05000390/LER-1917-008, Regarding Shield Building Inoperability and Potential Loss of Safety Function Resulting from Spurious Equipment Operation
| ML17226A297 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 08/14/2017 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 17-008-00 | |
| Download: ML17226A297 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3901917008R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 August 14,2017 10 cFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390 Licensee Event Report 39012017-008-00, Shield Building lnoperability and Potential Loss of Safety Function Resulting from Spurious Equipment Operation This submittal provides Licensee Event Report (LER) 39012017-008-00. This LER 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(aX2Xv).
There are no regulatory commitments contained in this letter. Please direct any questions concerning this matter to Kim Hulvey, WBN Licensing Manager, at (423) 365-7720.
Site Vice President Watts Bar Nuclear Plant Enclosure cc: see Page 2 aul Simmons
U.S. Nuclear Regulatory Commission Page 2 August 14,2017 cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident lnspector - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (04-2017)
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'o-tM LIcENSEE EVENr REPoRT (LER)
APPROVED BY OMB: NO.3150-0104 ExprRES: 03/31/2020
, 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 10F5
- 3. PAGE
- 4. TITLE Shield Building Inoperability and Potential Loss of Safety Function Resulting from Spurious Equipment Operation
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI OnV I yenn YEAR I tt-t'rtJ#'-
REV NO MoNTHI ony I yenn FACtLtry NAME ooCxrr wttrr/lern N/A lOsOoo 06 15 I 2017 2017 008 00 08 14 I 2017 FACTLTTYNAME 105000
- 9. OPERATING MODE II.THISREPORTISSUBMITTEDPURSUANTTOTHEREQUIREMENTSOFlOCFRg:
(Checkallthatapply) 1 tr 20 2201 (b) tl 20 2203(a)(3)(i) tr 50 73(aX2Xii)(A) tr 50 73(a)(2)(viii)(A) tl zo 2zo1 (d) tr zo zzo3(aX3xii)
I 50 73(aX2XiiXB) tr 50.73(a)(2Xvii.)(B) tr zo 2zo3(aX1) tr 20 2203(aX4) tr 50 73(a)(2)(iii) tr 50.73(aX2)(ix)(A) tr zo 2zo3(a)(2)(i) tl 50 36(c)(1)(i)(A) tr 50 73(aX2)(ivXA) tr 50 73(a)(2Xx)
- 10. POWER LEVEL 100 t] zo 22o3(aX2Xii) tr 50 36(cX1)(ii)(A) tr 50 73(a)(2XvXA) tr rc 11 (aX4)
I 20 zzo3(aX2Xiii) tr 50 36(c)(2) tr 50 73(a)(2Xv)(B) tl n 11 (a)(5) tr zo zzo3(aX2Xiv) tl 50 46(a)(3xi.)
X 50 73(a)(2XvXC) f fi77(a)(1) tr zo 22o3(a)(2Xv) tr 50 73(a)(2X.XA)
X 50 73(a)(2)(v)(D) tr 8 77(a)(2)(i) tr zo 2zo3(aX2Xvi) tr 50 73(a)(2Xi)(B)
I 50 73(a)(2Xvii) tr Br7(ar(2)(ii) tr 50 73(a)(2XiXC) tr OTHER 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) 423-452-4589
,I3. COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT cAUSE I svsrcnr lconreoNENrI,#+Ufl;- l*=?3?H.:..
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SYSTEM I COMPONENT MANU-I REPORTABLE FACTURER I TO EPIX x I ^, I orr ltt*P.'r*o*l y
- 14. SUPPLEMENTAL REPORT EXPECTED f] vEs (lf yes, comptete 15. Efl1ECTED su}Mtss/oru DATE)
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- 15. EXPECTED SUBMISSION DATE MONTH DAY YEAR ABSTMCT (Linit to 1400 spaces, r.e., approximately 15 single-spaced typewitten lines)
On June 15, 2017, at 1219 Eastern Daylight Time (EDT), Technical Specification (TS) Limiting Condition for Operation (LCO) 3.6.15 Condition B was entered for Watts Bar Nuclear Plant (WBN) Unit 1 annulus preisure not within limits, resulting in Shield Building inoperability. A11221 EDT, the WBN Unit 1 annulus pressure returned to normal, the Shield Building was declared operable, and LCO 3.6.15 Condition B was exited. Because the shield building is a non-redundant safety system, operation outside of TS allowable limits represents an event that could have prevented fulfillment of a safety function.
The temporary loss of the_Shield Building resulted from a loss of pressure control in the Auxiliary Building caused by a loss of Auxiliary Building General Ventilation due to a spurious cross zone fire alarm. The Auxiliary Building Gas Treatment System was started to maintain Auxiliary Building pressure within limits and the non-safety relaGd Annulus Vacuum system automatically restored annulus pressure. The fire detectors that resulted in the loss of the WBN Unit 2 Auxiliary Building ventilation supply fans were replaced.
NRC FORM 366 (04-2017)
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PLANT OPERATING CONDITIONS BEFORE THE EVENT
Watts Bar Nuclear Plant (WBN) Unit 1 was at 100 percent rated thermal power (RTP). WBN Unit 2 was in Mode 5 and was not impacted by the event.
DESCRIPTION OF EVENT
A. Event Summary On June 15,2017, at 1219 Eastern Daylight Time (EDT), Technical Specification (TS) Limiting Condition for Operation (LCO) 3.6.15 Condition B was entered for the WBN Unit 1 annulus pressure not within limits, resulting in Shield Building {EIIS:NH} inoperability. At1221EDT, the WBN Unit 1 annulus pressure returned to normal and LCO 3.6.15 Condition B was exited.
Because the shield building is a non-redundant safety system, operation outside of TS allowable limits represents an event that could have prevented fulfillment of a safety function.
The temporary loss of the Shield Building resulted from a loss of pressure control in the Auxiliary Building caused by a loss of Auxiliary Building General Ventilation due to a spurious cross zone fire alarm. The Auxiliary Building Gas Treatment System (ABGTS) {ElIS:VF} was started to maintain Auxiliary Building pressure within limits and the non-safety related Annulus Vacuum system automatically restored annulus pressure. The detectors that resulted in the loss of the WBN Unit 2 Auxiliary Building ventilation supply fans were replaced.
This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(v)(C) and (D) as an event or condition that could have prevented futfittment 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 No inoperable equipment contributed to this event.
C. Dates and Approximate Times of Occurrences
Date Time Event 6115t17 6115t17 6t15t17 6115t17 1217 1219 1221 EDT 1215 Cross zone fire alarm results in fire pump start and trip of Auxiliaiy Building Genera! Supply fans 2A and 28 Operations starts B train of ABGTS in accordance with system operating instruction 0-SOl-30.06, Auxiliary Building Gas Treatment System.
TS LCO 3.6.15 Condition B entered for annulus pressure not within limits.
TS LCO 3.6.15 Condition B exited when annulus pressure is within limits.
D. Manufacturer and Model Number of Components that Failed During the Event The fire detectors that failed are Model Dl-2 provided by Pyrotronics {EllS:DET}.
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 were received for the start of the high pressure fire pump and the trip of the WBN Unit 2 auxiliary building general supply fans.
G. Failure Mode and Effect of Each Failed Component Not applicable.
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.
CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
A spurious cross zone fire alarm resulted in the start of two electric fire pumps and the stopping of the auxiliary building supply fans 2A and 28.
B. The cause(s) and circumstances for each human performance related root cause.
No human performance uses have been attributed to this event.
ANALYSIS OF THE EVENT
The WBN containment design includes a free standing steel pressure vessel surrounded by a reinforced concrete shield building. The shield building is maintained at a negative pressure of -5 inches water gauge (WG) during normal operation by the annulus vacuum controlsystem, which is not safety-related. ln the event of an accident, the safety-related Emergency Gas Treatment System (EGTS) {ElIS:VC} would filter the exhaust from the shield building, reducing the offsite dose to members of the public and to control room operators from postulated leakage of the containment pressure vessel.
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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 negative pressure. While the 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 contiainment 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 data traces for this event indicate that the annulus pressure went as low as approximately { inches WG, 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 was not lost.
ASSESSMENT OF SAFETY CONSEQUENCES
As described in the previous section, the safety function of the shield building to mitigate a design basis accident was not lost. Therefore the consequences of this event are low.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event Both trains of EGTS remained operable during this event.
B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident Not applicable.
C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service The shield building was outside of its normal allowed negative pressure for approxim ately 2 minutes.
CORRECTIVE ACTIONS
This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under Condition Report (CR) 1307486.
A. lmmediate Corrective Actions Operations personnel took prompt action to start the Train B ABGTS to support proper auxiliary building ventilation operation.
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B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future The detectors that resulted in the spurious alarms were found outside of the required acceptance criteria and were replaced.
VII. PREVIOUS SIMILAR EVENTS AT THE SAME SITE
LER 390/2017-007 reported a number of events in the past three years where shield building vacuum was less than -5 inches WG. 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 actual loss 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.
VIII. ADDITIONAL INFORMATION
None.
IX. COMMITMENTS None.Page 5 of 5