05000318/LER-2025-002-01, Condition Prohibited by Technical Specifications Due to Condition 3.7.12.A Required Restoration Time Exceeded
| ML26023A162 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 01/22/2026 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML26023A160 | List: |
| References | |
| LER 2025-002-01 | |
| Download: ML26023A162 (0) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3182025002R01 - NRC Website | |
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APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/202, N~M,f.ORM 366 U.S. NUCLEAR REGULATORY COMMISSION Esbmated
- 1. Facility Name
~ 050
- 2. Docket Number 3.Page Calvert Cliffs Nuclear Power Plant, Unit 2 052 05000318 1 OF 4
- 4. Title Condition Prohibited by Technical Specifications due to condition 3. 7.12 A required restoration time exceeded
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Sequential Revision Facility Name Docket Number Month Day Year Year Number No.
Month Day Year 050 09 24 2025 2025 002 01 01 22 2026 Facility Name Docket Number 052
- 9. Operating Mode 1 - Power Operation 110. Power Level 100
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Abstract
At 1100 on 09/24/2025, Operations personnel were informed the results for Surveillance Test Procedure (STP) for 21 Penetration Exhaust commenced on 9/16/2025 and completed on 9/18/2025 were not acceptable. Based on the unsatisfactory results of the STP, Operations identified there was no reasonable expectation of 21 Penetration Room Exhaust Ventilation System (PREVS) operability and entered the applicable Technical Specification (TS) conditions.
Due to Human Performance issues using improper assumptions and mathematical errors, the unsatisfactory test results were reported beyond the TS 3. 7.12 A required seven-day restoration time beginning on 9/16/2025. The troubleshooting team identified clearance differences when comparing the newly installed filter trays against the previously removed. All trays have since been removed and reseated. 21 PREVS was restored to service on 9/25/2025 following a satisfactory performance of the STP. As a result of the event, it was identified that SR 3. 7.12.2 to verify the required PREVS filter testing in accordance with the Ventilation Filter Testing Program (VFTP) was already past its late end date.
PLANT AND SYSTEM IDENTIFICATION
- 2. DOCKET NUMBER YEAR 05000318 2025 -
- 3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.
01 Calvert Cliffs Nuclear Power Plant, Unit 2, is a Combustion Engineering Pressurized Water Reactor with a licensed maximum power level of 2737 megawatts thermal. The Energy Industry Identification System code used in the text is identified as [VH].
A. CONDITION PRIOR TO EVENT
Unit: 2 Date: September 24, 2025 Power level: 100 percent Mode: Unit 2 was in Mode 1 when the event occurred.
B. DESCRIPTION OF EVENT
At 1100 on 09/24/2025, Operations personnel were informed that the results for Surveillance Test Procedure (STP) for 21 Penetration Exhaust completed on 9/18/2025 were not acceptable. The STP is performed to test the function of 21 Penetration Exhaust Filters (High Efficiency Particulate Air (HEPA) and Charcoal). Based on the unsatisfactory results of the STP, Operations identified there was no reasonable expectation of 21 Penetration Room Exhaust Ventilation System (PREVS) operability and entered the applicable Technical Specification (TS) conditions. Due to Human Performance issues using improper assumptions and mathematical errors, the unsatisfactory test results were reported beyond the TS 3. 7.12 A required seven-day restoration time. The troubleshooting team identified clearance differences when comparing the newly installed filter trays against the previously removed. All trays have since been removed and reseated. 21 PREVS was restored to service on 9/25/2025 following a satisfactory performance of the STP. The cause of the event was due to human performance issues with the calculation of the flow results in STP M-544A-2. As a result of the event, it was identified that SR 3.7.12.2 to verify the required PREVS filter testing in accordance with the Ventilation Filter Testing Program (VFTP) was already past its late end date.
C. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES September 16, 2025 21 Pen Room Exhaust Fan is removed from service for scheduled maintenance. Applicable Limiting Condition for Operability (LCOs) actions were entered and logged when removed from service.
September 18, 2025 Site personnel from Instrument Maintenance Department (IMO) completed an STP for 21 Penetration Room Exhaust Filter Test. The data collected is incorrectly calculated and incorrectly determined to be satisfactory September 24, 2025
- 2. DOCKET NUMBER
- 3. LER NUMBER SEQUENTIAL REV YEAR NUMBER NO.
05000318 2025 -
002 01 1100: IMO supervisor identifies the incorrect calculation and informs Operations that the completed STP results on 9/18/2025 were UNSAT.
1110: Operations entered the applicable TS based on the initial log entries for the start of the maintenance on 9/16/2025.
September 25, 2025 1046: Operations exited the applicable TS following Satisfactory completion of the STP. The troubleshooting team identified clearance differences when comparing the newly installed filter trays against the previously removed. All trays have since been removed and reseated.
D. CAUSE OF EVENT
The cause of the event was due to human performance issues specifical calculation errors by technicians, due tc improper assumptions and mathematical mistakes as required in the STP. There was a failure at the PJB to identify the critical nature of their calculations and how it would affect the LCO condition of the unit. As a result o the errors, the unsatisfactory test results were reported beyond the TS 3. 7.12 A required seven-day restoration time. 21 PREVS was restored to service on 9/25/2025 following a satisfactory performance of the STP.
E. SAFETY ANALYSIS
21 PREVS, Penetration Room Exhaust Ventilation System, is designed to actuate upon receipt of the ESFAS (Engineering Safety Features Actuation System) signal CIS (Containment Isolation Signal). Following a CIS frorr a LOCA event, both fans associated with PREVS will start and will filter the exhaust through the HEPA and charcoal filters. The exhaust is directed into the plant ventilation stack.
The subject event satisfies the criteria in NUREG-1022, Revision 3, for any event or condition that resulted in exceeding the condition required by Technical Specifications. Therefore, this event is reportable pursuant to 1 O CFR 50.73(a)(2)(i)(B).
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 known.
F. CORRECTIVE ACTIONS
A prompt investigation and a HURB (Human Performance Review Board) were conducted. Two l&C technicians performed independent calculations using the data obtained during the conduct of the STP. The two technicians, each independently, used improper assumptions and made mathematical errors that resulted in incorrect result of a satisfactory performance of the test.
Enhancements to the test procedure were identified with actions in progress to revise the STP 21 Penetration Room Exhaust Filter Test.
G. PREVIOUS OCCURRENCES
- 2. DOCKET NUMBER YEAR 05000318 2025 -
- 3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.
01 Below is a list of previous LERs submitted due to Human Performance as a cause that resulted in a condition requiring licensee NRC notification and or a condition prohibited by technical specifications.
LER 317-2016-004 High Energy Line Break Barrier Breeched Due to Human Performance Error Causing Both Service Water Trains to be Inoperable LER 317-2018-004 Unauthorized Unescorted Access to the Protected Area Allowed due to Human Performance Error LER 317-2021-001 1A Diesel Generator Inoperable Due to Potential Transformer Failure LER 318-2019-001 Misapplication of Technical Specification Following Failed Surveillance Resulted in Operation Prohibited by Technical Specifications LER 318-2021-004 Unit 2 Manual Reactor Trip Due to Lowering Steam Generator Levels LER 318-2022-002 Unplanned Safety Injection Actuation Signal due to Human Error LER 318-2024-002 Automatic Reactor Trip Due to Main Turbine Loss of Load LER 318-2024-004 Automatic Reactor Trip Due to Main Turbine Loss of Load
H. COMPONENT FAILURE DATA
Component IEEE 803 FUNCTION ID: VH IEEE805 SYSTEM ID: FLT Page_4_ of _4_