ML070530053

Special Inspection Charter to Evaluate the Fort Calhoun Station Abb Circuit Breaker

ML070530053
Person / Time
Site:	Fort Calhoun
Issue date:	02/20/2007
From:	Chamberlain D Division of Reactor Safety IV
To:	Peck M NRC/RGN-IV/DRP/RPB-B
References
Download: ML070530053 (4)

Text

February 20, 207 MEMORANDUM TO: Michael S. Peck, Senior Resident Inspector, Callaway FROM: Dwight D. Chamberlain, Director, Division of Reactor Safety /RA/

SUBJECT:

SPECIAL INSPECTION CHARTER TO EVALUATE THE FORT CALHOUN STATION ABB CIRCUIT BREAKER FAILURES A Special Inspection Team is being chartered in response to the Fort Calhoun Station safety-significant ABB circuit breaker failures. An ABB breaker failed during the starting sequence for the B raw water pump on January 25, 2007. The apparent cause was determined to be a broken linkage/connector arm in the ABB circuit breaker mechanism operated cell (MOC). On Feb. 8, a second of their four (4) raw water pumps failed due to breakage of the same linkage arm. Because of the common cause aspect of this failure, the licensee declared 3 of the 4 pumps (all except B, which was repaired and returned to service on January 31) inoperable, which placed them in a 6-hour shutdown action (see NRC Event 43157) due to operation outside their technical specifications. This represented a potential common-mode failure concern for the raw water pump circuit breakers, as well as other 4160 volt breakers in safety-related applications at Fort Calhoun Station. The other potentially affected breakers include those for both low pressure safety injection pumps, the motor-driven auxiliary feedwater pump, the normal and alternate feeder breakers to the 4160 volt busses, and the feeder breakers from the 4160 volt busses to the 480 volt safety busses. Nonsafety-related buses and components may be affected as well (e.g., the feeder breakers to the nonsafety-related 4160 buses). The assigned Senior Reactor Analyst to support the team is Russ Bywater.

A. Basis On both January 25 and February 8, 2007, identical ABB circuit breakers for Fort Calhoun Station raw water pumps failed due to the same apparent cause. As stated previously, there are also other Fort Calhoun Station safety-significant breakers that may have this problem. This represents the potential of a significant common mode concern, as well as a potential generic issue. The combined deterministic criteria and risk evaluation, conducted under NRC MD 8.3, indicate supplemental inspection of this issue is warranted.

A Region IV Senior Reactor Analyst completed a preliminary estimate of the incremental conditional core damage probability for this condition using the SPAR model for Fort

Michael S. Peck Calhoun Station, Revision 3.31, and methods identified in the Risk Assessment Standardization Project (RASP) Handbook for performing Management Directive 8.3 assessments. Accounting for the plant conditions and configurations resulted in an incremental conditional core damage probability of 1.17E-6.

The licensee believes the cause of the ABB circuit breaker/MOC failures is most likely high-cycle fatigue of the linkage/connector arm. They also believe the potential adverse condition of the component only occurs after more than 1,000 cycles of the breaker.

However, this is yet to be substantiated. The licensee has sent the two failed components to labs for analysis. Additionally, high-cycle fatigue may only be the failure mechanism, not the root cause of the problem. Additional factors, such as breaker alignment and adjustment, may significantly alter the expected number of cycles before failure. This is evidenced by one of the breakers failing at 1,200 cycles when the other three raw water pump breakers did not fail with 1,600 cycles. Therefore, additional inspection is important to gain a more comprehensive understanding of this issue and the underlying cause(s).

This Special Inspection Team is chartered to review the circumstances related to the licensees ABB circuit breaker and MOC problems, and assess the effectiveness of the actions for resolving these problems. The team will also assess the potential for impact on other plant systems in addition to the raw water pumps and the potential for generic implications. The team will also assess the effectiveness of the immediate actions taken and the notifications made by the licensee in response to the pump failures that occurred on January 25 and February 8, 2007.

B. Scope The team is expected to address the following:

1. Develop an understanding of the ABB circuit breaker original design, the degraded conditions, and failures related to the raw water pump failures.

2. Determine if the licensees maintenance and monitoring programs were sufficient to maintain the ABB breakers/MOCs in their designed configuration and operating parameters.

3. Assess licensee effectiveness in identifying previous ABB circuit breaker problems, evaluating the cause of these problems, and implementation of corrective actions to resolve identified problems.

4. Review plant equipment records to verify a complete listing of the potentially affected breakers at the facility, the number of cycles of the components, and record keeping regarding transfer of operating data (cycles) when transferring parts from other breakers.

5. Identify and assess additional actions planned by the licensee for other similar safety-significant ABB circuit breakers at the facility.

Michael S. Peck 6. Assess the licensees root cause evaluation, the extent of condition, and the licensees common mode evaluation and assess the adequacy of corrective actions including immediate and long-term actions.

7. Evaluate pertinent industry operating experience and potential precursors to the January 25 and February 8 breaker/MOC failures, including the effectiveness of licensee actions taken in response to any operating experience.

8. Determine if there are any potential generic issues related to the failures of the ABB circuit breakers/MOCs. Promptly communicate any potential generic issues to Region IV management.

9. Determine if the technical specifications were met during the periods of each of the raw water pump failures.

10. Collect data as necessary to support a risk analysis of the degraded conditions and failures as appropriate.

C. Guidance Inspection Procedure 93812, Special Inspection, provides additional guidance to be used by the Special Inspection Team. Your duties will be as described in Inspection Procedure 93812. The inspection should emphasize fact-finding in its review of the circumstances surrounding the event. It is not the responsibility of the team to examine the regulatory process. Safety concerns identified that are not directly related to the event should be reported to the Region IV office for appropriate action.

The Team will report to the site, conduct an entrance, and begin inspection no later than February 20, 2007. While on site, you will provide daily status briefings to Region IV management, who will coordinate with the Office of Nuclear Reactor Regulation, to ensure that all other parties are kept informed. A report documenting the results of the inspection should be issued within 30 days of the completion of the inspection.

This Charter may be modified should the team develop significant new information that warrants review. Should you have any questions concerning this Charter, contact me at (817) 860-8180.

cc:

J. Clark, C:DRP/E W. Jones, C:DRS/EB1

Michael S. Peck SUNSI Review Completed: __Y______ ADAMS: /YesG No Initials: ___WBJ__

/ Publicly Available G Non-Publicly Available G Sensitive / Non-Sensitive C:\FileNet\ML070530053.wpd ML070530053 C:EB1 D:DRS WBJones/lmb DDChamberlain

/RA/ /RA/

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