ML20057C610

Forwards Response to GL 93-04, Rod Control Sys Failure & Withdrawal of Rod Control Cluster Assemblies, Documenting That Licensing Basis Satisfied for GDC 25 for Plants & Identifying long-term Efforts to Close Issue

ML20057C610
Person / Time
Site:	Catawba, McGuire, Mcguire
Issue date:	09/20/1993
From:	Tuckman M DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-93-04, GL-93-4, NUDOCS 9309290164
Download: ML20057C610 (4)

Text

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DukeIbwer Company M S Tlaa n P0 Esox 1006 Senior McePresident Onariane, NC2820H006 Nuclear Generation (704)382-2200 0Ihce (704)3824360 Tar  ;

DUKEPOWER September 20, 1993 U.'S. Nucilear Regulatory Commission >

Washington, D. C. 20555 Attention: Document Control Desk

Subject:

McGuire Nuclear Station Docket Numbers 50-369 and -370 Catawba Nuclear Station Docket Numbers 50-413 and -414 Duke Power Company's Response to Generic Letter 93-04 Attached is Duke Power Company's 90-day response to Generic Letter 93-04, " Rod Control System Failure and Withdrawal of Rod Control l Cluster Assemblies." The Generic Letter required that affected licensees provide a safety assessment of whether or not the ,

licensing basis for each facility is still satisfied with regard to t the requirements for system response to a single failure in the Rod ,

Control System (GDC 25 or equivalent).

By letter of August 5, 1993, Duke Power submitted a safety I assessment that indicated that for McGuire and Catawba Nuclear Stations Departure from Nucleate Boiling (DNB) does not occur for their worst-case asymmetric rod withdrawal. The letter also identified the short-term compensatory measures that Duke has taken '

to preclude an event similar to that described in the Generic Letter.

The purpose of this letter is to document that the licensing basis is satisfied for GDC 25 for McGuire and Catawba, and to identify long-term efforts that will be undertaken to close this issue.

5 If you have any questions regarding this response, please call Scott Gewehr at (704) 382-7581.

I declare that the statements and. matters set forth herein are true and correct to the best of my knowledge. ,

very trul

( % %y yours, M. S. Tuckman l

27 141 '7'30 9309290164 930920 PDR ADOCK 05000369 h 8 l -

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4 U. S. . Nuclear Regulatory Commission S,eptember 20, 1993 Page 2 cc: Mr. V. Nerses, Project Manager Office of Nuclear Reactor Regulation

. U. S. Nuclear Regulatory Commission Mail Stop 14H25, OWFN Washington, D. C. 20555 Mr. R. E. Martin, Project Manager Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 14H25, OWFN Washington, D. C. 20555 Mr. S. D. Ebneter, Regional Administrator U.S. Nuclear Regulatory Commission - Region II ,

101 Marietta Street, NW - Suite 2900 4 Atlanta, Georgia 30323 Mr. Mark Proviano Westinghouse Electric Corporation P. O. Box 344 ECE 4-08  !

Pittsburgh, PA 15230-0355 t

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Response to Generic Letter 93-04 Assessment of Licensina Basis Compliance '

The purpose of this response is to provide an assessment of whether or not the licensing basis for McGuire and Catawba Nuclear Stations remains satisfied with respect to the requirements for system response to a single failure in the rod control system (RCS), and to provide a supporting discussion for this assessment in light of 1 the information generated as a result of the Salem event.

The Westinghouse Owners Group (WOG) has undertaken the following initiatives to support the response to Generic Letter 93-04: ,

conducting RCS testing in the Salem training center, examining the existing RCS failure modes and effects analysis (FMEA), analyzing .

the worst-case asymmetric RCCA withdrawal combinations with three-dimensional analytical methods, and performing an equipment survey of Westinghouse plants to determine the frequency and significance ,

of control system circuit failures.

After extensive investigation, the WOG has concluded that GDC 25 continues to be met, but also recognizes that there are questions as to the interpretation of not only the intent of GDC 25, but also the appropriate definition of the specified acceptable fuel design limit as well.

l Based on previous communications, the NRC has conservatively  !

interpreted the GDC 25 fuel design limit to be the DNB design  !

basis. The WOG believes that this is a conservative definition if applied to all events. The equipment survey conducted by the WOG l demonstrated that the rate of card failures that could result in i the movement of less than a whole group is on the order of 4E-  !

8/ critical reactor-hours. This indicates that the likelihood of a Salem-type event is extremely remote. With this in mind, the WOG believes that a condition III or (IV) specified acceptable fuel design limit would be applicable.

Based on the WOG's understanding of GDC 25, the purpose of this criterion is to ensure that the appropriate limits (commensurate with the probability of occurrence) are not violated for a " worst-case" stand-alone single failure. The test program conducted at the Salem training center demonstrated that all the rods within a-given group would receive the same signals. The corrupted current orders generated by the logic cabinet failures at Salem were transmitted identically to all 8 RCCAs in Shutdown Bank A. The fact that only one RCCA withdrew in the plant was due to a second unrelated effect. Had all the rods in Shutdown Bank A responded, )

as predicted in the existing FMEA, all the rods would have withdrawn uniformly and would have been enveloped by FSAR accident analyses. In addition, existing rod motion surveillance requirements would detect the type of rod motion failure observed at Salem. Thus, the requirement that one single failure not result in a specified acceptable fuel design limit being exceeded, in this

e' case the DNB design basis, would remain satisfied.

JLssessment of the Safety Sionificance of Potential Asymmetric Roct Motion in the Rod Control System Westinghouse has also performed a safety analysis using three-dimensional safety analysis techniques to assist the WOG in its determination of the safety significance of an uncontrolled asymmetric rod withdrawal. WCAP-13803, Revision 1, documented the safety analysis program and concluded that the generic analysis and its plant-specific application demonstrates that DMB does not occur for a worst-case asymmetric rod withdrawal for all _affected Westinghouse plants. As such, the analysis program concluded that  :

there is no safety significance for affected Westinghouse plants  !

for a Salem-type rod withdrawal.

Duke's letter of August 5, 1993 provided a summary of the results of the generic safety analysis program conducted by the WOG and its applicability to McGuire and Catawba.

Lona-term Enhancements While the assessment indicates that the licensing basis is currently satisfied, there are measures which can be taken which ,

may provide additional assurance of compliance with GDC 25.

Duke will implement a current order trace surveillance at  ;

each of the McGuire and Catawba units during startup from each refueling outage, effective immediately. ,

It is also Duke's intent to modify the RCS current order >

timing to prevent any uncontrolled asymmetric rod withdrawal in the event of a failure similar to the one identified at Salem.

At this time, however, it is not feasible to identify a schedule for the current order timing modification. Information required to perform this modification is plant-specific, and is owned by Westinghouse. Duke will discuss this with Westinghouse, and foresees implementing the modification during the first refueling outage after the information is obtained_from Westinghouse, for each unit. Note also that the recommendation to perform this modification was only recently received from Westinghouse, and is  :

subject to further cost / benefit review. The uncertainty in the schedule is justified because existing rod motion surveillance tests provide assurance that the failure scenarios of an uncontrolled asymmetric rod withdrawal will be detected, and the .

analysis program performed and documented in WCAP-13803, Revision l 1, concluded that there was no safety significance for affected Westinghouse plants for a Salem-type rod withdrawal.

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