ENS 46073
ENS Event | |
|---|---|
17:05 Jul 6, 2010 | |
| Title | Post Contingency Low Voltage Alarm Received for Offsite Power |
| 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 offsite 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 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 34.5 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 1311 EDST on 07/06/2010. The plant was maintained at 100% steady state conditions throughout the event. Both circuits remain inoperable but available for use. And will be restored to operable status when the system reliability is assured. The licensee notified the NRC Resident Inspector.
The purpose of this report is to retract the event discussed in ENS report #46071 (July 6, 2010). The ENS report covered an offsite power related event which occurred on July 6, 2010. In this event, both sources of offsite power were declared inoperable following notification to the R.E. Ginna Nuclear Power Plant that the calculated post contingency off-site system voltage was below the required value necessary to ensure that offsite power would remain available following a design basis accident. Since the ENS report, an engineering analysis of the event has been completed. The analysis determined that the offsite power system was actually operable at all times on July 6, 2010. The 'Post Contingency Low Voltage Alarm (PCLVA)' computer model that is being utilized by the transmission system provider, Rochester Gas & Electric, to calculate the post contingency offsite system voltage, is inherently conservative in that it assumes the site is relying on a worst case single source of offsite power. However on July 6, 2010, both offsite power sources were available and the site was aligned in the 50/50 Normal offsite power configuration. The engineering analysis calculated the acceptable voltage in this configuration and identified that at no point did the calculated post contingency voltage decrease below the 50/50 Normal offsite power configuration's acceptable value. As such, the July 6, 2010 event is being retracted. The licensee notified the NRC Resident Inspector. R1DO (Burritt) was notified. |
| Where | |
|---|---|
Ginna  New York (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor | |
| Time - Person (Reporting Time:+0.95 h0.0396 days <br />0.00565 weeks <br />0.0013 months <br />) | |
| Opened: | Benjamin Chang 18:02 Jul 6, 2010 |
| NRC Officer: | Dong Park |
| Last Updated: | Aug 20, 2010 |
| 46073 - 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 | |