ML20215B676

Evaluation & Analysis of Point Beach Nuclear Plant Unit 1, Reactor Vessel Safety Injection Nozzle-to-Shell Weld Indication

ML20215B676
Person / Time
Site:	Point Beach
Issue date:	06/02/1987
From:	WISCONSIN ELECTRIC POWER CO.
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NUDOCS 8706170402
Download: ML20215B676 (40)

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EVALUATION AND' ANALYSIS OF POINT' BEACH-NUCLEAR PLANT, UNIT 1, REACTOR VESSEL SAFETY INJECTION

> ' NOZZLE-TO-SHELL WELD INDICATION 1

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1.01 BACKGROUND.

During the second 10-year inservice inspection of the Unit 1 Reactor Vesse1~,

one code-rejectable. indication was reported. It was detected with'the 10 degree, 2.25 MHZ retracted longitudinal wave ultrasonic transducer and the 0 1

degree, 2.25 MHZ longitudinal wave ultrasonic-transducer. The location and l volumetric nature of this indication in the weld material exenplified a series i of small slag. inclusions or voids. An evaluation of this indication (using 505 1 1

DAC sizing with beam spread resolution) to the acceptance standards in Table L

IWB-3512-1 of the ASME Boiler and Pressure Vessel Code Section XI, 1977 Edition

.through the Summer .1979 Addenda, resulted in an unacceptable indication by I examination.

'Using the rules of IWB-3600 and the guidelines of Appendix A from the above ASME Code Section XI, the indication is acceptable by evaluation with-andwithout beam spread resolution. The following sections discuss the examination technique used to locate, size, characterize, and evaluate the indication as well as the tracture mechanics evaluation of the indication.

2.0 ULTRASONIC EXAMINATION i Ultrasonic examination of ASME Code Class 1 Reactor Vessels is corducted in accordance with the rules of the ASME Code Section XI and Regulatory Guide 1.150. The 1977 Edition through Stanmer 1979 Addenda of Section XI requires Class 1 vessel welds in territic material greater than two (2) inches in thickness to be ultrasonically examined in accordance with Article 4 of the

' ASME Code Section V,- which provides acceptable techniques for distance

- anplitude correction (DAC), beam spread measurement, and indication dimensioning. Regulatory Guide 1.150 provides additional criteria tor instrument performance checks, calibration of equipment, near-surf ace examinations, beam profile, beam angles used for scanning the weld netal interf ace, and indication sizing in order to produce reliable flaw detection and evaluation.  :

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Examination of the reactor vessel was conducted in two phases; detection of indications and evaluation of results. During the April 1987 inservice inspection detection phase, the Safety In,)ection nozzle to shell weld at a vessel azimuth of 288.5 degrees was scanned from the nozzle bore using two separate search units. Based upon size and configuration of the nozzle, the l optimum transducer arrangement was determined to be a 0- degree, 2.25 MHZ l longitudinal wave (O L) and a 10 degree, 2.25 MHZ retracted. longitudinal wave (10 RL). Prior to examination, the ultrasonic instrument was calibrated by measuring ultrasonic responses from known ref erence reflectors machined into )

the basic calibration block and constructing a distance amplitude correction ,

(DAC) curve. The DAC curve was the primary ref erence level for recording  !

reflectors. Flaw indications were detected by threshold response signals  !

required to be recorded by criteria given in Section XI using a scanning j sensitivity of twice the primary reference level, and by interpreting the characteristics of the signals.

After the detection phase was complete, the indication that exceeded the recording criteria established by the ASME Code Section XI was evaluated to

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determine the best-fit diemnsions and gecnetric character 2stics.

3 0. INDICATION SIZING AND CHARACTERIZING It has been generally accepted by the ASME Code committee, the nondestructive testing industry, and the NRC statt that ultrasonic-based sizing procedures can magnify the dimensions of reflectors at or near the outside diameter (0.D.) of l a relatively thick-walled vessel when performing examinations from the inside surface. The amplitude of the return signal from a reflector depends upon many i

factors, including the ultrasonic instrument, mechanized equipment tolerances, transducer size, transducer frequency, distance to the Indication and l geometry. Considering these factors, the resolution ot' the beam spread yielded the sizing results described in Table 3-1. A detailed discussion of the resolution of the ultrasonic beam spread is provided in Appendix A. Figure 3-1 shows the location of the indication in the SI nozzle to shell Weld material.

Note the proximity of the indication to the root or the weld.

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Two 0.25 inch flat bottom boles (FBH) were drilled in the SI nozzle to shell weld calibration block at the appropriate netal path and angle associated with the two transducers used in the examination. Utilizing the sare transducers and ultrasonics instrunents, these FBH gave the same amplitude as the indication. Thus, the area presented by the FBH of 0.049 square inches is equivalent to the area presented by the indication. Considering the same flaw length,1 = 2.25 inches, the flaw depth, 2a would be approximately 0.022 inches. This results in an insignificant throughwall dimension and a/t ratio.

The indication was characterized as being a series of slag inclusions generated in the first several passes of the initial welding process. The signal amplitude presentation shows several peaks, suggesting the indication is actually a series of smaller indications. This is consistent with the nature of slag inclusions or voids. The weld end contiguration is shown in Figure 3-1. The depth of the weld root below the vessel inside surf ace is approximately 6.5" and the weld end preparation angle is 10 degrees. This gives a vessel surf ace opening for welder access of 2.25": This significantly impacts the manual stick electrode welding process used and ba:k-grinding process used in the deep groove of this nozzle to shell weld. Welds of this configuration have demonstrated an above average anount of small slag inclusions and voids in the heavy vessel industries.

1 Initial review of the construction radiographs does not show the indication in this weld, but based upon the orientation and material thickness in this location, this finding is not surprising.

Upon review of the previous 10-year inservice inspection of the Reactor vessel in 1976, this indication was observed but mis-called as transducer crosstalk.

The 1976 inspection does not provide enough raw information to meaningfully size the indication for comparison, other than location. Table 3-2 gives the information that could be correlated.

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TABLE 3-2: -SI Nozzle at 288 5 Exam Results Comparison

'Ind. No. }DA_C ' Nozzle Asimuth Me'tal Path Depth Below SbflLUp) Surf ace _

I 3 1987' (10 den RL/2.25 MHZ) 1 1005 26 6.0" 4 7'- 6.B" 1776 (10 den RL/2.25 MHZ). .j 150% 33 5.7" 5.0" j

'_1987 (0 den L/2.25 MHZ) l 1005 26 6.0" 4 7 - 6.B"

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1976 (O Den ~L/2.25 MiZ) 2005 35 5.6" 5.0" Further review of the Unit 1. Reactor Vessel preservice. inspection yielded no recordable indication at this location..

4.0 FRACTURE ANALYSIS There are two alternative sets of acceptance criteria for continued serviced-without repair in paragraph IWB-3600 of ASME Case Section XI:

1. Acceptance. criteria based on flaw size (IWB-3611)

2. Acceptance criteria based on stress intensity factor (IWB-3612)

Both criteria are comparable in accuracy for thick sections, and the more beneficial criteria has been used for evaluating the indication in the safety injection nozzle-to vessel weld.

j To determine the allowable flaw sizes in a weld, finite element analysis l methods were used, and the actual geometry modeled. The geometry is shown in Figure 4-1. j j

All applicable plant transients were analyzed to select the most severe stress profiles through the thickness ot the weld. The transients are listed in Table 4-1. In addition to the design transients, a low temperature overpressure transient was analyzed. Because such a transient would only occur as a result l of multiple tailures, it was classified as a faulted condition. The actual stress protiles were then approximated by third order polynomals and used for calculating the stress intensity tactor (K )yfor various crack sizes and aspect ratios.

The governing transient for all the normal, upset and test conditions was found to be the loss of flow transient, while for emergency and taulted conditions it was the large steamline break tansient. Since all the normal and upset conditions occur at relatively high temperature, the limiting transient is easily determined as that which has the highest inside surf ace stress. The selection of the limiting emergency and taulted transient is more ditricult, because the temperature is mch lower for these events, and the combination of pressure and thermal transients mst be considered. For a location Were irradiation damage is negligible, as is the case for the indication ot interest, the governing transient will be that with the highest stress, combined with the lowest temperature. For the safety injection nozzle, analyses were carried out for large and small LOCA and large and small steamline break, with the governing transient being the large LOCA.

The stress intensity factor was calculated using the expression of Shah and Kobayashi L1J, after representing the stress distribution as a thirti order polynomial. This stress intensity tactor expression has been shown to be applicable to vessels by the recent work of Lee and Bamford L2J.

The resulting K y's are compared to tracture toughness values (Kla) and  ;

KIC). Critical 1 law sizes are then obtained.

The satety injection' nozzles are located. in the nozzle'shell with the same

< centerline as the inlet and outlet nozzles, shown in Figure 4-2. As may be seen in Figure .4-3,- these nozzles are located far from the core region, and so the irradiation damage is negligible. This combined with the location of the indication near the center of the wall thickness led to the conclusion that irradiation damage could be neglected. The other key information necessary to determine the fracture toughness is the value of RTg. For the Pt. Beach Unit 1 Reactor Vessel the following properties are available:

Heat RT ET SI Nozzle EV 8261 60F Nozzle Shell. 122P237VA-1 50F Nozzle to Shell Weld 0F The RTg values were determined using the estimation procedures of reference L3J. The highest value, 60F was used in the analysis, and the upper sheit

toughness was 200 ksi 41n, since no irradiation ettects were considered.

The tinal step in the flaw evaluation process involves calculation of crack growth due to tatigue loading. All anticipated plant transients are utilized in determining the resulting flaw size for a specified period of time. This was done-for 10, 20, 30 and 40 year intervals, using the fbli set of normal, upset and test transients in Table 4-1. The ASME reterence law for air.

environments was used, and fatigue crack growth was f ound to be negligible.

In addition to satisfying the tracture criteria, it is required that the primary stress limits of Section III paragraph NC-3000 be satisfied. A local area reduction of pressure retaining membrane must be used, equal to the area of the indication; and the stresses increased to retlect the smaller cross section. For this location, an allowable penetration depth ot 64 percent of the wall was found. Therefore the tracture results are governing, in determining the allowable flaw size.

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1 Using the fracture analysis procedures and material properties dicussed above, a flaw evaluation chart was constructed f or the nozzle to vessel weld region. i The procedures used to construct this chart has been described in detail in the technical basis document for the Pt Beach Flaw Evaluation Handbook L4J, and the applicable portion of that document is excerpted as Appendix B of this report. J J

The flaw evaluation chart applicable to the safety injection nozzle to vessel weld has been presented in Figure 4-4, and the indication has been plotted on the chart. Both the zero and 10 degree inspection results have been plotted, It is clear from Figure 4-4 that the indication using the data of Table 3-1. ,

is acceptable by a comfortable margin.

For additional information, the stress intensity factor curves as a ibnction of flaw depth for indications of the appropriate shape have been plotted in Figure 4-5 and 4-6, for normal-upset-test, and emergency-faulted conditions respectively. The indication has also been plotted on these curves, so that These figures show that the indication available margins are clearly seen.

would be acceptable even if its dimensions before beam spread corrections were used la = 1.2, 1 = 2.5, S = 4.7J.

To ensure that all possible operational transients were considered, a low Since a transient of temperature overpressure transient was also evaluated.

this nature requires a tailure of the overpressure protection systen, along with other failures, its likelihood is low enough for classification as a faulted event. A presure of 1500 psi was used, at a temperature of 150 F, and the results show the maxinum value of stress intensity factor to be 18.2 kai nii. The allowable, cetermined from the tracture toughness KIC ; divided by 2 was calculated to be 118.8 ksi dn.

5.0 CONCLUSION

S f Based upon the character, location, and size of this indication, it is not a f service-induced flaw and therefore not expected to grow over the remaining lite (

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TABLE 4-1

SUMMARY

OF REACTOR VESSEL TRANSIENTS q l

NUMBER OF OCCURRENCES USED IN THE .)

NUMBER TRANSIENT IDENTIFICATION SPECIFIED ANALYSIS Normal Conditions 1 Heatup and Cooldown at 100*F/hr 1

'(pressurizer cooldown 200*F/hr) 200 200 2 Load Follow Cycles (Unit loading and unloading at.

5% of full power / min) 14600 14600*

s 3 Step load increase and decrease of 10% of full power 2000 2000 4 Large step load decrease, with steam dump 200 200 6

5 Steady state fluctuations Infinite 10 Upset Conditions 6 Loss of load, without immediate turbine 80 80 or reactor trip 7 Lossofpower(blackoutwithnatural circulation in the Reactor Coolant System 40 40 8 -Loss of flow (partial loss of flow, one pumponly) 80 80 9 Reactor trip from full power 400 400 Faulted Conditions 10 LargeLossofCoolantAccident(LOCA) 1 1 11 Large Steam Line Break (LSB) (other transients described in section 4) 1 1 f Test Conditions I

Turbine roll test 10 10

( 12 13 Primary Side Hydrostatic test conditions 50 50 Cold Hydrostatic test 5 5 14

• 6000 of these transients were used in the analysis of the outlet nozzle region,' based on actual documented plant performance, for both Unit 1 and 2.

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1 The fractura mechanics analysis of the indication was performed consistent with )

. the metnod provided in Appendix A of the 1977 Edition through Summary 1979 )

l I1 Addenda of Section XI. The transients considered in the analysis bound all service, test, and accident conditions including the special case of the low f temperature overpressure event. Based upon this fracture mechanics analysis, this indication is stable under the loading conditions considered and poses no threat to the continued safe operation of the reactor vessel.

6.0 REFERENCES

i

1. Shah, R.C and Kobayashi, A.S. , " Stress Intensity Factor for an Elliptical !

Crack Under Arbitrary Loading", Engineering Fracture Mechanics, Vol. 3, 1981, pp. 71-96.

2. Lee, Y.S. and Bamford, W.H. , " Stress Intensity Factor Solutions for a  !

Longitudinal Buried Elliptical Flaw in a Cylincer Under Arbitrary Loads",

presented at ASME Pressure Vessel and Piping Conterence, Portland Oregon, June 1983 Paper 83-PVP-92.

3 USNRC Standard Review Plan, NUREG 0800.

4. Bamford, W.H., et. al. Background and Technical Basis for the Handbock on Flaw Evaluation f or the Point Beach Units 1 and 2 Reactor Vessels" Westinghouse Electric WCAP 11498, April 1987

m Y

L ..-

APPENDIX A' RESOLUTION-OF THE ULTRASONIC BEAM SPREAD l' k FOR THE SAFETY INJECTION NOZZLE-TO-SHELL WELD INDICATION

.In.an effort to' determine the actual size of the reflectors in

'the' safety-injection nozzle-to-shell weld, a test reflector was designedito simulate the reflected signal from indications in-

.the Point Beach safety injection nozzles. The indications were detected with'two transducers directed radially outward from ,

-the nozzle bore approximately perpendicular to the centerline

'of.theiweld. The two beams (10 and 0 degrees) were calibrated on side-drilled holes placed at. varying depths, which provided a distancec amplitude correction (DAC) curve.that covered the E area of interest (weld and base metal on either' side of the weld). 1 Two flat-bottomed holes (FBH) were drilled in the cal'ibration

' blocks with the bottom of the hole perpendicular to the beams.

used to detect the indications in the nozzle weld. These-holes.

were used to simulate the postulated slag-like reflectors. The maximum reflector peak transducer position was found~

corresponding to'the center of the FBH.. The amplitude was >

noted to be the'same as that for the indication. The

~

transducer was moved axially to achieve a 50 percentiDAC in-both directions!from the peak amplitude. At the measured metal path, the transducer beam width was' measured to be the i-

. perpendicular distance between the 50 percent DAC curves (see i Figure A-1). :The' beam spread corrections'were:made based on  !

subtracting the flat-bottomed hole diameter from the total axial transducer movement on the inside surface of the calibration block. This correction from the beam spread measurements was then subtracted from the indication axial or through wall

-dimension noted during.the examinations. Using the corrected sizing parameters, the safety injection nozzle-to-shell weld indication was still'ASME code-rejectable in size, requiring a fracture mechanics analysis for acceptability. j i

a Figure A-1 Axial Beam Spread 100 T ransducer -

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b i APPENDIX B i

i SECTION 6 EMBEDDED FLAW EVALUATION 6.1 EMBEDDED VS. SURFACE FLAWS- .,

According to IWA-3300 of the ASME Code section XI, a flaw is defined as embedded, as shown in figure 6-1, whenever,

.S 3 a(for editions prior to 1980]

or S 3 0.4 a [For editions of 1980 and thereafter) where  ;

-S - the minimum distance from the. flaw edge to the' nearest vessel wall surface (clad-ba'se metal interface for flaws near the inside of the vessel) a the embedded flaw depth, (defined as the semi-minor axis of the elliptical flaw.)

Code Editions'of 1980 and Later The surface proximity rules were liberalized with the 1980 code, allowing flaws as near the surface as four-tenths their width to be considered embedde'd. This change resulted from the finding that.the original proximity rules'had been more restrictive for near-surface embedded flaws than for known surface flaws, which is clearly not technically correct. Specifically, the criterion for a flaw to be considered embedded was changed to S > 0.4 a, so I

substituting into the definition for 6 we now find:

ans.ma.mmuo 6-1

y 7. :

o

. La' = 6.- Sl

, 6 . > 1.4 a Therefore, the limit for a flaw to be considered embedded is,a,= 0.714 6 .,

for code editions of 1980 and thereafter. This more accurate criterion has be'en used throughout this handbook,.and is recommended for'all inspections,

regardless.of the_ edition of the code which is used for the inspection.

4 A! flaw lying within the embedded flaw. domain is to be evaluated by the embedded flaw evaluation charts generated in this section of the handbook.- On.

. the .other. hand, a flaw lying beyond;this domain should be evaluated as 'a surface flaw using the charts developed in section 5 of the handbook instead'.

The demarcation: lines between the two domain's are shown graphically in figure 6-3, for both earlier and'later code editions.

i In other.words, for any flaw indication detected by inservice inspection, the first step of evaluation is to define which category the flaw actually belongs to, then, choose the appropriate charts for evaluation.

6.2:. CODE CRITERIA As. mentioned in-section 1, the criteria used for the safe end and all the ,

g embedded flaws'are of IWB-3612 of Code section XI. Namely,

'K K g$dForNormalConditions(upset &testconditionsinclusive) q l

K K g5hForFaultedConditions(EmergencyConditionsinclusive)  ;

j

(

me. mue -

6-2

S 4

where. <

i Ky =' The maximum applied stress intensity factor for the flaw-size af to which a detected flaw will grow, during the ,

conditions under consideration. .,

K,y

= Fracture toughness based on crack arrest for the corresponding crack tip temperature.

'K =- Fracture toughness based on fracture initiation'for the j Ic 1 corresponding crack tip temperature.

The above two criteria must be met simultaneously. In this handbook only the most limiting results have been used as the basis of the flaw evaluation l charts.

6.3 BASIC DATA.

In view of the criteria based on stress intensity factor, three basic groups of data are needed for construction of embedded flaw evaluation charts. They' l are: K Ic, Ky ,, and Ky , respectively. The units used herein for all these three parameters are ksi / in.

K Ic and Ky , are the initiation and arrest fracture toughness (respectively) of the vessel material at which the flaw is located. They can be calculated by formulae:

K yc =.33.2 + 2.806 exp[.02(T-RTNOT + 100*F)] (6-1) and Ky , = 26.8 + 1.233 exp[.01 6(T-RTNDT+160*F)] (6-2) -]

Ky is the maximum stress intensity factor for the embedded flaw of interest. The methods used for determining the stress intensity factors for embedded flaws have been referenced in section 2. )

1 mwom. ammo 6-3

i Notice that both K gg and Kg , are a function of crack tip temperature T, and the material property of RTNDT at the tip of the flaw. The upper shelf  ;

fracture toughness of the reactor vessel steel is assumed to be 200 ksi/in in all regions except the beltline, where it is assumed to be 100 ksi / in. -

Ky n ed in the determination of the flaw evaluation charts is the maximum stress intensity factor of the embedded flaw under evaluation. It is important to note that the flaw size used for the calculation of Kg is not the flaw size detected by inservice inspection. Instead, it is the calculated  !

flaw size which will have grown from the flaw size detected by inservice inspection. That means that the embedded flaw size used for the calculation of Kyhad to be determined by using fatigue crack growth results, similar to  ;

the approach used for surface flaw evaluation, as illustrated in the previous ,

section.

However, unlike the surface flaw case, the fatigue crack growth for an embedded flaw (even after 40 years of service life) is very small in compari-son with that of a surface flaw with the same initial depth. Consequently, in the handbook evaluations, the detected flaw size has been used for evaluation by the charts without any appreciable error.* This simplifies the evaluation procedure without sac'ificing the accuracy of the results. A detailed ,

justification of this conclusion is provided in the next section.

6.4 FATIGUE CRACK GROWTH FOR EMBEDDED FLAWS The environment of an embedded flaw is considered to be inert, or air. The crack growth rate for air environment is far smaller than that of the water environment, to which the surface flaw is conservatively considered to be l exposed. Consequently, the fatigue crack growth for an embedded flaw must be l far smaller than that of an inside surface flaw (of the same size and under f f

• This conclusion holds for the range of flaw sizes acceptable by the rules of section XI, IWB-3600. It would not necessarily hold for very large flaws of the order of 50 percent of the vessel wall thickness.

l w .mn.mus" 6-4 )

I

1. '9  !

-)

r the same transient conditions). Numerkally, the fatigue crack growth of an J embedded flaw 'js 50. low that the differens.^ between thd biitial flaw depth and )

its final crad depth is negligible. l

'  ? ,

y y ,

' l

'r Thb ongineerir.g judgment has been da'taonstrated by an illustrative example, as V' '

follows: .

Evmph The beltline region of the Poini Beach teactor vessels was used as a demonstration. The crack growth results for axial inside surface flaws are as ,

follod, as also shown in appendix B. These flaws were assumed exposed to the

~

water environnunt.

Postulat4.

IrdUal Crack Depth Crack Depth (in.) After Year a

10- 20 30 40

.125 .126 .127 .128 p .125-

,P .250 .253 .256 .258 .261

.500 .512 .521 .531 .542

.750 .773 .,795 .817 .841 1.000 1.041 1.079 1.120 1.165

~

5 hilar crack growth analysis was performed using the embedded flaw case the same set of transients

• and the number of cycles

• as the surface flaw run, the results are as below. The air crack growth reference law was used.

~

• As specified in table 2-1.

mwom.mmuo 6-5

4

• Initial Crack Depth Cr' ack Depth (in.) Af ter Year 10 20 30 40

.125 .125 .125 .125 .125 ,

.250 .250 .250 .250 .250

.500 .500 .500 .500 .500

.750 .750 .750 .750 .750 1.000 1.000 1.001 1.001 1.001

- In comparing the results of the two types of flaws under the same service conditions, it is seen that the final crack growth for an embedded flaw is less than 1% of that for a surface flaw under the same operating conditions as tabulated below:

, Postulated Final Crack Depth (in) Crack Growth for Initial Crack After 40 Years Embedded Flaws, Depth, (in) Surface Flaws Embedded Flaws in (%)

.125 .12799 .12503 1.0%

.250 .26123 .25010 .9%

.500 .54241 .50037 .9%

.750 .84147 .75080 .8%

1.000 1.16496 1.00143 .8%

In conclusion: in the construction of the evaluation charts for the embedded

. flaws, the accuracy of the charts would not be impaired using the flaw size ,

found by inservice inspection directly.

6.5 TYPICAL EMBEDDED FLAW EVALUATION CHART The details of the procedures for the construction of an embedded flaw evaluation chart are provided in the next section.

~

nes.mus.musuo 6-6

In this section, instructions for reading a chart are provided by going through a-typical chart, figure 6-2, step by step. This would help the users to become familiar with the characteristics of each part of the chart, and make it easier to apply. This example utilizes the surface / embedded flaw demarkation criteria after the 1980 code. ,

Following are the highlights of a typical embedded flaw evaluation chart.

(Refer to figures 6-2 and 6-3). I i

1. -The absicissa of the' chart in figure 6-2 represents the flaw depth a,  ;

cf the embedded flaw.

2. As defined by code, the embedded flaws with a depth less than 3 a,= 0.714 6 should be considered as embedded flaws. Any embedded flaws beyond the domain of a,= 0.714 6, should be evaluated by means of surface flaw charts instead. l

3. A key parameter for evaluating an embedded flaw is 6, the distance between the flaw centerline and the nearest surface of the v3ssel wall (clad-base metal interface for the inside surface).

Arangeof6betweenftandfthavebeenconsideredin constructing figure 6-2.

4. Foreachspecificvalueof6,suchasht,ht,ft,etc.,afamilyof curves were plotted for a range of aspect ratios *, for 3:1 through 10:1. This corresponds to a/t values ranging from 0.167 to 0.050.

For any specific flaw depth a at the abscissa, a corresponding value Kg at the ordinate can be found in figure 6-2, for any distance to the surface, 6.

l l

l 2363s/0365s/042487.10 g.J l

[1 ,

5. The range of aspect ratios from 3:1 to 10:1 was chosen to encompass the range of- flaws which might be detected. Within this range, interpolation can be used for any other aspect ratio. Use the 3:1' curve as a lower bound and the 10:1 curve as an upper bound.  ;

6. In this' specific chart, the code acceptance limit line was .

K d = j[ = 63.3 ksi in because governing condition was an upset condition, and the. operating temperature of'the transient was over 500*F across the wall thickness at all times. The shelf value of 200 ksi / in'for Kj, was used.

• Note that aspect ratio AR = 2a/t I

7. The intersection of the Ky curve with the code acceptance limit line

'is the maximum flaw size acceptable by code for the specific curve'. .

8. In view of figure 6-2, it is seen that only the curves for 6 = ft intersect with the code. acceptance limit line. That means that, up to a distance. of 6 = ht (= 1.710"), all embedded flaws are acceptable by code criterion so long as their depth is within the domain of a, = 0.714 6. On the other hand, for flaws located at a distanceupto6=kt(=2.28"),themaximumacceptableflaw sizes for various aspect ratios are less than the domain of a g = .714 6.

Therefore, for flaws centered at this depth, separate allowable flaw lines are produced in the evaluation charts, as shown.in figure 6-3.

9. The maximum acceptable flaw size can be found from the chart by determining the abscissa of the intersection points. Namely, for 6 = 0.25 t, 1

i I

a m ,m m ,m m u n -  !

6-8

Aspect Ratio Maximum Acceptable of the Flaw a/t Flaw Size (in)

.10:1 'O.050 .96 6:1 0.083 .99 (< ao= 1.145) 3:1 0.167- 1.13

10. The maximum acceptable embedded flaw size for 6. =.ft hr.s been depicted in figure 6-3. This simpler flaw evaluatio'n chart, described in the following paragraph, is the type included in the handbook, as may be seen in- appendix A.

These; embedded flaw evaluation charts, constructed for various locations of the reactor. vessel, are presented in appendix A for each region:to.be inspected.

6.6- PROCEDURES FOR THE CONSTRUCTION OF EMBEDDED FLAW EVALUATION CHARTS A real example was used in this section to show how an embedded flaw evaluation chart was constructed step by step as follows:

' Example To construct an embedded flaw evaluation chart for longitudinal. flaws at the inlet nozzle to shell weld. The large LOCA was determined to be the governing condition for this example.

Step 1.

Calculate K ic for various distances underneath the inside vessel wall surface (clad-base metal interface) (in). The procedures of the calculation are as follows: ,

l l

1 i

f mwom.mmuo 6-9 1

+

p- s j

)

o Plot the temperature across the wall thickness'during the worst time step (100.sec.) of the transient LOCA, as shown in figure 6-4.

o. Calculate the corresponding K Ic by the formula given in equation (6-1). The values of RINDT at various 6 locations were also  ;,

]

determined. 1 l

K o

Calculatethevaluesofh.

Step 2 l

l Calculate Ky -values for embedded flaws of various sizes, various aspect ratios, and at various distances underneath the surface. In total, 72 cases ]

were analyzed by closed form stress intensity factor expressions [14].

The 72 analyzed cases were tabulated in table 6-1.

Step 3 The Ky results of the 72 cases were plotted in figure 6-4. These curves were combined into one single plot as the final chart, as shown in figure 6-2.

K Thecodeacceptancelimitof$wasplottedonallthesefiguresasa guideline for evaluation.

Step 4 Determine-the maximum acceptable flaw size:

am.mm.mmmo 6-10 i I

4 The basic concept of the evaluation is that the part of the curves under the K

- hlineareacceptablebythecodecriteria. Therefore, the intersection K

of a curveh with the indicates the maximum flaw depth acceptable by the ,

L code criteria.

J ,

(. The acceptable maximum flaw sizes for various distances of flaws beneath the vessel surface, 6, were plotted as shown in figure 6-11, which is the final

- flaw evaluation chart. By examining figure 6-7 for instance, for a flaw  ;

( located at 6 = jt with an aspect ratio of 3:1, the maximum flaw size acceptable is .50". For an aspect ratio of 10:1, a maximum flaw depth of .42" is acceptable.

The above four steps have completely described the procedures of the construction of an embedded flaw evaluation chart for longitudinal flaws at the inlet nozzle to shell weld.

i The basic concept for the interpretation of the curves in a typical evaluation chart is that any flaw size which lies on the curve above the code acceptance I

! limit line is not acceptable for continued service without repair. The intersection of a curve with the code acceptance limit line is therefore, the l maximum acceptable flaw size for that particular case.

6.7 COMPARISON OF EMBEDDED FLAW CHARTS WITH ACCEPTANCE STANDARDS OF IWB-3500 The handbook charts for embedded flaw do not show the acceptance standards of section XI, as the surface flaw charts do. Therefore, it is not clear from l the charts themselves how much is gained from the analysis process over the standards tables contained in IWB-3500. Such a comparison cannot be made l

l l

l l

l I

l l

l' am.mn.mmua -

6-11

directly on the embedded flaw handbook charts, because the charts are applicable for a full range of sizes, shapes and locations. The purpose of this section is to provide such comparisons, and to discuss the results of  ;

those comparisons.

The first example will be for the inlet nozzle to shell weld, whose handbook chart is provided in the appendix, and also in figure 6-2. The handbook chart values have been compared with the acceptance standards tables in figure 6-5.

In this figure the values from table IWB-3510 have been plotted as the base curve, and the limit curves for embedded flaws justified by analysis are shown as the other lines. It can be seen that the range of embedded flaw shapes and depths justifiable by analysis is related to the flaws location within the wall. The deeper the indication, the more benefit is obtained from the analysis.

Another example, which is applicable to all the locations where there are no separate acceptance limit lines for different flaw shapes (a/t), is shown in figure 6-6. This example is applicable to the cases where all flaws which are embedded are acceptable, up to a depth of 2a/t = 0.25. Again it can be seen that the advantage gained by use of the analysis is greater for flaws located further from the inside surface. The largest allowable flaw shown here is centered at one quarter the wall thickness from the surface. Note that the allowable depth for this type of embedded flaw is a/t = 0.125, or a total flaw width (2a/t) equal to 25 percent of the wall thickness. Carrying the calculations further would result in an allowable flaw depth for a mid-wall flaw (6 = 1/2t) equal to 50 percent of the wall thickness, but it is clearly not prudent to allow flaws of this size to remain. Therefore, the allowable flaw depths for embedded flaws have been limited to 25 percent of the wall thickness in total depth, and the upper curve of figure 6-6 has been labelled accordingly.

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} a s M .x

. .~, ,

w

^ S m g w m e fs

, '

• O  %

"g <.a's a ,1 F M r- O-y4 -

y *o

- p w-4 f a> >

es M _4 m $ -tt N L.o co-n dam .

4 00 o

m@r y a o  %./ 2 V U v N/

d. 3 E

6

~

6-13 i

i

- 1 SURFACE- s N_

\

\

\

\

\

\ \

.j

.J __

/

/

/

l l

/ i a0= the maximum embedded flaw size

/ (in depth direction) allowable {

EMBEDDED

/

/ per ASME XI*

S = the corresponding minimum depth j

0 FLAW of an embedded flaw (less than DOMAIN which it must be considered a a=a-o - surface flaw) a, FOR ALL EMBEDDED FLAWS:

~

• NOTE: If a > a , the flaw must be asa 0 $ charactefized as a surface flaw, with depth = a + 6.

Figure 6-1. Embedded vs. Surface Flaw smummno 6-14

t I_

a-w x J* $ g r

w t

eqq ., jj ,,

g'  ;

a m * \v1 '

i a u d,o -

t 3. N N

4 E t  :

~

c Q

o.Sf/'I = *O Q Fm a c # i S M4 u s . .

o ..

c d %L -

g w

w -

a m 8 m

8  ?.

_S

=  : - _.

_ __ __ s e  ;, a sso = *o g

$,9e -

? 'E '.

so -

v  % g- ..

a R. g .c u

e- o.

W c e o w

8 -

G

=

4 ,e c

z - - d = ,

8' -

- as = o w iw g - N.p h. ow

~ P- - . ,

[* d  %$ $ d  !

I S n  :. g -g w 6-- E -

. l

@ E 3 I C f w

w pi a

E >

so.  :

- L

>- C W

• =* 5 =. Y .

m- .u ,m.

EM Pam 1 W .M d O

-u o M Cz'

\'s N s

N f mo @S gg y

.M6- <

D C

Q

'. Q

=

L mE D

b- 4 k 4 ,

N -

[ -

6-15

4 i

i i

i SURFACE / EMBEDDED - l FLAW DEMARCATION LINE 0.13 . . _ . 8

ii EMSEDDED FLAW. . . .I.

~ *i.. .-..

1. it' E.. ild3i! Y [.. .liii II . . . . . . . .... _ FLAWS WITH 7

.; cowrioV..R., . . A..r.io..n,3.. . . .. . . .. . .

= _ ;.. . . ,..9.. 3., .%..

t;= . .

ABOVE THIS LINE ARE 0.12 ==.... p %m .=.af.:a==t:- --- =- ==-.. =-= :-

u.

-. na ,, =. :..

=- -

.; . .c =-: = NOT ALLOWABLE

'-g.- ..  ;.=~ =..

~ ~ 3~.g . ,,g g."'

e. q :. .

g.q .7 "'gq.g: ,,,. . . . g --~

=  : -- - - " -,' . ' ~-

0.11 -;='--="= ' = "n:=::= - ..:=: = = : =: -muj p=n.- = ne

n. . . u'. ' _

= .:  : == -  : d

,===:.. - :== = .. : -..: .= :--

,  ::  :-u

=: ==:

-e ennu .2- a=== .=. =

=. _: ..: / =E.t. . = ... .

0.10 = . .- _=.

. .:. . . ...= . .. .- . . ..= =.

= =..=.:. :.. . = .

..=. .. .=

. . . j u a - . '

_m.. .= . .. .. = . :_ . .m. . <

. . . . i

• ~~~ **

= . .~.2.* *; . : .:-

::.: ': *=.

t_=.:.::.._*..

_ * * ~ g. n'.

O.m. = .. .. = . ~ . .'.

u.

_=... ..

_ a/L = 0.167

,. 0.09 .. -

.._. ... .=.. .:..

. - ... j

.c ..- .t. =. =.g .:-..

.. .= . . .= . . _=.n..

..=. =

3., =- . . .

1

= . . .m:

.:: .- ::2k: :a '.: F1[~=::::..:= = * : * "~i

. g" 0.08 "1"s j

=-  :::

~ "

~

. a/t = 0.083 11 #is'Miis =, =#.33 Q, eav 1iiM g gi

.g 1 ----- -

g. ..:  :-; ye#=

.e -- alt = 0.050

== na r= , M: n..=..=r.v ..c=. =. n:-r = -=.- - .=: =::a. .

E l 0.07 =ii: . . . i. . .t . . .t . ,. ' . . .,7, . i.i.i.i.s.i.i.35.1.d...:..~....

~

2 ' ' .p..I.I.:.a/.d. .':2:t 6. .. .=. "i lb g -: i.:._.:..!.!* surface ~

N* * '" "'

~

..: r=: no. ..; =

% 0'06 ':. REGION MUST SE :s an:r dg"a:7** p#

F

.c .. ..-

~- "'.~

~ "'

0 .3 con 5tDERED  ;;!j." 3

[.iii_iE iii% %jM: .. .M jiSURFACE l

-"[I !55'i[ddi&8I?  :!E!5Eii 5 !- - " - EE D  : :

= .

i .= g_ .. : :iii - --

• ALL EMBEDDED FLAWS 1 4 - "-=

1b.:  : -" x*.:,eEG.

(ON THIS SIDE OF 3 0 04 -

fTu. -: .}rf:y- .._.

. . = . . .. . = . - ..-..-

..:=....

"" ~

DEMARKATION LINE)

". .q.:'

' /.-./..-

g.u . .?. .n.}./.a...)n E.. . .

ARE ACCEPTABLE PER u...r

!!!!!= i-

"!:Ei i:.f: ~Ei. M- =~ :i Ei Niii CRITERIA OF IWB 3600

~- *

- AS LONG AS 2, s .0.25 t

iE a t

0'02  !!H  :!!!!!!!!i"  :

li E L . " *'-  !!;,, :t Jnii HE !!!il  !!U 21

." '* .'s."-  :: -

.. = . . .. .i=. .T. . . -

T/'"P

~~.W. .:i. ..

r t

0.01

.: = . ...

= . . ... .. . ....

. .f. a.soc. ... . . . .. .t... . . .l . :. .

^

. .:3 '!!  ; .

[:j. G: ,, ..i{i 0.05 0.10 0.15 0.20 0.25 0

DISTANCE FROM SURFACE d) d i

1 i

Figure 6-3. Embedded Flaw Evaluation Chart for Inlet Nozzle to Shell Weld (for Longitudinal and Circumferential Flaws) l im.mm.mmme . 6-16

~

. 2 'N .

l

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W. fARW M

e m

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g" e,

o s

o l

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g.

- g 33VJ80S7 .

=

a d.J k h/ / 3 8Q Q M F '

N $

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nm Nd - - ,

h . .-

' 3  ;

E, in:2 )

o m -

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6-17

a

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l.

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5 . -

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_t

-r .. _;

=: .. .- -- . .r-

=:r.=- ==- -< ._ _  :.__. _ _ . _

~_ ,_.. :_..__

2._p=  :.,-

=n-= = _. - . . - _- . _- __ - _. . . . _ .._ =-r,..- _ ....s.__ - - - -

33 =rr.- =g= = .= =- =-- ==r= =_gg -;.2;;.= ..u ri.E

==.= =Egy=42:m

..;c-: .::t:; : ._: - .=  : - - -

.= = --

= . __ = _ _; .4

=,:- r: - :-

_ = _=_;;;g.:- = r._-

_=_

,)2 a= m =. _ . . _. - . ._1_--- == _ ..-_ .

--+ _--"...;=:- . t .

..c_= . - .__ d. . ...

4 _ . _ _ _. . . . . ._. . . ._._ ._ .. . .

,)j ' 1"~2 FM .--iid"? Gi ,__ _

=

~ ~3 E =s===-~ -

='-- ---

i=- ==

r2"I i-

.- . - ..a== .i e r. :_; = =- -

_ ,--J . - -

r_ .. _ . . . - 2 ; --

=..

.__ _ - _ _ .. . _=1 =

.m = - =- = , -

.10 a=-

--+= -t _ -= m:.:.=..

u. ,

_.. _ == . __ -.

_. .___._-__. _ __+_ + . - _ . . . _-t=_

. _ = = - ..

n== ;.;-=- .== -__.. -

=- ---

-=g =-= . . y-

.09 -m - - - --

-+--. .,,;,

- -=

--~

_-  ;,.g.,,.,, ,.-.; . .,,.;) 7_

,;p ,,. _--,-  ;;.-_;,,, _ _ , _ , ,

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-4= .: 2

_  ;;t ._ _i_..

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.- _.,,,m

r. - s....p. _

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--..;. gr 2:L- .:

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_ . =

_ -g._t_.3 r_--

d. 07

~"J:@ .Mi. E:i-MMOf ~ i-ML-E~IG-s 5 -  :

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,-- R5 .

id:V .-

- -, w.  :=r--_

=-

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x ria: = e.- 7- 2=

- - --f . - =ra y g,_ ._.,_..

~-

.a= --._= ~~-

=4

.y=.==., _'.re' g . 06 us- :- =-

-t=-

--& -- --.s pg;_-i_ .._. _ _

yq,=43g ]

s :_. _ __.=, _.;,_ ;-. s. . _ . . . . __ . _ - ._.. __ 2-- -:_ . - -

gs.- --

_=  :..

1 4 q= : -

.::. _- 'c- -  ;; = 2 t :::

ma;,'

_~

,,,z.,_,, c _._

d . 05

= _ .- K, . x1.

_ ,;.z _.;ym _;; . _ ._ .

. = x- - -

r.-= = -- . = __ ..

.r-

_._ -e -

.=

,,=yA-a . -

__- _ - . ._. 1

n= E;-- - =__ _ _-- _-- _ . _ .

~~

_ _d . .. :-- i

. .d. . . .

,hk -g r ..-

.m; . . _ -

w

.=_m

3.=.. . .7= =E. _ .

a . .s

~

__=:s -21.-2./

==

--M_ ,_ ___

""'g'=~~^~

.03 =

"'3. [- , ,_3_ == ; m;=a r,- .-

.==. -

- .c = -

: ,. - #= - ,,

w

.:3== r_g.  ;

,s aw ==

.02 4-. s_

a

- 'e.

a =a-pA- - -

m ._ u

-*=

gam @a.-

t-- . __.. - . .

._s__

. _ . , _ _. . =

_ =_. _.= r.=-= .:. =

;. .=_ - - -...----- # .-

_L__.:.:.=.2  :

M m ra - " .-

1

,=,,=,- -=- ~---

85___.___.__ _ . .n_ p--_,-y

1. .=.: - - "- El ;. , L,. O~ b> =.:- '~ -

-~

.$,:,;:,=:u.:

.01

==-

FMg.',

73

- - - ,hw_ . _

- s_., - - - -

,q

_- me

2

-_ _ . ..n- - _- ---9; Q, - + -n .->+

y 43 J J

.0 .1 .2 FLAW SHAPE (a/l)

Figure 6-5. Illustration of Advantages gained by Analysis for Embedded Flaws at the Inlet Nozzle to Vessel Weld j mwumo

• 6-18 ,

-c

~~  %-

1 j

I)I

~

--, . .t b$

s% .

' .a y x--- _

i

.14 - i i  !

i i  !

l ia=!dt  ;*

I i I y

l

- - ~

.13 I i ,  ; i . _ . . _ .

' I --

.12 fj  :

l

- I

)

i I '

.11 l

? 8 8 i i- l i I

i ' I _ _ .

' l

.10 6= t I  ! l

_l

.09

.y i l I  !

I i

'  ! I f i t i C . 08 ,

I  ! i . . . . . _ .

a --

'I I'

- I I I -

g.07 -

i 6=,it l t  ;  ;

n.

g -

' I Ie I  ! ' ,.*y.A A~ "a -

=LO___

E .06 . _ . _ . .

' i i l6=ibti i f,- - - -

d .05 , I

~~

' I MA - -

.04  : i 1

. .4' ,

I

.03 .

i .  :  : j A ^

i

~

2 L ' ' ' M* ' 0.5 l

• 02  ! i 1

,--- ) f i

t M M ACCEPTAllCE STANDARDS OF TABLES '

.; .IWB Jnig AND. Awu adiz ,uvuu EditTrn

.01 , j j i

- r signumw5 fidDR JO 1930TDIT!0N

.00 1  ! I

.5

.3 .4

.1 .2

.0 FLAW SHAPE (a/L)

Figure 6-6. Illustration of Benefits Gained by Analysis for Embedded Flaws in Regions where all embedded flaws are acceptable l I

i mm.mmne 6-19 i