ML18353B147

Proposed Technical Specification Changes for Steam Generator Inservice Inspection

ML18353B147
Person / Time
Site:	Palisades
Issue date:	11/10/1977
From:	Hoffman D Consumers Power Co
To:	Schwencer A Office of Nuclear Reactor Regulation
References
Download: ML18353B147 (9)

Text

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consumers Power REGUlAlDJY DOCKET fllE COPY

• company General Offices: Z12 west. Michigan Avenue, Jackson, Michigan 49201

• Area Code 517 788-0550 November 10, 1977 Director of Nuclear Reactor Regulation Att: Mr Albert Schwencer, Chief Operating Reactors Branch No 1 US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT - PROPOSED TECHNICAL SPECIFICATIONS CHANGE FOR STEAM GENERATOR INSERVICE INSPECTION Attached is a proposed Technical Specification change req~est for steam generator inservice inspection requirements at the Palisades Plant. This proposed Technical Specification change would also allow sleeving to be used as a repair method. The supporting information for this request was presented to the NRC staff on September 1, 1977 and November 8, 1977.

Consumers Power has previously indicated that we plan to utilize the sleev-ing process during the upcoming refueling outage. We would appreciate ap-proval of this .request by January 1, 1978.

David P Hoffman Assistant Nuclear Licensing Administrator CC: JGKeppler, USNRC

CONSUMERS POWER COMPANY Docket 50-255 Request for Change to the Technical Specifications License DPR-20 For the reasons hereinafter set forth', it is requested that the Technical Specifications contained in Provisional Operating License DPR-20, Docket 50-.255, issued to Consumers Power Company on October 16, 1972 be changed as described in Section I, below:

I. Changes*

Replace. Section 4.14 as follows:

Remove Pages (Dated) Insert Pages 4-68 ( 6-17-77) 4-68 4-68a (4-26-76) 4-'68a, 4-68b 4-69 (4-26-76) 4-69 II. Discussion The proposed. T.echn.i-ca.J.. Spec::ification would allow Consumers Power to use sleeving as an alternate technique for repairing degraded steam generator tubes. Combustion Engineering Report, ._"Palisades Steam Generator Tube Repair by Sleeving," CEN-59(P), dated August 26, 1977, has been provided to document the technical basis for this request. In addition, the speci-fications for inspection intervals and sampling requirements have been modified to reflect clirrent Palisades Plant steam

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• I generator conditions and industry practices. The attached "Inspection Plan" provides additional information to support this request. Table 4.14, "Operating Allowance" (pertinent only to the last insp~ction) has been changed to show the cur-rent "Maximum Allowable Degradation."

III. Conclusions The Palisades Plant Review Committee and the Safety and Audit Review Board have review~d the proposed change and recommend its approval.

CONSUMERS POWER COMPANY

& Transrp.is Sworn and subscribed to before me this 10th day of November 1977.

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Linda Thayer, otary Public Jackson County, Michigan My commission expires July 9, 1979.

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I 4.14 Augmented Inservice Inspection Program for Steam Generators I

• Applicability I!

Applies to the tub;es within both steam generators.

Objective To provide assurance of continued integrity of the steam generator tubes I*

over their serviceI lifetime.

Specification 4.14.1 :tnspectioµs will be m:ade at a frequency not less than 12 nor more I

than 24 c~lendar months after the pr~vio~s i~spection. Tube I

inspectio,n requirements will include inspection of all unplugged I

tubes wi~h an ECT indi,cation of greater than or equal to 30%

i in eithe~ of the previous two inspection periods. The conventional, circum:fer;entially wound ECT pull type probe shall be used to inspect all unplugged tubes for which an ECT indication greater than or equal

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• to 30% was noted in either of the two previous ECT inspections.

In addition, a random sample of 2% of the.tubes in the hot leg and 1%

I of the t,ubes in the cold leg of each steam generator will be inspected using t~e conventional, circumferentially wound. ECT probe.

For theipurposes of this Technical Specification, "tubes" refers I

to that; portion of the steam generator U-tube from the point of entry on the cold-leg side to the top support of the cold leg, or from the point o;f entry on the hot-leg side completely around the U-bend to the top support of the cold leg.

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4.14.2 Special inspection techniques shall be used to inspect all tube/

tube support plate intersections where an ECT indication was present during the last inspection which was greater than or equal to 45% but cannot be interpreted in the current inspection due to the presence of dents.

If the number of intersections to be tested under the criteria above is less than a total (for both generators) of 600, additional inter-sections shall be selected for testing. The additional examination sites shall be selected from previous ECT results for areas which co*u:Ia not be* inspected due" to dents *in the last; inspection* in descending order .with respect to the depth of the ECT indication.

4.14.3 When inspection reveals that the tube degradation plus an appro-priate operating allowance is equal to or greater than the maximum allowable degradation specified in Table 4.14, tube plugging or sleeving shall be performed.

Defect indications may be confirmed by averaging during a given inspection, but such averaging shall be based on not less than three readings.

4.14.4 The operating allowance will be determined using appropriate inspection results. This allowance will be approved by the NRC.

4.14:5 Sleeves will be installed such that, considering the axial location tolerances, swaging does not take place in an area of known degradation .. In addition, base line inspection of a statistically justified sample of sleeves will be performed.

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Basis Consumers Power has concluded that the change from coordinated phos-phate to volatile chemistry control for the secondary side of the steam generators has reduced the previous corrosion rate. The in-spection program provides .for verifying that the corrosion has been arrested; or, for quickly identifying any additional corrosion; or, for identifying .other problems.

The inspection program is also consistent with current industry prac-tices and includes appropriate measures to identify additional degrada-tion of the Palisades steam generators. Th'e operating allowance and p1.ugging c:d:teria"* were** deve*ioj:H:!'d' based* on c*ompara:tive

• resl.il ts between 0

steam generator inspections with consideratio~ given to defect type; location, past corrosion rate observed, etc.

Calculations have been performed to demonstrate that a tube uniformly thinned to 36% of its original nominal wall thickness (64% degradation) can withstand a differenti.al pressure of 1380 psi. Likewise, a sleeved tube can withstand the same differential pressure when the limits in Table 4.14 are observed. Combustion Engineering, Inc Report No CEN-59(P)

"Palisades Steam Generator Tube Repair by Sleeving," dated August 26, 1977, contains the analytical and test results of tube *sleeving.

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TABLE 4.14 Maximum Allowable Degradation Location Maximum Allowable Degradation Unsleeved Sections Degradation = 64%

Sleeved Section Region l(l) Sleeve degradation = 34% and tube degradation exceeding the maximum allowable degradation for an unsleeved section.(4)

Region 2( 2 ) Either (a) sleeve degradation = 25% when tube degradation., in Region lexceeds the maximum.

allowable degradatio~ for an unsleeved section;

.2L (b) tube degradation equal to the maximum allowable degradation for an unsleeved tube.(4)

Region 3( 3 ) Tube degradation equal to the maximum allowable degradation for an unsleeved section.

Footnotes:

(l)The undeformed region of the tube/sleeve assembly containing the original imperfection requiring sleeving.

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( 2 )The region containing the expansion joint. Specifically, the region .of the tube/sleeve assembly boun~ed by lines approximately 1/4 inch and 2 inches inboard from the sleeve ends.

( 3 )The region of the tube/sleeve assembly containing approximately 1/4 inch of each end of the assembly.

( )Degradation occurring in the parent tube ~t any location in a Region and 4

degradation occurring in the sleeve at any location in the same Region that exceeds the applicable maximum allowable degradation will require tube plugging.

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PALISADES STEAM GENERATOR

INSPECTION PLAN INTRODUCTION AND BACKGROUND Palisades Technical Specification, Section 4.14, currently requires tube sampling requirements for ECT to be in accordance with Regulatory Guide 1. 83, "Inservice Inspection of Pressurized Water Reactor Steam Generator Tubes," as it applies to inspections after the base line inspection . . In actual practice, past steam generator ECT inspections at Palisades have included inspection of 100% of the hot leg tubes and inspection of about 6% of the cold leg tubes. Improved oper-ating conditions and decreased rates*of wastage corrosion make 100% inspection unnecessary. Also, Regulatory Guide 1.83 does not address the situation where steam generator tubes are dented.. An alternate inspection plan is proposed.

In the_1976 ECT inspection of steam generator tubes at Palisades, some denting of the tubes was observed. The conventional, circumferentially wound ECT pull-through probe cannot detect defects in steam generator tubes at dents due to the large dep.t signal. rt* should be noted that the great majority of ECT indi-cations in the Palisades steam generators occur at tube/tube support plate intersections. During the 1976 ECT. inspection, approximately 3,449 inter-sections on 3 1 322 tubes were known to have wastage indications from previous inspections but could not be interpreted because of dents. 1,132 tubes in the A generator and 2,190 tubes in the B generator were affected. For that outage, a more stringent plugging criteria based on resUlts of the February 1975 ECT inspection was used for the defects obscured by dents. Experience with other operating plants indicates a significant probability that an in-creased degree of denting will be found in the next ECT inspection.

Special inspection techniques are being developed to allow inspection of steam generator tubes in the vicinity of dents. These techniques involve using a specially designed ECT probe which requires rotation and slow axial translation or an ultrasonic probe requiring similar movement. A disadvantage of these special techniques is that inspection time is much greater than that required for a conventional pull-through ECT probe. The time required to inspect the tubes using_these techniques makes it impractical to inspect each dent location.

INSPECTION PLAN DETAILS

1. The conventional, circumferentially wound ECT pull-type probe shall be used to inspect all unplugged tubes for which an ~CT indication greater than or equal to 30% was noted in either of the two previous ECT inspections.

In addition, a random sample of 2% of the tubes in the hot leg and 1% of the tubes in the cold leg C?f each steam generator will be inspected using the conventional, circumferentially wound ECT probe.

The number of tubes inspected under this criteria for the 1978 {nspection is approximately 1,650 tubes in the A generator and 1,340 tubes in the B generator. This is, respectively, 25% and 20% of the unplugged tubes in the A and B steam generators.

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f 2 .. Special inspection techniques shall be used to inspect all tube/tube support plate intersections where an ECT indication was present during the last inspection which was greater than or equal to 45% but cannot be interpreted in the current inspection due to the ~resence of dents.

If the number of intersections to be tested under the criteria above is less than a to.tal (for both generators) of 600; additional intersections shall be*

selected for testing. The additional examination sites shall be selected from previous ECT results for areas which could not be inspecteq due to dents in the last inspection in descending order with respect to the depth of the ECT indication.

DATA ANALYSIS AND TUBE PLUGGING The growth rate of ECT indications during the.. iast .. op.eratfng . cyc-ie-wiii *b~ -----

determined by comparison with r.esul ts Of previous Inspec. t"io.ns *. Based on t.hi~ . .

growth rate, an operating allowance will be determined. This operating allow-ance will be subtracted from the structural wall degradation limit of 65% to determine the plugging limit. The operating allowance will be selected to accommoqate the next operating cycle.

An increased operating allowance will be app.;l.ied to previous ECT indications not covered by this inspection to account for the period of time since the last measurement of these indications. A different plugging limit will be arrived at for tubes thus affected. (Tubes which will require plugging as a result of the application of *the increased operating al.lowance to previous inspection results may be inspected and a plugging decision made on the basis of the operating allowance for tubes inspected during the current outage.)

DISCUSSION REGARDING THE INSPECTION PLAN .

Adherence to Regulatory Guide requirements has resulted in 100% inspection of tubes in the hot leg and 3-6% of the tubes in the cold leg. The inspection plan proposed would result in inspection of approximately 1,650 and 1,340 tubes in the A and B steam generato,rs, respectively. This is 25% and 20% of the unplugged tubes in these generators.

The plan, by definition, concentrates on areas where the maximum amount and rate of corrosion have been measured.

The Palisades Plant has operated under the all-volatile chemistry regime since September of 1974.' Secondary side chemistry results ha:ve been. excellent and were reported to the NRC on numerous occasions. The condenser was retubed in December of 1974.. Condenser performance subsequent to retubing has been good. Prompt action has been taken to locate arid plug leaking condenser tubes and this has resulted in minimum input of condenser contaminates to the steam generators.

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Extensive modifications to the .feed-water system have been in progress for some time and are due for completion dliring the subsequent operating cycle. They include increased condensate storage capacity, increased demineralizer capacity for makeup water, feed-water bypass system, and a full flow condensate polishing system. The'se modifications have been made for the express purpose of limiting contaminant access to the steam generators and controlling the secondary water chemistry to proper administrative limits.

Operating experience with the steam generators has been excellent. No tube

~eakage has* bee.n identified since May of 1974. A very minor amount of primary-to-secondary leakage has been i.ndicated by ,statistical analyses of counting data.

There have been no indications of increase in this leakage in over two years of plant operation. Apparent rates of corrosion have decreased since conversion to volatile chemistry. Information from laboratory pot boiler tests and industry experience indicates further decrease in tube wastage rates can be expected.

While extensive inspection of tubing was previously necessary during periods of phosphate operation and convers~on to volatile control, a less extensive inspec-tion plan is appropriate now. The time required witn resulting increased radia-tion exposure for a complete ) . 00%.: exam'ination. is* not warranted in view of lower rates of wastage corrosion.

Another factor to be considered is associated with the negative influence of den.ts on the ability of the conventional ECT to accurately interpret wastage indications at support plate intersections and the vastly expanded inspection time required with special inspection techniques.

The inspection plan as proposed will be adequate to monitor the rate of progres~

sion of known corrosion and test for the presence of new indications of corrosion.

The test will also be adequate to monitor the incidence and severity of denting.

Data obtained from the inspection- will be more than adequate to determine the appropriate operating allowance for the subsequent cycle.

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