ML20196C839

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Rev 0 to GE-NE-B13-01980-030-2, Assessment of Crack Growth Rates Applicable to Induction Heating Stress Improvement (IHSI) Recirculation Piping in Quad Cities Unit 1
ML20196C839
Person / Time
Site: Quad Cities Constellation icon.png
Issue date: 11/30/1998
From: Caine T, Horn R, Mehta H
GENERAL ELECTRIC CO.
To:
Shared Package
ML20196C822 List:
References
GE-NE-B13-01980, GE-NE-B13-01980-030, GE-NE-B13-1980, GE-NE-B13-1980-30, NUDOCS 9812020109
Download: ML20196C839 (21)
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i GENuclearEnergy j TECHNICAL SERVICES GE-NE-B13 01980-030-2, Rev. O November 1998 l

- ASSESSMENT OF CRACK GROWTH RATES APPLICABLE TO INDUCTION HEATING STRESS IMPROVEMENT (IHSI) RECIRCULATION PIPING IN QUAD CITIES UNIT 1 l

l i

l Prepared for  :

I Commonwealth Edison Co. l 4

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,.. Prepared by.

GE Nuclear Energy - .

c175 Curtner Avenue"

" San Jose, CA 95125 9812O20109 981124 PDR ADOCK 05000254 P PDR

l GENuclearEnergy GENuclear Energy TECHNICAL SERVICES GE-NE-B13-01980-030-2, Rev. O November 1998 ASSESSMENT OF CRACK GROWTH RATES APPLICABLE TO INDUCTION HEATING STRESS l IMPROVEMENT (IHSI) RECIRCULATION PIPING IN QUAD CITIES UNIT 1 l

l l

l Prepared for Commonwealth Edison Co.

Prepared by GE Nuclear Energy l 175 Curtner Avenue l San Jose, CA 95125

GE Nuclear Energy Proprietary Informadon GE-NE-B13-C01980-030 2 l ASSESSMENT OF CRACK GROWTH RATES APPLICABLE TO INDUCTION HEATING STRESS l IMPROVEMENT (IHSI) RECIRCULATION PIPING IN l

QUAD CITIES UNIT 1 l

l November 1998 l

Prepared by: M, RM Horn, Engineering Fellow l Materials Technology l Reviewed by: TA b (cr HS Mehta, Technical Engineering Lead Structural Mechanics l Approved by: E I6b, n uN -Cer-l "

TA Caine, Manageyl Structural Mechanics and Materials I

l i

l l

GEN 31earEnerKY GE-NE-B13-01980-030-2, Rn. O IMPORTANT NOTICE REGARDING l

CONTENTS OF THIS REPORT l l

Please read carefully l

The only undertakings of the General Electric Company (GE) respecting infonnation in this document are contained in the contract between Commonwealth Edison Company (Comed) and GE, and nothing contained in this document shall be construed as changing the contract. The use l of this information by anyone other than Comed, or for any purpose other than that for which it is intended is not authorized; and with respect to any unauthorized use, GE makes no representation or warranty, express or implied, and assumes no liability as to the completeness, accuracy, or usefulness of the infonnation contained in this document, or that its use may not infringe upon privately owned rights.

i i

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

GENxdeerEnergy GE-NE-B13-01980-030-2. Rev. O EXECUTIVE

SUMMARY

There have been recent new data on cracking levels in recirculation piping at the Quad Cities Unit 1. The purpose of this report is to add understanding that can be used to assess these changes and to disposition some indications for at least one fuel cycle of operation. First, the report set about addressing the applicable crack growth rates that can be used to evaluate cracking in the upcoming cycle to disposition cracking in recirculation piping. Secondly, the report has provided insight into assessing the reasonable levels of crack growth that could occur in any one of the heat affected zones of the recirculation piping in the last cycle based on the same knowledge of crack growth rate behavior and plant water chemistry applicable to Quad Cities Unit 1. The report also discussed the possible contributors to perceived excessive growth. There are several conclusions that were drawn. The current operating water chemistry at Quad Cities Unit I supports the use of crack growth rates that are significantly slower than the rates given in the NRC NUREG-0313, revision 2. Therefore, the use of the NUREG rate in a structural margin assessment is i conservative. Specifically, the crack growth rates calculated using the GE PLEDGE model, which are deemed to predict realistic rates, are a factor of 3 lower under NWC conditions (K set at 25 ksi-in'*) and a factor of 8 lower when HWC is injected to the levels used in cycle 15 at Quad Cities Unit 1, the last operating cycle. The BWRVIP-14 model also predicts a factor of 4.5 lower crack '

growth rate (K set at 25 ksi-in'*) than that predicted using the NUREG-0313 curve.

It was found that previous experience with IHSI-treated recirculation piping has demonstrated that crack indication sizes can be different based on different UT inspections. Understanding of the IHSI-process and field experience strongly suggest that these changes are not indicative oflarge changes in crack ler.gth and depth changes. The understanding ofIGSCC behasior and the specific conditions at Quad Cities Unit I are inconsistent with any large amount of crack growth in any IHSI-treated piping HAZ over the last cycle. Explanation of the changes in the UT-determined depth are most likely due to changes in the visibility of an existing crack. These changes could be related to the changes in the piping oxide film due to the hydrogen injection coupled with zinc additions.

i iii

GEN:clearEnergy GE.NE.Bl3-01980-030-2. Rev. O TABLE OF CONTENTS

1.0 BACKGROUND

1 2.0 CRACK GROWTH RATES FOR QUAD CITIES UNIT 1 ASSESSMENT 2 2.1 Key Inputs to Crack Growth Modeling for the Quad Cities Unit Recirculation Piping.... . .. 2 2.1.1 Current Water Chemistry at QC Unit 1........... .. ............... .................. ... .......... ...... ... 2 2.1.2 Current Understanding ofIHSI-treated Recirculation Piping Welds.. ................ ........ . 3 2.2 Supporting Crack Growth Rate Assessments ..... ... ..... ... . ...... ......... ............. ............. . 3 2.2.1 BWRVIP-14 Crack Growth Evaluation .............. ......... . ......... . ........................ ....... .. 4 2.2.2 GE PLEDGE Crack Growth Rate Assessments: With and Without Hydrogen Injection. 4 2.2.3 SKI Based Assessment: With and Without Hydrogen.... . ... .......... .... . ............ ........... 5 2.3 Summary of Modeling Results ............. ...... . .... ................... . . ................. ...... . ........ .. 6 3.0 ASSESSMENT OF DEEP CRACKING IN IHSI-TREATED RECIRCULATION PIPING 6 3.1 Previous Field Performance ofIHSI treated welds ...... .. . ..... ... .. .......... . .... ... ... .........7 3.2 Understanding ofIHSI Treated Pre-cracked Piping.................... ... .. ....... .. ... ... .. . . .. ... 7 3.3 Influences of Operation Time and Conditions on IHSI-treated Pipe Characteristics....... . .. 7 3.4 Assessment of Rapid Growth in IHSI-treated Piping at Quad Cities Unit 1... .... . ... ...... ..... 8

4.0 CONCLUSION

S 8

5.0 REFERENCES

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I GENmclearEnergy GE-NE-B13-01980-030-2. Rev. 0 l

1.0 BACKGROUND

Following the detection ofintergranular stress corrosion cracking ( IGSCC) in the large diameter l piping in the BWR recirculation system, efforts were undertaken to develop crack growth rate data and to use the data to develop a crack growth model that could be used to predict the amount of crack growth that would take place during future periods of operation. The efforts resulted in NUREG-0313, rev.2 (reference 1) which put forth a metl adology for dispositioning IGSCC in piping (reference 2). This understanding of IGSCC also led to its use in setting inspection I intervals for austenitic recirculation piping in Generic Letter 88-01 (reference 3).

Examination of the data used to develop the crack growth rate information that is the basis of the NRC crack growth ntes show that it was all produced in laboratory facilities where the conductivity of the high temperature water used covered a wide range from 0.3 S/cm to 0.7 S/cm for tests conducted in 288'C,200 ppb oxygenated water to 0.5 to 1.5 S/cm for tests l conducted in 288 C,6000 ppb oxygen saturated water. (reference 4). The conductivity of the water resulted from actual additions of sulfate species to the water. These species are known to accelerate crack growth in a similar manner to chloride species in high purity water. The impurity levels that were required to achieve the high conductivity levels associated with the laboratory tests required the addition of ~90 to >200 ppb sulfate. However, in currently operating BWRs, sulfate and chloride species are nominally very low (~1~2 ppb) under normal operaJ2n and their lovels are restricted to a maximum level of 5 ppb before operating procedures require action. There fore, the data used to develop the NRC disposition line presented in NUREG-0313 and the resultant K-  ;

dependent rates can be assumed to be conservative in light of today's normal operation of a BWR plant.

l The purpose of this report is two fold. First, in the context of the NRC disposition curves, the report will review the expected crack growth rates that could occur during operation of the Quad Cities Unit 1 plant under normal operation. This assessrnent will also evaluate the benefits of Quad Cities Unit I hydrogen water chemistry (HWC) program which is expected to lead to significant reduction in crack growth rates in the recirculation system. This comprehensive evaluation will lead to a quantitative estimate of added margin over the rates predicted using the NRC NUREG-0313 crack growth disposition curve.

The second objective of this report is to evaluate the levels of inferred crack growth that could 4

occur in one of the heat affected zones in the recirculation piping system. Based on the same i

1 1

\

GEN:clearEnergy GE-NE-B13-01980-030-2, Rev. 0 1

knowledge of crack growth rate behavior and plant water chemistry, the report will address the likelihood of the newly detected crack segments occurring in only one cycle and contrast that possibility with initiation early in the operating life of the plant followed by measurable growth  !

during the pre-IHSI operational cycles.

2.0 CRACK GROWTH RATES FOR QUAD CITIES UNIT 1 ASSESSMENT l

There have been significant effons made to understand the rates of crack growth due to IGSCC in Type 304 stainless steel in BWR environments including measurements of actual crack gmwth rates in laboratory and plant water chemistry environments. These have resulted in three primary crack growth models that complement the NRC NUREG-0313 relationship. These models are (1) l the BWRVIP-14 Crack growth correlation (reference 5), (2) the GE PLEDGE model (reference 6)  ;

and (3) the SKI Crack Growth Rate Relationships (reference 7). These models relate the applied  !

stress intensity factor, K, to the resultant crack growth rate. In addition, they require an understanding of the plant water chemistry and location of the component ofinterest. Therefore,  !

the plant specific inputs will be first presented followed by an assessment of the predicted crack l

growth rates for each of the models.

2.1 Key Inputs to Crack Growth Modeling for the Quad Cities Unit Recirculation Piping The key factors that control crack growth that are directly rela,.ed to the three factors controlling IGSCC: material susceptibility, applied and residual stresses, and the water chemistry (environmental) parameters. These factors are common to all methods and can be evaluated for the Quad Cities Unit 1 IHSI-treated recirculation piping welds. However, the water chemistry is l the most important in that it can be compared directly to the water chemistry test conditions l applicable to the NUREG-0313 curve.

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2.1.1 Current Water Chemistry at QC Unit 1 l The water chemistry that was present last cycle at the Quad Cities Unit 1 is the best measure of the l water chemistry that will be present in the upcoming cycle. The key parameters are the conductivity as well as the specific anionic species in the coolant. The latter is often treated as

( directly related to the conductivity in many modeling approaches. In particular, it has been established by Andresen that the presence of specific species such as sulfates and chlorides are largely responsible for accelerating SCC processes. In that Qad Cities Unit 1 is also injecting 2

GEN:clearE ergy GE-NE-B13-01980-030-2. Rev. 0 l

l hydrogen into the feedwater, the expected electrochemical corrosion potential (ECP) is also an important parameter. Table I displays the Unit I cycle average conductivity values from the beginning of plant operation . The average conductivity over the last cycle, which is the most representative of the future operational levels, was 0.09 S/cm. Figure 1 displays day to day details of the conductivity history over one representative month for the latest cycle. The yearly chloride and sulfate levels are also given in Table I for the same time period. The average sulfate and chloride levels for the last cycle were 1.4 and 1.0 ppb, respectively. In addition, the plant only exceeded Action Level I conditions (based on 0.3 S/cm or sulfate or chloride levels exceeding i 5 ppb) a total of 112 hours0.0013 days <br />0.0311 hours <br />1.851852e-4 weeks <br />4.2616e-5 months <br /> with the longest transient event held to 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br />. Finally, Table I gives the hydrogen injection rate for the cycles where it has been injected. For the last cycle, the hydrogen was injected for 92% of the time. This injection level has reduced the dissolved oxygen l levels in the range of 10 to 15 ppb, a level that relates to an ECP level of-50 to -100 mV,she. It is apparent that Quad Cities Unit I has cunently been operating with very good water chemistry. l These environmental conditions are expected to significantly retard IGSCC crack growth rates from those represented by the NRC NUREG-0313 disposition curve.

2.1.2 Current Understanding ofIHSI-treated Recirculation Piping Welds While the emphasis of this study is crack growth rates, it should be acknowledged that the piping l in this plant is Type 304 stainless steel in the as-welded and IHSI treated condition. The welding process would be expected to produce sensitization levels typical of high carbon piping. While this condition is certainly susceptible to IGSCC in BWR NWC environments, its condition is certainly bounded by the sensitization treatment used in most of the test specimens used to characterize crack growth rates as the basis of the NRC curve as well as the other newer disposition curves.

The IHSI treatment was verified to produce no additional sensitization at the same time that it introduced favorable compressive i.d. surface residual stresses. For conservatism, the benefit of the treatment was not considered in the structural margin assessment.

2.2 Supporting Crack Growth Rate Assessments Current efforts by both the BWRVIP end the Swedish SKI as well as the on-going efforts by GE CR&D have led to models that can be used to evaluate crack growth rates. These correlative or fundamental models can be used to disposition cracks. They can also be used to predict expected i

3

GElteinerEnergy GE-NE-B13-01980-030-2 Rev. 0 cracking behavior as a function of water chemistry. Both types of evaluations are useful in l supporting ajustification for continued operation with the existing crack indications in QC Unit 1.

l As will be shown for each of the models, a rate lower than the NRC NUREG-0313 rate is predicted based on the good conductivity of the operating environment and on the hydrogen injection that will reduce the ECP in the recirculation piping at Quad Cities Unit 1. The I

assessments take.n together lend high confidence that the NRC NUREG-0313 crack growth rate relationship used in an analysis is a boimding one. l i

2.2.1 BWRVIP-14 Crack Growth Evaluaticn l The BWRVIP has documented in Reference 5 a methodology for evaluating crack growth behavior in stainless steels. While the objective of this effort was to evaluate crack growth rates in core l

internal components, the evaluation is also useful in assessing crack growth in recirculation piping.

Many of the crack growth rate data were obtained in CAV systems which employed water j environments suppliui by the recirculation system. The effort included a compilation of crack growth rate data that was used to generate a statistically determined crack growth rate correlation.

4 The report also provided a plateau rate of 2.2 x 10 in/hr that could be used in the dispositioning of cracking in core internals constructed of stainless steel. It also represented a rate that wm associated with a high stress intensity and a high ECP typical of the core. The correlation allows l

calculation of a rate based on K, conductivity and an ECP value. Using the data from the Quad Cities plant, 0.1 uS/cm and 100mV,SHE, respectively, values of crack growth rates were L

t calculated and are given in Table 2. The data is also plotted against the NUREG-0313 line in j Figure 2. In all cases the predicted rates are well below the NRC points.

2.2.2 GE PLEDGE Crack Growth Rate Assessments: With and Without Hydrogen Injection The PLEDGE model was developed by GE CR&D over 15 years ago for sensitized stainless steel, then later extended to non-sensitized, then irradiated stainless steel. It can be used to predict both crack growth rates as well as crack growth in different austenitic stainless steel structural l coniponents. The PLEDGE model has been bencianarked using crack growth rate data as well as field cracking experience (reference 6). Because of its ability to use all specific material and environmental information, the model is well suited to predicting the future crack growth in recirculation piping, particularly when the plant is injecting hydrogen. The model requires inputs

) of the material susceptibility and water chemistry variables that include (1) the ECP (electro-i I 4

GEN:clearEnerxy GE-NE-B13-01980-030J., Rev. O i

chemical corrosion potential) which depends on the level of oxidizing species in the location of interest and (2) the conductivity. The ECP value, measured directly in laboratory tests, is best selected based on plant measurements or values based on radiolysis modeling and benchmarked by measuremcats from similar BWRs. He effective conductivity used in the model can account for the specific anionic species that promote IGSCC as well in that crack growth data was developed using aggressive sulfate-containing environments. The material susceptibility is a parameter.

However it is usually given a value of 15 C/cm2 to bound the sensitization levels found in as-welded high carbon stainless steel The outputs of the PLEDGE calculations are also given in Table 2. The conductivity was set at a value of 0.1 S/cm. Crack growth rates were calculated for two ECP values. The first sets of rates were calculated for an ECP of 100mV,SHE which is representative of the corrosion potential in the recirculation system under NWC. It can be seen that the crack growth values are always less than the NUREG-0313 rate displayed in the table. The second set of calculations is based on the conditions that are representative of the hydrogen injection levels used in the last cycle. The ECP was set at a value of-50 mV, SHE. This value bounds the measurements made in Quad Cities Unit 2, a sister plant (reference 8). It also corresponds to the exygen levels measured in the piping:

10 to 15 ppb. The PLEDGE model is capable of using the specific ECP to calculate the crack growth rate. These values are also given in Table 2. It can be observed that the rate is at leart a factor of-8 slower than the PLEDGE NWC rate and a factor of 25 lower than the NUREG-0313 rate (as assessed at a K of 25 ksi-inv2). These predicted rate :M'erences between PLEDGE and the NRC line can be attributed to the lower conductivity and the lower ECP based on the second set of rates.

2.2.3 SKI Based Assessment: With and Without Hydrogen The Swedish Inspectorate has also established crack growth relationships for austenitic stainless steel (reference 7). These simple, easy to use relationships are based on a subset of the crack growth rate data compiled in the BWRVIP effort. The disposition lines incorporate a stress intensity factor dependence that is based on PLEDGE, thereby making use of the code's fundamental relationships between crack growth and stress intensity factor. Different cunes are recommended for good NWC as well as good HWC water chemistry, consisteni with the

fundamental principles of crack growth rate understanding. " Good water cherrastry is that which

! is below the EPRI Guidelines Action Level 1 (conductivity <0.3 S/cm)." The predicted growth rates are also given in Table 2. Both sets of crack growth rates predict lower rates than the NRC l

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GENuclearEnergy GE-NE-B13-01980-030-2. Rev. 0 disposition curve. While the previous operating parameters do not fully meet the criteria for the SKI HWC line (the ECP values were recorded to be >-230 mV,SHE), the curves clearly substantiate the benefit of the lower potentials.

2.3 Summary of Modeling Results As presented in the previous sections, there exist several crack growth rate formulations. The

results of calculations made using these models (presented in Table 2) can also be shown graphically for comparison. Figure 2 presents all of the calculated crack growth rates made using the different models. Each of the sets are compared to the NRC NUREG-0313 curve. The different curves clearly establish the benefits of good water quality
low conductivity and sulfate and chloride levels below 2 ppb. The HWC curves also establish the additional benefit of hydrogen injection. Specifically, the PLEDGE calculation has been made for a realistic ECP reduction of 100 mV,SHE to -50 mV, SHE for the 1.5 ppm injection level at Quad Cities Unit 1.

These are the best representation of the crack growth rates that would occur in the recirculation I piping. Therefore, a structural assessment for Quad Cities Unit I that calculates crack growth rates using the NUREG-0313 relationship will predict conservative rates of throughwall deepening. The l

expected rate, depending on the model used, would be 50% to 4.5 times slower under NWC '

conditions and 8 times slower with hydrogen injection levels used in the last cycle.

, 3.0 ASSESSMENT OF DEEP CRACKING IN IHSI-TREATED RECIRCULATION PIPING The operating history presented in Table 1 establishes that for the first several cycles, the Quad 4 Cities Unit I water chemistry was high in conductivity and had yearly average chloride levels as high as 30 ppb. These conditions are known to be conducive to IGSCC initiation and crack growth. The NUREG-0313 crack growth rate curve is very applicable to predicting growth during j these early cycles. With this as a basis, it is expected that many of the recirculation piping weld HAZs had cracking prior to the application ofIHSI. Therefore it is also expected that cracking would be detected following IHSI. In this context, it is appropriate to re-evaluate whether any comparable crack growth could occur in these welds in the last cycle. To aid in this evaluation, several factors will be reviewed: (1) the field history of the behavior of category C IHSI treated welds after application with probable or known IGSCC indications, (2) the understanding of l growth of pre-existing IGSCC cracks after IHSI application, (3) the potential for changes in

characteristics over post-IHSI operation.

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I GENxclearE ergy GE-NE-B13-01980-030-2. Rev. 0 l

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3.1 Previous Field Performance ofIHSI treated welds I

l Several operating BWRs have perfonned IHSI treatments of piping welds following a significant l amount of operating time. These include Oyster Creek Millstone, Browns Ferry Units, FitzPatrick, Hatch Unit I and the Quad Cities Units. The IHSI-treated welds did include ones with pre-existing crack indications. There have been differing experiences following IHSI treatment. Several of the l

plants did observe apparent changes in the cracking patterns following one or more cycles of l

operation. The plant owners took different actions. However, there was general acknowledgment I l that the apparent cracking patterns could change with time. There was also general acceptance that j the IHSI process was still an effective countermeasure for IGSCC in recirculation piping. Each of the plant owners continued forward, takmg credit for the mitigation of the well behaved welds.

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3.2 Understanding ofIHSI Treated Pre-cracked Piping l

The basis for accepting that IHSI was a viable IGSCC countermeasure was based on the extensive qualification program that was undertaken by GE under the sponsorship of the EPRI. The program l evaluated the relationship of the compressive residual stress state that was produced to the l application specification. The program also evaluated the effects ofIHSI treatment on pipe welds l which had pre-existing flaws. These studies included analytical studies and residual stress measurements. The analyses showed that arrest occurred for cracks that had significant depths (reference 9). Actual pipe tests were also conducted and esablished that the IHSI treatment did arrest the cracks that were in 4" pipes and had depths of up to 17% of wall thickness (reference l 10). These efforts substantiated that the process could arrest the cracking. The post-IHSI operating history also acted as a means of verifying that the pre-existing flaws were typical of those

evaluated in the qualification program. It was acknowledged that for some of the pipes where the l applied stresses were very high, the treatment benefits could be overwhelmed.

l l

l 3.3 Influences of Operation Time and Conditions on IHSI-treated Pipe Characteristics The experience at several utilities establishes that some of the IHSI-treated piping will exhibit different crack length characteristics from cycle to cycle. These changes are difficult to establish as being either (1) an existing crack that did not really change in depth or length or (2) an existing crack that did actually deepen and/or lengthen. The experiences at Oyster Creek established that the process was effective and only changed the crack tip characteristics by blunting it and therefore 7

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

. GENeedentEnergy GE-NE-B13-01980-0304, Rev. 0 1

opening it. Other utilities such as FitzPatrick have tied the changes , in part, to changes in UT technique. In small piping such as 12" diameter piping, deeper cracks have continued to grow, l suggesting that the pre-IHSI cracks' depths exceeded the depth of IHSI residual stress improvement. The knowledge of the changes that take place in recirculation piping suggest that the crack can also experience changes in the vicinity of the crack mouth. Studies of HWC and zinc

' addition have shown that the oxide films on the pipe surface will undergo modification and re-

structuring . These water chemistry parameters lead to a thinner oxide layer. Visual inspections

!' have verified differences ' on the surface of components as well. While not proven, the modifications could be postulated to change the amount of oxide in the crack which might change the reflectivity of the. crack mouth to UT.

4 3.4 Assessment of Rapid Growth in IHSI-treated Piping at Quad Cities Unit 1

{ Based on the current understanding of the Quad Cities Unit 1 operating history, it is clear that cracking most likely initiated during the early cycles. This is particularly true for the deeper indications. There has been no experience of cracking both initiating and propagating to significant depths when all the factors present at Quad Cities co-exist: the high purity low conductivity water, the injection of hydrogen lowering the corrosion potential and the earlier IHSI j processing that would at the least be expected to reduce the tensile magnitude of the residual

. stresses. The explanation for any new indication must be linked to one of the following
(1) a change in the crack's visibility to UT inspection, (2) a small change in the depth of an already existing deep indication to make its UT signature visible or (3) changes in the crack's visibility allowing it to be better differentiated from a pipe geometric feature. The explanation could also combine these factors. There is no reasonable way to explain crack growth rates greater than those proposed within the constraints of existing mechanistic knowledge and experience of IGSCC in operating BWRs.

4.0 CONCLUSION

S i'

The purpose of this report is two fold. First, the repert addressed the applicable crack growth rates that can be used to evaluate cracking in the upcoming cycle to disposition cracking in recirculation piping. The second objective of thic report has been to evaluate the reasonable levels of crack growth that could occur in any one of tne heat affected zones of the recirculation piping in the last j cycle based on the same knowledge of crack growth rate behavior and plant water chemistry applicable to Quad Cities Unit 1. The report also discussed the possible contributors to perceived excessive growth. The important conclusions are as follows:

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I GENucinerEcagy GE-NE-B13-01980-0304. Rev. O

1. The current operating water chemistry at Quad Cities Unit I supports the use of crack growth f rates that are significantly slower than the rates given in the NRC NUREG-0313, revision 2.

l Therefore, the use of the NUREG rate in a structural margin assessment is conservative.

i i 2. The crack growth rates calculated using the GE PLEDGE model, which are deemed to predict I

! ir2 realistic rates, are a factor of 3 lower under NWC conditions (K set at 25 ksi-in ) and a factor of 8 lower when HWC is injected to the levels used in cycle 15 at Quad Cities Unit 1, the last operating cycle.

3. The BWRVIP-14 model also predicts a factor of 4.5 lower crack growth rate (K set at 25 ksi-inir2 and under NWC conditions) than that predicted using the NUREG.0313 curve.
4. Previous experience with IHSI-treated recirculation piping has shown that the size of crack indications can appear to be different based on comparison of successive UT inspections.

Understanding of the IHSI-process and field experience strongly suggest that these changes are not indicative of actual large changes in crack length or depth.

5. The understanding ofIGSCC behavior and the specific conditions at Quad Cities Unit I are inconsistent with the occurrence of any large amount of crack growth in any IHSI-treated piping HAZ over the last cycle.
6. Explanations for the changes in the UT-determined depth are most likely due to changes in the visibility of an existing crack. These changes could be related to the changes in the stainless steel piping's oxide film. These changes are consistent with the changes that are known to occur due to hydrogen injection coupled with zine additions.

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5.9 REFERENCES

1. W.S. Hazelton: " Technical Report on Material Selection and Processing Guidelines for BWR +

l Coolant Pressure Boundary Piping, " NUREG-0313, Rev. 2, January 1988.  !

2.Section XI Task Group for Piping Flaw Evaluation, ASME Code, " Evaluation of Flaws in  ;

l Austenitic Steel Piping, J. of Pressure Vessel Technology, vol.108, p. 366, ASME,1986.

3. NRC Generic Letter 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping," January 25,1988.
4. R.M. Horn et al.: "The Growth and Stability of Stress Corrosion Cracks in Large Diameter BWR Piping," EPRI NP-2472, Vol. 2, July 1982.  !

l

5. BWRVIP Document, EPRI TR-105873, " Evaluation of Crack Growth BWR Stainless Steel l

l RPV Internals (BWRVIP-14)", March 1996.

l l 6. F.P. Ford and P.L. Andresen: " Prediction of Environmentally Assisted Cracking in Boiling ,

Water Reactors, Part I: Unirradiated Stainless Steel Components", GE NEDC-32613, June  ;

i 1996. l l \

7. K. Gott: "Using Materials Research Results in New Regulations - The Swedish Approach,"

Proceedings of Seventh International Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Volume 1 (pp. 639-649), August 1995.

8. P. Behrens: private communication in reference to Quad Cities 2 ECP measurement
9. EPRI NP-3375," Induction Heating Stress Improvement," November 1983.

. 10. EPRI NP-5881-LD, " Assessment of Remedies for Degraded Piping, " June 1988.

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l GEN clearEnergy GE-NE-B13-01980-030-2, Rev. 0 l Table 1: QC-1 Cycle and Yearly Water Chemistry Conductivity Averages Plant Cycle RW Cond. Cl SO4 HWC

( S/cm) (ppb) ( ppb) Availability

  • QC-1 1 .474 30.3 NA NA QC-1 2 .633 30.9 NA NA 1 QC-1 3 .208 30.2 NA NA l QC-1 4 .215 30.8 NA NA l QC-1 5 .288 20.3 NA NA QC-1 6 .308 20.2 NA NA QC-1 7 .145 20.1 Na NA l QC-1 8 .180 16.8 NA NA QC-1 9 .168 5.9 5.9 NA QC-1 10 .116 3.4 2.5 NA QC-1 11 .144 2.7 2.8 33.3 %

QC-1 12 .142 2.9 2.1 37.4 %

QC-1 13 .090 2.0 2.4 81.6 %

QC-1 14 .078 0.8 1.4 90.2 %

QC-1 15 .090 1.0 1.4 92.1 %

  • Injection rate and protection level different for each cycle i

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GENuclearEzertv GE-NE-B13-01980-030-2 Rev. 0 l

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l UNIT ONE REACTOR WATER

, CONDUCTIVITY No data for curve 3 l

,3<[TEuJuury M .; ul'lik; CClJ.;G;mlJ m m_-

- .,;g LA;;;;;; 100 COND(FT)(L) 1,RX l

v l l -

1 l COND( F T)-ulimit, x 1RX

)C AL1

( ------4 -------.

kpot 9 l '2 e P ## '*PP X

[. COND ( L) j kf*

  • 1CUI 4

1 fP =

E ,'

u - .

6 2

} <

50 E ~

2RX X

l

.1 f k

, vwee*%4 M

  • l 0 '

" O 7-98 B-98 9.'98

l Figure 1: Typi.al Conductivity levels during one month of operation at Quad Cities Unit 1.

12 l

l

GENuclear Energy GE-NE-B13-01980-030-2, Rev. 0 Table 2: Comparison of Crack Growth Rates (in/hr) for Different Crack Growth Models (For the BWRVIP and the PLEDGE

  • Models, a conductivity of 0.10 S/cm was used which bounds the average conductivity of the previous cycle's value of 0.090 S/cm. i f

Stress Intensity, NRC BWRVIP-14 PLEDGE PLEDGE SKI SKI  :

ksi-inl/2 NUREG-0313 (in/hr) (100mV,she) (-50 mV,she) (NWC) (HWC) l (in/hr) (in/hr) (in/hr) (in/hr) (in/hr) l 5.20E-06 10 1.095E-06 8.5E-07 6.18E-08 1.79E-06 4.71E-08 15 1.25E-05 2.65E-06 2.71E-06 2.54E-07 6.05E-06 1.59E-07 l 20 2.33E-23 4.96E-06 6.17E-06 6.93E-07 1.43E-05 3.77E-07 25 3.77E-05 8.08E-06 1.17E-05 1.50E-06 2.8E-05 7.37E-07 30 5.59E-05 1.20E-05 1.97E-05 2.85E-06 7.68E-05 2.02E-06 I l

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GENuclear Enery GE-NE-BI3-01980-030-2, Rev. 0 l

l 1.00E-03 _

+NRC NUREG-0313 Curve 1.00E-04 -- W -- PLEDGE: 0.1 uS/cm,100mV t- l - - D - - PLEDGE: 0.1 uS/cm, -50 mV

.-' *- BWRVIP-14: 0.1 uS/cm,100 mV E fe*_e**^ -T A

-*- SKI Curve- NWC E

--h**! >

h" 5 '*

1 g '00E-05 #- y .O -

E EN e$ .0' - '{ --E- SKI Curve-HWC g

e y y

, ._p -

l y_

o gf ',.O..- ,, gaX,,=

j 1.00E-06 a ^

~

U

. .9_.-

,- f**#

l q L

fpA j x

.qx - t- x 1.00E-07 -

'x Representative of

_g y' - {

x " Hydrogen injedion at Quad Cities Unit 1 using

! PLEDGE l l 1.00E S 10 15 20 25 30 35 40 45 50 K, ksi-in1/2 Figure 2: Crack Growth Rate vs. Stress Intensity for Different Models -

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t ATTACHMENT B l

l "A Fracture Mechanics Evaluation on Observed Indications at Two Welds in Recirculation Piping of Quad Cities, Unit 1 Station" l

SVP-98-353 1

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