05000323/LER-2021-001, Emergency Diesel Generator Declared Inoperable Due to Low Frequency Condition Discovery During Routine Surveillance

Emergency Diesel Generator Declared Inoperable Due to Low Frequency Condition Discovery During Routine Surveillance

ML21263A062
Person / Time
Site:	Diablo Canyon
Issue date:	09/20/2021
From:	Harbor C Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-21-065 LER 2021-001-00
Download: ML21263A062 (4)

LER-2021-001, Emergency Diesel Generator Declared Inoperable Due to Low Frequency Condition Discovery During Routine Surveillance

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
3232021001R00 - NRC Website

text

Pacific Gas and Electric Company "'

Cary D. Harbor Dlablo Ca n y o n Power Plan t Statio n Direc to r Mail code 104/5/502 P.O. Box 56 Avila Beach, CA 93424

805.545.4102 Intern al: 69 1.4102

September 20, 2021

PG&E Letter DCL 065

U.S. Nuclear Regulatory Commission 10 CFR 50.73 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 202 1-01-00, Emergency Diesel Generator Declared lno.perable due to Low Frequency Condit ion Discovery during Rout ine Surveillance

Dear Commissioners and Staff,

In accordance with the requirements of 10 CFR 50.73(a)(2)(i)(B) and 10 CFR

50. 73(a)(2)(v)(D), Pacific Gas and Electric Company (PG&E) hereby submits the enclosed Diablo Canyon Power Plant (DCPP) Unit 2 Licensee Event Report regarding a low frequency condition found for one of the three Unit 2 Emergency Diesel Generators during a routine surveillance test.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report. All 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,

~ f..,_ C. Ha..{.,.,..

Cary Harbor

dqmg/51126111 Enclosure cc/enc : Samson S. Lee, NRR Senior Project Manager Scott A. Morris, NRC Region IV Administrator Ayesha Athar, NRC Acting Senior Resident Inspector INPO Diablo Distribution

A member of the STARS Alliance Cal l away

• Diab l o Canyon

• Pa l o Verde

• Wolf Creek

Abstract

On July 22, 2021, with Diablo Canyon Power Plant (DCPP) Unit 2, operating at 100 percent power, DCPP personnel determined that since June 30, 2021, Emergency Diesel Generator (EDG) 2 - 3 would not have been able to attain Technical S pecification (TS) minimum frequency when started in automatic. Manual control of diesel frequency was not affected. This condition was discovered via a routine surveillance test which evaluates, in part, EDG frequency during standby and loading conditions.

This event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) as an operation of the plant in a condition prohibited by DCPP TS due to the EDG frequency being outside TS required limits for a period beyond the TS required completion time. This event is also being reported pursuant to 10 CFR 50.73(a)(2) (v)(D) as an event or condition that could have prevented fulfillment of a safety function. However, upon discovery, the remaining two of the three EDGs were operable.

The condition was corrected and the EDG was restored to Operable status on July 22, 2021. A subsequent evaluation determined that the low frequency condition did not prevent EDG 2-3 from performing its specified safety function.

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I. Reporting Requirements

This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) and the associated guidance of NUREG1022, -

Revision 3, as an operation or condition prohibited by Diablo Canyon Power Plant (DCPP) Technical Specifications (TS), due to the emergency diesel generator (EDG) frequency being outside TS required limits for a period beyond the associated TS required completion time.

This event is also being reported in accordance with 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented fulfillment of a safety function. However, it should be noted that two of the three EDGs were operable at the time of discovery.

II. Plant Conditions

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

III. Problem Description

A. Background

DCPP Units 1 and 2 each have three EDGs. The safety function of the EDGs is to provide AC power to Engineered Safety Features (ESF) loads when offsite power is unavailable. The specified safety functions of EDG 2-3 are:

a. to furnish sufficient power to mitigate a design basis accident in one unit and safely bring DCPP to coldshutdown for the other unit when both offsite power sources are unavailable.

b. to furnish power sufficient for a controlled shutdown of the plant whenever the main turbinegenerator and the-offsite power sources are not available.

To satisfy thes e functions, t he EDG 2-3 must be capabl e of automatically starting, accelerating to rated speed and voltage in under 10 seconds and connecting to its respective ESF B us on detecti on of Bus undervoltage (UV).

B. Event Description

On July 22, 2021, w ith DCPP Unit 2, oper ating at 1 00 percent power, DCPP personnel determi ned that sinc e June 30, 2021, EDG 2-3 woul d not hav e been able t o attain T S minimum frequency whe n start ed i n automatic. Manual control of di esel frequency was not affected.

On July 21, 2021, EDG 2 -3 was s tarted on a simulat ed UV signal f or r outine surveillanc e testing. The EDG was started with the mode select s witch in the " AUTO" position which indicates t he diesel was ali gned for dedicated supply t o its associated 4 KV vital electrical Bus. The frequency indicat ed 58. 90 Hz and diesel speed indicated 880 revolutions per minute. Per t he surveillance testing procedure, t he frequency should hav e been betw een 59. 5 Hz and 60. 5 Hz (accounti ng for i nstrument uncertainty) o n the start prior t o any adjustments.

EDG 2-3 was placed in manual, the frequency and speed were adjusted into their proper band, and then the surveillance test was completed meeting all acceptance criteria. However, due to the frequency attained following the automatic UV start, EDG 2-3 was declared INOPERABLE.

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

Diablo Canyon Power Plant, Unit 2 05000- 323 NUMBER NO.

2021 01 00 The low frequency condition discovered during the routine surveillance procedure for EDG 2-3 was below the TS 3.8.1 lower limit of 59.5 Hz (accounting for instrument uncertainty). This non-conforming condition has been determined to exist between June 30, 2021 (previous successful EDG 2-3 surveillance) through July 22, 2021 (when restored to Operable status).

A subsequent evaluation determined EDG 2-3 and the equipment powered from its associated vital 4 KV and 480 V Buses were capable of performing their specified safety functions.

C. Method of Discovery

This condition was discovered via a routine surveillance test which monitors, in part, EDG frequency during standby and loading conditions.

D. Operator Actions

The condition was corrected and EDG 2-3 was restored to Operable status on July 22, 2021.

F. Safety System Responses

There are no safety system responses associated with this event.

IV. Cause of the Problem

The cause of the EDG 2-3 low frequency condition was due to an inadequately performed post maintenance test. The testing sequence did not fully consider the need for revalidation of frequency following setting of the EDG governor following maintenance activities.

V. Assessment of Safety Consequences

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

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

VI. Corrective Actions

The condition was corrected and the EDG was restored to Operable status on July 22, 2021. Follow-up corrective actions to prevent recurrence will be managed in accordance with the DCPP Corrective Action Program.

VII. Additional Information

There have been no similar events for the EDGs at DCPP in the previous three years.

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