05000458/LER-2012-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 05-08-2012 |
|---|---|
| Report date: | 11-14-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4582012001R01 - NRC Website | |
On May 8, 2012, plant engineers confirmed that the lubricating oil in the Division 3 diesel generator (DG) (**DG**) was contaminated with fuel at a level that required its replacement. At the time of this discovery, a plant heat-up was in progress in preparation for return to service following a maintenance outage.
The oil sample that yielded these results had been drawn on April 25, and shipped off-site for vendor analysis. Plant engineers evaluated the trends of prior lubricating oil samples taken prior to May 8, and determined that the DC had become incapable of performing its design safety function on approximately October 28, 2011. It was concluded that this date was the like]y starting point of the internal fuel leak that contaminated the oil.
On May 8, the DG was removed from service in order to change the lubricating oil and repair the fuel leak.
This condition is being reported in accordance with 10CFR50,73(1)(2)(i)(B) as operations prohibited by Technical Specifications.
INVESTIGATION and CAUSAL ANALYSIS The Division 3 DG is an Electro-Motive Division (EMD) Model No. 20-645-E4. Many of the fuel system components are located internally, such that any fuel leakage will likely migrate to the oil sump.
The specified oil viscosity for this engine is 40 weight. Fuel dilution of approximately 5% thins the oil such that the viscosity becomes similar to 30 weight. EMD instructions direct that the engine must not be run with oil contamination greater than 5%. The sample drawn on April 25 contained approximately 4.29% fuel.
In October 2011, the DG was removed from service for scheduled maintenance, including removal and testing of the fuel injectors. Following re-installation of the injectors, a fuel system leak test confirmed that no leaks were present.
After the DG was removed from service on May 8, a ;uel leak was Mound at the jumper-to-filter cap connection on number 20 cylinder. The jumper was replaced, and a leak test was performed. The leak rate was reduced, but was not eliminated. The jumper was again removed.
While observing maintenance technicians performing the work, the system engineer directed that the two ends of the jumper be installed in a certain sequence using a specific technique. This technique appeared to cause less binding on the connection at the injector.
There is no guidance in any vendor manual that states exactly how to install the fuel line jumper (i.e., which side to install first). Only the final torque is specified. The system engineer discussed assembly technique with a vendor representative. The veAdor confirmed that it is a good practice to install the fuel line jumpers as the engineer had directed because the lead gaskets on each end of the jumper are easily damaged. The vendor suggested that these specific instructions be added to the model work package; to minimize the risk of damage to the gaskets.
This investigation found that the fuel leak was likely caisecl by gaske damage that occurred during the re-installation of the injectors in October 2011.
PREVIOUS OCCURRENCE EVALUATION
No similar failure has been reported by River Bend Station in the last five years.
CORRECTIVE ACTION TO PREVENT RECURP.ENCE Enhanced work instructions for fuel jumper installation have been added to the vendor manual and to mod& work orders.
SAFETY SIGNIFICANCE
With offsite power available, the high pressure core spray system remained capable of performing its safety function. There were no actual events Curing this period requiring the Division 3 DG to respond in the emergency mode.
The term "mission tim:-)" is nct precisely defined in the regulations — it is typically expressed as "for as long as needed". A 24-hour mission time is assumed foi
- the Division 3 DG in the RBS Probabilistic Risk Analysis (PRA), and is specified under the Mitigating Systems Performance Index program for the Division 3 DG.
To evaluate the ability of the DG to fulfill its design function with the as-found fuel leak, a third-party engineering report performed for a nearly identical DG at Clinton station was obtained. This report concluded that the Clinton's DG could have successfully operated at full load with up to 22 percent dilution of the lube oil. Given this conclusion, RBS' site engineers determined that the DG could have operated with the calculated fuel leakage rate for at least 164 hours0.0019 days <br />0.0456 hours <br />2.71164e-4 weeks <br />6.2402e-5 months <br /> (6.8 days) at full power before reaching 22 percent dilution. As such, the Division 3 DG could have successfully supported the PRA mission time with significant margin in the as-found condition. This event was, thus, of minimal safety significance with respect to the health and safety of the public.
(Note — Energy Industry Component Identification codes are annotated as (**XX**).)