ML18059A444

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Forwards Request for Addl Info Re Licensee Engineering Analysis & Root Cause Evaluation Rept Dtd 931007 for Pressurizer safe-end Crack at plant.TR-MCC-307 Rept Encl
ML18059A444
Person / Time
Site: Palisades Entergy icon.png
Issue date: 10/15/1993
From: Rogers D
CAROLINA POWER & LIGHT CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML18059A445 List:
References
TAC-M87760, NUDOCS 9310220095
Download: ML18059A444 (15)
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Text

consumers Power David W. Rogers Plant Sa/et)" and Licensing Director l'OWERINli MICHlliAN'S l'RDliRESS Palisades Nuclear Plant: 27780 Blue Star Memorial Highway, Covert, Ml 49043

. October 15, 1993 Nuclear Regulatory Commission

. Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT - PRESSURIZER SAFE END CRACK

- CRACK GROWTH ANALYSIS (TAC No. M87760)

In a letter dated October 7, 1993, we submitted the engineering analysis and root cause evaluation report for the PORV safe end crack. An NRC October 8, 1993 letter requested additional information concerning the safe end crack be provided prior to a scheduled October 12, 1993 meeting. The information was not docketed prior to the meeting, however, at the meeting at NRC headquarters, CPCo committed to a schedule for responding to each of the information request. The commitment included submitting our crack growth analysis (items 3 and 4 of the request) by Friday, October 15, 1993.

The attachment to this letter contains the reply to information requests 3 and 4 of the NRC's October 8, 1993 letter.

a'v.~e cv' u2-~

David W. Rogers Plant Safety and Licensing Director CC Administrator, Region Ill, USNRC NRC Resident Inspector - Palisades Attachment 22o n":i***.

9310220095 931015 '

PDR ADOCK 05000255 ~.

P PDR ~

A CMS CNCRGYCOMPANV

ATTACHMENT Corisumers Power Company Palisades Plant Docket 50-255 PRESSURIZER SAFE END CRACK ADDITIONAL INFORMATION RESPONDS TO ITEMS 3 AND 4 OF THE NRC OCTOBER!, 1993 INFORMATION REQUEST October 15, 1993

1 Request for additional inf~rmation regarding Consumer's Power's engineering

. analysis and root cause evaluation report dated October 7, 1993 for the pressurizer safe-end crack at Palisades plant.

NRC request:

3. Docket. the crack growth analysis referenced on page 7 in the Engineering Analysis and Root Cause Evaluation Report.

CPCo response:

Attached is CE report,"Crack Propagation Analysis For Circumferential Cracks In Alloy 600 Nozzle Safe-Ends" TR-MCC-307 whith contains the crack growth analysis.

NRC request:

4. Based on an estimate of the maximum flaw size that could exist
  • after completion of the NDE performed, provide an estimate of the time required for the crack to grow through-wan. Include
  • assumptions on stress levels and crack growth rates.

CPCo response:

The estimate of the time required for the crack to grow through wall is contained in Tables 1 and 2 of the attached CE report.,

"Crack Propagation Analysis For Circumferential Cracks In Alloy 600 Nozzle Safe-Ends" TR-MCC-307. Per the technical discussion held during the October 12, 1993 meeting with the NRC, CPCo is confident that the ~ondestructive ~xamination process can detect the flaws capable of propagating through wall during a fuel cycle.

CRACK PROPAGATION ANALYSIS FOR CIRCUMFERENTIAL CRACKS IN ALLOY 600 NOZZLE SAFE-ENDS TR-MCC-307 OCTOBER 1993 ABB COMBUSTION ENGINEERING NUCLEAR SERVICES COMBUSTION ENGINEERING, INC.

1000 PROSPECT HILL ROAD WINDSOR, CONNECTICUT 9310220100 931015 ~

PDR ADOCK 05000255 ~

P PDR l

TABLE OF CONTENTS INTRODUCTION 1 CRACK GROWTH RATE MODEL 1 CRACK GEOMETRIC AND PROGRESSION ASSUMPTIONS 2 LOADING AND INITIAL CONDITION ASSUMPTIONS 3 INPUT TO COMPUTATIONS 3 RESULTS 3 REFERENCES 4 r

I

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

  • Surge Line Safe-End
  • Spray Line Safe-End The ass~med mechanism {based ori 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 Smi~lowska et.al. {Reference 2). The only data specifically excluded were high {>7 ppm) .lithium data riot 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:

ln dL. = A + ~ ln ln {K-C) dt where: dL = crack growth rate {m/s) dt A = -25.942 B = 3*.595 K = Applied Stress Intensity .{MPa V m)

C = K1scc = 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~ Th~s 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 Pali.sades study. The first involves component temperature. The effect 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 I. 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 GEOMETRIC AND PROGRESSION ASSUMPTIONS On~-dimensional Linear Elastic Fracture Mechanics (LEFM) models were used in .

  • conjunction wit~ 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.

K1 = 1. 95av a/4>'

where K1 = applied stress ihtensity a = sectipn tensile stress a = fl aw depth

= 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 i.ncludes operating temperature, initial flaw depth and initial stress intensity, which in conjunction with the two governing equations completely define the mathematical system.

LOADING ANO INITIAL CONDITION ASSUMPTIONS 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) jn which various regimes of PWSCC crack growth were studied for Alloy 600. This assumed depth is deemed *appropri~te for separating the initiation and propagation parts of the PWSCC phenomenon and probably represents the

  • beginning of the true fracture mechanics regime.

The final major assumption concerned the* initial (and final) aspect ratio of the flaw. For the purposes of the Palisades CQmponents a range of flaw aspects was-used rangin~ from a semi-circular (2/1) to a long semi-elliptical (6/1) aspect ~atio flaw.

INPUT TO COMPUTATIONS The inptit for each Palisades compo~ent is given in Table l~ In the case of the PORV Safe-En~ computatioris were performed for two levels of applied stress. The first corresponded to the 17 KSI yield strength.cited in the*

_CERTS for the materi a1. The second corressponded to a 40 KSI assumed va 1ue

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

applied 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 inform~tion contained in Figures 1-5. The.

crack depths shown in the table represent the largest cracks which w9uld 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 al., "Effects of pH and Stress Intensity on Crack Growth Rate in Alloy 600 in Lithiated and Borated Water at High Tempertures," Proceedings, Fifth International Symp6sium 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 Design Guide, ASHE, 1971.
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.

Table 1 INPUT FOR PALISADES CRACK STUDIES 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 Spray Line .625 77 0.0032 540 5.36 7.08 7.58 Safe-End Table 2 CRACK DETECTION REQUIREMENTS PORV Safe-End (77 KSI) 20 .039 PORV Safe-End. (40 KSI) . 42 .175 Safety Valve Flange 38 .. 550 Surge Line Safe-End 41 .310 Spray Line Safe-End >350 .600

  • From crack initiation

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