05000425/LER-2019-002, Microswitch Failure Causes Closure of Main Steam Isolation Valve and Subsequent Automatic Reactor Trip

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Microswitch Failure Causes Closure of Main Steam Isolation Valve and Subsequent Automatic Reactor Trip
ML19247C285
Person / Time
Site: Vogtle Southern Nuclear icon.png
Issue date: 09/04/2019
From: Taber B
Southern Nuclear Operating Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-19-1061 LER 2019-002-00
Download: ML19247C285 (4)
v • d • e


LER-2019-002, Microswitch Failure Causes Closure of Main Steam Isolation Valve and Subsequent Automatic Reactor Trip
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
10 CFR 50.73(a)(2)
10 CFR 50.73(a)(2)(x)
10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
10 CFR 50.73(a)(2)(iv)(B), System Actuation
4252019002R00 - NRC Website
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text

A Southern Nuclear SEP 0 4 2019 Docket No:

50-425 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 B. Keith Taber Vice President VogUe Units 1-2 Vogtle Electric Generating Plant - Unit 2 Licensee Event Report 2019-002-00 7821 River RD Waynesboro GA, 30830 706-848-0004 tel 706-848-3321 fax NL-19-1061 Microswitch failure causes closure of Main Steam Isolation Valve and subsequent Automatic Reactor Trip Ladies and Gentlemen:

In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report, 2019-002-00 for Vogtle Electric Generating Plant Unit 2. This letter contains no NRC commitments. If you have any questions, please contact Matthew Horn at (706) 848-1544.

Respectfully submitted, B. Keith Taber Vice President Vogtle 1&2 BKT/KCW Enclosure: Unit 2 Licensee Event Report 2019-002-00 Cc: Regional Administrator NRR Project Manager-Vogtle 1 & 2 Senior Resident Inspector-Vogtle 1 & 2 RType: CVC7000

Vogtle Electric Generating Plant-Unit 2 Licensee Event Report 2019-002-00 Mlcroswitch failure causes closure of Main Steam Isolation Valve and subsequent Automatic Reactor Trip Enclosure Unit 2 Licensee Event Report 2019-002-00

NRCFORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020

(()4.2018)

Estimated butden per response to comply with thiS mandaiDry collection request eo hoors.

Reponed lessons learned w lncorporaiBd iniD the Dcensing proc8S£ and fed bade Ill

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LICENSEE EVENT REPORT (LER) industry. Send comments regarding burden estimale 1o the lnfonnation Services Branch

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(T-2 F43), U.S. Nuclear Regulatory Commission, WashingiDn, DC 20555-0001, or by e-mail (See Page 2 for required number of digits/characters for each block)

Ill lnfocollects.Resource@nn:.gov, and Ill the Desk Officer, Office of Information and (See NUREG-1 022, R.3 for instruction and guidance for completing this form Regaa'Qry Affairs, NEOB-10202. (3150-0104), Office of Management and Budget Washlnglon, DC 20503. If a means used lo inpose an information collection does not

!!!!l!:.n-w.m;~02'2h311 d'ISplay a currenUy valid OMB control number, the NRC may not conduct or sponiSOr, and a person is not required Ia respond 10, the inlonnalion coleclion.

  • Page Vogtle Electric Generating Plant, Unit 2 05000425 1 OF2
4. Title Mlcroswitch failure causes closure of Main Steam Isolation Valve and subsequent Automatic Reactor Trip
5. Event Date
6. LER Number
7. Report Date
8. Other Facilities Involved Sequential Rev Facility Name pocket Number Month Day Year Year Number No.

Month Day Year N/A 05000 07 19 2019 2019

- 002
- 00 o"t OJ.f (AO/Cf Facility Name bocket Number N/A b5000
9. Opnlng Mode
11. Ttis Report lsSubmltlad PlnlaltfD the of 10 CFR §: {Chedc all that apply) 1 0 20.2201(b) 0 20.2203(a)(3)Q) 0 50.73(a)(2)(iQ(A) 0 50. 73(a)(2)(viii)(A) 0 20.2201 (d) 0 20.2203(a)(3)Qi) 0 50. 73(a)(2)QQ(B) 0 50. 73(a)(2)(viii)(B) 0 202203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)QII) 0 50. 73(a)(2)(1x)(A) 0 20.2203(a)(2)Q) 0 50.36(c)(1)Q)(A) 181 50. 73(a)(2)Qv)(A) 0 50.73(a)(2)(x)
10. Pow.rlevel 0 20.2203(a)(2)[ri) 0 50.36(c)(1)QQ(A) 0 50.73(a)(2)(v)(A) 0 73.71(a)(4) 100 0 20.2203(a)(2)Qii) 0 50.36(c)(2) 0 50. 73(a)(2)(v)(B) 0 73.71(a)(5) 0 20.2203(a)(2)Qv) 0 50.46(a)(3)QQ 0 50. 73(a)(2)(v)(C) 0 73.77(8)(1) 0 20.2203(a)(2)(v) 0 50. 73(a)(2)Q)(A) 0 50. 73(a)(2)(v)(D) 0 73. 77(a)(2)(ii) 0 20.2203(a)(2)(vl) 0 50. 73(a)(2)Q)(B) 0 50. 73(a)(2)(vii) 0 73.77(a)(2)(iii) 0 50.73(a)(2)Q)(C) 0 Other (Specify in Abstract below or in NRC Form 366A
12. Licensee Contact for this LER u..ns.e Contact

~..- Nlmler (lnc:ludo-Code)

Vogtle Electric Generating Plant, Matthew Hom Regulatory Affairs Manager 06-848-1544 13._~0na Uneforaach Falkn Drecrlbed In this Rsport

Cause

System Component Manufacturer Reportable To ICES

Cause

System Component Manufacturer Reportable To ICES 8

SB 33 H260 y

NIA

14. Supplemental Report Expected Month Day Y*r 0 Yes (If yes, complete 15. Expected Submission Date) ~No
15. E.xped8d Submission Date NIA NIA N/A

~flact (linit ID 1400 spaces, la.,IIJIPII)Xi'nlllllly 14 s&V-paced typewrillltn lines)

~t 0945 EDT on July 19, 2019, with Unit 2 in Mode 1 and 100 percent power, the reactor automatically tripped due to the Loop 2 '8' Main Steam Isolation Valve failing shut. All systems responded as designed. All control rods fully inserted into he core, auxiliary feedwater started, and decay heat was removed through the main steam lines through the steam dumps land into the condenser. The plant was stabilized in Mode 3.

pue to the automatic actuation of systems listed in 10 CFR 50.73(a)(2)(iv)(B), specifically the Reactor Protection System land the Auxiliary Feedwater System, this event is reportable under 10 CFR 50.73(a)(2)(iv)(A).

Because all systems responded as designed and had no adverse effects on the health and safety of the public, this event is pf very low safety significance.

NRC FORM 388 (02-2018) (()4..2018)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150..0104 EXPIRES: 3/31/2020 Estima1ed the NRC may not conduct or sponsor, and a OOPJ/wNw rwc.q~022h31) person IS not required to respond to, the information collection

1. FACIUTY NAME
2. DOCKET NUMBER Vogtle Electric Generating Plant, Unit 2 05000425 YEAR 2019 NARRATlVE

A. Event Description

3. L..ER NliABER SEQUENTIAl NUMBER
- 002 REV NO
- 00 On July 19, 2019 at 0945 EDT, while Unit 2 was operating in Mode 1 at 100 percent power, the Loop 2 'B' Main Steam Isolation Valve (MSIV) failed closed. This failure was the result of a Honeywell LSYHC3K microswitch failure in the MSIV control circuitry due to water intrusion and subsequent corrosion of the microswitch wires. When this microswitch failed, it caused one of the MSIV dump solenoid valves to open which closed the MSIV.

As a result of the MSIV closure, automatic actuations of the Reactor Protection System and the Auxiliary Feedwater System occurred. All systems responded as expected. All control rods fully inserted into the core, auxiliary feedwater started, and decay heat was removed through the main steam lines, through the steam dumps, and into the condenser. There was no equipment which was out of service at the time that caused or contributed to the trip.

Because of the automatic actuation of the Reactor Protection System and the Auxiliary Feedwater System, which are systems listed in 10 CFR 50.73(a)(2)(iv)(B), this event is reportable under 10 CFR 50.73(a)(2)(iv)(A).

B. Cause of Event

The cause of the event was a failure of a microswitch in the MSIV control circuitry due to water intrusion which lead to corrosion and failure of the microswitch wires. The water intrusion was due to the conduit to the microswitch not being sealed properly due to its installation orientation.

C. Safety Assessment

The safety significance of this event is very low. When the reactor tripped, all systems responded as designed. All control rods fully inserted into the core, auxiliary feedwater started, and decay heat was removed through the main steam lines and into the condenser.

There were no adverse effects to the health and safety of the public.

D. Corrective Actions

The microswitch was replaced and tested successfully prior to returning the MSIV to service. Sealant was also added to the conduit leading to this microswitch to prevent further water intrusion. Additionally, the remaining microswitches on Unit 2 were inspected for corrosion and water intrusion and none was found. Sealant was added to all MSIV microswitch conduits on Unit

2. The Unit 1 microswitches will be inspected during the next refueling outage and repaired or replaced and their conduits sealed as necessary.

E. Previous Similar Events

None NRC FORM 368A (0+2018)

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