ENS 42957
ENS Event | |
|---|---|
18:34 Nov 2, 2006 | |
| Title | Automatic Turbine Trip/ Reactor Trip Due to Invalid Low Condenser Vacuum Signal |
| Event Description | At 1334 on 11-2-06 an Automatic Reactor Trip occurred from 100% power. All systems functioned as required. One safety valve stuck open on both OTSGs. They subsequently re-seated. An employee working on the roof at the time of the trip fell off a ladder and injured his leg. Emergency medical was contacted to assist with the injured worker. Two fire trucks and an ambulance was dispatched to the site to remove the injured worker. The worker was not contaminated. There is no indication of any OTSG tube leaks. Initial investigation indicates the reactor tripped, due to a turbine trip due to an invalid low vacuum signal.
State and local officials will be notified of this event by the licensee. I&C Techs were performing maintenance on one of the low pressure vacuum switches. An electrical fault fed to the other two low pressure vacuum switches causing a 2 out of 3 signal which resulted in a turbine trip followed by a reactor trip signal, as expected. All rods fully inserted into the core. One safety valve (9 safety valves on each OTSG) on each Once Through Steam Generator stuck open. OTSG "B" safety relief valve was open less than one minute. There are no leaking OTSG tubes. A condensate relief valve located in the turbine building opened/shut - nobody injured. The ICS (Integrated Control System) operated as expected. All emergency core cooling systems and the emergency diesel generators are fully operable plus the electrical grid is stable. A licensee working on the industrial coolers on top of the industrial building, standing on a ladder, fell off the ladder when OTSG relief valve opened. Licensee either broke or badly sprained his leg. The NRC Resident Inspector was informed of this event by the licensee.
Post trip evaluation determined that the Main Steam safety valves were not stuck open. The safety valves were operating within their tolerance band. The "B" OTSG Main Steam safety valve reseated with no operator action as steam pressure decreased. The "A" Main Steam safety valve was reseated when operators lowered OTSG pressure in accordance with Plant Operating Procedures. TMI-1 issued a press release on this event at 15:13 on 11/2/06." R1DO (John White) notified. The NRC Resident Inspector was notified of this update by the licensee. |
| Where | |
|---|---|
Three Mile Island  Pennsylvania (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(2)(iv)(B), RPS Actuation 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release | |
| LER: | 05000289/LER-2006-002 |
| Time - Person (Reporting Time:+-3.68 h-0.153 days <br />-0.0219 weeks <br />-0.00504 months <br />) | |
| Opened: | Joe Shoffnen 14:53 Nov 2, 2006 |
| NRC Officer: | John Mackinnon |
| Last Updated: | Nov 3, 2006 |
| 42957 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | A/R |
| Before | Power Operation (100 %) |
| After | Hot Shutdown (0 %) |
Three Mile Island with 10 CFR 50.72(b)(2)(xi), Notification to Government Agency or News Release, 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | |
WEEKMONTHYEARENS 565602023-06-06T13:37:0006 June 2023 13:37:00
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