|Vogtle Electric Generating Plant|
|Reporting criterion:||10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications|
|4252017001R01 - NRC Website|
|Person / Time|
|From:||Myers D J|
Southern Nuclear Operating Co
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17180A527 (4)|
Infocollects Resource@nrc.goy and to the Desk Officer Office of Information and Regulatory Affairs NEOB-10202 (3150-0104) Office of Management and Budget Washington DC 20503 If a means used to impose an information cm'ection does not display a currently valid OMB contra number the NRC may not conduct or sporsor and a person is not required to respond to the nformation collection Vogtle Electric Generating Plant 05000-425 2017
A. Event Description
On March 15, 2017 during a review of past events with the Unit 2 A-Train Emergency Diesel Generator (EDG)[DG], it was discovered that a power supply that supports the "B" ventilation supply fan NJ] failed between the diesel run on January 16, 2017 and February 13, 2017. The EDG has two power supplies supporting a common speed sensing circuit and one ventilation fan each. The EDG can successfully operate with one power supply supporting the speed sensing circuit. The "A" ventilation fan immediately starts upon EDG start. The "B. ventilation fan enters stand-by on EDG start and operates once thermostat temperature reaches 93F. Per Vogtle TS 3.8.3 Condition F, if a ventilation supply fan is not operable, the fan must be restored operable within 14 days or the associated EDG must be declared inoperable. This restoration time was not met as the condition was not identified by operators because no indication is available to reveal the failure while the EDG is in standby. Per TS 3.8.3, Condition G, operators should have declared the associated EDG inoperable on February 27, 2017 and entered TS 3.8.1.
Condition B. TS 3.8.1 Condition B allows a1 hour
completion time for verification of certain electrical parameters and if these are not completed, Condition C is entered, which is a 72-hour shutdown action. Because it was not recognized that the power supply was failed, these actions were not taken and the plant operated in a condition prohibited by TS from the time the power supply failed until the power supply was replaced on March 9, 2017.
Subsequently, between February 13 and February 22, 2017, the second power supply failed resulting in both ventilation supply fans being inoperable. This condition was also not identified by the operators due to no indication being available to reveal the failure. The TS required action for this condition (TS 3.8.3 Condition G) is to immediately declare the associated EDG inoperable. Declaration by the operators of the 2A EDG inoperable per TS 3.8.1 Condition B would have allowed a 1-hour completion time for verification of certain electrical parameters and if these are not completed, Condition C is entered, which is a 72-hour shutdown action. Because it was not recognized that these power supplies were failed, these actions were not taken and the plant operated in a condition prohibited by TS.
On March 8, the 2A EDG was started for a monthly surveillance; however, normal start indications were not working and the operators shut down the EDG and declared it inoperable. During troubleshooting, the two power supplies were found failed and both were replaced March 9, 2017. Once the work was complete, the 2A EDG ran successfully.
The unit operated in Mode 1 at 100 percent power during the entire time of these events.
Because the unit operated in a condition prohibited by Technical Specifications, these events are reportable as required by 10 CFR 50.73(a)(2)(i)(B).
B. Cause of Event
The cause of the operation in a condition prohibited by TS was a failure to recognize that the power supply had failed and rendered the ventilation supply fans inoperable. The reason for the failure of the power supplies has been attributed to random voltage spikes on the DC bus. The most likely cause is the battery charger on the circuit.
C. Safety Assessment During the first condition prohibited by Tech Specs, the EDG was able to start and load its associated safety related electrical bus because the second power supply was still available. As discussed in the Tech Spec Bases.
except in extreme temperatures, only one fan is needed to keep the temperature in the EDG room below the limit of 120F. During the time that this fan was inoperable, the outside temperatures remained well below the 93F limit for single fan operation as listed in the TS Bases. Because the EDG could perform its required safety function during this time, the safety significance of this event was very low.
For the second condition prohibited by Tech Specs, the EDG would have started but would not have automatically loaded the electrical bus due to an electrical permissive from the speed sensing circuit powered by the failed power supplies. During this time, the opposite train EDG was fully operable and both power supplies were verified comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission. Washington, DC 213555-0001. or by e-mail to used to impose an information coPection does rot display a currently valid OMB control number, the NRC may not conduct or sponsor and a person is not required to respond to, the information collection 2 DOCKET NUMBER 3. LER NUMBER 1. FACILITY NAME Vogtle Electric Generating Plant 05000-425 2017 - 001 - 01 to be operational. This would have allowed an electrical safety bus to be powered during an accident. Additionally, all required offsite electrical sources were available and the combustion turbines with blackstart capabilities, adequate fuel, along with the associated underground power line at Plant Wilson were available and were within their required reliability parameters. These capabilities were determined well after the condition occurred and the diesel was repaired. The capabilities of other electrical sources were not evaluated during the period of inoperability. However, with these additional measures available for supplying the safety related electrical bus, the safety significance of this event was very low.
D. Corrective Actions
Both power supplies for the 2A EDG were replaced when it was recognized that they were failed. The "A" battery charger that was in service upstream of these power supplies during all the failures was taken out of service and the "B" battery charger was put into service. During a recent 2A EDG maintenance period, the "A" battery charger was rebuilt and components sent off for failure analysis. Lastly, there is continuous monitoring of the DC bus looking for random voltage spikes. None have been detected since the monitoring was put into place.
E. Previous Similar Events: