ML20086S881

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Fracture Mechanics Evaluation of UT Indications Found in Cooper Feedwater-Nozzle-to Shell Weld
ML20086S881
Person / Time
Site: Cooper Entergy icon.png
Issue date: 12/13/1991
From: Caine T, Dias K, Ranganath S
GENERAL ELECTRIC CO.
To:
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ML20086S878 List:
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NUDOCS 9201060045
Download: ML20086S881 (13)
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. GENE 523 133-1191 DRF I?7-0010 Revision 1 FRACTURE MECHANICS EVALUATION OF UT INDICATIONS FOUND IN THE COOPER FEEDWATER N0ZZLE TO SHELL WELD December 13, 1991 Prepared by: k'k & WU/V K. P. Dias, Engineer '

Structural Analysis Services Verified by: h, 4 I ?_ fl3 et i T. A. Caine, Senior Engin er ' -

Structural Analysis Services Appr0ved by: /T" ^ l 131Tl

_S. Ranganath7 Manager Structural Analysis Services GE Nuclear Energy Nik bib'bh bI$hb!r e o en<

GENE-523-133-1191 Revision 1 IMPORTANT NOTICE REGARDING CONTE!1TS OF THIS REPORT Please Read Carefully The only undertaking of the General Electric Company (GE) respecting information in this document are contained in the contract between Nebraska Pub'lic Power District (NPPD) and GE, and nothing contained in this document shall be construed as changing the contract. The use of this information by anyone other than NPPD, or for any purpose other than that for which it is intended under such contract is not authorized; and with respect to any unauthorized use, GE makes no representation or warranty, and assumes no liability as to the completeness, accuracy, or usefulness of the information contained in this document, or that its use may not infringe privately owned rights.

i l

- GENE-523-133-1191

' Revision 1 Fracture Mechanics Evaluation of the UT Indications in the Cooner Feedwater Nozzle to Shg)1 Weld Introduction Revision 1 of this report incorporates two changes to the original analysis.

The revised fracture mechanics analysis is bas 9d on an RTNDT of 30'F instead of 18'F. The fatigue crack growth analysis has been revised to account for the cumulative. thermal / pressure cycles (720) rather than just those cycles (120) due to startup/ shutdown transients.

UT indications were found in the Cooper feedwater nozzle. (N4) forging to vessel shell weld. No indications were found in the nozzle bore or inner radius zones. The indications in the weld were subsurface. Most of them were'close to -the mid-plane and appeared to be f abrication related. The indications exceeded the acceptance sta'ndards of IWB-3512 of Section XI, ASME Code, and were therefore evaluated to determine whether the acceptance criteria of IWB-3600 were satisfied.

This report describes the fracture mechanics evaluation of the UT indications

'to demonstrate compliance with the Section XI acceptaate criteria. Based on the results of the' analysis, continued operation 'as is' is acceptable for the remainder of plant life.

I Descriotion of the Indications Indications at the 100% signal amplitude level (for ASM. de Criteria) were found in the N4-0 nozzle. All the indications were subsurface and were characterized in accordance with Section-XI, IWB 3000. The flaw parameters "a",-_ "L" (or'"1") and e (as shown in Figure 1) for the three_ indications I ' detected at the 100% amplitude level are listed in Table 1.

Other-indications were also found at 50%/20% signal amplitude levels (per Reg Guide 1.150) in nozzles N4-A, C and 0, but these were not detectable at the L

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GENE 523-133-1191 Revision 1 ASME Code 100% s'.gnal amplitude levels. The analysis for these indications was performed in a separate _ GENE report (Ref.1).

The fracture mechanics evaluation described here covers indication

  • 18 which bounds the other two indications shown in Table 1.

Analysis Backaround Objective The objective of the analysis is to determine whether the bounding indication for the flaws in Table 1 meet the acceptance criteria of IWB-3600.

Method The fracture mechanics methods used in the analysis are consistent with the procedures outlined in Sectio.1 XI, ASME Code, 1989 Edition.

Assumptions Based on the evaluation of the different transient conditicas, the hydrotest .s the most limiting condition from the fracture view point. This is because hydrotest conditions represent the most limiting combination of high stress and low temperature. The temperature for the pressure test (01100 psi) is assumed to be 208'F, based on the Tech Spec PT Curves (Figure 2).

The RTND, of the nozzle to shell weld material itself has not been located.

However, the NRC Branch Technical- Position MTEB 5-2 allows a conservative estimate of 10*F where the actual RTNDT information is not available. Data on weldments (SAW) used in the Cooper vessel are as shown-below. The measured CVN values for the different heats were:

Weldheat CVN at 10'F ft-lb 27204 & 12008 (Tandem) 71, 78, 60, 76, 78, 95 12420 1 12420 (Tandem) 67, 78, 83, 64, 69, 56 21935 (Single Wire) 62, 59, 60

GENE 523-133-1191 Revision 1 It is noted that all the CVN values exceed 45 ft-lb at 10'F so that the use of 10*F as RTNDT is consistent with MTEB 5 2. The above welds for which inforwtion is available have corresponding RTNDT values of -50*F. The RTNDT values for the intermediate shell plates (to which the nozzle forging is welded) are -10', 6' and 18'F (Ref 2). However, to ensure conservatism an RTNDT of 30*F will be assumed for this analysis Fracture Mechanics Analysis Applied Stresses All thermal and pressure transients occuring in the vessel and nozzle were considered. The hydrotest was found to be the most limiting condition for fracture mechanics assessment. Based on a two-dimensional, axisymmetric stress analysis of the Cooper feedwater nozzle (Ref. 3) the stress distribution at the location of the indication can be conservatively represented by a membrane stress of 28 ksi (Figure 3). This is also consistent with the stress distribution calculated by Gilman and Rashid (Ref. 4) from a three-dimensional analysis of a typical BWR feedwater nozzle under internal pressure (Figure 4).

Fracture Toughness The assumed RTNDT of 30*F can be conservatively used to determine the fracture toughness. For an RTNDT of 30*F and a hydrotest temperature of 208'F, the available fracture toughness, KIA, is conservatively estimated to be 192 ksifii)

(Figure 5). The allowable value including the Code safety f actor of /TO is calculated to be 61 ksi/in.

Fatigue Crack Growth The indication is subsurface and, thus, not exposed to the environment.

Because of the absence of water environment for the subsurf ace flaw, incremental growth is expected to be small, and thus a detailed fatigue crack growth analysis was not performed. Instead, a total of 720 cycles (120 startup i

.. i GENE 523-133 1191 ,

,, Revision-1 and 600_ thermal / pressure cycles) were conservatively assumed to cover the  :

entire cycle duty. This value takes into consideration both vessel and nozzle thermal cycles and, as such, is conside-ed a bounding value. Thus, for fatigue crack growth in air, a crack growth rate of da/dN=15 microinches/ cycle is predicted. For 720 cumulative cycles, this yields a total change in crack size of 0.02 inch giving an end-of life (EOL) crack depth of 2a+0.']2= 2(0.49)+0.02=

1.0 inch. .

Fracture Mechanics Assessment A fracture mechanics evaluation was performed in accordance with Section XI of the ASME Code for the most . limiting UT indication (#18, Table 1). An applied stress of 28 ksi membrane was used for tha inalysis. For an a/L 0.28 and E0L crack depth of 2a=1.0 inch that includes fatigue crack growth, the required fracture toughness, K I , is calculated to be 28 ksi/Ili.

The available fracture toughness (61 ksi/in) is well in excess of the requirement (28 ksi/Tn). The flaw therefore meets the criteria of IWB 3612 and continued operation is acceptable.

Summarv This report describes the fracture mechanics evaluation of the indications observed in the Cooper feedwater nozzle that exceed ~i ASME Code,Section XI, IWB-3512 criteria. Based on the evaluation of the UT data, a subsurface indication with a/L-0.28 and depth 2a= 0.98 inch was selected as a bounding 1 flaw size for the fracture mechanics evaluation. The plane of the flaw was conservatively assumed +9 be normal to the hoop direction. Since the indication is subsurface, only fatigue crack growth in air was considered. The predicted increment in depth was small (0.02 in.) and the total EOL crack depth, 2a, was

! calculated to be 1.0 inch.

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_ The limiting condition for fracture is the vessel hydrotest. For an assumed RTNDT=30*F and a hydrotest temperature of 208'F, the available fracture

-4

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1 4

GENE-523-133-1191.

Revision 1 toughness is 192 ksi/I'n'. The allowable value including the Code safety factor of /IT is calculated to be 61 ksi/Tii. This available toughness is well in excess of the applied K value of 28 ksi/iii. The flaw therefore meets the criteria of IWB-3612,Section XI, ASME Code and continued operation is acceptable.

References

[1] GE Report GENE 523-134-1191, Revision 1 " Fracture Mechanics Evaluation of UT Indications Found Per Reg. Guide 1.150 in the Cooper Feedwater Nozzle to Shell Weld," K.P. Dias, November 11, 1991.

[2] Letter from T.A. Caine, GENE, November 8,1991 (regarding RTNDT estimate for Cooper Feedwater Nozzle weld). DRF #137-0010.

[3] G.L. Stevens, DRF #B13-01541, Vol. 3, " Cooper Automated Monitoring".

[4] J.D. Gilman and Y.R. Rashid, "Three-Dimensional Analysis of Reactor Pressure Vessel Nozzles", Transactions of the 1st International Conference for Structural Mechanics in Reactor Technoloov (SMIRT), Vol. 4,-Part G, September, 1971.

s.

GENE-523 133-1191-Revision 1 TABLE 1 4

Dimensions of UT Indications Detected in the N40 Nozzle.

Indicat. Location e a L a/L a/T%

  1. Max Depth (in) (in) (in) (in) 11 4.09 0.76 0.40 0.94 0.42 6.75 14 4.40 1.05 0.40 0.81 0.50 6.85 18 4.45 1.03 0.49 1,73 0.28 8.25

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