ML25147A260
| ML25147A260 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  (DPR-029, DPR-030) |
| Issue date: | 05/28/2025 |
| From: | Jack Giessner NRC/RGN-III/DORS/RPB1 |
| To: | Benny Jose Division of Operating Reactors |
| References | |
| Download: ML25147A260 (0) | |
Text
MEMORANDUM TO:
Benny Jose, Senior Reactor Inspector, Team Lead Engineering Branch 2 Division of Operating Reactor Safety FROM:
John B. Giessner Regional Administrator, Region III
SUBJECT:
SPECIAL INSPECTION CHARTER FOR QUAD CITIES NUCLEAR GENERATING STATION TO UNDERSTAND THE CIRCUMSTANCES OF THE COMPLEX MAY 19, 2025, UNIT 1 SCRAM AND UNIT 2 RUNBACK On May 19, 2025, the Unit 1 reactor tripped on low level from the loss of the 1B and 1C reactor feed pumps due to an electrical transient. The outboard main steam isolation valves (MSIVs) went shut, resulting in the control room operators using a combination of reactor core isolation cooling (RCIC), a reactor feed pump for level control, and one of the emergency relief valves for pressure control. During the event, Unit 2 experienced a loss of a feed pump and a runback to approximately 80 percent reactor power.
The cause of the trip was associated with a degraded condition on the Unit 2 125 Vdc battery that was revealed during battery charger swapping activities on Unit 2 charger. The Unit 2 battery supplies dc control power to Unit 1 Division 2. Before the event licensee was performing maintenance on Unit 2 battery charger #2 and the alternate charger 2A was connected to the battery. As the maintenance on charger #2 was completed and during the restoration process there was a brief period when the Unit 2 125 Vdc battery was solely relied on to carry the dc loads. During this period, there were reports of wide dc voltage swings (from 0 to 130 Vdc) and an acrid odor reminiscent of high battery discharge. The large voltage swings caused a transient on Unit 1 Division 2 dc Bus that resulted in the loss of the 1B and 1C reactor feed pumps.
Following the trip, Bus 14 lost power when the designed auto bus transfer feature failed to transfer power from the unit auxiliary transformer to the reserve auxiliary transformer and the emergency diesel generator auto started to provide power to Bus 14-1. With the loss of both ac and dc power, the solenoids for the outboard Unit 1 MSIVs lost power and the MSIVs went closed. In addition, the 1A RFP did not trip on level 8 when it should have, nor was it able to be tripped from the control board, requiring in-field opening of the breaker. There were also unexpected interactions with the Unit 1 RCIC automatic control system.
CONTACT: Jasmine Gilliam, DORS, RIII 630-829-9831 May 28, 2025 Signed by Giessner, Jack on 05/28/25
B. Jose 2
On May 21, 2025, while performing a cell replacement in the Unit 2, 125 Vdc battery room, the licensee discovered that the intercell lug on battery cell 21 was completely sheared off upon removing the intercell connectors. It is not known how long the cell was in this condition, the overall impact the condition had on the capability of the Unit 2 125 Vdc battery to perform its specified safety function, and whether this was the cause of the electrical transient that occurred on May 19, 2025.
Subsequently, early on May 22, 2025, while performing a performance discharge test of the Unit 2 battery following the replacement of cell 21, approximately 2 minutes into the test, the control room received fire alarms for the battery room. Personnel at the room observed sparks and a flame in the battery cell adjacent (cell 22) to the replaced cell. The test was secured, and the onsite fire brigade extinguished the fire. Prior to the testing, the battery was declared inoperable and was disconnected from installed safety-related plant equipment. The cause of the fire is unknown and is being investigated. The fire also resulted in the licensee declaring an Unusual Event and making a 1-hour event notification (EN 57728) to the NRC.
The NRC completed an evaluation of the condition using Management Directive (MD) 8.3, NRC Incident Investigation Program. The condition met the MD 8.3 deterministic criterion of, Involving multiple significant unexpected system interactions; multiple failures in systems used to mitigate an actual event; and operations that may have exceeded, or were not included in, the design bases of the facility. NRC staff performed a risk assessment and determined follow up was warranted to understand the circumstances associated with the complex May 19, 2025, Unit 1 SCRAM and Unit 2 runback.
Accordingly, based on the deterministic and risk criteria in MD 8.3, and as provided in Regional Procedure 8.31, Special Inspections at Licensed Facility, a Special Inspection Team (SIT) will commence an inspection on June 2, 2025. The SIT will be led by you and will include Kenya Carrington, Senior Resident Inspector (North Anna) and Ijaz Hafeez, Senior Reactor Inspector.
The special inspection will determine the sequence of events and will evaluate the facts, circumstances, and the licensees actions surrounding these events. The specific charter for the team is enclosed.
Docket Nos. 05000254 and 05000265 License Nos. DPR-29 and DPR-30
Enclosure:
Quad Cities Nuclear Generating Station Special Inspection Charter
B. Jose 3
Memorandum to Benny Jose from John Giessner dated May 28, 2025.
SUBJECT:
SPECIAL INSPECTION CHARTER FOR QUAD CITIES NUCLEAR GENERATING STATION TO UNDERSTAND THE CIRCUMSTANCES OF THE COMPLEX MAY 19, 2025, UNIT 1 SCRAM AND UNIT 2 RUNBACK DISTRIBUTION:
Jack Giessner Mohammed Shuaibi Jason Kozal Billy Dickson Robert Ruiz Michael King Viktoria Mitlyng Prema Chandrathil Benny Jose NRR_Reactive_Inspection.Resource@nrc.gov ADAMS Accession No. (s): ML25147A260 PKG: ML25143A140 Inspection Report: ML26069A582 MD 8.3: ML25143A137 eConcurrence Case: 20250527-60021
Enclosure QUAD CITIES NUCLEAR GENERATING STATION SPECIAL INSPECTION CHARTER This special inspection team is chartered to: (1) review the facts associated with the complex Unit 1 SCRAM and Unit 2 runback that occurred at Quad Cities on May 19, 2025; 2) assess the licensees response and evaluation of the event; (3) identify any generic issues associated with the event; and (4) conduct an independent, risk-informed, extent-of-condition review, in accordance with Inspection Procedure 93812, Special Inspection, and will include, but not be limited to, the items listed below. This charter may be revised based on the results and findings of the inspection. The results will be documented in NRC Inspection Report ML26069A582. To accomplish these objectives, the following will be performed:
The inspection activities will include, but are not limited to, the items listed below:
1.
Establish a sequence of events related to the May 19, 2025, Unit 1 SCRAM and Unit 2 Runback and the May 22, 2025, Unusual Event. Include, as necessary, plant conditions, system line ups, and operator actions.
2.
Evaluate the licensees progress towards understanding the event and determining causal factors, extent of condition, and development of corrective actions. Independently review plant data, records, and licensees post-trip review.
This includes a review of the specific failure mechanism of the battery in the complex scram and the battery fire.
3.
Review the design of 125 Vdc system and the loss of the dc and ac buses (Unit 1 dc Bus 1B-1 and ac Bus 14-1), the 125 Vdc auto bus transfer control power scheme as it relates to providing alternate control power to the Unit 1 and Unit 2 emergency diesel generators (EDG) on a loss of the normal 125 Vdc bus.
Include a review of any potential for operator actions to recover these systems during transients that challenged them given the degraded condition(s).
4.
Review system interactions during the SCRAM and determine if the multiple subsequent malfunctions/interactions were expected and/or as designed. This includes, but is not limited to: Unit 1 RCIC automatic control system malfunction; the 1A RFP did not trip on reactor water level 8, nor was it able to be tripped from the control room, requiring in-field opening of the breaker; loss of Bus 14 and the failure of auto-swap to the reserve auxiliary transformer; the Unit 1 EDG starting and loading sequence; MSIV closure during the event; feedwater regulating valve leakage experienced and its potential impacts to plant operations.
5.
Evaluate previous adverse condition to quality documents for the Unit 2 125 Vdc battery, operating experience, and maintenance practices that led to or could have identified and prevented the failure mechanism.
6.
Evaluate applicable Operating Experience (e.g., Turkey Point) for similar battery issues, determine if they are applicable to Quad Cities, and if there is a potential for a generic industry issue.