05000391/LER-2016-007, Regarding Manual Reactor Trip Due to Loss of Main Feedwater
| ML16295A213 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 10/21/2016 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 16-007-00 | |
| Download: ML16295A213 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) |
| 3912016007R00 - NRC Website | |
text
Tennessee Valley Authority, Post ffice Box 2000, Spring City, Tennessee 37381 October 21,2016 10 cFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001
Subject:
Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391 Licensee Event Report 39112016-007-00, iianual Reactor Trip Due to Loss of ilain Feedwater This submittal provides Licensee Event Report (LER) 391/2016-007-00. This LER provides details concerning a recent event where the plant was manually tripped when the operating main feedwater pump turbine governor valve failed partially closed, resulting in reduced main feedwater flow. This report is being submitted in accordance with 1 0 cFR 50.73(a)(2)(ivXA).
There are no regulatory commitments contained in this letter. Please direct any questions concerning this matter to Gordon Arent, WBN Licensing Director, at (423) 365-2004.
Respectfully, /
Paul Simmons Site Vice President Watts Bar Nuclear Plant Enclosure cc: see Page 2
U.S. Nuclear Regulatory Commission Page 2 October 21,2016 cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident Inspector - Watts Bar Nuclear Plant
NRC FORM 366 (1 1-2015)
.p"tr'" "ou'.lo rffi U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
APPROVED BY OMB: NO.3150-0104 EXPIRESI 1013112018
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILIW NAME Watts Bar Nuclear Plant, Unit 2
- 2. DOCKET NUMBER 0500039 1
- 3. PAGE OF 5
1
- 4. TITLE Manual Reactor Trip Due to Loss of Main Feedwater
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI DAY I YEAR YEAR I tt-i,'^f$ft REV NO, MONTH I DAY YEAR FACTLTTY NAME I
DOCKET NUMBER N/A lln 08 23 I 2016 2016 -007
- - 00 10 21 2016 FACTLTTY NAME I
DOCKET NUMBER N/A lN/A
- 9. OPERATING MODE 1 I. THIS REPORT lS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR $: (CDeck all that apply) 1 tr 2o.2zo1(b) tr zo.22os(a)(3Xi) tr 50.73(aX2XiiXA) tr s0.73(aX2)(viii)(A) tr 20.2201(d) n 2o.22os(aX3)(ii) tr 50 73(aX2XiiXB) tr 50.73(aX2XviiiXB) tr zo.2zos(aX1) tr 2o.zzos(aX4) tr 50.73(ax2x.ii) tr 50.73(aX2)(ixXA) tr 20.2203(aX2Xi) tl 50.36(cxl xixA)
X 50.73(aX2)(iv)(A) tr s0.73(aX2)(x)
- 10. POWER LEVEL 48 tr 2o.22os(a)(2)(ii) n so.3o(cxl xiixA) tr 50 73(aX2Xv)(A) tr Ts.r1(aX4) tr 2o.2zo3(aX2Xiii) tr 50.36(c)(2) tr 50.73(aX2XvXB) tr rc.r1(aXs) tr 20 z2o3(aX2)(.v) tr 50.46(ax3xii) tr 50.73(aX2XvXc) n ft.rt(a)(1) tr 20 2203(aX2Xv) tr 50.73(aX2X.XA) tr 50.73(aX2)(vXD) tr Bl7(aX2Xi) tr 2o.z2os(a)(2Xv.)
tr 50.73(aX2XiXB) tr 50.73(aX2Xvii) tr B.TT(aX2)(ii) tr 50.73(aX2XiXc) tr OTHER Specify in Abstract below or in G. Failure Mode and Effect of Each Failed Component The use of incompatible hydraulic fittings led to the event.
H. Operator Actions
Operations personnel identified the reduced main feedwater flow and set a manual trip trigger point of 20 percent SG water level. When this limit was approached, operations personnel manually tripped the plant. The subsequent recovery and response to the trip were uncomplicated.
l. Automatically and Manually lnitiated Safety System Responses Operations personnel manually initiated the reactor protection system. Concurrent with the reactor trip, the AFW system automatically actuated as designed.
CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
This event was the result of an incompatible fitting being used in the hydraulic controls for the 2A MFP turbine governor valve.
B. The cause(s) and circumstances for each human performance related root cause.
The cause was determined to be a human performance error during the assembly of the 2A MFP control hose connections. The hose connection was assembled incorrectly during the Nuclear Construction work to bring the 2A MFP turbine from an unused layup condition to a condition that was ready for operation as a part of WBN Unit 2 construction. This connection is not visible because it is inside the MFP turbine's oil return system. Therefore this misconfigured connection could not have been identified by the system turnover processes. The connection also functioned correctly during Preoperational testing and for a short time during Power Ascension testing so that there were no adverse indications as precursors to the event.
ANALYSIS OF THE EVENT
WBN Unit 2was operating at approximately 48 percent power based on power range instrumentation when the 2A MFP governor valve started to close. This was caused by an incorrect hydraulic fitting installation that used a female fitting with a 37-degree flare seating service connected to a standard pipe nipple which is not intended to mate with a 37-degree seating surface. Over time the fifting loosened and the fitting began to leak excessively. Operations personnel identified the degrading main feedwater flow and established a trigger value for a manual trip of 20 percent SG water level. Following the manual trip, operations personnel progressed promptly through their trip response procedures and stabilized the plant.
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V. ASSESSMENT OF SAFEW CONSEQUENCES The loss of the 2A MFP led to a situation where operations personnel manually tripped the plant. The trip response and recovery were uncomplicated, and all safety systems operated as expected. The safety significance of this event was determined to be low.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event No safety systems failed 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 Not applicable.
VI. CORRECTIVE ACTIONS
This event was entered into the Tennessee Valley Authori$ (TVA) Corrective Action Program and is being tracked under condition report (CR) 1206191.
A. lmmediate Corrective Actions The incompatible fittings were replaced with the correct fittings for the application.
B. Corrective Actions to Prevent Recurrence Similar connections of both MFPs were inspected to confirm that no similar conditions existed. This event is being evaluated for inclusion in maintenance training related to pressure retaining connections.
VII. ADDITIONAL INFORMATION
A. Previous similar events at the same plant ln LER 391-2016-005-00, Watts Bar reported a trip of the 28 MFP when the 28 MFP turbine condenser lost vacuum. The loss of the 28 MFP led to an automatic reactor trip on low SG water level. While this earlier event involved a MFP trip, it was caused by operator errorwhen draining the 2A MFP turbine condenser, which is unrelated to this event.
B. Additional lnformation None.
C. Safety System Functional Failure Consideration This condition did not result in a safety system functionalfailure.
D. Scrams with Complications Consideration This reactor trip was determined to be uncomplicated.
VIII. COMMITMENTS
None.Paqe 5 of 5