05000423/LER-2020-002, 3, Automatic Reactor Trip Due to Main Generator Ground Fault

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3, Automatic Reactor Trip Due to Main Generator Ground Fault
ML20149K547
Person / Time
Site: Millstone Dominion icon.png
Issue date: 05/28/2020
From: Daugherty J
Dominion Energy Nuclear Connecticut
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
20-169 LER 2020-002-00
Download: ML20149K547 (6)
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LER-2020-002, 3, Automatic Reactor Trip Due to Main Generator Ground Fault
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
10 CFR 50.73(a)(2)(iv)(B), System Actuation
10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
10 CFR 50.73(a)(2)(viii)(A)
10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
10 CFR 50.73(a)(2)(viii)(B)
10 CFR 50.73(a)(2)(ix)(A)
10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
10 CFR 50.73(a)(2)(v), Loss of Safety Function
10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown
10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
4232020002R00 - NRC Website
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text

Dominion Energy Nuclear Connecticut Millstone Power Station 314 Rope Ferry Road Waterford, CT 06385 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2020-002-00 AUTOMATIC REACTOR TRIP DUE TO MAIN GENERATOR GROUND FAULT Serial No.: 20-169 MPS Lie/LO RO Docket No.: 50-423 License No.: NFP-49 MAY 2 8 2020 This letter forwards Licensee Event Report (LER) 2020-002-00, documenting an event at Millstone Power Station Unit 3, on April 1, 2020. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in manual or automatic actuation of systems listed in 10 CFR 50.73(a)(2)(iv)(B).

Should you have any questions, please contact Mr. Jeffry A. Langan at (860) 444-5544.

Sincerely,

// /7~

Jopt( R. Daugherty

)

Site Vice President - Millstone Enclosure: LER 423/2020-002-00 Commitments made in this letter: None

cc:

U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd.

Suite 100 King of Prussia, PA 19406-2713 R.V. Guzman NRC Senior Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C-2 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Serial No.20-169 Docket No. 50-423 Licensee Event Report 2020-002-00 Page 2 of 2

ATTACHMENT Serial No.20-169 Docket No. 50-423 Licensee Event Report 2020-002-00 LICENSEE EVENT REPORT 2020-002-00 AUTOMATIC REACTOR TRIP DUE TO MAIN GENERATOR GROUND FAULT MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2020 (04-2020)

3. Page Millstone Power Station Unit 3 05000 423 1

OF 3

4. Title AUTOMATIC REACTOR TRIP DUE TO MAIN GENERATOR GROUND FAULT
5. Event Date
6. LER Number
7. Report Date
8. Other Facilities Involved I

Sequential I Rev Facility Name Docket Number Month Day Year Year Number No.

Month Day Year 05000 Facility Name Docket Number 04 01 2020 2020 -

002 -

00 05 28 2020 05000

9. Operating Mode
11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 1 20.2203(a)(1) 20.2203(a)(4)
50. 73( a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(i) 50.36(c)(1 )(i)(A)

[Z] 50.73(a)(2)(iv)(A)

50. 73(a)(2)(x)
10. Power Level 20.2203(a)(2)(ii) 50.36(c)(1 )(ii)(A) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(B) 73.71 (a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C) 73.77(a)(1) 100 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(i) 20.2203(a)(2)(vi)
50. 73( a)(2)(i)(B) 50.73(a)(2)(vii) 73.77(a)(2)(ii)
50. 73(a)(2)(i)(C)

Other (Specify in Abstract below or in

3. ASSESSMENT OF SAFETY CONSEQUENCES

There were no safety consequences related to this event.

NUMBER NO.

I YEAR SEQUENTIAL REV

~-I 002 1-G As designed, operation of the main steam Atmospheric Dump Valves (ADVs) and turbine bypass valves prevented challenging the main steam safety valves following the reactor trip. The maximum Plant Process Computer (PPC) indicated Steam Generator (SG) pressure was 1083 psig, well below the nominal opening pressure of the first Main Steam Safety Valve (MSSV) at 1185 psig. No PPC indications of MSSVs opening were observed. As designed, following the trip, Main Feedwater was isolated and Auxiliary Feedwater (AFW) responded to restore SG level. All reactor coolant pumps continued to operate, and Reactor Coolant System (RCS) cold leg temperatures were maintained greater than 550°F following the event.

Following the reactor trip, the minimum post-trip pressurizer pressure was approximately 1982 psia, which is well above the Safety Injection (SI) setpoint (1892 psia). The minimum pressurizer level was 32% immediately following the reactor trip. The minimum pressurizer level remained above 26% after that due to RCS slight cooldown.

Following the reactor trip, control room area temperature (ECS-T64) remained steady. Also following the trip, containment temperature increased by approximately 4°F, and containment pressure increased by less than 0.1 psi. At approximately 19:47, the 'A' Reactor Plant Chilled Water Chiller was restarted, and containment temperature and pressure returned to their pre-event values. The values remained within the bounds of technical specifications 3.6.1.5 and 3.6.1.4 and there was no challenge to the containment pressure and temperature control safety function.

No safety functions were challenged, and plant operation was maintained within the bounds of FSAR Chapter 15 safety analysis. This event did not challenge the health and safety of the public or the environment.

4. CORRECTIVE ACTION

Access door gaskets in this IPSO section were sealed with RTV to prevent water intrusion and drains were installed on each phase of the IPSO.

Additional corrective actions are being taken in accordance with the station's corrective action program.

5. PREVIOUS OCCURRENCES

There have been no automatic reactor trips at MPS3 with a direct cause linked to the Main Generator ground fault in the past 3 years.

6. Energy Industry Identification System (EIIS) codes
  • IPBU - Bus, Isolated Phase Page 3

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