05000391/LER-2018-002, Loss of Shield Building Vacuum Due to Equipment Failure
| ML18190A205 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 07/09/2018 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2018-002-00 | |
| Download: ML18190A205 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| 3912018002R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 July 9, 2018 10 cFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391 Subject: Licensee Event Report 391/2018-002-00, Loss of Shield Building Vacuum Due to Equipment Failure This submittal provides Licensee Event Report (LER) 391/2018-002-00. This LER provides details concerning a brief loss of shield building vacuum due to a containment shield building annulus vacuum fan failure. This condition is being reported in accordance with 10 CFR 50.73(aX2XvXC) and 10 CFR 50.73(aX2XvXD) as an event or condition that could have prevented fulfillment of a safety function.
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.
Site Vice President Watts Bar Nuclear Plant Enclosure cc: see Page 2 Respectfully, Simmons
U.S. Nuclear Regulatory Commission Page 2 July 9, 2018 cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident Inspector - Watts Bar Nuclear Plant
oas NRG FORM 366 p2-2018)
U.S. NUCLEAR REGULATORY COMMISSION LTCENSEE EVENT REPORT (LER)
APPROVED BY OMB: NO. 3150-0104 EXPIRES:03131DA2A Estimated burden per response to comply witr tris mandatory collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons leanned are incorporabd into the licensing process and hd back b indusfy. Send commenB regarding burden estimab to the lnbrmation Servkps Branch [f-2 F43), U.S. Nuclear Regulatory Commissbn, Washington, DC 205550001,0r by e-ma{l to lnfocollecb. Resource@nrc.gov, and b he Desk Officer, Office of lnfurmation and Regulatory Afrairs, NE0B-10202, (315e0104), Office of Managernant and Budget Washington, DC 20503. lf a means used to impose an information collec{ion does not display a cunenty valid OMB conbol number, fie NRC may not conduat or sponsor, and a person is not reouired to respond b. the information collection.
L Facility Name Watts Bar Nuclear Plant, Unit 2
- 2. Docket Number 05000391
- 3. Page 1 0F5
- 4. Title Loss of Shield Building Vacuum Due to Equipment Failure
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities lnvolved Monthl Day I Year year I t"Ouential I
Number Rev No, Month Day Year Facility Name I
Docket Number N/A IOSOOO 05 I 11 12018 2018 -002 r00 07 I
2018 Facilitv Name IOU&",j*"t Numbei
- 9. Operating Mode 1l. This Report is Submitted Pursuant to the Requirements of 10 CFR $; (Ch*k all that apply) 1 n 20.2201(b) n 2a.z2os(aX3Xi) n 50.73(aX2Xii)(A) t] 50.73(aX2)(viiiXA) tr 2o.zzo1(d) tl za.z2os(a)(3Xii) n 50.73(aX2XiiXB) n 50.73(aX2XviiiXB) n 2o.2zot(a)(1) tl 2o.zzos(aX4) n s0.73(ax2xiii) n b0.73(a)(2)(ix)(A) n 2o.z2a3(a)(2)(i) tl s0.36(cx1Xi)(A) n 50.73(aX2XivXA) tr s0.73(aX2Xx)
- 10. Power Level n 20.2203(aX2Xii) m 50.36(cXlXiiXA) n 50.73(aX2XvXA) n rc.71(aX4) 100 n 2o.zza3(a)(2Xiii) n 50.36(cX2) n 50.73(aX2XvXB) n rc.71(aXs) tr 20.2203(aX2X.v) tr 50.46(ax3xii)
X s0.73(aX2XvXc) tr ts.TT(aX1) t] 2o.z2ol(aX2Xv) n s0.73(aX2XiXA)
E 50.73(aX2XvXD) tl fi.rr(ax2xi) tr 2o.2zo3(a)(2Xvi) tr s0.73(aX2XiXB) n s0.73(a)(2XviD tl 8.77(ax2xiu tr s0.73(aX2XiXc) n OTHER Specify in Abstract betow or in
F. Method of discovery of each component or system failure or procedural error
The failure of the 2A annulus vacuum control fan was identified by a low vacuum alarm received in the control room. The 28 annulus vacuum fan did not auto start resulting operations personnel manually starting the 2B annulus vacuum fan.
G. Failure mode, mechanism, and effect of each failed component The fan belt for the 2A annulus vacuum fan failed.
H. Operator actions
Operations personneltook action to start the 28 annulus vacuum controlfan.
L Automatically and manually initiated safety system responses Operations personnel took action to start the 28 annulus vacuum control fan.
ll1. Cause of the Event
A. Cause of each component or system failure or personnel error
The apparent cause of the shield building transient was the belt for annulus vacuum fan 2A failed.
The hand switch for the 28 annulus vacuum fan had not been reset to permit the fan to auto start on lowering annulus vacuum after previous surveillance testing. The need to place the hand switch in stop after power restoration to enable the automatic start feature was not documented in plant procedures.
lV. 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 greater than -5 inches w.g. as required by TS during normaloperation by the annulus vacuum control system {EllS:VC}, which is not a safety-related system. To address instrument uncertainty, the operations alarm for the shield building is set at -5.5 in. w.g. The annulus vacuum control system consists, in part of redundant paths for pressure control, consisting of redundant fans and redundant isolation and control dampers to maintain the shield building vacuum at a setpoint of -6.2 in. w.g. ln the event of an accident, the safety-related Emergency Gas Treatment System (EGTS) {EllS:BH} 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.
The EGTS is capable of achieving an acceptable negative pressure in the shield building annulus during an accident when starting from atmospheric 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 atmosoheric Dressure at event initiation. After blowdown. the annulus Dressure will increase rapidlv 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 data traces for this event indicate that the annulus pressure went as low as approximately -2.3 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 was not lost.
V. 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 The redundant annulus vacuum controlfan was available.
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 annulus vacuum control system is not a safety-related system.
Vl. Corrective Actions This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under Condition Report (CR) 1413807.
A. lmmediate Corrective Actions Operations personnel placed the redundant annulus vacuum control fan in service and restored shield building vacuum to the required value. The fan belt for the 2A annulus vacuum fan was replaced.
B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future The procedure for operation of the annulus vacuum fans has been revised to ensure that the standby fan will start following maintenance in the event the operating fan fails. A preventative maintenance change request is being processed to increase the frequency for inspection and replacement, as necessary, of the annulus vacuum fans belts.
NRC FORM 3664 (A4-2A171 Page 4 of 5
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Previous Similar Events at the Same Site
LER 390/2018-002-01 reported an event where shield building vacuum was less than -5 inches w.g. due to slow annulus vacuum damper operation. 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.
LER 390/2017-008 reported an event where shield building vacuum was less than -5 inches w.g. due to spurious equipment operation. 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.
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 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.
Additional lnformation None.
Commitments
None.Page 5 of 5