ENS 45726

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v t e ENS Event
19:18 Feb 25, 2010
Title	Invalid Actuation of Containment Isolation Valves
Event Description	This 60-day notification is being made in accordance with 10 CFR 50.73(a)(1), which states that in case of an invalid actuation reported under 10 CFR 50.73(a)(2)(iv)(A), other than the actuation of the Reactor Protection System (RPS) when the reactor is critical, the licensee may provide a telephone notification to the NRC within 60 days after discovery of the event instead of submitting a written LER. Because plant conditions necessary to prompt a containment isolation were not present, this event constitutes an invalid system actuation under 10 CFR 50.73(a)(2)(iv)(A). The condition meets the criteria of 10 CFR 50.73(a)(2)(iv)(B)(2) because the loss of the Unit 1 'B' RPS bus affected containment isolation valves in more than one system. On 1/4/2010 at 1418 hours0.0164 days <br />0.394 hours <br />0.00234 weeks <br />5.39549e-4 months <br />, the Unit 1 'B' RPS bus was lost. This event resulted in a half scram and primary containment isolations. By design, when the RPS MG set output breaker trips, all EPA breakers downstream of the MG set also trip resulting in a half scram and primary containment isolation signals. An event investigation found the Unit 1 'B' RPS MG set running with its output breaker tripped. The output voltage was indicating 120VAC, which indicates that the voltage regulator was operating properly. Upon removal of the MG set cover, the underfrequency relay (UFR) contacts were found to be chattering, with frequency steady at approximately 60 Hz. A review of plant drawings indicated that a chattering UFR could cause the MG set output breaker to trip. Voltage readings were taken and no additional electrical problems (other than the UFR) were identified. The affected RPS loads were subsequently powered from their alternate source and all actuations and isolations were reset. Inspection and test of the failed UFR found that one leg of a capacitor on the UFR electronic board had broken adjacent to its solder joint connection on the board. It is suspected that the capacitor lead may have been flawed during manufacture of the board. The failure was accelerated by the constant vibration that the connection is subjected to, as the UFR is mounted on the MG set. The failed UFR electronic board was subsequently replaced and successfully passed all functional tests. There were no actual safety consequences associated with this event. Valves affected by the invalid signal fulfilled their isolation function by successfully closing. The RPS loads were transferred to their alternate power supply and the trips and isolations were reset. In addition, the Unit 1 'B' RPS bus did not experience an underfrequency condition. The licensee has notified the NRC Resident Inspector.

ENS 45726 +/-
Where
Susquehanna Pennsylvania (NRC Region 1)
Reporting

10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation
Time - Person (Reporting Time:+-2.97 h-0.124 days <br />-0.0177 weeks <br />-0.00407 months <br />)
Opened:	David Borger 16:20 Feb 25, 2010
NRC Officer:	John Knoke
Last Updated:	Feb 25, 2010
45726 - NRC Website
v • d • e

v t e Emergency Notification System
Susquehanna with 10 CFR 50.73(a)(1), Submit an LER
WEEKMONTHYEAR2019-04-18T05:10:00 [Table view]
[ENS list for Susquehanna]

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