05000265/LER-2020-001, Loss of Both Divisions of Residual Heat Removal Low Pressure Coolant Injection Due to Swing Bus Failure to Transfer

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Loss of Both Divisions of Residual Heat Removal Low Pressure Coolant Injection Due to Swing Bus Failure to Transfer
ML20140A093
Person / Time
Site: Quad Cities Constellation icon.png
Issue date: 05/19/2020
From: Ohr K
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
SVP-20-036 LER 2020-001-00
Download: ML20140A093 (5)
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LER-2020-001, Loss of Both Divisions of Residual Heat Removal Low Pressure Coolant Injection Due to Swing Bus Failure to Transfer
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(v), Loss of Safety Function
10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
10 CFR 50.73(a)(2)(viii)(A)
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)(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)
2652020001R00 - NRC Website
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text

=~Exelon Generation SVP-20-036 May 19, 2020 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-30 NRC Docket No. 50-265 10 CFR 50.73

Subject:

Licensee Event Report 265/2020-001-00 "Loss of Both Divisions of Residual Heat Removal Low Pressure Coolant Injection Due to Swing Bus Failure to Transfer

Enclosed is Licensee Event Report 265/2020-001-00 "Loss of Both Divisions of Resid1:1al Heat Removal Low Pressure Coolant Injection Due to Swing Bus Failure to Transfer," for Quad Cities Nuclear Power Station, Unit 2.

This report is submitted in accordance with 1 O CFR 50.73(a)(2)(v)(D) for any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

There are no regulatory commitments contained in this letter.

Should you have any questions concerning this report, please contact Sherrie Grant at (309) 227-4833. Re/¥ Kenneth S. Ohr Site Vice President Quad Cities Nuclear Power Station cc:

Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - Quad Cities Nuclear Power Station

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

3. Page Quad Cities Nuclear Power Station, Unit 2 05000265 1

OF 4

4. Title Loss of Both Divisions of Residual Heat Removal Low Pressure Coolant Injection Due to Swing Bus Failure to Transfer

~

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 n/a 05000 Facility Name Docket Number 03 20 2020 2020 - 001 00 05 19 2020 n/a 05000

9. Operating Mode
11. This Report is Submitted Pursuant to the Requirements of 1 O CFR §: (Check all that apply)

D 20.2201(b)

D 20.2203(a)(3)(i)

D 50.73(a)(2)(ii)(A)

D 50.73(a)(2)(viii)(A)

D 20.2201(d)

D 20.2203(a)(3)(ii)

D 50. 73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B) 1 D 20.2203(a)(1)

D 20.2203(a)(4)

D 50.73(a)(2)(iii)

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

D 20.2203(a)(2)(i)

D 50.36(c)(1 )(i)(A)

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

D 50.73(a)(2)(x)

10. Power Level D 20.2203(a)(2)(ii)

D 50.36( c)( 1 )(ii)(A)

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

D 73.71(a)(4)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

D 50.73(a)(2)(v)(B)

D 73.71 (a)(5)

D 20.2203{a)(2)(iv)

D 50.46(a)(3)(ii)

D 50.73(a)(2)(v)(C)

D 73.77(a)(1) 100 D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

IZI 50.73(a)(2)(v)(D)

D 73.77(a)(2)(i)

D 20.2203(a)(2)(vi)

D 50.73(a)(2)(i)(B)

D 50.73(a)(2)(vii)

D 73.77(a)(2)(ii)

D 50.73(a)(2)(i)(C)

D Other (Specify in Abstract below or in SEQUENTIAL NUMBER 001 REV NO.

00 reperformed successfully, supporting the high contact resistance or failure to close of Contacts 2-6 as the cause tor the failure to auto-transfer. Detailed failure analysis of the relay revealed a manufacturing error that caused the bar.rel spring to be incorrectly positioned. The barrel spring aids in the closure of the normally closed contacts. This resulted in the inconsistent closure of Contacts 2-6 and the observed failure to auto-transfer.

Prior to installation of the relay in 2018, bench testing and calibration were performed with no issues noted.

Following installation in 2018, post-maintenance testing demonstrated proper function, The March 20, 2020 event showed a failure of the Contacts 2-6 to close. During failure investigation of the relay, there was inconsistent performance of Contacts 2-6 during repeated tests. The barrel spring is an internal feature of the relay, not visible during external inspections. These are the reasons that the condition was not identified during receipt inspection or bench testing.

Part 21 reporting consideration will be discussed with the manufacturer.

C. CAUSE OF EVENT

The cause of the failure of MCC 28/29-5 to transfer from Bus 29 to Bus 28 was a manufacturing error resulting in failure to close of Contacts 2-6 in the LPCI Swing Bus Time Delay Relay.

D. SAFETY ANALYSIS

System Design

480VAC MCCs are designed to supply power tor equipment vital to sate plant shutdown under accident conditions through Buses 28 and 29. Per Updated Final Safety Analysis Report (UFSAR) Section 8.3, the 480V MCC 28/29-5 is made up of two MCCs whose buses are connected with a copper link to form one continuous bus.

The purpose of this common bus is to provide a dual source of power to the residual heat removal (RHR) and recirculation valves tor operation in the low-pressure coolant injection (LPCI) mode. MCC 28/29-5 is normally supplied from Diesel Generator (DG) 2 through 4160V Bus 24-1 transformer TR-29 and Bus 29 during a LOOP with or without an accident signal. Should the DG 2 power source tail, the breaker and contactor feeding MCC_-28/29-5 from Bus 29 will open automatically, the breaker and contactor feeding MCC 28/29-5 from Bus 28 will close automatically restoring power to these buses from DG 1 /2¥.: through Bus 23-1, transformer TR-28, and Bus 28. Design changes were implemented that supplement the previously described automatic transfer logic to initiate an automatic transfer based upon voltage and frequency abnormalities when the 480VAC swing MCC_-28/29-5 is supplied from DG 2. This is accomplished with protective relay monitoring and generating a transfer signal based up on overvoltage, undervoltage, over frequency and underfrequency conditions.

Safety Impact Per TS Bases 3.8.1, AC Distribution sources are required to be operable in Modes 1, 2, and 3 to ensure that acceptable fuel design limits and reactor coolant pressure boundary limits are not exceeded as a result of Anticipated Operational Occurrences (AOOs) or abnormal transients and adequate core cooling is provided and containment operability and other vital functions are maintained in the event of a postulated OBA. The failure of the time delay relay reduced the functionality of the low-pressure injection safety systems by preventing the ability of Bus 28/29-5 to auto transfer and cause LPCI to actuate.

NRC FORM 366 (04*2020)

SEQUENTIAL NUMBER 001 REV NO.

00 The loss of both loops of LPCI is a limiting single failure which is analyzed for recirculation line break LOCAs.

UFSAR Section 8.3 includes discussion that the NRC accepts the design of the LPCI swing bus principally because the ECCS acceptance criteria can be met without any LPCI function. Therefore, the safety impact of the event is minimal.

Although the required LPCI function was not operable for a short period of time, this did not create any actual plant or safety consequences since Unit 2 was not in an accident or transient condition requiring use of LPCI during this period of time.

This event is a Maintenance Rule Functional Failure (MRFF) and a Safety System Functional Failure (SSFF).

E. CORRECTIVE ACTIONS

Immediate:

1.

Operations restored power to Bus 28/29-5.

2.

Maintenance replaced the degraded time delay relay.

Follow Up:

1.

Work with relay manufacturer to consider Part 21 reportability.

F. PREVIOUS OCCURRENCES

A review of previous QCNPS events reveals a similar event in 2011 in which a different component in the bus transfer logic prevented the MCC from properly transferring from Bus 29 to Bus 28. This event took place during conditions other than the bus transfer surveillance. Although similar in results, this is not considered a station experience which would have directly contributed to preventing the current event.

1. LER 265/2011-001-00, Loss of Unit 2 Essential Service 480 VAC Bus, 03/10/2011. A worker falling from a ladder inadvertently tripped a bus by depressing a switch. The expected transfer of MCC 28/29-5 did not take place. The cause was found to be intermittent binding of a plunger on the main contactor for the MCC.

G. COMPONENT FAILURE DATA

Failed Equipment: RELAY, TDR; 1" 600# S/N 80349 Component Manufacturer: Tyco Electronics (Agastat)

Component Model Number: E7022AD003 Component Part Number: N/A This event will be reported to IRIS.

NRG FORM 366 (04-2020)

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