ML19324C176

Hpi/Makeup Nozzle Weld Overlay Repair Contingency Plan.

ML19324C176
Person / Time
Site:	Davis Besse
Issue date:	10/30/1989
From:	Giannuzzi A, Riccardella P STRUCTURAL INTEGRITY ASSOCIATES, INC.
To:
Shared Package
ML19324C174	List: ML19324C173 ML19324C176
References
SIR-89-044, SIR-89-044-R02, SIR-89-44, SIR-89-44-R2, NUDOCS 8911150130
Download: ML19324C176 (18)

Text

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Report No.: SIR-89-044 .

Revision 2 l Project No.: TEco-01Q l October 30, 1989  !

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Davis-Besse Nuclear Power Station  !

HPI/ Makeup Nozzla Wald Overlay  !

Repair Contingency Plan '

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Prepared by:

Structural Integrity Associates i San Jose, CA  ;

Prepared fort  :

Toledo Edison Company Davis-Bosse Nuclear Station '

Cak darbor, OH I r

Prepared by: Ah Date! ._ Ib 30. O i Reviewed by: Date: ~

. J[ Gi ' uzz '"F '

Approved by: / su /4/I Dato: 4 38 di  !

P. C. RiccaEdelkh ' l l

I 8911150130 891200 PDR- ADOCK 0"000346 P

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TABLE OF CONTENTS  !

Section Page i i

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• INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . 1 l FRACTURE MECHANICS ANALYSIS UPDATE . . . . . . . . . . . . 2 WELD OVERLAY REPAIR DEVELOPMENT . . . . . . . . . . . . . 3 t

WELD OVERLAY PROCEDURE DEVELOPMENT AND NDE . . . . . . . . 5  ;

i REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . 6 .

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SIR-89-044, Rev. 2 i t-

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• i LIST OF FIGURES i Ficure  ;

1 ASME Section XI Allowable Flaw Depth Determination 2 Prior Allowable Flaw Size Determination (Reference 1) ,

3 Davis-Besse HPI Nozzle Reinforcement Requirements  !

4 Reinforcement Requirements as a Basis for Weld overlay Design f 5 Davis-Besse HPI Nozzle - Effect of Cracking on Nozzle  ;

Reinforcement 6 Davis-Besse HPI Nozzle - Required WOL Thickness for Nozzle r Reinforcement i Summary of Weld overlay Results 8 Finite Elcmant Model of Wald overlayed Norzle  !

(Accommodates Various WOL Thicknesses) ,

i 9 Davis-Desse HPI 11ozzle - Pressure Stresses / Weld overlay -

Effect  ;

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SIR-89-044, Rev. 2 11

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4> ASSONTRUC

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,5 HPI/ MAKEUP N0ZZLE WELD OVERLAY REPAIR CONTINGENCY PROGRAM INTRODUCTION In Reference 1, fracture mechanics analyses were performed for  !

the Davis-Besse HPI/ Makeup nozzle following the discovery of a j broken thermal sleeve and clad flaw-like indications on the l inside surface in the region of the nozzle-to-pipe knuckle. The i analyses concluded that the observed indications were the result of high cycle fatigue (thermal cycling) which resulted from the ,

cold makeup flow hitting the nozzle surface after the thermal sleeve broke. Also, these analyses established a conservhtive ASME Section XI allowable flaw size of 0.5 inches. Investigation  ;

of the actual flaws concluded that they were less than the .

cladding thickness (mt.inally 0.2 inches). A study of fley l growth using base metal preperties ovr2r to years with an intact ,

thermal sleeve showed that the flaw would not exceed thu 0.5 inch I allowable. Subsequent to plant startup after the 5th refueling  ;

outage, a plan for inspection and, if required, repair of ths l nozzle was submitted (Referance 2). This plan includes the use or weld overlay in the event thac the flaws were unexpectedly ,

deep and requiring additicnal reinforcement. It is intended to [

carry out the plan during the 6th refdeling outage. l As part of tho weld overlay design, additional fracture mechanics  ;

analysis was performed in order to determine at what flaw depth >

would weld overlay be required. This analysis indicates that the finw depth at which weld overlay is required results from ASME Section III nozzle structural reinforcement requirements, and not from brittle fracture allowable flaw depth considerations. The reason is that the Section XI allowable flaw is deeper than that which would violate the code structural reinforcement requirements. The flaw depth limit which would vjolate structural requirements was found to be 1.60 inches, whereas, for ASME Section XI brittle fracture considerations, the allowable SIR-89-044, Rev. 2 1

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ASSOCUGESINC

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'l flaw limit is greater than 3 inches or ocsentially through the original nozzle wall thickness.

The basis for the aforementioned conclusions and the resulting weld overlay design are presanted in the following sections.

1 FRACTURE MECHANICS ANALYSIS UPDATE l Figure 1 illustrates the basis for the revised Section XI allowable flaw depth. Stresses from a finite element stress [

t analysis of the nozzle were used as input to o fracture mechanics j analysis performed using the linear elastic frLeture mechanics ,

option of the pc-CRACK cemputer program (Reference 3). (Commonly i used computer sefe. ware for ASME Sect',)n XI flaw ovaluations in nucloat.- cou;onents which has been vorified shd nudited for nuclear safety-related applications) .

The stresses consirted or pressure (Figure Ib curve 1) and thermal (Figure ib curve 2) for an HPI flow transient. These '

stresses are in the hoop direction rale.r.ive to the nozzle area and are taken from section 11 of the finito element nodel (Figure la). This section is the governing orientation and location.

Each strens was curvefit utilizing a third order . polynomial to l account for the variation along the through-thickness direction.  !

A nozzle corner flaw fracture mechanics model which is directly applicable to the Davis-Besse HPI/ Makeup nozzle geometry was '

selected and used, linjan the pc-CRACK nozzle corner flaw model has been verified and found to be highly accurate (Reference 3) .

with respect to an experimental study of pressure vessels containing nozzle corner flaws. j SIR-89-044, Rev. 2 2

The ASME Section XI allowable flaw depth determination was performed using the stress intensity factor data of Figure Ic.

The material fracture toughness was assumed to be 200 ksi/G divided by a safety factor of the [16 (Figure ld curve 6) . The

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intersection of the total applied stress intensity f actor curve (pressure plus thermal) (Figure ld curve 5) and the factored fracture toughness value results in the Section XI allowable flaw d6pth for brittle fractura prevention. This yields an allowable flaw depth of >3 inches or through-wall which is considerably larger than the results reported previously in Reference 1 (Figure 2). The reason for the difference is the model utilized for the Reference 1 analysia. The model used was a single edce flawed plate which assumes that the stresses are uniform across the ecction at their inside surface value.

The mere representative nozzle corner flaw model results indicace that there is no concern .for brittic fracture and therefora the nozzle structural reinforcement requirements of ASME Section III are limiting vita e flaw depth ' Limit of 1.6 inches. The analysis supporting this limit is discussed in the following section.

WELD OVERIAY REPLIR DEVEIDPMENT l

The flaw depth at which weld overlay would be required is not dependent on brittle fracture allowable flaw size because the l Section XI allowable flaw size was determined to be larger than the nozzle wall thickness (23 inches). The point at which weld overlay would be applied is a function of the structural l reinforcement requirements of the nozzle geometry. The value of l the flaw depth at which there is a loss of structural I

reinforcement was determined using the approach set forth in ASME Section III. This requires that the material removed from the primary pressure boundary by the branch flow path be included as part of nozzle thickness. This requirement is depicted in Figure SIR-89-044, Rev. 2 3

3 as Areas. Area A g represents the pressure boundary material loss due to the branch connection and Ag+A +As represents the  ;

compensating material thickness to be included in the nozzle.

Also, the compensating material must be located within the

,L geometric limits specified by Lg and h (see Figure 3). The ASME  ;

Section III equations that relate the aforementioned nozzle ,

reinforcement areas to nozzle dimensions are listed in Figure 3.

Figure 4 lists the same equations modified to account for loss of reinforcement due to the effect of nozzle corner flaw depth (r c) . >

Using these equations, with the limits of L 3 and g , the thickness of the weld overlay (t.o1) was determined as a function of r c . IlQTE: The area created by re is considered to be a 360' ,

" flawed zone" that does not contribute to the nozzle structural reinforcement. The " flawed zone" is designed to envelope any flaw or combinatien of Llaws.

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The results utilizing the Davis-Besse HPI/ makeup nozzle actual dimensions are presented in Figures 5 and 6. Figure 5 presents the excess (or deficient) nozzle reinforcement as a function of the cracked zone radius (r ). It is seen from this figure for an e -

uncracked nozzle (rc =0), that there is about 5 square inches of excess reinforcement, which is adequate to compensate for a

" flawed zone" radius up to about 1.6 inches. For deeper flaws, additional reinforcement would need to be added in the form of a ,

wold overlay repair. The required weld overlay repair thickness as a function of " flawed zone" radius is illuritrated in Figure 6.  :

This figure assumes that the weld overlay is applied over the i entire length of the limits of reinforcement in the pipe and nozzle directions, as illustrated schematically in Figure 4. The resulting weld overlay dimensions for several " flawed zone" radii are tabulated in Figure 7.

To evaluate the effect of weld overlay on the Section XI allowable flaw size, the nozzle finite element model was modified to include the weld overlay (see Figure 8) . This model was used to evaluate pressure stresses as a function of nozzle wall SIR-89-044, Rev. 2 4

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I thickness for various weld overlay thicknesses. Thermal stresses j were not analyzed because the weld overlay will not adversely l affect them. The reason is that the additional thickness will  !

i not significantly change the temperature gradients through the wall. The resulting pressure stresses are shown on Figure 9.

The results show a lower pressure stress throughout the vall thickness for thicker weld overlays. This has the effect of increasing the allowab1'e flaw size, thus further decreasing the i concern for brittle fracture.

i WELD OVERLAY PROCEDURE DEVELOPMENT AND NDE Tho v?ld overlay will be applied using a qualified precedure for automatic gas tungsten are welding (GTAW). The wold metal will be a carbon steel that matchos tne nozzle base metal. Pre- and g post-weld heat treatment will be applied in accordance with ASME l Code requirements. The hert treatment will relieve the residual stresses that eculd be induced by the weld overlay process. The I weld procedure qualification will include the code requirements '

for tensile, bend and toughness testing.

The weld overlay deposit will be inspected by NDE in order to '

qualify the repair for the subsequent operating cycle. The NDr ,

will involve straight beam UT for bonding of the overlay to the nozzle surface and angle beam for volumetric soundness. The UT inspection will be manual, and will be qualified on standard ASME Section XI calibration blocks. During the outage following that in which the overlay is applied, an examination using an automated, enhanced UT process, capable of detecting the original flaw (s), will be performed. The goal of this inspection will be i to quality the weld overlay as a long term repair in accordance with ASME Section XI, by demonstrating no growth of the flaw (s) in the nozzle base metal or into the overlay . weldment. The enhanced UT will be qualified utilizing a weld overlaid nozzle ,

mockup during the fuel cycle following veld overlay application.

SIR-89-044, Rev. 2 5

I REFERENCES I I

1. Toledo Edison letter to NRC dated September 4, 1988, "High l Pressure Injection / Makeup Nozzle and Thermal Sleeve," Serial No. 1580.

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2. Toledo Edison letter to NRC dated June 19, 1989, "High l Pressure Injection / Makeup Nozzle and Thermal Sleeve," Serial l No. 1664. ,

3. pc-CRACK Fracture Mechanics Computer Software - Users Manual," Version 2.0, Structural Integrity Associates, 1989.  !

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l LIMITS OF REINFORCEMENT  ;

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Wald Overlay Design l

SIR-89-044, Rev. 2 10  ; IA g -

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l WOL WOL i Length Length l Required Along WOL Lenoth Alona Pine Along NZ J Crack Thick. Nozzle From NZ g, From NZ O.D. From Pipe Radius (tyny) (L'N) (L'A) (Q) 0.D. (Lyg) i 2.0" .21" 1.946" 5.92" 2.73" 1.64"  ;

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