ND-86-0018, Forwards Responses to Questions Re Util 860825 Tech Spec Change Request Concerning Steam Generator Tube Plugging

Forwards Responses to Questions Re Util 860825 Tech Spec Change Request Concerning Steam Generator Tube Plugging

ML20211C725
Person / Time
Site:	Farley
Issue date:	10/13/1986
From:	Mcdonald R ALABAMA POWER CO.
To:	Rubenstein L Office of Nuclear Reactor Regulation
References
ND-86-0018, ND-86-18, TAC-62283, TAC-62284, NUDOCS 8610220011
Download: ML20211C725 (3)

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Alabama Power Company 600 North 18th Street Post Office Box 2641 Birmingham, Alabarra 35291-0400 -

Telephone 205 250-1835

AlabamaPower enio V ce r sident ND 86-0018 October 13, 1986 1

Docket Nos. 50-348 50-364 Director, Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission l Washington, D. C. 20555 i Attention: Mr. L. S. Rubenstein Gentlemen:

Joseph M. Farley Nuclear Plant - Units 1 and 2 Steam Generator Tube Plugging Limit In response to questions raised by the NRC concerning Alabama Power

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Company's August 25, 1986 Technical Specification change request regarding steam generator tube plugging, the attached responses are

p rovided.

If there are any further comments, please advise.

i Respectfully submitted, W

.b R. P. Mcdonald i - RPM /BHW: dst-062 Attachment l

i cc: Mr. L. B. Long Dr. J. N. Grace Mr. E. A. Reeves

Mr. W. H. Bradford l \

8610220011 861013 8 PDR ADOCK 0500 g (.:

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c ATTACHMENT NRC Questions Regarding Steam Generator Tube Plugging Limits NRC Questions Tube plugging can result in more severe pump coastdown characteristics (non-LOCA events). Has the licensee considered this?

APCo Response The non-LOCA reactor coolant pump coastdown characteristics would become more severe if they were based on measured or best estimate flow which decrease with increased tube plugging. However, the RCP coastdown characteristics in the non-LOCA analyses are based on thermal design flow which does not change for 10% steam generator tube plugging. A study performed for various tube plugging levels for Farley 1 and 2 shows that the increased flow resistance due to 10% tube. plugging does not impact the thermal design flow (88500 gpm/ loop) used in the safety analyses. The pump coastdown for Farley is modeled using the PHOENIX computer code. A description of the model may be found in WCAP 7973, " Calculation of Flow Coastdown After Loss of Reactor Coolant Pump (PHOENIX Code)". The modeled pump coastdown in the current non-LOCA analyses will not become more severe, and the conclusions of the non-LOCA analyses in the FSAR remain valid.

NRC Questions Tube plugging of 10% would reduce the RCS volume by some factor (possibly 3 or 4%) and this would reduce dilution time during a boron dilution accident. What is the effect of the reduced RCS volume on operator reaction time for the above event?

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APCo Response An input to the boron dilution analysis for Modes 1 and 2 is the RCS active volume (i .e. the total RCS volume minus the volumes of the pressurizer, the pressurizer surge line, the dead volume of the reactor vessel head, and plugged steam generator tubes). Reduction of the RCS active volume is directly proportional to the reduction in operator response time for the baron dilution event described in the Farley FSAR. It is estimated that 10%

tube plugging will reduce the Farley active volume by approximately 4%.

Fron the current and most conservative Farley boron dilution analysis, it can be shown that the active RCS volume can be reduced by more than 4% and the operator action time limit (at least 15 min.) will still be met.

Therefore the 10% tube plugging level for Farley will not change the conclusions of the safety analysis.

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.1 NRC Question Has the licensee reviewed the possible effects of 10% tube plugging with regard to SBLOCA?

APCo Response The licensing basis small break LOCA analysis is based on a limiting power

' shape contained within an envelope of peaking factors with a maximum allowable total peaking factor (Fq) of 2.32. At low steam generator plugging levels (up to 20%), small break LOCA transients would not be affected by the tube plugging. The' proposed changes in Technical Specifications- will not impact or invalidate the current licensing basis small break LOCA analysis as represented in the Farley FSAR.

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