05000327/LER-2016-003, Regarding Control Room Door Unable to Close Causes Inoperable Control Room Envelope
| ML16187A053 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  (DPR-077, DPR-079) |
| Issue date: | 07/05/2016 |
| From: | Schwarz C Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 16-003-00 | |
| Download: ML16187A053 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3272016003R00 - NRC Website | |
text
Tennessee Valley Authority, Sequoyah Nuclear Plant, P.O. Box 2000, Soddy Daisy, Tennessee 37384 July 5, 2016 10 CFR 50.73 ATTN:
Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Units 1 and 2 Renewed Facility Operating License Nos. DPR-77 and DPR-79 NRC Docket Nos. 50-327 and 50-328
Subject:
Licensee Event Report 50-327 and 50-328/2016-003-00, Control Room Door Unable to Close Causes Inoperable Control Room Envelope The enclosed Licensee Event Report provides details concerning the inability to close a main control room door resulting in both trains of the Control Room Emergency Ventilation System being declared inoperable. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(v)(D), as an event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to mitigate the consequences of an accident.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Michael McBrearty, Site Licensing Manager, at (423)843-7170.
Resbectfulfyi,
^%r-Christopher J. Schwarz Site Vice President Sequoyah Nuclear Plant Enclosure: Licensee Event Report 50-327 and 50-328/2016-003-00 cc:
NRC Regional Administrator-Region II NRC Senior Resident Inspector-Sequoyah Nuclear Plant printed on recycled paper
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (11-2015)
^SP LICENSEE EVENT REPORT (LER)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018
, the NRC may not conduct or sponsor, and a person is not required to respondto,the information collection.
- 1. FACILITY NAME Sequoyah Nuclear Plant Unit 1
- 2. DOCKET NUMBER 05000327
- 3. PAGE 1
OF 6
- 4. TITLE Control Room Door Unable to Close Causes Inoperable Control Room Envelope Boundary
- 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 Sequoyah Nuclear Plant Unit 2 DOCKET NUMBER 05000328 05 03 2016 2016 003 00 07 05 2016 FACILITY NAME NA DOCKET NUMBER
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 1 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2201(d) 20.2203(a)(3)(H) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
- 10. POWER LEVEL 100 20.2203(a)(2)(H) 50.36(c)(1)(ii)(A) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(H) 50.73(a)(2)(v)(C) 73.77(a)(1) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(D) 73.77(a)(2)(i) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(vii) 73.77(a)(2)(H) 50.73(a)(2)(i)(C) l~l OTHER Specify in Abstract below or in SEQUENTIAL NUMBER 003 REV NO.
00 C.
Dates and approximate times of occurrences
Date/Time (EDT) 05/03/16, 0833 05/03/16, 0847 05/03/16, 0855
Description
Security received an open door alarm on a MCR door.
Security notified MCR staff of the door alarm and the door was incapable of closure. Both units enter TS 3.7.10, Condition B, due to the inoperability of the CRE.
After investigation, a screw was found, removed, and the door verified to close as designed. Both units exit TS 3.7.10, Condition B.
D.
Manufacturer and model number of each component that failed during the event
The failed component was associated with the door latch guard for the MCR door. The door latch guard is model number 1625, manufactured by Precision Hardware, Inc.
E.
Other systems or secondary functions affected
There were no systems or secondary functions affected by this event.
F.
Method of discovery of each component or system failure or procedural error
Security received an open door alarm associated with the MCR door.
G.
The failure mode, mechanism, and effect of each failed component, if known:
The screw that prevented the MCR door from closing was the bottom screw from the door latch guard and appears to have stripped loose and fallen into the rubber seal around the base of the MCR doorframe preventing the door from closing.
H.
Operator actions
Following notification of the issue to the MCR operators, both CREVS trains were declared inoperable in accordance with TS 3.7.10, Condition B, due to the inoperability of the CRE. MCR staff contacted individuals to evaluate and repair as necessary. Additionally, mitigating actions were initiated and met by verifying the availability of Potassium Iodine and self contained breathing apparatus to MCR operators within the CRE.
I.
Automatically and manually initiated safety system responses
There were no automatic or manual 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:
The cause of the event was the bottom screw in the door latch guard appears to have stripped loose and fallen into the rubber seal around the base of the MCR door frame preventing closure of the door.
B.
The cause(s) and circumstances for each human performance related root cause:
There was no human performance related root cause.
IV
ANALYSIS OF THE EVENT
The CREVS is a safety related Engineered Safety Features system required to operate during design basis accidents (DBAs) to mitigate the radiological consequences to the control room operators. The CREVS is designed to maintain a habitable environment in the CRE for a mission time of 30 days of continuous occupancy after a DBA without exceeding a 5 rem whole body dose or its equivalent to any part of the body. The operability of the CRE boundary must be maintained to ensure that the inleakage of unfiltered air into the CRE will not exceed the inleakage assumed in the licensing basis analysis of DBA consequences to CRE occupants. Additionally, the CRE boundary ensures occupants are protected from hazardous chemicals and smoke.
Engineering evaluation concluded that the requirement to support long term occupancy would not have been affected to the point that would have resulted in exceeding the design basis dose assumptions for the control room operators as the assumed unfiltered air inleakage would not have been exceeded. Therefore, the CREVS and the CRE would have been able to fulfill the required 30 days of continuous occupancy after a DBA.
V
ASSESSMENT OF SAFETY CONSEQUENCES
The temporary loss of abilityto close the MCR door did not challenge nuclear or radiological safety. No actual loss of safety function occurred. The CREVS maintained the ability to limit MCR operator doses below the required limits.
A.
Availability of systems or components that could have performed the same function as the components and systems that failed during the event:
Although the MCR door was ajar, the CREVS maintained the ability to limit MCR operator doses below the required limits.
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:
The event did not occur when the reactor was shutdown.
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 elapsed time from discovery of the open door rendering the CRE inoperable until the CRE was restored to operable status was 22 minutes.
VI.
CORRECTIVE ACTIONS
This event was entered into the Tennessee Valley Authority Corrective Action Program under Condition Report (CR) 1166927.
A.
Immediate Corrective Actions
MCR Operators contacted various organizations to investigate why the door would not close. During inspection of the sealing surface around the MCR door, a screw was found and removed. The MCR door was closed and TS 3.7.10, Condition B, was exited for both units.
B.
Corrective actions to reduce probability of similar events occurring in the future:
Corrective actions include evaluating existing preventive maintenance instructions associated with CREVS boundary doors to ensure screws are tightened, as needed, on a routine basis.
Additional actions include:
Initiating a work order to replace the missing screw on the door latch guard.
VII.
ADDITIONAL INFORMATION
A.
Previous similar events at the same plant:
There have been no similar events at SQN in the past three years with the same underlying
cause
B.
Additional Information
None.
C.
Safety System Functional Failure Consideration:
This condition did not result in a safety system functional failure as defined in NEI 99-02.
D.
Scrams with Complications Consideration:
There was no scram associated with this event.
VIII.
COMMITMENTS
None.
I.
PLANT OPERATING CONDITIONS BEFORE THE EVENT
At the time of the event, Sequoyah Nuclear Plant (SQN) Unit 1 and Unit 2 were in Mode 1 at 100 percent rated thermal power.
II.
DESCRIPTION OF EVENTS A.
Event:
On May 3, 2016, at 0833 Eastern Daylight Time (EDT), Security received an open door [EIIS Code DR] alarm [EIIS Code ALM] on a Main Control Room [EIIS Code NA] (MCR) door. At 0847, Security notified the MCR staff that the door would not maintain its seal and would not latch. Security remained in the vicinity of the door the remainder of the time it was unable to close. The leak was approximately a one-eighth-inch opening across the entire sealing surface [SEAL] of the door. As a result, both units entered Technical Specification (TS) 3.7.10, Control Room Emergency Ventilation System [EIIS Code VI](CREVS), Condition B, due to the inoperability of the Control Room Envelope (CRE).
During inspection of the sealing surface, a screw was found wedged under the rubber seal on the bottom edge of the door. The screw was the bottom screw from the door latch guard.
At 0855, the screw was removed and the door was verified to close as designed. CREVS was declared operable and TS 3.7.10, Condition B, was exited.
At 1513, an 8-hour non-emergency event notification (EN 51900) was made to the NRC in accordance with 10 CFR 50.72(b)(3)(v)(D), as an event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to mitigate the consequences of an accident. This LER is submitted based on NUREG-1022, Revision 3, Section 3.2.7 guidance which identifies that the requirements of 10 CFR 50.73(a)(2)(v)(D) apply when a system that is used to mitigate the consequences of an accident was declared TS inoperable and no redundant system or equipment could be declared operable. Engineering evaluation determined the requirement to support long term occupancy would not have been affected to the point that would have resulted in exceeding the design basis dose assumptions for the MCR operators. Therefore, no loss of safety function occurred.
The screw was the bottom screw from the door latch guard and appears to have stripped loose and fallen out.
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.
SEQUENTIAL NUMBER 003 REV NO.
00 C.
Dates and approximate times of occurrences
Date/Time (EDT) 05/03/16, 0833 05/03/16, 0847 05/03/16, 0855
Description
Security received an open door alarm on a MCR door.
Security notified MCR staff of the door alarm and the door was incapable of closure. Both units enter TS 3.7.10, Condition B, due to the inoperability of the CRE.
After investigation, a screw was found, removed, and the door verified to close as designed. Both units exit TS 3.7.10, Condition B.
D.
Manufacturer and model number of each component that failed during the event
The failed component was associated with the door latch guard for the MCR door. The door latch guard is model number 1625, manufactured by Precision Hardware, Inc.
E.
Other systems or secondary functions affected
There were no systems or secondary functions affected by this event.
F.
Method of discovery of each component or system failure or procedural error
Security received an open door alarm associated with the MCR door.
G.
The failure mode, mechanism, and effect of each failed component, if known:
The screw that prevented the MCR door from closing was the bottom screw from the door latch guard and appears to have stripped loose and fallen into the rubber seal around the base of the MCR doorframe preventing the door from closing.
H.
Operator actions
Following notification of the issue to the MCR operators, both CREVS trains were declared inoperable in accordance with TS 3.7.10, Condition B, due to the inoperability of the CRE. MCR staff contacted individuals to evaluate and repair as necessary. Additionally, mitigating actions were initiated and met by verifying the availability of Potassium Iodine and self contained breathing apparatus to MCR operators within the CRE.
I.
Automatically and manually initiated safety system responses
There were no automatic or manual 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:
The cause of the event was the bottom screw in the door latch guard appears to have stripped loose and fallen into the rubber seal around the base of the MCR door frame preventing closure of the door.
B.
The cause(s) and circumstances for each human performance related root cause:
There was no human performance related root cause.
IV
ANALYSIS OF THE EVENT
The CREVS is a safety related Engineered Safety Features system required to operate during design basis accidents (DBAs) to mitigate the radiological consequences to the control room operators. The CREVS is designed to maintain a habitable environment in the CRE for a mission time of 30 days of continuous occupancy after a DBA without exceeding a 5 rem whole body dose or its equivalent to any part of the body. The operability of the CRE boundary must be maintained to ensure that the inleakage of unfiltered air into the CRE will not exceed the inleakage assumed in the licensing basis analysis of DBA consequences to CRE occupants. Additionally, the CRE boundary ensures occupants are protected from hazardous chemicals and smoke.
Engineering evaluation concluded that the requirement to support long term occupancy would not have been affected to the point that would have resulted in exceeding the design basis dose assumptions for the control room operators as the assumed unfiltered air inleakage would not have been exceeded. Therefore, the CREVS and the CRE would have been able to fulfill the required 30 days of continuous occupancy after a DBA.
V
ASSESSMENT OF SAFETY CONSEQUENCES
The temporary loss of abilityto close the MCR door did not challenge nuclear or radiological safety. No actual loss of safety function occurred. The CREVS maintained the ability to limit MCR operator doses below the required limits.
A.
Availability of systems or components that could have performed the same function as the components and systems that failed during the event:
Although the MCR door was ajar, the CREVS maintained the ability to limit MCR operator doses below the required limits.
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:
The event did not occur when the reactor was shutdown.
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 elapsed time from discovery of the open door rendering the CRE inoperable until the CRE was restored to operable status was 22 minutes.
VI.
CORRECTIVE ACTIONS
This event was entered into the Tennessee Valley Authority Corrective Action Program under Condition Report (CR) 1166927.
A.
Immediate Corrective Actions
MCR Operators contacted various organizations to investigate why the door would not close. During inspection of the sealing surface around the MCR door, a screw was found and removed. The MCR door was closed and TS 3.7.10, Condition B, was exited for both units.
B.
Corrective actions to reduce probability of similar events occurring in the future:
Corrective actions include evaluating existing preventive maintenance instructions associated with CREVS boundary doors to ensure screws are tightened, as needed, on a routine basis.
Additional actions include:
Initiating a work order to replace the missing screw on the door latch guard.
VII.
ADDITIONAL INFORMATION
A.
Previous similar events at the same plant:
There have been no similar events at SQN in the past three years with the same underlying
cause
B.
Additional Information
None.
C.
Safety System Functional Failure Consideration:
This condition did not result in a safety system functional failure as defined in NEI 99-02.
D.
Scrams with Complications Consideration:
There was no scram associated with this event.
VIII.
COMMITMENTS
None.YEAR 2016
- 6. LER NUMBER SEQUENTIAL NUMBER 003 REV NO.
00