ML20236X331

Allowable Corner Flaws for Prz Upper Head Instrumentation Nozzle

ML20236X331
Person / Time
Site:	Calvert Cliffs
Issue date:	08/04/1998
From:	Killian D FRAMATOME
To:
Shared Package
ML20236X325	List: ML20236X323 ML20236X331
References
32-5002086, 32-5002086-00, NUDOCS 9808070300
Download: ML20236X331 (13)

Text

,

c.,

l 20697 J (12/95)

CALCULATION

SUMMARY

SHEET (CSS) f M Y.^?R^M I

Documentidentifier 32-5002086 - 00 l

Title ALLOWABLE CORNER FLAWS FOR PRZ UPPER HEAD INSTRU NOZZLE PREPARED BY:

REVIEWED BY:

q NAME D E. KILLIAN x,,

NAME P.F. WILLIAMS Sl! NATURE SIGNATURE

&!'/ A TITLE SUPV. ENGR.

DATE rh 7 i

TITLE PRIN. ENGR.

DATE COST REF.

TM STATEMENT; CENTER 41020 PAGE(S) 13 REVIEWE R INDEPENDENCE PURPOSE AND

SUMMARY

OF REGULTS:

Fracture mechanics analysis is utilized to evaluate a potential comer flaw in a pressurizer upper head instrumentation reezzle at BG&E's Calvert Cliffs Unit 2. Flaw evaluations are ps; formed according to the rules of the ASME Boiler and Pressure Vessel Code,Section XI, Paragraph IWB-3612.

l Various initial flew depths are considered, ranging from 15/16" to 1.71". The largest flaw that could be accepted is about 1.5",

since it would perm!t oVer 700 hestup/cooldown cycles to 2500 psi pressurt,. Additional results are presented in Section 8.0.

l l

l THE FOLLOWING COMPUTER CODES HAVE BEEN USED rN THIS DOCUMENT THE DOCUMENT CONTAINS ASSUMPTIONS THAT MUSl BE VERIFIED PRIOR TO USE ON SAFETY.

RELATED Wor <K CODENERSION/REV CODENERSION/REV 1

I YES NO r

9808070300 980804 ADOCK0500g8' Page 1

of 13 l

DR

,n w a _m w, w Framatome Technologies 32 5002086-00 RECORD OF REVISIONS Revision

.P_aggs Description of Revision Date O

All Origina1 Release g/98 6

1 0

0 t

l I

e 4

1 2

1

)

, +.... se..,,.,,.3.....,,s

I n

womamax w.am Framatome Technologies 32-5002086-00 CONTENTS i

SaliDa Titis Page 1.0 Introd u ction.....................................................4 2.0 Assumptions.........

...........5 3.0 Postulated Flaw Shape,...

6 4.0 Stress Intensity Factor Solution.......,..........

7 5.0 Applied Stresses......,..

9 6.0 Material Properties....

10 7.0 Flaw Acceptance Criteria.,,.

.I1 8.0 Re sult s.,,,....................................

12 9.0 Conclusions,..

.......................................I2 10.0 References....

13 i

l l

t I

l i

3 l

m w u m so n ws e.ws p.

hamatome Technologies 32-5002086-00

,1.0, Introduction L

Following the discovery of a leaking pressurizer upper head instrumentation nozzle at Baltimore Gas and Electric (BG&E) Company's Calvert Cliffs Unit 2, a long term repair design [1] was formulated for implementation prior to plant restart, it was determined that the pressure boundary has been violated by a crack extending through the Alloy 600 partial penetration attachment weld between the Alloy 690 instrumentation nozzle and the carbon steel upper head.

The repair design consists of severing the nozzle above the weld and forming a new pressure boundary by welding the outboard portion of the nozzle to a newly created weld pad on the outside surface of the head. Since this design left the inboard portion of the original nozzle in place and UT was not performed to characterize the extent of the flaw, it has been conjectured that the flaw may extend through the weld and into it the carbon steel head material. To address such a scenario, a typical nozzle inside comer flaw is postulated to be present in the head material and fracture mechanics analysis is performed to evaluate the consequences of flaw growth under cyclic loading conditions. The objective of the flaw evaluation is to determine the number of allowable heatup/cooldown cycles for several initial sizes of postulated nozzle comer flaws extending through the weld, butter, and into the base metal. Failure is associated with unstable crack initiation, as indicated (with safety margin) by the lower bound fracture toughness reference curve of Section XI of the ASME Boiler and Pressure Vessel Code [2]

l l

l l

l l

l

}

4

m wewusse p g3 i

1 Framatome Technologies 32-5002086-00 2.0 Assumptions Listed below are assumptions that are pertinent to the present fracture mechanics evaluation

1. It is assumed that the effects ofirradiation at the upper head location are negligible and that a value of 40 *F may be used to approximate the RTwor of the upper head material l

[7).

l

2. Thermal stresses may be ignored since the upper head instrumentation nozzle is located a i

steam dome which, due to low film coefficients, minimizes heat flux into and out of the head under cyclic thermal loading conditions.

3. Attached piping loads at the location of the weld pad on the outer surface of the head are i

assumed to have a negligible effect on stresses in the comer region.

~

4. Weld residual stresses and cladding effects are assumed to be secondary in nature and need not be included in the present analysis.

5. Faulted condition pressure loads are assumed to be bounded by the 2500 psi design load used for evaluation ofnormal and upset condition loads.

)

6. It assumed that increases in pressurizer pressure are limited by operational l

pressure / temperature (PT) limits and that the highest pressure load is bounding.

l i

5

. -. s

. ~ -

~

,gmammm pg Framatome Technologies 32-5002086-00 t

l 3.0 Postulated Flaw Shape A quarter circular shape is used to represent a flaw at the inside comer of the upper head penetration for the instrumentation nozzle. The postulated nozzle comer flaw is located in a radial plane relative to the nozzle, starting at an extension of the'inside surface of the base metal and including the area of the J-groove, as depicted below.

I s

1 Comer Oaw l

inside comer The flaw is oriented in the radial plane since the dominant stress in the head is the pressure hoop stress around the penetration. Per paragraph 4.7 of the design specification [1], the mmimum assumed flaw depth shall be 1-1/16 inches, the height of the J-grooved weld prep Although this dimension is used in the fracture mechanics analysis for an initial flaw depth, results are also reported for an initial depth o 15/16 of an inch, which is the distance to the inside surface of the weld butter. It is noted that flaw evaluations are performed for a base metal comer flaw by considering that portion of the flaw included in the cladding, weld, and butter areas as being part of the complete flaw,

)

i l

6 l

g..., e,.

4 +

, _se n Framatome Technologies 32-5002086-00 i

4.0, Stress Intensity Factor Solution Although detailed finite element analysis could be utilized to obtain accurate stress distributions through the nozzle, head, and weld regions, and to derive stress intensity factors for specific flaw shapes, the present flaw evaluation relies on available stress intensity factor solutions from the literature usin8 undamental descriptions of stress.

f 4.1 Nozzle Comer Flaw For an arbitrary stress distribution through the vessel head, described by the third-order polynomial, o = A + A,x + A x + A x*,

[ Ref 3, egn. (G-2.1) )

o 3

3 where x is measured from the inside corner, the stress intensity factor solution for a simulated three-dimensional nozzle corner flaw is:

K, = M 0.706Ao + 0.537 2a' A, + 0.448 aA + 0.39 4aA '

r s n; 2,

3 3x 3

j

[ Ref. 3, egn (G-2.2) )

where "a" is the radius of the circular-shaped crack front.

I i

l 7

7

.__..m._,

w a y,w, y,,

Framatome Technologies 32-5002086-00 4.2 Irwin Plasticity Conection i

The Irwin plasticity conection utilized in linear elastic fracture mechanics to account for a moderate amount of yielding at the crack tip is defined for plane strain conditions by i

I f

2 r, =

K,(a)3 1

6x o, j l

wherc; l

K,(a) = stress intensity factor based on the actual crack length, a, o, = yield strength.

A stress intensity factor, K (a.), is then calculated based on an effective crack length, i

a, = a + r,,

l l

l l

l j

8

,.,:.,,......-~..

c.,

Framatome Technologies 32-5002086-00

,5.0 Applied Stresses For pressure loading, a rnembrane hoop stress is calculated for the spherical head at the nozzle penetration as follows:

PR' o,=SCF% xSCF,,,. x 2t where:

Design pressure, P = 2500 psi [1]

Radius to the upper head base metal, R, = 48.4375 in. [4]

Upper head thickness,

't = 3,875 in. [4]

and Stress concentration for the hoke, SCF. - 2.0 [5]

Stress concentration for the effect of an oblique, or hillside, nozzle penetration, SCF,,.. = 1.2 (6) l Then the hoop stress used for the evaluation of the radial comer flaw is e, - 37.5 ksi, and the polynomial stress coefficients used for the stress intensity factor solution are Ao = 37.5 ksi A,=0 A,=0 A =0 3

i 9

l

.,. =,

,.r,+.

, f.

t

.y.

e

• + = - +

o

~

wamace m mxem

v. n l Framatome Technologies 32-5002086-00 6.0 Material Properties Material properties are developed for 'the SA-533 Grade B, Class 1, upper head low alloy steel plate material [4] for an operating temperature of 653 *F [1].

l l

6.1 Fracture Toughness and Yield Strength l

The upper head material is included in the list of ferritic steels for which the lower bound fracture toughness curves in Fig. A-4200-1 of Section XI [2] may be used At a temperature of 653 *F and for a RTmn of 40 *F [7), the Ku and Ku curves are both well above the t;per shelf value of 200 ksiVin.

A yield strength of 43.5 ksi at 650 *Fis obtained from Section III of the ASME Code (8]. This value is used in the Irwin plasticity correction to calculate an effective flaw de.pth.

6,2 Fatigue Crack Growth Flaw growth due to cyclic loading is calculated for the upper head material using the fatigue crack growth rate model from Article A-4000 of Section XI [2],

i da

'I

- = C(AK,)*,

1 dN where AKi is the range of applied stress intensity factor in terms of ksiVin, da/dN is in terms of inches / cycle. Considering cyclic pressure loads during plant heatup and cooldown conditions, such that the minimum stress intensity factor K i. = 0, the constants C and m are determined from Fig. A-43001 of Section XI [2] using R - K.,./Km = 0 For AKi> 19 ksiVin, C = 1.01x10 7 l

m = 1.95 For the stress intensity factor solution presented in section 4.1, this flaw growth model can be integrated to express the final flaw depth, ar, in terms of an initial flaw depth, ai, for a specified number of fatigue cycles, N, as follows:

a, = a,**) + (1 - m / 2)C (0.706A/E)* N 10 1,

.zs....,,,....,,,..

3

--. ~ -

- -w "u

wemme P.32 j

l Frcmatome Technologies i

32-50020F4-00 i

7.0 '. Flaw Acceptance Criteria For a nozzle corner flaw, the postulatO initial flaw size is considered to be acceptaHe for a given amount of crack growth if the appliled stress intensity factor satisfies the fracture toughness requirement of the ASME Code,Section XI, Paragraph IWB-3612 [2] for normal and upset conditions, 1

i Ku Ki(ar) < g I

where, K,(a,) - applied stiess intensity factor at the final flaw depth, i

K,,

- crack arrest fracture toughness.

i i

1 l

1 I

e r

11

a n n,_

,,u Framatome Technologies 32 5002086-00

• 8s0 Results Results of the flaw growth evaluation of postulated nozzle corner flaws are presented below in the form of table of allowable cycles for several values ofinitial flaw size, ranging from 15/16 inch to 1.71 inches.

Allowable Number of Heatup/Cooldbwn Cycles vs. Initial Flaw Size for Nozzle Corner Flaws a4 N(ai)

N at K(aer)

(in.)

(ksiftn)

(cycles)

(in.)

(ksiVin) 0.9375 45.44 3299 1.7112 63.25 1.%25 48.37 l

2616 1.7109 63.25 1.5000 57.47 726 17110 63.25 4

1.7106 61.37 1

1.7109 63.25 1

9.0 Conclusions Based on 500 heatup/cooldown cycle' for a 40-year design life [1], a nozzle corner flaw could s

have an initial depth into the upper head base metal of 1.5 inches, measured from the " extended" base metal' corner, as depicted in the figure on page 6. Such a flaw would grow to about 1.7) inches in 726 cycles to 2500 psi pr' essure Above 1.5 inches, only a few cycles would be permitted, until the flaw would reach critical size at 1.71 inches.

i i

f a

'l l

i.

1 12

_u___:__=__=_

--y-

-s us saeaee s e s m e p.ge e

Framatome Technologies 32-5002086-00 10.0. References 1.

FTI Doc. No. 08-5002022-00, " Design Specification for Repair / Replacement of Pressurim Upper Head Instruinentation Nozzles," August 1998.

2.

ASME Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Comoonents,1983 Edition with Summer 1983 Addenda.

3.

Marston, T.U., " Flaw Evaluation Procedures - Background and Application of ASME Section XI, Appendix A," EPRI Repon NP-719-SR, August 1978.

4 FTI Dwg. No. 02-5002019B 0, " Specification Drawing - Upper Head Instrumentation Nozzle Repair / Replacement" 5.

Roark, R.J., Formulas for Stress and Strain, Fourth Edition, McGraw-Ifill Book Company, New York,1965.

6.

FTI Doc. No. 32-1176542-02,

• Hillside Nonle Stress Comparison"-

l 7.

FTI Topical Report BAW-10046A, Rev. 2, " Methods of Comphance with Fracture Toughness and Operational Requirements of10 CFR 50, Appendix G," June 1986.

8.

ASME Boiler and Pressure Vessel Code,Section III, Rules for Construction of Nuclear Power Plam Comoonents. Division 1 - Anoendices.1986 Edition.

t l

l I

i I

13

........