ENS 42995
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ENS Event | |
|---|---|
05:18 Nov 16, 2006 | |
| Title | Reactor Trip Due to Turbine Trip and Discovery of After-The-Fact Emergency Condition of an Unsual Event |
| Event Description | At 0018 Calvert Cliffs Unit 2 experienced an automatic reactor trip due to a turbine trip. "At the time a clearance order was being performed for upcoming maintenance on P-13000-2 [transformer]. As a result of the turbine trip, RCS pressure rose to approximately 2420 psia causing the PORV's to open. Unexpectedly, a Pressurizer Safety Valve, RV-200 also lifted and reclosed when RCS pressure was lowered to approximately 1500 psia. As a result of the pressure decrease, a Safety Injection Actuation Signal (SIAS) occurred. Once the Pressurizer Safety Valve reclosed, RCS pressure began to rise to return to normal values.
Decay heat is being removed via normal methods through the Turbine Bypass Valves to the Condenser. Normal Feedwater is being used. No Auxiliary Feedwater actuation occurred. Two Reactor Coolant Pumps were secured as a result of the SIAS. The plant responded normally to the event. The plant is currently stable and operators are conducting a plant cooldown to mode 5. All control rods fully inserted. The licensee notified the NRC Resident Inspector.
The automatic trip was due to high RCS pressure from the closure of the Turbine Intercept Valves. Both PORV's opened as designed. One remained open approximately 1.5 minutes causing RCS pressure to reduce to 1500 psia. The PORV should have closed at 2400 psia. Relief Valve 200 (RV-200) did not open as previously reported and was not the cause of the RCS pressure lowering. Acoustic monitoring indication were due to the close proximity of the PORV. Since the SIAS signal did not cause a reportable ECCS actuation, the reported 50.72(b)(2)(iv)(A) ECCS Actuation is retracted. The licensee notified the NRC Resident Inspector. Notified R1DO (P. Henderson).
Upon further review, the licensee has determined that this event met the criteria for Unusual Event Emergency Action Level (EAL A.U.2.2.1) for identified RCS leakage greater than 25 gpm. The licensee met this criteria for the duration that the PORV valve remained open (less than 2 minutes). The licensee did not recognize that it had met the criteria at the time of the event and is reporting this as an after-the-fact emergency condition of unusual event per the guidance in NUREG-1022. The licensee notified the NRC Resident Inspector. Notified R1DO (P. Henderson), NRR EO (Ross-Lee), and IRD Manager (Leach). |
| Where | |
|---|---|
Calvert Cliffs  Maryland (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(2)(iv)(B), RPS Actuation 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
| Time - Person (Reporting Time:+-2.27 h-0.0946 days <br />-0.0135 weeks <br />-0.00311 months <br />) | |
| Opened: | Kevin Umphrey 03:02 Nov 16, 2006 |
| NRC Officer: | Bill Gott |
| Last Updated: | Nov 17, 2006 |
| 42995 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | A/R |
| Before | Power Operation (100 %) |
| After | Hot Standby (0 %) |
Calvert Cliffs with 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation | |
WEEKMONTHYEARENS 573722024-10-10T09:57:00010 October 2024 09:57:00
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