ENS 42751
ENS Event | |
|---|---|
15:27 Aug 2, 2006 | |
| Title | Post Contingency Low Voltage Alarm |
| Event Description | The Rochester Gas and Electric (RG&E) Energy Control Center (ECC) notified Ginna Operations that the Post Contingency Low Voltage Alarm was received for the off site power system. Ginna Operations entered procedure O-6.9, operating Limits for Ginna Station Transmission, and declared the offsite power inoperable per ITS 3.8.1[72 hour LCO]. Per NUREG-1022, section 3.2.7, if either offsite power or onsite emergency power is unavailable to the plant, it is reportable per 50.72(b)(3)(v)(A) regardless of whether the other system is available.
The RG&E Energy Control Center (ECC) monitors 115 Kv voltage using their State Estimation and Contingency Analysis System. The State Estimation portion of the system evaluates real time system power flow and voltages on the 115 and 345 Kv transmission systems. The Contingency Analysis portion analyzes the voltage effect of a Ginna main generator trip concurrent with worst case accident loading. If the Station 13A voltage would drop below the minimum required voltage for offsite power alignment a Ginna Post Contingency Low Voltage Alarm occurs. If the main generator should trip, then the absence of a Post Contingency Low Voltage Alarm on the RG&E State Estimation and Contingency Analysis System will ensure that the subsequent offsite 115kV system voltage transient will not result in Ginna Station experiencing an under voltage condition on the 480V Safeguard Busses. The RG&E ECC notified Ginna operations that the Post Contingency Low Voltage Alarm cleared at 1408 EDST on 08/02/2006 and the LCO for ITS 3.8.1 was exited at 1704 after observation of grid stability. The plant was maintained at 100% steady state conditions throughout the event. The licensee notified the NRC Resident Inspector.
This is an additional notification for EN #42751 that was reported on 8/2/06 for offsite power being declared inoperable. A subsequent investigation revealed that offsite power was also inoperable on 7/17/2006 from 1427 to 1448 and on 8/1/2006 from 1022 to 1843 for which a notification was not completed. The licensee notified the NRC Resident Inspector. Notified R1DO P. Finney
The purpose of this report is to retract one of the events discussed in ENS report #42751 (August 2 and 3, 2006). The ENS report covered three separate off site power related events which occurred on July 17, 2006, August 1, 2006 and August 2, 2006. For each of the events, both sources of off-site power were declared inoperable following notification to R.E. Ginna Nuclear Power Plant that the calculated post contingency off-site system voltage was below the required value necessary to ensure that off-site power would remain available following a design basis accident. Since the ENS report, an engineering analysis of the July 17, 2006 event has been completed. The analysis determined that the off site power system was actually operable at all times on July 17, 2006, The 'post contingency low voltage alarm (PCLVA)' computer model that is being utilized by Rochester Gas & Electric to calculate the post contingency off site system voltage is inherently conservative in that many of the automatic voltage regulators associated with the other generating units are assumed to be in the manual mode. The computer simulation that resulted in the alarm was repeated and by 'turning on' the voltage regulators for four of the nearby generator units, the post contingency voltage improved to above the alarm set point. The four voltage regulators that were turned on in the computer simulation were confirmed to be in the automatic mode on July 17, 2006. As such, the July 17, 2006 event is being retracted. The licensee notified the NRC Resident Inspector. NRC R1DO (Ray Powell) notified. |
| Where | |
|---|---|
Ginna  New York (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor | |
| LER: | 05000244/LER-2006-002 |
| Time - Person (Reporting Time:+3.23 h0.135 days <br />0.0192 weeks <br />0.00442 months <br />) | |
| Opened: | Doug Gomez 18:41 Aug 2, 2006 |
| NRC Officer: | Bill Gott |
| Last Updated: | Dec 20, 2006 |
| 42751 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 460732010-07-06T17:05:0006 July 2010 17:05:00
[Table view]10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor Post Contingency Low Voltage Alarm Received for Offsite Power ENS 427512006-08-02T15:27:0002 August 2006 15:27:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor Post Contingency Low Voltage Alarm 2010-07-06T17:05:00 | |