NG-05-0388, Request to Extend the Third 10-Year Inservice Inspection (ISI) Interval for Reactor Vessel Welds VLA-A001 and VLA-A002

Request to Extend the Third 10-Year Inservice Inspection (ISI) Interval for Reactor Vessel Welds VLA-A001 and VLA-A002

ML052070659
Person / Time
Site:	Duane Arnold
Issue date:	07/14/2005
From:	Vanmiddlesworth G Nuclear Management Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NG-05-0388
Download: ML052070659 (6)

Text

Committed to Nuclear Excellene Duane Arnold Energy Center Operated by Nuclear Management Company, LLC July 14, 2005 NG-05-0388 10 CFR 50.55a(a)(3)(ii)

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Duane Arnold Energy Center Docket No: 50-331 Op. License No: DPR-49 Request to Extend the Third 10-Year Inservice Inspection (ISI) Interval for Reactor Vessel Welds VLA-AO01 and VLA-A002 Pursuant to 10 CFR 50.55a(a)(3)(ii), Nuclear Management Company, LLC (NMC) requests NRC authorization of an alternative that extends the third ten-year interval for the examination of two Duane Arnold Energy Center (DAEC) reactor pressure vessel (RPV) lower shell vertical welds. The DAEC is currently in its third ISI interval, scheduled to end on October 31, 2006. Extension of the interval for welds VLA-AO01 and VLA-A002 is requested until the completion of RFO 20, currently scheduled to begin in February of 2007.

Ultrasonic (UT) examinations of these two welds were scheduled to be performed as part of the ten-year vessel examinations conducted from the inside diameter of the vessel during Refueling Outage (RFO) 19 in the Spring of 2005. While the examinations of the other six vertical shell welds were performed -successfully with -

examination coverages of essentially 100% (greater that 90%) and no recordable indications, welds VLA-AOOI and VLA-A002 were not examined due to access obstructions, as described in the enclosed request.

To facilitate planning for RFO 20, NMC requests approval of this request by April 1, 2006. -

3277 DAEC Road

• Palo, Iowa 52324-9785 Telephone: 319.851.7611

Document Control Desk Page 2 This letter contains no new commitments and no revisions to existing commitments.

Ga an Middlesworth Site Vice President, Duane Arnold Energy Center Nuclear Management Company, LLC Enclosure cc: Administrator, Region 111, USNRC Project Manager, DAEC, USNRC Resident Inspector, DAEC, USNRC

ENCLOSURE Request to Extend the Third 10-Year Inservice Inspection Interval for Examination Of Welds VLA-A001 AND VLA-A002 1.0 ASME Code Component(s) Affected Code Class: 1

References:

- --~ - ~--- 230a- -IA- ~

IWA-2430(d)

IWB-2500(a)

Table IWB-2500-1 Examination Categories: B-A Item Number: B1.12

Description:

Reactor Pressure Vessel (RPV) Longitudinal Shell Welds Component Numbers: VLA-AO01, VLA-A002 2.0 Applicable Code Edition and Addenda ASME Section Xl 1989 Edition/No Addenda.

3.0 Applicable Code Requirement IWB-2500(a) requires components to be examined as specified in Table IWB-2500-1.

Table IWB-2500-1 Category B-A, Item B13.12 requires examination of applicable Class 1 pressure retaining welds, which includes essentially 100% of weld length once during

-the ten-year interval.

IWA-2430(a) requires that the inservice examinations required by IWB shall be completed during each of the inspection intervals for the service lifetime of the power unit.

IWA-2430(d) requires that for components inspected under Program B, each of the inspection intervals may be extended or decreased by as much as 1 year. Adjustments shall not cause successive intervals to be altered by more than 1 year from the original pattern of intervals.

1 of 4

4.0 Reason for Request The DAEC's third ten-year interval RPV weld examinations were scheduled to be performed during Refueling Outage (RFO) 19 (Spring of 2005) from the inside diameter using an automated tool. Examination from the inside diameter (ID)was planned rather than examination from the outside diameter (OD) in order to achieve significantly lower dose, as well as to maintain the ability to perform the examinations in parallel with refueling operations. Industry experience had indicated that examination coverage comparable to that obtained from the OD could be achieved.

Prior to RFO 19, a computer model of the vessel was developed to determine clearances, appurtenances and possible OD reflectors. While the jet pump restraining bracket guides had been identified as a potential access concern in the VLA-AO01 and VLA-A002 weld region, the model indicated that greater than 90% examination coverage would be obtained for the two welds. It was believed that sufficient clearance existed for the examination tool to move around the obstructions and access the remainder of the weld from below the obstructions. During the refueling outage, while attempting to perform examinations of VLA-AO01 and VLA-A002, it was determined that sufficient clearance for the automated equipment did not exist on the ID and performance of those examinations could not be completed from the ID as planned.

RFO 19 was the last refueling outage scheduled for the third ten-year interval.

Extension of the third interval beyond ten years would cause successive intervals to be altered by more than 1 year from the original pattern of intervals, since the second ten-year interval had been extended by one year in accordance with the ASME Code.

5.0 Proposed Alternative and Basis for Use NMC requests NRC authorization of an alternative to extend the third ten-year interval for the examination of RPV longitudinal welds, YLA-AO01 and VLA-A002 until the end_ -

6f RFO 20. RFQ 20 is currently scheduled to begin in February of 2007. This alternative allows time for the development of a smaller inspection tool to be used to examine these welds from the ID during RFO 20.

Pursuant to 10 CFR 50.55a(a)(3)(ii), NMC requests this alternative on the basis that requiring examination of these two welds prior to the end of the third ten year ISI interval (October 31, 2006) presents a hardship without compensating increase in level of quality or safety. Extending the interval for the examination of reactor vessel longitudinal welds VLA-AO01 and VLA-A002 results in about ten years and four months between the examinations of these welds. As discussed below, the last examinations of the two welds were performed in November 1996.

2 of 4

A September 8,1992 revision to 10 CFR 50.55a(g)(6)(ii)(A) contains an augmented examination requirement to perform a one time volumetric examination of essentially 100% (greater than 90%) of all circumferential and axial reactor pressure vessel (RPV) shell assembly welds. During RFO 14 in 1996, the DAEC performed the augmented weld examination of the reactor vessel using the General Electric Reactor Inspection System (GERIS) 2000 ultrasonic examination system. These examinations were performed from the vessel outside diameter using a composite of automated and supplemental manual UT examination techniques. Longitudinal weld VLA-A001 received 96.6% coverage and weld VLA-A002 received 96.7% coverage. Examination results were acceptable to the requirements of ASME Xl, 1980 Edition, Winter 1981

-Addenda,-Category B-A-welds-and'USNRC'Rguilat6ry Guide'1.150.-.'-

Also, during RFO 19 in Spring of 2005, essentially 100% (greater than 90%) coverage was achieved on the remaining six RPV vertical welds (VLB-AO01, VLB-A002, VLC-B001, VLC-B002, VLD-B001 and VLD-B002) with no recordable indications.

Based on the 1996 examination results for VLA-A001 and VLA-A002, as well as the 2005 results for the remaining six RPV vertical welds, NMC concludes that the current inspection interval can be extended for VLA-AO01 and VLA-A002, while providing an acceptable level of quality and safety.

6.0 Duration of Proposed Alternative The interval for examination of welds VLA-AO01 and VLA-A002 will be extended until the end of RFO 20, currently scheduled to begin in February of 2007.

3 of 4

IlCC-B2

/ TOP 111CMD DOlL[Al PATE CLOSU'RE FLANGE REGION SCHEMATIC OF THE RPV SHOWING ARRANGEMENT OF VESSEL PLATES AND WELDS 4 of 4