05000317/LER-2025-001, Nuclear Power Plant, Unit 1, Control Room Loss of Ventilation Due to Smoke Detector Failure Causing Common Supply Damper to Shut
| ML25270A004 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 09/29/2025 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25270A002 | List: |
| References | |
| LER 2025-001-00 | |
| Download: ML25270A004 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3172025001R00 - NRC Website | |
text
Abstract
On July 31, 2025, at 1744, the Main Control Room (MCR), shared by Units 1 and 2, experienced a loss of ventilation due to the Control Room supply damper fully closing. Closure of the damper isolated the ventilation flow to the Control Room which resulted in both trains of the Control Room Emergency Ventilation System (CREVS) and Control Room Emergency Temperature System (CRETS) being inoperable, resulting in Technical Specification Limiting Condition for Operations (LCO) 3.7.8 and 3.7.9 not being met, respectively, for Units 1 and 2. At time 1745, the Units exited the associated LCO after the damper returned to its normal, open position. Field troubleshooting isolated the cause of the intermittent closure of the damper to a MCR ventilation smoke detector. The smoke detector functions to shut the MCR supply damper by energizing the associated solenoid valve. This event is reportable in accordance with 10 CFR 50.73(a)(2)(v)(D) and 10 CFR 50.73(a)(2)(vii). The cause of the smoke detector failure is under investigation and will be reported in a supplement to this LER.
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) Page 3 of 3
D. CAUSE OF EVENT
Troubleshooting to determine the cause of intermittent closure required leads to the smoke detector to be lifted via a controlled process. The cause of the issue is under investigation. The supplement LER will provide detailed information from the causal product.
E. SAFETY ANALYSIS
The subject event satisfies the criteria in NUREG-1022, Revision 3 Supplement 2, 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 and a common cause of inoperability. Therefore, this event is reportable pursuant to 10 CFR 50.73(a)(2)(v)(D) and 50.73(a)(2)(vii).
No SSCs that were inoperable at the start of the event contributed to the event and the failure mode, mechanism, and the effect of each failed component is under investigation. The results will be provided in the supplemental LER.
F. CORRECTIVE ACTIONS
The cause of the issue is under investigation. The Supplemental Report to the LER will provide corrective actions from the causal product.
G. PREVIOUS OCCURRENCES The cause of the issue is under investigation. A similar issue occurred in July 2018 as documented in LER 317-2018-003-00 and supplement LER 317-2018-003-01.
H. COMPONENT FAILURE DATA
Component IEEE 803 IEEE805 FUNCTION ID SYSTEM ID Breaker DET VI