ENS 44715

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v t e ENS Event
18:18 Oct 24, 2008
Title	Inadvertent Actuation of Engineered Safeguards System from Relay Sensing Circuit
Event Description	This event is being reported via a telephone notification to the NRC Operations Center within 60 days after discovery of the event instead of submitting a written LER. In this case, the telephone report is not considered an LER. This report is being made under 10CFR 50.73 (a)(2)(iv)(A). During Engineered Safeguards Actuation System (ESAS) logic testing on October 24, 2008, an invalid actuation of the following heat removal systems occurred: 'B' train of the Decay Heat River Water System (DR), 'B' train of the Decay Heat Closed Cooling Water System (DCCW), and the 'B' train of the Nuclear Services River Water System (NR). There was no injection into the Reactor Coolant System. The invalid actuation occurred when the channel under test was taken to its tripped position. Since ESAS utilizes a 2 out of 3 logic for actuation, another actuation signal was present on one of the two channels not being tested, satisfying the actuation logic for the affected systems. The invalid actuation of these heat removal systems during testing on October 24, 2008 was due to oxidation on a silver-plated contact in one of the other two channels that was not being tested. This contact oxidation caused a higher input resistance to the timer relay, which resulted in an inadvertent actuation of the relay and its associated systems. The contact oxidation was caused as a result of using silver plated contacts in a low voltage application (approximately 12 VDC). During this invalid actuation, the heat removal systems were fully actuated. These heat removal systems functioned successfully and the operation of these systems did not have any adverse impact on plant operation. All of the silver-plated contacts in the affected circuits will be replaced with gold-plated contacts. The contacts are scheduled to be replaced by December 18, 2008. The NRC Resident Inspector has been notified.

ENS 44715 +/-
Where
Three Mile Island Pennsylvania (NRC Region 1)
Reporting

10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation
Time - Person (Reporting Time:+1165.12 h48.547 days <br />6.935 weeks <br />1.596 months <br />)
Opened:	Adam Miller 08:25 Dec 12, 2008
NRC Officer:	Karl Diederich
Last Updated:	Dec 12, 2008
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v • d • e

v t e Emergency Notification System
Three Mile Island with 10 CFR 50.73(a)(1), Submit an LER
WEEKMONTHYEAR2017-03-24T18:25:00 [Table view]
[ENS list for Three Mile Island]

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