ML20214J924

Nonproprietary NRC Presentation Rept on Steam Generator Tube Integrity for DC Cook Unit 2,Sept 1986

ML20214J924
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Site:	Cook
Issue date:	09/30/1986
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References
WCAP-11330, NUDOCS 8612020058
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WESTINGHOUSE CLASS 3 WCAP-11 30 O

NRC PRESENTATION REPORT ON STEAM GENERATOR TUBE INTEGITY FOR DC COOK UNIT 2. SEPTEMEER 1956 1

SEPTEMBER, 1986 4

b WESTINGHOUSE ELECTRIC CORPORATICN POWER SYSTEMS P. O. BOX 355 PITTSBURGH,PA 15230-0355 pgA202ggg8ggggggge P

TABLE OF CONTENTS NRC PRESENTATION REPORT ON STEAM GENERATOR TUBE INTEGRITY FOR DC COOK UNIT 2, SEPTEMBER 1986 List of Tables and Figures Reference Submittals INTRODUCTION 1.0 OVERVIEW 0F RECENT PLANT OPERATING HISTORY

1.1 Background

1.2 Operating Experience During Remainder of Cycle 5 2 1.3 April /May 1986 Eddy Current Testing - Inspection Plan and Results

1. 1.4 April /May 1986 Eddy Current Testing - Summary of Results 1.5 Cycle 6 Operating Experience 2.0 APRIL /MAY 1986 EDDY CURRENT TESTING - DISCUSSION OF RESULTS 2.1 General Eddy Current Analysis Criteria 2.2 Special Analysis Criteria for Hot Leg Tube Support Plates 2.2.1 Definitions 2.2.2 Review of Inservice Inspection Criteria 2.2.3 Development of the Threshold Voltage Concept 2.2.4 Verification of Threshold Voltage Concept 2.3 Overview of 1986 Eddy Current Inspection Results

• 2.4 Present Growth Rate Data Derived from "85" "86" Inspection Results STD6030 i

TABLE OF CONTENTS - (Cont.) -

3.0 EVALUATION OF OPERATION THROUGH END OF CYCLE 6 -

3.1 Structural Integrity Conservatism 3.2 Leak Before Break Verification 3.3 Operating Interval Determination 4.0 STATUS OF REMEDIAL MEASURES 4.1 Improve and Maintain Proper Water Chemi:try ,.

4.2 Boric Acid Treatment Assessment 4.3 Study of Corrosion Factors 4.4 Mechanical Repairs l

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LIST OF TABLES AND FIGURES list of Tables 1.1.1 Chronology of S. G. Events through December 1985 1.2.1 Operating Experience During Remainder of Cycle 5 j 1.3.1 Operating Experience for Beginning of Cycle 6 l.4.1 April /May 1986 ECT Inspection Plan 2.2.1 Eddy Current Signal Classification,1986 2.2.2 1985 Outage Tube Support Plate Inspection Results 2.2.3 March 1986 Rotating Probe Inspection 2.4.1 Cook 2 Degradation "85" "86"  !

2.4.2 Comparison of "84" "85" and "85" "86" Degradation Rates 4 3.1.1 DC Cook Unit 2 S. G. Tube Minimum Acceptable Wall Requirements

1. 3.1.2 DC Cook Unit 2 Allowable Wall Loss Determination 3.3.1 Operating Internal Justification DC Cook Unit 2 4.0.1 Status of Remedial Measures 4.2.1 Remedial Actions Based on Causitive Factors 4.2.2 Boric Acid Test Program, Conclusions l

l 4.2.3 Evaluation of Boric Acid Treatment on Cook 2 Steam l Generators 1

4.2.4 Evaluation of Boric Acid Treatment on Cook 2 Steam Generator

- Conclusions to Date I

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List of Fiaures .

1.1.1 Westinghouse Series 51 Steam Generator -

1.5.1 Summary of S. G. Hot Leg ECT Inspection Results - April /May 1986 2.1.1 Comparison of "85" and "86" Plugging Criteria 2.2.1 Large Amplitude Signal in Mix Channel 2.2.2 Small Amplitude Signal in Mix Channel 2.2.3 Eddy Current Measurement Accuracy, Stress Corrosion Cracking 2.2.4 Signal Threshold Establishment in Mix Channel 2.2.5 Typical Support Plate Mix Signals 2.2.6 Pancake Coil 2.2.7 Pancake Coil " Imaging" 2.2.8 Support Plate NDD ,

2.2.9 Support Plate DI s

2.2.10 Support Plate DI Confirmation 2.2.11 Support Plate Euantifiable 2.2.12 Support Plate Quantifiable Confirmation 2.3.1 S. G. 2, March "86" Hot Leg, % Incications/Non-Quantifiable j Indications Map i

2.3.2 S. G. 2, March "86" Cold Leg, % Indication Map 2.3.3 S. G. 2, March "86" Hot Leg, Indication Count 2.3.4 S. G. 2, March "86" Cold Leg, Indication Count 2.3.5 S. G. 2, March "86", Pluggable Indications l 2.3.6 Composite, March "86", Pluggable Indications .

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4.1.1 S. G. Cation Conductivity - Yearly Average I -

4.1.2 S. G. Sodium - Yearly Average STD6030 iv l

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kjst of Fiaures - (Cont.)

4.1.3 SJAE Air Flow - Yearly Average 4.1.4 Condensate and Feedwater D.O. - Yearly Average 4.2.1 Effect of Boric Acid in Reference SCC Tests 4.2.2 Effect of Boric Acid on Pre-Initiated Cracks 4.2.3 Effect of Boric Acid on Reference IGA Tests i 4.2.4 Update of Boric Acid Operating Experience 4

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Reference Subtittals

1. AEP:NRC: 0936A, letter to Mr. Harold R. Denton, NRR-USNRC,

" Steam Generator Tube Plugging - Interim Status Report", dated -

October 10, 1985, plus Attachments 1,2, and 3.

2. AEP:NRC: 0936C, letter to Mr. Harold R. Denton, NRR-USNRC,

" Steam Generator Tube Integrity - Interim Status Report", dated February 7,1986, plus Attachment 1,2,3, and 4.

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INTRODUCTION

. On September 16, 1986 American Electric Power Service Corporation (AEPSC), acting on behalf of Indiana & Michigan Electric Company (I&M), presented to the NRC staff a discussion of recent DC Cook Unit 2 steam generator issues. The presentation served to provide justification for continued operation through the end of the current fuel cycle and to inform the staff of I&M's intentions regarding future replacement of the steam generators. The purpose of this report is to document that portion of the presentation dealing with continued operation.

1.0 OVERVIEW 0F RECENT PLANT OPERATING HISTORY

1.1 Background

DC Cook Unit 2 incorporates a nuclear steam supply system manufactured by Westinghouse, and is licensed for 3411 MW t*

Initial criticality occurred on March 10, 1978. The unit is currently operating in its sixth fuel cycle; as of August 31, 1986, about 5.4 effective full power years of operation have been accrued.

Unit 2 has four Westinghouse Series 51 steam generators of the type 5

illustrated in Figure 1.1.1. A description of significant features and a review of the types of tube degradation experienced prior to g November 1983 are contained in Reference Submittal 2.

l. The first significant indication of secondary side tube corrosion in

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the Unit 2 steam generators occurred in November 1983. A chronology of steam generator events from then until December 1985 is attached as Table 1.1.1. Details of these events are documented in Reference Submittals 1 and 2, and were presented and discussed by AEPSC in a meeting with the NRC staff on December.4, 1985.

As a result of that meeting, I&M was given approval to continue Cook 2 operation through the end of Cycle 5, at which time steam generator tube surveillance would be required in accordance with plant Technical Specifications. The NRC staff also agreed that, following surveillance and plugging of any degraded tubes in excess of the plugging limit that may be found, I&M could restart and operate Cook 2 for up to three effective full power months in Cycle 6 without further review by the NRC.

1.2 Operating Experience During Remainder of Cycle 5 l_

Unit 2 operated from October 24, 1985 through the remainder of Cycle 5. A summary of operating experience for the period is given in Table 1.2.1.

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From start-up in October 1985 (following the last forced outage due .

. to tube leakage) until February 28, 1986 (when the Cycle 6 refueling outage began), the reactor generated 6,959,834 MWt hrs., or about 85 effective full power days (EFPDs). -

Unit thermal power output was administratively limited - typically to about 80 percent - in order to reduce the primary side temperature and perhaps slow the rate of tube degradation. Secondary side chemistry treatment included on-line addition of boric acid to inhibit caustic-induced tube corrosion; boron concentration was maintained at 5 to 10 ppm. The apparent impact of these measures is addressed in Section 4.0.

Two outages occurred during the period but were unrelated to steam 4

generator tube degradation. Following the second of these outages, primary-to-secondary steam generator leakage, which had been consistently measured at about 0.001 gpm since the October start-up, increased to about 0.038 gpm, an order of magnitude less than the Technical Specification limit of 0.35 gpm.

Upon unit shutdown, visual inspection of each steam generator's i

primary tubesheet surface under a static head of water revealed no leakage. After establishing a 600 psi nitrogen overpressure, water was observed to be slowly dripping from the hot leg tube end of tube R16C45 in SG 22. Subsequently, eddy current testing confirmed the ,

presence of an indication in the tubesheet crevice region.

Steam generator activities during the refueling outage included .

bobbin coil probe eddy current testing in accordance with Technical Specification requirements, tube plugging as required, and crevice flushing and low power soaks with boric acid. Also, limited eddy current testing with a rotating pancake coil probe to validate the analysis techniques used at support plate intersections was performed. These activities are discussed in later sections of this

report.

1.3 April /May 1986 Eddy Current Testing - Inspection Plan and i Results

! A steam generator tube eddy current inspection in accordance with

Technical Specification 4.4.5.0 surveillance requirements was performed in April /May 1986. Table 1.4.1 summarizes the initial sample selection and subsequent expansions to include the appropriate 4

areas of each steam generator.

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Data collection and primary evaluation were performed by Westinghouse. An independent analysis of the data was performed by Conam Inspection. Conam also conducted a comparison of each indication (including distorted indications or other anomalous eddy current signals, etc.) with corresponding data from the Fall 1985 inspection, and re-evaluated the 1985 data using the analysis criteria developed for the 1986 inspection. The 1986 analysis criteria are based on Westinghouse and AEPSC correlation of bobbin coil data with tube sample metallographic results, and are discussed in detail in Section 2.0.

Approximately 75 tubes were also inspected by Westinghouse with a rotating pancake coil eddy current probe, primarily to help validete the analysis criteria used at the tube support plate intersections.

Results are discussed in Section 2.0.

1.4 April /May 1986 Eddy Current Testing - Summary of Results Figure 1.5.1 is a tabulation of eddy current results for the hot legs of the four DC Cook Unit 2 steam generators. The area inside tha boundary represents the plugging criteria implemented by I&M.

1.5 Cycle 6 Operating Experience i

= Unit 2 began operation in Cycle 6. A summary of operating experience through August 31, 1986 is given in Table 1.3.1.

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• Thermal power output remains administratively limited again to L

! typically 80 percent, although operation' at 90 percent has occurred in order to perform certain tests and to meet high system load demand during the summer peak period. Thermal generation through the e'nd of-l August has been 3,015,035 MWt hrs, or about 37 EFPDs.

l l Frtz start-up on July 7 through the date of this writing in late October 1986, no indication of steam generator primary-to-secondary leakage has been detected.

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2.0 APRIL /MAY 1986 EDDY CURRENT TESTING - DISCUSSION OF RESULTS 2.1 Eddy Current Analysis Criteria The eddy current analysis criteria used during the 1986 inspection for ~

dispositioning tubes was derived from prior eddy current results at Cook Unit 2 and usir.g the tube pull examination data collected in 1985. A summary of the criteria used for tube plugging is shown in Figure 2.1.1. This is shown by the enclosed area which indicates tube condition definitions which were plugged in the "85" outage and in the "86" outage. The enclosed area is larger in the 1986 outage compared to the 1985 outage. The area of expanded administrative plugging was at the tubesheet surface.

In general, the technical specification plugging criteria of indications greater than 40% was used in two areas, the tube support plate elevations and with miscellaneous indications. In all other locations, more conservative administrative plugging criteria were utilized. In 1985, this included all indications observed in the crevice region and those indications that were at or above 30%

through-wall at the tubesheet surface. In 1986, the plugging criteria was expanded to include all indications observed at the tubesheet surface.

Conservatism was implemented in the 1986 inspection in the regions of the crevice and the tubesneet surface through the elimination of a -

threshold voltage criteria which is typically used as a signal to noise measure to discriminate between reportable and nonreportable indications. In 1985 a threshold voltage criteria was utilized; -

however, in 1986 any indication, independent of the amplitude or voltage, was considered. Consequently, a more conservative plugging plan was implemented in the area of the tubesheet crevice and just above the tubesheet. Relative to distorted indications at the tube support plate elevations, an inspection criterion based on signal amplitude, i.e., threshold voltage, was developed and used.

2.2 Special Analysis Criteria for Hot Leg Tube Support Plates 2.2.1 Definitions In the 1986 outage an overall signal classification plan for the hot leg tube support plates was implemented which benefitted from the tube sample metallography and additional laboratory diagnostics conducted prior to the outage. A summary of the signal classifications is shown in Table 2.2.1. The first classification is that of a percent through-wall indication which was based upon criteria of a distorted 400 KHZ support plate signal with a signal in the mixed channel output -

whose magnitude exceeded a threshold voltage level. This degradation was treated as tube wall degradation in excess of the technical STD6030 4

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specification plugging limit of 40 percent. The threshold voltage level will be discussed later but was based upon data obtained from the tube pull from DC Cook Unit 2 and additional laboratory generated specimens. The second criteria, a Distorted Indication or DI, was that associated with a distorted 400 KHZ support plate signal with a signal in the mixed channel whose magnitude was less than the threshold voltage. This condition was treated as tube wall degradation but less than the plugging limit of 40% and would be identified such that it could be monitored during subsequent inspections. The third condition identified is No Detectable Degradation or NDD. This is a condition which is observed to be typical of signals obtained from normal tube support plate intersection tube signals not indicative of tube wall degradation.

2.2.2 Review of Inservice Inspection Criteria To better understard the 1986 inspection criteria implemented for the hot leg tube suppert plate intersections, a brief review of the eddy current data observed in 1985 is provided. Figure 2.2.1 is typical of a large amplitude signal observed in the 1985 inspection. The top half of the figure demonstrates the information obtained using single frequency 400 KHZ diagnostics and the bottom of the figure illustrates a mix of 100/400 KHZ frequencies. In contrast, Figure 2.2.2 shows a small amplitude signal. The normal depth

. interpretation of a signal is based upon the phase angle of the signal. However, due to the small amplitude of signals as shown in Figure 2.2.2, this methodology was not considered to be reliable.

4 Consequently, tube samples were removed during the 1985 outage and e analyzed with the objective of refining the eddy current evaluation technique.

Table 2.2.2 summarizes the actions which have been implemented to disposition the tube degradation occurring at the tube support plate intersections. For the 1986 outage, the correlations established for eddy current inspection analysis were based on metallographic data and were confirmed utilizing a rotating pancake eddy current probe.

2.2.3 Development of the Threshold Voltage Concept In developing the 1986 inspection criteria, a comparison of the eddy current estimated depth based upon the 100/400 KHZ mix was compared to the depth of degradation as determined by metallographic examination. Based on measuring tube wall degradation utilizing signal ghase angle, as can be seen in Figure 2.2.3, above

[ .]a, ,e wallde0radationeddycurrentaccuracyismaintained

. within a [ .]a,c, scatterband. The extent of the tube wall depth of penetration is also reflected in eddy current signal amplitude, which is measured by voltage as shown in Figure 2.2.4. Eddy current i

signal displays representing both classes of signals, small and large l

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amplitude, are shown in Figure 2.2.5. Based upon the above, a threshold signal amplitude voltage was selected which discriminates ~

between low voltags signals in which the phase angle determination of depth is not as accurate and high voltage signals in which the phase angle determination of depth is more accurate.

2.2.4 Verification of Threshold Voltage Concept To confirm the 1986 criteria, a supplemental eddy current inspection program was conducted. This program utilized a rotating pancake coil probe inspection to validate the logic for dispositioning the indications at the hot leg support plates and to confirm that degradation conditions were still confined within the support plate.

See Table 2.2.3.

The basic design of the rotating probe, illustrated in Figure 2.2.6, utilizes a surface riding eddy current probe forced into contact 4

against the inner diameter of the tube by a spring loaded mechanism.

The assembly is rotated circumferentially as it is translated axially through the tube resultin5 in a closely spaced helical pattern.

Utilizing this inspection technique, a detailed description of the condition of localized tube degradation can be obtained and characteristics of the indication morphology identified. Shown in Figure 2.2.7, this type of information is demonstrated for an -

inspection standard consisting of several artificially induced flat bottom holes. In addition, the edge of a tube support plate placed in proximity to the tube with the flat bottom holes is also indicated.

Each class of signal in whiAh the bobbin coil inspection criteria was implemented was confirmed dtilizing the rotating pancake coil.

Figure 2.2.8 illustrates a comparison between the bobbin coil data and the rotating pancake coil data for a class of signals identifiea as No Detectable Defect (NDD). As observed in the top half of this figure, an essentially normal tube support plate signal is shown in the 400 KHZ frequency, and in the bottom half of the figure, the rotating probe data is shown which illustrates the absence of any significant irregularities in the eddy current field.

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Figure 2.2.9 demonstrates the Distorted Indication or DI class. As discussed earlier, this class was concluded from the tube sample examination results to be evidence of actual wall degradation but below the plugging limit. The results of the rotating pancake coil inspection is shown in Figure 2.2.10. In the top half of the figure the isometric image of the area inspected is shown and it reveals minor " peaks and valleys" indicative of some minor wall degradation.

Also, in the vertical channel, the data confirms that these indications are confined to the space within the support plate. The use of phase angle determination of wall depth with the rotating pancake coil inspection at the deepest indicated location showed that the depth of penetration is indeed less than the plugging limit.

The third classification of signals were those determined to be quantifiable in terms of depth of penetration. As shown in Figure 2.2.11, both the 400 KHZ detection frequency and the 100/400 mix show the presence of quantifiable wall degradation. Utilizing the criteria of the inspection these would be quantified using the phase angle from the 100/400 KHZ mix, and in the particular case shown, determined to be a pluggable indication. To confirm this condition the rotating pancake coil probe was applied as shown in Figure 2.2.12. The isometric display of the data shows more pronounced

" peaks and valleys" than is shown in the case for the distorted indication. Also shown are the edges of the tube support plate. As

= can be seen in the vertical display, the extent of degradation is confined to the support plate region.

d From the comparison of the bobbin coil criteria developed from the tube samples and the rotating pancake coil supplemental inspections, several conclusions can be derived:

o Based upon the bobbin coil probe inspection, the threshold voltage concept is accurate in discriminating between pluggable and nonpluggable tubes based on a 40 percent wall reduction level.

o Rotating pancake coil probe data confirms that the tube degradation in the DC Cook Unit 2 steam generators is confined to within the thickness of the tube support plate.

t o Areas in which no wall degradation has been observed based upon the bobbin coil inspection data have no evidence of wall degradation using the rotating pancake coil probe data.

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2.3 Overview of 1986 Eddy Current Inspection Results Figures 2.3.1 through 2.3 6 demonstrate the spatial location and extent of wall degradation in the steam generator tubing. Figure 2.3.6 indicates the areas of pluggable indications and demonstrates -

the contribution of pluggable indications both on the basis of quantifiable percent wall loss based upon typical eddy current data interpretation as well as the areas of less quantifiable interpretation which were administratively plugged. This figure shows that the crevice area is the dominant area of tube degradation followed by the area at the tubesheet surface (which is significantly influenced by the conservative plugging limit imposed in which all evidence of degradation was removed from service). Most importantly, tubes with wall degradation at the hot leg tube support plate intersections in excess of 40% wall loss have been removed from service.

The integrity of the tube bundle has been established in two manners. First, the condition of the steam generator tubing has been assessed through eddy current inspection. The uncertainties associated with inspection have been minimized through knowledge from tube pulls and complementary inspection techniques transferred to the nominal inspection method. Secondly, conservative, administrative, plugging levels have been implemented by I&M for DC Cook Unit 2 in areas where corrosion growth rates have historically been more significant. .

2.4 Present Growth Rate Data Derived from "85" "86" Inspection Results .

In addition to the absolute level of wall degradation, a comparison of the eddy current indicated wall degradation in 1985 to 1986 was made to both assess the extent of degradation in the various portions of the steam generator and determine the rate of growth within the different tube bundle elevations. Also, the effect of revised operating conditions was considered in the growth assessment and will be discussed in Section 4.

In general, the rate of degradation in the various portions of the steam generator; the tubesheet crevice, the tubesheet surface, and the tube support plate were compared to the prior observations in 1985. The observations in the "85" to "86" operating period are consistent with that previously ob:erved. The apparent rate in the tubesheet crevice is above that at the tubesheet surface which leads the tube support plates. This comparison is shown in Table 2.4.1 which also shows the percent wall penetration change at each of the three locations. .

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Additionally the rates observed in the operating periods in "84" to "85" and "85" to "86" were compared on a per effective full power

. month basis. The results of this comparison are shown in Table 2.4.2. Not only is the trend of rate of degradation among each of the three most significant locations consistent between the two operating periods, but also there is a consistent trend of reduced wall degradation in the overall comparison of "84" "85" and "85" "86" data. The variation in the three locations can be associated with the conditions in the steam generator in terms of potential for corrodent concentration. The change in degradation between the different operating periods can be associated with the changes in secondary side water chemistry and also operating conditions. These will be discussed in Section 4.0. Because of the consistency of the degradation rates observed in the three locations and the consistency between these rates and the change in operating conditions, the "85" to "86" corrosion / degradation rates are considered to be the rates most appropriate for evaluation of current conditions within the steam generators.

3.0 EVALVATION OF OPERATION THROUGH END OF CYCLE 6 3.1 Structural Integrity Conservatism Minimum wall requirements for the DC Cook Unit 2 steam generator tubing were calculated in accordance with the criteria of USNRC Regulatory Guide 1.121, entitled " Basis for Plugging Degraded PWR Steam Generator Tubes". Confirmation of consistency with these requirements was demonstrated previously in 1985 based upon tube sample examinations and testing. They are summarized in Tables numbered 3.1.1 and 3.1.2. The basic requirements consist of:

1. Allowable minimum wall determination per the following:

l 1. For normal plant operation, primary tube stresses are limited such that a margin of safety of 3 is provided against exceeding the ultimate tensile strength of the tube material, and the yield strength of the material is not exceeded, considering normal and upset conditions

2. For accident condition loadings, the requirements of l paragraph NB-3225 of Section III of the Code are to be met.

I In addition, it must be demonstrated that applied loads are less than the burst strength of the tubes at operating temperature as determined by testing.

3. For all design transients, the cumulative fatigue usage factor must be less than unity.

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II. Leak Before Break demonstration, i.e., that a single -

through-wall crack with a specified leakage limit (Technical Specification leak rate limit) during normal operation would not propagate and result in tube rupture during postulated accident -

condition loadings.

In establishing the safe limiting condition of a tube in terms of its remaining wall thickness, the effects of loadings during both the normal operation and postulated accident conditions must be evaluated. [

]a,c,e Therefore, Item I.3 above need not be addressed for the DC Cook Unit 2 steam generator tubes.

In the calculation of tube minimum wall, three distinct areas of tube degradation within the DC Cook Unit 2 steam generators were addressed: tubesheet crevice, tubesheet surface (defined as the area from the very top of the tubesheet on the secondary side extending approximately 6 inches into the free span of the tube) and tube support plate intersections.

Based on the destructive examination of the five tube samples removed from steam generator 22 in 1985, the tube minimum wall determination for localized tube degradation occurring at the tube support plate .

elevations in the DC Cook Unit 2 steam generators assumed:

1. Tube degradation was characterized as multiple SCC, 0.1-0.2 inch in axial extent.

2. Partial through-wall cracking was evaluated as single and multiple cracks. '

l l 3. As tube support plate degradation was confined to the thickness j of the tube support plate, the maximum macrocrack length is

! equal to support plate thickness or 0.75 inch.

4. Link up of multiple SCC was considered improbable at postulated accident condition pressure differential as reflected in the tube specimen burst tests.

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- Likewise, a tube minimum wall determination for localized tube degradation occurring at the tubesheet crevice / top of the tubesheet assumed:

1. Tube degradation to be characterized as either multiple SCC or intergranular SCC combined with shallower, more widely spread intergranular attack (IGA / SCC).

2. Tubesheet crevice / top of the tubesheet tube wall degradation was evaluated as equivalent thinning (as a result of IGA) with a superimposed crack.

3. The axial extent of the equivalent thinned length of tube degradation is 1.5 inches. Also, the IGA (equivalent thinning) was uniform around the tube circumference.

Per NUREG/CR-718, " Steam Generator Tube Integrity program Phase I Report", a tube uniformly thinned around its circumference for an axial length of 1.5 inches would be expected to have a burst pressure equivalent to an undegraded tube having the same wall thickness and outside diameter as the thinned region.

Results of these calculations are provided in Table 3.1.1 for each of

, . the above areas of the tube degradation. Moreover, Table 3.1.2 provides a summary of minimum wall determination for the three regions of localized tube degradation occurring in the DC Cook Unit 2

. steam generators. In each case, the limiting criterion for determining the allowable tube wall reduction is the RG 1.121 i criterion for normal operation that requires a margin of safety of 3 l against exceeding the ultimate tensile strength of the tube material.

l 3.2 Leak Before Break Verification l

l The leak before break rationale is to limit the maximum allowable primary-to-secondary leak rate during normal operation such that the l associated crack length through which technical specification leakage

, occurs is less than the critical crack length corresponding to tube l

burst at the maximum postulated pressure condition loading (FLB).

Thus, on the basis of normal operation, unstable crack growth is not expected to occur in the unlikely event of the limiting accident.

Previously, it has also been demonstrated that growth of partial i through-wall cracks exhibit a limited aspect ratio. This characteristic results in crack extension through-wall prior to reaching the SLB/FLB critical crack length.

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For tube support plate intersections, an examination of .

metallographic sections from steam generator 22 has characterized the morphology of the cracks to be multiple SCC. All tube support plate SCC has been.of short axial extent (0.1-0.2 inch) confined within the -

tube support plate thickness. The single crack length corresponding i

to the plant Technical Specification leak rate limit of 0.35 ggm at a normal operating pressure differential is approximately [ ] ,c.e

inch. The critical crack length corresponding to burst during a postulated FLB accident is approximately [ la,c.e inch;

therefore, a leak before break margin of 52 percent is demonstrated. j 1

For the tubesheet crevice region, localized tube wall degradation has been characterized through metallography to be multiple SCC. At a range of 0 to 6.0 inches above the top of the tubesheet, metallography has shown localized tube wall degradation to be combination IGA / SCC.

The superimposed crack length corresponding to a leak rate of 0.35 gpm at normal operating pressure differential for a tube " thinned" uniformly 62 percent through-wall around the circumference for an axial length of 1.5 inches is approximately [ ]a,c.e inch. The

critical crack length corresponding to burst during a postulated FLB event is approximately [ ]a,c.e inch; therefore a leak-before-break margin of 25 percent is demonstrated.

The utilization of a leak rate monitoring policy which emphasizes i both absolute leak rate reasurement and rate of change and includes the initiation of action prior to reaching the Technical .

Specification limit (0.35 gpm) yields additional safety margin; for example, at a leak rate of 0.25 gpm and a pressure of 1400 psid, the

. factor of safety is at least [ Ja ,c,e relative to tube burst. It is important to note that very low leakage rates are detectable by leakage monitoring.

3.3 Operating Interval Determination The influence of the operating environment may affect some of the tubes in a steam generator and result in localized wall degradation.

As part of a preventative program to detect tubing wall loss,

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inservice inspection using eddy current techniques is performed.

! Affected tubes with a wall thickness greater than the minimum 4

acceptable wall thickness are acceptable for continued service, j provided margin is added to the minimum required tube wall thickness a to account for eddy current measurement uncertainty and an operational allowance for continued degradation until the next scheduled inspection. ,

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Table 3.3.1 summarizes the operating interval justification for locally degraded steam generator tubing, by tube elevation, upon

. completion of Cycle 6 operation of DC Cook Unit 2. The required tube plugging levels are based on the maximum permissible wall loss per tube location calculated in accordance with RG 1.121 criteria

([ percent for the tubesheet crevice / top of the tubesheet,

[ ]}a,c.e'C percent for tube support plate location degradation), the established eddy current measurement uncertainty for steam generator tube degradation ([ ]a,c.e percent), growth rate allowances from Section 2.4, and the duration of Cycle 6 (13.5 EFPM's). The eddy current measurement uncertainty and crack penetration growth rate allowance utilized in the above safety margin determinations represent conservative allowances based on previously reported tube sample metallography results.

4.0 STATUS OF REMEDIAL MEASURES Table 4.0.1 provides a checklist of remedial measures undertaken by I&M to mitigate the effects of steam generator tube degradation. The first item, continuation of the leak rate monitoring program, is not a remedial measure per se, but is included here to emphasize that I&M has been able to detect and successfully deal with tube leaks well l below the leakage rate allowed by the plant Technical Specifications. This fact provides even more margin on the l

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leak-before-break demonstration discussed in Section 3.2.

!' 4.1 Improve and Maintain Proper Water Chemistry Reference Submittal 2 discusses I&M's efforts to improve secondary i and maintain proper water chemistry at DC Cook Unit 2. That effort l

is continuing and has been quite successful. Figures 4.1.1 through 4.1.4 provide yearly average values for four important chemistry parameters - steam generator cation conductivity, steam generator

! sodium, steam jet air ejector air flow, and condensate /feedwater l dissolved oxygen. These plots show that the better chemistry realized as a result of an all-out effort beginning in 1983 is still continuing, and is still improving.

1 STD6030 13 l

4.2 Boric Acid Treatment Assessment In the past both empirical and field information on the effects of boric acid treatment in reducing the occurrence and rate of IGA and IGSCC have been presented. The remedial actions have been based upon caustic factors. These are summarized in Table 4.2.1 and in overview are expected to: a) neutralize the caustic environment which has contributed to the stress corrosion cracking and IGA occurrence, b) change the environment to move the alloy 600 from the susceptible electrical potential range for corrosion, c) prevent mass' transfer within the inhibitor film or by reformation of passive film.

Additionally, I&M has been supporting these reductions of caustic factors through processes to open restrictive crevices and remove sludge and to reduce contamination input through improved chemistry control.

In the prior meeting, the effects in laboratory tests of the reduction of stress corrosion cracking incidence through the use of boric acid, as shown in Figure 4.2.1, and also in the effect of boric acid in reducing the growth rate of preinitiated cracks, as shown in Figure 4.2.2, were presented. Additionally the reduction of the occurrence of IGA has been demonstrated in laboratory tests as shown in Figure 4.2.3 with overall conclusions that boric acid has prevented crack initiation in testing in reference conditions, that '

boric acid has reduced crack propagation rate with preexisting cracks by a substantial margin, and that boric acid has inhibited ,

intergranular attack in reference environments.

The translation of the laboratory observed conditions to plant observed conditions is given in Figure 4.2.4 which shows the performance of an international operating plant over several years without boric acid treatment and the effect of boric acid addition in terms of reduced number of ECT indications. As can be seen in this figure, for several years before the introduction of boric acid treatment, the number of eddy current indications was increasing steadily. The number of indications reduced substantially following the introduction of boric acid to reduce intergranular attack and stress corrosion cracking in crevice locations. Additionally a second plant was introduced to this treatment and its experience was also similarly positive with a corresponding reduction in tubing ECT indications. The latter also is illustrated in Figure 4.2.4.

ST06030 14

. The assessment of the boric acid treatment recently initiated at DC Cook Unit 2 is summarized in Table 4.2.3. This assessment used the most relevant data available which is the eddy current testing results from "84" to "85" in comparison to the results from "85" to "86". The effects of the somewhat reduced temperatures associated with recent operation are also encompassed in this comparison. In order to compare the "84" to "85" results on an equivalent basis to the "85" to "86" results, the eddy current data of "84" to "85" was reevaluated using the "85" to "86" analysis criteria. This comparison provided a basis for determining, in a near-term manner, that the remedial effects _are directed in the proper direction of reducing corrosion rate and thus tube plugging level. As shown in Table 4.2.3, the data indicates that the plugging rate trend is lower as a result of the boric acid treatment than that which would be expected had no changes in operating chemistry or parameters been implemented. Although these data are based upon relatively short operating experience, the results are clearly in the appropriate and anticipated direction.

In addition the growth rate data previously discussed was compared to the plugging rate data previously developed in the above paragraph.

This data is also shown in Table 4.2.3 and reveals that the "85" "86" growth rate is somewhat below the "84" "85" growth rate. This is consistent with the expected versus observed plugging rate data.

. These observations in both plugging levels and growth rate are consistent in trend and magnitude. Regarding the growth rate data, the most substantial improvements in growth rate reduction have been a seen in the area in the tubesheet and just above the tubesheet. The

, lowest reduction has been seen in the tube support plate area which has previously exhibited the lowest level of growth rate. These conclusions are summarized in Table 4.2.4.

4.3 Study of Corrosion Factors As noted earlier, in addition to the improved secondary chemistry efforts and the use of boric acid treatments, I&M has administratively limited thermal power on Unit 2 to reduce the primary temperature and possibly slow the rate of corrosion.

i To assess the effectiveness of this temperature reduction, AEPSC and l Westinghouse are conducting a sensitivity evaluation of parameters i

affecting tube corrosion rate in the Unit 2 steam generators. The intent of the study is to illustrate the impact on corrosion rate of various parameters (e.g. - temperature, pressure, bulk water chemistry) so that the benefits of the current temperature reduction

- program can be better quantified and a more formal temperature reduction program - if warranted - implemented using optimum conditions for corrosion rate reduction consistent with plant i -

capabilities.

ST06030 15

Study results are due later this year, and will be used to make recommendations for future operation of Unit 2. ,

4.4 Mechanical F airs l i . i AEPSC has commissioned and received licensing studies for tubesheet sleeving from two domestic vendors. However, because of degradation 1 at higher elevations in the tube bundle, I&M has no current plans to pursue a Technical Specification change to allow tubesheet sleeving in the Unit 2 steam generators.

Because of the significant economic impact of reduced power operaticn and poor unit availability, I&M is currently planning to replace the Unit 2 steam generators. New state-of-the-art steam generator lower assemblies have been purchased from Westinghouse, and are scheduled for delivery in August 1988. Planning and preparation are being made to support a replacement outage beginning as early as mid-1988, although the actual date of the replacement will depend on the success of current actions to arrest the corrosion in the existing steam generators. AEPSC is preparing a Steam Generator Repair Report describing the proposed project for submittal to the NRC staff for review.

I

.l O

STD6030 16

1

"' " ICE DEMISTERS SECONDARY

. MotSTURE SEPARATOR s

. J l

- SECONDARY MANWAY a

ORIFICE NNGS ,

b( '. I u

. A ,

g UPPER SHELL SWIRL VANE PRIMARY ) 7 MOLSTURE SEPARATOR s FEE 0 WATER INLET y

[

l H

~

1 2

~ '

I 1410ZZLES l

ANTMBRATION BARS l

TUBE BUN 0!I

) I /

LOWER SHELL f [  :

WRAPPER .

r ,' C l

TUBE SUPPORT MATES f

l 3 .

jj lt l BLOWDOWN UNE . a h '

A-7 SECONDARY HANDHOLE Tg ( flr m

t

/

. PRIMARY MANWAY \ l .

FPtYARY COOLANT INLET af!! MARY C0CLANT OUTLET actrcsau

@ SERIES 51 STEAM GENERATOR Figure 1.1.1 99'6 17

D. C. COOK UNIT 2 CHRONOLOGY OF SG EVENTS THROUGH DECEMBER 1985 March 10, 1978 Initial Criticality November 7, 1983 Forced Outage - first SG tube leak due to secondary side corrosion SG 21 Tube R16C40

- Leakkate0.29gom ECT of 1225 Tubes in 2 SGs

- Plugged 3 tubes Restart November 22 March 10, 1984 Refueling Outage 100% ECT all 4 SGS 7 tubes samoles removed

- Plugged 402 tubes (320 were Row 1 tubes)

- Restart July 7 ,

July 15, 1985 Forced Outage - SG Tube leak SG 23 Tube R16C56

- Leakkate0.22gpm ECT of 25 tubes in SG 23

- Plugged 2 tubes

- - 'Attemoted restart August 2

! August 2, 1985 Forced Outage - SG Tube leak .9urino Start-Vo SG 23 Tubes R7C28 a R14C70 Leak kate Measurements Not Dossible ECT of 1500 Tubes in SG 23

- Plugged 35 tubes Initiated Boric Acid Treatment (low Power Soak, On-Line Addition) i

- Restart August 22 August 23, 1985 Forced Outage - SG Tube leak Durinn Low Power Sock ,

- SG 22, Tube R14C41, SS 24, Tube R1.9C52 Leak Rate 0.2 com '

1007, ECT All 4'SGs 5 tube samoles renoved

- 110 tubes olugged l

Restart October 23 l

Table 1.1.1' 18

D. C. COOK UNIT 2 OPERATING EXPERIENCE DURING REMAINDER OF CYCLE 5 (October 24, 1985 - February 28, 1986) 0 Unit power level administratively limited 0 6,959,834 MW-HRS generated; corresoonds to 85 EFDDs

~

0 2 outages during the oeriod (Mode 5), both unrelated to SG tube degradation O SG leakage in the range of 0.001 to 0.038 gom O

Visual insoection after shutdown revealed one leakino tube - SG 22, Tube R16C45 19 Table 1.2.1

I D. C. COOK UNIT 2 OPERATING EXPERIENCE FOR BEGINNING OF CYCLE 6 (July 7, 1986 - Present) 0 Unit oower level administratively limited 0

3,015,035 MW-HRS generated as of August 31, 19P6; corresponds to 37 EFPDs -

0 One outage during the oeriod (Mode 3), unrelated to '

. SG tube degradotlon

- 0 Steam generator leakage virtually undetectable Table 1.3.1 -

20

D. C. COOK UNIT 2 APRIL /MAY 1986 ECT INSPECTION PLAN O

Performed requirementsin 4.4.5.0 accordance with Tech. Soec. surveillance 0

Initial samole selection SG 21 - 165 1811: 288 SG 24 - lhQ Total 550 (4.1%)

0 SG 22 entered C-3 category, which reautred exoansion to 100% of SG 22, olus an additional 2S tubes in the remainino SGs

- 0 l

Subsequent classification of SG 24 ns C-3 made it necessary to expand the insoection to include the offected creas of

(

,-- the remaining tubes in all four SGs O

Prompt notification of C-3 classification was made to NRC ,

in accordance with Tech. Soec. 4.4.5.5c 0

l Inspection results and intended actions were discussed via telecon with NRC staff on Aoril 23, 1986 l

Table 1.4.1 21 l

i D. C. COOK UNIT 2

SUMMARY

OF SG HOT LEG EDDY CURRENT INSPECTION RESULTS .

l l

l APRIL /MAY 1986

< 20 20-29 30-30 1 40 DI SQR UDS Total Supoort Plates 1 5 10 , 19 '

279 N/A NR 314 Crevice Region O 1 1 33 0 56 3 94

~

Tubesheet surface 7 3 8 8 11 ' N/k NR 37 l i y l Miscellaneous 27 13 13 0 -

0 N/A NR 53 1

. ,- l J~ Total 35 22 32 60 290 56 3 498 1

\

i D1 - DISTORTED INDICATION N/A - NOT APPLICABLE l SQR " SQUIRREL" NR - NOT REPORTED  !

UDS - UNDEFINED SIGl!AL 1 i

Figure 1.5.1. 22

C0MPAR150N OF *05 & *0E PLU56IN5 CR!TERIA

. ...*......... 1905**..........*.......

LOCATION (20 20-25 30-39 >40 50R O!

I-----I I I SUPPORT PLATE I I AD HOC I l

• CRITERIA I I l---------------------I l---------------I

! I CREVICE REGION I THRESHDLD i i VOLTAGE I l--------------I l---------------!

! I T*5HEET SURFACE I I g......

1 I

, I I MISC. g ...:

. ...............t30g....................

~~

. LOCATION (20 20-29 30-29 >40 50R 01 g.....g i i SUPPORT PLATE I I CRITERIA SASED ON I 1 *05 TUGE PULL g... ........... g........ .....g i  !

CREVICE RE6!0N I N0 THRESHOLD I I VOLTAGE I

, I i g g........ . ..:

T

• SHEET SURFACE I I l---------------------I I I i I I MISC. g ...:

Figure 2.1.1

• 23

ED5Y CURRENT $16NAL CLASSIF! CATION .

t90E -

TUBE $UPP0RT PLATE RE6 ION o PERCENT THR0U6H-WALL ( 5) 0I5T0RTED 469 KHZ $UPPQRT PLATE

$!4NAL WITH A $16NAL IN THE M!XED CHANNEL QUTPUT WH0$E MA6NITUDE EXCEED 5 A THRESHOL0 VOLTA 6E o D!$TORTED !NDICATION ( D!)

DI5TORTED 498KHZ SUPPORT PLATE SI6NAL WITN A 5ISNAL IN THE mix CHANNEL WH0$E MA6N!TUDE I5 LESS THAN A THRESH 0LD V0LTA6E: TREATED A5 TUBE WALL DE6RADATION LESS THAN THE PLU66ING LIMIT. MON!T0 RED l DURING FyTURE INSPECTIONS

', o NO DETECTABLE DE6RADATION ( NDD) .

• $TATI$TICALLY* NORMAL SUPPORT

,"~ PLATE SI6NAL CREV!CE RE6!ON o *50UIRREL*

A $I6NAL IN THE TUSE$HEET CREVICE WH0$E TRACE AT 404KHZ  !$ C0MPLEX ANO PHA$E ANGLE UNCLEAR: SI6NAL EXHIBITS CHARACTERI5 TICS 0F TUBE WALL DE6RADATION.

Table 2.2.1 24

LAR6E AMPLITUDE 516NAL

. IN M!X CHANNEL a,c,e

l l

l l

l l

l l

l l

l t

- 25 Ib Figure 2.2.1

i 5 MALL AMPLITUDE SIGNAL

!N M!X CMANNEL ,,

I 1

I i -

i i

l .

l l

a-Figure 2.2.2' 26 l

1985 OUTA6E TUSE SUPP0RT PLATE 1NSPECT10N RESULTS l

IN-PLANT 08SERVATIONS e EDDY CURRENT INDICATIONS AT HOT-LES SUPP0RT PLATES F1RST 0CCURRENCE IN A 00MESTIC l PWR. NEEDED TO ElTABLISM CAUSE e ANALY$15 0F !N-PLMNT EDOY CURRENT DATA WA$ $!V!NG INCON$!$ TENT RESULTS TME 198KMZ/40SKH2 MIX $ MOWED INCONSISTENC!ES SETWEEN $!6NAL AMPL17UDE AND PHA5E ANGLE

SUSGESTING TME PRESENCE OF TUBE

! WALL DEGRADATION AND P055IBLY I -

CREVICE JEPOSIT5.

ACT10N$

i

,-- o PULLED FIVE TUSES o C0NDUCTED EXTEN$1VE METALLO6RAPHY AT SUPPQRT PLATE INTERSECT!ON$

o ESTAOLISNED CORRELATION OETWEEN IN-PLANT EDOY CURRENT 50BBIN C0!L DATA AND METALL0$RAPHY RESULTS e E57AtLI5HED ANALYSI5 CRITERIA FOR USE DURING MARCH I986 INSPEC7 ION l

e CONDUCTED !N-PLANT CONFIRMAT10N WITM ROTATING PANCANE COIL

• I l

Table 2.2.2- 27

_ _ _ _ _ _ _ _ _ _ _ _ -- . - , - - m. - - . . - - _ - . - , . - - . - --- - - _ . - - - - -_.

EDDY C'U A'R E N T MEA 5UPEMENT ACCURACY 5TRE55 C0RR0$I0N CRACK!N6 -

100 ..

O

[

90

. / *

, 80 .,

g  ! .

[

70 g . , .

t IS:

j 60 - -

/ Scatter Band -

/ For Depth >40t

'o - '

1  :- s i

/ \

../

/

2 Y 30

/

/

E a /

/

g 20 -

10 "

f 10 20 30 40 50 60 70 80 90 100 Meta 11ographic Depth,1 TW -

Figure 2.2.3 28

. SI6NAL THRE5 MOLD E5TA8L!$MnENT IN MIX CHANNEL

' o u t,e i .

B

• ii

=

4 3

ll-E

. M i

Metallographic Depth, t TW i

Figure 2.2.4 29

TYPICAL SUPPORT PLATE MIX SIGNALS - a,c.e t

I 1

l l.

i I

- Figure 2.2.5 30 I.

ii

MARCN I 986

- ROTATIN6 FR0BE IN$PEC7 ION o C8JECTIVES

- VALIOATE L04IC F0R 0I$P0$ITIONIN6 INOICATI0N$ AT HQT LE6 5UPPORT PLATE $

o 0UANTIF1 ABLES ( 1)

.o DIST0RTEO INOICAT10N$ ( 0I's )

o NO DETECTASLE INDICATIONS

( N00*s l j CDNFIRM STRESS CDRR0$I0N 'CRACNING

.  !$ C0NFINED W! THIN $UPPORY

• LATE

.- ED6ES i

Table 2.2.3 31

- - - - - - - - - - - - -- - , . , - , , - - - - - - - - , . . , - - - ---c ---,,,.--------.-,---..--,.7, -

PANCAKE COLL .

Spelog loaded

% 'N -:! i =

E x w i

l i

sin mis l

l l

t l

l

. pe l

l l 0

,a ,

d / f -

tube - / / - '

Q s-d' . " ")

/

[

~ < 'D' ,,, p.. b

, / A

",#~)s' y crock v M' '

r  ;

$ V , " s

" ^

h' , , . ".s 7i <

i 0

%Rr

/

s s s

s

? 7' ** ', os'b r

.s <- .

'7 s, J

..# l modified 8 scon

.:( -

i Figure 2.2.6 32

~ '

PANCAKE COLL "lMAGING" O

e 1

f l

O mum

~

33 Figure 2.2.

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

- i I

Support Plate N00 a,c.e

f. '

O 34 Figure 2.2.8

Support Plate DI

. \

a c.e l

l l

l

, . I 1

l i

- Figure 2.2.9 35

S@ PORT PLATE DI CONFIRMATION a s t,c O

1 1

1 1

1 s's's - Figure 2.2.10 36

Support Plate Quantifiable

.. - a ,c.e O

D Figure 2.2.11 37

~

SUPPORT PLATE QUANTIFIA8tE CONFIRMATION a c.,

?

i I

3

]

b Figure 2,g,gg 38

DONLJ C00I UN:" 2 S G :. Eode' 5:.

1 March 1986 Hot Leg Inspection I

% Indications /Non-Quantifiable Indications

[g** ((*p*** g Top of Tube Sheet Support Plates o 40 - 100 Percent M Above Tube Sheet U - Bends

[ (**{"y 7 W W Below Top of Tube Sheet & Tu End i . . 4 i

= g 40 . 40 g f2T

)

dos _

r3gy N.

8 o

\ g .. : -

U

~

~

f --  %  %

g _

g 20 t

-*-u 20 w

m

^^

?i _,. __. . T

a. N

.; . 1 1. .

7

' ~

10 i

• i .

10 i

.I

;  ; i t g

1.__...1.. . . _. .... _.

, 7-l -- -- -- -- l-

g g g g y ypggggggg 90

. .. 8k;. 0 60 5k, _k 4 30 20 Ma w ay **I*

DATE PLOTTE 86/ 7/28 16: 7 O GENESIS Steam Generator Analysis System Coppfht Tarl0yhouse Eectric Corp.1M6

J0NA:i) C001 UNI" 2 SG1 Eoc el 51 March 1986 Cold Leg Inspection PERCENT INDICATION MAP o < 20 Percent Top of Tube Sheet 3 Support Plates a 29 - 39 Percent O Above Tube Sheet Anti-Vibration Bars

~

x cho 17 Plu ed "] Within Tube Sheet ni 4

~

i

, s a

l i l 40 i

,. i-40 $

w

{ [

, x-l l ,

l  : it

% x h

c3

.  ! 6 Ns N

s

/ ,

I is

x 20

1. " M P0 P

M! .  ; M 5; l

l j.

'l =l w__

.g i

l l -

, [  ;

p 10 , j ;;  ; l 3j

,

10

+

i _.__.

M! HHHHHHHHHHHHHHHHHHHHHHH HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH 90 80 70 60 50 40 30 20 10 Manay Nozz1e DATE PI#1TED 86/ 7/15 12:31 8 GENASYS Steam Generator Analysis System Copptht T@ hoax Rectric Corp JMs

S. G. 2, MARCH '86' HOT LEG, INDICATION COUNT .

D.C. COOK UNIT 2 INDICATION COUNT 3/8E30 en

-70 8 60 Q o

50 g z

40 H

. er/ 9 u_

q 30 o 2

)

a 20 $

m

r

: ?i j 10 g E

= /av4" d'Ef/M"ri /

,y/2E'/sm% k: h r/ Afevice J l 9w/ As

/4m/w5%"~'='"'?kggv/a ==

j y/ A r m/m/"*?/in 9/ss;/s/X t 7/ /2 n e

. rer/ m /s:ws / m / a m T j {V/ A o r

"'*4r/m/"'M/m/m,5,,,,;9/ _

/t e n p'.}~c7 m/m/m/rr-rA=V/ /s e t r m / m / m /sm/sm/ /s u o

/AEW/fMMU/ m /AE7/AE7/AE7/ /7 5

< 20 20-29 30-39 > 40 SOR DI 3

PERCENT INDICATIONS S/G 2 HOT LEG

5. G. 2$ $RCH '86', COLD LEG. INDLCATION COUNT D.C. COOK UNIT 2 INDICATION COUNT 3/86,g 9 E l 8

-7 0

6

. 6 a 5 5

. 4 e 3

'e 2 5

to i

9

/

41:M i Ez r== h f ffr /E//JEEF/AEF/AEF/AEF/

E /(NEVICE X N MY } WW/4EW/A!EV/AEW/ /TS Mdi ! h 59?3 f/ T 7/JEF/4EEF/rss/

"Y!^h /1 T h!N ? IY m / m /as/--'/ m / /2 n e 1-N I JEW /JE!F/JEEF/JEF/AEF/ /3 0 T E'% fr/EM/EEw/AEW/AEEV/AEW/ /4 P A

'/ - IfliE7/AEEV/AMY/AEW/Efff/ /5 P L

/ w / m /zz7/ m / m / m / /s u o t'ars/r/wr/m/AM/m/m/ /1 s

~

< 20 20-29 30-39 > 40 SOR DI  !

PERCENT INDICATIONS S/G 2 COLD LEG

& 3 # 9 4 9

s. G. i.i MARCH '86', PLUGGABLE INDICATIONS D.C.C00K UNIT 2 PLUGGABLEINDICATIONGo en

\ -

35 $

H 30 Q 25 ~

/ 20 9

M

/ '

15 a 2 /,

/ -

• so lE a ergris m

, --~

lu -d 5 w

t ____ m =___. Z

/ lfbf

/ yfTA( "}'j'l lC?EVICE

/ m/tE2/susTT$V/m /m/ /s i

/MM/ m / sus / 2/rzwei/ m / /2 R E

/ m / m / sew / m / = / m / /3 o 1

/ y'Z/ms/as/m/m/=/=/ 2 7 / m / m / a w / m / = / /s- p t

/t e n

/m/m/as/m/rzs-/=/

//E;WffUnH7/nWe[ EPM /EMar//E27/

/s u e

. < 20 20-29 30-39 > 40

/7 5 '

" SOR DI TYPE OF INDICATION S/G 2 3/86

COMPOSITE MARCH '86', PLUGGA8LE INDICATIONS s D.C. COOK UNIT 2

~

PLUGGABLEINDICATIONyg en KfMM4 60 H

5

$ $ 50 $

=a ~

-. _y 30 g s tf"'j 2c 55 ij 2

!E CD 10 I

[

-= 5 Mw " "T

""17A2% /. .: 7/ /cSEVICE

, / x= >] ... -. / hlhY.9/22/w..J/ /Ts

//'~~7/O/gnag J/ggg/,/ m /

/g i h;/ rrssw/nzzzr/ /2 R E fray

/AW/urs/uss/ / mar /ggdjij/AW/AEV/ ~

f /3 0 i

/BM/EG//EM/MM/ ass /mm/ /4 P A

//~~7//~"7/EE7/A"w//AW/saw/ /s p L

/ESF/BM/AM/B2F/urs/AEV/ /6 U P

/AW/BW/MM/AMir/AW/AW/

< 20 20-29 30-39 .> 40 SOR DI

/7 s i TYPE OF INDICATION COMPOSITE 3/86 -

O 9 0 $ .

I l

I 1

COOK 2 0E6RA: ATI0N 85- 86 O COMPARIS0N OF IN5PECT!ON R E S 'U L T 5

!NO!CATE THAT CORR 05!ON PATE VARIE5 W!TH ELEVATION IN THE 5 TEAM 6ENEAR7OR l

TU8E5HEET ABOVE SUPPCRT

{

CREVICE 708E5HEET PLATE 5 0 C0RR05!ON RATE VARIATICN WITH ELEVATION O8SERVEO OURIN6 *85 *86 OPERATION C0NSI5 TENT WITN THAT 5EEN OURIN6 *84- *85 0PERATION.

0 *85 *SE DESIADATION '

0E6RA0ATION 085ERVED RE6 ION

__ 1 WALL i

TU8E5HEET I

CREVICE 4.81 I

A80VE TU8E$HEET 2.51 l

! TU8E SUPPORT PLATE I .S1 l

l Table 2.4.1 45

l l

l .

C0t1PARISON OF '84' '85* AND '85' '86*

DEGRADATION RATES,X PER MONTH LOCATION OPERATING TL2ESEET ABOYE TUBE SUPPORT PERIOD CREVICE TUBESHEET PLATES -

amannuses menenneen aannamaan saunannamann

'8485' 2.66X I.33X 0.76X

'65' '86' 1.60% 0.82% . - - 0.665 Table 2.4.2 , 46 i

DC CDCE INIT 2 FIEAM GENDUdtR 'IUBE MDUN.M ACCEPD3210J1 REQUIRDENIS

'R71tr sunuu PDdT M7VATICN G.TIERIA CI2CITICN MINDG MAIL FINCHES) yygga m a,c.e A!EE CIXE FAULTID V3 N

'IUEESHEIT GEVIG AND AIDVE 'fHE 'ICP CF THE N M3VATICN

, G.TIIRIA (I2OITICN MINDE WATT. (INGES)

YIEID NCmMAL a,c,e ASME CIXE FAULUD V3 NCmMAL Table 3.1.1 47

1 i

DC CDW tNIT 2 mrrruntr NAIL IDSS IE3HMINNIIW SG GEME3RIC  %

ICCXrICN CDIDITIM 3kiI3 TUEE SUPK RP IECRAIKTICH a,c,e PIAIT AXIAL DCIINT I2MITED 20 0.75 IN.

TOP OF MERADEFIN ' -

TUBESHEET AXIAL EXITNT G EAITR THAN .

1.5 IN. --

TUBC5HEIT MIRADNTIW N AXIAL EX11NT c -

GEXIIR THAN 1.5 IN. - + "

e

~~

. 1UBE ALIDWAIEZ MAIL ICSS IS BASID CH THE FOIENING RG 1.121 ~

CINSIIERATICNS: .~- .

-~

-s y .z .r.,.~.;G.

• IURING NCEMAL OPDATICN, PRD9 der TUIE SISESSIs' ARE 12MITID sum 7 HAT A MARGIN OF 3 IS PRCNIIED JGAINSI EXC2ZDING THE ULTIMNTE TINSIII SIRESS OF THE TUBE MNIERIAL

• IURING NCEMAL OPDATICN, 'IHE YIEID SIRESS OF 3HE MNTDIAL IS Nor EX N

• RR POSIUIATED FY'TTTNT CINDITICNS, THE REQUI3EMENTS OF SECTICH NID-3225 OF SECTICH III OF 'IHE ASME CIXE ARE MET CDISmVATIVELY, 'DfE OtNSIRAINING EF7ECT OF THE TUBE 5HEIT/IUBE SUPKRT -

PIATE IN RESISIDG TUBE RRST IS N0r CINSIM3ED -

Table 3.1.2 48

OPERATING INIUVAL JUSTIFICKTIN DC CDCE INIT 2 CATIDORY GEVI2 AIENE TS M.

mg a,c e MN GICWIH 22** 11** 10**

P!11GGING IZVEL 24 35 44 REX 2UIlUD (4)

PIDGGING IZVEL AIL AIL 40 IMPIDENIID (4)

• TUBE RJRStr WrIHIN '1HE 75 CREVI2 CR EE TUBE SUPPCRP PIATE IS CINSIIERED TO BE IN7GDIBIE

• • PIC7ECIID GR:WIH RAIE 7tR 13.5 D"IM OPDATICH PER RESPECTIVE TUBE EIEVATI N l

r i

l l .

Table 3.3.1 49 I

I

D. C. COOK UNIT 2 STATUS OF REMEDIAL MEASURES 0

Continuing leak rate monitoring orogram O

Continuing emphasis on imnroved water chemistry 0

Continuing boric acid treatment crevice flushing (2000 com) low Dower socks (50 com) on-line addition (10 com) .

O Unit-specific study of interactive SCC oarometers currently in orogress .

0

._ Mechanical repairs SG tube sleeving SG replacement Table 4.0.1 50

U.:.  ::0( UNF 2 S.C CRT COND (UHHOS) YERRLY RVC 4

~

___ S.C.21 ES.C.22 3- ,x Es g,23 I

~

SS.C.24

{

i i E 2- l I

- I _ -

I .

I j-

~

E3 f

1. r_ ,

_ __ , _, _ ~

O' 1979 3 G0 1981 1982 1983 IW1 1985 1936 e

D.:. :00( UN T 2 S.C SODIUM (ppb) YERRL 7 NG si .

50-

[ S.c.21

. ES.c.22 Es.c.23 g 48- Es.c.24 i -

5 h 30- .

2i- .

3 4

16- _ .

E

,1 1979 1980 1981 1982 1%3

_ l l.E.]E_

1% 1985 1986

o

=

m, 6A

a

9 g  :

e

~

R CL

- E * =

+= ,

F Figure 4.1.3 53

m

== .

x 8& -

l w

WN g

~

~

w

2: % lwd O%

wh E ~5 O .

O m O 8

~

Q .

.Q h I

a

% I d N

-t cn N l M h

h'h'='

=

h =:=

Figure 4.1.4 54

1 REMEDIAL ACTIONS BASED ON CAUSATIVE FACTORS Q

U-

1. Neutralize caustic l 2. Keep alloy 600 out of susceptible potential range

3. Prevent mass transfer with an inhibitor film or by E reformation of passive film

- 4. Open restricted crevices - remove sludge

5. Reduce contaminant input - improve chemistry control i e

S; ese misestmes

e EFFECT OF BORIC ACID IN REFERENCE SCC TESTS -

a

?

P J

4 P 4

• 6 4 5

5 8 s 4 g S e g I

EFFECT OF BORIC ACID ON PRE-INITIATED CRACKS -

2 a i ru

. Io e

80001000F.002 C

.a.

ee

t BORIC ACID TEST i)ROGRAM CONCLUSIONS Ow-e Boric acid prevented crack initiation in the reference [

- Without boric acid throsghwall cracking in [ [ .

e - With boric acid no crack!ng in 3 ..e.e C

e Addition of boric acid after crack initiation reducea the crack propagation rate by a factor of[ ]

e Boric acid inhibited lG,A ,in the reference [

l - -

..c..

l - Without boric acid _

..lGA t

_With b9r,ip acid, isolated Intergranular penetrations ' '

5e'ep g . ./

\

l o

l . . . . . .

L ___

. f EFFECT OF BORIC ACID IN REFERENCE IGA TESTS Q

U-l lGA Depth pm

..e.

'e l 2

?

w l

l

~

• g esessenero u

. c

P s ,

UPDATi 0F BORIC ACID OPERATING EXPERIENCE MSTIN6 HOUSE i MTW DITUD4ATIG4AL PLANT OPUtATINS EXPUUENCE l WITH SGuc ACS

-,a.c.e 1

9 MRSER OF ECT

1. CICATIOtS O

Figure 4.2.4'

s t

' ~ '

EVALUATION OF BORIC ACID TREATPENT ON COOK 2 STEAM GENERATORS ASSESSMENT BY TUBE PLUGGING RATE -

OPERATING LOCATION RERIDD CREVICE ABQME I.S. Isg TOTAL i 84-85 (i) 75 51 16 145 84-85 m) 138 77 33 248 85-86 (2) 37 21 9 65 (e (EXPECTED WITHOUT BORIC ACID) (3) 85-86 (2) 28 9 2 39

~

(1) 84-85 INSPECTION /PLUSSING CRITERIA.

(2) 85-86 INSPECTION /PLUSSING CRITERIA.

( LINEAR EXTRAPOLATION BY TIME.

_3)

. ,,c,,

f ASSESSMENT BY GROWTH RATE, X PER MONTH -

OPERATING LOCATION PERIOD CREVICE ABOVE I,5, ISE o 84-85 2.66X 1.33X 0.762 a 85-86 1.602 0.82X 0.66X Table 4.2.3 61

[

J i 5 EVALUATl001 0F BORIC ACIO TREATPENT 000 COOK 2 STE#l GDERATORS C000CLU560005 TO DATE -

1. TIBE PLUGGINE RATE ASSESSSIT -

- IDCICATES A SIGNIFICAlli EDUCTeci III IEW IEW PLUEGAKE Tm

- IEDUCTl0Il 15 CDPTAllAOLE TO OT6ER EXPERIENCE.

2. GRDWTH RATE ASSES 29ff -

- CBSERVED RATES LESS WITH BORIC ACID TIEATPENT.

3. EFFECTIVDESS III EMElis m I

- IID DETRatENTAL EFFECTS OBSERVED.

~

- ALL 906CATORS SHOW IEMICED C0f5405100L 4 IECortOOATl0015 -

- C00fT10EK BORIC ACID TIEATPENT.

- U5E OVER A LONER EFFECTIVE PUtiOD TO AC&GEVE MAXittM MIEFITS.

Table 4.2.4

._