ML20058P136

Crack Propagation Analysis for Circumferential Cracks in Alloy 600 Nozzle Safe-Ends

ML20058P136
Person / Time
Site:	Palisades
Issue date:	10/31/1993
From:	ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
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Shared Package
ML18059A445	List: ML18059A444 ML20058P136
References
TR-MCC-307, NUDOCS 9310220100
Download: ML20058P136 (12)

Text

. :. .

CRACK PROPAGATION ANALYSIS -

FOR CIRCUMFERENTIAL CRACKS ,

IN ALLOY 600 N0ZZLE SAFE-ENDS i

TR-MCC-307 i

r OCTOBER 1993 i

ABB COMBUSTION ENGINEERING NUCLEAR SERVICES ,

COMBUSTION ENGINEERING, INC.

~

1000 PROSPECT HILL ROAD WINDSOR, CONNECTICUT t

9310220100 931015 EL

• PDR ADOCK 05000255 h P PDR k;-

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4

-TABLE OF CONTENTS ,

TITLE PAGE INTRODUCTION 1 ,

CRACK GROWTH RATE MODEL 1

^

CRACK GE0 METRIC AND PROGRESSION ASSUMPTIONS 2-LOADING AND INITIAL CONDITION ASSUMPTIONS .3 INPUT TO COMPUTATIONS 3 RESULTS 3 REFERENCES 4 f

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INTRODUCTION 4

This report documents crack propagation studies performed for selected Alloy 600 components in the pressurizer of the Palisades NSSS. The components include:

e Safety Valve Flange e PORV Safe-End e Surge Line Safe-End e Spray Line Safe-End The assumed mechanism (based on recent failure analysis results) for crack propagation in all analyses is primary water stress corrosion cracking (PWSCC). The methodology used in these studies was developed for specific application to the problem of crack propagation in CEDM nozzles (Reference 1).

CRACK GROWTH RATE MODEL The basic crack propagation model used in the analyses is based on a subset of the Alloy 600 data published by Smialowska et.al. (Reference 2). The only data specifically excluded were high (>7 ppm) lithium data not representative of Palisades primary chemistry. All experiments utilized in the final correlation analysis were performed at a temperature of 330*C.

The crack growth rate correlation is given by:

in di - A + B in in (K-C) dt where: dl = crack growth rate (m/s) dt A = -25.942 B = 3.595 K = Applied Stress Intensity (MPa s/ m)

C-Kisce - 0 (for this case)

The crack growth rate versus stress intensity is shown in Figure 1. It should be noted that no explicit threshold stress intensity is required for crack propagation in this correlation form. This feature was incorporated to permit investigation of crack growth for CEDM nozzles in which observed cracks were extremely shallow (<.4 mm).

Two corrections are necessary to the growth rate correlation for application to the Palisades study. The first involves component temperature. The effect t of temperatures unequal to 330*C is accommodated using an Arrhenius rate law with an activation energy of 33 Kcal/ mole. This is consistent with Reference

1. The second correction reflects the effect of the prior cold work present in the Smialowska data. Scott (Reference 3) has suggested reduction in growth rate by a factor of between 5 and 10. A factor of 5 is utilized in the present work.

CRACK GE0 METRIC AND PROGRESSION ASSUMPTIONS One-dimensional Linear Elastic Fracture Mechanics (LEFM) models were used in conjunction with the crack rate correlation to compute crack progression. The assumed configuration for the initial crack is an embedded semi-elliptical surface flaw with Mode I opening. The applied stress is computed using the equation given in Figure 2.3.3 of Reference 4.

K, - 1.95g v' a/$

where K, - applied stress intensity rr - section tensile stress a - flaw depth Q - complete elliptic integral of the second kind Evaluation of crack growth is performed by numerical integration using the crack growth rate correlation and the stress intensity equation. The required input includes operating temperature, initial flaw depth and initial stress intensity, which in conjunction with the two governing equations completely I

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define the mathematical system. l LOADING AND INITIAL CONDITION ASSUMPTIONS ]

l In the absence of detailed finite element computations, an assumption of net section yield was made for all components. No credit was taken for reduction of yield strength with temperature. This assumption is consistent, however, with finite element analysis results documented in Reference 1 for CEDM nozzles in the partial penetration weld region.

Initial flaw depth was assumed to be approximately 3 mils, consistent with )

results of detailed experiments performed by Boursier et.al. (Reference 5) in 1 which various regimes of PWSCC crack growth were studied for Alloy 600. This-assumed depth is deemed appropriate for separating the initiation and propagation parts of the PWSCC phenomenon and probably represents the beginning of the true fracture mechanics regime.

l The final major assumption concerned the initial (and final) aspect ratio of _ ,

the flaw. For the purposes of the Palisades components a range of flaw aspects was used ranging from a semi-circular (2/1) to a long semi-elliptical (6/1) aspect ratio flaw. ,

i INPUT TO COMPUTATIONS j l

The input for each Palisades component is given in Table 1. In the case of j the PORY Fafe-End computations were performed for two levels of applied stress. The first corresponded to the 77 KSI yield strength cited in the CERTS for the material. The second corressponded to a 40 KSI assumed value ,

obtained from material near or in a softened weld heat affected zone. For the

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other components CERT yield strength values were used in the analysis.

RESULTS The results of the crack growth assessment for the Palisades PORV safe-end are shown in Figure 1 for the 77 KSI applied stress and in Figure 2 for the 40 KSI I

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appl.ied stress. The safety valve safe-end crack growth assessment is shown in Figure 3 for a 77 KSI applied stress. The surge line and spray line safe-end crack growth assessment, are shown in Figures 4 and 5 respectively.

Table 2 is a derivative of the information contained in Figures 1-5. The ,

crack depths shown in the table represent the largest cracks which would theoretically permit operation for 15 effective full power months prior to throughwall propagation. The Palisades PORV Safe-End case at 77 KSI applied stress is the most limiting with a required crack detection threshold of 40 mils.

REFERENCES

1. ABB Combustion Engineering, " Safety Evaluation of the Potential for and  ;

Consequences of Reactor Vessel Head Penetration Alloy 600 ID Initiated Nozzle Cracking," CEN-607, May 1993.

2. Smialowska, Z. S. et a1. , " Effects of pH and Stress Intensity on Crack Growth Rate in Alloy 600 in Lithiated and Borated Water at High I Tempertures," Proceedings, Fifth International Symposium on ,

Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Monterey, Aguust, 1991.

3. Scott, P. M., "An Analysis of Primary Water Stress Corrosion Cracking in '

PWR Steam Generators," Proceedings, Specialists Meeting on Operating Experience with Steam Generators, Brussels Belgium, September 1991.

4. R. L. Cloud et al., Brittle Fracture Desian Guide, ASME,1971.

l

5. J. Boursier et al., " Stress Corrosion Cracking of Alloy 600 in Water:  !

Influence of Strain Rate on the Different Stages of Cracking," EUROCORR

'92, June 1992.

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Table 1 INPUT FOR PALISADES CRACK STUDIES I

initial Stress intensity W all Applied Crack Temperature Component Thickness Stress Depth . (*F)' 2/1 4/1 6/1 (in) (KSI) (in) (KSI V in) -

PORV .438 77 0.0032 640 5.36 7.08 7.58 Safe-End PORV .438 40 0.0032 640 2.78 3.68 3.94 Safe-End Safety 1.3 77 0.0032 640 5.36 7.08 7.58 Valve Flange Surge Line .75 51 0.0032 640 3.54 4.69 5.02 Safe-End 4 Spray Line .625 77 0.0032 540 5.36 7.08 7.58 Safe-End Table 2 CRACK DETECTION REQUIREMENTS i Time to Throughwall. . Crack Depth 15 Months i Component Crack Prior to T/W Crack (Months) .' ' (inches):: 1 PORV Safe-End (77 KSI) 20 .039 PORV Safe-End (40 KSI) 42 .175 f

Safety Valve Flange 38 .550 Surge Line Safe End 41 .310 l

Spray Line Safe-End > 350 .600 1

• From crack initiation l

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