05000328/LER-2019-001, Component Cooling Water System Train a Inoperable Longer than Allowed by Technical Specifications

Component Cooling Water System Train a Inoperable Longer than Allowed by Technical Specifications

ML19322A627
Person / Time
Site:	Sequoyah
Issue date:	11/15/2019
From:	Rasmussen M Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 2019-001-00
Download: ML19322A627 (8)

LER-2019-001, Component Cooling Water System Train a Inoperable Longer than Allowed by Technical Specifications

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
3282019001R00 - NRC Website

text

Tennessee Valley Authority, Sequoyah Nuclear Plant, P.O. Box 2000, Soddy Daisy, Tennessee 37384 November 15, 2019 10 CFR 50.73 ATTN:

Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Unit 2 Renewed Facility Operating License No. DPR-79 NRC Docket No. 50-328

Subject:

Licensee Event Report 50-328/2019-001 -00, Component Cooling Water System Train A Inoperable Longer Than Allowed by Technical Specifications The enclosed licensee event report provides details concerning the inoperability of one train of the Component Cooling Water System for longer than allowed by Technical Specifications.

This report is being submitted in accordance with 10 CFR 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the unit's Technical Specification. Additionally, this event is being reported in accordance 10 CFR 50.73(a)(2)(v), as an event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to:

(B) remove residual heat 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. Andrew McNeil, acting Site Licensing Manager, at (423) 843-8098.

Respectfully, Matthew Rasmussen Site Vice President Sequoyah Nuclear Plant Enclosure: Licensee Event Report 50-328/2019-001-00 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 APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)

, the NRC may not conduct or sponsor, anda person is notrequired to respond to,the informationcollection.

3.LERNUMBB*

Sequoyah Nuclear Plant Unit 2 05000-328 YEAR SEQUENTIAL NUMBER REV NO.

- 00 B.

2019 001 train of the CCS was inoperable for approximately 72 days and 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> without completing Required Action A.1 or C.1, this is a condition prohibited by TS and is therefore being reported in accordance with 10 CFR 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the unit's TS.

Additionally, a review of redundant equipment in the opposite train was performed for the timeframe between June 17, 2019, at 1723 EDT and August 28, 2019, at 2330 EDT. The review considered occurrences when Train B of the Unit 2 CCS and other equipment or systems redundant to Train A were inoperable. The review found there were forty occurrences when redundant equipment or systems in the opposite train, which included the Emergency Diesel Generators [EMS: DG], Emergency Core Cooling System (ECCS)

[EMS: CB], and the Containment Spray System [EMS: BE], were declared inoperable. As a result, this event is reportable as a Condition that Could Have Prevented the Fulfillment of a Safety Function in accordance with 10 CFR 50.73(a)(2)(v)(B) and (D).

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

June 17, 2019, 1723 The temporary modification was implemented that provided incorrect specified throttling positions for manual valve, 2-VLV-67-551.

TS LCO 3.3.7.A became applicable.

August 24, 2019 During the flush of a CCS heat exchanger, manual valve 2-VLV-67-551 was placed in one of the specified throttled positions.

Shortly thereafter, CCS alarms were received in the MCR which caused operators to terminate the flush and restore ERCW flows.

August 28, 2019 Section XI test data were evaluated and it was determined that the throttled positions implemented by the modification did not allow the required flow.

August 28, 2019, 2330 A flow balance was conducted and the correct positions were determined. TS LCO 3.3.7.A was no longer applicable.

September 20, 2019 A past operability evaluation determined that Unit 2 Train A of CCS was inoperable from June 17, 2019, at 1723 EDT until August 28, 2019, at 2330 EDT.Page 3 of 7(04-2018)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET 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 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, 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,the informationcollection.

& LER NUMBER Sequoyah Nuclear Plant Unit 2 05000-328 YEAR 2019 SEQUENTIAL NUMBER

- 001 REV NO.

- 00 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

The ECCS and Containment Spray System are systems supported by the CCS.

F.

Method of discovery of each component or system failure or procedural error

During the flush of a CCS heat exchanger, manual valve 2-VLV-67-551 was placed in one of the throttled positions determined as part of the temporary modification. Shortly after beginning the flush, CCS alarms were received in the MCR which caused operators to terminate the flush and restore ERCW flows. Subsequently,Section XI test data were evaluated and it was determined that the throttled positions implemented by the modification did not allow the required flow.

G.

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

There was no component that failed during the event.

H.

Operator actions

After receiving CCS alarms in the MCR during CCS heat exchanger flushing, operators terminated the flush and restored ERCW flows I.

Automatically and manually initiated safety system responses

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

Cause of the Event

A.

Cause of each component or system failure or personnel error

The cause of this event is the failure to adequately recognize the risk of relying on an indirect method (counting number of turns vice performance of a flow balance) to determine the throttle valve positions. The assumption that counting the number of turns would be adequate was not challenged during design reviews.Page 4 of 7(04-2018)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

<?'

7 APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 Estimated burden perresponseto 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 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, 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 conductor sponsor,anda personis notrequired to respondto,the informationcollection.

3. LER NUMBER Sequoyah Nuclear Plant Unit 2 05000-328 YEAR 2019 SEQUENTIAL NUMBER 001 REV NO.

- 00 B.

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

1)

The causes of this human performance event were:

a.

There was an assumption that the internals of MOV 2-FCV-67-146 and manual valve 2-VLV-67-551 were the same such that the throttle positions could be derived based on the equivalent number of turns between the two valves. Additionally, there was an assumption that the actuator's characteristic curve for manual valve 2-VLV-67-551 was linear.

It was later determined that the valve's actuator characteristic curve was non linear. These incorrect assumptions resulted in the determination of incorrect throttle positions.

b.

The draft version of the temporary modification required a flow balance; however, during review itwas requested that the flow balance not be performed due to the impact to the plant. There was a misunderstanding that the flowtest would have been required during the outage (the temporary modificationwas developed during an ongoing outage) which would have impacted the outage schedule. Because of this misunderstanding the decision was made to revise the temporary modification to no longer require a flow balance.

2)

The circumstances associated with this human performance event were:

a.

The individuals involved were utility personnel in the Engineering department and they were not licensed.

b.

The temporary modificationwas developed during the Unit2 fall outage of 2018 in a short period of time with 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> shift coverage. The fast track schedule and the miscommunication that a flow balance test would be required during the outage contributed to the decision to not perform the flow test.

IV.

Analysis of the Event

The CCS provides a heat sink for the removal of process and operating heat from safety related components during a Design Basis Accident (DBA) or transient. During normal operation, the CCS also provides this function for various nonessential components, as well as the spent fuel storage pool. The CCS serves as a barrier to the release of radioactive byproducts between potentially radioactive systems and the ERCW System, and thus to the environment. Some of the systems served by the CCS are: (1) Reactor Coolant System, (2) Residual Heat Removal System, (3) Chemical and Volume Control System, (4) Safety injection System, and (5) Containment Spray System.Page 5 of 7(04-2018)

• " 0 U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET 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 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, 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,the informationcollection.

3. LER NUMBER Sequoyah Nuclear Plant Unit 2 05000-328 YEAR 2019 SEQUENTIAL NUMBER 001 REV NO.

- 00 The CCS trains are independent of each other to the degree that each has separate controls and power supplies and the operation of one does not depend on the other. In the event of a DBA, one CCS train is required to provide the minimum heat removal capability assumed in the safety analysis for the systems to which it supplies cooling water. To ensure this requirement is met, two trains of CCS must be operable. At least one CCS train will operate assuming the worst case single active failure occurs coincident with a loss of offsite power.

The design basis of the CCS is for one train to remove the post loss of coolant accident (LOCA) heat load from the containment sump fluid during the recirculation phase. This provides a gradual reduction in the temperature of the fluid as the fluid is supplied to the Reactor Coolant System by the ECCS pumps.

An Engineering evaluation determined that had a Unit 2 LOCA occurred (or any transient requiring Unit 2 Safety Injection [SI]), the ERCW System and CCS would have been able to perform their UFSAR required functions of core cooling and containment vessel protection for the accident unit.

Additionally, the ERCW System and CCS would have been able to provide the required equipment cooling functions for the non-accident unit (Unit 1).

The evaluation also determined that had a Unit 1 LOCA occurred (or any transient requiring Unit 1 SI), the Unit 2 A Train of CCS would not have been able to perform its required equipment cooling function for the non-accident unit (Unit 2) without intervention from Operations. Based on this determination, Unit 2 A Train of CCS was declared inoperable from June 17, 2019, to August 28, 2019.

V.

Assessment of Safety Consequences

There were no actual safety consequences as a result of this event.

A Probabilistic Risk Assessment evaluation of this condition determined there was no risk increase for Unit 1, and the risk increase for Unit 2 during the time this condition existed was 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:

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.Page 6 of 7(04-2018)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET 7

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020

, the NRC may not conduct or sponsor,anda personis notrequired to respondto, the informationcollection.

3. LB?NUMBER Sequoyah Nuclear Plant Unit 2 05000-328 YEAR 2019 SEQUENTIAL NUMBER

- 001 REV NO.

- 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:

Initially, the Unit 2 A Train of the ERCW System was declared inoperable at 1658 EDT on August 28, 2019. After performance of a flow balance test, the Unit 2 A Train of the ERCW System was declared operable at 2330 EDT on August 28, 2019. The elapsed time was approximately 6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. After completion of the past operability evaluation it was determined that the event affected the Unit 2 A Train of the CCS vice the ERCW System.

VI.

Corrective Actions

The reactor trip event was entered into the Tennessee Valley Authority Corrective Action Program (CAP) under CR 1544846.

A.

Immediate Corrective Actions

Once the issue was identified a flow balance test was completed to determine the correct throttle positions for manual valve 2-VLV-67-551.

B.

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

Corrective actions include completing a required reading and lessons learned for the Engineering Department regarding the event and the circumstances associated with the event. The lessons learned will include: (1) adequately identifying risks and actions to mitigate error precursors when developing design changes, (2) the importance of documenting critical thinking and challenges to designs formerly on comment sheets, (3) the compensating actions that should be implemented when there is time pressure to perform a task, and (4) properly identifying and validating assumptions when developing design changes.

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 7 of 7