05000391/LER-2017-006, Regarding Manual Reactor Trip in Response to Indication of Multiple Dropped Control Rods
| ML18040A620 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 02/09/2018 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2017-006-00 | |
| Download: ML18040A620 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3912017006R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 February 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 39112011-006-00, Manual Reactor Trip in Response to lndication of Multiple Dropped Gontrol Rods This submittal provides Licensee Event Report (LER) 39112017-006-00. This LER provides details concerning a manual reactor trip after control room staff observed multiple dropped control rods. This condition is being reported as a system actuation in accordance with 10 cFR 50.73(a)(2)(ivXA).
There are no regulatory commitments contained in this letter. Please direct any questions concerning this matter to Kim Hulvey, wBN Licensing Manag er, at (423) 36s-l7zo.
Respectfully, aul Simmons Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Page 2
U.S. Nuclear Regulatory Commission Page 2 February 9, 2018 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),
Jl$utq**"
W LICENSEE EVENT REPORT (LER)
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- 1. FACILITY NAME Watts Bar Nuclear Plant, Unit 2
- 2. DOCKET NUMBER 05000391
- 3. PAGE 1
OF 5
4, TITLE Manual Reactor Trip in Response to lndication of Multiple Dropped Control Rods
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI ONY I YEAR YEAR I tt-T-flf$'
REV NO.
MONTH I DAY YEAR fffirLrrY NAME I
DocKEr NUMBHR 12 I 11 12017 2017 -006
- - 00 a2 09 2018 JffiIL]rY NAME I
DOCKET NUMBER
- 9. OPERATING MODE I 1. THIS REPORT lS SUBMITTED PURSUAilT TO THE REQUIREIIIENTS OF 10 CFR g: (Check ail that appty) 1 tl 20 2201(b) il 2o.2zas(aX3Xi) tr 50.73(aX2)(iiXA) n 50.73(aX2)(viiiXA) il 20.2201(d) il za.22o3(aX3Xii) n 50.73(a)(2XiiXB) n 50.73(aX2XviiiXB) il 20.22a3(aX1) il za.22as(aX+)
n s0.73(ax2xiii) n 50.73(aX2XixxA)
X zo.zzo3(aX2Xi) il s0.36(c)(1XiXA)
X 50.73(aX2Xiv)(A) n s0.73(aX2Xx)
- 10. POWER LEVEL 97 n 2a.22aa(aX2Xii) il s0.36(c)(1)(iiXA) n s0.73(aX2XvXA) n rcl1(aX4) il 20.2203(aX2Xiii) il 50.36(c)(2) n 50.73(aX2XvXB) n rc.r1(aXs) t] 2o.zzot(aX2Xiv) il 50.46(a)(3xiD tr 50.73(a)(2)(v)(c) n rc.rr(a(1) n 2o.2zai(aX2Xv) tl 50.73(aX2XiXA) tl 50.73(aX2XvXD) n fi.7r(ax2xi) n 2o.2zo3(aX2Xvi) il s0.73(aX2XiXB) n 50.73(a)(2)(vii) n fi.rt(ax2xiD il 50.73(ax2xi)(c) n OTHER Specify in Abstract betow or in D. Manufacturer and Model Number of Components that Failed During the Event The event was caused by intermittent connection issues between the stationary control cards and the power cabinet backplane connector in Westinghouse designed power cabinet 2AC. Atl control cards that could have caused the event were subsequently tested by Westinghouse. There were no confirmed card failures.
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
The intermittent connection issue was discovered during troubleshooting after the manual reactor trip.
G. Failure Mode and Effect of Each Failed Component During troubleshooting in the 2AC power cabinet, several backplane connector pins were found to have intermittent connections. One of the suspect pins supplies +24 volts DC to hold control bank A group 2 control rods stationary. Without this voltage, the rods would drop into the core.
H. OperatorActions There were no complications with the manual reactor trip. The normal expected trip response procedure progression was utilized to stabilize the plant.
L Automatically and Manually lnitiated Safety System Responses All automatic and manual safety systems responded as designed.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
Based on results of troubleshooting and internal operating experience, the cause for the four dropped control rods was an intermittent connection in one of the three stationary control cards associated with control bank A group 2 rods.
B. The cause(s) and circumstances for each human performance related root cause.
The event was not attributed to human performance.
IV. ANALYSIS OF THE EVENT
The WBN Plant Unit 2 reactor was manually tripped at 0857 (EST) on December 11,2017 in accordance with 2-AOl-2, Malfunction of Rod Control System, due to multiple dropped control rods. All control and shutdown bank rods inserted properly in response to the manual reactor trip. The plant was promptly stabilized in Mode 3 with decay heat removal through the Steam Dump System. Troubleshooting revealed intermittent connections in one of the three stationary control cards which caused a loss of +24 volts DC to the firing card thereby resulting in the four dropped rods.
V. ASSESSMENTOFSAFETYCONSEQUENCES During the event and subsequent recovery actions, there was no loss of safety systems, structures or components. The Auxiliary Feedwater system started as expected and remained available to remove decay heat after the reactor trip. Other plant systems functioned as required following the manual reactor trip. Control room operators responded appropriately by manually tripping the reactor as required by procedure. The reactivity effects during this event had no impact on the safety of the core and thus, the event was determined to be of low safety significance.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event All safety systems operated as designed 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, controlthe 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 Authority (TVA) Corrective Action Program and is being tracked under Condition Report (CR) 1367005.
A. lmmediate Corrective Actions All five control rod power cabinets had a 100 percent inspection of backplane connectors on the card cages. Backplane connectors were reformed and aligned as necessary to attain suitable electrical and mechanical connection. Circuit cards in power cabinet 2AC were replaced.
Additionally, all associated circuit cards for the power cabinets had their connectors re-formed with a precision tool.
B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future Long term corrective action to replace the card cage backplane connectors will be entered into Plant Health Committee for future consideration.
VII. PREVIOUS SIMILAR EVENTS AT THE SAME SITE
LER 2017-004 documents a rod control malfunction for WBN Unit 2 that occurred on July 25, 2017.
During a reactor start-up, two associated control rod group demand position indicators deviated greater lhan2 steps from each other. ln accordance with TechnicalRequirement 3.1.7, Position lndication System, Shutdown, with one or more group demand position indicators inoperable, the reactor trip breaker are to be opened immediately. Operations personnel opened the reactor trip breakers immediately by initiating a manual trip of the Reactor Protection System. The rod control demand indication deviation was determined to be caused by a failed logic card in the rod control system.
While both of these events are associated with the Rod Control System, they are different in that one involved a circuit card failure and the other an intermittent connection issue between the card and connector.
VIII. ADDITIONAL INFORMATION
None.
IX. COMMITMENTS None.
NRC FORM s66A (04-2017)