05000296/LER-2024-001, Primary Containment Isolation Valve Inoperable Due to Incorrect Motor Operated Valve Setup

Primary Containment Isolation Valve Inoperable Due to Incorrect Motor Operated Valve Setup

ML24113A201
Person / Time
Site:	Browns Ferry
Issue date:	04/22/2024
From:	Sivaraman M Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
LER 2024-001-00
Download: ML24113A201 (1)

LER-2024-001, Primary Containment Isolation Valve Inoperable Due to Incorrect Motor Operated Valve Setup

Event date:
Report date:
2962024001R00 - NRC Website

text

Post Office Box 2000, Decatur, Alabama 35609-2000

April 22, 2024 10 CFR 50.73 10 CFR 50.4(a)

ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001

Browns Ferry Nuclear Plant, Unit 3 Renewed Facility Operating License No. DPR-33 NRC Docket No. 50-296

Subject: Licensee Event Report 50-296/2024-001 Primary Containment Isolation Valve Inoperable due to Incorrect Motor Operated Valve Setup

The enclosed Licensee Event Report provides th e details of an inoperable Primary Containment Isolation Valve on Browns Ferry Nuclear Plant, Unit 3. The Tennessee Valley Authority is submitting this report in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plants Technical Specifications.

There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please cont act David J. Renn, Site Licensing Manager, at (256) 729-2636.

Respectfully,

Manu Sivaraman BFN Site Vice President

Enclosure: Licensee Event Report 50-296/2024-001 Primary Containment Isolation Valve Inoperable due to Incorrect Motor Operated Valve Setup U.S. Nuclear Regulatory Commission Page 2 April 22, 2024

cc (w/ Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant NRC Project Manager - Browns Ferry Nuclear Plant

Abstract

On February 21, 2024, it was identified that primary containment isolation valve (PCIV)[FCV] 3-FCV-001-0055 Inboard Main Steam Drain Line Isolation Valve may not have been capable of fully closing and adequately sealing during a design basis accident with design basis differential pressure due to the setup of the closing control circuit of the motor operated valve (MOV). While the vulnerability has existed since the initial design of the MOV, per the Past Operability Evaluation (POE), this condition has existed since March 16, 2014. The safety function of containment isolation was maintained by the outboard isolation valve 3-FCV-001-0056, ensuring the function of primary containment was maintained at the affected penetration.

The cause of this condition is a legacy issue related to the close control wiring scheme for 3-FCV-001-0055. This valve has had this control wiring scheme since development of the NRC Generic Letter (GL) 89-10/96-05 MOV Program.

There were two Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future: 1)

Engineering Change Package (ECP) BFN-24-12 to remove the close torque switch and LS-16 from the control circuit and use LS-8 as the close limit switch for 3-MVOP-001-0055 has been implemented and 2) reviewed all MOV Program valves in the Tennessee Valley Authority (TVA) nuclear fleet for extent of condition and no additional valves with this issue were identified.

I. Plant Operating Conditions before the Event

At the time of discovery of this event on February 21, 2024, Browns Ferry Nuclear Plant (BFN)

Unit 3 was in Mode 5 during a refueling outage.

A. Event Summary

On February 21, 2024, it was identified that primary containment isolation valve (PCIV) [FCV]

3-FCV-001-0055 may not have been capable of fully closing and adequately sealing during a design basis accident with design basis differential pressure due to the setup of the closing control circuit of the motor operated valve (MOV). While the vulnerability has existed since the initial design of the MOV, per the Past Operability Evaluation (POE), this condition has existed since March 16, 2014.

An issue associated with testing all MOV function s had been previously identified at Sequoyah Nuclear Plant (SQN) and documented in TVAs corre ctive action program in Non-Cited Violation (NCV) Condition Report (CR) 1603101. Although this issue was identified in 2020 at SQN and an extent of condition was performed at other TVA nuclear sites; this issue was not identified on this component at BFN until February 21, 2024.

Unit 3 Technical Specifications (TS) 3.6.1.3, Primary Containment Isolation Valves (PCIVs),

requires primary containment isolation valves, e xcept reactor building-to-suppression chamber vacuum breakers to be operable in Modes 1, 2, and 3. With a PCIV inoperable, TS 3.6.1.3, Action A.1 requires isolating the affected penetration flow path by use of at least one closed and de-activated automatic valve, closed manual valve, blind flange, or check valve with flow through the valve secured within four hours except for the main steam line. If this action is not met, then the unit must be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and be in Mode 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.

Due to the length of time that 3-FCV-001-0055 was inoperable, the associated TS Actions were not complied with. Additionally, mode changes were made with the PCIV inoperable which is prohibited by TS 3.0.4.

The Tennessee Valley Authority (TVA) is submitting this report in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plants Technical Specifications (TS).

B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event

There were no structures, systems, or components (SSCs) whose inoperability contributed to this event.

C. Dates and approximate times of occurrences

DATE AND APPROXIMATE TIMES OCCURRENCE (times are Central Time)

March 16, 2014, at 0408 U3R16 As-Left torque switch setting resulted in negative margin for this issue.

February 21, 2024, CR 1911827 identified 3-FCV-001-0055 is susceptible to the at 2343 condition identified in SQN NCV CR 1603101 and cannot be setup to meet the design requirements.

ECP BFN-24-012 implemented to remove the close torque switch and close torque switch bypass limit switch from the March 2024 control circuit allowing 3-FCV-001-0055 to be setup to meet design requirements and to no longer be susceptible to the condition identified in SQN NCV CR 1603101. Operability was established prior to starting up from the outage.

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

No components failed during this event.

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

Engineering evaluation of MOV setup identified that PCIV [FCV] 3-FCV-001-0055 may not have been capable of fully closing and adequately sealing during a design basis accident with design basis differential pressure due to the setup of the closing control circuit of the MOV. This condition was documented in CR 1911827.

G. The failure mode, mechanism, and effect of each failed component

No components failed during this event.

H. Operator actions

No Operator actions were taken during this event.

I. Automatically and manually initiated safety system responses

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

A. Cause of each component or system failure or personnel error

The cause of this condition is a legacy issue related to the close control wiring scheme for 3-FCV-001-0055 and failure to identify this valve as being susceptible to the SQN NCV CR 1603101 during the extent of condition review. While the vulnerability has existed since the initial design of the MOV, per the POE, this condition has existed since March 16, 2014.

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

A latent error resulting from failure to modify the close control circuit on 3-FCV-001-0055 resulted in a human performance (HU) error trap due to the condition only being identified on the electrical drawings and in the Motor Op erated Valve Diagnostic Testing procedure.

Because the close torque switch and close torque bypass limit switch were not identified in the MOV Program Database, a more thorough review than that performed would have been required to identify the condition.

The MOV Program Engineer that performed the SQN NCV extent of condition had a missed opportunity to identify this condition as early as 2020.

IV. Analysis of the event

The as-found setup of the MOV circuit did not ensure the valve would close under all design basis conditions. Under Design Basis Accident conditions, if the differential pressure across the valve was great enough to cause the torque switch to open prior to the limit switch opening, the result of the open close torque switch bypass limit switch could be that the valve would not fully close or seal hard enough to prevent seat leakage.

The as-found setup essentially results in this MOV being setup on torque switch control for the close direction. Review of the MOV Program Database evaluation for this condition results in negative margin. Past Operability associated with the As-Found condition was evaluated in CR 1912313.

The extent of condition review concluded that th is condition is limited to 3-FCV-001-0055.

V. Assessment of Safety Consequences

The nuclear safety function of the Primary Contai nment Isolation System (PCIS)[JM] is to provide timely protection against the onset and consequences of accidents involving the gross release of radioactive materials from the fuel and nuclear system process barrier, the PCIS initiates automatic isolation of appropriate pipelines which penetrate the primary containment whenever monitored variables exceed preselected operational limits.

For a gross failure of the fuel, the PCIS initiates isolation of the reactor vessel to contain released fission products. For a gross breach in the nuclear system process barrier outside the primary containment, the isolation system acts to interpose additional barriers (isolation valve plugs) between the reactor and the breach, thus stopping the release of radioactive materials and conserving reactor coolant. The Main Steam Drain Line penetrates primary containment and has inner and outer automatic operated PCIVs (3-FCV-001-0055 and 3-FCV-001-0056).

For gross breaches in the nuclear system proces s barrier inside the primary containment, the PCIS acts to close off release routes through t he primary containment barrier, thus trapping the radioactive material coming through the breach inside the primary containment.

Based on a review over the past three years, Inboard Main Steam Drain Line Isolation Valve 3-FCV-001-0055 was determined to be open over four separate occasions for a total of 182 hours0.00211 days <br />0.0506 hours <br />3.009259e-4 weeks <br />6.9251e-5 months <br /> to support the High-Pressure Coolant Injection Syst em (HPCI)[BJ] and/or Reactor Core Isolation Coolant System (RCIC)[BN] and associated equipm ent maintenance. This leaves the plant in a single point vulnerability of degrading primary containment isolation having to rely on the outboard isolation valve 3-FCV-001-0056. The redundant outboard isolation valve 3-FCV-001-0056 remained operable during the period of time when the inboard isolation valve 3-FCV-001-0055 was inoperable.

According to the BFN Probabilistic Risk Analysis (P RA) - Risk Evaluation of MOVs calculation, the Inboard Main Steam Drain Line Isolation Valve BFN-3-FCV-001-0055 is modeled in the BFN PRA Computer Aided Fault Tree Analysis (CAFT A) model. In the BFN PRA model, MOVs are modeled according to the most significant failure m odes (fails to open, fails to close, spurious operation, plug, etc.) to the system being modeled. Specifically, basic event MOCFC3FCV_0010055 valve 3-FCV-1-55 fail to close on demand is modeled. The results of the model indicate that this event would be low sa fety significance with a Max Risk Achievement Worth (RAW) of 1 and Max Fussell-Vesley (F-V) of 0.00E+00.

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

The condition described for 3-FCV-001-0055 was the result of a design inadequacy in the closing control scheme and MOV diagnostic setup procedure for the subject MOV. Based on a review of the past three years, the redundant MOV 3-FCV-001-0056 in the same system was operable and available to perform the required safety function. 3-FCV-001-0056 control scheme did not have the same design deficien cy as 3-FCV-001-0055. The redundant MOV closing control scheme consists of a single closed limit switch with the torque switch disabled.

Additionally, the redundant MOV had met all its required surveillances and satisfied all acceptance criteria and met all program requirements including the Appendix J, In-Service Testing (IST) and the MOV program.

The redundant outboard isolation valve 3-FCV-001-0056 remained operable during the period of time when the inboard isolation valve 3-FCV-001-0055 was inoperable during the last three years, ensuring the function of primary containment was maintained at the affected penetration.

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 condition was identified in Mode 5 during a refueling outage; however, the valve 3-FCV-001-0055 is only required to be operable in Modes 1, 2, and 3.

C. For failure that rendered a train of a safety system inoperable, estimate of the elapsed time from discovery of the failure until the train was returned to service

This condition was discovered on February 21, 2024, during a shutdown in a mode where it was not required. The valve 3-FCV-001-0055 was returned to operability before reaching a mode where it was required (Modes 1, 2, or 3) in March 2024.

VI. Corrective Actions

Corrective Actions are being managed by the TVA corrective action program under CRs 1911827 and 1912313.

A. Immediate Corrective Actions

There were no Immediate Corrective Actions for this event.

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

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

1) ECP BFN-24-12 to remove the close torque switch and LS-16 from the control circuit and use LS-8 as the close limit switch for 3-FCV-001-0055 has been implemented.

2) Reviewed all MOV Program valves in the TV A nuclear fleet for extent of condition and no additional valves with this issue were identified.

VII. Previous Similar Events at the Same Site

A search of LERs from BFN, Units 1, 2, and 3 over the last five years identified no similar events.

VIII. Additional Information

There is no additional information.

IX. Commitments

There are no new commitments.