05000323/LER-2024-001, LCO 3.0.3 Completion Time Limits

LCO 3.0.3 Completion Time Limits

ML24141A032
Person / Time
Site:	Diablo Canyon
Issue date:	05/17/2024
From:	Rogers J Pacific Gas & Electric Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
DCL-24-054 LER 2024-001-00
Download: ML24141A032 (1)

LER-2024-001, LCO 3.0.3 Completion Time Limits

Event date:
Report date:
3232024001R00 - NRC Website

text

Pac ific Gas and Electric Company ""

Justin E. Rogers Diablo Ca nyon Powor Plant Sta tion Direc tor Mail code 104151502 P.O. Bo x 56 Avila Bea c h, CA 93424

805.545.3088 Ju stin.Rogers@ pge.c o m

PG&E Letter DCL-24-054

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

Docket No. 50-323, OL-DPR-82 Diablo Canyon Power Plant, Unit 2 Unit 2 Licensee Event Report 2024-001-00, Unit 2 LCO 3.0.3 Completion Time Limits

Dear Commissioners and Staff,

In accordance with the requirements of 10 CFR 50. 73(a)(2)(i)(B), Pacific Gas and Electric Company (PG&E) hereby submits the enclosed Diablo Canyon Power Plant (DCPP) Unit 2 Licensee Event Report.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report. Corrective actions identified in this letter will be implemented in accordance with the DCPP Corrective Action Program.

This event did not adversely affect the health and safety of the public.

If you have any questions or require additional information, please contact Mr. James Morris, Regulatory Services Manager, at (805) 545-4609.

Sincerely,

Justin E. Rogers r -z-'1 Date

dqmg/ 51229466-7 Enclosure Diablo Distribution Mahdi 0. Hayes, NRC Sen ior Resident Inspector INPO Samson S. Lee, NRC Senior Project Manager John D. Monninger, NRC Region IV Administrator

A m e mber of th e STAR S Allia n ce Callaway

• Dia blo Ca n yo n

• Pa lo Verd e

• Wo lf Creek

Abstract

On March 19, 2024, Pacific Gas and Electric Company requested, and the Nuclear Regulatory Commission (NRC) verbally granted, additional time to resolve a maintenance issue affecting an exhaust fan associated with the Auxiliary Building Ventilation System (ABVS) due to its redundant exhaust fan being concurrently inoperable. The cause of the inoperable redundant ABVS fan was elevated temperature on the "C" Phase between the contactor and the breaker.

The additional time granted by the NRC allowed Diablo Canyon Power Plant ma intenance personnel to perform needed maintenance and restore the exhaust fan to operable on March 19, 2024. As required by NUREG - 1022, exceedance of Technical Specification completion times are still required to be reported per 50.73(a)(2)(i)(B), even though be ing granted enforcement discretion. There was no impact to the health and safety of the public or plant personnel.

I. Reporting Requ irements

This event is being reported in accordance with 10 CFR 50. 73(a)(2)(i)(B) and the associated guidance of NUREG-1022, Rev ision 3, as a condition prohibited by Technical Specifications (TS). The total time that Auxi liary Bu ilding Ventilation System (ABVS) was inoperable exceeded the tota l time allowed per Diablo Canyon Power Plant (DCPP) TS 3.0.3.

II. Plant Cond itions

At the time of the event, DCPP Unit 2 was in Mode 1 at 100 percent power.

Ill. Problem Description

A. Background

The ons ite power systems cons ist of all sources of electric power and their associated distribution systems within the DCPP. Included are the main generators, emergency diesel generators (EOG), and the Class 1 E and non-Class 1 E station batteries.

!The ABVS provides all outside air supply for the auxiliary building under all operating conditions. It also serves its primary purpose of providing cooling air for the engineered safety features pump motors. The fans for the system receive power

~rom the Class 1 E 480-V buses. The supply system consists of two full capacity fans (each powered _ from a separate Class 1 E bus). The exhaust system consists of two full capacity fans (each powered from a separate Class 1 E bus).

~BVS exhaust fans' functions are to limit the maximum ambient temperature in rooms containing safety related equipment, and during accident conditions to provide for conta inment excess pressure relief and min imize radioactivity released via the plant vent.

B. Event Description

On March 19, 2024, Pacific Gas and Electric Company (PG&E) requested, and the Nuclear Regulatory Commission (NRC) verbally granted, additional time to resolve a maintenance issue affecting an exhaust fan associated with the ABVS due to its redundant exhaust fan being concurrently inoperable.

The additional time allowed DCPP maintenance personnel to perform needed maintenance and restore an exhaust fan to operable (note that an exhaust fan remained in service and available), thereby preventing an otherwise unnecessary down-power or the shutdown of Unit 2 without a corresponding health and safety benefit. As requ ired by NUREG-1022, the exceedance of TS completion times are still required to be reported per 50.73(a)(2)( i)(B),even though being granted enforcement discretion. A discussion of this occurence is provided below:

NR C FOR M 366A (04-02-2024 ) Page 2 of 4

On March 18, 2024, during planned maintenance of EDG 2-2, ABVS exhaust fan E-1 tripped on thermal overload (TOL).

Following reset and investigation of the TOL condition, fan E-1 was declared inoperable at 19:43 Pacific Daylight Time (PDT). Fan E-1 was not restored within four hours, and therefore in accordance w ith the provisions of TS 3.8.1 Required

~ction 8.2, ABVS exhaust fan E-2 (which was supported by EDG 2-2) was declared inoperable at 23:43 on the same day.

TS 3. 7.12 for ABVS does not describe a Required Action for two inoperable ABVS trains, and TS 3.0.3 was entered.

DCPP personnel determined that the add itional repairs necessary to restore ABVS fan E-1 would exceed the TS 3.0.3 LCO completion times and requested enforcement discretion. Verbal enforcement discretion was granted by the NRC on March 19, 2024, at 05:36 PDT, which allowed an add itional period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to restore an ABVS fan to operab le condition. Fan E-1 was restored to operab ility at 17:30 on March 19, 2024, and the applicable TS Conditions were exited.

There was no impact to the health and safety of the public or plant personnel.

C. Status of Inoperable Structures, Systems, or Components that Contributed to the Event

EDG 2-2, ABVS Fan E-1, and ABVS Fan E-2 are discussed above.

rrhere were no other structure, system, or component failures associated with this event.

D. Method of Discovery

Self-Revealing.

E. Operator Actions

Operations pe rsonnel responded to the trip of ABVS exhaust fan E-1 in accordance with plant procedures. Although declared inoperable in accordance with TS, exhaust fan E-2 rema ined available and in service.

NR C FOR M 366A (0 4-02-2 024 ) Page 3 of 4

F. Safety System Responses

There were no safety system responses related to this event.

IV. Cause o f the Problem

The cause of the ABVS fan failure E-1 was a degraded "C" phase contactor in the breaker cubicle providing power to the

~an.

V. Assessment of Safety Consequences

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

VI. Corrective Actions

The immediate corrective action was to implement repairs in the breaker cubicle providing power to ABVS Fan E-1.

Operations declared E-1 operable at 1730 PDT on March 19, 2024. Additional follow-up corrective actions will be managed in accordance with the DCPP Corrective Action Program.

IVII. Additional Information

rrhere have been no similar events at DCPP in the previous three years.

NR G FOR M 366A (04-02 -2024) Page 4 of 4