05000305/LER-2006-004

LER-2006-004,

Docket Number
Event date:	05-19-2006
Report date:	12-28-2006
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3052006004R01 - NRC Website

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3)

Event Description:

At Kewaunee Power Station (KPS), both emergency diesel generators (EDGs) are required to exceed their continuous operating rating of 2600 kW during a loss of coolant accident (LOCA) concurrent with loss of off-site power (LOOP). Operation outside this continuous operating rating is acceptable provided the duration of the loading and the maximum combustion air temperatures are not exceeded.

In 2000, KPS evaluated and implemented EDG de-rating curves (which reduce the maximum allowed ratings as combustion air intake temperature increases).

At 21:54 on May 19, 2006, with the plant in Hot Shutdown, KPS determined that the de-rating curves for the EDGs were incorrectly applied. This resulted in the potential to operate the EDGs outside of the vendor recommended ratings during the initial diesel loading (from 0 to 1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> per Kewaunee Updated Safety Analysis Report Table 8.2-1) following a design basis event.

A preliminary review in June of 2006 showed that seven times in the preceding three years, (for a total of 26.35 hrs) outdoor air temperatures exceeded the limit for EDG A which should have resulted in an inoperability determination for EDG A. At no time during those three years were the EDG B temperature limits exceeded.

At no time during the seven occurrences was EDG A operating. It was never operated when de-rating was required, and thus never operated outside the vendor recommended ratings.

On 10/25/2006, additional evaluation determined that EDG A would have successfully performed its mission if called upon over the preceding three years, including the seven instances discussed above.

On 11/15/2006, in response to an NRC question, the station identified that both EDGs would periodically not have been able to meet Technical Specification (TS) Surveillance 4.6.a.5 due to elevated ambient temperatures. TS Surveillance 4.6.a.5 states: Each diesel generator shall be loaded to 2950 kW (nominal) for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> every operating cycle.

These surveillance tests are performed during refueling outages which generally occur in the Spring and Fall so ambient temperatures have never previously impeded the load test. EDG A passed this surveillance on 9/22/06, and EDG B passed it on 10/6/06. However, during the reporting period, ambient temperatures have periodically exceeded the limits that would prohibit performance of these tests.

Event Analysis:

The maximum load allowed for the EDGs is a function of combustion air temperature which, at KPS, is a function of outside air temperature. Current engineering evaluation states that the EDGs can be loaded to 2950 kW for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> at an outside air temperature below approximately 80°F. Based on historic temperature profiles, it is projected that this outside air temperature will not be reached until June.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Kewaunee Power Station 05000305 YEAR Per Technical Specification 4.0.a, "Failure to meet a surveillance requirement, whether such failure is experienced during the performance of the surveillance or between performances of the surveillance shall be failure to meet the OPERABILITY requirements for the LCO.

Since periods existed during the reporting period where the surveillance would not have been able to be performed, this event is being reported in accordance with 10CFR50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications.

Safety Significance:

During the three year reporting period, EDG A & B would have been able to meet their post-accident loading requirements. Therefore, periodic conditions that would have established a failure to meet TS Surveillance 4.6.a.5 have no safety significance.

Cause:

The cause of the event was a failure to properly apply the EDG derating curves after they were received from the vendor.

Corrective Actions:

Through enhanced interaction with the EDG vendor, the EDG derating curves are now being properly applied.

This has resulted in the following conclusions and a requirement to take the following additional actions:

The EDGs can be loaded to 2950 kW for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> at an outside air temperature below approximately 80°F.

Based on historic temperature profiles, it is projected that this outside air temperature will not be reached until June of 2007. Prior to that date TS 4.6.a.5 will be modified as appropriate.

In addition, the EDG Margin Recovery Project has been initiated. This project consists of two phases; A design study to be completed by the end of 4th quarter 2006 and development and implementation of required Design Change Requests.

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