ML20211N057
| ML20211N057 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 10/07/1997 |
| From: | Maine Yankee |
| To: | |
| Shared Package | |
| ML20211N055 | List: |
| References | |
| NUDOCS 9710160004 | |
| Download: ML20211N057 (4) | |
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- ) !!NCLOSURiiTO Ll!1TliR GDW 94 29, Rev.1 l PAGli 27 of 59 15,.3 .S/G Tube Runture Considerations lhe degraded tubes identined in the 1994 inspection would not have been expected to suddenly fail under operating conditions nor would they have been expected to contribute to a multiple tube rupture if any other tube were to rupture. A tube with PWSCC usually exhibits uneven growth through the tube's wall and is expected to leak extensively before it is likely to rupture. The tube's remaining cross section free of cracks and the noncorroded ligaments present in PWSCC circumferential cracks can be expected to provide signincant remaining tube strength even aner leakage starts.1his was the case at Maine Yankee where the in situ pressure testing demonstrated that the leaking tubes and the tubes with large MRPC indicated Avg l 1W circumferential cracks could still be expected to withstand 3.3 (4,170'/1450) times the normal operating l in situ differential pressure loads. Tubes with this much remaining structural margin would not have been l expected to suddenly rupture during normal operations.1his is consistent with the industry experiences noted in Reference 15 where no S/G tube rupture has been attributed to stress corrosion cracking circumferential defects. This type of corrosion progression coupled with Maine Yankee's low (50 gpd) administrative primary to secondary leakage limit should ensure Maine Yankee shuts down and makes repairs before any tube would not be abie to withstand its design loads with only minimal leakage.
During normal operations, the degraded tubes identined in the 1994 inspection would have been expected to withsti.nd the impacting orjetting a neighboring ruptured tube may have imparted on them. Should any tube rupture at the tubesheet, the impact force it may impart on a neighboring tube was calculated by Allil l C E in Reference 11 to be 491 pounds. The maximum jet impingement force a tube may expect to experience at operating conditions was calculated by Ailli C li in Reference 16 to be 136 pounds. Each of these loads is 1:ss than the circumferential cracked tubes' nomial operations remaining structural shear load l margin of 650 pounds calculated below:
l In situ Testing Demonstrated Tube Max Shear Stress for Normal l Tube Max Shear Stress = Operations & Coincident Shear Load 3
' A ,P,' _
A,P,'2 2 I h 2A, , 2A, A,,
$ 3 ( (
l Where: iA = Tube inside Diameter Area = 4 5 - 2 00W = .336 in.2 l 4 l A 2= Tube Cross Sectional Area (This value cancels out in above equation).
l Pi = Normal Operations Tube Differential Pressure = 1,450 psi.
l Pa = In situ Pressure Test Differential Pressure = 4,170' psi.
l F, = Max Shcar Load that may be Resisted Coincident with Normal Operations Tube
( l Differential Pressure l F, = 650 lbs.
l The degraded tubes would have been expected to maintain their integrity even ifimpacted by a neighboring w hipping orjetting tube.
l ' Lowest of a tube's maximum in situ pressure values identified in Table 3 (envelops both 1994 and 1995 l testing) compensated for difference in operation and test temperatures (4,800/l.15 = 4,170).
9710160004 971007 PDR ADOCK 05000309 G PDR
- l ENCLOSURE TO LE1TER GDW 94 29, Rey,1 l PAGE 30 of 59 REFERENCES
- 1. Allil C E Letter M PENG 94 008 dated 10/07/94 to C. Eames of Maine Yankee; Subjec:: "In Situ Test Results for Maine Yankee July 1994 Outage, M PENG TR 004, Rev. 00."
- 2. Alll) C E Report M PENG TR 004 dated October 1994:
Subject:
"in Situ Pressure Test Results for Maine Yankee July 1994 Outage."
- 4. Allil C E report CENC-1934," Maine Yankee Steam Generator Analysis of Circumferentially Flawed tubes at Tubesheet," January 1991.
- 5. Allll C E Design Analysis MY SS 900," Steam Generator Tube Loads for Tube Lock Ups," October 5,1994.
- 6. Allll C E Design Analysis MY SS 901," Steam Generator Tube Loads Due to Main Steam Line Dreak,"
October 5,1994.
- 7. Allll C E Design Analysis CENC 1965, " Amended Analysis of Maine Yankee Steam Generator Circumferentially Flawed Tubes at Tubesheet," Dated October 10,1994.
- 8. Ailll C H Technical Report M-PENG TR 002," Maine Yankee Run Duration Limit Evaluation for Circumferential Cracking," October,1994,
- 9. Yankee Atomic Electric Co. Memo TAG MY 94-051," Maine Yankee S/G Tube Leakage Assessment -
Summary of Results", dated October 27,1994.
- 10. Yankee Atomic Electric Company Memo REG 203/94 "Offsite Doses as a Function of Primary-to.
Secondary Leakage due to MSLil with Induced Steam Generator Tube Leakage (Rev.1)," Dated October 26,1994.
I 11. Ailll C E letter M.PENG-97 005 to Maine Yankee dated February 11,1997;
Subject:
" Steam Generator l Tube Whipping impact."
Subject:
" Transmittal of Documents: MRPC Sizing of Circumferential Cracks"
- 13. Proceedings: 1992 EPRI Workshop oa PWSCC of Alloy 600 in PWRs. EPRI TR 103345 dated December 1993: Paper " Potential Benefits of Zine Addition to PWR Coolant" by R.E. Gold,
- 14. Al3B C-E Report CE NPSD-957 (CEOG Task 729)"S/G Tube Degradation at the Support Plates" by G. C. Fink and S. M. Schloss; October 1994.
i 4
l ENCLOSURE TO LlilTER GDW.94 29, Rev.1 I PAGE 31 of 59 l
- 15. Allil C.E Letter M PENG 94-013 dated Novemter 10,1994 to C. Eames of Maine Yankee:
Subject:
S/G Tube Rupture in PWR Plants.
- 16. Aill) C-E Letter DJA 94 060TD dated November 10,1994 to C. Eames of Maine Yankee;
Subject:
S/G Tube Jet Velocity Loads.
l 17. "In Situ Pressure Test Results for Maine Yankee During the Spring 1995 Refueling Outage" Allli C.E l Report 96-TR PSW.Oll, Rev.0.
s i
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l !!NCl.OSURl! TO 1.liTIliR GDW 94 29. Rev.1 l PAGli34 of 59 l 1994 & 1995 IN SITU PRESSURE TEST Rl! SUI TS S'O # ROW l.IN!! VOllS h1RPC 1.IINGTil h1RPC h1AX. 1.l!AK h1AX% % IN SITU RATP.@
TW AVG. PRIISS. h1AX TW PRilSS GPhi 1 62 27 9.57 97 360 97 4,800' s.004 1 66 33 8.98 94 360 94 4,800' s.004 1 106 63 14.82 98 320 88 4,800' s.004 2 38 131 4.68 94 360 94 4,800' s.004 2 49 124 6.36 92 360 92 4,800' s.004 24 49 126 6.23 95 132 35 4,800' s.004 2' 81 72 23.96 92 181 47 4,800' s.004 l 2 49 122 12.26 94 360 94 4,000/5,650' O.488/N/A' l 2' 89 46 18.84 94 262 69 2,700/5,825' O.496/N/A' l 1 70 55 10.41 89 360 89 2,900/5,950' O.527N/A' .
' hiaine Yankee originally identified a 3 times operating differential pressure target lower that identified in subsequent Lnalysis.
2 Not measured, but assumed equal to the maximum pump capacity of.496 gpm at 2800 psi.
o 8 Flow is reported for a maximum sustained pressure of 2700 psi as 2900 psi could not be maintained once leakage started at 2900 psi.
- Selected fu testing to identify an expected leakage rate at the maximum design pressure differential.
l 5 Retests performed in 1995 Refueling Outage, j References 1,2, and 17 TABLE 3 GDW.94 92 _ __