ML20058N065
| ML20058N065 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 08/07/1990 |
| From: | Taylor D COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-009, IEB-88-9, NUDOCS 9008130194 | |
| Download: ML20058N065 (10) | |
Text
{{#Wiki_filter:, / Commonwealth Edison ') 1400 Opus Place -( Downers Grove, HHnois 60$15 August 7, 1990 U.S. Nuclear Regulatory Commission ATTN: DOCUMENT CONTROL DESK Hashington, D.C. 20555
Subject:
Zion Station Unit 1 and Unit 2 Response to NRC Bulletin 88-09 ECJocket No. 50-295 and_50dQ4 i
References:
(a) NRC Bulletin 88-09, dated July 26, 1988. (b) H. Morgan (CECO) letter to U.S. NRC, dated September 23, 1988.
Dear Sir:
NRC Bulletin 88-09 (Bullettn) requested that addressees establish and implement an inspection program to periodically confirm incore neutron monitoring system thimble tube integrity at Westinghouse designed nuclear power reactors. In accordance with the Bulletin, this letter presents the detalls of the incore thimble tube inspection program (Bulletin Action 1) and the results of the thimble tube inspections (Bulletin Action 2.a) performed during the Zion Unit 1 Fall 1989 (Z1Ril) refueling outage and the Zion Unit 2 Spring 1990 (Z2R11) refueling outage. U QILValt_.1 Prior to the performance of the thimble tube inspections at Zion Unit 1 (performed using eddy current testing), thimble tube wear acceptance criteria was. established using a finite element structural analysis to evaluate the stresses in a worn bottom mounted instrumentation thimble tube. For this analysis, the wear scar geometry was assumed to be a flat bottom scar localized on one side of the thimble. It was determined that a sixty percent (60%) maximum wall loss was acceptable in accordance with ASME Code material allowables. However, the wear scar calibration geometry used for the Zion Unit 1 inspections varied from the wear scar geometry assumed by the analysis. The wear scar calibration geometry for the inspections simulated the average wear scar pattern on thimble tubes which had been previously removed from Unit 2 (during the Fall 1988 refueling outage). Subsequently, the thimble tubes were reanalyzed for sixty-five percent (65%) and seventy percent (70%) wall loss, assuming a wear scar geometry which approximated the . wear scar pattern on the removed thimble tubes, it was determined that a maximum wall loss of sixty-seven percent (67%) was acceptable in accordance uith ASME Code material allowables. For evaluation of the Zion Unit 1 eddy current inspection data, a wall loss criteria of sixty-two percent (62%) was adopted (assuming a five percent (5%) uncertainty). I 1 I 9008130194 900807 FDR' ADOCK 05000295 '[M Q PDC
i U.S. Nuclear Regulatory Comission August 7, 1990 i The thimble tube inspections were performed using eddy current i testing. Fifty-seven of fifty-eight incore thimble tubes for Zion Unit I were - inspected from the seal table to the end of the thimble tube. Thimble - location P-4 was previously utilized for a RVLIS modification and thus was not tested. The results of these inspections are presented in Attachment 1 to this letter. The Unit ! thimble tubes, with the exception of the tubes at core f locations "B-13" and "F-1", have been in service for 11 cycles of operations. There have been no thimble tube leaks due to wall loss from flow-induced vibration. The tubes were repositioned (withdrawn approximately 1.5 inches) during a modification to the high pressure seals at the seal table between - operating cycles 8 and 9. Consequently, many of the tubes had more than one location which exhibited an indication of wall loss, however, only the maximum wall loss value for each tube is presented on the Attachment to this letter. Twenty-three (23) thimble tubes exhibited wall loss indications which . exceeded the sixty-two percent (62%) wall loss criteria. The majority of 1 these indications were in the vicinity of the core plate and the diffuser plate (located below the core plate). The location of the thimble tube wear indicates that the vibration induced fretting was the probable cause of the wall loss. To minimize the possibility of any potential thimble tube leakage, it was determined that the 23 thimble tubes which exceeded the wall loss criteria of sixty-two percent (62%) should be isolated during the course of the - upcoming operating cycle (and replaced during the next refueling outage). The thimble tubes (a total of 3 tubes) which exhibited greater than eighty percent (80%) wall loss were isolated prior to leaving " Cold Shutdown". These thimble tubes were isolated at the seal table by closing the thimble specific isolation salve. The remaining-thimble tubes (a total of 20 tubes) were isolated following acquisition of an acce" ble full-power flux map during unit.startup. Unit startup with these tutas in service prior to acquisition of a full-power flux map, was determined to be acceptable based on the following. It was determined that the allowable stress of the thimble tube L material is 54.8 KSI at 650'f based upon Code Material Test o Reports for materials of this type. The stress at eighty percent ~ (80%) wall loss was determined to be 34.8 KSI, (63.5% of the L allowable stress). This demonstrated that sufficient conservatism existed to allow startup with these tubes in service. Timely detection of thimble tube leakage is assured through the leakage detection system for the thimble tubes on the radiation monitor located inside the seal table room. L f
I l ~U.S. Nuclear Regulatory Commission August 7, 1990 t i Additionally, an evaluation was performed prior to unit startup which addressed unit operation with a reduced numoer of thimble tubes. During the next refueling outage for Zion Unit 1, which is presently scheduled.for September 1991, the 23 thimble tubes which are presently i isolated will be replaced. 2 Zion Un1t 2 Prior to the performance of thimble tube inspections for Zion Unit 2, l (performed using eddy current testing), thimble tube wear acceptance criteria l was established utilizing the Zion Unit I criteria with uncertainties added for additional conservatism. Thus, for evaluation of the Zion Unit 2 eddy current inspection data, a wall loss criteria of fifty seven percent (57%) was i adopted. As previously stated, the thimble tube inspections were performed using eddy current testing. Fifty six (56) of fifty eight (58) incore thimble tubes for-Zion Unit 2 were inspected from she seal table to the end Of the thimble tube. One of the two thimbles not tested, P-4, was utilized for a RVLIS modification. The other, 0-10 was capped during the previous Unit 2 Fall 1988 refueling outage (Z2R10) and was replaced auring Z2R11. The results of the thimble tube inspections are presented in Attachment 2 to this letter. Fifteen (15) thimble tubes exhibited wall loss indications which exceeded the fifty seven percent (57%) wall loss criteria. The majority of -these indications were in the vicinity of the core plate and the diffuser plate (loca' id below the core plate). The location of the thimble tube wear indicates that vibration induced fretting-was the probable cause of the wall loss. These fifteen (15) thimble tubes were replaced during Z2R11-in addltion to the replacement of thimble D-10. lhus, sixteen (16) thimble tubes were replaced during the Z2R11 outage. Ongoing Aciloat for both Units 1 and 2, thimble tube inspections will be performed at every refueling outage untti sufficient data has been accumulated on thimble tube wear to warrant adjustment of the inspection frequency. In addition, it should be noted that the Zion Unit 2 wall loss acceptance criterla; fifty seven percent (57%), will be utilized for all future inspections at Zion Station. When addressing thimble tube wear during future refueling outages, thimble tube replacement will be the preferred resolution.
J. n a g 40.S. Nuclear Regulatory Commission' August 7, 1990 '} E This response completes the reporting-requirements of NRC Bulletin 88-09 for Zion Station Units 1 and 2. E Please. direct any.' questions that you may have concerning this response to this office. e Respectfully; i. S.L. Taylor [ Generic Issues Administrator E i E Attachments
- cc:- A.B. Davis - Regional Administrator, Region III Senior Resident' Inspector - Zion-Station 7
C. Patel - NRR Project Manager. m E tim /ID102~ ilih ' SUBSCRIBED AND SHORP TO E -;BEFORE ME.THIS- \\ DAY m ./ - E 0F r. t uSG ' , 19 ~ 6 g [ E-OdA' ~ 4 0 F NOTARY PUBLIC.'^ ? m [ J E E E [-
,l lti { ' '. _ ^ -{G t t i [ ?; ;.- -ATTACHMENT 1 a: .v-UNIT-:1_ THIMBLE TUBE' INSPECTION RESULTS APPROX. APPR0X. LOCATION
- THIMBLE TV'BE-HALL LOSS.
Of WALL LOSS (RELATIVE
- 001LLOCA110N 1HQ1 CATION (%)
TO COPJ PLATE)(IN.)- COMMENTS -i A-9~ 59 -66. l 'A-11l 44' 2 'B-3 65 -60 ' NOTE (1)- B-6 49 B-8 .66 l'. 5 -NOTE =(1)- B-13 45 2 f i f C-5 66 -85 NOTE (1)'. C-7: 25 -3 r C-8 62 -105 D-3' 55 -29 n D-8 75 -72 NOTE (1) 'D-10 77 -69 NOTE (1). t D-12 71 -78 NOTE (1) _ q l 5 0-141 64 2- ' NOTE (1) j E 57 -- -88 E-9 21- -103 E-11: 56 -63 L -I 1 42 -91 i I
- F-.31 79
-2 NOTE (1)- l' F-7' ~49 -85 Fa8 74 -88 NOTE (1) ,F-14 38 -67 I U-5 64 0 NOTE (1) L G-9: 66 -86 NOTE (1) ? 3 6.! i (A-1)
- i
}{; 1 -[ ATTACWIENT 1. ~~ o - 1 UNIT 1 THIMBLE TUBE INSPECTION RESULTS -APPROX. APPROX. LOCATION l HALL LOSO OF' HALL LOSS (RELATIVE- -THIMBLE TUBE ' iu CORE LOCATIQH- . INDICATIOL(7d TO CORE PLATE) COMMENTS .G 63- -83 NOTE (1) H5 41, H-3 40 -76 -H-4: 28 -81 .H-6 52- -85 <r.
- H-il 41
-85 ~H-13. 65 0 NOTE.(1) .f H-15 26 0 J-1 84 NOIE (2) J-7 56' -98
- J-8 78-
-92 NOTE (1) 'J-!O 52 -107 J-14
- 18 0
.K-2 67 -84 NOTE (1) K-6: 64 -71 NOTE (1). j K-12 54 -80 L-5 14 -67' ' L-8. 54 -75 j L 43 -82 -L -- NO INDICATIONS j 1 (A-2) f ,i
s-d- - e f j .o
- (,.
cc ~ n ATTACHMENT 1-
- b UNIT 1THIMBLETUBE'INSPECTIdNRESULTS' w...
, APPROX. APPR0X. LOCATION " i 4'" - THIMBLE TUBE-HALL LOSS OF HALL LOSS (RELATIVE CORE LOCATION INDICATION'(%) TO CORE PLATE) COMMENTS -[ ... J. L-13 80 0 ~ NOTE (2): L-15r 51 -1 L C e H EO -96 NOTE (2) y N-2 69 -66 NOTE (1): N-4 NO INDICATIONS 1 N-6' -39 -77 N-8 25 0 N-13 44- -89 l - N-14 '. 60 0 P-9 76 -71 NOTE (1) i gg. R-6 49 -1 c>g T .R-8 77 0 NOTE (1)- .m W - R-11 77 -S9~ NOTE (1) pp y gjt f',,, m o 4;n:,l e [. l t ,s. . NOTE (1): ISOLATED FOLLONING RECEIPT OF FIRST FULL-POWER FLUX MAP. G c: NOTE (2): : ISOLATED PRIOR TO LEAVING COLD SHUTDOWN. ~? el'. i aj. i ti ,i (A-3) a 4 t[,, h i. ' ? ;.' o, n, - i
.a 1; 3 g '" 1 -. e , ATTACHMENT 2 ' UNIT 2 THIMBLE: TUBE INSPECTION RESULTS .APPR0X. APPROX. LOCATION THIMBLE TUBE HALL LOSS- -0F HALL LOSS (RELATIVE W
- CORE LOCATION. INDICATION (7.)
TO CORE PLATE) (IN.) CQttiMIS i A-9 47 0.6-A-11 35 2.2 $3' B-3 51 0.0 .t B-6 No Indications j Bi8 78 -77.3 Note (1) p f B-13 44- -0.4' C-5 40 0.0 ~. C-7. .77 -82.5 Note (1) i No Indications C-8 D-3 63 - 0.7 Note (1) i D-8 65 1.6 Note (1)- D-10 Note (2) D-12' 53' -19.6 'D-14 72 -59.6 Note'(1) E-5 No Indications No Indications E-9 E-11 No' Indications i P F-1 42 -44.1 F-3 64 -0.4 Note (1) .F-7 47 0.0 1 (A-4)
- c t
Qi;
ATTACHMENT 2 . UNIT 2 THIMBLE TUBE-INSPECTION RESULTS 4 1 APPROX. APPR0X. LOCATION l HALL LOSS-0F HALL LOSS (RELATIVE i . THIMBLE' TUBE CORE LOCAll0B. ' INDICATl0N (7.) TO CORE PLATE) (IN.) CONtiMIS F-8 No Indications F-14' 75 -41.0 Note (1)- G 44 -74.3 I G-9 38 0.5 .i G-12 53 -73.2 l H-2 46-0.8 .H-3 48 -55.5 -i . Indications i H-4 H-6 25 .0.9 H-ll No Indications H-13 42 1.3
- H-15 No Indications
~! { J-1 No Indications .J-7 51 0.6 J-8 78 1.3 Note (1)'
- i J 79
-88.1 Note (1) J-14 51 -0.5 l K-2 68 -18.7 Note (1) i K-6 46 1.9 t K-12 38 0.9 L 34 0.3 L-8 59 -0.6 Note (1) (A-5) l
4 ATTAC MENT 2 UNIT 2 THIMBLE TUBE INSPECTION RESULTS w = APPROX. APPROX. LOCATION LTHIMBLE TUBE HALL LOSS OF HALL LOSS (RELATIVE CORE LOCATIO11 1ELC6 HOR _1M TO CORE PLATE) (IN.) .CQMMQlS 4 'L-10 49 -93.5 -l L 58 -65.8 Note (1) J l .61- -63.8 Note (o _j No Indications L-' I 5 4-7 52 -97.1 -N-2 38 -246.4 .i 'N-4 57 -0,5 1 N-6 49 -86.3 No Indications l N-8 N-13 64 -73.6 Note (1)' { 1 N-14 40 0.7 P-9 81 -71.8 Note (1)- l No Indications d R-6 t R-8 44 0.9 1 R-ll 56 0.0 r Note 1 - Replaced during Z2R11 i 1 Note.2 'Previously capped during Z2R10, Replaced during Z2R11 I l } (A-6) ,}}