05000391/LER-1917-001, Regarding Containment Airlock Function Lost Due to Equalizing Valve Not Closing
| ML17123A367 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 05/03/2017 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 17-001-00 | |
| Download: ML17123A367 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| 3911917001R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 May 3, 2017 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 39112017-001-00, Containment Airlock Function Lost Due to Equalizing Valve Not Closing This submittal provides Licensee Event Report (LER) 39112017-001-00. This LER provides details concerning a loss of the containment airlock function when the inboard equalizing valve was found open with the outer airlock door open, leading to a brief loss of containment safety function. This report is being submitted in accordance with 1 0 cFR 50.73(aX2)(vXC).
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.
Respectfully, Paul Simmons Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Pag e 2
U.S. Nuclear Regulatory Commission Page 2 May 3, 2017 cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident lnspector - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (06-2016)
LTCENSEE EVENT REPORT (LER)
APPROVED BY OMB: NO.3150-0104 EXPIRES: 1013112018 Estimated burden per response to comply with this 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 learned are incorporated into the licensing process and fed back to industry, Send comments regarding burden estimate to the FOIA, Privacy and lnformation Collections Branch (T-5 F53), U.S, Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to lnfocollects,Resource@nrc,gov, and to the Desk Officer, Office of lnformation and Regulatory Affairs, NE0B-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503 lf a means used to impose an information collection does not display a currently valid OMB control number, 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 2
- 2. DOCKET NUMBER 0500039 1
- 3. PAGE of 5
1
- 4. TITLE Containment Airlock Function Lost Due to Equalizing Valve Not Closing
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHT DAY I YEAR YEAR I tt-ir'^f}#'
REV NO MONTH I DAY YEAR l\\i)il
- NAME I
DocKEr NUMBER 03 09 I 2017 2017 - 001 00 05 03 2017 l\\l?ff
- NAME I
DocKEr NUMBER
- 9. OPERATING MODE
- 11. THIS REPORT lS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR g: (CDeck ail that apply) 1 tr zo z2o1 (b) tr 20 2203(aX3Xi) tr 50 73(aX2XiiXA) tr so 73(aX2)(viiixA) tl 20 zzo1 (d) n 20 2203(aX3)(ii) tl 50 73(aX2XiiXB) t] 50 73(a)(2)(viiiXB) tr zo z2o3(aX1) tr 20 z2o3(aX4) tr 50 73(ax2xiii) tr 50 73(ax2)(ix)(A) tr zo zzo3(aX2)(i) tr 50 36(cxl XIXA) t] 50 73(aX2XivXA) t] so 73(aX2Xx)
- 10. POWER LEVEL 100 tr zo zzo3(a)(2Xii) n 50 36(cxlXiiXA) tr 50 73(aX2XvXA) tr n 11 (aX4) t] zo zzo3(a)(2)(iii) tr 50 36(c)(2) tl 50 73(aX2)(v)(B) tr rc 11 (a)(5) t] zo zzot(a)(2Xiv) t] 50 46(ax3xii)
X 50 73(aX2XvXC) tr fiTl(a)(1) tr zo 22o3(aX2Xv) tr 50 73(ax2xixA) tr 50 73(a)(2XvXD) tr fi 77(aX2Xi) tr 20 2203(aX2Xvi) tr 50 73(aX2XiXB) tr 50 73(a)(2Xvii) tr ft tt(ax2xii) n 50 73(aX2XiXC) t]
OTHER Specify in Abstract betow or in D. Manufacturer and Model Number of Components that Failed During the Event The three inch Class 2 containment airlock pressure equalizing device was manufiactured by Trentec.
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 leaking equalizing valve was found by a plant operator during a routine containment entry.
G. Failure Mode and Effect of Each Failed Component A damaged element of the equalizing valve operating linkage was discovered after this event occurred.
H. Operator Actions
Upon discovery, Operations personnel promptly entered the appropriate TS LCO conditions for the inoperable containment and containment airlock. The inner door mechanism was cycled and the equalizing valve properly seated in the closed position.
l. Automatically and Manually lnitiated Safety System Responses There were no safety system responses associated with this issue.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
The cause of the equalizing valve failing to seat is due to a damaged pin in the equalizing device closure mechanism.
B. The cause(s) and circumstances for each human performance related root cause.
The failure to recognize the need to report this event at the time of occurrence is attributed to not performing a review of operating experience associated with loss of airlock function, The event was subsequently reported on March 17,2017.
IV. ANALYSIS OF THE EVENT
While entering containment to perform a routine surveillance activity, a plant operator heard the sound of air moving through the equalizing valve for the inboard containment airlock door. The operator then closed the outer door, cycled the inner door to seat the equalizing valve, and then reopened the outer airlock Page 3
door. No indication of leakage was found after cycling the inner airlock door, An inspection of the equalizing valve closing mechanism identified a part that needed replacement.
As a result of this condition, an unquantified amount of leakage existed through the inner containment airlock door equalizing line which was not closed. An estimated 3-inch open containment penetration was created with the equalizing valve not fully shut and the outer airlock door open for egress into the upper containment.
V. ASSESSMENT OF SAFEW CONSEQUENCES The event resulted in a bypass of the containment function for approximately five minutes. During the event, the equipment involved was under constant control by a plant operator. ln the event of an accident, the operator would have been able to promptly close the outer containment airlock door. The probability of an accident with core damage and a large early release is estimated to be much less than 1E-7, or very small.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event The outer containment airlock door remained fully operable at the time of the 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 containment bypass condition existed for about five minutes.
VI. CORRECTIVE ACTIONS
This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under Condition Reports (CRs) 1270608 and 1273873.
A. lmmediate Corrective Actions When the leaking equalizing valve was found, the inner door was cycled and the equalizing valve properly seated. The issue with this seating function has not recurred.
B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future A damaged element of the valve closure mechanism was identified following this event. The airlock remains functional, and an operations caution order was put in place related to use of this air lock.
The airlock will be repaired prior to Unit 2 returning to Mode 4.
4 Page 4 of 5
VII. PREVIOUS SIMILAR EVENTS AT THE SAME SITE
No previous events associated with the containment airlocks were identified at WBN.
VIII. ADDITIONAL INFORMATION
None.
IX, COMMITMENTS None.
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