05000327/LER-2020-001-01, 1 for Sequoyah Nuclear Plant, Unit 1, Containment Vacuum Relief Lines Found Isolated
| ML20083F591 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/20/2020 |
| From: | Rasmussen M Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2020-001-001 | |
| Download: ML20083F591 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3272020001R01 - NRC Website | |
text
Tennessee Valley Authority, Sequoyah Nuclear Plant, P.O. Box 2000, Soddy Daisy, Tennessee 37384 March 20, 2020 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Unit 1 Renewed Facility Operating License No. DPR-77 NRC Docket No. 50-327
Subject:
Licensee Event Report 50-327/2020-001-00, Containment Vacuum Relief Lines Found Isolated The enclosed licensee event report provides details concerning containment vacuum relief lines found isolated during normal operation. These events are being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), as an event that resulted in a condition prohibited by Technical Specifications and in accordance with 10 CFR 50.73(a)(2)(ii)(B), as a condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Jeffrey Sowa, Site Licensing Manager, at (423) 843-8129.
Respectfully, Matthew Rasmussen Site Vice President Sequoyah Nuclear Plant Enclosure: Licensee Event Report 50-327/2020-001-00 cc:
NRC Regional Administrator - Region II NRC Senior Resident Inspector-Sequoyah Nuclear Plant printed on recycled paper
NRC FORM U.S.NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 366 (04-2018)
Estimated burden perresponse tocomply 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 tied back to 0^*"*°%,
LICENSEE EVENT REPORT (LER) industry. Send comments regarding burden estimate to the Information Services Branch
- 1
,\\
(T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail
- %AS$ %
(See Page 2for required number ofdigits/characters for each block) to lnfbcollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and
\\wBEr/ (SeeNUREG-1022,R.3forinstmctionandguidanc>>forcompletingthisforTTi ***** ^^f0^0202' 01fiW>>°* m<>> ^Ji^mtJ^^a^
y*WTf htto://wwww.nic^^
Washington, DC 20503 If ameans used to impose an information collection does not d,sP,ay a currently valid OMB control number, the NRC may not conduct orsponsor, and a person is not reauired to respond to. the information collection.
Sequoyah Nuclear Plant, Unit 1 05000327
- 3. Page 1 OF6
- 4. Title Containment Vacuum Relief Lines Found Isolated
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Month Day Year Year Sequential Number Rev No.
Month Day Year Facility Name NA Docket Number 05000 01 21 2020 2020 001 00 03 20 2020 Facility Name Docket Number NA 05000 a OperatingMode 1
) £3 No Abstract (Limitto 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)
On January 21, 2020, at 2218 Eastern Standard Time (EST) Operations Personnel identified that 3-out-of-3 containment vessel vacuum relief isolation valves were isolated. Operations Personnel declared the containment vessel vacuum relief lines inoperable. Operations Personnel restored the vacuum relief lines to operable status at 2223 EST by opening the vacuum relief isolation valves. Investigation of the condition determined that while in a refueling outage on November 13, 2019, a Licensed Operator incorrectly closed the vacuum relief isolation valves during the performance of a surveillance instruction. The cause of the event was a failure to follow the surveillance instruction by the Licensed Operator. The Operator assumed that a process was in place to restore the valves to open position. Itwas also determined that Operations Leadership did not establish a rigorous outage oversight plan, which precluded the ability to identify degraded or declining operator fundamental behavior. Actions being taken to address this event include a formal oversight plan to reinforce use of Operator Fundamentals, monitoring for shortfalls, and coaching to standards.
Also, a revision to the common operating procedure for unit startup willensure the vacuum relief system is aligned for Mode 4 entry.
NRC FORM 366 (04-2018)
I.
Plant Operating Conditions Before the Event
At the time of the condition, Sequoyah Nuclear Plant (SQN) Unit 1 was in Mode 1 at 100 percent rated thermal power.
II.
Description of Event
A. Event Summary:
On January 21, 2020, at 2218 Eastern Standard Time (EST) Operations Personnel identified that 3-out-of-3 containment vessel vacuum relief isolation valves [ENS Code: ISV] were isolated.
Operations Personnel declared the containment vessel vacuum relief lines inoperable. Limiting Condition for Operation (LCO) 3.0.3 was entered because LCO 3.6.9, Vacuum Relief Valves, does not provide an action for more than one vacuum relief line being inoperable. Operations Personnel restored the vacuum relief lines to operable status at 2223 EST by opening the vacuum relief isolation valves.
Investigation of the condition determined that on November 13, 2019, Operations Personnel were verifying containment isolation in preparation for fuel handling using surveillance instruction, 1-SI-OPS-Q88-006.0, Containment Building Ventilation Isolation. During performance of the surveillance instruction, a Licensed Operator incorrectly closed the vacuum relief isolation valves.
On November 24, 2019, Unit 1 entered into Mode 4. From this date until the vacuum relief lines were restored on January 21, 2020, the actions of LCO 3.6.9 and LCO 3.0.3 were not fulfilled.
This resulted in a condition prohibited by Technical Specifications (TS) and is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B).
B. Status of structures, components, or systems that were inoperable at the start of the event and contributed to the event:
No inoperable structures, components, or systems contributed to this event.(04-2018)
Page 2 of 6(04-2018)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instructionand guidance for completingthis form http://www.nrc.gov/reading-rnVdoc-collections/nuregs/staff/sM022/^
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 Estimated burden perresponseto complywiththis 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 intothe licensing process and ted backto industry. Send comments regarding burden estimate to the Information Services Branch (T-2 F43), U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001,or bye-mail to lntbcollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, anda personis notrequired to respondto, the informationcollection.
a LER NUMBER Sequoyah Nuclear Plant Unit 1 05000-327 YEAR 2020
C. Dates and approximate times of occurrences
SEQUENTIAL NUMBER
- 001 REV NO.
- 00 Date/Time (EST)
Description
November 13, 2019 Licensed Operator closed all 3 vacuum relief isolation valves.
November 24, 2019 at 1427 Unit 1 enters into Mode 4. LCO 3.6.9 lowest Mode of applicability.
January 21, 2020 at 2218 Operations Personnel determined the vacuum relief lines were inoperable and took action to correct the condition.
January 21, 2020 at 2223 Operations Personnel declared vacuum relief lines operable.
D. Manufacturer and model number of each component that failed during the event
There was no component that failed during the event.
E. Other systems or secondary functions affected
No other systems or secondary functions were affected by this event.
F.
Method of discovery of each component or system failure or procedural error
Operations Personnel while conducting a quarterly valve stroke surveillance instruction identified 3-out-of-3 of the vacuum relief isolation valves' indication showing closed.
G. Failure mode, mechanism, and effect of each failed component:
There was no component that failed during the event.
H. Operator actions
Operations Personnel, upon determining the containment vacuum relief lines were isolated in a Mode of TS applicability, declared the lines inoperable, entered into appropriate TS actions, and took action to restore the vacuum relief lines to operable condition.
I.
Automatically and manually initiated safety system responses
There were no automatic or manually initiated safety system responses associated with this event.Page 3 of 6(04-2018)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3for instruction and guidance forcompleting thisform http://Www.nro.gov/reading-rm/do(HX)llections/nuregs/sta1!ysr1022/r3/)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 Estimated burden perresponse to comply with thismandatory 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 intothe licensing processand ted backto industry. Send comments regarding burden estimate to the Information Services Branch (T-2 F43), U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001,or bye-mail to lnfbcollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget Washington, DC 20503. if a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, anda person is notrequired to respond to,theinformat'oncollection.
a LER NUMBER Sequoyah Nuclear Plant Unit 1 05000-327 YEAR 2020 SEQUENTIAL NUMBER
- 001 REV NO.
00 III.
Cause of the Event
A. Cause of each component or system failure or personnel error:
The Licensed Operator who closed each of the vacuum relief isolation valves understood the procedure requirement specified in the containment isolation surveillance instruction was verification only. The Operator did not follow the procedure, believing the intent of the procedure step was to isolate the valves to closed position instead of to verify the status of the valves. The Operator further assumed that a process was in place to restore the valves to open position.
As described above, a Licensed Operator, under no time pressure, did not comply with procedure requirements and assumed that a process was in place to restore the valves to open position. TVA also determined a contributing factor wherein Operations Leadership did not establish a rigorous outage oversight plan, which precluded the ability to identify degraded or declining operator fundamental behaviors.
IV.
Analysis of the Event
The primary containment vessel is fitted with a vacuum relief (VR) system [EIIS Code: BF]. The purpose of the VR system is to protect the vessel from an excessive external force. It is a self-activated system that limitsexternal pressure on the vessel in the event of maloperation or inadvertent operation of systems that result in additional external forces on the containment vessel. Those limiting external forces are created by design basis transients: inadvertent containment spray [EIIS Code: BE] actuation, inadvertent containment air return system [EIIS Code: BK] operation and simultaneous occurrence of both. The VR system consists of 3 containment relief pathways (i.e. vacuum relief lines,) each containing a normally closed self-actuated vacuum relief valve and position indication. In series with the vacuum relief valve is a normally open, fail open, pneumatically operated containment isolation valve with necessary instrumentation and controls. The containment vessel VR system assures that the external pressure differential on the containment vessel does not exceed the design external pressure of 0.5 pounds per square inch delta (psid) assuming one vacuum reliefvalve fails to open in keeping with single failure criteria. When an external pressure exceeds a relief valve actuation force it opens allowing air flow from the annulus space through the VR pathway into the containment vessel.
Additional details may be found inSection 6.2.6, "Vacuum ReliefSystem," of the Updated Final Safety Analysis Report (UFSAR).
The containment relief pathway's pneumatically operated containment isolation valve closes when containment pressure with respect to annulus pressure reaches a instrument set point of 1.5 psid. A high pressure signal is developed from either of two sets of instrument sensors and is completely independent of the other containment isolation signals. The containment relief pathway's isolationPage 4 of 6(04-2018) f/J U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instructionand guidance for completingthis form http://www.nrc.gov/reading-rTWdo(>KX)l!ec*ons/nuregs/staff/sr1022/^
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 Estimated burden perresponse to comply with thismandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessonslearned are incorporated intothe licensing process and fed backto industry. Send comments regarding burden estimate to the Information Services Branch (T-2 F43), U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or bye-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEO6-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, anda person is notrequired to respond to,the informationcollection.
- 1. FACILITY NAME 2
DOCKET NUMBER 1
LER NUMBER Sequoyah Nuclear Plant Unit 1 05000-327 YEAR 2020 SEQUENTIAL NUMBER 001 REV NO.
00 valves provide containment isolation and containment integrity to control the release of radioactive materials from the containment atmosphere during design basis accidents.
Closure of all 3 containment relief pathway isolation valves ensured pathway containment isolation and integrity in the unlikely event of a design basis accident that requires mitigation of consequences, which could result in potential offsite exposure.
Closure of all 3 containment relief pathway isolation valves defeated the vacuum relief lines single failure capability, challenging the integrity of a fission product barrier in the unlikelyevent of a design basis transients that results in limiting external pressure on the containment vessel. This is considered to be an event that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety in accordance with 10 CFR 50.73(a)(2)(ii)(B).
Nevertheless, during the time of the inoperable containment vacuum relief lines, there were no actual safety significant consequences as a result of this event. No event occurred that required the use of the vacuum relief lines.
V.
Assessment of Safety Consequences
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event:
Analysis for excessive external forces where the relief function of the containment vacuum relief is necessary, assumes one vacuum relief valve fails to open. During the time period of inoperability, no mitigation of these forces would have been available, because all 3 vacuum relief lines were isolated.
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:
For events requiring isolation, the containment vacuum pathway containment isolation valves were isolated preforming their safety function.
C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from discovery of the failure until the train was returned to service:
The vacuum relief lines are not train designated, yet form a single system. None-the-less, an estimated elapsed time of 58 days, 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> and 56 minutes passed from November 24, 2019 at 1427 EST until the vacuum relief lines were restored to operable status on January 21, 2020 at 2223.Page 5 of 6(04-2018)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instructionand guidance for completingthis form http://www.nrc.gov/reading-nri/docKX3llections/nui^s/staff/sM022/r3/)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 Estimated burden perresponse 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 intothe licensing processandfed backto industry. Sendcomments regarding burden estimate to the Information Services Branch (T-2 F43), U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001,or bye-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, anda personis notrequired to respondto,the informationcollection.
a LER NUMBER Sequoyah Nuclear Plant Unit 1 05000-327 YEAR 2020 SEQUENTIAL NUMBER
- 001 REV NO.
00 VI.
Corrective Actions
A.
Immediate Corrective Actions
Operations Personnel entered into the TS LCO actions and un-isolated the containment vacuum relief isolation valves.
B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future:
Corrective Actions are being managed via the Tennessee Valley Authority's corrective action program under condition report number 1580587. The corrective actions to be taken to address the causes of this event include:
1.
Developing a Unit 2 Cycle 23 Refueling Outage Safety-Human Performance Plan to reinforce use of Operator Fundamentals, monitor for shortfalls, and coaching to standards.
2.
Revising the common operating procedure for unit startup from cold shutdown to hot standby with steps to ensure vacuum relief system is aligned for Mode 4 entry.
VII.
Previous Similar Events at the Same Site
There were no previous similar events at SQN occurring within the last three years.
VIII.
Additional Information
There is no additional information.
IX.
Commitments
There are no commitments.Page 6 of 6