05000390/LER-1917-006, Regarding Structural Degradation of 161 Kv Line Pole Leads to a Condition Prohibited by Technical Specifications
| ML17212A373 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 07/31/2017 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 17-006-00 | |
| Download: ML17212A373 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) |
| 3901917006R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 July 31, 2017 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 39012017-006-00, Structural Degradation of 161 kV Line Pole Leads to a Condition Prohibited by Technical Specifications This submittal provides Licensee Event Report (LER) 39012017-006-00. This LER provides details concerning the degradation of an offsite power source line pole that led to a condition prohibited by Technical Specifications. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(iXB).
There are no regulatory commitments contained in this letter. Please direct any questions concerning this matter to Kim Hulvey, wBN Licensing Manager, at (423) 36s-7220.
Respectfully, Paul Simmons Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Pag e 2
U.S. Nuclear Regulatory Commission Page 2 July 31, 2017 cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident Inspector - Watts Bar Nuclear Plant
NRC FORM (o4-2O17) o#'%'*ffi 366 U.S. NUCLEAR REGULATORY COMMISSION LTCENSEE EVENT REPORT (LER)
APPROVED BY OMB: NO.3150-0104 EXPIRES: 0313112020
, 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 10F5
- 4. TITLE Structural Degradation of 161 kV Line Pole Leads to a Condition Prohibited by Technical Specifications
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI DAY I YEAR YEAR I t=-ir,,;#Jrt REV NO.
MONTH I DAY YEAR FACTLTTY NAME I
DOCKET NUMBER N/A 105000 06 01 l 2017 2017 r006
- - 00 07 31 2017 FACILITY NAME I
DOCKET NUMBER 105000
- 9. OPERATING MODE
'II.THlSREPORT:SSUBMITTEDPURSUANTTOTHEREQUIREMENTSOFl0CFR$:
(Checkallthatapply) 1 n zo 2201 (b) tl 2o.2za3(ax3)(i) n 50 73(a)(2)(iixA) n 50.73(aX2Xviii)(A) n 20 2201 (d) n 20 2203(aX3Xii) n 50 73(aX2Xii)(B) n 50 73(a)(2)(viii)(B) n zo,zza3(aX1) n 2o,zzo3(aX4) n 50.73(ax2xiii) n 50.73(aX2Xix)(A) n 2o.zzo3(aX2Xi) n s0,36(cx1)(iXA) tr 50 73(a)(2Xiv)(A) n 50.73(ax2xx)
- 10. POWER LEVEL 100 n 2o.22os(aX2Xii) n 50,36(cxt Xii)(A) n 50 73(aX2Xv)(A) tr rc.l1 (a)(4) n zo 22o3(aX2)(iii) tr 50 36(cx2) tr 50 73(ax2xvXB) tr rc.l1 (aXs) n zo.22o3(a)(2x.v) tr 50 46(ax3xii) n 50 73(aX2XvXC) tr fiTl(a)(1) tr 20.2203(aX2Xv) n 50.73(aX2XiXA) tr 50.73(aX2XvXD) n fi,77(ax2)(i) n 20.2203(aX2Xvi)
X 50 73(ax2xixB) n 50 73(ax2Xvii) tr ftlt(a)(2xii) n 50 73(ax2xixc) n OTHER Specify in Abstract below or in
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 degraded condition WBH Line B pole 9 was discovered by TVA transmission personnel during investigation of the condition of the offsite power system serving WBN following a loss of the WBH Line B during a storm on May 27,2017. The condition of the pole was promptly reported to site operations personnel.
G. Failure Mode and Etfect of Each Failed Component Material degradation (corrosion).
H. Operator Actions
Upon discovering the degraded condition of the WBH Line B pole, operations personnel declared the B offsite power source to be inoperable.
l. Automatically and Manually lnitiated Safety System Responses Not applicable.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
The WBH Line B pole g described in this report had been subject to significant corrosion prior to the May 27, 2017 storm. The collapse of two adjacent poles on May 27,2017 resulted in the partial circumferential crack near the base of pole 9.
B. The cause(s) and circumstances for each human performance related root cause.
No human performance causes have been attributed to this event.
IV. ANALYSIS OF THE EVENT
Two '161 kV transmission lines extend approximately 1.5 miles from Watts Bar Hydro Plant switchyard to the Watts Bar Nuclear Plant site to furnish preferred power to the nuclear plant. The transmission line structures for 161kV iines are designed for wind and heavy icing conditions in excess of those that would be expected to occur in this area. The 161 kV line poles are fabricated of COR-TEN, a steel alloy that is intended to create a protective oxide coating to prevent atmospheric corrosion.
A storm on May 27,2017 resulted in multiple poles falling over, causing the loss of one of the two required preferred power sources (WBH Line B). lt has been concluded the failure of these poles, coupled with existing wall thinning of pole 9, resulted in a significant load being applied to pole 9, cracking it. During
repair and investigation efforts for the May 27,2017 event, the crack in pole 9 was not immediately identified because heavy vegetation was in place over the crack. When this vegetation was removed several days later by transmission personnel during further extent of condition review, the crack was revealed. The assessment of the crack and wall thinning of pole 9 due to corrosion by transmission personnel concluded that the pole could not support expected design ice and wind loads and should be promptly replaced. Transmission personnel brought this information to operations personnel on June 1 2017 and the pole and associated offsite power source were declared inoperable.
V. ASSESSMENT OF SAFETY CONSEQUENCES
The offsite power system at WBN has historically been highly reliable. During the storm on May 27,2017 that caused a failure of WBH line B, the other offsite power source remained operable. Following the initial restoration of WBH line B on May 29, 2017, all required TS surveillances were met for offsite power. WBN is also provided with onsite power in the event offsite power is lost. Based on the redundancy inherent in this design, the safety consequences of this event are considered 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 The WBH lirte A power source remained available during the time period described in this LER.
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 While the offsite power system is not specifically safety related, the WBH line B was returned to service the day following identification of pole g degradation.
VI, CORRECTIVE ACTIONS This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under Condition Reports (CRs) 1302767 and 1301565.
A. lmmediate Corrective Actions Upon discovering the WBH line B pole 9 in a degraded state, the WBH line B offsite power source was declared out of service. The affected pole was replaced and the WBH line B offsite power source was returned to service the following day.
B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future NRC FORM 3664 (04-2017)
TVA transmission personnel have performed additional investigations of the offsite power system lines serving WBN. Additional poles have been replaced, though none were in the condition identified for pole 9. Future actions are planned to replace all of the COR-TEN poles in WBH lines A and B with poles of a different design.
VII. PREVIOUS SIMILAR EVENTS AT THE SAME SITE
No previous similar occurrences associated with the offsite power system have occurred within the last three years.
VIII. ADDITIONALINFORMATION None.
IX
COMMITMENTS
None.
NRC FORM 3664 (04-2017)