NLS2008042, Response to Request for Additional Information 10 CFR 50.55a, Request RI-35, Revision 1

Response to Request for Additional Information 10 CFR 50.55a, Request RI-35, Revision 1

ML081120113
Person / Time
Site:	Cooper
Issue date:	04/11/2008
From:	Minahan S Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2008042
Download: ML081120113 (8)

Text

N Nebraska Public Power District Always there when you need us NLS2008042 April 11, 2008 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Subject:

Response to Request for Additional Information Regarding 10 CFR 50.55a Request RI-35, Revision 1 Cooper Nuclear Station, Docket No. 50-298, DPR-46

References:

1. Letter from Carl F. Lyon, U. S; Nuclear Regulatory Commission, to Mr. Stewart B. Minahan, Nebraska Public Power District, dated April 7, 2008, "Cooper Nuclear Station - Request for Additional Information Re: Relief Request RI-35 (TAC No. MD8025)"

2. Letter from Stewart B. Minahan, Nebraska Public Power District, to the U. S. Nuclear Regulatory Commission, dated March 27, 2008, "Response to Request for Additional Information Regarding 10 CFR 50.55a Request RI-35, Revision 0, and Submittal of RI-35, Revision 1",

Dear Sir or Madam:

The purpose of this letter is for the Nebraska Public Power District (NPPD) to submit a response to the Nuclear Regulatory Commission (NRC) Request for Additional Information (RAI) dated April 7, 2008 (Reference 1). The additional information requested by the RAI is in support of the NRC review of the 10 CFR 50.55a request (RI-35, Revision 1) for the Cooper Nuclear Station (CNS) submitted by letter dated March 27, 2008 (Reference 2). The 10 CFR 50.55a request submitted by Reference 2 was a request to use alternatives to the dissimilar metal weld requirements of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code.

The response to the RAI is provided as Attachment 1. Approval of RI-35, Revision 1 is requested as soon as practicable in order to support weld repair work, if needed, for Refueling Outage 24. Based on discussions with the NRC Project Manager for CNS, verbal approval can be issued if needed, provided that the request is justified.

Should you have any questions regarding this submittal, please contact David Van Der Kamp, Licensing Manager, at (402) 825-2904.

COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 Ji.-.

www.nppd.com

NLS2008042 Page 2 of 2 Sincerely, Stewart B. Minahan Vice President-Nuclear and Chief Nuclear Officer

/dm Attachment cc: Regional Administrator w/ attachment USNRC - Region IV Cooper Project Manager w/ attachment USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/ attachment USNRC - CNS Nebraska Health and Human Services w/ attachment Department of Regulation and Licensure NPG Distribution w/o attachment CNS Records w/ attachment

NLS2008042 Page 1 of 5 Attachment 1 Response to Request for Additional Information (RAI)

Related to Relief Request RI-35, Revision 1 Cooper Nuclear Station (CNS), Docket No. 50-298, DPR-46 The NuclearRegulatory Commission (NRC) staff has reviewed the Nebraska Public Power District(the licensee)[NPPD]March 27, 2008, Response To Request ForAdditional Information regardingRequest RI-35, Revision 1 for the Cooper Nuclear Station (CNS) and has determined that additionalinformation is necessary to complete the review of their requestfor relief Based on the staff's review, pleaseprovide a response which addresses the following requestfor additionalinformation questions.

1. NRC Request The licensee has stated that the weld overlay of the dissimilarmetal welds may require welding on more than 300 square inches of surface on some of the materials shown in Table 1 of Request Number RI-35, Revision 1. Provide sketches and calculations tojustify the basisfor the maximum surface area of weld overlay for ComponentNumbers RAS-BF-1, RBS-BF-1 and RAS-BF-12 shown in Table ] of Request Number R-1-35, Revision 1.

NPPD Response The following table is provided in lieu of sketches and calculations. The design rules require that the weld overlay extend a sufficient distance on either side of the defect location to provide for effective load transfer across the defect location. The repair length on the safe end side and the nozzle side will be extended to provide sufficient access to allow for ultrasonic testing examination of the repair and underlying volume. Based on the nominal diameters and the calculated size of the repair, the minimum required areas for each side of the flaw are summarized below. The maximum areas include some additional margin:

Nozzle Nominal WOL Minimum Minimum Maximum 4 OD CircumferenceI WOL WOL Area 3 WOL Area (in) (in) Length2 (in 2) (in2)

(in)

RAS-BF-1 29.0625 91.3 4 365.2 420 RBS-BF-1 29.0625 91.3 4 365.2 420 RAS-BF-12 20 62.8 2.5 157 180 Note 1: Circumference = OD x 7c Note 2: L = 0.75*/Rt where L is the full thickness length of the repair on each side of the observed weld. Note the length is rounded up.

Note 3: Area= circumference x length Note 4: Maximum area is based on minimum area required plus a 15% margin.

NLS2008042 Page 2 of 5

2. NRC Request In Table I of Request Number RI-35, Revision 1, and "Material1 "for several components is shown as "Nozzle.: A-508 Class 2 CS. " This implies thatASME SA-508 Class 2 is a carbon steel material (P-1 material). This is incorrect. ASME SA-508 Class 2 is a low alloy steel material (P-3 material). As this clarificationis importantwith respect to the qualificationof the welding procedurewhich will be used to apply the weld overlay, please correct this discrepancy.

NPPD Response NPPD did not intend any confusion in using the CS suffix for A-508 Class 2 material. NPPD used it to clarify that the nozzle material is different from the stainless steel safe end. NPPD concurs that this material is P-3 (low alloy steel) per ASME Section IX.

3. NRC Request In Table I of Request Number RI-35, Revision 1, one of the materials to be welded is shown as, "Pipe:A-155 Class ] CS. " NRC cannotfind a material with this class of A-155. Please identify the material designation of this material, including materialtype or class and year of this designation. As noted above, documentation of this information is significant with respect to ensuringproper qualification of the welding procedurewhich will be used to apply the weld overlay.

NPPD Response A- 155 is an older standard for electric-fusion-welded steel pipe suitable for high-pressure service for use at high, intermediate, or low temperatures. The class 1 designation means that the pipe was required to be heat treated and radiographed. The grade is KC-70. This material specification was annulled by the ASME in 1980 and was replaced by SA-671, SA-672, or SA-691. The use of A-155 Class 1 was allowed by the construction code, ANSI B31.1-1967. A copy of the material specification (circa 1976) can be obtained directly from ASME.

4. NRC Request The reliefrequest states thatfull ultrasonic examination of the final weld surface and band area (1.5T width) will not be performed. Provide a sketch similarto Figure 1 in P1-35 to describe how much of the final weld surface and band area will be post-weld examined using the ultrasonic method and how much of the final weld surface and band area will be examined by the liquidpenetrant method. Provide a detailedexplanationfor the basis that the liquid penetrantmethod can be substitutedfor the ultrasonicmethod in areas where the ultrasonicmethod will not be used.

NLS2008042 Page 3 of 5 NPPD Response Full ultrasonic examination of the 1.5T band will not be possible due to geometric interferences. The ultrasonic examination may not extend up to the very edge of the overlay.

The weld overlay will extend into the blend radius of the nozzle for structural reinforcement.

This extension into the blend radius eliminates a stress riser on the nozzle and may provide additional surface area for ultrasonic examination of the defect area in the original weld.

Figures 1 and 2 identify the extent of coverage expected for scans in the circumferential and axial directions. The full WOL surface will be scanned.

Because this is a surface application of a temperbead welding process (specifically performed to minimize heat input into the ferritic steel nozzle), there is minimal impact to the volume of the ferritic shell nozzle material in the area surrounding the weld overlay. Also, no additional useful information can be gained by a volumetric examination of the area beyond the physical boundaries of the weld overlay. The weld and heat affected zone beneath the weld overlay will be volumetrically examined after welding to ensure that sound weld metal has been deposited and that the process did not introduce flaws into the base material.

Surface examinations of the weld overlay surface will be performed (See Figure 3 for the examination area). This is sufficient to verify that defects were not introduced in either the ferritic steel nozzle or stainless steel safe-end due to welding.

Later editions of Section Xl as well as Code Case N-638-2 have deleted the requirement for the 1.5T examination band for both ultrasonic examination and surface examination. This is consistent with the less restrictive requirements for ultrasonic examination of the ferritic nozzle because hydrogen cracking away from the temper bead weld is not considered a concern. The nondestructive examination (NDE) requirements in these documents apply to any type of welding where a temperbead technique is to be employed (which includes weld repairs of excavated flaws) and is not specifically written for weld overlay. For the weld overlay type of repair, any ferritic steel base material cracking would occur in the HAZ directly below or adjacent to the weld overlay and not in the 1.5T examination band of ferritic material beyond the edges of the weld overlay. If this type of cracking occurs it will be detected by the NDE of the weld overlay and adjacent ferritic steel surfaces as described in the relief request and non-mandatory Appendix Q.

NLS2008042 Attachment I Page 4 of 5 Weld Overlay Required Ultrasonic (UT) E_xamination Coveraqe A B Z ý Weld Overlay C

Examination Volume A,-B-C-D Note:

(1) The UT Axial scan coverage of the\ Neld Overlay material will only be limited in the taper areas by transducer wedge element size and taper transitions, both of which are outside the Code Required Examination Volume. UT scans will be performed in opposing upstream and do .wnstream directions.

(2) The UT Circumferential scan covers age of the Weld Overlay material is expected to be limited at eac :h edge of the overlay by approximately 0.5" as determined by thie dimension of the transducer wedge element and taper trzansitions. UT scans will be performed in opposing clockwise an d counter-clockwise directions.

Figure 1 Weld Required (PSI/ISI) Ultrasonic Examination Coverage 1/" in. Note 1 - -1 in.

/2"~-W

/Weld Overlay D/ C t

'*\Assumed as-found flaw Examination Volume A-B-C-D Note:

(1) For axial or circumferential flaws, the extent of the examination volume shall extend at least 1/2 in. beyond the as found flaw and at least 1/2 in. beyond the toes of the original piping weldment, including weld end butter, where applied.

(2) The Ultrasonic Axial and Circumferential scans will achieve 100% of the Code Required Volume.

Figure 2

NLS2008042 Page 5 of 5 Weld Overlay (PSI) Liauid Penetrant Examination Coveraae

. . . . . j I J U 1/2" in.

/

The weld overlay and adjacent base material for 1/2 inch from each side of the overlay shall be examined using the Liquid penetrant method.

Figure 3

ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS@

ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS@

Correspondence Number: NLS2008042 The following table identifies those actions committed to by Nebraska Public Power District (NPPD) in this document. Any other actions discussed in the submittal represent intended or planned actions by NPPD. They are described for information only and are not regulatory commitments. Please notify the Licensing Manager at Cooper Nuclear Station of any questions regarding this document or any associated regulatory commitments.

COMMITMENT COMMITTED DATE COMMITMENT NUMBER OR OUTAGE None N/A N/A I

i i I PROCEDURE 0.42 REVISION 22 PAGE 19 OF 26