05000237/LER-2025-001, Ultimate Heat Sink Inoperable Due to River Grass Accumulation
| ML25280A003 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 09/29/2025 |
| From: | Hardik Patel Constellation Energy Generation |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVPLTR 25-0060 LER 2025-001-00 | |
| Download: ML25280A003 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 2372025001R00 - NRC Website | |
text
Constellation September 29, 2025 SVPL TR 25-0060 U.S. Nuclear Regulatory Commission ATTN : Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Units 2 and 3 Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450 10 CFR 50.73 Renewed Facility Operating License Nos. DPR-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249
Subject:
Licensee Event Report 237/2025-001-00, Ultimate Heat Sink Inoperable due to River Grass Accumulation Enclosed is Licensee Event Report 237/2025-001-00, Ultimate Heat Sink Inoperable due to River Grass Accumulation. This report describes an event being reported in accordance with 10 CFR 50.73(a)(2)(v)(B) for an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat.
There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this letter, please contact Mr. Daniel J. Murphy, Regulatory Assurance Manager, at (779) 231-7443.
~
Hardik Patel Site Vice President Dresden Nuclear Power Station
Enclosure:
Licensee Event Report 237 /2025-001-00
Abstract
On July 30, 2025, at 1645 CDT, Technical Specification (TS) 3.7.3, "Ultimate Heat Sink (UHS)" Limiting Conditions for Operation (LCO) was not met, and Condition A, UHS Inoperable, was entered due to UHS water level below 501.5 feet. TS 3.7.3 Condition A was exited at 1653 CDT when UHS water level was restored to >/= 501.5 per Surveillance Requirement (SR)
- 3. 7.3.1. The cause of the low water level was due to accumulation of river vegetation and grass on the Unit 2/3 Intake Bay 13 bar racks. Corrective actions included clearing river vegetation from the Unit 2/3 Intake Bay 13 bar racks, troughs, and traveling screens, as well as transitioning the lake cooling system to partial closed cycle. An evaluation of the event is currently in progress to determine any contributing causes to the event as well as additional corrective actions.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(B), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat."
PLANT AND SYSTEM IDENTIFICATION - UNIT 2
- 2. DOCKET NUMBER
- 3. LER NUMBER SEQUENTIAL REV YEAR NUMBER NO.
00237 2025 -
001 00 General Electric - Boiling Water Reactor, 2957 megawatts thermal rated core power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
A. CONDITIONS PRIOR TO EVENT
Unit: 2 Reactor Mode: 1 Event Date: July 30, 2025 Mode Name: Power Operation Event Time: 1645 CDT Power Level 100%
No systems, structures, or components that were inoperable at the start of the event contributed to the event.
B. DESCRIPTION OF EVENT
On July 30, 2025, at 1635 CDT, Operations entered the abnormal operating procedure for 2/3 Cribhouse [NN]
plugging due to intake bay levels at 503 feet. At 1645 CDT, a non-licensed operator reported that Bay 13 level was less than 501.5 feet due to a significant grassing event impacting the Cribhouse [NN] Intake Canal log boom and bar racks. This condition did not meet Technical Specification (TS) 3.7.3, "Ultimate Heat Sink (UHS)" [BS], and required entering Condition A, UHS Inoperable. The associated Required Actions and Completion Times were A.1, be in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and A.2, be in Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Actions were taken to clear river vegetation and grass from the intake bar racks, troughs, traveling screens. Condition A was exited when U HS [BS] water level was restored to >/= 501. 5 feet at 1653 CDT.
The NRC was notified via ENS 57841 at 2341 CDT on July 30, 2025.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(B), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat."
C. CAUSE OF EVENT
The cause of low water level was due to accumulation of river vegetation and grass on the Unit 2/3 Bay 13 Intake bar racks. An evaluation of the event is currently in progress. A supplemental report will be submitted with the conclusions of this evaluation.
D. SAFETY ANALYSIS
The UHS [BS] consists of water sources from either the Kankakee River (normal) or the cooling lake (alternate) and can be aligned as either a closed cycle operating system utilizing the cooling lake and canals, or an open cycle operating system with the discharge returning to the Illinois River.
The Ultimate Heat Sink (UHS) [BS] provides a suction pathway for the cooling water associated with Containment Cooling Service Water (CCSW) [Bl], and Diesel Generator Cooling Water (DGCW) [LB] systems.
The TS Surveillance Requirement (SR) verifies water level in the suction bays is sufficient for proper operation of the CCSW [Bl] and DGCW [LB] pumps [P]. The CCSW [Bl] pumps [P] take suction from Bay 13.
- 2. DOCKET NUMBER
- 3. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.
00237 2025 -
001 00 There were no actual safety consequences affecting the general safety of the public, nuclear safety, industrial safety, or radiological safety because of this event. The station did not operate beyond TS Required Action Completion Times. The duration of the degraded condition (i.e., UHS [BS] inoperability) was 8 minutes.
E. CORRECTIVE ACTIONS
Corrective actions included clearing river vegetation from the Unit 2/3 Intake Bay 13 bar racks, troughs, and traveling screens, as well as transitioning the lake cooling system to partial Closed Cycle. An evaluation is in progress to determine any contributing causes, as well as additional corrective actions.
F. PREVIOUS OCCURENCES
A 5-year internal corrective action program and Licensee Event Report (LER) database review was performed for Dresden Nuclear Power Station (DNPS). One similar event at DNPS occurred in 2022 and was reported in LER 2022-002-01. The root cause of this event was determined to be procedures and processes were not aligned with industry excellence standards to prevent intake blockage events. The primary corrective action was implementation of a new site-specific procedure to implement predictive measures for macrophyte blockage events and prevent grass intrusion into the intake structure by calling for vendor support to sweep away upstream debris, cleaning the log boom, and transitioning to closed cycle. This occurrence is being reviewed for potential applicability to the issue documented in this report as part of the evaluation currently in progress.
G. COMPONENT FAILURE DATA
Not applicable Page_3_ of _3_