05000390/LER-2021-001, Control Room Emergency Ventilation System Inoperable Due to Main Control Room Door Being Left Open
| ML21110A087 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 04/20/2021 |
| From: | Anthony Williams Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WBL-21-012 LER 2021-001-00 | |
| Download: ML21110A087 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3902021001R00 - NRC Website | |
text
1V4 TENNESSEE VALLEY AUTHORITY Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 WBL-21 -012 April 20, 2021 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Units 1 and 2 Facility Operating License Nos. NPF-90 and NPF-96 NRG Docket Nos. 50-390 and 50-391 10 CFR 50.73
Subject:
Licensee Event Report 390/2021-001-00, Control Room Emergency Ventilation System Inoperable due to Main Control Room Door Being Left Open This submittal provides Licensee Event Report (LER) 390/2021-001-00. This LER provides details concerning the inoperability of the Control Room ventilation system from a Main Control Room door being left open. This condition is being reported as an event or condition that could have prevented fulfillment of a safety function in accordance with Title 10 of the Code of Federal Regulation (10 CFR) 50.73(a)(2)(v)(D).
There are no new regulatory commitments contained in this letter. Please direct any questions concerning this matter to Tony Brown, WBN Licensing Manager, at (423) 365-7720.
nthony L. Williams IV Site Vice President Watts Bar Nuclear Plant
U.S. Nuclear Regulatory Commission WBL-21-012 Page 2 April 20, 2021
Enclosure:
LER 390/2021-001-00, Control Room Emergency Ventilation System Inoperable due to Main Control Room Door Being Left Open cc (w/Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Region II
ENCLOSURE Tennessee Valley Authority Watts Bar Nuclear Plant Unit 1 LER 390/2021-001-00, Control Room Emergency Ventilation System Inoperable due to Main Control Room Door Being Left Open
Abstract
At 1511 Eastern Standard Time (EST) on March 1, 2021, a Main Control Room (MCR) alarm was received for low control room positive pressure. In response to the alarm, a Control Room Envelope (CRE) door was found ajar and immediately closed. Technical Specification Limiting Condition for Operation (LCO) 3.7.10, Control Room Emergency Ventilation System (CREVS), was declared not met for both trains and Condition B entered. At 1513 EST on March 1, 2021, the alarm cleared, CREVS was declared operable and LCO 3.7.10, Condition B was exited.
The direct cause of this event was a human performance error when an individual traversing the control building complex did not fully challenge and ensure a MCR envelope boundary door was properly latched and secured.
Contributing to this event, standards had not been properly established, communicated, and reinforced with plant staff related to operation of plant doors. Immediate corrective actions included closing the MCR door and coaching the individual. Actions to reduce the probability of recurrence include the development and communication of management expectations associated with operating plant doors.
This condition is being reported as an event or condition that could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident in accordance with 10 CFR 50.73(a)(2)(v)(D).
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I.
Plant Operating Conditions Before the Event
Watts Bar Nuclear Plant (WBN) Unit 1 was in Mode 1 at 100 percent rated thermal power (RTP) and Unit 2 was in Mode 1 at 90 percent RTP.
II.
Description of Event
A. Event Summary
On March 1, 2021 at 1511 Eastern Standard Time (EST), a Main Control Room (MCR) alarm was received for low control room positive pressure. In response to the alarm, a Control Room Envelope (CRE) door {EIIS:DR} was found ajar and immediately closed. Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.10, Control Room Emergency Ventilation System (CREVS) {EIIS:VI}, was declared not met for both trains and Condition B entered. At 1513 EST on March 1, 2021, the alarm cleared, CREVS was declared operable and LCO 3.7.10, Condition B was exited.
This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(v)(D), as an event or condition that could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident.
B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event No inoperable structures, systems, or components contributed to this condition.
C. Dates and approximate times of occurrences
Date Time (EST)
Event 03/01/21 1511 MCR alarm was received for low control room pressue. TS LCO 3.7.10 was declared no met for both trains and Condition B entered. The MCR door was manually closed and latched.
03/01/21 1513 Units 1 and 2 exited TS LCO 3.7.10, Condition B due to annunciators clearing.
D. Manufacturer and model number of each component that failed during the event
No equipment failures occurred during the event.
Page 3 of 5 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Watts Bar Nuclear Plant, Unit 1 05000-390 YEAR SEQUENTIAL NUMBER REV NO.
2021
- - 001
- - 00
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
Plant alarms indicated a low MCR positive pressure. The response procedure for low MCR pressure requires that the MCR doors be checked for proper closure, at which time door C036 was found open.
G. Failure mode, mechanism, and effect of each failed component No equipment failures during this event
H. Operator actions
Operators performed the Alarm Response Instruction (ARI) and shut door C036.
I.
Automatically and manually initiated safety system responses
The MCR low pressure alarm properly actuated when the pressure door was left open.
III.
Cause of the Event
A. Cause of each component or system failure or personnel error
No equipment failures occurred during this event.
The direct cause of this event was a human performance error when an individual traversing the control building complex did not fully challenge and ensure a MCR envelope boundary door was properly latched and secured. Contributing to this event, standards had not been properly established, communicated, and reinforced with plant staff related to operation of plant doors.
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Page 4 of 5 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Watts Bar Nuclear Plant, Unit 1 05000-390 YEAR SEQUENTIAL NUMBER REV NO.
2021
- - 001
- - 00 IV.
Analysis of the Event
The CRE is required to be operable in Modes 1 through 6 and during movement of irradiated fuel assemblies. Operability requires integrity of the CRE such that it will have a low unfiltered in-leakage during accident conditions to maintain the dose to operators within the requirements of Criterion 19, of 10 CFR 50, Appendix A. Technical Specifications allow the CRE boundary to be opened intermittently under administrative control, normally to allow routine personnel ingress and egress from the control room envelope. Administrative controls in the case of boundary doors are that an individual is in control of the door when it is opened.
On March 1, 2021, an individual traversing the control building complex did not fully challenge and ensure the MCR boundary door C036 was properly latched and secured. This action left this door ajar, resulting in operations personnel entering TS LCO 3.7.10, CREVS, for one or more CREVS trains inoperable due to an inoperable CRE boundary. Low positive pressure (less than 0.125 inches of water gauge WG) in the control room for 90 seconds results in a control room alarm. Upon receipt of the alarm, the CRE door was promptly closed. For this event, the CRE boundary was restored approximately two minutes after the MCR alarm was received. An engineering evaluation of a similar event is bounding for this event, and concludes that General Design Criteria (GDC) 19 dose limits to operators would not be exceeded when considering closure of the pressure boundary door for accidents analyzed in the Updated Final Safety Analysis Report.
V.
Assessment of Safety Consequences
A review of this event indicates, when considering the actual system capability and the response of equipment and personnel, a loss of safety function capable of impacting public health and safety did not occur with respect to the control room. This equipment is not analyzed in the site specific Probabilistic Risk Assessment (PRA), but the impact of this door on an accident would be 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 CRE equipment designed to protect the pressure boundary remained operable.
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 For this event, the MCR envelope door was closed within two minutes of receipt of the MCR alarm.
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Page 5 of 5 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Watts Bar Nuclear Plant, Unit 1 05000-390 YEAR SEQUENTIAL NUMBER REV NO.
2021
- - 001
- - 00 VI.
Corrective Actions
This event was entered into the Tennessee Valley Authoritys (TVA) Corrective Action Program and is being tracked under Condition Report (CR) 1675314.
A. Immediate Corrective Actions
The open control room door was identified and promptly closed. The worker was coached on this issue. Administrative controls were put in place to ensure proper door operation pending further investigation.
B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future Actions to reduce the probability of recurrence include the development and communication of management expectations associated with operating plant doors. An effectiveness review plan has been approved to track and validate improvement of future human performance behaviors associated with proper door operation.
VII.
Previous Similar Events at the Same Site
LER 391/2020-001-00, reported an instance where the control room boundary door had been left open due to personnel error and promptly closed by operations in response to a low control room positive pressure alarm. The cause of this event is similar.
There have been other events in with the MCR doors such as LER's 390/2020-003-00,390/2019-001-00, 390/2019-004-00, 390/2018-003-00, 390/2018-004-00, 390/2017-007-001 and 390/2017-014-00 with similar causes.
VIII.
Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.
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