05000219/LER-2010-001
| Oyster Creek | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2192010001R00 - NRC Website | |
Plant Condition Prior to Event Event Date: October 7, 2010 Event Time: 1141 EDT Unit 1 Mode: Power Operation Power Level: 100%
Description of Event
On October 7, 2010, the 'D' 4160V Safety-Related Bus ('D' Bus) was lost during the performance of surveillance 632.2.002, "Grid Undervoltage Channel Functional Test." This test requires the installation of test equipment for the time delay portion of the test. The test equipment was installed and the electricians were waiting for permission to open the test switch for the undervoltage relay, 27 —11D when the control room received the undervoltage alarm, T-3E "Bus 1D Lo Voltage" .
This was followed ten seconds later by alarm T-4E "Bus 1D Volts Lo —Lo" followed approximately two seconds later by a trip of the 'D' Bus main breaker. The No. 2 Emergency Diesel Generator started and loaded as designed in response to the undervoltage condition on the 'D' Bus. Plant response and operator actions were as expected for the event. The normal supply breaker to 'D' Bus was closed at 17:01 and the No. 2 EDG breaker was opened at 17:03. No. 2 EDG was secured at 17:09.
Cause of Event
The cause of the trip of the 'D' Bus main breaker was test equipment failure from chemical attack on the plastic test jacks.
Both the failed terminal and the adjacent terminal exhibited signs of chemical attack from oils, solvents, and/or cleaners.
Additionally, sparks were reported during the event coming from the test equipment jacks. Further investigation found that the test equipment, AVO MultiAmp SST-9203 Digital Timer, connection jack showed signs of electrical pitting and arcing and was internally shorted to ground. After the test equipment was installed and failed, the voltage on two of the undervoltage relays decreased below the set points for degraded voltage conditions opening the 'ID" Bus normal feed breaker and subsequently initiated a valid undervoltage start signal for the No. 2 EDG.
Analysis of Event
This event is being reported pursuant to 10CFR50.73(a)(2)(iv)(A): Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section. The trip of the 'ID' Bus main breaker resulted in the No. 2 Emergency Diesel Generator starting and loading as designed. The Emergency Diesel Generator is a system listed in paragraph 10CFR50.73( (a)(2)(iv)(B).
Corrective Actions
The procedure for test equipment installation will be revised to include pre-use testing of the timer to ensure that the battery of the digital timer is acceptable for use and that the terminals are not shorted or grounded. Additionally a placard will be installed on the timers stating, "Caution — Do not use cleaners or solvents to clean terminals on this unit. Avoid contact with oil on terminals.
Previous Occurrences
There have been no similar Licensee Event Reports submitted at Oyster Creek in the last three years.