05000331/LER-2015-005
| Duane Arnold Energy Center | |
| Event date: | 10-20-2015 |
|---|---|
| Report date: | 12-16-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 51484 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3312015005R00 - NRC Website | |
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I. Description of Event:
On October 20, 2015 at 1800, while operating at 100% power, a voltage transient due to a lightning strike resulted in an automatic start of both of the site's Emergency Diesel Generators (EDGs) (IEE Code EK). Neither EDG loaded onto its respective essential bus.
The EDGs started as a result of a dip in essential bus voltage to 62% that did not fully recover for approximately 24 cycles. A review of the system design showed that since the EDGs started on an automatic start signal of essential bus voltage less than 65% for greater than 12 cycles, the EDGs operated as designed. The 'A' EDG was secured at 1930 on October 20, 2015. The 'B' EDG was secured at 1947 on October 20, 2015.
There were no radiological releases associated with this event. There were no other structures, systems or components inoperable at the start of this event that contributed to the event.
II. Assessment of Safety Consequences:
The automatic starting of the EDGs in response to a short-duration under voltage condition had no personnel or radiological safety significance. Since the EDGs were capable of fulfilling their safety function throughout this event, there was no nuclear safety significance.
This event resulted in an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> reportable event. The Resident Inspector was notified, and Event Notification Number 51484 was made pursuant to 10 CFR 50.72(b)(3)(iv)(A) due to a valid system actuation. This event did not result in a safety system functional failure. There were no automatically or manually initiated safety system responses.
III. Cause of Event:
An Apparent Cause Evaluation was completed. The apparent cause of the starting of both EDGs was a storm-induced voltage dip (fault) that was not appropriately mitigated by the Transmission Operator's 900MHZ radio trip signal. A review of the system design showed that since the EDGs started on an automatic start signal of essential bus voltage less than 65% for greater than 12 cycles, the EDGs operated as designed.
IV. Corrective Actions:
The 'A' EDG was secured at 1930 on October 20, 2015. The 'B' EDG was secured at 1947 on October 20, 2015.
Actions have been initiated by the local balancing authority and the Transmission Operator to replace the 900MHZ radio path with fiber optic cable to prevent an electrical storm from, blocking the signal path.
Duane Arnold Energy Center 05000-331
V. Additional Information:
Previous Similar Occurrences:
A review of DAEC Licensee Event Reports from the past 5 years identified one similar occurrence. Reference LER 2014-005, "Automatic Start of Standby Diesel Generators Due to Grid Disturbance".
EIIS System and Component Codes:
EK — Emergency Onsite Power Supply System Reporting Requirements:
This event is being reported due to a valid system actuation, 10CFR50.73(a)(2)(iv)(A).