pressure initially went more negative than normal and the modulating damper 1-pCO6S-4g overcorrected, resulting in a reduction in annulus vacuum below that required by TS 3.6.i5. When the assistant operator isolated the backup control damper, the plant response was not as expected, and the unit supervisor directed_swapping to the backup control dampers to restore pressure. The slow response of damper 1-PCO5-49 contributed to this event.
On April 3, 2018, annulus vacuum was found lowering, and operations personneltransferred vacuum controlto the backup controldamper. Subsequent troubteshooting of 1-PCO65-49 required the replacement of the positioner pneumatic-relay and the actuator cohtroller.
vilt IX because the safety function of the EGTS to reduce radiological dose is performed even if the shield building is not at a vacuum.
LER 390/2017-007 reported a number of events in the past three years where shield building vacuum was less than -5 inches w.g. These events were the result of either unexpected plant response during Unit 2 power ascension testing or were the result of equipment failures. As described above, no actualloss of safety function capability occurred because the safety function of the EGTS to reduce radiological dose is performed even if the shield building is not at a vacuum.
ADDITIONAL I NFORMATION None.
COMMITMENTS
None.
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