ML20063P946

Provides Plans for Ultimate Disposition of Recirculation Inlet Nozzle to Safe End Weld Indication.Alternative Corrective Actions to Disposition Nozzle to Safe End Weld Indication Include Repair by Weld Overlay W/O Monitoring

ML20063P946
Person / Time
Site:	Limerick
Issue date:	08/10/1990
From:	Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-88-01, GL-88-1, NUDOCS 9008160012
Download: ML20063P946 (7)

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4-PHILADELPHIA ELECTRIC COMPANY j NUCLEAR GROUP HEADQUARTERS l

= 955 65 CHESTERBROOK BLVDc  !

WAYNE, PA 19087 5691- O

- tu s);uo.sooo August 10, 1990 Docket'No. 50-352 License No. - NPF-39 ; []

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U.S. Nuclear ' Regulatory Commission ATTN: Document-Control Desk i; Washington, D.C. 20555.

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SUBJECT:

Limerick Generating Station,_ Unit 1- 2 Plans for the Ultimate-Disposition i of the Recirculation Inlet' Nozzle to Safe End Weld Indication i

-Gentlemen:- (

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During.the 1989 Limerick Generating Station (LGS) Unit 1' Refueling Outage. a number of-normally required and augmented In-Service Inspections (ISI)_

of austenitic stainless steel piping welds were performed in accordance with the. y requirements of-the American Society of Mechanical' Engineers (ASME) Boiler:and; y Pressure Vessel (B&PV) Code Sectton XI, and NRC Generic. Letter 88-01,_"NRC <

Position on IGSCC In:BWR Austenitic Stainless Steel- Piping," dated January 25, 1988. As a result 'of these inspections, an indication was discovered-in one of "

1 the' reactor vessel nozzle (identified as.the N2H nozzle)-to safe end welds. Our letter dated April 3.-1989, submitted a summary report of our evaluation of the N2H nozzle to, safe end weld indication, and the justification for proceeding with cycle 3 operation of Unit1 with theLindication in the "as found" condition, for NRC review and approval. Our April-3. 1989 letter also stated that the corrective action that will be taken to ultimately dispostion the H2H 4

nozzle to safe end weld indication will be established prior to shutdown of. Unit 1 for the third refueling outa a Safety Evaluation Report (SER)ge. NRC letter approving cycledated May 2,of1989, 3 operation Unit forwarded 1-with the' the indication in the "as found" condition, and stated the NRC's understanding that the final corrective action will be. established prior to or during the third Unit 1 Refueling Outage. Currently, the third Unit 1 Refueling Outage is planned to begin,on-September 8, 1990. Accordingly, this letter provides our..

plans for.the ultimate disposition of the N2H nozzle tn safe end weld i indication. As discussed below, there are a number of corrective actions that can be taken, and the specific corrective action will be selected based on;the-results of the N2H nozzle to safe end weld ultrasonic (UT) inspection that'will ~

be performed during the third Unit 1 Refueling Outage.

9008160012 900G10 PDR ADOCK 05000352 f P PDC 0

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Document Control Desk August 10. 1990

. Page 2

Background

A seven inch circumferencial f16w indication was found in the N2H nozzle to safe end weld as a result of UT inspectii as performed during the 1989 Unit 1 Refueling Outage. As shown in Figure 1. the inJ1 ration is located on the nozzle side of the weld in the alloy 82 weld and/or i 1 Inconnel 600 that was left in place after the original Inconnel 600 safe ena was removed. With the wall thickness being 1.40 inches, the average depth of the indication is 0.25 inches (i.e. approxleately 18% through wall), and a part of the indication. 0.5 inches in length, is 0.40 inches deep (i.e., approximately 295 through wall).

The indication is located 31.8 inches to 38.8 inches from top dead center of the nozzle, clockwise with flow. Since actual visual inspection of the indication could not be performed, whether the indication is due to intergranular stress corrosion crack W (IGSCC) or is a pre-existing construction flaw could not be confirmed.

A crack growth rate analysis and structural margin assessment using conservative 1989. The st, anse )tions was provided to the NRC by our letter dated April 3

..ral margin assessment was performed assuutng that the indication wat in fact a creck, and that it was connected to the weld internal  ;

diameter (10). Two crack The lower crackgrowthrateofIX10'growthrateswereusedinthisassessment.  !

inches / hour represents the expected crack growth rateassumingatargetreactorwategconductivityof0.1ustement/ca,anda higher crack growth rate of 5 X 10' inches / hour reflecting an upper bound growth rate value for ' worst case" reactor water conductivity levels. Using the  ;

higher crack growth rate value, the depth of the crack was calculated to be 0.85 inches t' theaver(agemeasuredindicationdepthof0.25 inches.i.e. 60%

Starting from the through wall) by maximum.

j the indication depth of 0.40 inches, the end of cycle depth was calculated to be 1.0 inch (i.e., 71% through wall) using the higher crack growth rate. The allowable '

crack XI. The size was then calculated in accordance with the ASME B&PV Code. Section results showed that the calculated crack growth by the end of cycle 3 was acceptable, even when the higher crack growth rate was assumed, in order to confitt ' nsuits of the crack growth analysis, and to provide additional assurance tnat the structural margio of the N2H nozzle to safe end weld would be maintained during cycle 3 operdion, a Crack Advance Verification System (CAVS) was installed and put into operation prior to M i startup from the 1989 Refueling Outage. The CAVS. which has continued to operate during cycle 3. provides inferential monitoring of cracks by using a

' pre-loaded specimen with a known flaw which is placed in an autoclave through which reactor coolant flo m The specimen is thereby subjected to the same reactor coolant conditions as the crack, and the crack growth of the specimen is electronfcally monitored using a reversing DC potential. Based on the CAVS data, we weld, safe end committed to perform the following inspections of the N2H nozzle to If after nine months of cycle 3 operation, the CAVS specimen i indica m a crack growth greater than or equal to 0.2 inches, the N2H nozzle to safe end weld will be inspected if the plant is  ;

shutdown for a forced outage that is planned to last for greater than two weeks i

' Document Control Desk August 10, 1990 Page 3 If after nine months of' cycle 3 operation, the CAVS specimen indicates a crack growth greater than or equal to 0.3 inches, the plant will be shut down and an inspection of the N2H nozzle to safe end weld will be perfonned.

CAVS Results A thorough evaluation of the CAVS data for the first nine months of cycle 3 operation has been perfonned. The data show a small crack growth at the endofninemonthsofoperationofonly0.018inchesintheCAVSspecgaen.

represents a maximum everage speclaen crack growth rate of 2.72 X 10' This inches /

5X10'pr.significantlylessthanthehighercrackgrowthrateof inches / hour used in the structural margin assessment. Since neither crack growth threshold value was reached (i.e., 0.2 inches or 0.3 inches

- af ter nine months of operation), the additional inspections were not perfonned.

The d (i.e.,1X10'gfferencebetweenthepregictedcrackgrowthrate inches / hour and 5 X 10' inches / hour) and the crack growth rata determined from the CAVS data can be attributed to the excellent reactor water chemistry maintained during cycle 3. During the first nine months of cycle 3 operation, the CAVS operated 95.8% of the time, and Unit 1 operated' at or near full power conditions for almost all of the period. When the CAVS was occasionally shutdown, hostver, the resulting transient may have caused additional indication.crack groAh not experienced by the N2H nozzle to safe end weld Accordingly, the CAVS data most likely represents a aare conservative (i.e., higher) crack growth rate than may have been experienced by the nozzle to safe end weld indication.

Corrective Action Plans The following four corrective action alternatives for dispositioning the N2H nozzle to safe end weld indication have been identified and evaluate The selection of the corrective action that will be implemented will be based on .

the results of the inspection of the N2H nozzle to safe end weld during the upcoming 1990. Unit I refueling outage currently scheduled to begin on September 8 1.

Leave in the "as-found" condition with continued CAVS aonitoring 2.

Apply the Mechanical Stress leprovement Process (MSIP) with or without CAVS monitoring 3.

Repair with weld overlay with or without continued CAVS monitoring

4. Replacement of the N2H nozzle safe end Each of these corrective action alternatives was evaluated based on various factors which included maintaining an acceptable structural margin, viability, i

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• Document Contrel Desk August 10, 1990 i Page 4 l

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, cost, worker radiation exposure, and time required for implementation. The safe i

end replacemen', alternative was eliminated since it did not satisfy most of the

! evaluation acceptance criteria.

i Tae 1989 UT inspection results for the N2H nozzle to safe end weld have been rev',ewed again. We consider that there is a possibt;ity that the j l'

indication is not due to IGSCC. but instead is an original construction flaw and  !

not IP connected. This possibility would be further supported if the upcoming )

UT inspection results A.ow no change in the dimensions of the indication.

, Accordingly, the identical UT inspection which resulted in the identification of j

the N2H nozzle to safe end weld indication during the 1989 Refueling Outage will 1

be repeated to the extent possible (i.e., use of the same UT technique, equipment, and technicians) during the upcoming Unit 1 Refueling Outage.

With r6spect to the corrective action alternatives. CAVS monitoring

! would not be continued if either the application of MSIP or weld overlay is selected due to the fact that the CAVS specimen would no longer represent actual

nozzle to safe end weld conditions. With respect to the selection of MSIP without monitoring as the corrective action, section 4.2 of NUREG 0313. Revision 4

2. " Technical Report on Material Selection and Process Guidelines for BWR Coolant Pressure Boundary Piping." recomends that MSIP be applied only if the

! flaw indication is less than 30% through wall and 10% of the circumference. The i

dimensions of the N2H nozzle to safe end weld indication are not within these bounds. We expect, however, that an elastic-inelastic finite element analysis l

1 will demonstrate that the MSIP variables can be controlled such that application

' of the MSIP to a flaw of greater depth than 30% and a circumfrential length greater than 10% can be put into an arrested state. We have recently initiated this analysis and expect to discuss the results with the NRC once they are I

available.

1he bounding tsnditions for application of the MSIP and weld overlay to the N2H nozzle to safe end weld will be established prior to the upcoming Unit 1 Refueling Outage. We have e established conditions for detemining whether there has been any growth ,,he indication. These conditions were derived from the anticipated uncertaints band of depth resolution of the UT inspection technique. If the change in the length and depth of the indication is within the tolerances for repeatable t'T inspections, the conclusion that there has been no growth is justifiable.

If the change in th crackgrowthrateof1X10'gindicationlengthanddepthisconsistentwitha inches / hour or less, we may request NRC approval to allow Unit 1 to operate for additional cycPs with the indication in the "as found" condition. If the chan shossacrackgrowthrateof2.5X10'geintheindicationlengthanddepth inches / hour or less, we may request NRC approval to allow Unit 1 to operate for only the next cycle with the indication in the "as found" condition since the size of the indication at the end of next (i.e., fourth) cycle would not exceed the ASME Code allowabic flaw size.

l if the UT inspection results show no growth of the indication, as explained above, or if the indication size has increased but is within the bounding .onditions for the application of the MSIP. we may request NRC approval

Document Control Desk August 10, 1990 Page 5 to apply the MSIP to the N2H nozzle to safe end weld, if the change in the length and depth of the indication is greater that the established conditions for "use as is," or the bounding conditions for the application of the MSIP, we would request NRC approval to repair the N2H nozzle to safe end weld using weld overlay.

As described above, the alternative corrective actions to disposition the N2H nozzle to safe end weld indication incluie continued operation in the "as found" condition with CAVS monitoring, application of MSIP without continued monitoring, or repair by weld overlay without continued monitoring. The selection of the specific corrective action to be implemented will be based on the established bounding conditions, and the results of the UT inspection of the N2H nozzle to safe end weld that will be perfomed during the upcoming Unit 1 Refueling Outage, currently scheduled to begin on September 8, 1900. Figure 2 provides a flowchart depicting the selection process that will be followed otte '

UT inspection results have been obtained, if you have any questions, or require further in4,mation, please contact us. ,

Very truly yours, f, 'q G. lunger, Jr.

Manager Licensing Section Nuclear Engineering and Services cc: 1. 1. Martin, Administrator, Region I, USNRC T. J. Kenny, USNRC Senior Resident Inspector, LGS

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