05000237/LER-2009-006
| Docket Number Sequential Revmonth Day Year Year Month Day Year Dresden, Unit 3 05000249Number No. | |
| Event date: | 11-12-2009 |
|---|---|
| Report date: | 12-17-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2372009006R01 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Dresden Nuclear Power Station (DNPS) Unit 2 is a General Electric Company Boiling Water Reactor with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as [XX].
A. Plant Conditions Prior to Event:
� Unit: 02� Event Date: 11-12-2009 Event Time: 1114 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.23877e-4 months <br /> CST �Reactor Mode: 5 � Mode Name: Refueling Power Level: 000 percent
B. Description of Event:
On 11/12/2009 plant personnel were performing the integrated functional test of the Division 2 Undervoltage (UV) and Emergency Core Cooling System (ECCS) actuation logic in accordance with plant procedures. The test was being performed to demonstrate Technical Specification Surveillance Requirements specified in Sections 3.3.5.1 ECCS Instrumentation, 3.3.8.1 LOP Instrumentation, 3.5.1 ECCS - Operating, and 3.8.1 AC Sources - Operating.
During the logic test, initiation signals for the Unit 2 Emergency Diesel Generator (EDG) [EK] and ECCS system are injected to cause system actuations. In the event of an UV, the logic is designed to shed electrical loads and sequence selected loads onto buses being supplied by the EDG. This logic prevents the EDG from being overloaded. Some required loads are designed to be manually reestablished following a successful start of the associated EDG.
At approximately 1114 hours0.0129 days <br />0.309 hours <br />0.00184 weeks <br />4.23877e-4 months <br />, plant personnel attempted to manually reestablish the 480 VAC loads, Motor Control Center (MCC) 29-8 [ED], associated with the control room emergency ventilation system [VI] by closing the feeder breaker from Bus 29 [ED]. However, the feeder breaker failed to close. Operation personnel entered Dresden Abnormal Operating Procedures due to the failure of the control room emergency ventilation to start.
In accordance with Abnormal Operating Procedures, control room doors were opened to maintain control room temperature within prescribed limits. With the doors opened, the control room envelope boundary was declared inoperable which required entry into Technical Specification 3.7.4 Condition B.
Following the failure of the breaker to close, troubleshooting activities were commenced.
The breaker malfunction resulted in the inability of the control room emergency ventilation system to perform its intended safety function. Therefore, this condition is being reported as an event that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident in accordance with 10 CFR 50.73(a)(2)(v)(D).
C. Cause of Event:
As a part of troubleshooting, the breaker was racked out and inspected. During the cubicle inspection, plant personnel observed a dark discoloration on the secondary contact slides. The discoloration appeared to be baked on lubrication and oxidation. The secondary slides were thoroughly cleaned until the discoloration had been removed.
The failed breaker was quarantined and subsequently sent to a vendor for failure analysis. The failure analysis testing could not repeat the conditions which the breaker exhibited when installed at the site. Reduced control voltage testing at 90 Vdc was also performed with only one case where the breaker did not close due to the closing coil not being allowed to cool down between tests. However, at full voltage the coil operated successfully each time.
Based on the troubleshooting by plant personnel and the vendor performed failure analysis, the most likely cause of the breaker failure is poor continuity between the secondary contacts and the contact slides. The existing PM activities did not require the contact slides to be thoroughly cleaned. This allowed a buildup of lubricant and oxidation on the contact slides.
D.S Safety Analysis:
The health and safety of the public was not compromised as a result of this condition due to the availability of safety systems needed to mitigate offsite releases and remove residual heat.
Therefore, the safety significance of this event is minimal. Additionally, the capability to shut the plant down and maintain it in a safe condition was not compromised during this condition. Offsite power was available during the course of this event. The function was restored well within the required completion time of the plant's technical specifications.
E. Corrective Actions:
The breaker was replaced and the system successfully tested. Troubleshooting and a failure analysis were performed.
The four-year preventative maintenance activity for these types of cubicles was revised to include an activity to clean the secondary contact slides with an abrasive pad to remove the buildup of baked on lubricant and oxidation.
Since the closing coil exhibited an intermittent malfunction during the failure analysis testing, the closing coil was replaced.
F. Previous Occurrences:
A review of DNPS Licensee Event Reports (LERs), which occurred within the past three years was performed and no control room emergency ventilation failures due to breaker failure events were identified.
G. Component Failure Data:
Manufacturer Model Component General Electric AK-25 Circuit Breaker