ML20151P175

Rev 0 to SIR-98-067, Evaluation of NMP Unit 2 Feedwater Nozzle-to-Safe End Weld Butter Indication (Weld 2RPV-KB20, N4D)

ML20151P175
Person / Time
Site:	Nine Mile Point
Issue date:	06/16/1998
From:	Giannuzzi A, Gordon B, Marisa Herrera STRUCTURAL INTEGRITY ASSOCIATES, INC.
To:
Shared Package
ML20151P172	List: ML20151P169 ML20151P175
References
SIR-98-067, SIR-98-067-R00, SIR-98-67, SIR-98-67-R, NUDOCS 9806230285
Download: ML20151P175 (24)

Text

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, JUN-17-98 HED 08:34 AM LICENSING FAX NO. 3153491400 P. 04 i

ATTACHMENT A l

l EVALUATION OF THE NINE MILE POINT UNIT 2 FEEDWATER NOZZLE-to-SAFE END WELD BUTTER INDICATION (WELD 2RPV-KB20, N4D) j 1

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Report No.: SIR-98-067 Revision No.: O Project No.: NMPC-12Q File No.: NMPC 12Q-40I )

June 1998 l

Evaluation of the Nine Mile Point Unit 2 F edwater Nuulo to-Sare End

' **8d 8"*r 1*di"i>*

REVIEWED (Weld 2RPV-KB20, '440)

NtAGARA MOHAWK POWER

. ORPORATION NUC'.EAi< ENGINEERING DEPARTMENT j I

DISPOSmON OF SutwrTAL:

WACCEPTED E! ACCEPTED WITH CHANGES NOTED '

CNOT ACCEPTED frcparedfor:

O REVISE & RESUOMT SIGNATURE: DA - ara Mohawk Powcr Corporation otsapuME M" '7~ UNm 2 Prepared by:  ;

Structural !ntegrity Associates. Inc.

San Jose, California I'repared by: / A*- +- Date: $$//l Marcos L. liertera, P. F..

/

/) A Mvh Date: i [/t., [#7 7 trarry M. oordon P.E.

Reviewed and Approved by /

(' L'A44 ) Datc* $ll Ll9[

~

iony Giannuzu #d)

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REYtSION CONTRO1, SHEET l

Document 14 umber. SIR 98-067. Rev.A l l

Title:

Evalmilon of the Nine Mile Point Unit 2 Feedwater No:ct.le-to-Safe End Weld Buuer  !

Cr* kine Client: Ninearn Mohawk Power Corooration SI Project Number: Nhi'QL1Q Pages Revision Date Comments Secunn '

All 0 6/16/1998 truual Jssue All i

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l SIR 98 067.Rev.O li 4

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Table of Contenu Section East 8.n INTRODUCTSON - . . --- - .. -.l.8

-..--.- . 21 2.0 CllARACTERIZATION OF INDICATION- --- - -- -

2.I R > vicw or twmemow DAT4. .. .. . . .. .- - . . . . . . ~. ... . . . . .. .. .. . . 2 1 2.2 ALLov i 42 Fsk1.D EXPFRitNCl!~-. ..-. - .. . . ., ... ..... -. ... .. .. 22 22.I rityrum necurewletice Inlet w::le . .. ... .. . ... ... . . .. .. .. . . . . . . .. ...... 22 2.72 etnr need .. . . .... . ... . .-. .... . .. .. . .. .... . . . .. . . . . . . . . . . . . . ... .. .. . . . 2 3 thier ilWMs.. -.... . . ....... . .... .. .... . .. ... 2 4 2.2.3 . .. ... .....-

2.3 CIIAIL,ACl > W.A T!ON OF INtwATION CONCt MON-..m --.m... ... .-... ...... . ...m . ... 2 4 3.0 STRUCTUMA1. INTECRITY F.VA1 UATION OF INDICATION -- - --. - _ s.1 1 31 1 LAW r, vat.tI AT10N .. .. .. .... .... - . ~.~ .- ..- . . . .... . 3.I

). l. I Cetoch Grawuh Anely7is Apprnoth .. .. ..- ... .. .. . .... ... .... . .. . .... .. . ..... . .. . 3 I 3.1.2 C Crockiirowh nare and!redtermoEnd-*lI Orte Cruei Sise. . . . . . . . . . . . . . . . . . . . .32 31.J Allowable Flaw.%ize Eruleanton.. .. .. .. ... .. .... .. .. ... .-... . ..... 3 6 3.2 51 wiKmmAL tviuintTY UVAI.UAnow C0NCLustoW. . . . .. . .... ..... .- ..... .... . . . . 3 8 4.0 $UMM A RY - -- - . - . . . . - ~ . - -- 41 i s.o Mr.rERENCrs-. .. .

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t.0 INTMODUCTION ,

This report presents elk evaluation provided by Structuralintegrity Associates (SI) in support of l the dispo.sition of the observed indication in the Nine Mile Point Unit 2 (NMP2) feedwater nozzle-to-safc end weld butter (Weld 2RFV KB20). The weld butter is made using Alloy 182 material. UT inspection of the weld was performed during the 1998 outage 11). Dased im the UT inspection results, the indication is 0.29 inch deep and 5.3 inches in length and is connected to the inside surface. The indication has been seen by tJr inspection daring earlier inspections in .

1995 and 1990. Figure 1-1 shown the nozzle geometry and location orthe indication.

f As part of this effort, SI performed a review of the inspection data and field experience with similar locations to detennine a most likely cause for the indication. Based on the results of this i

evaluation. it is most likcly that the cause of the indication is fabrication related, l Although the evaluation of the fabrication, field experience and inspection information suggests the likely cause for the indication is fabricatiot related, a fracture mechanics evaluation was >

performed assuming the crack was an actively growing intergranular stress conomion crack. In this calculation crack growth was added to the depth and length using intergranular statss corrosion cracking (IGSCC) growth rate.s. The end-of-cycle allowable fimw size was detennined usmg the ASME Code.Section XI procedure for austenitic steel (Appendix C) and ferritic steel (Appendix H) since the indication is in the vicinity of the Alloy 182 weld butter-to-safe end (carbon steel) fusion line. The end.cf cycle calculated flaw size was then compared against the nilowable flaw size to demonstrate that the flaw is acceptable for at least one operating cycle (16.000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />).

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i SIR-%-067 Rev.O l-1 1

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Feedwater Nozzle (cartson steel)

Safe End (caton steel)

Weld Butter (Alloy 182)

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um 7

Cladding Location of Indication (A y 82)

(stainless steel)

Figure 1-1 Nine Mile Point Unit 2. Fcedwater Non.le (N4D) l SIR-98 067 Rev.o 1-2 l

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e 2.0 CHARACTER 12AT10N OFINDICATION This acetion presents a discussion regarding the indication detected in the subjoet weld. A review ofinspection data history regarding the indication and field history for similar locations is presented.

1.1 Review ofInspection Data a

Weld 2RPV-KB20 (N4D) has been inspected during three outages. he inspections occurred in 1990,1995, and 1998. A review of the inspection data from these three inspections was perfiermed and is summarized in Reference [2]. In addition, a review of the original radiographs was performed.

Tlw indication in question was noted on the Exanunation Summary Sheets for both 1995 and 1998 as a planar indication. The 1990 Examination Summary Sheet did not specifically note any one particle area. however it did note non relevant indications. inside surface geometry and

' i acoustic signals. Abr reevaluation of the 1995 data,it was concicied in (2). that the indication I

had the saune dimensions as was recorded during the 1998 inspection. The methods used in the 1995 and 1998 inspections were very similar (Smart 2000 system using 45'shcar wave. 45* )

refracted longitudinal wave, and 60* refracted longitudinal wave).  !

i=

l De 1990 examination was performed with the first generation Smart system (using 45' shear  !

wave,45' refiracted longitudinal wave, and tiO* refracted longitudinal wave). The imaging system was different than that used in 1995 and 1992. During the 1990 inspectinn no televant Indications were noted in the evaluation repmt. However, a re-review of this data determined that these indications were present (by all three search units) in the general location recorded during the 1995 and 1998 inspections. The 1990 re-review also appears to show that the indications are similar in airc to the results from the 1995 and 1998 innpections. There has been no axial branching noted in any of theu examinations.

sir-9P.-067. Rev. 0 2-1

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d There appears to be no evidence from a re review of the original radiographs, that these indications west present. However, due to the configuration of the sare end weld butter. this technique may not be the optimum for detection of small fusion flaws located at or near the interface. Thus, it can not be concluded the. 'hese indications were present since the time of fabrication based on the original radiogrraphs.

Rased on the evaluation presemed in Reference [2], it is likely that the indicatism is not growing or i= growing at a very low crack growth rate.

2.2 Alley 182 Field Experience Tids section presents a brief summary of field experience with indications at similar Alioy 182 locations. These cases show that field experience at these weld butter locations is primarily with fabrication related flaws and not iOSCC initiated flaws. It should be noted that IGSCC cannot be ruled cct if a fabrication flaw is open to the inside surface since it will be exposed to the BWR  ;

environment and create a crevice.

2.2.1 Pilgrim Recircularkm inlet NotrJe in May 1984, dyc penetrant test (PT) examination of a 12 inch recirculation inlet nozzle at Pilgrim revealed multiple crack indications on the pipe's inside surface (31. This location differs fmm the NMP2 recdwater nozzle since the safe end was str.inless steel. Subsequent examination of the remaining inlet nuales disclosed two additional nnules with multiple cracks in the Alloy 182 weld build-up area. Additional PT examinations on the two 2R inch diameter recirculation outlet nozzles also revealed multiple cracks in one of the two Alloy 1,2 weld build.up areas.

The observed cracks were primarily oriented in the axial direction and located in the Alloy 182 weld " butter" on both the nuale :.ide and the safe end side of the weld. There were some indications of crack propagation into the sudnicas steel (safe end side) base matcrial, while no propagation was observed into the low alloy steel base material or Alloy 12 root pass material.

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er The meta!!urgical'results fium one of the single boat samples removed from the 2R inch diameter recirculatism outlet nople Ni-B Indicated that the cracking wm the result ofinterdendritic stress corrosion cracking GDSCC). Thus, in this case, the observed IDSCC was found to be axially located.

2.2.2 RiverBend A circumferential crack indication was identified in the safe cnd side of the N4 A-2 inlet feedwater non.le-to safe end Alloy 182 weld butter at River Bend in March 1989 [4]. This 1

mdication was ultrasonically re-exammed during the necond and third refueling (RF) cycles in i March 1990 and September 1991. respectively, and during mid. cycle of the third fuel cycle in November 1990. Crack growth was reported during cach examination, Table 2-1. The safe end ,

l was replueed during the fourth refueling outage in 1992, i l

Table 2-1. Rher Dend Feedwater Nozzle Cracking History F. vent /Date UT Depth UT Length UT % Through well mm (im.) mm (in.) _

RF.2/ Marsh lYPU 3.1(0.20) ISS(6.1) la Mid-cycle 3/ November 1990 3.1(0.20) 168(6.6) la RF.3/ September 1991 8.4 (0 33) 196 (7.7) 30 I Mid- f:le 4 10.2 (u.10) 19s (7.8) 36 TrTuive exanunation 1992 23.4 (0.92) sclual 176 (7.0) actuat 44 netual ]

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The metalhtrgical destructive examination tevealed that the cause of crack growth was IDSCC that initiated at a la of fusion weld defect. Although there appears to be a discrepancy l

between the destructive examination measurements and the UT mesurement, the change in I measured 1JT depth was small, indicating that the crack was growing slowly.

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2.2.3 Osher BWJts There have been several other instances ofindications at similar locations as seen at NMP2 believed that in most casex, the cause for the indication was fabrication relsted. Similar cruck- '

like indications have also been observed by ITT at Vermont Yankee [SJ. Brunswick 2 [5] and )

Brunswick l [6J.

2.3 Charae erization ofIndication Conclusion Dased on the discussion provided in this section, there is significant evidence that the indication has not grown to date and that it originated during fabrication. The UT inspections have detected the indication since 1990 and the absence of the indication in the original radingmph is not unexpected. Dere have boca instances of defects in Alloy 132 weld butters believed to have initiated by fabrication. some being similar to the NMP2 indication. la cases wirre there was clearly IGSCC (or IDSCC) initiating in the Alloy 182 weld butter, the indications have been '

axia:ly oriented instead of circumfmntially orientw as in the case for NMP2.

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3.0 STRUCTURAL INT 7.GRtTY EVAL.UATION OF INDICATION In Section 2.0. a detailed discussion regarding the likely cause of the indication was presented.

Based on the discussion provided in Section 2.0 the indication origin is likely fabdcatinn )

related. Although negligible change in crack size has occurred to date and there is justification for assuming a very low crack growth rate, an evaluation was performed assuming the indication to be actidly growing IGSCC. The demonstration that structural integnty is maintained during the next operating cycle is shown by determining the crack sire at the end of the next operating cycle and companns this siae against the allowable flaw size. The allowable flaw size is determined using the ASME Code,Section XI. Appendix C and Appendix H [7] methodology l for austenitic and ferritic steel, respectively. Sinec the flawis in the vicinity of the weld fusion line. allowable flaw sizes were calculated using both materials and the limiting allowable crack site was used to determine the acceptability of the indication for continued operation.

l 3.1 Flaw Evaluation i There are two aspects of this evaluation: crack Crowth analysis and allowable flaw size determination. These are described in further detailin the following sections.

3.1.1 Croch Growth Analysir Approach 1

l As mentioned earlier, the indication is likely a fabrication flaw. Itowever, for the purposes of 1

! demonstrating structural integrity the flaw will be assumed to be active IGSCC. Thus,it is assumed in the analysis that any crack growth will be due,to IGSCC.

l Iratigue cracking at this location is considered unlikely. For the triple them'ai slecec design.

which is present at NMP2, fatigue cracking would bc caused by leakage flow past the reals mixing with the hotter downcomer flow. This cracking has been obsen ed on other plants only in the thicker nozzle blend region where the thermal mixing occurs. NMP2 ha: not seen S1 R.9 R.067. Itev. 0 31

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cracking at this location und thus,it is appropriate to assume that leakage past the seals has not occuned. Thus, thermal cyclins at the noale-to asic end location is not an issue. This conclusion regardaag fatigue crack grnwth is cimsistent with the absence of crack growth based on the 1990.1995 and 1998 sure end-to norrJe weld inspections. *lhetefore, fatigue crack growth can be excluded from the crack growth calculation.

3.1.2 Creek Growth Rete and Predicted End4f-Cycle Cnck Size The following is a summary of an evaluation of crack growth rates (COR) for nickel-ba.w Alloy 182 weld metal as related to the NMP2 feedwater indication. In addition to the CGR based am this evaluation, additional assumptions were made regarding CGR and are discussed later in this section.

Metallurgical evaluations from boat samples removed fromvarious Alloy 182 hsutered now.les at other faellities indicated that the cracking was the result ofinterdendritic stros corrosion cracking (IDSCC) or ADSCC that propagated from a welding flaw such as lack of fusion or miemtissuring.  ;

. l The presence of microtissuring in nickel. base alloy welds has been recognized for years and has been occasionally observed in some BWR compcments. Due to their localized nature. l I

microfissures typically do not adversely affect mechanical prtyperties. However, no systematic studies have been reported to date that examine the implicatisms of miemfissuring on IDSCC.

1 Microlissures create an interdendritic crevice that essentially sets like an IDSCC pre-crack. The microlissure not only forms a crack tip stress riser, but also creates aggressive localired crevice chemistry.

Experiments have been performed on Alloy 182 fructure mechanics compact tensinn specimens to ticiermine the material's susceptibility to IDSCC in D WR type environmcots. Real time crack

)' growth rates were measured using the highly accurate reversing DC potemial drop technique on SIR-98-067. Rev. 0 3-2 i

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t both as. deposited and furnace sensitized material as a function of dissolved oxygen concentration, water purity, temperature and loading condition. The results of these smdies l

mdicate and countm the following:

1. The crack propagation rate of Aliny 182 decreases with decreasing oxygen content (corrosion potential) and conductivity. The crack propagation rate of Alloy 1 R2 increascs with increasing stress latensity.

2. Based on results obtained on stainless steels and Alloy 600, the crack propagation rate of Alloy 1 A2 would be expected to reach a peak at approximately 200 *C (392 *F).

The observed peak in crack gmwth is attributed to two competing effects: the increase in growth rate vs. temperature from increasing kinetics of mass transport and the observed decrease in corrosion potential.

3. Alloy 182 crack growth rates obtained from an actual BWR at NMP-2 feedwater temperatercs are drarnatically lower than values obtained in similar laboratory studics.

4

4. Based on the relevant available data, an upper limit value of 5x10" mm/hr (2x10 in/hr) for Alloy 182 crack propagation rate appears valid for the NMP-2 feedwater nozzic.

Three approaches were used to determine the end-of. cycle llaw size. The three approaches are summarized below.

4

+ CGR bcsed on the discussion above. The CGR of 2.0x10 in/hr was based on relevant data for application to the NMP2 conditions.

• CGR hased on the recently issued U.S. NRC Safety F. valuation Report of the BWR Vessel & Intemals Project BWRVIP 14 [Al for stainless steel material.

I

• CGR based on the Swedish State Nucicar PowerInspectorate Statue Book SKlFS 1994:1 [9] for Alloy 1 R2 material in normal water chemistry.

b l CGR = 2.0x1rr#i n/hr 4

The first calculation u.ws the COR of 2x10 in/hr amlit is conservatively assumed that the rate is constant during the entire operating period and that h does not vary as a function of stress intensity factor. The stress intensity factor varies significantly through the pipe wall thickness.

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l SIR-98 067. Rev. 0 34

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Reference [10] pmvides the detailed discussion for the ute of the crack growth rate or2.0x10'8 1

in/hr l

Based on the crack growth rate of 2x10'5 in/hr. the end of cycle crack depth may be determined.

Fur an initial crack size of 0.29 inch and considering 16.000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> in the next eycle. the end nf cycle fisw depth is.

ar= a; + 2x104in/hr (16,000 hr)- 0.61 inch 4

Ira li t 2x10 in/hr(16.000 hr)(2)- 5.94 inches in terms of percentage uf nozzle thickness and . nozzle circumference, the end-of-cycle Daw depth is 50.8% of pipe wall. and the end of cycle icngth is 13% of the pipe circumference.

CGR - 2.2x104 in/hr 4

Based on the recently issued SliR regarding BWRV!P-14, a crack grow rate of 2.2x10 in/hr was used. Although this value in for stainless steel,it was included sir ireflectx crack growth rates based un field experience und laboratory testing in BWR cavironry nts. In Reference [8J. It i is stated that this CGR inay be used provided the stress intensity factor is less than 25 ksiVin and )

that the F.PRI BWR Water Chemistry Guidelinen are met. Figure 3-1 shows the through-wall stress distribution for the indication location. The stress in this figure is comprised of the i sustained stress which includes weld residual strces, thermal stress, pressure stress, and deadweight stress. %c computer pmgram pe-CRACK (111, was used to determine the through.

wall stress intensity factor variation u. sing the solution for a circumferential crack in a cylinder i i

for t/R-0.2. Figure 3 2 shows the through-wall variation in the stress intensity factor at the indiention location based on the Stress distribution in Figurc 3-1. He stress distribution shown in Figure 3-1 is comprised of weld residual stress (from NURF.G-0313 Rev. 2 (12]) and applied normal operating stress of 4.2 kui. As can be seen in Figure .12. the stress intensity factor remains below 25 ksiVin. NMP2 has also met the EPR1 RWR Water Chemistry Guideline.

$1R-98-067, Rev. 0 3-4 j l

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e l . i Daned on the crack gmwth rate'or2.2x10'8 in/hr. the end-of-cycle crack depth and length were i

determined to he, ,

i ar- a + 2.2x10'8 in/hr (16,000 hr) = 0.64 inch it= l +

i 2.2x10.s in/hr(16.000 hr)(2)- 6.00 inches l

l l

In tenna of percentage of nonic thickness and nonle circumference, the end-of cycle flaw depth l~ is 53.5% of pipe wall. and the end-of-cycle length is 13% of the pipe circumference CGR Based on SK1FS 19941 The CGR presented in Reference [9] for Alloy 182 in normal water chemistry (water l conductivity < 0.3pS/cm, and ECF > .230 mV) is, l

daldt = 2.2x10*"(Ki ) (1) 4 1

l The units for K in equation (1) are MPaVm, and the units for da/dt are mm/sec. A crack growth calculation was performed to determine the end-of-cycle crack depth using the stress intensity factor dependant expression for da/dt. The stress imensity factor distribution used in this calculation is shown in 1'igure 3-2. At the end of 16,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />, the crack depth is 0.34 inch, or

! 29% of wall. Figure 3-3 shows the crack growth versus time. Note that the units are in meters.

NilREG 0313. Rev. 2 [12]. addresses UT inspection of BWR coolant pressure boundary piping.

Sectinn 5.2.2 orthe N1JRF.G states that the NitC staff believes that flaw sizes determined by examinations and procedures qualified by test will not be granty underestimated or overestimated provided that an inspcetable weld joint configuration and wcld surface exist.

Thus, for this case no uncertainty was added to the crack depth. It should be noted that crack l depth uncertainty could he considered as part of the assumpdon that crack growth is occurring although the crack has essentially not changed since at least IWO. in addition.the margin between the calculated end-of-cycle crack depth and the allowable crack depth (calculated in Section 3.1.3) can also serve to compensate for any uncertainty in UT crack depth sizing.

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i SLR-9R-067. Rev. 0 35

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. 3.1.3 AlloweMe FlewSite Evolustion Since the indication is,in the vicinity of the fusion line, it is prudent to perfoms analyses assuming that the allowable flaw size is based on the weld butter and another analysis assuming that it is based on the naa.lc low alloy steel material. IJoth of these analyses are discussed I helow.

l Allowable Flaw Size Raved on Allov iR2 Weld Uutter This case assumes that the a!!owable flaw size is based on the Alloy 182 material. l'or this caxe.

the allowable flaw size is determined using the methodology provided in the ASME Code, I Section XI. Appendix C. The evaluation was performed using the methodology for austenitic steels such as Alloy 182. The rules for flux welds (shielded metal are or submerged are welds) were used in this evaluation. 't he methodology ofiWB 3640 has been incorporated into the pc-CRACK lilj computer software, and therefore this software was used to perfonn the evaluation for the Alloy 182 weld.

i The allowab!c flaw size is determined using net.section collapse methodology. This l methodology determinc> the a!!owahic crock parameters at the point ofincipient collapse, which also includes the ASM11 Code, Section XT required safety factors (2.77 for normal and upset.

1.39 for emergency and faulted).

1 Anplied Loadt and Stresses Since the indication in in the circumferential direction. the axial stresses at the weld will conj the crack growth or predicted failure point. The stresses tpquired for the evaluation of the allowable llaw size are the primary membrane (P ). primary bending (P,). and expansion l stresses (P ). The seconda y stresses areincluded since this is a flux wcld and the ASME Code.

Section XI methodology requires the consideration of these stresses. Note that wcld residual stress is not considered in the calculation of the allowable flaw site. The primary stresses (P,,..

1 1 ,

51R 98 067, Rev.0 36 l l  !

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.n Pn) and the expansion stresses (P.) are comprised of stresses from various sources.. These are shown below:

1% = Primary membrane stress such as pressure stress P. = Primary bendmg stress due w dead weight and neismic P. - Expansism stresses due to theemal loads The applied Itals for various loading conditions mL the nozzle-to-piping location were obtained from the NMP2 piping analysis (13). Table 3-1 summarizes the applied loads adjusted to the nozzle-to-safe end weld location. These loads and load combinations are consistent with the NMP2 FS AR. Comparison of the stress values determined that the faulted condition was limiting. Therefore, a safety factor of 1.39 was used.

Table 3-1 Applied Forces and Mamments at Non.le-to-Safe End Weld l'orces and Moments (F - Ibs. M = ft-lbs)

FX l'Y l'4 MK MY MZ Load

-735 -128 2743 1979 -1150s Deadweight 75

-3955 -2791 27151 40244 -25938 Thermal 2169 (envelop)

• 896 153 514 1177 2589 OBEA 253 3545 3122 20$$ 18191 17266 OilF.I.OCCU 2775 4959 8384 7027 3715 39949 ' 43042 OBEl. OCCE 7330 3987 41757 44R54 SSEl. OCCF 6021 8773 (Z-I/c-148.23in'. A-*49.2in

Dased on the nozzle geometry and thickness the stresses determined for this location were detennined to be:

Pe, - 5.91 ksi P. = 3.K7 ksi Pm = 3.36 ksi The pc-CRACK calctdated attawabic is deeper than 60% of wall but is limited to 60% by the ASME Code. Comparison of the maximum predicted end-of-cycle crack depth (53.5% of pipe SIR.9R-067. Rev. 0 37 O

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wall) to the allowgc of 60% orpipe wall demonstrates that the required safety factors are maintained throughout the next operating cycle. The length was also used in determining the acceptability of the Indication. Tabic 3 2 shows the results of the allowable llaw calculations as a function of fluw length / pipe circumference.

Table 3-2 Allowable Flew Sizes for Naxale-to-Safe End L.ocation: Alley 182 (Flaw length)/(Flpe circumference) 0.0 0.1 0.2 0.3 0.4 0.5 Allowable alt 0.6 0.6 0.6 0.6 0.56 0.42 (At end-of-cycle: length / circumference a 0.13, a/t = 0.53.5) l l

Allowable Finw Slme Raned on Low Allov Steel &zzle  !

in this analysis, the indication is assumed to remain in the low alloy steel nozzle material. For this analysis. the methodology of Appendix H of the ASME Code.Section XI was used. ne i 1

methodology of Appendix H has also been incorporated into the pe-CRACK computer mitware, and therefore this software was used to perform the evaluation for the low alloy matcrial, in addition, the properties for low alloy steel 11ux wclds was used in order to include consideration for the proximity to the Alloy 182 weld. The pc CRACK program also perlimns the screening criteria check to determine the method rur the allowable flaw analysis (limit load, clastic-plastic fracture mechanics (EPFM) or linear clastic fracture mechanies). The screening criteria  !

determined that failure shnuld be based on EFFM methodology. Using the methodology of Appendix 11 for FPFM, the pc-CRACK pmgram calculates the allowable flaw depth to bc 75%

ofpipe wall.

3.2 Structural Integrity Evaluation Conclusion

h. sed on the results of the calculations. it is determined that the allowable naw size based on limit load orthe Alloy 182, results in the limiting condition. nc allowable flaw depth was determined to be 60% of the pipe wall (maximum per ASME Code). The maximum predicted SIR-98-067. Rev. 0 3-R

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. depth at the end-of. cycle (ansuming active IGSCC) was determined to be 53.5% of the pipe wall

! by considering AGSCC growth using threc different assumptions for CGR. Therefore the -

required ASME Code safe 4y factors are maintained throughout the next operating cycle.

it is noteworthy that during the prior three UT examinations at this location. tids defect was' l

observed essentially the same size as is presently measured. This obsenution providen significant cvidence that the defect is utable and propagating very slowly, irat all.

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4.0 SUM!bfARY This report presemed the evaluation of the indication found in the Alloy 182 wcld butter of the nonle-to-safe end wcld (Weld 2RPWKB20, N4D). Dased im a review of the indication .

characteristics, inspection history and field experience for similar locations. it was determined that the indication is likely a fabrication flaw.

Although the flaw was considered to be a fabrication flaw and has shown canentially no growth  ;

hased on three UT Inspections. an unalysis was performed assuming active IGSCC. A crack growth prediction and allowable flaw calculation were performed (using both austenitic and ferritic piping methodologies) to determine the acceptability of the flaw for continued operation.

liased on the results of thens calculations, structural integrity of the noulc4o-nafe end wcld j location for the next operating cycle (16,000 hrs) was demonstrated.

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SIR 98-067. Rev. 0 41 1

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5.0 REFERENCES

l i 1. GE Nuclear Energy,1998 Examination Report No. RA 00A. June 1998

2. Niagara Mohawk Internal Correspondence.N.L. Rademacher to W. Yaeger.

Subject:

l l' Planar indication in Fcedwater Nozzle Weld #2RPV-KB20 (N4D), Junc 16.1998.

3. C. J. Czajkowski " Evaluation of Type 182 Weld Metal Cracks at the Pilgrim Nuclear Power Station," paper #253 presented ut Corrosion 86. NACE, llouston. TX, March 17.1986.

l 4. C. J. Czajkowski et al.. " Metallurgical 11 valuation of a Fcedwater Nozzic to Safe.Und Weld

! rn>m River Bend Station Unit 1." Brookhaven National Laboratory, May 1995.

1

5. McMinn and J. i,. Nelson," Stress Corrosion Cracking Experience with Existing and l

Potential Safe End Materials," paper presented at the Third International Symposium on i

' Envinmment Degradation of Materials in Nuclear Power Systems - Water Reactors,"

August 30.1987, published in proceedings of same edited by O. J. Theus and J. R. Weeks.

l TMS. Warrendale. PA.198R, p. 389.

6. " Flaw Evaluation uTUT indication for Feedwater Nozzle Weld IB2tN4D-5-SWl-2 at  !

I Brunswick Unit I,' SIR 90 081, December 2R 1990 1

1

7. American Society of Mechanical Enginecru (ASME) Boiler & Pressure Vessel Code, l Section XI 19R9 Edition.

8. US Nuclear Regulatory Cornmission," Safety Evaluation of the B WR Vessel und Internals Project BWRVIP-14 report (TAC No. M9497.5)", June 8,1998

9. Swedish State Nuclear Powerinspectorate Statue Book, SKlFS 1994:1, October 10.1994

10. StructuralIntegrity Associates," Evaluation of Alloy I82 Crack Growth Rate for the Nine Mile Point Unit 2 Feedwater-to Safe End Wcld Butter Indication (Weld 2RPV-Ki320 N4D). Report No. SIR-98-068. Rev. O, File NMPC-12Q.402, Junc 1998.

I1. Structural InLegrity Associates, "pe-CRACK User's Manual". Version 3.0.

12. US Nuclear Regulatory Commission,'-Technical Report on Material Selection and Processing Guidelines for llWR Coolant Pressure Roundary Piping," NUREG-0313. Rev.

2. January 1995.

13. Niagara Mohawk Nuf,1 car Engineering, Calculation Continuation Sheet, Calculation No.

AX 017A, Rev. 7.

1 SIR-98-067 Rev 0 5-1 l

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