ENS 57694
ENS Event | |
|---|---|
01:08 May 7, 2025 | |
| Title | Specified System Actuation - Automatic Start of Emergency Diesel Generator |
| Event Description | The following is a summary of information that was provided by the licensee via phone and fax:
At 2108 EDT, on May 6, 2025, with Unit 3 in mode 5 at zero percent power, the plant received main steam line isolation, containment isolation phase 'A', and a safety injection signal which caused the emergency diesel generator to automatically start. The initiation signals were cause by inadvertent clearing of the pressurizer pressure low interlock during maintenance. There was no impact to decay heat removal, no injection into the core, and no loading of the emergency diesel generator. Operations staff responded and returned the plant to normal mode 5 operations. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.
The following is a summary of information that was provided by the licensee via phone and email: Millstone Unit 3 is retracting NRC event notification57694 regarding the inadvertent main steam line isolation, containment isolation phase 'A' and a safety injection (SI) signal which caused the emergency diesel generators to automatically start on May 6, 2025. This was reported as a valid actuation under 10 CFR 50.72(b)(3)(iv)(A). Subsequent evaluation has determined that the actuations were the result of an invalid signal caused by pinching a wire during a maintenance activity, which automatically unblocked the P-11 permissive. P-11 is a reactor protection permissive that automatically enables SI actuation when pressurizer pressure increases above 2000 psia. The permissive was unblocked as the result of the spiked pressurizer pressure indication caused by the pinched wires coincident with bistables associated with a separate pressurizer pressure channel tripped to support rescaling activities. With the plant shutdown, steam line pressures were low which met the condition to require a SI actuation with P-11 unblocked. This unblocking and resultant actuation was not a result of valid signals and was not an intentional manual actuation. The pinching of a wire causing a spike is not a valid signal and was not representative of actual plant conditions. Therefore, this condition is not reportable, and NRC EN 57694 is being retracted. The basis for this conclusion has been provided to the acting NRC Senior Resident Inspector." Notified R1DO (Warnek) |
| Where | |
|---|---|
Millstone  Connecticut (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
| Time - Person (Reporting Time:+1.65 h0.0688 days <br />0.00982 weeks <br />0.00226 months <br />) | |
| Opened: | Adam Stachowiak 02:47 May 7, 2025 |
| NRC Officer: | Kerby Scales |
| Last Updated: | Jun 19, 2025 |
| 57694 - NRC Website
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