05000237/LER-2003-002
| Dresden Nuclear Power Station Unit 2 05000237 | |
| Event date: | 7-10-2003 |
|---|---|
| Report date: | 09-08-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2372003002R00 - NRC Website | |
B. Description of Event:
This event Is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident? On July 10, 2003, Operations personnel observed excessive noise and vibration from the Unit 2 High Pressure Coolant injection (HPCI) room cooler. The room cooler was secured, restarted later for troubleshooting, secured again and taken out of service. On July 11, 2003, personnel replaced the inboard and outboard fan shaft bearings and the system was declared operable. The rotating equipment component engineer examined the removed bearings. The outboard bearing was found to be in good condition. However, the inboard bearing, though still round, was severely worn and pitted on the entire surface of each ball, indicating inadequate lubrication.
C. Cause of Event:
The root cause for the event was that the lubrication frequency for the HPCI room cooler was incorrectly changed in 1996 from quarterly to every two years, which resulted in inadequate bearing lubrication. Quarterly lubrication of the bearings would have prevented this condition from developing. Additionally, the root cause determined that at the time the frequency was changed, there were inadequate controls in place to prevent this event from occurring.
(NRC Cause Code E) An extent of condition review was performed and determined that during the last two years there have been major revisions to the Performance Centered Maintenance (PCM) templates, including relays, turbine generators, emergency diesel generators, heating, ventilation and air conditioning, air operated valves, pumps, compressors, motor operated valves, and switchyard components. There were two areas that were considered to be applicable to the extent of condition for this issue. These areas were in oil and grease applications. The oil change and sampling program underwent a one hundred percent review in the second hair of 2001 and early 2002. This effort rebaselined the oil program system by system, consistent with post-extended power uprate operation. This effort has not been applied to the grease preventative maintenance tasks. Although this level of review has not been performed specifically from a grease perspective, there have only been two grease related issues during the last two years. The two grease related issues were this issue and an issue with a misinterpreted preventative maintenance (PM) change request, which also originated from a 1994 vintage PM change.
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COMMISSION
REPORT (LER) t7-0it
LICENSEE EVENT
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Dresden Nuclear Power Station Unit 2 05000237 (If more space is required, use additional copies of NRC Form 366AX17)
D. Safety Analysis:
The main function of the HPCI System Is to provide make up coolant to the reactor in the event of a small-break loss of coolant accident. An inoperable HPCI room cooler fan would not have prevented the HPCI System from initiating and injecting to the reactor. Continued operation of the HPCI System under these conditions would result in a room temperature for which the equipment in the HPCI room Is not designed to withstand. The potential for early loss of HPCI as a consequence of loss of the room cooler has been investigated. While room cooler mixing is necessary to support extended operation of the HPCI system, the HPCI turbine would operate for considerable time without the fan.
Had the HPCI System become unable to operate due to elevated room temperatures, the Isolation Condenser, Automatic Depressurization System, and Low Pressure Emergency Core Cooling Systems, (Low Pressure Coolant Injection, Core Spray) were available to provide reactor pressure and Inventory control during any postulated Design Basis Accident. Therefore, the consequences of this event were minimal and the event had minimal impact on the health and safety of the public and reactor safety.
E. Corrective Actions:
The Unit 2 HPCI room cooler fan shaft bearings were replaced.
The Unit 3 HPCI room cooler was observed to verify that no abnormal condition associated with the room cooler was present and the Unit 3 HPCI bearings were greased.
The frequency of the bearing lubrication for the Unit 2 and Unit 3 HPCI room coolers was changed to quarterly from every two years.
The Component Maintenance Organization will review grease preventative maintenance items for critical components.
The preventative maintenance program has undergone extensive revision since the event resulting in a robust program requiring a multi-discipline review of all revisions prior to implementation. This program incorporates industry experience, vendor information, OPEX, and plant specific application of a system or component.
F. Previous Occurrences:
None
G. Component Failure Data:
N/A