05000483/LER-2019-001, Unplanned Loss of Switchyard Bus B Results in System Actuation

Unplanned Loss of Switchyard Bus B Results in System Actuation

ML19157A296
Person / Time
Site:	Callaway
Issue date:	06/06/2019
From:	Ameren Missouri
To:	Office of Nuclear Reactor Regulation
Shared Package
ML19157A294	List: 05000483/LER-2019-001, Unplanned Loss of Switchyard Bus B Results in System Actuation
References
ULNRC-06506 LER 2019-001-00
Download: ML19157A296 (5)

LER-2019-001, Unplanned Loss of Switchyard Bus B Results in System Actuation

Event date:
Report date:
Reporting criterion:	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)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(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)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)
4832019001R00 - NRC Website

text

NRC FORM 366 US. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB:

NO. 3150-0104 EXPIRES: 03/31/2020 (04-20 1 8)

, the NRC may not conduct or sponsor, and a 0

person is notrequired to respundts, the information collection.

1. Facility Name 12 Docket Number f3.

Page Callaway Plant Unit I 05000 483 I

OF

4. Title Unplanned Loss of Switchyard Bus B Results in System Actuation

8. Other Facilities Involved I Facility Name Docket Number 05000 Docket Number 05000 I Facility Name I I. This Report is Submitted Pursuant to the Requirements of I 0 CFR §: (Check all that apply)

LI 50.73(a)(2)(ii)(A)

J 50.73(a)(2)(viii)(A)

D 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B)

D 50.73(a)(2)(iii)

D 50.73(a)(2)(ix)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)

D 50.73(a)(2)(v)(A)

LI 73.71(a)(4)

El 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(B) 73.71(a)(5)

LI 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C)

J 73.77(a)(1) 000 D 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(i)

LI 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(vii)

J 73.77(a)(2)(ii)

El 50.73(a)(2)(i)(C)

Other (Specify in Abstract below or in 6.

CAUSE OF THE EVENT

A ground wire was inadvertently added on circuit breaker MDV55 as part of a design change under modification package 1 6-0021 that was implemented in the fall of 201 7 (during Refueling Outage 22) in which several switchyard breakers were replaced with new and differenttype manufactured by Mitsubishi. When MDV53 was closed for the backfeed on April 17, 201 9, this additional ground created a path for current to flow through the protective relays associated with MDV55, and this caused the protection circuitry for MDV55 to detect an unexpected current surge due to the main transformer windings drawing current in order to charge the transformers field windings. The protective relay actuated on this inrush and initiated a B Bus fault clearing of the other breakers. Specifically, the activation triggered circuit breakers MDV45, MDV75, 52-3, and 52-4 to open and clear the bus of load. The opening of 52-3 isolated the B safeguard transformer from the B switchyard bus, which in turn de-energized ESF transformer XNBOI which was powering the NBOI bus and caused an actuation of Engineered Safety Features equipment.

7.

CORRECTIVE ACTIONS

The added ground wire that was part of the newly installed Mitsubishi breakers was removed from MDV55.

In addition, drawings of the switchyard were reviewed for duplicate current transformer (CT) grounds of recently modified switchyard breakers, and that review confirmed no similar situations exist that would lead to a similar plant event.

Investigation into the event is ongoing and additional information will be provided in a supplement to this LER. Corrective action to prevent recurrence will be generated as part of the root cause analysis process.

8. PREVIOUS SIMILAR EVENTS

A review of Callaway LERs for the past three years did not identify any other examples of system actuations caused by the same or similar reasons for the event. Upon completion of the root cause team findings, another search will be completed using the new information to determine if previous similar events have occurred.

9. OTHER INFORMATION:

A figure of the Callaway switchyard is on the next page.

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TO BLAND TO LOOSE TO MONTGOMERY SUB.

XFMR-A 4:

U.G.

CABLES SITE FEEDER SEE FIGURE 8.3-I GEN-l REV. 15 1 0/07 UNION ELECTRIC COMPANY CALLAWAY PLANT FINAL SAFETY ANALYSIS REPORT FIGURE 8.2-5 345KV ONE LINE AND GENERAL ARRANGEMENT CALLAWAY PLANTPage 5

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