05000265/LER-2024-001, Automatic Actuation of Reactor Protection System During Scram Discharge Volume Leak Rate Testing

Automatic Actuation of Reactor Protection System During Scram Discharge Volume Leak Rate Testing

ML24131A015
Person / Time
Site:	Quad Cities
Issue date:	05/10/2024
From:	Hild D Constellation Energy Generation
To:	Office of Nuclear Material Safety and Safeguards, Document Control Desk, Office of Nuclear Reactor Regulation
References
SVP-24-031 LER 2024-001-00
Download: ML24131A015 (1)

LER-2024-001, Automatic Actuation of Reactor Protection System During Scram Discharge Volume Leak Rate Testing

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2652024001R00 - NRC Website

text

Constellation, SVP-24-031 May 10, 2024 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 265/2024-001-00 "Automatic Actuation of Reactor Protection System During Scram Discharge Volume Leak Rate Testing" Enclosed is Licensee Event Report 265/2024-001-00 "Automatic Actuation of Reactor Protection System During Scram Discharge Volume Leak Rate Testing," 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 Conner Bealer at 779-231-6207.

Doug Hild Site Vice President Quad Cities Nuclear Power Station cc:

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

Abstract

At 2046 on 3/27/24, with Unit 2 in Mode 5, an automatic actuation of the Reactor Protection System (RPS) occurred during a Local Leak Rate Test (LLRT) of the Scram Discharge Volume (SDV). The LLRT procedure did not bypass the scram signal and leakage of water from a Hydraulic Control Unit (HCU) scram outlet valve into the SDV caused a high-level condition while drains were isolated for testing. No control rod movement occurred due to the actuation as all rods were already full-in.

The cause of the actuation was a deficient procedure that allowed a scram signal to remain active when it was not required.

The LLRT procedure did not bypass the scram signal and leakage of water into the SDV caused a high-level condition while drains were isolated for testing. Completed corrective actions include a temporary procedure change to perform the test along with an HCU repair. Planned actions include a permanent procedure change to the SDV LLRT surveillance procedure.

This report is being submitted per 10 CFR 50. 73(a)(2)(iv)(A) for an event that caused a valid RPS actuation.

PLANT AND SYSTEM IDENTIFICATION

2. DOCKET NUMBER YEAR 00265 2024

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 Automatic Actuation of Reactor Protection System During Scram Discharge Volume Leak Rate Testing CONDITION PRIOR TO EVENT Unit: 2 Reactor Mode: 5 Event Date: March 27, 2024 Mode Name: Refueling Event Time: 2046 CDT Power Level: 0%

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

A. DESCRIPTION OF EVENT At 2046 on 3/27/24 with Unit 2 in Mode 5, an automatic actuation of the Reactor Protection System (RPS) occurred during a Local Leak Rate Test (LLRT) of the Scram Discharge Volume (SDV). On the previous shift before the event, a Hydraulic Control Unit [HCU] was returned to service following an overhaul. On 3/27/24 an Issue Report (IR) was generated to document an air leak on a union associated with the scram outlet valve[V]. When an attempt was made to tighten the union, it was identified that the line was cracked and would require a work order revision to repair. Another IR was also generated on 3/27/24 documenting audible water leakage past the scram outlet valve for the same HCU. This water leakage in conjunction with isolating the SDV vent and drains during the LLRT caused the SDV level to increase. An automatic RPS actuation occurred when the trip setpoint was reached for high SDV water level, in accordance with Function 7 of Technical Specifications 3.3.1.1, "Reactor Protection System Instrumentation."

B. CAUSES OF EVENT The cause of the RPS actuation was leakage of water into the SDV causing a high-level condition while drains were isolated for testing. No Control Rod Drive (CRD) movement occurred due to the actuation as all rods were already full-in.

C. SAFETY ANALYSIS SYSTEM DESIGN The SDV is used to limit the loss of and contain the reactor vessel water from all the drives during a scram. The SDV consists of the header piping leading from each HCU scram outlet valve to the instrument volumes. There are two scram discharge headers, one for each bank of HCUs and two instrument volumes, one for each scram discharge header. The header piping is sized to receive and contain the water discharged by the drives during a scram independent of the instrument volumes. During normal operation, the SDV is empty, with both its double isolation drain and vent valves open.

During a scram, the SDV partly fills with the water from the over piston area of the CRDs. While scrammed, the CRD seal leakage continues to flow to the SDV until the discharge volume pressure equals reactor vessel pressure or until the scram valves are reset. When the scram signal is removed from the RPS, the scram valves may be closed and the discharge volume may be drained. The two instrument volumes [TK] drain into the drain header of the reactor building equipment

2. DOCKET NUMBER

3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.

00265 2024 -

001 00 drain tank (TK]. The scram discharge instrument volumes provide for the measurement of the volume of water discharge from the CRDs to the SDV for alarm and control purposes. There are a series of diverse and redundant level switches connected to each instrument volume. The alarm and control functions of these instruments are as follows: high level alarm, rod block, and reactor scram.

SAFETY ANALYSIS There were no safety consequences as a result of this event. The operators performed actions in accordance with the procedures and training. An automatic scram occurred without complications. All rods were previously fully inserted and no rod movement occurred due to the actuation. This event did not affect the availability of systems needed to maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident. Offsite power was maintained on both Units supplying power to the 4 kV safety busses. The Emergency Diesel Generators (EDGs) 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. A temporary procedure change was made to support completion of the LLRT with the SDV high level RPS signal bypassed.

2. The HCU leak was repaired.

Follow up:

1. Evaluate and implement as appropriate permanent changes to LLRT procedure.

E. PREVIOUS OCCURRENCES The station events database, LERs and INPO Industry Reporting Informational System (IRIS) were reviewed for similar events at Quad Cities Nuclear Power Station during the last six years. A similar event occurred on Unit 2 on 12/15/18 when performing a fill and vent of the reactor water cleanup system and a lifting relief valve caused an unexpected SDV rod block. No scram or LER came out of this event. This event is similar to the most recent event on 3/27/24, in that the SDV rod block signal actuates prior to the scram signal. During the 3/27/24 event the rod block did actuate prior to the scram signal.

No other relevant events were identified during the previous 6-year history.

F. COMPONENT FAILURE DATA System: Control Rod Drive [AA]

Component: Valve [V]

Manufacturer: Hammel Dahl Nomenclature: Scram Outlet Valve Model Number: 2500 ASA-V999Z1204 Page_3_ of _3_