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

ML21265A503
Person / Time
Site:	Sequoyah
Issue date:	09/22/2021
From:	Marshall T Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 2021-001-00, LER 2021-002-00
Download: ML21265A503 (12)

LER-2021-001, & LER 2021-001-00 for Sequoyah Nuclear Plant, Units 1 & 2, Ice Bed Inoperable Due to Exceeding Surveillance Requirement Frequency

Event date:
Report date:
3272021001R00 - NRC Website

text

Sequoyah Nuclear Plant, Post Office Box 2000, Soddy Daisy, Tennessee 37384 September 22, 2021 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 Reports 50-327/2021-002-00, Ice Bed Inoperable Due to Exceeding Surveillance Requirement Frequency and 50-328/2021-001-00, Ice Bed Inoperable Due to Exceeding Surveillance Requirement Frequency The enclosed licensee event reports provide details concerning inoperable Unit 1 and Unit 2 ice beds due to exceeding the Frequency specified by Surveillance Requirement 3.6.12.1.

These events are being reported, in accordance with 10 CFR 50.73(a)(2)(v), as events or conditions that could have prevented the 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.

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, Thomas Marshall Site Vice President Sequoyah Nuclear Plant

Enclosures:

Licensee Event Report 50-327/2021-002-00 Licensee Event Report 50-328/2021-001-00 cc: NRC Regional Administrator - Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

LICENSEE EVENT REPORT (LER) Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to (See Page 3 for required number of digits/characters for each block) Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not (See NUREG-1022, R.3 for instruction and guidance for completing this conduct or sponsor, and a person is not required to respond to, a collection of information unless form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) the document requesting or requiring the collection displays a currently valid OMB control number.

1. Facility Name 2. Docket Number 3. Page Sequoyah Nuclear Plant Unit 1 05000327 1 OF 5

4. Title Ice Bed Inoperable Due to Exceeding Surveillance Requirement Frequency

5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved Facility Name Docket Number Sequential Rev Month Day Year Year Number Month Day Year NA No. 05000 Facility Name Docket Number 09 26 2018 2021 - 002 - 00 09 22 2021 NA 05000

9. Operating Mode 10. Power Level 1 100

11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 10 CFR Part 20 20.2203(a)(2)(vi) 50.36(c)(2) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2201(b) 20.2203(a)(3)(i) 50.46(a)(3)(ii) 50.73(a)(2)(v)(A) 10 CFR Part 73 20.2201(d) 20.2203(a)(3)(ii) 50.69(g) 50.73(a)(2)(v)(B) 73.71(a)(4) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C) 73.71(a)(5) 20.2203(a)(2)(i) 10 CFR Part 21 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D) 73.77(a)(1)(i) 20.2203(a)(2)(ii) 21.2(c) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 73.77(a)(2)(i) 20.2203(a)(2)(iii) 10 CFR Part 50 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 73.77(a)(2)(ii) 20.2203(a)(2)(iv) 50.36(c)(1)(i)(A) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(v) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)

Other (Specify here, in Abstract, or in NRC 366A).

12. Licensee Contact for this LER Licensee Contact Phone Number (Include Area Code)

Scott Bowman 423.843.6910

13. Complete One Line for each Component Failure Described in this Report Cause System Component Manufacturer Reportable To IRIS Cause System Component Manufacturer Reportable To IRIS X BC TR Y006 N

14. Supplemental Report Expected Month Day Year

15. Expected Submission Date No Yes (If yes, complete 15. Expected Submission Date)

16. Abstract (Limit to 1560 spaces, i.e., approximately 15 single-spaced typewritten lines)

On September 26, 2018, at 1525 eastern daylight time (EDT), the SQN Unit 1 ice bed temperature monitoring system stopped providing accurate data for the ice bed due to the failure of a temperature recorder in the system. The data is used to complete a surveillance instruction (SI) to verify the ice bed temperature does not exceed 27 degrees Fahrenheit (F) as required by Technical Specification (TS) Surveillance Requirement (SR) 3.6.12.1 at a Frequency of every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. At 2333, SR 3.6.12.1 was successfully performed; however, this exceeded the specified Frequency plus the 25 percent extension allowed by SR 3.0.2 by 32 minutes (SR 3.6.12.1 had last been completed at 0801). Therefore, the Unit 1 ice bed was declared inoperable for 32 minutes from 2301 until 2333.

The cause of the Unit 1 ice bed inoperability was the failure of the ice bed temperature monitoring system temperature recorder. The corrective action for this event was to replace the ice bed temperature monitoring system temperature recorder. This was completed via Engineering Change Package SQN-19-877 and Work Order 121519017.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 1 05000-327 NUMBER NO.

2021 - 002 - 00 NARRATIVE I. Plant Operating Conditions Before the Event At the time of the event, Sequoyah Nuclear Plant (SQN) Unit 1 was in Mode 1 at 100 percent rated thermal power.

II. Description of Event A. Event Summary:

On September 26, 2018, at 1525 eastern daylight time (EDT), the SQN Unit 1 ice bed

[EIIS: BC] temperature monitoring system stopped providing accurate data for the ice bed due to the failure of a temperature recorder [EIIS: TR] in the system. The data is used to complete a surveillance instruction (SI) to verify the ice bed temperature does not exceed 27 degrees Fahrenheit (F) as required by Technical Specification (TS) Surveillance Requirement (SR) 3.6.12.1 at a Frequency of every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Due to the failure, Main Control Room (MCR) operators authorized the performance of 1-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring, which requires calling in instrumentation and controls technicians to take resistance temperature detector readings on individual temperature elements inside containment.

At 2333, SR 3.6.12.1 was successfully performed; however, this exceeded the specified Frequency plus the 25 percent extension allowed by SR 3.0.2 by 32 minutes (SR 3.6.12.1 had last been completed at 0801). Therefore, the Unit 1 ice bed was declared inoperable for 32 minutes from 2301 until 2333.

This event was not identified as reportable until July 30, 2021, when a similar event occurred on SQN Unit 2 (reported in Event Notification 55379). During development of lessons learned for the Unit 2 event, Operations personnel discovered the September 26, 2018, event. The failure to provide a report in accordance with 10 CFR 50.72(b)(3)(v), as an event or condition that could have prevented the 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 was documented in Condition Report 1711038. This LER is submitted based on NUREG-1022, Revision 3, Section 3.2.7 guidance that identifies that the requirements of 10 CFR 50.73(a)(2)(v) apply when a system that is within the scope of the criterion is declared inoperable and no redundant system or equipment could be declared operable (the ice bed is a single train system).

Although the Frequency of SR 3.6.12.1 was exceeded and required the Unit 1 ice bed to be declared inoperable, the Unit 1 ice bed remained below 27 degrees F and capable of performing its required safety function to provide a heat sink during a Design Basis Accident (DBA) in containment. Therefore, no loss of safety function occurred.

NRC FORM 366A (08-2020)

Page 2 of 5

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 1 05000-327 NUMBER NO.

2021 - 002 - 00 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.

C. Dates and approximate times of occurrences:

Date/Time (EDT) Description 09/26/18, 0801 SR 3.6.12.1 successfully performed.

MCR operators recognized the Ice Bed Temperature Monitoring 1525 System was nonfunctional.

SR 3.6.12.1 declared not met due to exceeding the specified Frequency plus the 25 percent extension allowed by SR 3.0.2 2301 (15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> total). Unit 1 entered TS 3.6.12, Condition A in accordance with SR 3.0.1.

Conditional performance of SR 3.6.12.1 successfully completed.

2333 Unit 1 ice bed declared operable and TS 3.6.12, Condition A exited.

D. Manufacturer and model number of each component that failed during the event:

SQN-1-TR-061-0138 is an ice bed temperature monitoring system temperature recorder manufactured by Yokogawa Corporation of America, model number Y006/HR2500E.

E. Other systems or secondary functions affected:

There were no other systems or secondary functions affected by this event.

F. Method of discovery of each component or system failure or procedural error:

The component failure was identified by operator walkdown.

G. Failure mode, mechanism, and effect of each failed component:

The failure mode and mechanism of the component are unknown. The failure of the component caused the ice bed temperature monitoring system to become nonfunctional.

H. Operator actions:

Operations personnel authorized a conditional performance of 1-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring.

NRC FORM 366A (08-2020)

Page 3 of 5

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 1 05000-327 NUMBER NO.

2021 - 002 - 00 I. Automatically and manually initiated safety system responses:

There were no automatic or manually initiated safety system responses associated with this event.

III. Cause of the Event A. Cause of each component or system failure or personnel error:

The cause of the Unit 1 ice bed inoperability was the failure of the ice bed temperature monitoring system temperature recorder.

B. Cause(s) and circumstances for each human performance related root cause:

There was no identified human performance related root cause.

IV. Analysis of the Event:

The ice bed consists of a minimum of 1,916,000 pounds of ice stored within the ice condenser. The primary purpose of the ice bed is to provide a large heat sink in the event of a release of energy from a DBA in containment. The ice would absorb energy and limit containment peak pressure and temperature during the accident transient. Limiting the pressure and temperature reduces the release of fission product radioactivity from containment to the environment in the event of a DBA.

The Unit 1 ice bed remained below 27 degrees F and remained capable of performing its required safety function to provide a heat sink during a DBA in containment.

V. Assessment of Safety Consequences There were no actual safety consequences as a result of the ice bed inoperability. No actual loss of safety function occurred. The ice mass required for a DBA in containment was available.

A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event:

None.

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 shut down.

NRC FORM 366A (08-2020)

Page 4 of 5

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 1 05000-327 NUMBER NO.

2021 - 002 - 00 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 ice bed is a single train safety system that was rendered inoperable for approximately 32 minutes.

VI. Corrective Actions The event was entered into the Tennessee Valley Authority Corrective Action Program (CAP) under condition reports (CRs) 1711038.

A. Immediate Corrective Actions:

Operations personnel authorized the conditional performance 1-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring, so the ice bed temperatures could be obtained.

B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future:

The corrective action for this event was to replace the ice bed temperature monitoring system temperature recorder. This was completed via Engineering Change Package (ECP) SQN-19-877 and Work Order 121519017.

VII. Previous Similar Events at the Same Site:

LER 2-2021-001-00 was submitted for an inoperable Unit 2 ice bed (It was during the review of previous similar events for Unit 2 that this Unit 1 event was discovered). The cause of the Unit 2 event was the failure of the Unit 2 ice bed temperature monitoring system remote scanner. The corrective actions for the Unit 2 event include developing procedural guidance for the response required for a nonfunctional ice bed temperature monitoring system and replacement of obsolete instrumentation in the ice bed temperature monitoring system.

VIII. Additional Information There is no additional information.

IX. Commitments:

There are no commitments.

NRC FORM 366A (08-2020)

Page 5 of 5

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

LICENSEE EVENT REPORT (LER) Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to (See Page 3 for required number of digits/characters for each block) Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not (See NUREG-1022, R.3 for instruction and guidance for completing this conduct or sponsor, and a person is not required to respond to, a collection of information unless form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) the document requesting or requiring the collection displays a currently valid OMB control number.

1. Facility Name 2. Docket Number 3. Page Sequoyah Nuclear Plant Unit 2 05000328 1 OF 6

4. Title Ice Bed Inoperable Due to Exceeding Surveillance Requirement Frequency

5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved Facility Name Docket Number Sequential Rev Month Day Year Year Number Month Day Year NA No. 05000 Facility Name Docket Number 07 25 2021 2021 - 001 - 00 09 22 2021 NA 05000

9. Operating Mode 10. Power Level 1 100

11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 10 CFR Part 20 20.2203(a)(2)(vi) 50.36(c)(2) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2201(b) 20.2203(a)(3)(i) 50.46(a)(3)(ii) 50.73(a)(2)(v)(A) 10 CFR Part 73 20.2201(d) 20.2203(a)(3)(ii) 50.69(g) 50.73(a)(2)(v)(B) 73.71(a)(4) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C) 73.71(a)(5) 20.2203(a)(2)(i) 10 CFR Part 21 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D) 73.77(a)(1)(i) 20.2203(a)(2)(ii) 21.2(c) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 73.77(a)(2)(i) 20.2203(a)(2)(iii) 10 CFR Part 50 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 73.77(a)(2)(ii) 20.2203(a)(2)(iv) 50.36(c)(1)(i)(A) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(v) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)

Other (Specify here, in Abstract, or in NRC 366A).

12. Licensee Contact for this LER Licensee Contact Phone Number (Include Area Code)

Scott Bowman 423.843.6910

13. Complete One Line for each Component Failure Described in this Report Cause System Component Manufacturer Reportable To IRIS Cause System Component Manufacturer Reportable To IRIS X BC MPX Y006 N

14. Supplemental Report Expected Month Day Year

15. Expected Submission Date No Yes (If yes, complete 15. Expected Submission Date)

16. Abstract (Limit to 1560 spaces, i.e., approximately 15 single-spaced typewritten lines)

On July 25, 2021, at 0544 eastern daylight time (EDT), the SQN Unit 2 ice bed temperature monitoring system stopped providing accurate data for the ice bed. The data is used to complete a surveillance instruction (SI) to verify the ice bed temperature does not exceed 27 degrees Fahrenheit (F) as required by Technical Specification (TS) Surveillance Requirement (SR) 3.6.12.1 at a Frequency of every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Due to the failure, Main Control Room operators authorized performance of 2-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring. At 1258, SR 3.6.12.1 was successfully performed; however, the completion time exceeded the specified Frequency plus the 25 percent extension allowed by SR 3.0.2 by 20 minutes (SR 3.6.12.1 had last been completed at 2138 on July 24). Therefore, the Unit 2 ice bed was declared inoperable for 20 minutes from 1238 until 1258.

The cause of the event was the failure of the ice bed temperature monitoring system remote scanner due to an internal power supply failure. Corrective actions for this event include developing procedural guidance for the response required for a nonfunctional ice bed temperature monitoring system and replacement of obsolete instrumentation in the ice bed temperature monitoring system.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 2 05000-328 NUMBER NO.

2021 - 001 - 00 NARRATIVE I. Plant Operating Conditions Before the Event At the time of the event, Sequoyah Nuclear Plant (SQN) Unit 2 was in Mode 1 at 100 percent rated thermal power.

II. Description of Event A. Event Summary:

On July 25, 2021, at 0544 eastern daylight time (EDT), the SQN Unit 2 ice bed [EIIS: BC]

temperature monitoring system stopped providing accurate data for the ice bed due to the failure of a remote scanner [EIIS: MPX] in the system. The data is used to complete a surveillance instruction (SI) to verify the ice bed temperature does not exceed 27 degrees Fahrenheit (F) as required by Technical Specification (TS) Surveillance Requirement (SR) 3.6.12.1 at a Frequency of every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Due to the failure, Main Control Room (MCR) operators authorized performance of 2-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring, which requires calling in instrumentation and controls technicians to take resistance temperature detector readings on individual temperature elements inside containment.

At 1258, SR 3.6.12.1 was successfully performed; however, the completion time exceeded the specified Frequency plus the 25 percent extension allowed by SR 3.0.2 by 20 minutes (SR 3.6.12.1 had last been completed at 2138 on July 24). SR 3.0.1 states, in part, [f]ailure to perform a Surveillance within the specified Frequency shall be failure to meet the LCO [limiting condition for operation]. Therefore, the Unit 2 ice bed was declared inoperable for 20 minutes from 1238 until 1258.

At 1600, an 8-hour non-emergency event notification (EN 55379) was made to the NRC in accordance with 10 CFR 50.72(b)(3)(v), as an event or condition that could have prevented the 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. This LER is submitted based on NUREG-1022, Revision 3, Section 3.2.7 guidance that identifies that the requirements of 10 CFR 50.73(a)(2)(v) apply when a system that is within the scope of the criterion is declared inoperable and no redundant system or equipment could be declared operable (the ice bed is a single train system).

Although the Frequency of SR 3.6.12.1 was exceeded and required the Unit 2 ice bed to be declared inoperable, the Unit 2 ice bed remained below 27 degrees F and capable of performing its required safety function to provide a heat sink during a Design Basis Accident (DBA) in containment. Therefore, no loss of safety function occurred.

NRC FORM 366A (08-2020)

Page 2 of 6

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 2 05000-328 NUMBER NO.

2021 - 001 - 00 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.

C. Dates and approximate times of occurrences:

Date/Time (EDT) Description 07/24/21, 2138 SR 3.6.12.1 successfully performed.

The Plant Engineering Data System indicated the maximum ice bed 07/25/21, 0538 temperature was 20.93 degrees.

MCR operators recognized the Ice Bed Temperature Monitoring 0544 System was nonfunctional.

Operations personnel authorized a conditional performance of 1030 2-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring.

SR 3.6.12.1 declared not met due to exceeding the specified Frequency plus the 25 percent extension allowed by SR 3.0.2 1238 (15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> total). Unit 2 entered TS 3.6.12, Condition A in accordance with SR 3.0.1.

Conditional performance of SR 3.6.12.1 successfully completed.

1258 Unit 2 ice bed declared operable and TS 3.6.12, Condition A exited.

D. Manufacturer and model number of each component that failed during the event:

SQN-2-XS-061-0138B is an ice bed temperature monitoring system remote scanner manufactured by Yokogawa Corporation of America, model number 38826-232-12/NS-SR.

E. Other systems or secondary functions affected:

There were no other systems or secondary functions affected by this event.

F. Method of discovery of each component or system failure or procedural error:

The component failure was identified by operator walkdown.

NRC FORM 366A (08-2020)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 2 05000-328 NUMBER NO.

2021 - 001 - 00 G. Failure mode, mechanism, and effect of each failed component:

The failure mode and mechanism of the component are unknown. The failure of the component caused the ice bed temperature monitoring system to become nonfunctional.

H. Operator actions:

Operations personnel authorized a conditional performance of 2-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring.

I. Automatically and manually initiated safety system responses:

There were no automatic or manually initiated safety system responses associated with this event.

III. Cause of the Event A. Cause of each component or system failure or personnel error:

The cause of the event was the failure of the ice bed temperature monitoring system remote scanner due to an internal power supply failure.

B. Cause(s) and circumstances for each human performance related root cause:

There was no identified human performance related root cause.

IV. Analysis of the Event:

The ice bed consists of a minimum of 1,916,000 pounds of ice stored within the ice condenser. The primary purpose of the ice bed is to provide a large heat sink in the event of a release of energy from a DBA in containment. The ice would absorb energy and limit containment peak pressure and temperature during the accident transient. Limiting the pressure and temperature reduces the release of fission product radioactivity from containment to the environment in the event of a DBA.

The Unit 2 ice bed remained below 27 degrees F and remained capable of performing its required safety function to provide a heat sink during a DBA in containment.

V. Assessment of Safety Consequences There were no actual safety consequences as a result of the ice bed inoperability. No actual loss of safety function occurred. The ice mass required for a DBA in containment was available.

NRC FORM 366A (08-2020)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 2 05000-328 NUMBER NO.

2021 - 001 - 00 A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event:

None.

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 shut down.

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 ice bed is a single train safety system that was rendered inoperable for approximately 20 minutes.

VI. Corrective Actions The event was entered into the Tennessee Valley Authority Corrective Action Program (CAP) under condition reports (CRs) 1709839 and 1709881.

A. Immediate Corrective Actions:

Operations personnel authorized the conditional performance 2-SI-IXX-061-138.0, Backup Ice Condenser Temperature Monitoring, so the ice bed temperatures could be obtained.

B. Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future:

Corrective actions for this event include developing procedural guidance for the response required for a nonfunctional ice bed temperature monitoring system and replacement of obsolete instrumentation in the ice bed temperature monitoring system.

VII. Previous Similar Events at the Same Site:

LER 2-2020-001-00 was submitted for an inoperable Unit 2 ice bed. The cause of the event was the failure of a gasket on vendor supplied equipment at the flanged connection of the Auxiliary Glycol Cooling System skid. The corrective action was to repair the skid.

LER 1-2021-002-00 was submitted for an inoperable Unit 1 ice bed (although reported in 2021, the event occurred in 2018). The cause of the event was the failure of the Unit 1 ice bed temperature monitoring system temperature recorder. The corrective action was to replace the ice bed temperature monitoring system temperature recorder.

NRC FORM 366A (08-2020)

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

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 />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments LICENSEE EVENT REPORT (LER) regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e- mail to CONTINUATION SHEET Infocollects.Resource@nrc.gov, and the OMB reviewer at: OMB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk ail: oira_submission@omb.eop.gov. The NRC may not conduct or (See NUREG-1022, R.3 for instruction and guidance for completing this form sponsor, and a person is not required to respond to, a collection of information unless the document https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) requesting or requiring the collection displays a currently valid OMB control number.

1. FACILITY NAME 2. DOCKET NUMBER 3. LER NUMBER YEAR SEQUENTIAL REV Sequoyah Nuclear Plant Unit 2 05000-328 NUMBER NO.

2021 - 001 - 00 VIII. Additional Information There is no additional information.

IX. Commitments:

There are no commitments.

NRC FORM 366A (08-2020)

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