ML20207E663

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Rev 0 to EMECH-0713-1, Operational Assessment of SG Tubing at Beaver Valley Unit 1,Cycle 13
ML20207E663
Person / Time
Site: Beaver Valley FirstEnergy icon.png
Issue date: 01/28/1999
From: Begley C, Begley J, Brose W
External (Affiliation Not Assigned)
To:
Shared Package
ML20207E659 List:
References
EMECH-0713-1, EMECH-0713-1-R00, EMECH-713-1, EMECH-713-1-R, NUDOCS 9903110030
Download: ML20207E663 (33)
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DUQUESNE LIGHT COMPANY Nuclear Power Division Nuclear Engineering Department AN OPERATIONAL ASSESSMENT OF STEAM GENERATOR TUBING AT BEAVER VALLEY UNIT 1. CYCLE 13 Principal Authors:

J.A. Begley

'W.R. Brose C.J. Begley M.G. Peck E-MECH TECHNOLOGY INCORPORATED (Report EMECH 0713-1, January,1999, Revision 0) y lE*"1ff"E Alberti Nuclear Engineering Department DUQUESNE LIGHT COMPANY b <<<,- , MW/l28

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W.R. Kline, Manager Nuclear Engineering Department DUQUESNE LIGHT COMPANY

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Section 14 l

. INTRODUCTION i

-. i LA deterministic operational assessment of steam generator (SG) tubing at Beaver Valley Unit 1 1 1

was performed.- The severity of degradation at the End of Cycle (EOC) 13 was projected to i l

determine if required structural and leakage integrity margins would be maintained. The scope of this evaluation included the following forms of tubing degradation: l 1,

i e  ; Cold leg thinning i

. . Wear at Anti-Vibration Bars (AVBs)  !

i e  !

Primary Water Stress Corrosion Cracking (PWSCC) at Row I and Row 2 U-bends i

e ~ Axial PWSCC at Expansion Transitions i e Circumferential ODSCC at Expansion Transitions  !

i e Pitting l i

Axial outside diameter stress corrosion cracking /intergranular attack (ODSCC/lGA) at drilled tube support plate intersections is covered in a separate analysis. This present report is an i i

updated, restructured version of an earlier report by one of the principal authors.'  ;

.As described in a previously completed condition monitoring report,2 the forms of degradation l considered in this evaluation did 'not present serious challenges to the 3AP structural margin requirement at the end of the last cycle of operation. A simple comparative approach to operational assessment leads to a similar expectation for the next cycle of operation. '!

4 The _ deterministic operational assessment approach, described in the following sections, is i strrdghtfo/ ward.- Instances of axial and circumferential ODSCC and PWSCC are removed from j service upon detection. Projections of worst case EOC crack sizes are obtained by assuming that  ;

the worst case Beginning of Cycle (BOC) crack size is equal to the value giving a probability of Page1 l

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. __ _ _ - - . - .~. . . - . . _ . - _

detection of 0.95. An upper 95'h percentile growth rate is applied and the resultant EOC crack j size is required to exhibit a minimum burst strength of 3AP, that is,4375 psi. Burst pressure calculations include consideration of both variations in material properties and uncertainties in the burst pressure equations. l; l

i The depth of wear at anti-vibration bars and the depth of cold leg thinning at peripheral tube  !

support plate intersections is determined from bobbin probe phase angle evaluations. Indications l with measured maximum depths less than 40% remain in service. Here, degradation growth and l

non-destructive examination (NDE) uncertainty are both considered in developing a worst case l; EOC projection. An upper 95* percentile NDE measurement error is added to the repair limit  ;

depth of 40% throughwall(TW) to obtain an estimate of a worst case BOC degraded tube.- An  !

upper 95* percentile growth rate is assumed to develop the EOC worst case projection. Again a degraded tube minimum burst strength at EOC of 3AP is required. Variations in tensile properties and the scatter in burst pressure relationship are included in the analysis.

l Figure 1.1 provides - a schematic illustration of the deterministic operational assessment '

methodology. Note that the assumed BOC degradation size for a plug on detection approach is the size leading to a probability of detection of 0.95, whereas, for a plug on sizing approach, the BOC degradation size is the repair limit plus an upper 95* percentile NDE uncertainty. The 3AP j

operational assessment structural limit considers both material property uncertainties and burst pressure relationship uncertainties. A worst case degraded tube projected to be at this operational l assessment structural limit at EOC will meet the 3AP structural margin requirement'with a j probability of 0.95 at 95% confidence.

i Leakage integrity evaluations are based on either of two approaches. The first approach of no

expected leakage depends on a projected worst case degradation severity which does not lead to l- - penetration of the tube wall. The second approach of possible leakage but of small and acceptable magnitude is based on past EOC in situ leak rate test results and limited numbers of expected degradation sites.

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. 3AP Operational Assessment Structural Limit 3 8

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Allowable Cycle Length '

Time, EFPY Figure 1.1 Schematic Illustration of Deterministic Operational Assessment Methodology

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Section 2 EDDY CURRENT INDICATIONS AT EOC 12 l

l Other than ODSCC/ IGA at drilled tube support plate intersections, approximately 308 tubes  ;

exhibited various forms of degradation at EOC 12. The majority of this number involved tubes  !

t

.with cold leg thinning and wear at AVBs 137 and 31, respectively. About 107 tubes had axial ODSCC indications in the sludge pile region. Fifteen tubes had PWSCC indications in U-bends, i i

14 Row I U-bends and 1 Row 2 U-bend. At expansion transitions,8 tubes had circumferential j indications considered to be ODSCC and 10 tubes exhibited axial PWSCC. There were also two j instances of pitting on the cold leg. The length of Cycle 12 was 1.14 effective full power year (EFPY). The expected length of Cycle 13 is in the vicinity of 1.37 EFPY, approximately a 20%

increase in operating time.

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Section 3 COLD LEG THINNING AND AVB WEAR t

For structural analysis purposes, both cold leg thinning and wear at AVBs can be idealized conservatively as uniformly deep. wall thinning over a given length. If wall thi ming is restricted l to less than about a third of the circumference, the burst strength of the degraded tube is l increased compared to the case of 360" wall thinning. With wear at AVBs and cold leg thinning,

- wall thinning is restricted to only part of the tube circumference and usually is tapered in depth l l rather than of uniform depth. For wear at AVBs, the degraded length is limited to the width of i

the AVBs,0.375 inches. Cold leg thinning occurs at tube support locations. Here, the maximum I degradation length is restricted to the tube support plate thickness,0.75 inch. Actual extents of cold leg thinning at Beaver Valley Unit I are approximately half of this value as determined from I

sample rotating pancake coil (RPC) profiling, with a worst case value of about 0.45 inches. l l

Figure 3.1 shows a plet of degradation depth ersus depadation length at the 3AP limit bust

]

pressure of 4375 psi.~ In this case wall thinning is less than 135'in circumferential extent. Three -l 1

curves are shown. Using the nomenclature of the Electric Power Research Institute (EPRI)  ;

Steam G%o & Nradation Specific Flaw Handbook,' the upper curve is the structural limit curve. It u based on a best fit burst pressure equation and average material properties. The next curve defines the combinations of degradation depth and degradation length having a burst pressure of 4375 psi with a probability of 0.95 at 95% confidence. This curve can be termed an operational assessment structural limit curve. It is obtained via a Monte Carlo calculati a which j includes uncertainties in the burst pressure equation and variation in material tensile properties.

The hwest curve is based on 95/95 lower tolerance limit tensile properties and a lower 95*

percentile tolerance interval to the burst pressure test data. As is the general case for burst pressure equations, use of 95/95 lower tolerance limit tensile properdes and a lower 95*

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i-

. percentile tolerance interval (or even prediction interval) burst pressure equation is slightly more conservative' than using a Monte Carlo convolution of uncertainties to find the exact conditions leading to a 0.95 probability ofmeeting a 3AP minimum burst pressure at 95% confidence.

l l

1- j Based on RPC eddy current inspection results, a length of 0.45 inches is a good bunding value for the axial length of cold leg thinning. From the operational assessment structural limit curve {

l (Figure 3.1), the worst case allowable EOC degradation depth is 72% TW. This value refers to a j uniform 'or average' depth. If a maximum axial length for wear at AVB locations is taken as 0.375 inches, the width of the AVB, the worst case allowable EOC degradation depth for AVB  !

wear is 74% TW (Figure 3.1).

l The repair limit for AVB wear and cold leg thinning is an eddy current ind cated maximum depth of 40% TW, thus 39% TW is the maximum allowable eddy current depth to be left in service.

An NDE error must be added to this value to obtain an estimated worst case actual BOC depth.

Using sizing data from the Examination Technique Specification Sheet (ETSS) generated in l

accordance with the requirements of Appendix H of the EPRI Pressurized Water Reactor (PWR)

Steam Generator Examination Guidelines,' the standard error of estimate of actual maximum depth'is 3.3% TW for AVB ' wear. The upper 95* percentile measurement uncertainty is then

~

. 5.4% TW. At an eddy current indicated depth of 39% TW, the best estimate actual depth is 41% -

TW. Hence, the assumed worst case BOC depth fer AVB wear indications is 41% TW plus l 5.4% TW for measurement uncertainty for a. total'of 46.4% TW. A conservative grov.th allowance must be added to this value to develop a worst case EOC projected depth.

i For cold leg thinning, the sizing data from the ETSS leads to a standard error of estimate of  !

l

actual maximum depth of 13.3% TW. At an eddy current depth indication of 39% TW, the best  !

f estimate actual maximum cold leg thinning depth is 34% TW. The upper 95* percentile NDE I

y  !

! measurement error is about 1.65 times'the standard error of estimate, that is,21.9% TW. The Page 6 i j

estimated worst case BOC actual depth of cold leg thinning is 55.9% TW. Again a conservative growih allowance must be added to this value to develop a weret case EOC projected depth. i Growth rates for AVB wear and cold leg thinning have been developed by Framatome ,

Technologies incorporated (FTI).' The growth rates for AVB wear wem developed from bobbin +

coil TW depth data for Cycles 10,11, and 12, while the growth rates for cold leg thinning were based on a reandysis of Cycle 12 bobbin coil TW depth data. Data from all three steam generators in Unit I were included.

Figure 3.2 is a plot of the cumulative probability of growth rate for AVB wear in SG A for Cycles 10,11, and 12. This plot illustrates that the highest 95% probability growth rate was for Cycle 11, at a value of 11% TW/EFPY. The plot also illustrates that the average growth rates are relatively low and the scatter high. Table 3.1 gives the 95% probability growth rates for each SG and each cycle.

Figure 3.3 is a plot of Cycle 12 growth rates versus BOC 12 depth for cold leg thinning in all SGs. The 95% probability growth rate was highest in SG B, the value again being 11%

TW/EFPY. As with AVB wear, the plot also reveals a relatively low average growth rate and high scatter. Table 3.2 gives the 95% probability growth rates for each generator.

TABLE 3.1 AVB WEAR 95% PROBABILITY GROWTH RATES IN */.TW/EFPY l

SG A SG B SG C Overall Cycle 10 9 5 3 5 Cycle 11 11 11 7 11 Cycle 12 8 4 10.5 8 Composite 10 9.5 8 9.5 l

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TABLE 3.2 COLD 1.EG THINNING 95% PROBABILITY GROWTH RATES IN %TW/EFPY SG A SG B SG C Overall

' Cycle 12 - 7 11 6 10 I

- From the above data, it ir. apparent that i1% TW/EFPY is ayonservative choice for an upper 95' percentile. growth rate for both AVB wear and cold leg thinning. It should also be noted that no  ;

1 attempt was made to account for the fact that NDE measurement errors merease maximum  ;

I apparent growth rates with respect to actual physical growth rates. For any single growth rate  ;

i based on NDE measurements, the actual physical growth may be higher or lower depending on i 1

1

- whether NDE errors fall high or low. However, when a distribution of measured growth rates is considered, NDE errors spread out this measured growth rate' distribution compared to the distribution of actual physical growth rates. Hence,'the upper 95* measured growth rate is conservative with respect to the actual physical upper 95* percentile growth rate.

Having established the worst case BOC depth, the allowable EOC depth and the worst case

. growth rate, it is a simple matter to find the allowable cycle length such that the 3AP structural requirement is not exceeded. This is the difference in depths divided by the growth rate. For

- AVB wear and cold leg thinning the calculated allowable cycle lengths are 2.5 and 1.46 EFPY, respectively. At 1.37 EFPY, the ext:cted length of Cycle 13, the EOC predicted worst case

- AVB degradation would be approximately 61.5% TW. For cold leg thinning (CLT), the EOC 13 predicted worst case degradation would be approximately 71% TW. These calculations are conservative. ' Neither AVB wear nor cold leg thinning pose a challenge to structural requirements for the expected actual cycle length of 1.37 EFPY.

Leakage at normal operation or postulated steam line break (SLB) conditions is not an issue.

Leakage, even at 3AP, is not expected. In situ testing has demonstrated this expectation to be

- true.

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I Figure 3.3 Cycle 12 Growth Rate VS BOC12 Depth For Cold Leg Thinning in AllGenerators Page 11

l Section 4 AXIAL CRACKING AT AND NEAR THE TOP OF THE TUBES 11EET Both axial ODSCC in the sludge pile and axial PWSCC at expansion transitions are considered together since a common structural evaluation is appropriate. Figure 4.1 shows a plot of 1

allowable depth versus length of partial depth axial cracks meeting the 3AP minimum burst pressure requirement of 4375 psi. The burst pressure equation for axial partial TW cracks can be found in the EPRI Steam Generator Degradation Specific Management Flaw Handbook. Itis based on an adaptation of the Cochet' or Framatome' equation to pulled tube test data, including i I

five pulled tubes from Beaver Valley Unit 1.

Figure 4.1 shows the combinatior.s of axial crack length and depth leading to a burst pressure of 4375 psi, the required 3AP value for Beaver Valley Unit 1. The highest curve, the EPRI defined structural limit curve, is based on a best fit burst pressure equation and average material properties. The next curve defines the combinations of degradation depth and degradation length having a burst pressure of 4375 psi with a probability of 0.95 at 95% confidence. This curve can be termed an operational assessment structural limit curve. It is obtained via a Monte Carlo calculation which includes uncertainties in the burst pressure equation and variation in material tensile properties. The lowest curve is based on 95/95 lower tolerance limit tensile properties l and a lower 95* percentile tolerance interval to the burst pressure test data. It is convenient to calculate but is slightly more conservative than the actual 95/95 curve. l l

Figure 4.2, using Beaver Valley pulled tube data, shows that axial degradation lengths based on i Plus Point data are conservative indicators of the true structurally significant lengths.

Structurally significant lengths and depths can be calculated from actual depth / length profiles L using a procedure specified in the EPRI Flaw Handbook. The structural length and depth define the actual critical section of a crack profile and provide t eh parameters used in the burst equation.

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l The ' distribution of Plus Point crack lengths found in the most recent inspection is shown in i Figure 4.3. A length of 0.70 inches is a conservative upper 95* percentile estimate of the structural length of axial cracks near the tubesheet. From Figure 4.1, the allowable EOC average q depth at the worst case length of 0.70 inches is 63% TW. l i

The maximum assumed BOC depth can be developed with the aid of Figure 4.4. The probability j of detection of axial cracks.with the Plus Point probe is plotted versus the average crack depth. l This curve was constructed by a log logistic fit to pulled tube data.7 The average crack depth at a POD of 0.95 is 37% TW, This provides a conservative estimate of the BOC crack depth since ' l 1

pulled tube data from Beaver Valley I suggests the average crack depth at a POD of 0.95 is 35%

l TW when utilizing the Plus Point probe.

The crack growth rate distribution can be estimated from a historical review of Plus Point eddy current data for axial indications at and near the top of the tubesheet. Figure 4.5 is a plot of ,

-l

' change in maximum depth versus BOC depth for. Cycle.12. As has been demonstrated previously from computer simulation . studies, growth data at low BOC depths or from previously i

undetected degradation is inherently unreliable. The set of data to the right in Figure 4.5, while

continuing significant measurement errors, can be used to develop conservative estimates of growth rates. When only positive, apparent growth points are considered, the cumulative fraction plot of growth in maximum crack depth of Figure 4.6 is obtained. From this figure, the 95* percentile growth in depth is about 20% TW This converts to an upper bound axial crack l growth rate of 17.5% TW/EFPY. Use of maximum depth, retention of measurement errors and discarding of negative apparent growth rates adds significantly to the conservatism of the )

! 1 selected upper bound growth rate. These conservatisms combined with the conservatism associated with BOC crack depth are utilized to account for non-quantified NDE uncertainties.

Page 13

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J For a cycle length of 1.37 EFPY, th' e maximum expected growth is 24% TW. When this is t

added to the worst case BOC depth of 37% TW, the projected EOC worst case depth is 61% TW.

This is less than the allowable depth of 63% TW. The 3 AP deterministic structural requirement

- is met for the worst case projected axial degradation near the tubesheet.

The average ratio of maximum axial crack depth to average crack depth is 1.28. The upper 95*

percentile of this ratio is 1.53. Applying this larger factor leads to a worst case projected maximum crack depth of 93% TW. No leakage is expected from axial cracks at and near the top of the tubesheet at EOC at either normal operation or postulated accident conditions.-In situ testing of worst case flaws at EOC 12 provides further data to support the no leakage conclusion. I i

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Section 5

< PWSCC IN ROW I AND ROW 2 U-BENDS Eddy current inspections at EOC 12 indicated PWSCC at 14 Row I U-bends and 1 Row 2 U-bend. _- Axial cracking was the primary degradation mode. Two tubes exhibited some degree of ,

1 circumferential cracking. In one case, the indicated geometry was consistent with a kinked axial '

crack. Here the expected burst strength should be based on the projected axial crack length. In the other case, a more discrete circumferential crack was indicated with a length of 0.34 inches.  ;

i Burst test results on Row I U-bends with machined TW axial cracks placed at various locations .i show that axial cracks in short radius U-bends, have a burst strength at least a factor of 1.34  !

higher than the same crack size in a straight length of tubing.' On this basis,'the TW crack length needed to reduce the burst pressure of a short radius U-bend to less than the required 3AP value of 4375 psi is 0.65 inches. Work hardening of the U-bend is the primary strengthening mechanism. Annealing of the Row I and Row 2 U-bends at Beaver Valley Unit 1. decreased ,

residual stresses and presumably caused a small drop in tensile strength. This possible decrease

' in strength is offset by a bounding assumption of TW cracking.

I Projection of a worst case crack depth for PWSCC in Row I and Row 2 U-bends is difficult I

because of a scarcity of growth rate data. However, for structural analysis purposes a i completely TW assumption is useful. The worst case projected crack length can be set equal to l the maximum length observed at the last inspection,0.32 inches. Even if this value is doubled to I 0.64 inches and complete TW cracking is assumed, the minimum required burst pressure of 4375 psi will be maintained at EOC. This assumption demonstrates the margin that exists i between projected worst case results and structural integrity limits. Such margin provides significant latitude to account for non-quantified NDE uncertainties.

1 In the case of the one instance of a circumferential crack in a U-bend, the 3AP structural requirement would be met by a 100% TW circumferential crack with a length of 1.96 inches.

This is in excess of a 5 fold increase in the maximum observed circumferential U-bend crack at Page 21 -

1 EOC 12. A' maximum 1bserved length of 0.34 inches for a partial TW, circumferential U-bend crack at the last inspection clearly demonstrates that this form of degradation is far from a limiting consideration.

Projected leakage at postulated SLB conditions at EOC 13 is based on in situ test results at EOC

12. One leaking Row 1 indication was discovered via in situ testing. Converting of the measured in situ leak rate to postulated SLB conditions leads to a value of 0.012 gpm at temperature. The length of this flaw from eddy current measurement is 0.27 inches. The in situ leakage data suggests that the TW extent of this flaw that contributed to the observed leakage i was only 0.13 inches. Considering that the cycle length is only 20% longer than Cycle 13, a  ;

similar leak rate at EOC 13 is a reasonable best case projection. For a worst case projection,  !

assume full TW cracking of the worst case EOC 13 projected crack length (0.32 iriches). This represents a 250% increase in length from that of the U-bend flaw that leaked during in situ testing at EOC 12. The projected worst case leak rate at SLB conditions at EOC 13 would then be 0.25 gpm. The number of U-bend indications projected for EOC 13, assuming a conservative Weibull slope of 6, is about 20. Axial crack length distributions have been shown to be relatively insensitive to large changes in cycle lengths. Hence, with a similar number of indications and virtually the same length distribution, the maximum crack length expected at the end of the next cycle is about the same as EOC 12. A worst case leak rate estimate based on the i assumption of 100% TW cracking of a 0.32 inch long crack is conservative and again highlights the margin that exists to account for non-quantified NDE uncertainties.

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l' l Section 6 l l

CIRCUMFERENTIAL ODSCC AT EXPANSION TRANSITIONS  !

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-A total of eight cir umferential indications at expansion transitions were found in all three
generators' in the EOC - 12 inspection. The largest observed arc length lof circumferential )

degragation was 90*. If a bounding assumption of TW cracking is applied, the limiting value of i l

percent degraded area (PDA) was 25 at the EOC 12. j i

i Figure 6.1, based on the EPRI Flaw Handbook approach, shows that the allowable EOC PDA value is 76. A lower bound burst curve was used in conjunction with 95/95 lower bound tensile

. properties and a 3AP minimum burst pressure requirement of 4375 psi.

A plug on detection approach with a Plus Point probe inspection insures that any expansion transition circumferential degradation present at the BOC 13 will be of minimum severity.

!- Probability of detection versus PDA is shown in Figure 6.2 for circumferential degradation in

. explosive transition.' ' A conservative assumption for the largest degradation level which raay I L have been undetected by the Plus Point is a PDA value of 31. The probability of detection at this .

level is 0.95.

The limited number of circumferential indications at Beaver Valley Unit 1 prevents any.

substantial . evaluation of growth rates. However, a number of other ' evaluations of circumferential ODSCC growth rates at explosive expansion transitions are available. Based on analyses submitted to the NRC,' " an upper 95* percentile growth rate of 20 PDA/EFPY is i

appropriate. This is a good choice for an upper bound growth rate in a deterministic operational assessment, j l A'PDA of 31 is assumed at BOC with an allowable EOC value of 76. With an upper bound L

l growth rate of 20-PDA/EFPY,' more than 2 EFPY of operation is needed before the 3AP i

Page 23

, . . _ _ _ _ _. . . . . _ . _ __ _ . _ . . _ . - . . _ _ _ _ . - _ _ - . ._...__._m..._-. . _ _ . _. __.___

.;+ .- .

l I

structural limit is approached. Circumferuitial degradation at the top of the tubesheet is not a limiting run time consideration. Leakage is not. an issue. The low number ofindications at the

. EOC 12 inspection and lack ofleakage during in situ testing provide the basis for a projection of no leakage from the circumferential top of the tubesheet degradation at EOC 13. t

[..

i 1

i f

i  ?

l- ,

1 l I

i i

i a

i 1

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3

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Page 24 l- '

. i. . , c, . - - - , - ,. .

,, . +. .

l OD Circumferential Area L -

i l 12.00  :

\. l l

+ Structural Limit

-g Bounding with 95/95 LTL Properties 10.00 . I

= \.

s.N=s.N I 8.00 h. _ _

_N"N. x 1 3 - "N,IN.N

! N"N"N E 6.00 - _ - _ _ . _

1

.I NNh.N.x_. .

i l

l x.N.N.\

I 4375 psi \= .

4.00 = _ . _ . .

1 1

a 2.00 __ _ _

= i i

0.00 \.

0 20 40 60 80 100 Percent Degraded Area Figure 6.1 Illustration of Structural Limit for Circumferential ODSCC at Beaver Valley Unit 1 Page 25

c( r . . , l l

t I

. Section 7 PITTING Pitting is included for completeness. Pitting is not a structural issue since the typical degradation l dimensions preclude burst even at 3AP pressures. Two pits were detected at EOC 12 and I plugged. ' The maximum axial and circumferential extent was on the order of 0.15 inches. Even '

if the degradation were 100% TW, this is very far removed from 3AP allowables.

)

i l

In situ testing at EOC 12 up to 3AP pressures did not lead to leakage. Hence the best estimate of l i

leak' rate from a pit at EOC 13 at postulated SLB conditions is 0. However, to account for the j longer operating cycle and non-quantified NDE uncertainties in sizing, a worst case estimate is -

obtained by assuming that, under SLB pressure differentials, the bottom of a 0.15 inch pit cracks-open. The conservative associated SLB leak rate for a 0.15 inch long axial crack is 0.018 gpm at temperature.- The margin between this value and the limit of I gpm is very substantial.

Numerous pits (approximately 55) could leak at this magnitude before encroaching on the 1.0 I gpm accident induced leakage limit. Even when combined with the worst case projected leakage from U-bend PWSCC degradation, in excess of 41 pits would have to leak at this predicted rate i to exceed 1.0 gpm.  !

i

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4 Page 26 -

i

i Section 8  ;

SUMMARY

AND CONCLUSIONS A' deterministic operational assessment of steam generator tubing at Beaver Valley Unit I was

.' performed. The severity of degradation at the EOC 13 was projected to determine if required .;

structural and leakage integrity margins would be maintained. The scope of this evaluation  ;

included the following forms of tubing degradation:

  • Cold leg thinning 1
  • . Wear at AVBs ' i

-. . . Axial ODSCC in the Sludge Pile Region -

  • PWSCC at Row I and Row 2 U-bends

. Axial PWSCC at Expansion Transitions

  • Circumferential ODSCC at Expansion Transitions

. Pitting

. Axial ODSCC/ IGA at drilled tube support plate intersections is covered in a separate analysis.

. Worst cases were assumed for BOC degradation severity, degradation growth rates and EOC allowable degradation. Essentially all parameters were selected at the bounding 95* percentile level. A 3AP structural margin will be maintained for the expected operating cycle length of 1.37

' EFPY. - The best estimate EOC leak rate at posulated SLB conditions is 0.012 gpm. The worst

. case estimate for all degradation mechanisms combined is 0.43 gpm. Table 8.1 summarizes the controlling parameters of the deterministic operational assessment.

4 Page 27

.c t

~

Table 8.1 r Summary Deterministic Operational Assessment Repair Best Estimate NDE Worst Case Upper Bound Operational Worst Case Allowable Best Worst Limit Actual Depth Uncertainty BOC Depth Growth Rate Assessment EOC Cycle Estimate Case

(%TW) at Repair (95th (%TW) (%TW per Structural Limit Projection Length EOC SLB Estimated Mechanism Limit (%TW) percentile, EFF t') (%TW) (%TW) (EFPY) Leak Rate SLB Leak

%TW) (gpm) Rate (gpm)

AVB Wesr 40 41 5.4 46.4 11 74 61.5 2.5 0 0 Cold Leg Thinning 40 34 21.9 55.9 11 72 71 1.46 0 0 l Axial ODSCC Sludge ROD - -

37 17.5 63 61 1.48 0 0 Pile PWSCC at U-bends ROD - -

Bounding Assiemptions- Limited Length Precludes 0.012 0.25  ;

Burst Axial PWSCC at ROD - -

37 17.5 63 61 1.43 0 0 ,

Expansion Transitions 0 I Circumferential ROD - -

31 20 76 58.4 2.25 0 ODSCC (PDA) (PDA) (PDA) (PDA)  !

Pitting ROD - - Limited Length Precludes Burst 0 0.018  !

I ROD - Repair On Detection PDA - Percent Degraded Area i

{

Page 28

.- - . . . .. . _ - - . - - . . =. - . . - .

g . ow ,

Section 9 l REFERENCES

1. Begley, J. A. and Brown, S. D.,"An Operational Assessment of Steam Generator Tubing at Beaver Valley Unit 1, Cycle 13," APTECH Engineering Services, Inc., Report AES97053068-1-2, Rev 0, November 1997.
2. Begley, J. A. and Brown, S. D.,"A Condition Monitoring Assessment of Steam Generator Tubing at EOC 12 at Beaver Valley, Unit 1," APTECH Engineering Services, AES97053068-1-1, November

-1997.

i'

3. Keating, R. F., Begley, J. A., Brose, W. R., and Lagally, H. O., " Steam Generator Degradation Specific Management Flaw Handbook," EPRI Project S550-7, to be published.

1

. 4. "PWR Steam Generator Examination Guidelines, Rev. 5," Electric Power Research Institute, Palo

- Alto, CA, September 1997.

5. Fleck, J. M.," Beaver Valley Power Station Unit 1 - AVB Wear and Cold Leg Thinning Study,"

Framatome Technologies,51-126464-00, January 1998.

. 6. Cochet, B., " Assessment of the Integrity of Steam Generator Tubes - Burst Test Results- Validation of Rupture Criteria {FRAMATOME DATA)," Palo Alto, C A, Electric Power Research Institute, NP-6865-L, Vol.1, June 1991.

7. Docketed Submittal to NRC, Docket 50361, Begley, C. J., Woodman, B. W., and Begley, J. A.,"A-Probabilistic Operational Assessment of Steam Generator Tube Degradation at SONGS Unit 2 for
Cycle 9," APTECH Engineering Services, Report AES 97043057-1-1, September 1997.
8. Begley, J. A., unpublished test data. l 9.' " Depth Based Structural Analysis Methods for Steam Generator Circumferential Indications,"

Electric Power Research Ir.stitute, Palo Alto, CA, November 1997.

10. Docketed Submittal to NRC, Docket 50335, Begley, J. A., Woodman, B. W., Brown, S. D., and >

Brose, W. R.," Analysis of ODSCC/ IGA at Tubesheet and Tube Support Locations at St. Lucie, Unit 1," APTECH Engineering Services,Inc, Report, AES 96052749-1-1, October 1996. l

11. Docketed Submittal to NRC, Docket 50361, Begley, J. A. and Begley, C. J.,"An Updated Probabilistic j Operational Assessment for SONGS Unit 2, Second Mid Cycle Operating Period, Cycle 9," APTECH l Engineering Services,Inc., Report AES 98033327-lQ-1, April 1998.

,~. 1 V

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Page 29 1

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. e.  %

3 ATTACHMENT B

, Beaver Valley Power Station, Unit No. 1 Response to Request for Additional Information Concerning License Amendment Request No. 261 Summary of In Situ Testing Performed at Beaver Valley Unit 1 During 1R12 l

l l

l l

C-D,*-

l 1

Summary ofIn Situ Testing l Performed at Beaver Valley Unit 1 i During 1R12 l

l i

l Total tubes subjected to in situ testing = 24 i

All tubes subjected to Main Steam Line Break (MSLB) and 3APuo pressures. l l

Criteria for selection of tubes for in situ testing:  !

Axial ODSCC at Top of Tubesheet (TTS)

1. StructuralIntegrity.

test all tubes that encroach on theoretical stmetural limit (3APuo) based on ,

l crack length vs average depth - 3 tubes tested i

, 2. Leakage I test flaw with maximum depth - 3 tubes tested test additional tubes to bound depth vs volts and length vs volts - 4 tubes tested Circumferential ODSCC at TTS

1. Stmetural Integrity no testing required due to limited circumferential exter.t of flaws I
2. Leakage test flaw with maximum depth 4 tubes tested  !

test flaw with maximum voltage Axial PWSCC below TTS

1. StructuralIntegrhy no testing required since tubesheet inhibits burst .

l

2. Leakage  ;

test flaw with maximum depth '

4 tubes tested test flaw with maximum voltage i U-bend PWSCC

1. StructuralIntegrity no testing required due to limited axial flaw length and circumferential flaw extent
2. Leakage test flaw with maximum depth test flaw with maximum voltage 4 tubes tested as a matter of conservatism, test all circumferential indications

. . . - . ~ . .

> .. \.

Cold Leg Thinning

1. StructuralIntegrity no testing required due to limited flaw depth and length
2. Leakage test flaw in excess of 40% TW with maximum voltage - 1 tube tested Pitting
1. StructuralIntegrity test flaw with maximum depth - 1 tube tested NOTE: ALL TUBES WERE SUBJECTED TO MSLB AND 3APuo REGARDLESS OF REASON FOR SELECTION Test Results '

All tubes tested withstood 3APuo pressure Only one tube exhibited leakage at MSLB pressure  ;

one U-bend indication - leakage at MSLB pressure = 0.012 gpm Historical data available to evaluate BVPS Unit I steam generators at the EOC 12 (all tubes tested at MSLB and 3APso):

e Unit 1 pulled tubes (IR08, IR10, IR11) laboratory results

=> TTS ODSCC 6 tubes

- axialindications acceptable lesk and burst test results t

. Unit 2 In Situ test results from 2R06  :

=> TTS ODSCC axialindications (4 tubes)  ;

circumferential indications (4 tubes)

- acceptable test results - no leakage b.

!

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