05000265/LER-2023-001, Turbine Trip and Automatic Reactor Scram Due to High Moisture Separator Level

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Turbine Trip and Automatic Reactor Scram Due to High Moisture Separator Level
ML23284A284
Person / Time
Site: Quad Cities Constellation icon.png
Issue date: 10/10/2023
From: Wake B
Constellation Energy Generation
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
SVP-23-052 LER 2023-001-00
Download: ML23284A284 (1)
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LER-2023-001, Turbine Trip and Automatic Reactor Scram Due to High Moisture Separator Level
Event date:
Report date:
2652023001R00 - NRC Website
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text

Constellation SVP-23-052 October 10, 2023 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 265/2023-001-00 "Turbine Trip and Automatic Reactor Scram due to High Moisture Separator Level" Enclosed is Licensee Event Report 265/2023-001-00 "Turbine Trip and Automatic Reactor Scram due to High Moisture Separator Level," for Quad Cities Nuclear Power Station, Unit 2.

This report is being submitted in accordance with 10 CFR 50. 73(a)(2)(iv)(A) for an event or condition that resulted in manual or automatic actuation of the reactor protection system including a reactor scram.

There are no regulatory commitments contained in this letter.

Should you have any questions concerning this report, please contact Rachel Luebbe at (309) 227-2813.

Respectfully, Brian Wake Site Vice President Quad Cities Nuclear Power Station cc:

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

Abstract

On August 11, 2023, at 0329, Quad Cities Unit 2 had an automatic scram from full power due to a trip of the main turbine. A fault in the Essential Service System (ESS) caused a feedwater heater (FWH) system transient. The drain valve for the 2A Moisture Separator Drain Tank (MSDT) did not open rapidly enough to prevent water level in the moisture separators from reaching the established turbine trip setpoints. The Unit 2 Main Turbine tripped as designed and generated an automatic reactor scram. All control rods inserted and the scram was uncomplicated. Containment isolation valves actuated closed in multiple systems on a valid Group II signal.

The cause of the event is an improperly tuned Level Controller for the 2A MSDT allowing the high level turbine trip to be reached following a FWH transient. Completed corrective actions are component replacements and recalibrations. Planned actions are procedure changes.

This report is being submitted per 10 CFR 50. 73(a)(2)(iv)(A) for an event that resulted in manual or automatic actuation of the reactor protection system including a reactor scram.

PLANT AND SYSTEM IDENTIFICATION

2. DOCKET NUMBER YEAR 05000-265 2023
3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.

00 General Electric - Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in text as [XX].

EVENT IDENTIFICATION Turbine Trip and Automatic Reactor Scram due to High Moisture Separator Level CONDITION PRIOR TO EVENT Unit: 2 Reactor Mode: 1 Event Date: August 11, 2023 Mode Name: Power Operation Event Time: 0329 CDT Power Level: 100%

No structures, components, or systems that were inoperable at the start of the event that contributed to the event.

A. DESCRIPTION OF EVENT On August 11th, 2023, at 0329, Quad Cities Unit 2 had an automatic scram from full power due to a trip of the main turbine [TRB]. A fault in the Essential Service System (ESS)[UJX] caused a feedwater heater (FWH)[HX] system transient. The drain valve [LC] for the 2A Moisture Separator Drain Tank (MSDT)[SN][TK] did not open rapidly enough to prevent water level in the moisture separators [MSR]

from reaching the established turbine trip setpoints. The Unit 2 Main Turbine tripped as designed and generated an automatic reactor scram. All control rods were inserted and the scram was uncomplicated. Containment isolation valves actuated closed in multiple systems on a valid Group II signal.

B. CAUSES OF EVENT The cause of the scram was an improperly tuned emergency level control valve (LCV) for a MSDT. The controller's [LCO] setpoints were configured to provide a slower response than was appropriate for responding to a FWH level transient. In this case, the valve did not respond rapidly enough to prevent overfilling the associated MSDT and eventually tripping the turbine on high level in the moisture separators.

C. SAFETY ANALYSIS SYSTEM DESIGN

[81 050 0

052 Moisture Separator Drain Tank Level Controller

2. DOCKET NUMBER YEAR 05000-265 2023
3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.

00 High pressure turbine exhaust steam is routed to four moisture separators prior to entering the low-pressure turbines. Steam passes through chevron separator elements to remove water droplets which drain to two MSDTs. On a High Level in the MSDT, the MSDT emergency drain valve opens and the normal MSDT LCV remains open. On loss of power from ESS, the normal MSDT LCV fails closed and level is maintained by the emergency drain valve.

SAFETY ANALYSIS There were no safety consequences as a result of this event. The operators performed all actions in accordance with the procedures and training. An Automatic scram occurred without complications due to a turbine trip caused by moisture separator high level. All expected ESF actuations occurred as designed to bring the reactor to a safe shutdown condition. Adequate makeup to the vessel was available at all times from the feedwater system, as well as from the ECCS systems. The event was within the analysis of the UFSAR Chapter 15, UFSAR Chapter 6, and there were no radioactive releases. Off-site power was maintained on both Units supplying power to the 4 kV safety busses. The Emergency Diesel Generators (EOG) were available if required. Unit 1 was not affected by the Unit 2 scram.

This is not a Safety System Functional Failure per NEI 99-02, Revision 7.

D. CORRECTIVE ACTIONS Immediate:

1.Tuned the emergency MSDT LCV to ensure appropriate transient response (Complete)

Follow Up:

1. Implement procedure change to provide additional direction for MSDT LCV tuning at all power levels.

E. PREVIOUS OCCURRENCES The station events database, LERs, and INPO Industry Reporting Information System (IRIS) were reviewed for similar events at Quad Cities Nuclear Power Station in the last three years. A similar event had occurred on 2/26/2020, in which a failure of a component in the Unit 2 ESS UPS had resulted in a FWH level transient (reference IR 4321603). This event differed from the more recent event on 8/11/2023, in that the emergency LCVs functioned appropriately to control level in the FWH system. This ESS UPS

2. DOCKET NUMBER
3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.

05000-265 2023 -

001 00 component failure factored into the decision to replace/upgrade the ESS UPS systems on both Unit 1 and Unit 2 at Quad Cities Nuclear Generating Station. This upgrade was installed on Unit 1 in 2023 during the refuel outage and is scheduled for installation on Unit 2 during the 2024 refueling outage.

No other relevant events were identified during the previous 3-year history.

F. COMPONENT FAILURE DATA Level Controller Manufacturer: Fisher Controllers Supplier: Fisher Controllers Nomenclature: Pneumatic Controller Model/Part Number: 4195KB Page _4_ of _4_

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