ML17325B681

Provides Results of 840910 Shutdown Due to Steam Generator Primary to Secondary Leakage.Westinghouse Safety Evaluation Checklist Encl

ML17325B681
Person / Time
Site:	Zion File:ZionSolutions icon.png
Issue date:	10/05/1984
From:	Cascarano R COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
9273N, NUDOCS 8410160250
Download: ML17325B681 (9)

Text

REGULATOR i INFORMATION DISTRIBUTION S>i ~TEN (RIDS)

ACCESSION NBR;8410160250 DOC,DATE: 84/10/05 NOTARIZED: WO DOCKET P.

FACIL:50"295 Zion Nuclear Power Stations Unit ip Commonweal th

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Edis 05000295 AUTHNAtdE AUTHOR AFFILIATION CASCARANO<R,N, ~ Commonwealth Edison Co,~

RECIP ~ NAME RECIPIENT AFFILIATION Office of Nuclear Reactor Regulationi-Director

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SUBJECT; Provides results of 840910 shutdown due to steam genei ator primary to secondary leakage,Westinghouse safety evaluation check list encl.

DISTRIBUTION CODE: A001D COPIES RECEIVED;LTR ENCL TITLE: OR Submittal: General Distribution NOTES: 05000295 OL: 12/26/68 RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL NRR ORB1 BC 01 7 7 INTERNAL: AD~/LFHB 0 ELD/HDS3 I

NRR/DE/tlTEB 1 NRR/DL D IR NRR/DL/ORAB 0 NETB NRR/DS I/RAB 1 1 BEG PQ RGN3 1 1 EXTERNAL: ACRS 09 6 6 LPDR 03 NRC PDR 02 1 1 NSIC 05 NTIS 1 1 TOTAL NUHBER OF COPIES REQUIRED: LTTR 26 ENCL 23

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c e Commonw~h Edison One First Natio~Plaza, Chicago, illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 October 5, 1984 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Zion Generating Station Unit 1 Shutdown Due to Steam Generator Primary to Secondary Leakage NRC Docket No. 50-295 References (a): June 18, 1982 letter from D. Wigginton to L. 0. DelGeorge.

(b): May 21, 1982 letter from F. G. Lentine to H. R. Denton.

Dear Mr. Denton:

In accordance with a request made by the Zion Pro ject Manager, this letter is to inform you of the results of the September 10, 1984 Zion Unit 1 shutdown because of steam generator primary to secondary leakage.

The Unit 1 steam generator tube plugging level has increased from 528 to 567 during the recent outage. Thirty-five of the new pluggable tubes are from review of 1983 eddy current results using refined interpretation methods. Four of the tubes in B steam generator are new indications from the 1220 tubes checked during the outage. The remaining 10 indications in B S/G can be seen in 1983 tapes with the refined technology. All of the 25 indications in the C steam generator are within the first 1" to 2 1/4" of the tube, i.e. the rolled area.

This increase in steam generator tube plugging brings the plugging level to 4.18X.

Reference (a) transmitted Technical Specification Amendment No.

74 to Facility Operating License No. DPR-39 for Zion Unit l. Amendment No. 74 reduced the Unit 1 Fq limit from 2.17X to 2.13X to account for steam generator tube plugging which, at that time, had reached 3.7X.

Reference (b) included a sensitivity analysis in support of Amendment No.

74. A review of all FSAR accidents showed that only the LOCA analysis is affected by low steam generator plugging levels; other analyses can accommodate greater levels of tube plugging. The following sensitivities were used in support of the 1982 amendment:

841005 84101b0250 05000295 PDR ADOCK PDR 8

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H. R. Denton October 5, 1984 (1) For low levels of plugging, the Peak Clad Temperature (PCT) is linearly proportional to the percentage of plugged tubes.

(2) For 3-loop plants, a lX increase in tube plugging results in a 12.4oF increase in PCT.

(3) The increase in PCT due to tube plugging for 4-loop plants is less than for 3-loop plants.

(4) A 10oF increase in PCT can be offset by a reduction of 0.01 in Fq.

Although Reference (b) specifically identified 4X plugged steam generator tubes as the basis for the Technical Specification amendment, using the above sensitivities it can be shown that the Fq limit reduc-tion of 0.04 allows a 40oF increase in PCT. Thus:

40oF 12.411F = 3.2K Since the base case LOCA allows for 1K tube plugging, the existing 2.13 Fq limit allows a 4.2X uniform steam generator tube plugging. This additional margin is supported by Westinghouse in the attached September 27, 1984 Nuclear Safety Evaluation Checklist.

Furthermore, the 1984 LOCA reanalysis, now ready for, submittal to the NRC, supports up to lOX steam generator tube plugging and establishes a 2.32% Fq limit using models which are more accurate than those used for the current LOCA analysis.

Based on the above, station On-Site and Off-Site reviews have been performed and Unit 1 return to service authorized.

If there are any further questions regarding this matter, please contact this office.

Sincerely, R. N. Cascarano Nuclear Licensing Administrator lm cc: 3. Norris NRR 9273N

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Results of sensitivity studies reported in 1(CAP-8986 show that the relationship between percentage tubes plugged and increase in peak clad temperature {PCT) is

)/near for low levels of uniform steam generator tube plugging. These studies also show that a 4>>loop ulant has less increase in PCT for percentage tub plugging than a 3-loop plant. A sensitivity stvdy to tube plugging performed for a 3-loop plant predicts an increase of 12.4'F in PCT for one percent tube plugging. Using this result and the relationship that a rise of 10'F in PCT is worth about - 0.0l in Fq, han'd calculations were performed for the. Zion units to predict an estimated PCT and Fq for a steam generator tube plugging 'level of 4.2'i-,

~For CVE COll At 1': tube plugging 2048.3 2.17+

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-la ~,gp, Zn+S5 ( 'Z,I3 The tube plugging level of 4.2" requires no change in the current Tech Spec Fq value of 2 'I~

Rgz represents the currently docketed Kccs perforrance analysis result adjusted to include the burst and blockage (NURKG-0630} Fq penalty. A subsequent, soon to .be docketed ECCS analysis for Z5on using the SNT evaluation Yodel.demonstrates accept-able performance at an Fq of 2.32 with a 10'team generator tube plugging level.

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