05000318/LER-2002-001
| Calvert Cliffs, Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3182002001R00 - NRC Website | |
I. � DESCRIPTION OF EVENT On January 24, 2002, during a biennial inspection of the Calvert Cliffs Unit 2, 2A Emergency Diesel Generator (EDG) (Fairbanks-Morse), abnormal wear (pitting) was noted on the pump flexible drive gear. This gear drives the auxiliary pumps necessary for operation of the diesel generator, including the cooling water pumps, oil pump, governor, air start distributor, and fuel oil pump. The amount of wear discovered was unexpected because the gear had only approximately 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> of operation since the last biennial inspection and only about 3000 hours0.0347 days <br />0.833 hours <br />0.00496 weeks <br />0.00114 months <br /> of total run time. A vendor representative was contacted, inspected the gear, and concluded that was operating at 100 percent rated thermal power.
Unit 2 had entered Technical Specification 3.8.1, "AC Sources-Operating," Condition B at 3:00 am on January 24, 2002 to conduct the biennial inspection. After discovery of the abnormal wear on the pump flexible drive gear, the Unit remained in Technical Specification 3.8.1, Condition B. Condition B specifies that, when in Modes 1-4, with one of the separate and independent EDGs inoperable, the inoperable EDG must be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If the inoperable EDG is not restored to operable status, Condition H must be entered.
Condition H specifies that the Unit be placed in Mode 3 within six hours and Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
Calvert Cliffs personnel evaluated the situation and came to the conclusion that:
1. Replacement of the pump flexible drive gear would take more time than allotted in the Technical Specifications (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) prior to requiring a Unit shutdown.
2. Based on the apparent root cause of the pump flexible drive gear pitting and the estimated time to complete repairs, a Unit 2 shutdown was not warranted.
Nuclear Regulatory Commission (NRC) Region I was contacted on January 26, 2002 to request regional enforcement discretion from Technical Specification 3.8.1. Regional enforcement discretion was verbally granted at 12:15 am on January 27, 2002. A written follow-up request for regional enforcement discretion was submitted to NRC Region I on January 29, 2002 [letter from C. H. Cruse (CCNPP) to Document Control Desk (NRC), dated January 29, 2002, Request for Regional Enforcement Discretion]. The NRC issued a written Notice of Enforcement Discretion (NOED) on January 31, 2002 (NOED No. 2002-01-01).
The NOED exercised discretion not to enforce compliance with Technical Specification 3.8.1 for the six day period starting at 3:00 am on January 27, 2002 and ending at 3:00 am on February 2, 2002. The NOED was contingent upon the following compensatory measures being in place:
1. � Postponement of elective maintenance on the redundant Unit 2, 2B EDG.
2. Suspension of discretionary maintenance or testing on any Unit 2 safety-related equipment or the off-site power system.
3. Ensuring that all four offsite power circuits were available, even though only two were required to be operable by Technical Specifications.
4. A commitment to shutdown Unit 2 if threatened by severe weather with the potential to interrupt offsite power.
5. Training and stationing a dedicated operator to utilize the non-safety-related 5400 kW OC EDG to power either Unit 2 vital bus in event of a loss-of-offsite power, as well as cross- connect key motor control centers to provide power to necessary equipment.
6. Assigning an operator to control the auxiliary feedwater flow control valves in the event that flow control was lost following a loss-of-offsite power.
These compensatory measures were implemented and maintained until the EDG was returned to service. Various pumps and pump drive gears including the pump flexible drive gear were replaced. Number 2A EDG passed its post-maintenance testing and was declared operable at 2:35 pm on January 31, 2002.
II. CAUSE OF EVENT
After performing many measurements and inspections of the pump flexible drive gear and associated equipment, Calvert Cliffs personnel discovered several installation errors and two out- of-specification conditions. First the backlash between the lube oil pump drive gear and the lube oil pump driven gear was zero (specification is 0.004 to 0.008 inches). Second, alignment of the two bearing bores in the pump flexible drive gear assembly exceeded the manufacturers specifications. Calvert Cliffs believes the installation errors and bearing bores caused the gears to be mis-aligned and resulted in the abnormal gear wear. However, since the errors would have occurred over 25 years ago, the human performance aspects of the out-of-specification conditions could not be validated.
A formal root cause analysis is still in progress.
III. ANALYSIS OF EVENT
The EDGs provide onsite electrical power to vital plant systems in the event that offsite electrical power is interrupted. Calvert Cliffs Unit 2 has two safety-related EDGs, 2A and 2B. Calvert Cliffs also has a high quality non-safety-related diesel generator that can be manually aligned to either of the Unit 2 4 kV busses that are served by 2A and 2B EDG.
The 2A EDG was actually out-of-service from January 24, 2002 at 3:00 am until January 31, 2002 at 2:35 pm. The risk significance of 2A EDG being out-of-service from January 24 until February 2, 2002 was evaluated by Calvert Cliffs personnel and NRC (Reference NOED 2002-01-01) and concluded not to involve any undue impact on the health and safety of the public. Based on these conclusions, this event had no adverse impact on the health and safety of the public.
This event is considered reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), Any event or condition prohibited by the plants Technical Specifications. Although NRC Region I granted enforcement discretion for Technical Specification 3.8.1 for a period of six days, the plant was not in compliance with the Technical Specification from 03:00 on January 27, 2002 until 2A EDG was returned to service at 2:35 pm on January 31, 2002.
IV. � CORRECTIVE ACTIONS The following corrective actions were taken as a result of this event:
1. Various pumps and pump drive gears including the pump flexible drive gear were replaced and the 2A EDG was returned to service on January 31, 2002. The replaced parts will be sent to the manufacturer for inspection.
2. The other similar EDGs (Fairbanks-Morse) at Calvert Cliffs were inspected for a similar problem with their pump flexible drive gears. No abnormal wear or conditions were found.
3. A formal root cause analysis concerning this event is in progress. Additional corrective actions may be implemented as determined by the results of this causal analysis.
V. � ADDITIONAL INFORMATION A. Affected Component Identification IEEE 803 � IEEE 805 System Component or System � EIIS Function � ID Emergency Diesel Generator � DG � EK Flexible Drive Gear � GR � EK Auxiliary Feedwater Flow Control Valve � FCV � BA
B. Previous Similar Events
There have been no previous similar events at Calvert Cliffs involving a failure or degradation of the pump flexible drive gear.