05000277/LER-2020-001, Emergency Diesel Generator Shutdown Due to Intercooler Low Pressure Results in Condition Prohibited by Technical Specifications
| ML20115E369 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 04/24/2020 |
| From: | Herr M Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CCN: 20-46 LER 2020-001-00 | |
| Download: ML20115E369 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2772020001R00 - NRC Website | |
text
10CFR 50.73 CCN: 20-46 April 24, 2020 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Peach Bottom Atomic Power Station (PBAPS) Unit 2 and Unit 3 Renewed Facility Operating License No. DPR-44 and DPR-56 NRC Docket No. 50-277 and 50-278
Subject:
Licensee Event Report (LER) 2-20-001 Enclosed is a Licensee Event Report concerning a trip of our E-1 emergency diesel generator, which resulted in a violation of Technical Specifications. In accordance with NEI 99-04, there are no regulatory commitments contained in this correspondence. If you have any questions or require additional information, please do not hesitate to contact Matthew Rector at 717-456-4351.
Sincerely, Matthew J. Herr Site Vice President Peach Bottom Atomic Power Station MJH/dnd/IR 4321794 Enclosure cc:
US NRC, Administrator, Region I US NRC, Senior Resident Inspector R. R. Janati, Commonwealth of Pennsylvania S. Seaman, State of Maryland B. Watkins, PSE&G, Financial Controls and Co-Owner Affairs Unit Conditions Prior to the Event Unit 2 and Unit 3 were both operating in Mode 1 at approximately 100% rated thermal power. There were no structures, systems or components out of service that contributed to this event.
Description of Event
On 2/26/20, at approximately 2110, operators began a monthly surveillance test of the E-1 Emergency Diesel Generator [EIIS:DG]. At 2126, a slow start of E-1 was performed in accordance with station procedures. Shortly after the engine was raised to full speed, a local alarm indicated low pressure in the intercooler coolant system.
While the equipment operator was in the process of reporting the alarm to the Main Control Room, the engine automatically tripped at approximately 2129. The test was aborted and the engine placed in its normal shutdown lineup. In accordance with Technical Specifications (TS), offsite and onsite electrical power breaker alignment and a power availability check was performed to verify critical loads are connected to their preferred power source and that appropriate independence of offsite circuits was maintained.
Troubleshooting identified air in the intercooler coolant system, which prevented the pump from establishing the normal system pressure. A series of venting evolutions was performed to remove the air. During the first venting, it was estimated that approximately one cubic foot of air was released. Smaller amounts were released during subsequent ventings, which were performed when the diesel was not running, when it was running unloaded and running loaded. A final run of the diesel was performed on 2/27/20 at 1436 and the engine ran without incident for approximately three hours. A final vent produced no air and E-1 was returned to operable on 2/27/20 at 2030.
For the above testing and venting, the E-1 diesel was inoperable for approximately 23.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> from the start of the test on 2/26/20 until the engine was returned to operable on 2/27/20.
Analysis of Event
The sites four Emergency Diesel Generators are standby units that provide adequate power to safely shutdown both units in the event of a design basis accident with a loss of offsite power (LOOP). The accident analysis assumes one of the four diesel generators fails. Each diesel generator starts automatically on a LOOP, low reactor water level or high drywell pressure. Periodic testing ensures the diesel engines can start automatically and reach full speed within 10 seconds. The engines can also be started manually for testing and maintenance purposes.
Each diesel engine has several protective features that automatically trip the engine under the following abnormal conditions:
- 1. Engine overspeed
- 2. Jacket coolant high temperature or low pressure
- 3. Lube oil high temperature or low pressure Peach Bottom Atomic Power Station Unit 2 277 2020 001 REV NO.
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NRC FORM 366 (04-2020)
- 4. Crankcase high pressure
- 5. Engine overspeed
- 6. Intercooler coolant low pressure
- 7. Fuel oil low pressure In the event of a design basis loss of coolant accident (LOCA), all of the above trips are bypassed except for engine overspeed, which is considered indicative of a condition that could result in significant equipment damage. The remaining trips are considered non-critical and identify potential equipment degradation. Although they are bypassed during a LOCA, they are not bypassed during a LOOP with other postulated abnormal operating conditions.
On 1/26/20, the E-1 diesel was taken out of service for planned maintenance, which involved draining both the intercooler coolant and jacket water systems. Following maintenance, the systems were filled and vented. During post maintenance testing (PMT), the engine was started and stopped a total of nine times to support a series of break-in runs required based on the maintenance that had been performed and also to address issues identified during the PMT. Following completion of these activities, the E-1 diesel was returned to an operable status on 2/7/20 at 0230.
Further investigation of the trip on 2/26/20 determined that the air was likely introduced into the system during the maintenance activities performed earlier in the month. Since the engine tripped due to low intercooler coolant pressure during the first run of the engine following the maintenance, it is assumed it would have tripped if it had been required to perform its safety function during a non-LOCA transient at any time following completion of the maintenance on 2/7/20. As a result, it was inoperable from 2/7/20 at 0230 until the intercooler coolant system had been fully vented and the diesel generator returned to operable on 2/27/20 at 2030, for a total of 20 days and 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />.
TS LCO 3.8.1.b requires all four diesel generators to be capable of supplying the onsite Class IE AC electrical power distribution system. With one diesel generator inoperable, TS 3.8.1 Condition B requires several actions (B.1 through B.5) to be completed at varying frequencies, including restoring the diesel generator to operable within 14 days. Since these actions were not performed between 2/7/20 at 0230 until 2/26/20 at 2110 (19 days, 18.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />),
TS were not complied with during that time period. This event is being reported as a violation of Technical Specifications in accordance with 10 CFR 50.73(a)(2)(i)(B).
During the period where it was determined the E-1 diesel generator was inoperable (2/7/20 to 2/26/20), surveillance tests were performed for diesel generator E-2 on 2/7/20, diesel generator E-3 on 2/24/20 and diesel generator E-4 on 2/18/20 to demonstrate operability in accordance with TS surveillance requirements and the Surveillance Frequency Control Program. When performing these surveillance tests, the diesel generator is inoperable for a short period of time. For each of these tests, the diesel generators were inoperable for less than five hours. This is less than the maximum allowed time in TS 3.8.1 Conditions F and G of 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> for two inoperable diesel generators. Therefore, there was no inadvertent violation of these two TS conditions.
There were no actual safety consequences as a result of this event. There was no LOOP during the period of inoperability or other condition resulting in a diesel generator start signal.
Cause of the Event
The cause of the event was inadequate venting of the intercooler coolant system during maintenance. Venting was performed during the start of one of the initial PMT runs and not performed when the engine was hot. Following this event, the vendor recommended the system should be vented when the engine is loaded, but this was not known prior to the maintenance and was not specified in the procedures in use at the time.
Corrective Actions
The intercooler coolant system was vented which allowed the diesel generator to be returned to operable. In order to improve guidance for venting following maintenance and prior to returning the diesel generator to operable, procedures are being revised to require venting to be performed when the engine is hot and loaded. Additional corrective actions are documented in the corrective action program.
Previous Similar Occurrences There have been previous cases where E-1 has tripped due to air in the system when the diesel generator was out of service for maintenance. In all cases, prior to returning the diesel generator operable, adequate venting was performed. This was the first case where post maintenance testing did not identify the condition prior to returning the diesel generator to operable.
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