05000390/LER-2014-002, Regarding Non-Conservative Operator Manual Actions Identified in Appendix R Analysis
| ML14101A146 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 04/11/2014 |
| From: | Church C Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 14-002-00 | |
| Download: ML14101A146 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| LER closed by | |
| IR 05000390/2015000 (30 April 2015) | |
| 3902014002R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 April 11,2014 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 39012014-002, Non-conservative Operator Manual Actions ldentified in Appendix R Analysis This submittal provides Licensee Event Report (LER) 39012014-002. This LER provides details concerning a postulated fire induced event which could result in Pressurizer Overfill at Watts Bar Nuclear Plant, Unit 1. This report is being submitted in accordance with 10 cFR 50.73(aX2)(iiXB).
There are no regulatory commitments in this letter. Please direct any questions concerning this matter to Gordon Arent, WBN Licensing Director, at (423) 365-2004.
Res a
Site Vice President Watts Bar Nuclear Plant
U.S. Nuclear Regulatory Commission Page 2 April 11,2014 Enclosure cc (Enclosure):
NRC Regional Administrator - Region Il NRC Senior Resident lnspector - Watts Bar Nuclear Plant NRC Project Manager - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGUI.ATORY COMMISSION
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(See Page 2 for required number of digits/characters for each block)
APPROVED BY OMB: NO.3l50-0104 EXPIRES: 0113112017 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 />.
Reprted lessons leamed are incorporated into the licensing process and hd back to indusfy.
Send commenB regarding burden estimate to he FOIA, Privacy and lnformation Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 2055$0001, or by intemet +mail to Infucollects.Resource@nrc.gov, and to the Desk Officer, ffice of lnfurmation and Regulatory Afiains, NE0810202, (315O0104), ffice of Management and Budget, Washington, DC 20503. lf a means used to impose an information mllection does not display a cunently valid OMB conhol number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
{. FACILITY NAME Watts Bar Nuclear Plant, Unit 1
- 2. DOCKET NUMBER 05000390
- 3. PAGE OF 5
1
- 4. TITLE Non-conservative Operator ManualActions ldentified in Appendix R Analysis
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI DAY I YEAR YEAR l t=-t'rTg$'- I ft="Y MONTH I DAY YEAR FACILITY NAME N/A DOCKET NUMBER N/A 02 11 I 2014 2014 - 002 - 00 04 11 2014 FACILITY NAME N/A DOCKET NUMBER N/A
- 9. OPERATING MODE II.THISREPORTISSUBMITTEDPURSUANTTOTHEREQUIRETIENTSOFI0CFR$: (Checkallthatappty) 1 tr 2o.2zo1(b) tr 20.2203(aX3)(.)
tl 50.73(aX2XiXc) tr s0.73(a)(2Xvii) tr 20.2201(d) tr 20.2203(aX3Xii) tr 50.73(aX2XiiXA) n s0.73(a)(2)(viii)(A) tr zo.zzos(aX1) tr 20.2203(a)(4)
X 50.73(aX2XiiXB) tr 50.73(a)(2XviiiXB) tl 2o.zzos(ax2xi) tr s0.36(c)(1Xi)(A) tr 50.73(ax2)(i.i) n 50.73(aX2XixXA)
{0. POWER LEVEL 100o/o tr 2o.2zos(aX2Xii) tr s0.36(c)(lxiixA) n s0.73(a)(2)(ivXA) tr 50.73(aX2)(x) tr 2o.22os(aX2)(iii) tr s0.36(c)(2) tr 50.73(a)(2XvXA) tr rc.r1(a)(4) tr 20.2203(aX2Xiv) tr s0.46(ax3xii) tl 50.73(aX2XvXB) tr n.r1(aXs) tr 20.2203(aX2Xv) tr 50.73(aX2)(iXA) tr s0.73(aX2XvXc) tr orHER tr 20.2203(aX2Xvi) tr 50.73(aX2X.XB) tr 50.73(aX2XvXD)
Specify in Abstract below or in
I.
PLANT CONDITIONS
At the time of discovery, Watts Bar Nuclear Plant (WBN) Unit 1 was operating in Mode 1 at 100 percent rated thermal power (RTP).
II.
DESCRIPTION OF EVENT
A. Event On February 11,2014, Watts Bar Nuclear Plant (WBN) engineering and operations personnel discovered that non-conservative operator manual action (OMA) completion times were incorporated in Appendix R procedures. Preliminary Westinghouse transient analysis calculations of WBN Unit 1 fire protection features revealed that there is less time than previously credited to perform certain OMAs to prevent pressurizer overfill during certain Appendix R fire scenarios.
Specifically, an assumed 10 CFR 50 Appendix R fire in rooms 713.0-A6, 713.0-A28,737.0-A1A, 757.0-l2,757.0-45, 757.0-49, 772.0-41,772.0-A2, or 772.0-AS could result in spurious operation of multiple components in the normal and emergency charging flow paths. Westinghouse's analysis demonstrated the required time to isolate the normal charging path, secure the second charging pump and isolate the emergency charging path is approximately 12.5 minutes. Watts Bar Unit 1 procedures are non-conservative in that they allow these actions to be completed in 18 minutes.
This event is reportable under 10 CFR 50.73(aX2XiiXB).
B. lnoperable Structures, Components, or Systems that Contributed to the Event None
C. Dates and Approximate Times of Occurrences
Date Time Event o2t1it14 or4a ;'13:flllrtr:l,Ui?Ji,'33Si;"riminary anarysis resurts to wA.
02111114 1800 TVA confirms analysis applicability to WBN Unit 1.
02111114 1928 WA reports this event in accordance with 10 CFR 50.72 (EN#49818)
D. Manufacturer and Model Number of Components that Failed.
There were no failed components associated with this event.
E. Other Systems or Secondary Functions Affected
There were no systems or secondary functions associated with this event.
F. Method of discovery of each Component or System Failure or Procedural Error
There were no failed components associated with this event. However, there was a latent design error in a WBNl fire protection program design calculation that was discovered during a detailed design review of Appendix R scenarios completed for WBN Unit 2 as part of plant licensing.
G. Failure Mode and Effect of Each Failed Component There were no failed components associated with this event.
H. OperatorActions
' Operator actions are noted in section ll.C above.
L Automatically and Manually lnitiated Safety System Responses There were no automatic or manually initiated safety system responses associated with this event.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known There were no failed components or systems associated with this event. The cause of this event was determined to be a latent design enor in an Appendix R related calculation that occurred during the initial design of WBN Unit 1.
B. The cause(s) and circumstances for each human performance related root cause N/A
IV. ANALYSIS OF THE EVENT
Prior to licensing, WBNl had performed an Appendix R analysis of spurious equipment operation where the consequence of the event is pressurizer overfill. For the rooms identified in Section ll above, a fire is assumed to occur in one of the rooms, which then results in equipment failures. The fire is assumed to short equipment control cables routed within the room, resulting in spurious equipment operation.
Electrical cables associated with the charging pumps, the reactor coolant letdown isolation valve, and the emergency core cooling flow path isolation valves from the charging pumps to the reactor coolant system (also called the Boron lnjection Tank [BlT] valves) are located in the listed rooms. For the rooms identified, it is assumed that the fire will result in the start of a second charging pump, the isolation of reactor coolant letdown, and the opening of a BIT isolation valves. The net result is that more water will be injected into the reactor coolant system than is being removed, and the pressurizer will begin to fill.
Operator action outside the control room is required to isolate the BIT flow path and the normal charging flow path and to shutoff the second charging pump before the pressurizer becomes water solid. The original analysis determined that with spurious equipment operation, operations personnel would have 18 minutes to isolate plant features to prevent pressurizer overfill. Watts Bar Unit t had demonstrated that the required actions to prevent pressurizer overfill could be completed within 15 minutes, and thus the associated OMAs were acceptable.
While performing design reviews in support of WBN Unit 2 licensing, engineering personnel identified that a Chemical and Volume Control System (CVCS) {EllS: CB} malfunction event was very similar to certain Appendix R fire sequences where high charging flow could occur concurrent with loss of letdown. Since the time available for this event was somewhat less than the Appendix R analysis indicated, TVA contracted Westinghouse to perform a more detailed analysis of the plant's response to these fire events.
The result of those preliminary analyses demonstrated that less time was available to take operator action than previously calculated. Based on this preliminary analysis, this condition was determined to be reportable pursuant to 10 CFR 50.72.
ASSESSMENT OF SAFEW CONSEQUENCES A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event The Appendix R event described involves the simultaneous spurious start of a second charging pump, opening of the safety injection flow path from the charging pumps, and the isolation of letdown.
For this event to occur, a fire would need to start in one of the rooms identified in Section ll above.
The combustible loading in each of these rooms ranges from low to moderately severe. The fire would then have to be large enough to cause specific control cables to short but not fail catastrophically. No credit is taken for either the detection or suppression that is present in these rooms. While required for consideration, the simultaneous actuation of the affected components remains unlikely.
Operator action will be taken during this event to open a pressurizer Power Operated Relief Valve (PORV) to prevent over-pressurizing the reactor coolant system. This would result in a release of reactor coolant to the Pressurizer Relief Tank (PRT) until excess charging flow is secured, at which point the PORV would not need to be opened to control reactor coolant pressure. Reactor coolant system inventory would be maintained by seal injection, with the reactor head vent valves being used to provide a letdown flow path.
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 N/A 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 N/A
CORRECTIVE ACTIONS
The corrective actions for this issue are being tracked within the WBN Corrective Action Program (CAP) under Problem Evaluation Reports (PERs) 845185, 857207, and 852332.
A. lmmediate Corrective Actions V.
vt.
Upon determining that operator actions could not be completed in the required time frame to respond to an Appendix R fire in the rooms identified, compensatory Appendix R fire watches were initiated.
B. Corrective Actions to Prevent Recurrence Modifications will be completed during the WBN 1 Fall2015 refueling outage that will reduce the number of fire related failures in the rooms identified such that operator action may be taken prior to a pressurizer overfill condition occurring.
To ensure that the Fire Hazards Analysis (FHA) is properly supported, a detailed review of other supporting analyses and evaluations is being conducted for the Watts Bar plant to address the potential generic implications of this event. A similar review will also be performed for TVA's Sequoyah plant. This event was due to a latent design engineering enor.
VII. ADDITIONALINFORMATION A. Previous similar events at the same plant On January 13,2014, TVA submitted LER 390/2013-005, "Postulated Fire lnduced Failure of Chemicaland Volume ControlSystem CentrifugalCharging Pumps." This LER describes an unanalyzed condition where a potentialfire induced failure of both Unit 1 Chemicaland Volume Control System Centrifugal Charging Pumps (CCPs) could occur due to a fire in the Auxiliary Building. The event described in LER 390/2013-005 involved the same underlying cause of a latent design engineering error during initial plant licensing as the event being reported in this LER.
Because this event is similar to a previous reportable event, additional corrective actions are described above to address this issue.
B. Additional lnformation None C. Safe$ System Functional Failure Consideration While this event could have resulted in a sequence where the pressurizer would overfill, no actual equipment failures (other than those resulting from the assumed fire) are expected to occur. ln the event that operator action cannot be taken in time to terminate excess charging flow, one or both of the PORVs will lift to prevent reactor coolant system over-pressurization before the code safety valves lift. Once excess charging flow is isolated, the PORV(s) would reclose, or could be isolated by its associated block valve. Accordingly, this is issue does not represent a safety system functional failure.
D. Scrams with Complications Consideration N/A
VIII. COMMITMENTS
None.