05000454/LER-2015-003
| Byron Station, Unit 1 | |
| Event date: | 10-08-2014 |
|---|---|
| Report date: | 08-27-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4542015003R01 - NRC Website | |
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Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocdlects.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 collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor and a person is not required to respond to, the intonation collection, A. Plant Condition Prior to Event Event Date/Time: October 8, 2014 / 2130 hours0.0247 days <br />0.592 hours <br />0.00352 weeks <br />8.10465e-4 months <br /> CST Unit 1 - Mode 1 - Power 100 percent Reactor Coolant System [AB]: Normal operating temperature and pressure.
B. Description of Event
On November 20, 2014 at 1248 hours0.0144 days <br />0.347 hours <br />0.00206 weeks <br />4.74864e-4 months <br />, the Byron Station Main Control Room (MCR) received an alarm identifying that fuel oil level was low on one of two Diesel Oil Storage Tanks (DOSTs) associated with the Unit 1, B-train (1B) Emergency Diesel Generator (DG). At 1328 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.05304e-4 months <br />, the MCR received an alarm identifying level was also low in the second DOST associated with the 1B DG. Operators determined that the low level condition was due to leakage to the Unit 1, A-train (1A) fuel oil storage system through one of two 1 A DOST inlet valves. This meant that diesel fuel oil was being transferred from the 1B DOSTs to the 1 A DOSTs. Operators identified leak- by through the normally closed 1A DG DOST inlet valve (1D0001C). The valve was immediately cycled in order to re-seat the valve. The valve was verified to be closed and the overflow was stopped.
On December 22, 2014 at 1351 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.140555e-4 months <br />, the same overflow condition occurred for a second time at the same inlet valve. This condition prompted Engineering to determine if the 1B DOSTs would be able to supply enough fuel to the 1B DG for the required design basis mission time of seven days. The analysis concluded that the loss of volume from the 1B DOSTs to the 1 A DOSTs would result in the 1B DG not meeting its design mission time without Operator intervention.
The Corrective Action Program investigation identified that leakage initially occurred when an adjacent manual isolation valve was verified opened on October 8, 2014 to complete a FLEX modification, after which the 1A DG DOST inlet valve was left as a single isolation point.
Two periods of time were identified during which the 1B DG was determined to be previously inoperable. They occurred as follows: October 8, 2014 through November 20, 2014 (32 days), and December 10, 2014 through December 22, 2014 (12 days). The 1A DG was operable and available at all times.
Byron TS 3.8.3, "Diesel Fuel Oil," Condition A requires each DG have a storage volume of at least 44,000 gallons of fuel. The Byron TS Bases B 3.8.3 states that the stored diesel fuel oil is required to have sufficient supply for seven days of post-accident load operation. Although the station was still in compliance with TS 3.8.3, Condition A (i.e., diesel fuel oil volume never dropped below 44,000 gallons) when it was determined the 1B DG could not meet its required mission time, the DG would have been considered inoperable in accordance with TS 3.8.3, Condition D, "One or more DGs with diesel fuel oil not within limits for reasons other than Condition A, B, or C.
Condition D requires the associated DG to be declared inoperable immediately. Byron TS 3.8.1, AC Sources — Operating,' Condition B "One required DG inoperable," provides for an allowed completion time of 14 days to restore the respective DG. The 14 day allowed outage time for TS 3.8.1, Condition B was exceeded during the 32 day period that the 1B DG was inoperable. Additionally, Byron TS 3.8.1 contains Required Actions to be performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> that were not performed during either the 32 day period or the 12 day period. This condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) for an operation or condition prohibited by Technical Specifications.
Byron Station, Unit 1 05000454 Byron Operations subsequently performed a review of opposite train equipment status during the time periods identified to determine whether a Loss of Safety Function occurred. This review identified that the 1A DG was operable and available at all times; therefore, there was no Loss of Safety Function during these periods.
C. Cause of Event
The cause of the event was leak-by from the 1D0001C inlet valve that allowed fuel to transfer from the B-train tanks to the A-train tanks The cause for the DOST inlet valve (1 D0001 C) leaking is under investigation, and the valve has not been repaired or replaced. This condition is acceptable until the inlet valve is replaced, as the mitigating action to close inline manual valve, 1 D0055B, has stopped all loss of fuel oil inventory. Leaking inlet valve 1 D0001 C will be repaired under Byron Work Order 01796243.
This event has been thoroughly reviewed under an Equipment Apparent Cause Evaluation in the Byron Corrective Action Program. (Reference Byron Issue Report 2506852).
D. Safety Significance
This event is not considered risk significant. The results of the PRA risk review of this event indicate that the 1B DG was available based on the large volume of fuel oil still available, even though it would have been inoperable in accordance with TS 3.8.3, Condition D. The PRA risk review also indicates that the short period that the CS pumps were declared inoperable is not risk significant as modelled in the Byron PRA. The 1 A DG was operable and available at all times.
E. Corrective Actions
Apparent Cause - Leaking inlet valve 1D0001C will be repaired under Byron Work Order 01796243.
F. Previous Occurrences
There have been no other occurrences of this nature in the previous three years.