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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 55421 | 20 August 2021 13:05:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Auxiliary Building Gas Treatment Systems Inoperable | At 0905 EDT, it was discovered both trains of Auxiliary Building Gas Treatment System (ABGTS) were simultaneously INOPERABLE due to the auxiliary building secondary containment enclosure (ABSCE) being inoperable; therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v). There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. ABSCE and ABGTS were returned to operable.
This is a retraction of the 8-hour Immediate notification (EN55421) made to the NRC by Sequoyah Nuclear Plant on August 20, 2021. Sequoyah is retracting this event notification based on the following: Regulatory Guidance in NUREG-1022, Revision 3, 'Event Reporting Guidelines 10 CFR 50.72 and 50.73', Sections 2.8 'Retraction and Cancellation of Event Reporting', and 4.2.3 'ENS Notification Retraction'. On August 20, 2021 personnel found door A-118 open. This door is part of the ABSCE. During the initial investigation, it was found that other personnel had the door open using Precaution A of 0-TI-SXX-000-016.0 which allows material access through ABSCE doors if the door is closed within three minutes. It was found that A-118 door had been open for greater than three minutes. With this door open the ABSCE was beyond its capability for ABGTS fan to maintain the required pressure during an Aux. Building Isolation. Thus, the site declared the ABSCE and both Trains of ABGTS inoperable per LCO 3.7.12 Conditions A, B and E. With the ABSCE being a single train system, this caused a condition that "could have prevented the fulfillment of the safety function" which requires an Immediate Notification to the NRC within eight hours under 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.72 (b)(3)(v)(D). This Immediate Notification was reported on August 20, 2021 at 1600 EDT. It was later determined that at 'Time of Discovery', although Door A-118 was open, it was not obstructed, the door was open by normal means, was capable of being closed and was now attended. The time requirement per 0-TI-SXX-000-016.0 for closure of an open ABSCE door is within three minutes of notification. Although the individual found holding the door was unaware of the requirement of 0-TI-SXX-000-016.0 to close the door, communications were established and the Main Control Room (MCR), upon discovery of the 'Open Door', could have directed closure starting at the Time of Discovery if required. Since the MCR was aware the door was open, had communications established with personnel at the door, the door was capable of closure and not restricted, the three minute closure requirement of 0-TI-SXX-000-016.0 was met. Subsequently, the door was closed within approximately two minutes of notification to close. The closure of the door with these procedural measures met confirmed the integrity of the ABSCE and therefore Operability of ABGTS. Based on the above critical thinking, entry into LCO 3.7.12 Condition A, B, and E was retracted on August 22, 2021 at 2044 EDT. With the LCO conditions retracted and the above determination that at the Time of Discovery safety function was maintained, the Immediate Notification per 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.72 (b)(3)(v)(D) was not required. The issue of Past Operability remains for instances in time that the door did not have appropriate compensatory measures in place. Any further notification required for this event will be submitted as a Licensee Event Report. Notified R2DO (Miller) | Secondary containment Auxiliary Building Gas Treatment System | |
| ENS 55379 | 25 July 2021 16:38:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Surveillence Frequency Exceeded for Ice Condenser Temperature | At 1238 EDT on July 25, 2021, the Unit 2 Ice Bed became INOPERABLE due to SR (Surveillance Requirement) 3.6.12.1 exceeding its surveillance interval. LCO (Limiting Condition for Operation) 3.6.12 was declared not met as required by SR 3.0.1. SR 3.6.12.1 to verify maximum ice bed temperature is less than or equal to 27 degrees F could not be completed due to a failed temperature recorder. The results of the backup method of temperature verification were verified satisfactory at 1258 EDT and the LCO condition was then exited. The ice bed is a single train system which functions to control radiation release and mitigate the consequences of an accident by scrubbing radioactive iodine and providing a heat sink to limit containment pressure within design limits, therefore the requirements of 10 CFR 50.72 (b) (3) (v) (C) and (D) were met. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. | 05000327/LER-2021-001, & LER 2021-001-00 for Sequoyah Nuclear Plant, Units 1 & 2, Ice Bed Inoperable Due to Exceeding Surveillance Requirement Frequency & LER 2021-001-00 for Sequoyah Nuclear Plant Units 1 & 2 Ice Bed Inoperable Due to Exceeding Surveillance Requirement Frequency | |
| ENS 54800 | 24 July 2020 05:05:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Ice Bed Inoperable | At 0105 (EDT) on 7/24/20 it was discovered Unit 2 Ice Bed was INOPERABLE. Therefore, since this is a single train system the requirements of 50.72 (b)(3)(v)(C) and (D) have been met. This condition is being reported as an 8-hour non-emergency NRC Notification. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. This condition put the unit in a 48-hour LCO. The old chillers were put into service to bring the temperature of the ICE bed down. At 0833 EDT, the technical specification limit was no longer exceeded and the unit exited the LCO. | ||
| ENS 53751 | 24 November 2018 05:00:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Auxiliary Building Door Blocked Open | At 1420 (EST) on November 24, 2018, operators discovered that a door was blocked open creating a breach of the auxiliary building secondary containment enclosure (ABSCE) boundary that exceeded the allowed ABSCE breach margin (of three minutes). As a result, Unit 1 entered Technical Specification Limiting Condition of Operation (LCO) 3.7.12 Condition B for two trains of Auxiliary Building Gas Treatment System (ABGTS) inoperable due to an inoperable ABSCE boundary in MODE 1, 2, 3, or 4, and both Units entered Condition E for one required ABGTS train inoperable with fuel stored in the spent fuel pool. In MODES 1, 2, 3, and 4, the analysis of the loss of coolant accident (LOCA) assumes that radioactive materials leaked from the Emergency Core Cooling System are filtered and absorbed by the ABGTS. For the fuel handling accident, the analysis assumes that the ABSCE boundary is capable of being established to ensure releases from the auxiliary and containment buildings are consistent with the dose consequence analysis. The event is reportable in accordance with 10 CFR 50.72(b)(3)(v) as an event or condition that could have prevented fulfillment of the safety function of structures or systems that are needed to: (C) control the release of radioactive material and (D) mitigate the consequences of an accident. No actual LOCA or fuel handling accident occurred while both trains of ABGTS were inoperable. The condition had no impact on the health and safety of the public. The NRC Resident Inspector has been notified. This situation occurred because of maintenance activities. A breeching permit had been initiated however, the required personnel to ensure the door could be closed within the required three minutes were not assigned. The door was closed approximately 15 minutes after the situation was noticed. | Secondary containment Auxiliary Building Gas Treatment System Emergency Core Cooling System | |
| ENS 52597 | 7 March 2017 13:30:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Breach in Auxiliary Building Secondary Containment | At 0830 (EST) on March 7, 2017, operators discovered that on March 3, 2017 at 2046 a door was blocked open creating a breach of the auxiliary building secondary containment enclosure (ABSCE) boundary that exceeded the allowed ABSCE breach margin. As a result, both Unit 1 and Unit 2 entered Technical Specification Limiting Condition of Operation (LCO) 3.7.12 Condition B for two trains of Auxiliary Building Gas Treatment System (ABGTS) inoperable due to an inoperable ABSCE boundary in MODE 1, 2, 3, or 4. The condition has been corrected and ABGTS was restored to operable as of 0949 March 7, 2017. In MODES 1, 2, 3, and 4, the analysis of the loss of coolant accident (LOCA) assumes that radioactive materials leaked from the Emergency Core Cooling System are filtered and adsorbed by the ABGTS. For the fuel handling accident, the analysis assumes that the ABSCE boundary is capable of being established to ensure releases from the auxiliary and containment buildings are consistent with the dose consequence analysis. The event is reportable in accordance with 10 CFR 50.72(b)(3)(v) as an event or condition that could have prevented fulfillment of a safety function of structures or systems that are needed to: (C) control the release of radioactive material and (D) mitigate the consequences of an accident. No actual LOCA or fuel handling accident occurred while both trains of ABGTS were inoperable. The condition had no impact on the health and safety of the public. The NRC Resident Inspector has been notified. | Secondary containment Auxiliary Building Gas Treatment System Emergency Core Cooling System | 05000327/LER-2017-001 |
| ENS 49476 | 27 October 2013 21:30:00 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | Auxiliary Building Gas Treatment System Inoperable | At 1730 EDT on 10/27/2013, SQN (Sequoyah Nuclear) discovered that Unit 1 containment penetration X-108 had a maintenance flange installed with a service air connection attached. The service air connection was connected to a temporary air compressor supplying air to maintenance loads inside Unit 1 containment. Contrary to the requirements of the breaching permit, personnel were not stationed at the penetration to isolate the service air connection in the event of the air line rupturing inside Unit 1 containment or upon initiation of an auxiliary building isolation signal. Since the Unit 1 containment is open to the auxiliary building as part of outage activities, if the service air line had ruptured, the additional air into the Unit 1 containment could have exceeded the capacity of the Auxiliary Building Gas Treatment System (ABGTS) and potentially have impacted the ability of the ABGTS to perform its design safety function. This resulted in both trains of the ABGTS being declared inoperable requiring Unit 2 to enter the action of LCO 3.0.3. The service air line was isolated immediately and Unit 2 exited the action of LCO 3.0.3 at 1732 EDT. At the time of the event, Unit 1 was defueled and did not require ABGTS to be operable. Unit 1 subsequently entered Mode 6 at 1904 EDT on 10/27/2013 and is currently conducting refueling operations. Unit 2 remains in Mode 1, 100% power and stable. There were no actual operational impacts to either unit. The licensee has notified the NRC Resident Inspector.
Sequoyah Nuclear Plant, Units 1 and 2, are retracting the 8 hour non-emergency notification made on October 27, 2013 at 2229 EDT (EN# 49476). The notification on October 27, 2013, reported that if the service air line (associated with penetration X-108) had ruptured, the additional air into the Unit 1 containment could have exceeded the capacity of the Auxiliary Building Gas Treatment System (ABGTS) and potentially have impacted both trains of ABGTS from performing its safety function(s). Subsequent engineering analysis concluded acceptable margin was available. Both trains of ABGTS would have remained operable and capable of performing its design function(s) at all times. The engineering analysis results are captured in the licensee's corrective action program. Based on the new analysis, the condition reported in EN #49476 did not result in a potential uncontrolled radioactive release. This event report is being retracted. The NRC Resident Inspector has been briefed on the analysis results and informed of this retraction. Notified R2DO (McCoy). | Auxiliary Building Gas Treatment System |