2CAN109903, Forwards Response to RAI Re Proposed Tech Specs Change for Special SG Insp

Forwards Response to RAI Re Proposed Tech Specs Change for Special SG Insp

ML20217G387
Person / Time
Site:	Arkansas Nuclear
Issue date:	10/14/1999
From:	Vandergrift J ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2CAN109903, TAC-MA6224, NUDOCS 9910210276
Download: ML20217G387 (10)

Text

_. _

y y Entergy operations, Inc.

1448 S.R 333 RusseMo. AR 72801 Td 501858 5000 October 14,1999 2CAN109903 U. S. Nuclear Regulatory Commission Document Control Desk Mail Station OPI-17 Washington, DC 20555

Subject:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Additional Information Regarding Proposed Technical Specification Change for Special Steam Generator Inspection (TAC. NO. MA6224)

Gentlemen:

By letter dated July 29,1999 (2CAN079903), Entergy Operations submitted a proposed technical specification change to support the special steam generator inspection to be performed at Arkansas Nuclear One, Unit 2 (ANO-2), during the 2P99 mid-cycle outage scheduled to begin on November 5,1999. The proposed inspection scope and expansion criteria were submitted for review on August 6,1999 (2CAN089901). Based upon a review of these submittals, the NRC Staff issued a request for additional information (RAl) on October 8,1999 (2CNA109901). Entergy Operations' responses to the RAI are attached.

If you have any questions concerning this submittal, please contact me.

Ve truly yours, A

Jin D. Vander /

Director, Nuc! car Sa' ety f

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{00t 9910210276 991014 PDR C ADOCK 05000368 PDR

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U. S. NRC

. Octob:r 14,1999 2CAN109903 Page 2

. cc: Mr. Ellis W. Merschoff Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Insp ctor Arkansas Nuclear One P.O. Box 310 London, AR 72847:

Mr. Chris Nolan I' NRR Project Manager Region IV/ANO-2 U. S. Nuclear Regulatory Commission NRR Mail Stop 04-D-03 One White Flint North ,

11555 Rockville Pike Rockville, MD 20852 A

Attachment to '

. 2CAN109903 Page 1 of 8 Additional Information to Support 2P99 Special Steam Generator Inspection N.RC Question No.1 Concerning Axial indications Please provide information from past inspections that demonstrate how the size of the indications varies with eggerate support. Something similar to Figure 1 of the August 6,1999 (2CAN089901), submittal would be appropriate. However, this '

information should be provided in terms of indication size rather than just number of indications.

1 I

Entergy Operations' Response A comparison has been made using data from the last three outages (2R12, 2P98 and 2R13). For each outage, a 100% bobbin examination was performed. Several parameters can be used to evaluate sizes of flaws. These parameters include length, depth, and amplitude or voltage. Depth can be measured as a maximum depth by bobbin / rotating l pancake coil (RPC) or as an average depth. Typically, average depth is only taken on the larger flaws as part of the in-situ pressure test screening criteria. Ther-fore, this data is not available for all indications. Maximum depth, as measured by bobbin, is based on phase angle and generally is not accurate at low amplitudes (less than 0.5 volts).

Amplitude does correlate well, but is influenced by such things as deposits and stmetures.

Based on these factors, the length measurement (by RPC) was used as the variable for comparison. Length (which is directly tied to structural integrity) is conservatively measured with RPC and is available for all indications.

Figures 1 and 2 depict the relative lengths of the axial indications at the hot leg support plates by steam generator (SG). The values are plotted as length in inches for each support plate. The outages are in chronological order from top to bottom. As shown, the number of indications decrease with higher elevation and by subsequent outage. The lengths of the flaws generally decrease as distance from the tubesheet increases. This condition is consistent with the decreasing operating temperatures higher in the tube bundle. The largest flaws each inspection have consistently been observed at the OlHot support plate. The largest flaws at the 02 Hot and higher supports that have been tested have not resulted in a tube burst or excessive leakage (21 gam). It is also noted that during the first outage trended (2R12), the number ofindications and lengths appear to be much higher than the other outages. This occurred because 2R12 was the first outage that a larger diameter bobbin coil was used in conjunction with a change in philosophy related to repair on detection. Prior to 2R12, axial flaws in the eggerates were sized by bobbin l and left in service if determined to be less than 40 percent through wall (TW). Several indications identified for repair during 2R12 had been in service for several outages. All indications identified during 2R12 were repaired by mechanical plugging regardless of depth.

l

Attachment to 2CAN109903 Page 2 of 8 FIGURE 1: "A" SG COMPARISON SGA EGGCRATE AXlAL LENGTH FOR 2R12 2.5 2.25

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SGA EGGCRATE AXIAL LENGTH FOR 2P98 2.5 2.25 7 2 3

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SGA EGGCRATE AXIAL LENGTH FOR 2R13 2.5 2.25 2

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Attachment to 2CAN109903 Page 3 of 8 FIGUBE 2: "B" SG COMPARISON SGB EGGCRATE AXIAL LENGTH FOR 2R12 2.5 225 175

! 1.5 I h 125 ^ -

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Attachment to 2CAN109903 Page 4 of 8 {

l NRC Question No. 2 Concerning Axial Indications Confirm your plans to in-situ pressure test tubes that meet the Electric Po,ver Research Institute (EPRI) guidelines if the indications in the tubes have not been bounded by previous test results. ,

Entergy Operations' Response Every indication will be evaluated against the criteria in the EPRI In-situ Pressure Test Guidelines. Any indications that meet the requirements for testing that are not bound by previous in-situ test results will be tested in 2P99.

NRC Question No.1 Concerning Circumferential Indications Provide information that demonstrates that the size of newly identified circumferential indications has decreased over the past operating cycles. You provided information on the number of these indications decreasing over the past inspections in Figure 2 of the August 6,1999, submittal. In addition, include a discussion of the inspection techniques utilized in this area since 1992 to fully characterize the information provided regarding crack number and size.

Entergy Operations' Response The inspection results from the last ten outages were compared to evaluate the relative i

sizes of the circumferential cracks identified at the hot leg expansion transition. Several parameters - _ associated with the size of the crack including length (measured circumferentially), maximum depth, and percent degraded area (PDA) or average depth can be evaluated. The PDA is the most accurate of the variables. The extensive circumferential evaluation prograrn developed by Entergy Operations and the Electric Power Research Institute (TR-107197-P1, " Depth-Based Structural Analysis Methods for l Steam Generator Circumferential Indications," Nov.1997) identified that the arc length I was consistent with PDA. Calculating PDA is a resource intensive process, therefore it is performed only on the largest indications. PDA is performed primarily to support in-situ test screening criteria. Because of this, arc length was chosen as the variable to evaluate the change in circumferential crack sizes from outage to outage. Figure 3 is a comparison of the lengths of flaws by outage. The magnitude of the flaws has generally decreased in .

the more recent outages when compared with the flaws that were identified in the early outages (1992-1994).

' Attachment to 2CAN109903 Page 5 of 8 The following is a breakdown of the average and maximum values of arc length for the previous outages:

OUTAGE "A" SG "B" SG l Average Maximum Average Maximum 2F92/1992 0.76" 2.36" 0.54" 2.36" 2R9/1992 0.67" 1.56" 0.41" 0.91" 2P93/1993 0.59" 1.65" 0.44" 0.73" 2R10/1994 0.56" 2.36" 0.37" 0.61" 2P95/1995 0.57" 1.99" 0.53" 1.44" )

I 2R11/1995 0.52" 2.36" 0.30" 1.43"

{

2F96/1996 0.54" 1.55" 0.61" 1.98" i

2R12/1997 0.63" 1.95" 0.42" 1.42" l 2P98/1998 0.49" 1.11" 0.46" 1.51" l

4 2R13/1999 0.51" 1.53" 0.42" 1.27" Theiubing for ANO-2 is 3/4" OD. Therefore, arc length for a 360 flaw would be (2 x lI x radius) or (2 x 3.14 x 0.375) = 2.356 inches. "

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Attachment to

, 2CAN109903 Page 6 of 8 1

. Various techniques have been used over the years to identify circumferential cracking at the top of the tubesheet. To date, there is no EPRI Appendix H qualified sizing method.

- The 0.115" pancake coil, which is approved for detection, provides consistent data for comparison. Listed below are the previous outages and corresponding scopes and equipment used: 1 OUTAGE  % HL SAMPLE # HL CRACKS DETECTION PROBE 2F92 (3/92) 100 469 0.080" RPC 2R9 (9/92) 100 25 0.080" RPC l l

2P93 (5/93) 100* 48 0.080" RPC 2R10 (3/94) 100 170 0. I15" RPC 2P95 (1/95) 100* 283 0.115" RPC 2R11 (9/95) 100 702 PLUS POINT 2F96 (11/96) 100 26 0.115" RPC i 2R12 (5/97) 100 119 0.115" RPC 2P98 (3/98) 100 70 0. ll 5" RPC 2R13 (1/99) 100 76 0.ll 5" RPC

• 100% of the sludge pile region

. i Attachment to i l

2CAN109903 Page 7 of 8 Ft'GURE 3: CIRCUMFERENTIAL COMPARISON SGA CIRCUMFERENTIAL LENGTH BY OUTAGE 2.50 , ,

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1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 YEAR SGB CIRCUMFERENTIAL LENGTH BY OUTAGE 2.50 ,

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1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 YEAR

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L Attachment to l f 2CAN109903 l . Page 8 of 8

.. NRC Question No. 2 Concerning Circumferential Indications Please provide a basis for your selection criteria for tube inspection if results from the "A" l steam generator indicate that the ."B" steam generator must be inspected.

Entergy Operations', Response 1

l Only one circumferential indication has been identified in the "B" SG that could be l considered significant (i.e., would meet the in-situ pressure test guidelines had they existed at that time). That flaw was identified in the 2F92 outage and was located in an under

- expanded tube. The crevice depth was ~ 4 inches and the flaw was located at a dent at the top of the tubesheet. .No other circumferential flaws have challenged the structural or j leakage limits in the "B" SG. Therefore, no inspection area exists in the "B" SG similar to l

' that proposed for the "A" SG which isolates areas that contain tubes that challenged j leakage limits in previous outages. Expansion into the "B" SG would consist of a random 20% selection of non-sleeved tubes. I I

NRC Question No. 3 Concerning Circumferential Indications Consider expanding the inspection scope to ensure a two-tube buffer exists around any tube that meets the in-situ pressure test criteria, regardless of whether the tube is tested or I not. . This would support the logic that the inspection area is comprised of the most limiting tubes.

Entergy Operations' Response If a tube is found to meet the in-situ screening criteria'(regardless of whether it is actually tested or not) and is on the outer perimeter of the test plan (not bound by two tubes),

further testing will be performed to ensure that a two tube buffer exists.

~ NRC Question Concerning Both Axial and Circumferential Indications Confirm your plan to perform condition monitoring and an operational assessment based on the mid-cycle inspection findings and that the results from these efforts will be included in a report submitted to the NRC.

Entergy Operations' Response

)

Condition monitoring and operational amssments based on the mid-cycle mspection findings will be' performed per the guidance of NEI 97-06. The results of these l assessments will be provided to the NRC within 90 days of entering Mode 4.

i