05000391/LER-2024-003, Inoperability of Both Trains of Unit 2 Low Head Safety Injection

Inoperability of Both Trains of Unit 2 Low Head Safety Injection

ML24193A307
Person / Time
Site:	Watts Bar
Issue date:	07/11/2024
From:	Reneau W Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
WBL-24-029 LER 2024-003-00
Download: ML24193A307 (1)

LER-2024-003, Inoperability of Both Trains of Unit 2 Low Head Safety Injection

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function
3912024003R00 - NRC Website

text

TENNESSEE VALLEY 1\\14 AUTHORITY

Tenn essee Valley Authority, Pos t Office Bo x 2000, Spr ing C ity, Tennessee 373 8 1

WBL-24-029

July 11, 2024

10 CFR 50.73

ATTN : Document Control Desk U.S. N uc lea r Re gul ato ry Commission Washington, D.C. 20555-0001

Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No. 50-391

Subject: Licensee Event Report 391/2024-003 -00, lnoperability Of Both Trains Of Unit 2 Low Head Safety Injection

Pursuant to the report ing requ irements of 10 CFR 50. 73, attached is the subject Licensee Event Report concerning the lnoperability Of Both Trains Of Un it 2 Low Head Safety Injection on May 13, 2024.

There are no new regulatory comm itments conta ined in this letter. Please d irect any questions concerning this matter to Jonathan Johnson, WBN Licensing Manage r, at jtjohnsonO@tva.gov.

Respectfully,

William C. R au Site Vice President Watts Bar Nuclear Plant U.S. Nuclear Regulatory Commission WBL-24-029 Page 2 July 11, 2024

Enclosure : Tennessee Valley Authority. Watts Bar Nuclear Plant, Unit 2,

LER 391/2024 -003-00, lnoperability Of Both Trains Of Unit 2 Low Head Safety Injection

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 2

LER 391 /2024 -003 -00, " lnoperab i lity Of Both Trains Of Unit 2 Low Head Safety Injection "

WBL-24-029 E1 of 1

Abstract

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I. Plant Operating Conditions before the Event

Watts Bar Unit 2 was at 100 percent rated thermal power (RTP).

A. Event Summary

This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D) as an event that could have prevented fulfillment of the safety function of a system 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

The "A" train of the Unit 2 RHR [EIIS:BP] system was out of service for preplanned maintenance.

C. Dates and approximate times of occurrences Dates and Approximate Occurrence Times 05/13/2024 0100 EDT The "A" train of the Unit 2 RHR is rendered inoperable for preplanned maintenance.

In support of an instrument calibration requiring flow control valve [EIIS:FCV] manipulation, a control room operator 05/13/2024 0917 EDT erroneously closes 2-FCV-74-2 8. The operator should have closed the A train RHR heat exchangers outlet flow control valve (2-FCV-74-16).

05/13/2024 0921 EDT 2-FCV 28 is reopened.

05/13/2024 1640 EDT The eight hour emergency report is made to the NRC (event notification 57126).

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

There were no components which failed during this event.

E. Other systems or secondary functions affected

None.

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

Using local indications and control board indications, the other members of the crew detected the erroneous manipulation and subsequently corrected it.

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

There were no components which failed during this event

H. Operator actions

A control room operator erroneously closed 2-FCV 28. Four minutes later, the remainder of the crew detected that the incorrect valve was closed and subsequently reopened it.

I. Automatically and manually initiated safety system responses

No safety system responses occurred during this event.

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

The operator who manipulated the wrong component disregarded human performance (HU) tool usage. Specifically, he did not participate in a pre-job brief associated with the activity, reviewed the procedure but did not have it with him when he manipulated the wrong hand indicating controller (HIC)[EIIS: HIC], considered flagging the appropriate HIC but did not, and did not obtain a peer-check for the manipulation of the HIC. A lack of supervisor oversight contributed to this event.

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

The operator who closed 2-FCV-74-28 did not value HU tool usage at the individual level. A lack of preparation for the task contributed to the operators action.

The roles of the Nuclear Unit Senior Operator (NUSO) were not executed with respect to oversight.

I V. Analysis of the event

The Watts Bar large break loss of coolant (LBLOCA) analysis requires a minimum LHSI flow.

This may be seen in the final safety analysis report (FSAR) table 15.4-23d. Had a LBLOCA occurred during the four minutes which this event occurred, Unit 2 would not have been provided the minimum LHSI flow. A LBLOCA is a condition IV fault and as such is a casualty which is not expected to take place during the lifetime of the plant. The event was modeled using the Phoenix Risk Monitor. Both core damage frequency and large early release frequency remained green for the duration of the event.

V. Assessment of Safety Consequences

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

Not applicable.

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, estimate of the elapsed time from discovery of the failure until the train was returned to service

Both trains of RHR (LHSI) were inoperable for four minutes.

VI. Corrective Actions

This event was entered into the TVA Corrective Action Program and is being tracked under Condition Report 1930872.

A. Immediate Corrective Actions

The control room operator who manipulated the wrong component was removed from watch standing.

Additional guidance was put in place for all MCR activities.

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

The following correct ive actions were developed for this event:

1. A remedial plan was developed for the involved Control Room Operator (CRO) and will be implemented prior to his return to shift duties.

2. Expectations for NUSOs role in upholding the standards contained in OPDP-1, Conduct of Operations will be clarified.

3. Modify 2-SI-74-63-A, 18 Month Channel Calibration of Remote Shutdown Control RHR Heat Exchanger A Outlet Flow Loop 2-LPF 16, and similar procedures to require a concurren t verification ( CV) for manipulation of a controller.

4. Require that a pre-job brief be conducted for all operations support activities for maintenance.

VII. Previous Similar Events at the Same Site

None

VIII. Additional Information

None.

IX. Commitments

None.