ML20056E229
| ML20056E229 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/17/1993 |
| From: | ENTERGY OPERATIONS, INC. |
| To: | |
| Shared Package | |
| ML20056E207 | List: |
| References | |
| RTR-REGGD-01.121, RTR-REGGD-1.121 92-R-2025-01, 92-R-2025-01-R01, 92-R-2025-1, 92-R-2025-1-R1, NUDOCS 9308230008 | |
| Download: ML20056E229 (94) | |
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ENTERGY OPERATIONS INCORPORATED operations ARKANSAS NUCLEAR ONE 20 a 2o O b ENGINEERING REPORT FOR ARKANSAS NUCLEAR ONE RUSSELLVILLE, ARKANSAS [ a l i 7 9308230008 930811 ;; PDR ADOCK 05000368 ,,. ! P PDR w 1 I 6/n /qs M mor Rev.s.ons f o< C 'e r d A +'. - kM k I O 9/2/92 Initial Issue No. kC8% M kNih DATE Rzy15 IONS BY CH'E APPR. l ANO-2 STEAM GENERATOR DEGRADED TUBE 92-R-2025-01 1g g g ANALYSIS PER REG GUIDE 1.121 FORM TITLE FORM NO. REV. ' ver:Terrvinr; TEPORT COVER SHEET 5010.017A 0
I i i 92-R-2025-01 Rev. 1 j Page 1 of 4 j TABLE OF CONTENTS l t 1.O PURPOSE .; f i t 2.0
SUMMARY
OF APPROACH I 3.0
SUMMARY
OF RESULTS , 4.0 ATTACHMENTS -- [ Attachment A - C-E Report CR-9417-CSE92-1102, REV. O,
" Evaluation of Circumferential Defects at j the Expansion Transition in. Arkansas !
Nuclear One Unit 2 Steam Generator .l' Tubes". , i Attachment B - MPR Associates, Inc. Report dated August' f 26, 1992, " Evaluation of Arkansas Nuclear [ One Unit 2 Steam Generator Tube Wall -! Degradation". ! i i f i
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i ! I h i 92-R-2025-01 Rev. 1 ; Page 2 of 4 !
- 1.0 PURPOSE l
In March 1992, ANO-2 was shut down as a result of a tube leak l
, in the "A" steam generator (one of two steam generators: 2E24
- A & B). Inspections were performed to determine the extent of degradation associated with the leaker. These inspections 2
revealed significant degradation in the expansion transition region of the tubing, just above the tubesheet, on the hot leg i side, primarily in the "A" generator, but also in the "B" ; generator. This degradation was essentially circumferential l in nature, with axial extent limited to less than 0.25 inch, i based on eddy current testing. This is also consistant with j the limited axial extent of the expansion transition where the ' residual stresses imposed on the tube by the expansion ; contribute to the stress corrosion cracking which caused the ; defects, based on tubes pulled from the generators for ! l examination. Due to the large size of the defects (both i circumferential and thru-wall extent), an evaluation of the : allowable tube wall degradation was performed. The purpose of l this report is to document the evaluation done to determine ! I the maximum allowable tube wall degradation in accordance with i i (draft) Reg Guide 1.121. This allowable degradation is used i to support the tube plugging criteria and related safety l margins for ANO-2 steam generators. i l 1 t 4- 2.O
SUMMARY
OF APPROACH l 2 : ! A structural evaluation of maximum allowable degradation was l } performed by Combustion Engineering (C-E) in accordance with !
- the Reg Guide requirements, as interpreted by C-E. The report i a
of this work is contained in Attachment A. This report was , then independently reviewed by MPR Associates, Inc. Their j l' review, along with their interpretations of the requirements ! of the Reg Guide, were factored into their report, Attachment ! B. In addition, since axial cracking in the egg crate support ! . region is also an emerging issue for ANO-2, MPR was tasked to ! i expand their results to include additional information to ! support criteria specifically for axial cracks. l i 2.1 C-E Approach ! j C-E evaluated the structural integrity of the flawed
]
tubing for normal operating conditions including flow ; i induced vibration, and accident loads coincident with ; 1 Safe Shutdown Earthquake (SSE) loads. These loads were j , considered for three cases- i i
- 1) Unlimited axial and circumferential extent, I
} 2) A limited axial extent of 0.25 inch maximum and
- unlimited circumferential extent, and i i
a l I i 2_-_ . . . . ,, __. - _
1 i i 92-R-2025-01 Rev. 1 ! Page 3 of 4 i
- 3) A limited axial extent of 0.25 inch maximum, and [
the maximum allowable 100% thru-wall defect was !
, determined.
The analysis considered both Code required minimum material strength, and a conservative estimate of actual-material strengta expected in ANO-2 based on yield i strengths of typical tubing supplied to C-E in accordance l with their tubing specifications. In addition, the ; analysis also considered degradation initiating on both i the inside and outside of the tubing. l 2.2 MPR Approach [ MPR provides a point by point discussion of the Reg Guide ; requirements, compares the C-E analysis to them, and provides additional evaluations where necessary, based on i their interpretation of the Reg Guide. Significant items l from the report are:
- 1) MPR agrees with the results of the first case for unlimited axial and circumferential extent. !
- 2) The C-E evaluation uses the tube burst data i directly to estimate the allowable degradation for the second case defect. The MPR evaluations also !
utilize the burst test data, but account for l dif ferences in tubing and defect parameters between < the burst test tubing and the ANO-2 tubing.
- 3) The results for C-E's third case of limited axial extent and 100% thru-wall are misleading, as they ,
actually apply to slot type defects rather than a i defect which is 0.25 inch wide. However, based on l burst tests for other tubing with defects similar ! to ANO-2, it is expected that ANO-2 tubing will i behave such that average remaining wall thickness 1 is the appropriate criteria. See Attachment B, j pages 3-6 and 3-7, for additional information. 3.O
SUMMARY
OF RESULTS The overall results are summarized in Table 1, below.
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92-R-2025-01 Rev. 1 2
.Page 4 of 4 f
4 TABLE 1 ; t t Tvoes of Dectradation' C-E Results MPR Results f Unlimited axial and 65.8% 66% I circumferential extent j 0.25 inch max axial 77% 79% !
- length at 360 circ !
extent , axial slot type NA See Attach. B,-Fig. 1 j i I Y l\ , 1
} $
asymmetrical defects at the tubesheet or tube support ; elevations, or symmetrical defects at any location ! i 2 conservative best estimate tubing properties ; i i Based on a detailed review of Attachments A and B, Design Engineering considers a limit of 79 % through wall to be l appropriate for the pertinent defects of current interest (0.25 i inch maximum axial length, 360 degree circumferential extent). ! Notably, this 79% value is based on calculations / tests for planar defects and is, therefore, conservative with regard to actual ANO-2 defects which have ligament strength between microcracks. t E l I i i j
. -~ _.
ABB COMBUSTION ENGINEEIGNG NUCLEAR POWER Combustion Engineering, Inc. l EVALUATION OF ' CIRCUMFERENTIAL DEFECTS AT THE l EXPANSION TRANSITION IN ARKANSAS NUCLEAR ONE UNIT 2 STEAM GENERATOR TUBES CR-9417-CSE92-1102, REV. 0 4 r
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1 NCS ENGINEERING CALCULATION REPORT CR-9417-CSE92-1102. REV. O EVALUATION OF CIRCUMFERENTIAL DEFECTS AT THE EXPANSION TRANSITION IN ARKANSAS NUCLEAR ONE - UNIT 2 STEAM GENERATOR TUBES PREPARED BY: (.z.86dfI //e<O/dd- DATE: M23/tz.
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'7ERIFIC ATION STATUr- COMPLETE I The Safety-Related desian information containoc in this cOcument nas teen verified to7be correct Ov means of Deslon ,
Review usina Checxlist(s) -f QhM-1C1. Name d. A. b C"' Signature C'.'b M Date WJ2 Indepencent :-eviewer j l l(" APPROVED BY' J.H %decocencM u . -e DATE: 4 In f 92_ ; i l l ik It BE MIBEB
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} PARAGRAPH (s) j PREPARED ; INDEPENDENT APPROVED
; NUMBER { DATE ; INVOLVED BY l
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0 l04/23/92 ! original !ssue Stubbe l B.A. Bell ! Sodergren
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i i CR-9 417-CSE92-1102, REV. O Page 3 of 40 j TABLE OF CONTENTS ; r PAGE ? I
1.0 INTRODUCTION
4 2.0
SUMMARY
OF RESULTS 5 -
3.0 REFERENCES
6 2.0 GEOMETRY DESCRIPTION OF S/G TUBE BUNDLE S 5.0 STRUCTURAL ANALYSIS 9 5.1 LOADINGS TO BE CONSIDERED 9 a t 5.2 ASSUMPTIONS APPLICABLE TO STRUCTURAL LOADINGS 11 ! 5.3 NRC REQUIRED STRUCTURAL LNTEGRITY MARGINS 11 i h 5.4 STRESS EVALUATION OF TUBE WITH UNLIMITED AX1AL AND CIRCUMFERENTIAL DEFECTS 13 l i-5.5 NRC REGULATORY GUIDE 1.121 EVALUATION OF TUBE WITH AX1AL DEFECT OF 0.25 INCH MAX. AND UNLIMITED CIRCUMFERENTIAL . j DEFECT 34 ! i 5.6 NRC REGULATORY GUIDE 1.121 EVALUATION OF TUBE WITH AXIAL i i DEFECT OF 0.25 INCH MAX. AND ALLOWABLE CIRCUMFERENTIAL , 100% THRU-WALL DEFECT 37 ! t j
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I i i 4 I CR-9417-CSE92-1102, REV. O I Page 4 of 40 i
1.0 INTRODUCTION
i The analysis presented herein is performed to establish the maximum allowable tube wall degradation for the Arkansas Nuclear One - Unit 2 steam generator tubes per the ; requirement of NRC Regulatory Guide !.121. The results of this analytical study will ; be used in conjunction with prior pressure testing results to assess the steam generator l tube integnty when subjected to either inner diameter or outer diameter circumferential I cracking at the tube expansion transition region. This report addresses the structural aspects of NRC Regulatory Guide 1.121 regarding the minimum wall thickness of steam generator tubing. The report does not address the primary to secondary leakage rate data used in meeting Regulatory Position C.3.(d)(3). The structural integrity of the flawed tubing is evaluated based on normal operating l conditions and possible accident conditions such as Loss of Coolant Accidents (LOCA) i plus Safe Shutdown Earthquake (SSE) loads and Main Steam Line Break (MSLB) plus ,[ SSE loads. Since the tubes containing flaws may be located near the outer periphery of l { the tube bundle the tubes will also be evaluated for flow induced vibration due to the : ! recirculating fluid. 1 j l The report also considers two tube cases with localized defects. The first case has an i i i axial defect of 0.25 in, maximum and an unlimited circumferential extent. The second ! l case also has an axial defect of 0.25 in. maximum, but the allowable circumferential extent for 100% thru-wall detect is determmed. I i j . 4 i i ' i
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SUMMARY
OF RESULTS ! 1 I This analysis evaluates the loading of a flawed tube due to normal operation, Loss of I Coolant Accident (LOCA), Main Steam Line Break (hiSLB), and Safe Shutdown Earthquake (SSE). The allowable tube wall degradation is established to be 61.5% for [ the case of unlimited axial and circumferential extent of defect in accordance with the ! stress allowed by the ASME Code Section III and the structural integrity margins ; required by NRC Regulatory Guide 1.121. When the probable tube material properties are used in place of the ASME Code allowables, the allowable tube wall degradation can be increased to 65.8% for the case of unlimited axial and circumferential extent of defectand still meet the structural integrity margins required by NRC Regulatory Guide 1.121. The maximum stress intensity due to a 61.5% degraded tube was found to be 26.75 ksi and 30.24 ksi for a 65.8% degraded tube, which is less than the allowable of 56 ksi for f the steam generator tube matenal, inconel SB-163. t For the two tube cases with specific defects, the maximum allowable tube defect per ' NRC Regulatorv Guide 1.121 tube burst requirements is 77% tube wall degradation for i an axial extent of 0.25 in. maximum and unlimited circumferential extent. With 100% . thru-wall defect, the maximum allowable circumferential extent is 274*, with 86* of the total circumference having no tube wall degradation. I i i CSE-92-164
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I i i CR-9417-CSE92-1102, REV. O Page 6 of 40 j i
3.0 REFERENCES
i 3.1 U.S NRC Regulatory Guide 1.121, " Bases for Plugging Degraded PWR Steam ! Generator Tubes", August 1976. i i i 3.2 Analyses to Determine Allowable Tube Wall Degradation for Palisades Steam ; Generator. CENC-1264, P.evision 03, January 1976. ! i I 3.3 Arkansas Steam Generator Structural Analysis of Tubes for Pipe Rupture Accidents, ; CENC-1262-1, September 23,1977 i 3.4 Maine Yankee Steam Generator Analysis of Circumferentially Flawed Tubes at Tubesheet, CENC-1934, January 1991. 3.5 ASME Boiler and Pressure Vessel Code. Section III for Nuclear Power Plant i Components. [ 3.6 Connors, H.J., Jr., "Fluidelastic Vibration of Tube Arrays Excited by Nonuniform Cross Flow", Flow-Induced Vibration of power Plant Components, ASME, PVP-41, p. ;
- 93. I i
3.7 Heilker, W.J. and Vincent, R.Q., " Vibration in Nuclear Heat Exchangers Due to Liquid ! and Two-Phase Flow". Engineering for Power, April 1981, Vol.103, No.2. I h 3.8 ANSYS Engineering Analysis System. Finite Element Computer Program. Revision 4.1, March 1,1983, John A. Swanson. Ph.D. i 3.9 Lowry, J.C. memo to J.H. Sodergren on Hydraulic Conditions at the Tube Bundle - Entrance for Arkansas Steam Generator " ATH-92-069, April 10,1992. i 3.10 Heilker, W.J. and Beard, N.L.. " Flow induced Vibration Analysis in Support of the ! Design of the Yongwang Units 3 and 4 Steam Generators", Proceeding of the ! International Symposium on Pressure Vessels Technology and Nuclear Codes and [ Standards. April 19-21, 1989 Seoul, Korea. 3.11 Drawing E-234-825 " Baffle and Tube Suppon Assembly, Rev. 04. I 3.12 Engineering Specification for a Steam Generator Assembly, Specitication No. 06370-PE-120. l' i b CSE-92-164 . V.%n's gnot A 9PAGE 2 - R- 2 025 -0_ 7 CF4I .!
i i CR-9417-CSE92-1102, REV. O i Page 7 of 40 ' i 3.13 Analytical Report for Arkansas Nuclea One Unit 2 Steam Generator CENC-1223, ' July,1974 ! 3.14 Roark, R.J. and Young, W.C., " Formulas for Stress and Strain", Fifth Edition,1975. i 3.15 " Design Guide for Calculating Hydrodynamic Mass Part I: Cylindrical Structures", { Chen, S.S. and Chung, H.. June,1976, Argonne National Laboratory. 3.16 Main Steam Line Break Analysis of Palisades Steam Generator Internals (Including Tube ; Sleeves), CENC-1288, June 3.1977. 3.17 Analytical Report for Arizona Public Service Company Palo Verde Unit No. 3 Steam i Generators. CENC-1479, August,1981. i ) 3.18 Annual Progress Report for Steam Generator Tube Integrity Program, NUREG/CR- ! 0277, PNL-2684 R5, January 1-December 31,1977. ) i e E ,i d t t 4 i 1
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r l CR-9 417-CSE92-1102, REV. O j q Page 3 of 40 [ i J.0 GEOMETRY DESCRIPTION OF S/G TUBE BUNDLE l The Arkansas steam generator tube bundle is comprised of 0.75 inch diameter tubes with 0.048 inch wall thickness which are supported by grid type (" egg-crate") tube ; suppons in the axial Row region. In the cross flow region the tube bundle is supported - l by three different types of supports. Two of these, drilled phtes and " egg-crates", i suppon the vertical portion of the tubes and " batwing" conngurations support the '
- horizontai section. This report is concerned only with the stresses occurring in the tube expansion region of the bundle and is therefore only considering forces acting on the j
- vertical ponion of the tube bundle. i
- The egg-crate and drilled support plates are spaced incrementally up the tube bundle as i shown m Figure 5.4-1. The 6rst support is located at 28.125 inches above the tube l 1
sheet. The remaming full and partial supports are located vertically in the following ( ) merements tall in inenes). 30. 33, 35. 30, 33, 35. 25.5. 26.5, 22. The last three ; j increments correspond to locations of partial supports. (Reference 3.11) j i l Tube Row 110 is modeled in ANSYS to be evaluated throughout this report. This tube ! j row is chosen as a bounding condition and corresponds to the location evaluated in the
- l Palisades steam generator report (Reference 3.2). Resulting time history displacements from this Palisades report will be applied to the ANO2 steam generator and it is l necessary that the identical locanon in the ANO2 generator be modeled to produce ,
l compatible results. l 1 ; 4 4 } f
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i CR-9417-CSE92-1102, REV. O Page 9 of 40 5.0 STRUCTURAL ANALYSIS 5.1 LOADINGS TO BE CONSIDERED l 5.1.1 LOCA Rarefaction Wave A Loss-of-Coolant Accident (LOCA) produces a rarefaction wave which propagates at the speed of sound away from the break location. As the rarefaction wave passes through the tubes in the bend region of the steam , generator, it imparts a lateral pressure loading on the tube bundle. The pressure loading on a particular tube is proportional to the pressure difference acting
. between the midpoints of the bends. Fluid friction and the centrifugal forces generated as the fluid negotiates the bends also contributes to the lateral loading ,
on the tube bundle. The net force on a particular horizontal section of the tube , , is the algebraic sum of the pressure. niction, and centrifugal forces. 5.1.2 Pipe Break Impaise Response A LOCA accident produces an externally applied impulse to the steam generator , caused by the Guid escaping from its respective loop. A detailed system LOCA !
- analysis has been done for the Palisades steam generator, Reference 3.2. The results of this analysis were time history displacements at the steam generator uppermost full eggerate tube support. These displacements were used in a ;
dynamic ANSYS Enite element analysis on a model of the Maine Yankee steam i
- generator to calculate the tube stresses near the secondary face of the tubesheet and at the uppermost eggerate support. The following discussion will show that these results can be conservatively applied to the ANO2 steam generator tubes.
5 Palisades analyzed the stress at the uppermost eggerate while Maine Yankee i 1 (MY) calculated this stress as well as the stress at the secondary tubesheet face. . The stress calculated for both plants at the uppermost eggerate was the same. l Tht steam generators for these two plants are compared with ANO2 on the bases of volume and geometry. The volume of the Maine Yankee generator is smaller than Palisades and ANO2 (the volume of ANO2 is similar to Palisades), but the geometry of MY is more unstable than Palisades. Since the resulting stress calculated at the uppermost eggerate for both plants was the same and the geometry of ANO2 is more stable than that for Palisades and MY, it is assumed : that the results obtained by MY for the stresses at the tubesheet are conservative j for ANO2. l 1 CSE-92-164 EQM '9 2 - R- 2 02.5 -01; ) tmsot A PAGE 10 c; 4 [ ~ l
l l CR-9417-CSE92-1102, REV. 0 l Page 10 of 40 ! 5.1.3 MSLB Secondary Side Blowdown 1 A Main Steam Line Break (MSLB) produces a transient pressure loading on the l steam generator internals. The pressure loading results from the relative rates at which the secondary Duid leaves adjacent region. In general, the blowdown rate following a main steam line break depends upon the steam generator geometry, the secondary pressure, the secondary mass, and the nozzle area. Previous analyses of a main steam line break for a wide range of operating conditions and different steam generator geometries (References 3.16 and 3.17) indicate that peak pressure loads on steam generator intemals are realized at either zero or low power operation. This is due to the fact that the secondary pressure increases to near 900 psi under zero and low power operation, from 825 psi during normal operation. The pressure load across the tube bend region caused by this blowdown is maximized at zero percent power. During the main ateam line break, the rapid depressurization of the secondary Guid and its accelermon toward the break location are unaffected by the primary system. 5.1.4 Flow induced Vibration A tube placed perpendicular to a Dowing Duid tends to extract energy from the fluid and vibrate with some amplitude. The steam generator tubes in the tubesheet region are affected in this manner by the recirculating Guid in the generator. Reference 3.7 gives a method of calculating an equivalent static loading using How mduced vibration evaluation methods which are based on the velocity of the fluid cross Dow. the natural vibration frequencies of the tube, and the mode shapes of the tube vibration. 5.1.5 Differential Pressure OP) Dunng the MSLB event a tube is subjected to a net pressure force which produces an axial force in the vertical straight ponion of the tube. With the pnmary pressure remaining approximately constant during the secondary side blowdown at a maximum of 2500 psia, a differential pressure stress is developed which increa. from normal operating differential stress to some maximum value which vanes from plant to plant. In order to select a conservative value, it will be assumed that the secondary side has dropped to atmospheric pressure while the pnmary side is at design condition. Dunng the LOCA event a P.be is subjected to a net pressure force which produces an axial force in the vertical straight portion of the tube. With the CSE-92-164 Gi g ~9 2 - R- 2 02 5 -01) yma A L nGE flCF 41 ]
CR-9417-CSE9 2-1102, REV. O Page 11 of 40 secondary pressure remaining approximately constant during the LOCA event at 900 psia, a differential pressure stress is determined based on this pressure and the primary pressure at the time of maximum LOCA stresses. Since the pressure in the primary side will not exceed 2500 psia, the maximum AP caused by LOCA will be less than that caused by MSLB. Therefore, the stress caused by the .1P due to the MSLB will be evaluated in th is report and will envelope that caused by the LOCA. The analysis concludes that tube buckling is not a concern, with the higher AP being outside the tube, due to the circumferential nature of the defects. 5.1.6 . Safe Shutdown Eanhquake (SSE) The project specificanon for the ANO2 unit states that the steam generator shall be capable of withstanding a maximum seismic loading equivalent to a 1.5G lateral and 1.4G venical simultaneously applied static loading (Reference 3.12). 5.2 ASSUMPTIONS APPLICABLE TO STRUCTURAL LOADINGS 5.2.1 The stresses in the tube at the tubesheet expansion location caused by LOCA Impulse response as calculated by Maine Yankee in Reference 3.4 are conservatively assumed to apply to the ANO2 steam generator tubes 5.2.2 The velocity flow in the tubesheet region due to recirculating fluid is constant over the verucal span of 0-15 inches above the tubesheet and zero from there to the top of the tube. 5.2.3 The maximum amount of degracation for the unlimited axial and circumferential extent of defect is calculated for both the ASME Code allowables and the
" probable" tube matenal propemes.
5.2.4 The stress caused by .1P due to a main steam line break envelopes that caused by a LOCA event. 5.2.5 Where exact data and equations are not applicable, the stress caused by the degradation of the tube will be estimated from the stress resulting on the healthy tube, using a factor based on the percent of degradation. 5.3 NRC REQUIRED STRUCTURAL INTEGRITY MARGINS In Secuon 5.1. vanous loadincs including postulated pipe break accident, earthquake, flow induced vibranon. and operational differential pressure were identi6ed as CSE-92-164
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CR-9417-CSE92-1102, REV. O Page 12 of 40 conditions which in combination must satisfy appropriate ASME Code, Section III allowable stresses. In addition to those requirements, the NRC Regulatory Guide 1.121 requires that certain structural integrity margins be satisfied for flawed tubes which have not been removed from service: These c iteria include:
- 1. Tubes with detected acceptable defects will not be stressed during the full range of normal reacter operation beyond the elastic range of tube material.
- 2. The factor of safety against failure by bursting under normal operating conditions
, is not less than three at any tube location where defects have been detected.
These criteria represent margins of safety which are inherent in the design rules of Secuon 111 of the ASME Code. It is possible for flawed tubes to meet these requirements because steam generator tubes are designed with margins much larger than the minimum ASME Code requirements. The following sections verify that a 61.5% degradation for unlimited axial and circumferential extent of defect irrespective of 0.D. or I.D. initiation when using the ASME Code allowables for Sy and S,. The minimum required thickness is based on pressures. temperature and material properties at normal operating conditions. Dimensions of a healthy tube are R, = 0.327. R, = 0.3750, and t = 0.048 inches 5.3.1 Tube Degraded from the Inside New dimensions: R, = 0.3565. R, = 0.3750, and t = 0.0185 inches
- 1. Flawed tube not stressed beyond elastic limit The code equation for required minimum tubewall thickness (t,) in cylindrical shells is used with the most conservative combination of pressure loadmgs. S, is used to evaluate the required thickness with respect to the elastic limit of the material.
(P1 - P-) Ri (2.25 - 0.900)(.3565) Sy - 0 . 5 ( P, + P )
= 0. 018 3 in . Equation 1 3 27. 9 - 0. 5 ( 2. 2 5 + 0. 9 00)
CSE-92-164 Gs(Gg I92 - R- 2 025 01" l-nes ) ! not /3 er 4 I m
CR-9417-CSE92-1102, REV. O Page 13 of 40
- 2. Flawed tube maintains a safety factor of 3 i 1
i The code equation for required minimum tubewall thickness in cylindrical shells is ; used with the most conservative combination of pressure loadings. So is used to i show that the factor of 3 is maintained with regard to the ultimate strength of the matenal. { 3 ( P, - P ) R. c.= ' - - 3(2.25-0.900)('3565) . I i 4 S., - 0. 5 (P +P)
=
= 0. 018 4 .in . Equacion 2 :
2 80 - 0.5(2.25 - 0.900) ; i
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l i 5.3.2 Tube Degraded from the Outside ; 4 i New dimensions: Ri = 0.327, R, = 0.3455, and t = 0.0185 inches j
- 1. Flawed tube not stressed beyond elastic limit
- The code equation for required minimum tubewall thickness (t,) in cylindrical shells is used with the most conservative combination of prer me loadings. S, is used to evaluate the required thickness with respect o the elastic limit of the material.
i
- Using Equation 1. t, = 0.0168 in t
- 2. Flawed tuce mamtains a safety factor of 3 I i
) The code equation for required minimum tubewall thickness in cylindrical shells is used with the most conservative combination of pressure I i loadings. S,,is used to show that the factor of 3 is maintamed with j regard to the ultimate strength of the material. Using Equation 2, t, = 0.0169 in : 4 i 5A STRESS EVALUATION OF TUBE WITH UNLIMITED AXIAL AND CIRCUMFERENTIAL DEFECTS l The following analyses will be discussed based on three states of the tube: healthy ! degraded on the inside. and degraded on the outside. The individual loading conditions j [ may have been evaluated for one, two or three of these cases. Where only the healthy l a tube was analyzed, a factor based on the percent degradation will be applied to estimate i f CSE-92-164 l 4 l 1 4?(N [9 2 - R- 2 02 5 -01 l yA jeE /1f c:41 ; j
. - - 1
t CR-9417-CSE92-1102, REV. O Page 14 of 40 the stress in the degraded cases. Where the degraded cases were analyzed the actual ; resuldng stress is known. However, this factor of degradation will be also applied to the healthy case and the largest of the actual and estimated stress will be used. Factor of Degradation: ' maximum allowable percent degradation = 61.5'5 factor = 141.615) = 2.60 : f 5.4.1 LOCA RAREFACTION WAVE '
?
The LOCA rarefaction wave can cause severe lateral loading at the top of the tube bundle. as desenbed in Section 5.1.1. However, the tube flaws being evaluated in this study occur exclusively in the tube expansion region. ; Therefore, the rarefaction wave produces no stress at the location of interest in ; this analysis. I 5.4.2 PIPE BREAK IMPULSE RESPONSE ! The postulated LOCA event causes a shock loading to the steam generator which ; causes the steam generator shell to deflect as a rigid body about the bottom of the sliding base (Figure 5.4-2). The time history displacements of the steam generator shell at the uppermost full eggerate support locations are calculated in { Reference 3.2 and shown in Figure 5.4-3. These displacements were applied to an ANSYS finite element model of the vertical portion of a Maine Yankee steam generator tube in a dynamic analysis of the tube (Reference 3.4). The results * , showed that the maximum stress at the tubesheet was 0.5 ksi. Figure 5.4-4, and , l the maximum stress, occurring at the uppermost eggerate was 2.0 ksi. This stress at the uppermost eggerate is consistent with the results of the Palisades t steam generator report. (Note: the input data for the MY analysis was taken from the Palisades report) The volume of ANO2 is similar to that of Palisades l and the geometry of ANO2 is more stable, with the tube supports being closer together. Therefore. the results of the MY analysis showing the maximum stress ; at the tubesheet to be 0.5 ksi can be conservatively applied to the ANO2 steam generator tubes. k The previously mentioned analysis was done for a healthy tube. As discussed , above a factor based on the percent degradation will be applied to this value to 4 estimate the stress which would occur on a degraded tube. This stress will be applicable to degradation on the inside or outside of the tube. Stress on degraded tube = 0.5 x 2.60 = 1.3 ksi. : CSE-92-164 l
. 8 E4M_ p 2 - R - 2 025 -01,, l pm.& A ( not /5 c41 - -- _ )
4 t CR-9417-CSE92-1102, REV. O I Page 15 of 40 ' 5.4.3 MSLB SECONDARY SIDE BLOWDOWN i i The tubes in the cross-Dow region are subjected to an external flow induced ! loading during the MSLB event. The loading imposed on the horizontal span of l each tube is based on the assumption that the force acting is proportional to the . ratio of an individual tube's projected area to the total cross-flow tube area of the ' bundle. Since the tune Daws being evaluated in this study occur exclusively in the expansion region just above the tubesheet, the Dow forces described above produce no signiGcant primary loading at this location. ' i 5.4.4 FLOW INDUCED VIBRATION ! An ANSYS model of the straight ponion of a Row 110 ANO2 steam generator I tube was created. It consists of 109 STIF16,3-D pipe elements with supports at 10 locanons above the tube sheet. Figure 5.4-5. The boundary conditions are: (1) the model is Oxed at Node 1. the tubesheet face, and (2) the tube is simply supported at each tube support locanon. This model was used to generate an t Eigenvalue analysis to give frequencies and mode shapes which are required to } evaluate the Dow induced vibrations loading. ; The resulting Eigenvalues are listed in Table 5.4-1 for a healthy tube and for a ( tube degraded on tne outside. Mode 9 is the critical mode for both cases, since l the maximum displacement in this mode occurs in the first span. The mode shape plot is similar for both cases and is shown in Figure 5.4-6 for Mode 9. i Table 5.4-2 and 5.4-3 give the expanded Eigenvector for Mode 9 for the healthy ' tube and tube degraded outside. respectively. , I The effective mass is reouired for this analysis and is calculated as follows: Om = t 1/A g)(p,A, on,A, + CsaoA,) Equation 3 (Reference 3.15) Where: g = Acceleration due to gravity (in/sec2) A, {
=
Area of tube wall per inch of tube (in2) ; o, = Density of tube (iblin3 ) t A, = Area of displaced Cow based on inside radius per inch of tube f (in ) ; t pr, = Density of primary Guid (lb/in ) 3 i A ., = Area of displaced Cow based on outside radius per inch of tube i (in) 2 ! va = Density of secondary fluid (iblin ) 5 ' Cm = Virtual mass coef0cient ' i CSE-92-164
"#N j92 R- 2 025 01
.mf[A lPAGE /6 C* 41
i I CR-9417-CSE92-1102, REV. O Page 16 of 40 i When tubes m a heat excnanger are subjected to a Guid cross Dow. there is a threshold velocity where the onset of fluid-elastic unstable vibrations occur. This ' is cenned as the critical velocity and is given by the equation: v vc: = != xd i "' 5] ] "' Equa cion 4 i p, r , (Reference 3.7) , t' Where:
. f,, = Natural frequency of nth mode of vibration (Hz)
K = Threshold of instability constant , d = Tube O.D. (in) M ., = Reference mass of tube per unit length (iblini 5, = Logarithmic decrement = 2r( i = Damping ratio of tube in fluid { go = Reference Guid density (lb/in') The above parameters are obtained from the tube geometry and from test and operating plant data. i A comprehensive Dow test program was conducted by Combustion Engineering to evaluate the vibration behavior of various tube bundle arrangements when subjected to liqW cross dow (References 3.7 and 3.10). The triangular pattern with 0.75 O.D tubes used in the CE generators was one of those evaluated. The i tubes were driven to instability and critical velocities were determined for various
- Dow orientations. The K value for the subject tube geometry was determined to i be 3.2 (Reference 3.10). .
If the cross dow velocity is not constant over the entire tube span, an effective velocity must be determined. Reference 3.10 presents a method for calculating Va,. The equation is: ,
.,a =
I p (x) / p J
/;(x) $'(x) dx .,
zquacion 5 1 (M(xt /M,) 45 (x) dx Where: p
= Density of secondary Guid M = Effective mass of tube 6 = Modal displacement (in)
V = Cross Dow gap velocity (in/s) CSE-92-164 Mifs )2 R- 2025 -01
,mer / ime /7 er 4 I w-
CR-9417-CSE92-1102, REV. O Page 17 of 40 All parameters vary with distance along the tube. x. The onset of instability occurs when the stability ratio reaches 1. This is based on a procedure of de5ning, from test data, critical velocity corresponding to the onset of instability to be the velocity at which the tube response suddenly deviates from lineanty or exceeds an rms displacement of 10 mils. Stability ratio is denned as S.R = Ve, / V;, (Reference 3.10) The flow data for the tube span oetween the tubesheet and the Srst tube support
.is taken from Reference 3.9. The velocity pro 61e is assumed to be constant over the Dow region. Although this results in a lower maximum velocity than a linear distnbution, the equation for effecuve velocity is such that velocity and modal displacement are related. The velocity corresponding to the maximum modal displacement for constant velocity distnbution is larger than that for a linear distribution. Therefore the constant velocity distnbution is conservative.
5.4.4.1 Flow induced Vibration for Healthy Tube dffective Mass: Substituting the following values into Equation 3 gives, py, = 0.001948 lb-sec2 /in 4 Where: G = 3S6 inisec2 A, = 0.106 in; p, = 0.305 lblin 3 A, = 0.336 in; p,y = 0.026 lb/in 3 A, = 0.442 in2 p,, = 0.0282 lblin' C, = 3.1 l Critical Velocity: Substituting the following values into Equation 4 gives, V , = 364.7 inis CSE-92-164
'.%jNs ~9 2 R- 2025 -01 1
,fe A = /s em l
CR-9417-CSE92-1102, REV. O Page 18 of 40 l Where: ' r, = 191 Hz ! K = 3.2 ! d = 0.75 in
- M ., = 0.0797 lb/in 5, = 2rt = 0.126 i = 0.02 !
g, = 0.0282 lblin' r Effective Velocity: Using the equation previously defined with the effective mass of the tube and the density of the secondary fluid constant over the tube span, a velocity of 11.44 ft/s from 0-15 inches above the tubesheet. and modal displacements from Table 5.4-2. the ; effective velocity is calculated to be 83.8 in/s. Stability Ratio: ' S.R. = 83.8 / 364.7 = 0.23 - Tube Loading: ' i F,. = C.- d (pVj / 2g) = 0.0770 lblin Equation 6 l t Where: C. = 0.4 (Reference 3.7) , d = 0.75 in i p = 0.0282 lb/in3 V, a = 83.8 in/s g = 386 in/sec2 , t This loading of .077 lb/in is inputted as static load to the l previously described ANSYS model. Figure 5.4-5. The maximum ! stress is calculated to be less than a .I ksi at the tubesheet face. 5.4.4.2 Flow Induced Vibration for Tube Degraded Outside ! Effecuve Mass: f Substituimg the following values into Equation 3 gives. ' i CSE-92-164 FSiiWs 9 2 R- 2 025 -0_1. . f MA A l NE f 9 c; 41 ' l
CR-9417-CSE92-1102, REV. 0 .j Page 19 of 40 ! par = 0.003225 lb-sec:/in' , Where: ' g = 386 in/sec A, = 0.0447 in: , p, = 0.305 lb/in3 - A, = 0.336 in2 0,r = 0.026 lb/in' { A, = 0.3807 in: o,r = 0.0282 lb/in' ' Cm = 3.1 , J Critical Velocity: Substituting the following values into Equation 4 gives, v,, = 292.5 in/s . Where. f,, = 183.3 Hz ! K = 3.2 ' d = 0.696 in
- M, = 0.05565 lb/in 5, = 2rf = 0.126 i i = 0.02 !
- p ,, = 0.0282 lb/in' !
a 1 Effective Velo.ity: i Using the equation de6ned above with the effective mass of the l tube and the density of the secondary Guid constant along the tube , span, a velocity of 11.44 ft/s from 0-15 inches above the ' tubesheet, and modal displacements from Table 5.4-3. the
.l effective velocity is calculated to be 83.8 in/s.
l t Stability Ratio: S.R. = 83.8 / 292.5 = 0.29 I i i Tube Loading: 1 Substitutmg the following values into Equation 6 gives, ; i CSE-92-164 Nf;pWj 92 - R- 2 025 01 ~ t mot A . me 20 c; 4 l
CR-9417-CSE92-1102, REV. O Page 20 of 40 Fr = 0.0803 lblin Where: Cy = 0.45 (Reference 3.7) d = 0.696 in a = 0.0282 lb/in' Vm = 83.8 in/s g = 386 in/sec2 This loading of 0.0S0 lblin is inputted as a static load to the previously
, desenbed ANSYS model. Figure 5.4-5. The maximum stress is calculated to be less than .1 ksi at the tubesheet face. Since the healthy tube had a stress of 0.10 ksi at the tubesheet, a degradation factor of 2.60 is applied to this value. thus producing an estimated stress of 0.260 ksi for the degraded cases.
5.4.5 DIFFERENTIAL PRESSURE As discussed in Section 5.1.5, the differential pressure for MSLB will be conservatively assumed to be the difference between the primary side pressure remaining constant at a maximum of 2500 psia and the secondary side dropping to atmospheric pressure. O psia. The resulting pressure differential is:
.1P = t Pi - P,) = 2500 - 0 = 2500 psia The membrane stress intensity associated with this pressure differennal is calculated below. The coordinate system used is shown below:
a.-o.= ( P. - ?. ) R[ ( P. + P- ) Equa cion ? 2R, 2 Where: a, = tagential (circumferential) stress o, = longitudinal stress a, = radial stress e % R, R .,,
= inner radius (in)
= mean radius (in) /
/r
, G.y
(#; 1 t = average wall thickness (in) k .j
- P, P,
= pnmary side pressure (ksi)
= secondary side pressure (ksu, (p-CSE-92-164 M($J '92 - R 2 02 5 -01 r uu n A ,
PAGE 21cr4r
I i CR-9417-CSE92-1102, REV. O Page 21 of 40 } Healthy Tube: Dimensions: R, = 0.327, R, = 0.3750, and t = 0.048 inches { Substituting these dimensions into Equation 7 gives, ; i o, - o, = 0.18 ksi ' Degraded Outside: ! Dimensions: R, = 0.327, R, = 0.3455, and t = 0.0185 inches Substituting these dimensions into Equation 7 gives, ! o, - o, = 22.74 ksi ' Degraded inside: Dimensions: R, = 0.3565, R, = 0.375, and t = 0.0185 inches { Substituting these dimensions into Equation 7 gives, , o, - o, = 24.73 ksi t Since these stresses are calculated using code equations with actual plot specific data the actual stresses will be used, and the degradation factor will not be applied to the case of the healthy tube to estimate the stress for the degraded cases. 3 5.4.6 SAFE SHUTDOWN EARTHQUAKE (SSE) The model as described in Section 5.4.4 is utilized to apply a 1.5G Jateral,1.4G vertical static seismic loading to the steam generator tube. This loading is i applied in ANSYS as an acceleration and produces the stress at each nodal location. This loading was applied to all three tube cases, with the maximum stress at the tubesheet being 0.178 ksi and the overall maximum stress occurring , at the uppermost full eggerate and being 0.302 ksi. Both of these maximums are l from the case of degradation from the outside : The healthy tube had a stress of 0.177 ksi at the tubesheet. Applying the degradation factor to this value produces 0.460 ksi for the estimated stress of the degraded cases. t i I CSE-92-164 : MtNi '9 2 - R- 2 025 -01 . ! tma A PAGE 2Ecr41 ~ t
^
CR-9417-CSE92-1102, REV. O Page 22 of 40 5.4.7 COMBINED STRESSES ON TUBE WITH ASME CODE ALLOWABLES The resulting stress acting on the tube at the tubesheet interface is compared to the guidelines as specined in Appendix F of Section III. This Appendix F of the ASME Code dennes the allowable membrane stress allowable for the faulted ; conditions considered in this report asmS ., = 0.7 So. The ultimate strength for ' the SB-163 Inconel is Su = 80.0 ksi ar the maximum operating temperature of 600 F. Therefore, the allowable membrane stress in the steam generator tube is: ; S = 0.7 Su = 56.0 ksi
.The resulting stress intensities from the loadings of the previous sections are ;
combined arithmetically as follows: i Loading Healthy Degraded Degraded Condition Tube Outside inside ,
, Pipe Break Impulse Response (ksi) = 0.5 1.30 1.30 Flow induced Vibration (ksi) = 0.1 0.260 0.260 Maximum .1P During MSLB (ksi) = 9.18 22.74 24.73
, Safe Shutdown Earthquake (ksi) = 0.177 0.460 0.460 Total Stress Intensity = 9.96 24.76 26.75 i I Maximum S.I. = 26.75 < 56.0 ksi ! Therefore, c1.5% degradation of the steam generator tubes is allowable and ful611s both NRC and ASME requirements. 5.4.8 COMBINED STRESSES ON TUBE WITH " PROBABLE" TUBE MATERIAL PROPERTIES When the " probable" tube material properties for S, and S, are used in place of the ASME Code allowables mentioned earlier, a 65.8%, degradation can be considered for unlimited axial and circumferential extent of defect irrespective of 0.D. or 1.D. initiation. The Factor of Degradation = 1/(1.658) = 2.92. The minimurn required thickness is based on pressures and temperature at normal operating conditions. A. Dimens:ons of a healthy tube are R. = 0.327, R, = 0.3750. and t = 0.048 inches. 1 CSE-92-164 2;#;(j '9 2 - R- 2 02 5 -01 yma A , RAGE 23 cr 41
?
i i CR-9417-CSE92-1102, REV. 0 , Page 23 of 40 l l B. Tube Degradation From the Inside :t New dimensions: R, = 0.3586, R, = 0.3750, and t = 0.0164 inches ! i
- 1. Flawed tube not stressed beyond elastic limit using Equation {
l with S, = 35.2 ksi, t, = 0.0144 in. i
- 2. Flawed tube maintains a safety factor of 3 using Equation l
2 with S., = 90.0 ksi, t, = 0.0164 in. ! C. Tube Degraded From the Outside t New dimensions: R, = 0.327. R, = 0.3434, and t = 0.0164 inches !
- 1. Flawed tube not stressed beyond clastic limit using Equation ;
I with S7 = 35.2 ksi, t, = 0.0131 in. ;
- 2. Flawed tube maintains a safety factor of 3 using Equation i 2 with S, = 90.0 ksi, t, = 0.0150 in. <
i 5.4.8.1 LOCA Rarefaction Wave i As mentioned earlier there is no stress at this location of interest. J 5.4.8.2 Pipe Break Impulse Response Stress on degraded tube = 0.5 x 2.92 = 1.46 ksi. -
~
5.4.8.3 MSLB Secondary Side Blowdown I There is no significant primary loading at this location. 5.4.8.4 Flow Induced Vibration > Stress on degraded tube = 0.10 x 2.92 = 0.292 ksi. ; 5.4.8.5 Differential Pressure : f A. Degraded Outside: o - 0; = 25. 56 ksi Using Equation 7 l 1 1 i CSE-92-164 E#t;% 92 - R- 2 02 5 -01 ymen A n u g y er 4 i ~
I l CR-9417-CSE92 1102, REV. 0 l Page 24 of 40 ; i B. Degraded Inside: o g - o, = 27 . 97 ksi Using Equacion 7 l 5.4.8.6 Safe Shutdown Eanhquake (SSE) Stress on degraded tube = 0.177 x 2.92 = 0.517 ksi.
- 5.4.8.7 Summary of Stresses The resulting stress intensities from the previous loading are combined ;
arithmetically as follows: ' Loading Healthy Degraded Degraded ! Condition Tube Outside Inside l Pipe Break Impulse Response (ksi) = 0.5 1.46 1.46 Flow Induced Vibration (ksi) = 0.1 0.292 0.292 Maximum .1P During MSLB (ksi) = 9.18 25.56 27.97 Safe Shutdown Earthquake (ksi) = 0.177 0.517 0.517 , Total Stress Intensity = 9.96 27.83 30.24 , Maximum S.I. = 30.24 < 56.0 ksi f Therefore. 65.8% degradation of the steam generator tubes is allowable when the probable tube matenal propernes are used. t i I CSE-92-164 fi:pfMJ '9 2 - R- 2 025 -01 tmos A PAGE 26 CF 41 '
-t i
CR-9417-CSE92-1102, REV. O ! Page 25 of 40 t i a i t 1 1 i _ . _ _ e. , ..,_a...-,._. 1
.! I } } j
.w. e = ns . _ _ . . _~, ..,. _ ,. .. .
.,..ww 1
w
=
-w ,. , . , ,a.,
n...i
~ .. ..
- . 1 , - - i 7 l ' gT ' --rl<;-rlft Y
d ,{;{ b , ; x > ~ . _
,O f ;) ll f! fI E- ',
f fl fh / / l I/ W & !j"Gi lb \Y ,l \ ll kl '$ \ \b
\
v, =./ , i gen.p l
.c .
, 3 ,
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I I ll 4 - Irb.!!d$ Se %$ f !f$, kj$ 4- I.L b' 2/ y,ai , 5% '\ \\ ' ll ,l 4
, ll ,i
',l l !l, ,i $, ,i ! .
'*= . 4 a
%- _. + -]%' ._l, %! %_Md_M_Gi3Nl&!&!GN[..
a ,,,unc.--
. -= -
+
" $ ./. ag' .. ., Q, we ers,y/! wa ts%;E,* - ,
,Mr 2,i -
, Q - g z pr gu< . t_y t R< ur J 'r!
t- ' t-r ut '.%, n i
=
L.0, = ~ X,- Ly , a.l' a M., .e.E ls c.1 ..
-t aw : . - t
=== -=g i
> L'=mmmO. -
l 1 i i t Figure 5.4.1 l Location of Support Plates ! for ANO2 Steam Generator ! CSE-92-164 l I?d!W 92- R- 2025 01: ta t A PAGE 26 cr 4 1_ ;
I CR-9417-CSE92-1102, REV. O Page 26 of 40 >
""" Y ,
I y ,1 I.I
\
M ~. , I .
- et1 .
'T Tli:
e~i i i!i..a Li i
%, s , 0:0 _,_ /
. N .g. ,
,e //,I\-
3 mm 1 ,
.It "g 2 A_ .. A..s_! 6.A ---
Displacement )' t\d - l T Tube Relative to I N., ** M W Tubesheet lD/f .n - i
._i i
B ~
.m m a. m aiat o Location of 01splacements ff '
l
. K.
J wAmm I I ! i 1 - j - y[
.t t
f/\ . RigidG. S Shell : I ' 1 . 1 i - Displacement f2 , j
~
V 4 MEM l
'fl
,' b !f -
y .
.' qF '
t.:. -l
.p- T Tp -< rt, c- ,
, y .
e ('*. ?gh Is ' b i' a . I l
.t+
.au:st NQ *)
s lI g
}
em a x::-i . rewrimx=I
._[ j Q. l I
y I Bottom of Sliding Base ) Figure 5.4-2 Displacement of Steam Generator Tube cpi-92-164
$7%
92 R- 2025 01" g wa A ; PAGE 27cr41
5 CR-9417-CSE92-1102, REV. 0 l Page 27 of 40 O* 2- 3 _N !
's c- s s
- r N -
N_ ! 1 i
.. g i 2 3 ,. $ S~ f f 1
a "N ~~
~
l t! 1 i t 7 3 E b d d, 2 3 I h . . . . l Di2 placement (inches) Figure 5.4-3 i Applied Time History Displacements Due to LOCA Impulse Response CSE-92-164 Isl?tf,% '9 2 - R- 2025 -0 I r nen A .PAGE 2Bcs4If
CR-9417-CSE92-1102, REV. O Page 28 of 40 i l i 800.0 - ; 720.0 - 640.0 - P _ 560.0 -
; I 3 480.0 -
0 ' E 400.0 - E' 320.0 - 1
; \ n
) h
$ 2A0.0 -
\ f L i
160.0 - ( h1 80.0 j i
'1 g -{a\) .o
- i i i i i i i i 1 0 I .2200 l .0400 l .0600l .08001 1000
.01000 .0300 .0500 .0700 .0900 Tir.e (sec) l l
Figure 5.4.4 Resultant Time History Bending ; Stress at the Tubesiieet ! CSE-92-164
'idE!'$ s 2 - R- 2 025 0_1 Fm A i PAGE 29 c 41
1
?
i i CR-9417-CSE92-1102, REV. O Page 29 of 40 i
- > llo
> nm
) 91 :
t b 92 L
) M. l t
i
) 17
> n
; a i
) !.0 t
i
? 45 a'i !
/ / / / / / // 5 Figure 5.4-5 ,
ANSYS Model of ANO2 Steam Generator Tube 1 CSE-92-164 Is?fMElJ
- p 2 R 2 025 _01..l 2
l'51_0_.I* 30 fl41
i 1 CR-9417-CSE92-1102, REV. O Page 30 of 40 j i i I i I :
\ !
\
I ikr i i' k
- /
/ -
1
')
V N{
.N Figure 5.4-6 Mode Shape 9 for ANO2 Steam Generator Tube CSE-92-164 I Efl,jf,"; ~9 2 - R- 2 02 5 -O 1 t "T" A l PACE Si c; 41
I CR-9417-CSE92-1102, REV. O t Page 31 of 40 , i a ,._ HEALTHY TUBE l DEGRADED OUTSIDE 1 70.5 l 1 67.6 l i i 2 77.9 l 2 74.7 I 3 98.2 l 3 94.2 l 4 110.9 4 106.4 l I 5 113.6 l 5 126.2 ; { o 136.4 l 6 130.8 7 154.1 7 147.8 ' 8 186.3 8 178- : i 9 191.0 l 9 183.3 f f 10 234.6 10 225.1 , 1I 293.0 11 281.I ; { 12 381.2 l 12 366.0 t l 13 391.9 13 376.3 i i 14 504.7 14 484.7 i f 15 526.4 15 505.8 _ I 4 s t Table 5.4.-l , Eigenvector for Healthy and Degraded l ANO2 Steam Generator Tube i CSE-92-164 l [@#WR 9 2 - R- 2 02.5 -0]j J out* A lmE 32 c: 41 . ~ ,
i l 1 CR-9417-CSE92-1102, REV. O Page 32 of 40 ' 1 Heal:ny suce ! I mode =oce mode noce a .spt. noce g ;,,,i. node disp /. 5.0110 1 0.0000 41 S1 0.3220 ' 2 0.1998 42 3.4786 S2 0.4705 5 0.7189 43 2.1087 S3 0.5060 i 4 1.5213 44 0.9375 S4 0.4041 l 5 2.5717 45 0.0000 85 0.1756 5 3.8344 46 -1.1805 56 0.0000 5.2733 47 -0.3321 87 0.0855 3 6.8546 48 1.9417 88 0.2473 i 9 S.5441 49 5.0432 39 0.3297 l 10 10.3057 50 S.4260 90 0.2521 i
'1 - 12.1096 51 11.5491 91 0.0185 l '2 13.9242 52 13.9026 92 0.0000 3 15.7151 53 ;5.2720 93 0.2879 ,
14 17.4581 54 15.4738 94 0.5752 15 19.1260 55 14.3653 95 0.7306 16 20.6881 56 12.1952 96 0.6673 l 17 22.1271 57 9.2530 97 0.3516 ' 18 23.4223 58 5.8548 98 0.0000 19 24.5481 59 2.5713 99 -0.1653 20 25.4959 60 0.0000 100 -0.1279 21 26.2523 61 -1.2420 101 0.0124 ) 22 26.7988 62 2.4087 102 0.1453 23 27.1359 63 5.9409 103 0.1664 24 27.2557 64 5.5407 104 0.0000 25 27.1570 55 2.6731 105 -0.2922 t' 25 26.5403 56 0.0000 ;26 -0.5573 27 26.3125 57 -0.3940 107 -0.7039 2S 25.5727 iS 3.3394 108 -0.6635 29 24.6382 59 ' 9751 _. 109 -0.3956 ' 30 23.5219
'O 1. 268 110 0.0000 22.2314 31 ~; 0.7152 0.0000 32 20.7918 ~2 0.0000 33 19.2230 ~3 0.2177 34 17.5415 74 0.3153 -
35 15.7773 75 1.2;7s 36 13.9570 76 ;.0045 37 12.1041 77 0.4543 i 38 10.2522 73 0.0000 l 39 3.4322 79 -0.0535 l 40 6.6734 50 0.1037 l l i Table 5.4-2 Expanded Modal Displacements for Mode 9 1 on a Healthy Tube l l CSE-92-164 l E$i'N3 h 2 . R- 2 02.5 01 { _ _. s Pnm A lPAGE 33 CF4[
CR-9417-CSE92-1102, REV. O Page 33 of 40 1 2egraced Outside mode mode mode rode % /. node d::pl. node d s pt. 1 0.0000 41 7.6997 S1 0.4930 _ 2 0.3041 42 5.3442 22 0. "t 221 3 1.0997 43 3.2390 63 0.7777 4 2.3315 44 1.4396 34 0.6217 5 3.9450 45 0.0000 SS 0.2706 6
~
5.8854 46 -1.8224 SS 0.0000 S.0970 47 -0.5216 S7 0.1287 3 10.5280 48 2.9739 88 0.5770 9 13.1254 49 7.7445 89 0.5046 10 15.8342 50 12.9483 90 0.3869 11 18.6081 51 17.7527 91 0.0294 12 21.3985 52 21.3756 92 0.0000 13 24.1528 53 23.4835 93 0.4384 14 26.8334 54 23.7939 94 0.8770 15 29.3986 55 22.0914 95 1.1144 16 31.8013 56 18.7542 96 1.0178 17 34.0147 57 14.2280 97 0.5365 18 36.0067 58 9.0021 98 0.0000 19 37.7386 59 3.9528 99 -0.2530 20 39.1966 60 0.0000 100 -0.1965 21 40.3600 61 -1.9167 101 0.0176 22 41.2010 62 3.7006 102 0.2207 23 41.7198 63 9.1350 103 0.2536 24 41.9087 64 5.5235 _04 0.0000 25 41.'525 55 4.1120 105 -0.4457 26 41.2660 66 0.0000 .06 -0.8504 27 40.4544 57 -0.6079 '07
- -1.0743 28 39.3165 58 1.2902 108 -1.0126 29 37.379E 69 3.0376 109 -0.6039 30 36.1529 70 2.6567 _10 0.0000 31 24.1786 'l 1.1003 32 31.9647 ~2 0.0000
.~. d~ . .a.~c .. c. ,
- e..,,40 s
34 26.9663 74 1.2529 35 24.2535 75 1.8716 36 21.4542 76 1.5448 37 18.6050 77 0.6988 38 15.7575 78 0.0000 39 12.9592 79 -0.0833 40 10.2552 50 0.1576 Table 5.4-3 Expanded Modal Displacements for Mode 9 on a tube Degraded from the Outside CSE-92-164 idgi% 9 2 - R 2 0P_5 -01
4
- CR-9 417-CSE92-1102, REV. O j Pace 34 of 40 i
~ \ 5.5 NRC REGULATORY GUIDE 1.121 EVALUATION OF TUBE WITH AXIAL DEFECT OF 0.25 INCH hiAX. AND UNLlhilTED CIRCUh1FERENTIAL DEFECT I Section 5.4 serined that tubes with unlimited axial and circumferential extent of defects ! up to 65.8% of the wall thickness satisfy the Reference 3.1 safety factor against tube Milure for operational and accident loadings. f { i
- This section will show that the Regulatory Guide 1.121 margin against burst is satisfied i
{ for a 77% uniformely degraded tube with a limited (1/4" max.) axial defect. i J Figure 13 of Reference 3.18 presents burst pressure test data for various thinning ( defects. These tests were performed on 0.875" diameter x .050" wall tubing. !
- i. i The aforementioned Figure 13 indicates that a tube with a .25 long umform defect with
[ a wall thmmne of PO% can withstand a burst pressure up to 5100 psi. The ratio of wall thickness / diameter for the test specimen is: I ] 0.050
= .057
.87 5 !
c - i By companson the ratio for the ANO-2 tubes is,
.048
= .064 i 750 i r
It can be therefore ne concluded that at ANO-2 the burst pressure for a .25 inch long uniform defect with a 3-80% wall thinning will exceed 5100 psi. . . , The operationai .1P for ANO-2 is 1350 psi. (3)(1350) = 4050 e < !00 psi i : l The ANO-2 tubes are strucuonally adeauate to meet the Regulatory Guide 1.121 safety margin against burst with uniform (360*) defects that ar .25 inches !one and 77% decradation. 5.5.1 Differential Pressure The maximum pressure differential loading will occur dunng a postulated i SiSLB event. The membrane stress miensity associated with this pressure e different:al is calculated below: L l CSE-92-164 1 Vi% ;92 - R- 2 02 5 -01_. me A_ _ _ _ _ lm 35 s 41 l
*' " " =
l f CR-9417-CSE92-1102, REV. 0 - Page 35 of 40 l ( ?. - ?. ) Ei'
' ( ?. + ?. )
- a. - o = -
+
Equacion 7 2 Emc 2 Where: Pi = 2500 psia ! P, = 0 psia Ri = 0.327 in Rm = 0.3325 in t = .0110 in 4 Therefore; c . - o , = 3 7 . 8 ksi , l 5.5.2 LOCA Rarefaction Wave i The rarefaction wave produces no stress component at the secondary face of the tube sheet. This loading condition produces no stress component affecting tube burst. 5.5.3 Pipe Break Impulse Response It was determined in section 5.4.2 that a pipe break shock loading would I meur a maximum 0.5 ksi at the tubesheet elevation. This stress was for a i healthy inot degraded) tube and adjusting for a 77Pc degraded tube results in 2.2 ksi. i 0.5 ( ) = 2. 2 ksi 5.5.4 MSLB Secondary Side Blowdown ! 6 This loading condition will cause a drag load on the honzontal leg of the j tube bundle. The load produces an axial stress component only and hence i will have no inDuence on the tube burst. . 5.5.5 Safe Shutdown Earthquake (SSE) I, The dist2mee between the tubesheet and the Orst tube support is 28.125" l Calculating the weight of the tube and the duid inventory m this span , vields. 1 CSE-92-164 ! Mifs l92 - R 2 025 0_1-i meS A l PACE 36 C7 4 } l
CR-9417-CSE9 2-1102, REV. 0 l Page 36 of 40 l W = 1.15 lbJi ! Fsse = .l .5 x 1.15 = 1.7 lb. ' The resultant moment from this force is.
- .1 = 1. ? 8'1 5
= 23 . 9 in .lb 2 ,
The stress produced at the tubesheet elevation from this moment is in significant and hence can be neglected. 5.5.6 Flow induced Vibration ' t The minute flow forces will not produce significant stresses in the tubes at l the tubesheet elevation. l 5.5.7 Inside Flow inducement This loading only produces an axial stress component at the tubesheet elevation and therefore will have no influence on the tube burst. ! 5.5.8 Combined Stresses On Tube
~i The resulting stress intensities from the loadings of the previous sections are combined arithmetically as follows:
STRESS I LOADING CONDITION INTENSITY , Maximum AP During MSLB (ksi) l 37.8 ! L LOCA Raretaction (ksi) 0 , Pipe Break Impulse Response (ksi) 2.2 o MSLB Secondary Side Blowdown tksi) 0 Safe Shutdown Eanhquake (ksi) l 0 l i Flow induced Vibration (ksi) l 0 ; i ' i Inside Flow inducement (ksi) l 0 i Total Stress Intensity l 40.0 ksi Maximum S.I. = 40.0 ksi < 56.0 ksi j l Therefore. 77% tube wall thickness degradation will not be subject to burst l and its maximum stress intensity is below 56.0 ksi. ii.ff"% ,92- R- 2 025 0( tya A ; PAGE 3_7 c54.1 j cw-m _ , a
m . . CR-9417-CSE92-1102, REV. O Page 37 of 40 I 5.6 NRC REGULATORY GUIDE 1.121 EVALUATION OF TUBE WITH AXIAL j DEFECT OF 0.25 INCH MAX. AND ALLOWABLE CIRCUMFERENTIAL 100% ' THRU-WALL DEFECT I Figure 5.6-1 shows the type of defect that will be considered in this section. "F" t represents the total axial force pulling on the tube. i' Y p~w.cn m,om a
~
R = 0750 - 0.048
, .o+e m = g. = 0.351 in.
4& .750'
- 1 2 FOor c'
/tn+ L ' "* *
- t = 0.048 in
, R, = 0.327 in '
i For SB-163 (600) Inconel Tubing at 650*F
- t o'S'(~s} S, = 23.3 ksi I t - eo e o - - - -
Su = 80.0 ksi r'ecue/vr i S, = 27.9 ksi i Figure 5.6-1 ql 1 5.6.1 LOADINGS TO BE CONSIDERED FOR THE AXIAL FORCE 5.6.1.1 Differential Pressure during MSLB ; During a main steam line break, the differential pressure creates two types of axial loads on the tube. The first one is a drag load and the second, an internal piston load. The drag load will be discussed in ; Paragraph 5.6.1.4. The internal piston load occurs when the maximum pressure difference of 2500 psi is pushing on the I.D. of the tube. This load is:
= 2500 psi x (R,)2
= 2500 psi x x (.327)2
= 839.8 lbs.
. ;, ,s,J,l ;92 - R 2 025 01 5.6.1.2 LOCA Rarefaction Wave le (mE 3_B c; 41_
As mentioned earlier. the rarefaction wave produces no stress at the > location of interest in this analysis. Thus. the axial loading is zero. ) l c c. r. _ n , _. , e a j
l CR-9 417-CSE9 2-1102, REV. O ! Page 38 of 40 5.6.1.3 Pipe Break Impulse Response Since there is no Y - Displacement for the pipe break impulse response * (Reference 3.4), the axial loading is zero. , 5.6.1.4 MSLB Secondary Side Blowdown Reference 3.3 determined that this type of pressure differential due to r secondary side blowdown resulted in a total drag load of 113, 290 lbs. I across the cross flow region of the tube bundle. Since there are 8411 , tubes in the steam generator, the drag load / tube is 113,290 lbs/8411 : tubes or 13.5 lbs. ! 5.6.1.5 Safe Shutdown Earthquake (SSE) I i j Using the 1.4 G vertical applied static loading (Reference 3.12) results in the fol!owing equation for the SSE contribution to the total axial load. 1 F = 1.4 y W (Weight of tube) 3 i 1 Where: W = (Density of Primary Fluid) x (Volume of Fluid) + (Density of Tube) x (Volume of Tube) l t Substituting: l 2 W = (0.0260 x r/4 x 0.654 x 326.7) + ' (0.305 x r/4 x ((0.75)2 - (0.654)2) x 326.7) , i 4
= 2.85 + 10.55 -
~
i i i
= 13.4 lbs. i Therefore. F = 1.4 x 13.4 = 18.8 lbs.
3 i i 5.6.1.6 Flow Induced Vibration t Since the Dow forces do not produce a signi0 cant loading at the ; tubesheet interface, the axial loading is zero. 4 5.6.1.7 Inside Flow Inducement The axial loading due to inside flow inducement is dependent upon the j Guid velocity and the pressure drop through one third of the total tube l
.,a bend length. The equauon for this type of loading isp"vPE ~92 -&R-NO 2025 -( !
t imot A .mE 39 cr4_1 $ i ra c= r* _ rs e 1 C A i
CR-9417-CSE92-1102, REV. O Page 39 of 40 i F, = PA Y + AP x 2 (Ri) : 2 h Where : 1 F7 = force due to inside flow inducement, Ibf ; p = Density of fluid = 44.928 lb/ft 1 A = Cross flow area = 0 336 in l V = Fluid velocity, it/sec ,
= (Primary Flow Rate / Tube)/ pA
= (60.2 x 106 lb/hr/ 8411 tubes)/ pA i g = gravity = 32.2 ft/sec l
.1P = Pressure drop through one third of total tube bend length l
= 36 psi /3 (Page A-1014 of Reference 3.13) !
R = 0.327 in ! I i Substituting: ) [ 6 0. 2 x 10* g 1 32 j 841 600 F = pA 36
+ 12 x (.327)2 l 32.2 pA x 44.928 x . ;
144 i r t
= 1.2 + 4.0 :
= 5.2 lbs :
1 Therefore, the total axial force is . ' F = 839.8 + 0 + 0 a 13.5 + 18.8 + 0 + 5.2 i
= 877.3 lbs !
i 5.6.2 STRESS DUE AXIAL LOADING l The equation for calculating the stress due to the axial loading is: ! a=F/2rRt l Where: a = Stress, psi F = Total Axial Load, 877.3 lbs I R = Mean Radius of healthy tube,0.351 in l
- t = tube wall thickness. 0.048 in Effy"% '9 2 - R 202 5 0_ Ig jmia A ;PAGE 40 c 4i
{ 1 n -
CR-9417-CSE92-1102, REV. O ! Page 40 of 40 Substituting: o 877.3 / 2r x 0.351 x 0.048 ! o = 8287.4 psi < l.0 S or 23,300 ps.i, the allowable value of the i General Primary Membrane Stress Intensity (NB-3221.1 of reference i 3.5) for the average stress across the solid section excluding , discontinuities and concentrations. ; 5.6.3 ALLOWABLE CIRCUMFERENTIAL 100% THRU-WALL DEFECT For a solid section which considers discontinuities, the allowable value for the . local membrane stress intensity (NB-3221.2 of Reference 3.5) is 1.5 S or 34,950 psi. The NRC Regulatory Guide 1.121 (Reference 3.1) refers to NB-3225 of Reference 3.5 for Level D Service Limits which also refers to i Appendix F of Reference 3.5. Paragraph F-1331.l(b) of Appendix F supports l the 1.5 S, value for the localized membrane stress intensity of the case in Figure 5.6-1. l 1 ! om = 1. 5 S 3 = 2xRt ( 360 - ) 360 } Where: ! e = Circumferential extent of thru-wall defect a i a 1 Substituting, I i 34,950 = 3 *
~
2n x . 3 51 x . 04 8 (360 - s60) < l l
+ = 274*
l Therefore. the maximum circumferential extent of 100% thru-wall defect is
, 274*
Ififl(T [92 R- 2 025 01 4 Pno'- A IPm 4/ cW[
MPR ASSOCIATES, INC. August 26,1992
?
Evaluation of Arkansas Nuclear One Unit 2 Steam Generator Tube Wall Degradation t Prepared for { Entergy Operativ. 3 Arkansas Nuclear One Unit 2 Russellville, Arkansas 72801
!s it!M 92 R- 2.025 -0 l' pmen B PME l OF 4 l'
MPR ASSOCIATES. INC. CONTENTS Section Page 1 INTRODUCTION 1-1 Background 1-1 Purpose 1-2 - 2 SUMhiARY 2-1 3 DISCUSSION 3-1 NRC Regulatory Guide 1.121 Requirements 3-1 ABB Combustion Engineering Evaluations 3-5 i , MPR Structural Evaluations 3-7 Allowable Tube Wall Degradation 3-8 4 REFERENCES 4-1 APPENDIX A MPR Calculation 62-81-HWM-1," Acceptable Tube Wall Thinning for 0.25 in. Axial Length. 360 Circumferential : Degradation" > APPENDIX B MPR Calculation 62-81-HWM-3," Allowable Tube Wall Degradation for Axial, Slot-type Defects" ii hit;W '9 2 - R- 2 025 -01 prrn B PAGE
- 2. CF 4 ]
MPR AESCCIATES. INC-i Section 1 ; INTRODUCTION [ r BACKGROUND NRC Regulatory Guide 1.121 (Reference 1) desenbes a method for determining , allowable limits for degradation of steam generator tubing. Tubes with degradation , beyond these limits are required to be removed from service by the installation of plugs , at each end of the tube (or modified to be acceptable for further service by the
~
installation of suitable sleeves which meet Regulatory Guide 1.121 requirements). As part of the technical justification for continued safe operation, structural adequacy of the tubing can be demonstrated by showing that tube degradation will not exceed Regulatory Guide 1.121 allowables at any time during plant operation. This report calculates maximum allowable degradation. Suitable NDT (sensitivity and frequency), conservative plugging / sleeving criteria and operating experience of Arkansas Nuclear One ! Unit 2 (ANO-2) and other similar plants can then be used to ensure tube degradation will not exceed the allowable degradation determined herein. r i To further ensure tubing structural adequacy during plant operating periods between j NDT inspections, an administrative limit is imposed at ANO-2 requiring shutdown for a i leak rate of 0.1 gpm per steam generator. . For ANO-2, this leak rate limit is estimated to provide reasonable assurance of tubing structural adequacy as well as being practical, e.g., in terms of detectability. ANO-2 experience and other work supports this. In Reference 2, ABB Combustion Engineering (ABB CE) performed an evaluation of certain types of tube wall degradation recently found in the ANO-2 steam generators. ! The ABB CE report considered three bounding configurations of possible degradation as l' follows-
. Unlimited axial and circumferential extent and partially through-wall. ,
- Axial length of 0.25 in. maximum, unlimited circumferential extent and panially j through-wall. )
- Axial length of 0.25 in. maximum, essentially through-wall and limited j circumferential extent. l 44tf('S '9 2 - R- 2 025 -01
- ca 1-1 W
rW 8 FAGE 3 CF 4 }
These evaluations utilized what ABB CE considered to be the limiting requirements of , Regulatory Guide 1.121 which pertain to the structural integrity of the tubing for normal l operaung and accident conditions. ! PURPOSE The purpose of this report is to address all of the structural requirements in Regulatory Guide 1.121, utilizing the ABB CE evaluations of Reference 2, as applicable, and additional MPR structural evaluations as needed based on our review of Reference 2. These additional evaluations included consideration of axial, slot-type defects (axial cracks). Consistent with NDT findings and expectations for ANO-2 this report is limited (except as discussed herein) to tube degradation either within or close to , a +ube support or at the top of the tube sheet. i i h { i i i i i i i i i r Y47%S 92 - R 2 025 -0); ' 1-2 pno B MGE 4 c5 41_
MPR Assoc:ATEs.INC. Section 2
SUMMARY
l The evaluations in this report address the structural requirements of NRC Regulatory ! Guide 1.121 for certain types of degradation in the Arkansas Nuclear One Unit 2 steam l generator tubing. The evaluations are based on the structural analyses performed by l ABB Combustion Engineering and additional MPR structural evaluations and , calculations. The tubing degradation considered is either within or close to a tube support or at the top of the tube sheet. Slightly reduced values would be calculated for _l allowable tube wall degradation for non-axisymmetric degradation configurations at other t locations due to tube bending stresses resulting from less lateral support of the tube, ; e.g., in areas between supports. For tubing degradation configurations which are r axisyrnmetric and therefore do not result in tube bending stresses, the degradation allowables in this report are also applicable at areas away from tube suppons (as well as at supports). The maximum allowable tube wall degradation determined herein is summarized in Tables 2-1 and 2-2. For the intended purpose of determining the maximum allowable l tube degradation per Regulatory Guide 1.121, we consider use of the " probable tubing ! material properties", as appropriate, rather than ASME Code minimums. Further, if ! desired, Entergy could possibly obtain as-built materials properties which we believe would allow even greater degradation than indicated herein for " probable" material properties. Accordingly, we consider the maximum allowable degradation as shown in Table 2-1 to be appropriate and conservative. Notably, the values for maximum allowable degradation calculated herein are somewhat i different from the values calculated in Reference 2 by ABB CE. The main causes of j these differences are discussed later in this report. Other differences are in the details of i the calculations, also presented later in this report. For convenience, Table 2-3 shows a l comparison of the ABB CE and MPR calculated values for the case of a .25 in. l maximum axial,360* circumferential, part through-wall tube degraded area. Also shown l is the value from public documents (Reference 3) for Millstone 2 (which has the same tubing size as ANO-2). As indicated, the values in Table 2-3 are similar as they should be. Notably a lower value (59Fe) has been published for Maine Yankee (Reference 4); however, this is not applicable since this (lower) value was based on a defect of unlimited axial extent along with some other minor differences in calculations. Accordingly, we conclude the value of 79Fc as computed herein is appropriate for ANO-2. 2-1 1 Mff% '9 2 - R 2 02.5 -01 r et B noE f c5 41 ; , i
Table 2-1 Allowable Steam Generator Tube Wall Degradation for Various Degradation Types (For Probable Tubing Material Properties)I Tvpe of Degradation 2 Allowable Tube Wall Degradation Unlimited axial and circumferential 66Fc maximum extent 0.25 in. maximum axial length, 79Fc averace around cie tube 360" circumferential circumference 3 Axial slot-type defect 4 - Less than 0.25 in. long 100rc - 0.25 - 0.50 in. long S49 5 5 - 0.50 - 1.5 in. long 73Fc - Longer than 1.5 in. 66Fc I Mill test certificates with actual properties were not available for use at this time, otherwise, actual materials properties would have been used. 2 Any of the types of degradation indicated herein can be considered applicable to either a support location or a location at the top of the tubesheet. If the degradation is symmetric about the tubing axis, the specified degradation allowable is also applicable at locations away from support locations. 3 As an example, this 79Fc averace value equates to an accumulated total of 234 of 1007c deep defect penetration together with the remainder at 40Cc deep. As discussed later in this report, burst test data for actual defect configurations confirm that the accumulated average penetration is the controlling parameter for these defects at ANO-2. Burst pressure data is available for tube wall degradation to 84Fc. Extrapolation of this data indicates that the allowable slot depth would be 1009 (i.e.. essentially through-wall). These values actually apply for the maximum of the slot defect lengths indicated. Other values can be obtained from Figure 1 if desired. ,y - 7 '
- . . s .n 9 2 - R- 2 025 g,n 8 ;4st 6 cs g
^ Table 2-2 Allowa'le u Steam Generator Tube Walt Degradation for ' i Various Degradation Types (For ADfE Code 51inimum Tubing 3faterial Properties) 4 Type of Degradation 1 Allowable Tube Wall Degradation
^
Unlimited axial ano circumferential 62Fc maximum ; extent 0.25 in. maximum asial length, 76Fc average around the tube : 360* circumferential circumference l Axial slot-type defect l 2 j
- Less than 0.25 it.. long 100Fc
- 0.25 - 0.50 in. long 77 % l
- 0.50 - 1.5 in. loar 67Fc !
1 t j - Longer than 1.5 5n. 62Fc l 4, 1 1 i ! i I l . i 1 Any of the types of degradation indicated herein can be considered applicable to l either a support location or a location at the top of the tubesheet. If the degradation is syrnmetric about the tubing axis, tl,e specified degradation i allowable is also applicable at locations away from suppon locations. 1 1 3 , - Burst pressure data is available for tube wall degradation of 84Fc. Extrapolation of this data indicates that the allowable slot depth would be 100Fc (i.e., essentially through-wall). E:5Nd '9 2 - R- 2 02 5 -01 t ma B PAGE ~/ CF 41
i Table 2-3 i Average Percent Through Wall Defect Penetration Allowable per Regulatory Guide 1.121 for Degradation of Tube at Top of Tube sheet l For ANO-2 For Millstone-2 - ABB-CE MPR Per Reference 3 6 77 79 79 : i f t i I i ks/NJ 92 - R 2025 -0}l l pnen B mE B c5 41 R i I
^
100 1 90 , c S e . E E 80 C =
~
$_5 O e 70 3 m i i i l i 1 60 0 i i i i . 0.0 0.25 0.50 0.75 1.00 1.25 1.50 Arial Length of Defect (Inches) l ALLOWABLE TUBE WALL DEGRADATION l FOR AXIAL SLOT TYPE DEFECTS ( AXIAL CRACKS) FIGURE 1 l l l l E?dnM 9 2 R- 2 02 5.-01 rma e ms 9 o 43 =; .
MPR AS$CCIATES. INC. Section 3 DISCUSSION NRC REGU1ATORY GUIDE 1.121 REQUIREMENTS Regulatory Guide 1.121 provides requirements for evaluating the allowable wall degradation of steam generator tubing, beyond which the defective tubing must be removed from service. As stated, the Regulatory Guide requires the consideration of three factors: (1) the wall thickness required to sustain the imposed loadings under , normal and accident conditions; (2) an allowance for further degradation during operation until the next inservice inspection; and (3) the crack size permitted to meet the primary-to-secondary leakage limit allowed by the plant's technical specifications. Section C of Regulatory Guide 1.121 provides the speci5c structural requirements which ' must be satisfied for degraded steam generator tubing for normal operation and accident conditions. Most of these requirements can be bound by a reduced set of requirements at the end of this section; and, others are shown to be not pertinent as follows: For normal operation, the requirements from NRC Regulatory Guide 1.121 are: From C.2., " Minimum Acceptable Wall Thickness,"
* ' Tubes with detected part through-wall cracks should not be stressed during ;
the full range of normal reactor operation beyond the elastic range of the i tube material" (C.2.a.(1)).
* " Tubes with part through-wall cracks, wastage, or combinations of these should have a factor of safety against failure by bursting under normal i operating conditions of not less than three at any tube location" (C.2.a(2)).
* "The margin of safety against tube rupture under normal operating conditions should be not less than three at any tube location where defects have been detected" (C.2.a(4)).
* "Any increase in the primary-to-secondary leakage rate should be gradual !
to provide time for corrective action to be taken" (C.2.a(5)). 3-1 hsiNd 9 2 - R- 2 025 -01 F" B ;PAGE 10 CF 4
L Experience at ANO-2 and at other similar plants has demonstrated this requirement to be met; accordingly, this requirement is not included in the . reduced set of requirements at the end of this section.
. "An additional thickness degradation allowance should be added to the minimum acceptable tube wall thickness to establish the operational tube thickness acceptable for continued senice. An imperfection that reduces the remaining tube wall thickness to less than the sum of the minimum acceptable wall thickness plus the operational degradation allowance is designated as an unacceptable defect. A tube containing this imperfection ,
has exceeded the tube wall thickness limit for continued senice and should i be plugged before operation of the steam generator is resumed" (C.2.b). This requirement is addressed by the current practice at ANO-2 of sufficient NDT examinations and sleeving or plugging (and stabilizing) for any actual indicated degradation (irrespective of tube wall penetration) for tube locations where experience (at ANO-2 and others) indicates sufficiently rapid degradation should be expected. Also, experience (at ANO-2 and others) is used to ensure degradation between NDT i examinations will not exceed structural allowables. From C.3, " Analytical and Loading Criteria Applicable to Tubes with either Part Thru-wall or Thru-wall Cracks and Wastage," e "I.oadings associated with normal plant conditions, including start up, operation in power range, hot standby, and cooldown, as well as all , anticipated transients (e.g., loss of electricalload, loss of offsite power) that : are included in the design specifications for the plant, should not produce a ' primary membrane stress in exr:ss of the yield stress of the tube material . at operating temperature" (C.3.a.(1)). i ' e "The margin between the maximum internal pressure to be contained by the tubes during normal plant conditions and the pressure that would be required to burst the tubes should remain consistent with the margin incorporated in the design rules of Section III of the ASME Code" ! (C.3.a.(2)). :
. "The fatigue effects of cyclic loading forces should be considered in determining the minimum tube wall thickness. The transients considered in the original design of the steam generator tubes should be included in the fatigue analysis of degraded tubes corresponding to the minimum tube wall thickness established. The magnitude and frequency of the temperature and pressure transients should be based on the estimated number of cycles anticipated during normal operation for the maximum service interval 3-2 E.4Nb [9 2 - R- 2 02.5 -01 pne B lPAGE )j CF 41 j i
I
expected between tube inspection periods. Notch effects resulting from , tube thinning should be taken into account in the fatigue evaluation" l l . (C.3.b(2)). t
- This requirement is addressed by the current practice at ANO-2 of l sufficient NDT examinations and sleeving or plugging (and stabilizing) for
- any actual indicated degradation (irrespective of tube wall penetration) for i tube locations where experience (at ANO-2 and others) indicates l sufficiently rapid degradation should be expected. Also, experience (at
ANO-2 and others) is used to ensure degradation due to fatigue between NDT examinations will not exceed structural allowables. j . 'The maximum permissible length of the largest single crack should be such ; that the internal pressure required to cause crack propagation and tube ! rupture is at least three times greater than the normal operating pressure. l The length and geometry of the largest permissible crack size should be ! determined analytically either by tests or by refined finite element or l fracture mechanics techniques. The material stress-strain characteristics at i temperature, fracture toughness, stress intensity factors, and material flow properties should be considered in making this determination" (C.3.d(1)). , . . 'The primary to-secondary leakage rate limit under normal operating ! pressure is set forth in the plant technical specifications and should be less l l than the leakage rate determined theoretically or experimentally from the largest single permissible longitudinal crack. This would ensure orderly -
- plant shutdown and allow sufficient time for remedial action if the crack size increases beyond the permissible limits during senice" (C.3.d(3)).
~
This requirement is addressed by an administrative limit requiring shutdown for a leak rate of 0.1 gpm per steam generator. For ANO-2, this leak rate i 3 limit is estimated to provide reasonable assurance of tubing structural , adequacy as well as being practical, e.g., in terms of detectability. ANO-2 j experience and other work supports this. !
- . " Conservative analytical models should be used to establish the muumum ,
acceptable tube wall thickness generally applicable to those areas of tube length where tube degradation is most likely to occur in service due to cracking, wastage, intergranular attack, and the mechanisms of fatigue, vibration, and flow-induced loadings. The wall thickness should be such that sufficient tube wall will remain to meet the design limits specified by Section III of the ASME Boiler and Pressure Vessel Code for Class 1
- components, as well as the following criteria and loading conditions" (C.3.a.).
j 3-3
- M ,92 - R 2 025 01 7
% B [ pace /2, er 41 "
^ l
r This requirement is interpreted as being covered by other requirements in Regulatory Guide 1.121 as discussed herein. The only conflict is per ! requirement C.3.a(1) which limits to yield stress versus a lower limit per , Section III of the ASME Code. In this case we consider the stated Regulatory Guide limit per C.3.a.(1) of yield stress to be appropriate and note that others have done the same. For accident conditions, the requirements from NRC Regulatory Guide 1.121 are: From C.2. " Minimum Acceptable Wall Thickness," e "If through-wall cracks with a specified leakage limit occur either on a tube - wall with normal thickness or in regions previously thinned by wastage, they should not propagate and result in tube rupture under postulated accident conditions" (C.2.a(3)).
. "He margin of safety against tube failure under postulated accidents, such as a LOCA steam line break, or feedwater line break concurrent with the SSE, should be consistent with the margin of safety determined by the stress limits specified in NB-3225 of Section III of the ASME Boiler and i
~
Pressure Vessel Code" (C.2.a(6)). i From C. 3, " Analytical loading criteria applicable to tubes with either part through-wall or through-wall cracks and wastage,"
. " Loadings associated with a LOCA or a steam line break, either inside or '
outside the containment and concurrent with the SSE, should be ; accommodated with the margin determined by the stress limits specified in i NB-3225 of Section III of the ASME Code and by the ultimate tube burst strength determined experimentally at the operating temperature" (C.3.a.(3)). l
* 'The stress calculations of the thinned tubes should consider all the stresses and tube deformations imposed on the tube bundle during the most adverse loadings of the postulated accident conditions. The dynamic loads j should be obtained from the modal analysis of the steam generator and its }
support structure. All major hydrodynamic and flow-induced forces should i be considered in this analysis" (C.3.b.(1)). I i t i 3-4 U$ '792 - R- 2 025 -01 ~ { cwt B Jn 13 c5 41?
i
. 'The combination of loading conditions for the postulated accident !
conditions should include, but not be limited to, the following sources .
- Impulse loads due to rarefaction waves during blowdown, l
- Loads due to fluid friction from mass fluid accelerations,
- Loads due to the centrifugal force on U-bend and other bend regions caused by high velocity fluid motion,
- Seismic loads, i
Transient pressure load differentials" (C.3.c).
. " Adequate margin should be provided between the loadings associated with a large steam line break or a LOCA concurrent with an SSE and the loading required to initiate propagation of the largest permissible longitudinal crack resulting in tube rupture. The loadings associated with the postulated accident conditions should include the transient hydraulic '
and dynamic loads listed in C.3.c." (C.3.d.(2)). l The pertinent NRC Regulatory Guide 1.121 tube structural requirements as stated above i can be reduced to the following set of requirements: ! For Normal Operation:
. The tube stress intensity should be less than the tube material yield stress.
e The tube burst pressure should be greater than three times the pressure ! difference across the tube wall. i For Accident Conditions:
. The tube stress intensity should be less than the lesser of 2.4 times the
- design stress intensity (Sm ) or 0.7 times the ultimate stress.
- The tube burst stress should be greater than the pressure difference across I the tube wall.
ABB COMBUSTION ENGINEERING EVALUATIONS In Reference 2, ABB Combustion Engineering performed an evaluation of ANO Unit 2 steam generator tubing structural adequacy for degradation in the expansion transition 3-5 se 1 9 2 - R 2 025 -01 pnet B jms /4c;41]
i region (at the top of the tube sheet). For each type of degradation the ABB CE evaluations considerec$ the requirements of NRC Regulatory Guide 1.121 and determined ; the allowable tube wall degradatian. Based on our review of this work, we have the 4 following comments: , d
. The tubing degradation in the expansion transition region is in close proximity to the tube sheet. As a result of the constraint to tubing lateral displacement due to the close clearance between the tubing outside ,
diameter and the tube sheet bore, and as a result of lateral support of the tube from the_ adjacent tube support grid, the axialload on the tube for accident conditions does not result in primary bending stresses in the tubing even for a non-uniform degradation profile around the tubing ; circumference. As a result, the average cross-sectional area of the degraded area of the tube determines its axialload capability. This is based on the results of tube burst tests with typical degradation profiles . which are reported in References 4 and 6. !
. The pressure difference calculations across the tube for the case of a steam !
line break do not include stress amplification due to rapid depressurization i of the steam line. We consider this appropriate based on previous MPR i calculations which demonstrate that the pressure around the tubes inside the steam generator does not fall rapidly (relative to the appropriate , natural frequency of the tubes) and no amplification of tube stress will ; occur. In essence, even though the pressure will fall rapidly within the steam line, it does not fall rapidly within the steam generator -- because the resulting boiling of the water tends to hold the pressure up inside the steam generator (as in a pressurizer).
- . The ABB CE evaluations considered degradation which originated either from the tubing outside diameter or inside diameter. In all cases, the required tubing remaining wall thickness is greater for the degradation which originates from the tubing inside diameter.
. The ABB CE evaluations considered both ASME Section III minimum l tubing properties (yield and ultimate stress) as well as " probable" material properties. We consider this appropriate as discussed herein.
. The ABB CE evaluations for 0.25 in. axial-length, through-wall, partial-circumference defects are not applicable if the defects are actually .25 in.
long for their full penetration (up to 100%) extent, since premature failure would occur within the essentially 100% through-wall portion of the .25 in. long defect due to circumferential stresses from internal pressure. 3-6 kN {92 - R- 2 025 01 gm B iPAGE ff CQ l
However, this would not be the case for a circumferential slot-type o defect (due to support of the defected portion of the tube from non-defected adjacent areas). Accordingly, these evaluations are applicable to circumferential slot-type defects (circumferential cracks) with essentially no axial extent. This ABB CE analysis may be applicable for actual defect areas .25 in. long in the steam generator (e.g., with ligaments between cracks); however, burst tests would be needed to demonstrate this. Notably, the circumferential defects found thus far at ANO-2 are not of the type which need to be covered by the ABB CE analysis mentioned above (.25 in. long,100Fc through-wall, partial circumference). Instead, all circumferential defects found thus far at ANO-2 can be covered by the case analyzed herein for .25 in. maximum axial length,360* circumferential extent with average penetration of 79?o per Table 2-1. Accordingly, there is no need to use the above mentioned part of the ABB CE analysis (which otherwise requires either limiting to a slot-type defect or tube burst tests).
. For the case of interest for circumferential defects (.25 in. maximum axial extent, 360, partial through-wall, i.e., 79Fo average per Table 2-1), local areas around the defected portion of the tube may be degraded greater than the 79Fc average value. This is acceptable based on burst tests fmm tube pulls with similar defects at another plant (Reference 6). These tests show ' hat the average (and not maximum) penetration is the pertinent parameter to establish structural adequacy; and, in any event, even in the worst-case, only a tube leak would result if a local area of a defect goes through wall. Accordingly, the 79Fo average defect case is considered the controlling case for circumferential defects at ANO-2.
i MPR STRUCTURAL EVALUATIONS MPR performed additional tubing stress analyses based on the tubing loads determined by ABB CE in order to adjust certain ABB CE evaluation results based on our interpretation of Regulatory Guide 1.121 requirements. (See Appendices A and B of this report.) The following should be noted:
- The ABB CE evaluations for 0.25 in. long 360* circumferential degradation utilized burst test data to determine the allowable degradation. This burst j test data was obtained for simulated degradation originating from the tube outside diameter. In addition, the measured burst pressure for the tested 77 percent defect was significantly greater than the required pressure of 4050 psi. The MPR evaluations in Appendix A estimate the permitted wall ;
degradation from the inside diameter which would provide a margin of three to burst based on the tubing wall differential pressure during normal , 3-7 hN ;9 2 R- 2 025 0_ I.
& B tm 16 c 41
_ _ . . - ..e i I plant operation. The calculations consider code minimum and probable tubing material properties. :
. Evaluations are provided in Appendix B for axial, slot-type defects of l lengths 0.25 in.,0.50 in. and 1.5 in. These evaluations used burst-test data i from Reference 5. The calculations consider code minimum and probable tubing material properties. ;
ALLOWABLE TUBE WALL DEGRADATION Based on the ABB CE and MPR evaluations, the allowable tube wall degradation for f various types of degradation of the ANO Unit 2 steam generator tubing was determined. The results of the evaluations in Table 3-1 and Table 3-2 show the permitted degradation , extent for the types of degradation which were addressed. , i i 3-8
.ir#7% '9 2 - R - 2 025 -0_1
; mn B PAGE f"/ C1 41 .
Table 3-1 1 Allowable Steam Generator Tube Walt Degradation l For Various Degradation Types (For Probable Material Properties)1 Type of Ilmiting Regulatory Allowable Tube Wall Degradation, - Guide 1.121 Structural Degradation Requirement Unlimited axial and Burst pressure should be 66% maximum circumferential extent greater than 3x(pm-pm) 0.25 in. axial length, 360* Burst pressure s'aould be 79Fo average around the tube circumferential greater than 3x(pm-py circumference Axial slot-type defect Burst pressure .thculd be
. Less than 0.25 in. long 100Fo 3 - 0.2.5 - 0.50 in. long 84 % - 0.50 - 1.5 in. long 73 % - 12mger than 1.5 in. 66 %
1 Mill test certificates with actual properties were not available for use at this time, otherwise, actual materials properties would have been used. 2 Any of the types of degradation indicated herein can be considered applicable to either a support location or a location at the top of the tubesheet. If the degradation is symmetrie about the tubing axis, the specified degradation allowable is also applicable at locations away from support locations. 3 Burst pressure data is available for tube wall degradation to 84%. Extrapolation of this data indicates that allowable slot depth would be 100% (i.e., essentially through wall). M ~~ ? 2 - R 2 025 -01 mot B Nor 16 or 4 I' 5
Table 3-2 Allowable Steam Generator Tube Wall Degradation For Various Degradation Types (For ASME Code Minimum Tubing Material Properties) l Type of Limiting Regulatory Allowable Tube Wall Degradation 1 Guide 1.121 Structural Degradation Requirement r Unlimited axial and Burst pressure should be 62Cc maximum circumferential extent greater than 3x(p7a pm) 0.25 in. axial length, 360* Burst pressure should be 76Fe average around the tube circumferential greater than 3x(pra-Psy circumference Axial slot-type defect Burst pressure should be greater than 3x(p73 psy
- Less than 0.25 in. long 100Fe2
- 0.25 - 0.50 in long 77Fe
- 0.50 - 1.5 in.long 679c
- Longer than 1.5 in. 627c I
Any of the types of degradation indicated herein can be considered applicable to either a support location or a location at the top of the tubesheet. If the degradation is syrnmetric about the tubing axis, the specified degradation allowable is also applicable at locations away from support locations. Burst pressure data is available for tube wall degradation to 847c. 15trapolation of this data indicates that the allowable slot depth would be.lMTc_.fi.e... essentially through-wall). 7 ss. 9 2 - R 2 0? 5 01,
! L'E B lmE 19 c 41
MPR ASSOCIATES. INC. Section 4 i REFERENCES i f
- 1. US Nuclear Regulatory Commission Regulatory Guide 1.121," Bases for Plugging Degraded PWR Steam Generator Tubes," August 1976.
- 2. ABB Combustion Engineering NCS Engineering Calculation Report CR-9417-CSE 92-1102, Rev. O, " Evaluation of Circumferential Defects at the Expansion Transition in Arkansas Nuclear One-Unit 2 Steam Generator Tubes."
April 23,1992. l
- 3. US Nuclear Regulatory Commission Docket No. 50-336, " Summary of hieeting with Representatives of Northeast Utilities Concerning the Assessment of the Steam Generators at hiillstone 2, August 28, 1991," September 23,1991.
- 4. Niaine Yankee letter from S. E. Nichols, hianager Nuclear Engineering &
Licensing, to Document Control Desk, US Nuclear Regulatory Commission dated June 20,1991, "hiaine Yankee Steam Generator Tube Evaluation . (RG 1.121 Report)". 4
- 5. PNL-2684 (NUREG/CR-0277), " Steam Generator Tube Integrity Program - ;
Annual Progress Report for January 1 - December 31,1977," Battelle Pacific Northwest Laboratory, August 1978.
- 6. US Nuclear Regulatory Commission Docket No. 50-336, " Summary of hieeting ,
with Representatives of Northeast Utilities Concerning the Assessment of the ; Steam Generators at hiillstone 2, February 22,1990," hiarch 22,1990; and Summary of hiceting with Representatives of Northeast Utilities Concerning the Assessment of the Steam Generators at hiillstone 2, August 28,1991, : September 23,1991. ! i 4-1 i _f..;
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- APPENDIX B MPR Calculation 62-81-HWM-3, " Allowable Tube Wall Degradation for Axial, Slot-type Defects" .
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