ML20003A905

Submits Results of Reanalysis of Auxiliary Feedwater Sys Reliability.Current Design Is Acceptable

ML20003A905
Person / Time
Site:	McGuire, Mcguire
Issue date:	02/04/1981
From:	Parker W DUKE POWER CO.
To:	Harold Denton, Youngblood B Office of Nuclear Reactor Regulation
References
NUDOCS 8102100038
Download: ML20003A905 (5)

Text

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DUKE POWER COMPANY Powra Buttonwo 422 Socru Cnuncu Srazzr, CnAnt.orrs, N. C. asa4a WILLI A M O. PA R M E R, J R,

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February 4, 1981 v a-ac e)

Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Comenission Washington, D. C.

20555 Attention:

Mr. B. J. Youngblood, Chief Licensing Projects Branch No.1 Re: McGuire Nuclear Station Docket Nos. 50-369, 50-370

Dear Mr. Denton:

Attached are the results of a re-analysis of the reliability of the McGuire Auxiliary Feedwater System (AFS). These analyses were performed at the re-quest of the NRC Staff in a meeting with Duke and Westinghouse representatives in Bethesda on December 18, 1980. These analyses show that for the four cases analyzed, assuming credit for operator action or using more realistic assump-tions, the reliability of the McGuire AFS is in the "high" category.

Based on the results of these analyses and previous evaluations of the AFS, Duke concludes that the current design of the AFS is acceptable. Currently, Duke is evaluating several possible modifications which could simplify the operation of the system. This evaluation may result in some changes to the system in the long term.

Please advise if you have any questions regarding this matter.

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2 William O. Parker, Jr, GAC:pw Attachment ec:

T. J. Donat Mr. George H. Bradley Senior Reeldent Inspector Sandia National Laboratories McGuire Nuclear Station A'

,uerque, New Mexico 87185 Joo /

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MCGUIRE NUCLEAR STATION UNIT 1 RELIABILITY ANALYSIS OF THE AUXILIARY FEEDWATER SYSTEM Duke Power Company reported the results of the McGuire Nuclear Station Unit I auxilf ary feedwater system (AFWS) reliability analysis to the NRC in WCAP-9751.

Th6 results of the study indicated that the reliability ranking of the McGuire AFWS, compared to the reliabilities as defined and reported for Westinghouse plants in NUREG-0611, is medium for a loss of main feedwater transient and low for a loss of main feedwater coupled with a loss of offsite power transient.

As discussed in WCAP-9751, the reliability analysis did not take credit for manual action by the operator to increase the quantity of auxiliary feedwater flow injected into the steam generators or did not investigate the benefits that are available using "better" estimate transient analysis assumptions and initial conditions. The results of a study which incorporated the effects of operator action and "better" estimate assumptions and initial conditions are presented herein.

Four additional loss of normal feedwater analyses were performed to determine the transient characteristics of the McGuire Unit I as a function of operator action time and "better" estimate assumptions and initial conditions. The loss of normal feedwater transients analyzed were as follows:

1) FSAR assumptions and initial conditions are assumed. Offsite power is assumed to be lost coincident with the loss of feedwater. The operator is assumed to take manual action at 15 minutes following initiation of the transient to increase the auxiliary feedwater to two steam generators from 340 gpm to 490 gpm by fully opening the throttle valves in the auxiliary feedwater lines.

2) The assumptions for this case are similar to case 1 except that offsite power is not assumed to be lost during the transient.

3) "Better" estimate assumptions and initial conditions are assumed. Off-site power is assumed to be available throughout the transient. The analysis assumes that 340 gpm of auxiliary feedwater is injected into two steam generators within one minute of automatic reactor trip.

N' operator action is assumed during the transient.

4) The assumptions for this case are similar to case 3 except that offsite power is assumed to be lost coincident with the loss of feedwater.

These analyses were performed to determine if the licensing acceptance criteria is rtet following a loss of normal feedwater. The acceptance criteria adopted is that no uater relief will occur via the pressurizer safety and/or relief valves folicwing a loss of normal feedwater due to reactor coolant system expansion because of an insufficient quantity of auxiliary feedwater being injected into the steam generator for secondary heat removal. This acceptance criteria was met since the pressurizer did not become water solid in any of the four cases analyzed.

The comparative reliability results are presented in Figure 1.0.

Indicated on this figure are the system reliability results for each of the four cases studied. The basis format for this figure, including the reliability character-istics of low, medium and high reliability of the AFWS of other Westinghouse NSSS plants, was adopted from NUREG-0611. The intent of this figure is to show the relative reliability ranking of the McGuire AFWS for each of the four cases studied and to compare the results to those obtained by the NRC. Because the input data are only estimates of component and human error failure probabilities, absolute values of calculated system reliability are de-emphasized and the results are used on a relative basis for purposes of comparison.

System unavailability values for each of the cases are:

Case 1 - 6.6 x 10-5 Case 2 - 1.96 x 10-5 Case 3 - 9.5 x 10-6 j

Case 4 - 4.2 x 10-6 The top level logic of the fault tree presented in WCAP-9751 was changed so that system failure would require 3 of 4 steam generators to have inadequate flow.

j The unreliability of system operation associated with o;:erator action in Cases l

1 and 2 was factored into the analyses.

I As indicated in Figure 1, relative to other AFWS of plants employing a Westinghouse l

NSSS, the McGuire AFWS exhibits a high reliability for Cases 2 and 3, loss of main feedwater; and high reliability for Cases 1 and 4, loss of main feedwater/ loss of i

offsite power.

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' Comparison of the reliability results obtained from these four cases with those presented in WCAP-9751 demonstrates the increased system reliabilities that are available if credit is taken for operator action and "better" estimate i

assumptions and initial conditions.

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