05000352/LER-2013-002
| Limerick Generating Station, Units 1 And 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| Initial Reporting | |
| ENS 49239 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3522013002R00 - NRC Website | |
Unit Conditions Prior to the Event Units 1 and 2 were in Operational Condition (OPCON) 1 (Power Operation) at 100% power. The 10 Bus (EIIS:BU) offsite source and the D23 emergency diesel generator (EDG) (El IS:DG) were inoperable due to an in progress surveillance test (ST). There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On Monday, August 5, 2013, Limerick Units 1 and 2 were operating at 100% power. At 0912 hours0.0106 days <br />0.253 hours <br />0.00151 weeks <br />3.47016e-4 months <br />, the quarterly 4kv Emergency D23 Bus Undervoltage Channel/Functional Test (ST-2-092-323-2) was commenced. The 101-D23 undervoltage relay (EIIS:27) portion of the test was completed successfully.
At 1224 hours0.0142 days <br />0.34 hours <br />0.00202 weeks <br />4.65732e-4 months <br />, the D23 Diesel Generator Fast Start Operability Test Run (ST-6-092-317- 2) was commenced. The D23 EDG was declared inoperable as required by the D23 EDG ST. The 20 Bus offsite source was declared inoperable as required by the D23 EDG ST when the 201 Safeguard Transformer (El IS:XFMR) tap changer was placed in the manual mode in order to prevent the potential of unexpected load swings. At 1241 hours0.0144 days <br />0.345 hours <br />0.00205 weeks <br />4.722005e-4 months <br />, the D23 EDG was synchronized to D23 Bus and the D23 Bus offsite source was transferred from 201 Safeguard Bus to 101 Safeguard Bus to support testing of the 201- D23 Bus offsite source undervoltage relay.
At 1456 hours0.0169 days <br />0.404 hours <br />0.00241 weeks <br />5.54008e-4 months <br />, the 201-D23 Bus source undervoltage relay was declared inoperable since it could not be calibrated within the 1-hour TS AOT. The inoperability of the 201- D23 Bus source undervoltage relay resulted in racking out the 201-D23 breaker and both offsite sources being concurrently inoperable on the D23 Bus. Also, D23 EDG was inoperable at the same time due to the in progress monthly EDG ST.
TS 3.3.3 Emergency Core Cooling System Actuation Instrumentation, Action "b" was entered when the undervoltage relay was declared inoperable. Action "b" requires taking Table 3.3.3-1 Action 37, when the 4.16 kV Emergency Bus Undervoltage (Degraded Voltage) channel is inoperable. Action 37 requires placing the inoperable channel in the tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. This action was completed as required.
The 201-D23 breaker was racked out prior to exceeding the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> action.
TS 3.8.1.1 A.C. Sources — Operating, Action "a" was entered when D23 EDG was declared inoperable as required by the D23 EDG ST. The requirements of Action "a" were satisfied and the EDG was restored to operable status within the 30 day AOT.
TS 3.8.1.1 Action "d" was entered when one offsite circuit and one EDG were declared inoperable as required by the EDG ST. The 72-hour AOT was satisfied when the ST was completed which restored the affected offsite source and EDG to operable status.
TS 3.8.1.1 Action "f" was entered when the 10 Bus offsite source was declared inoperable due to placing the 101 Safeguard Transformer tap changer in manual mode as required by the D23 EDG ST.
TS 3.8.1.1 Action "g" was entered when both offsite circuits were declared inoperable during the undervoltage relay ST. The 24-hour AOT to restore one offsite circuit was satisfied.
TS 3.0.3 was entered at 1456 hours0.0169 days <br />0.404 hours <br />0.00241 weeks <br />5.54008e-4 months <br /> when the 20 Bus offsite source breaker was racked out to meet the TS action with the existing inoperability of the 10 Bus offsite source and the D23 EDG. TS 3.8.1.1 does not specify an Action for this condition. TS 3.0.3 was exited at 1513 after 101 Safeguard Transformer tap changer was placed in automatic mode which restored 10 Bus offsite source to operable.
The 20 Bus offsite circuit was restored to operable at 1653 hours0.0191 days <br />0.459 hours <br />0.00273 weeks <br />6.289665e-4 months <br /> when the 201-D23 breaker was racked in. The EDG ST was completed and D23 EDG was returned to operable at 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br />.
An 8-hour NRC ENS notification was required by 10CFR50.72(b)(3)(v) for a condition that at the time of discovery could have prevented fulfillment of a safety function. The ENS notification (#49239) was completed on Monday, August 5, 2013, at 2138 EDT.
This event involved a condition that could have prevented fulfillment of a safety function.
Therefore, this LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(v).
Analysis of the Event
There was no actual safety consequence associated with this event. The potential safety consequences of this event were minimal. The period when both offsite sources were inoperable was brief (17 minutes). Only the D23 Bus was affected by the inoperability .
of the relay The 20 Bus offsite source remained operable for the D11, D12, D13, D14, D21, D22, and D24 Buses.
The inoperable undervoltage relay trip as-found trip setpoint was within the acceptable and required test limits. However, the relay as-found reset setpoint exceeded the upper acceptable limit and was equal to the upper required limit. The relay was successfully recalibrated during the test.
Cause of the Event
,IRC FORM 366A (10-2010) The cause of the undervoltage relay inoperability was setpoint drift.
Corrective Action Completed The inoperable relay was recalibrated during the test.
Corrective Action Planned The affected EDG operating procedures will be revised to add specific guidance to place the 101 or 201 safeguard transformer tap changer to auto if undervoltage testing will be performed in conjunction with the diesel generator being run in parallel with the offsite source. Monitoring of the EDG loading will be performed during periods when the tap changer is in auto with the EDG synchronized to the grid.
Previous Similar Occurrences There were no similar occurrences of both offsite sources being inoperable due to undervoltage relay setpoint drift in the previous three years.
On November 13, 2012, TS 3.3.3 Emergency Core Cooling System Actuation Instrumentation, Action "b" was entered when the 20 Bus offsite source D24 Bus undervoltage relay was declared inoperable during testing. TS Table 3.3.3-1 Action 37 was entered and the 201-D24 4 kV breaker was racked out. The 10 Bus offsite source was operable during the period that the 20 Bus offsite source was inoperable.
Component Data Component Number 127Z-11702 Component Name 201-D23 Safeguard Transformer Breaker Feed Undervoltage Relay Manufacturer ASEA, Brown Boveri Model Number 411T6375HF