NLS2014041, Response to Nuclear Regulatory Commission Follow-Up Request for Additional Information Regarding Fulfillment of License Renewal Commitment No. NLS2009100-1, Revision 1, for the Core Plate Hold-Down Bolts at Cooper Nuclear Station

Response to Nuclear Regulatory Commission Follow-Up Request for Additional Information Regarding Fulfillment of License Renewal Commitment No. NLS2009100-1, Revision 1, for the Core Plate Hold-Down Bolts at Cooper Nuclear Station

ML14143A366
Person / Time
Site:	Cooper
Issue date:	05/19/2014
From:	Limpias O Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2014041
Download: ML14143A366 (4)

Text

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Nebraska Public Power District Always there when you need us NLS2014041 May 19, 2014 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Subject:

Response to Nuclear Regulatory Commission Follow-Up Request for Additional Information Regarding Fulfillment of License Renewal Commitment No.

NLS2009100-1, Revision 1, for the Core Plate Hold-Down Bolts at Cooper Nuclear Station Cooper Nuclear Station, Docket No. 50-298, DPR-46

References:

1. Email from Andrea George, U.S. Nuclear Regulatory Commission, to David Van Der Kamp, Nebraska Public Power District, dated April 21, 2014, "Request for Additional Information - License Renewal Core Hold-Down Bolts Commitment Review (TAC No. MF3557)"

2. Letter from Oscar A. Limpias, Nebraska Public Power District, to the U.S.

Nuclear Regulatory Commission, dated October 1, 2013, "Supplemental Information Related to Response to Request for Additional Information Regarding Core Plate Hold Down Bolt Stress Analysis"

Dear Sir or Madam:

The purpose of this letter is for Nebraska Public Power District to submit a response to a Follow-Up Request for Additional Information (RAI) from the Nuclear Regulatory Commission (NRC)

(Reference 1) resulting from review of Reference 2. The RAI requested information in support of the NRC's review of Cooper Nuclear Station's revised commitment related to inspections of the core plate hold-down bolts.

The response to the specific RAI question is provided in the Attachment.

This letter does not contain any new regulatory commitments.

If you have any questions concerning this matter, 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 www.nppd.com

NLS2014041 Page 2 of 2 I declare under penalty of erjury that the foregoing is true and correct.

Executed on: 5 I  !(.-

(Date)

Sincer y, sa A. Limpia2-Vice President - Nuclear and Chief Nuclear Officer Jo

Attachment:

Response to Nuclear Regulatory Commission Follow-Up Request for Additional Information Regarding Fulfillment of License Renewal Commitment No.

NLS2009100-1, Revision 1, for the Core Plate Hold-Down Bolts at Cooper Nuclear Station 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 NPG Distribution w/o attachment CNS Records w/ attachment

NLS2014041 Attachment Page 1 of 2 Response to Nuclear Regulatory Commission Follow-Up Request for Additional Information Regarding Fulfillment of License Renewal Commitment No. NLS2009100-1, Revision 1, for the Core Plate Hold-Down Bolts at Cooper Nuclear Station Cooper Nuclear Station, Docket No. 50-298, DPR-46 The Nuclear Regulatory Commission (NRC) follow-up request for additional information regarding the Core Plate Hold-Down Bolts is shown in italics. The Nebraska Public Power District (NPPD) response to the request is shown in block font.

NRC Request By letter dated October 1, 2013 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML13283A010), Nebraska Public Power District (NPPD,the licensee) revised its commitment related to inspections of the core plate hold-down bolts at Cooper Nuclear Station to state the following:

Until the NRC endorses the revised inspectionguidance ofB WR VIP-25, ["B WR Vessel and Internals Project,B WR Core PlateInspection and Flaw Evaluation Guidelines,"December 1996,] NPPDwill perform VT-3 inspections on the top side of a 50 percent sample of the Core Plate Hold Down Bolts every other refueling outage.

Based on its review of the above inspection plan, the staff has determined that additional information is needed to make a determination regardingthe adequacy ofperforming a VT-3 visual examination of 50 percent of the core plate hold-down bolts every other refueling outage.

The staff notes that its approvalof this same inspection planfor the core plate hold-down bolts at Vermont Yankee NuclearPower Station (VYNPS) was based, in part,on its determinationthat the licensee adequately demonstrated that their core plate hold-down bolts would have a low susceptibility to intergranularstress corrosion cracking (IGSCC). This determinationis documented in Section 3.2.2 the staffis March 28, 2012 safety evaluationfor the VYNPS core plate hold-down bolt inspectionplan and stress analysis (ADAMS Accession No.

ML120760152). The staff's determinationregardingIGSCC susceptibility at VYNPS was based on the fact that the VYNPS core plate hold-down bolts are not sensitized, the bolts were procured to a specificationprohibitingcoldforming operations after solution heat treatment, and there were no instances of stress corrosion cracking (SCC) of these bolts in the boiling water reactor (B WR) fleet at that time.

The staff will need to evaluateplant-specific information regardingthe IGSCC susceptibility of these bolts in order to determine whether a VT-3 visual examination of 50 percent of the core plate hold-down bolts every other refueling outage is an acceptable inspection strategyfor Cooper Nuclear Station. Therefore, pleaseprovide information regardingthe fabrication practices (i.e., sensitization, cold working of the materialbefore or after solution heat treatment, etc.) for the core plate hold-down bolts at Cooper Nuclear Station, as they relate to IGSCC susceptibility. Additionally, please indicate whether any instances of SCC have been observed

NLS2014041 Attachment Page 2 of 2 for these bolts at Cooper Nuclear Station or other U.S. BWRs, based on operatingexperience in the domestic B WRfleet to date.

NPPD Response:

The Cooper Nuclear Station (CNS) core plate hold-down bolts were fabricated from non-sensitized Type 304 annealed stainless steel. The original material specification required this austenitic stainless steel material to be solution heat treated following the cold roll threading process. In addition, the procurement specification also limited the as-fabricated material surface hardness to be below BHN-201 thus limiting the amount of cold work introduced as part of the thread forming process. The machined threads were liquid honed to a matte finish to remove any burrs or residual surface roughness and the upper nut thread surfaces were electrolyzed to minimize the potential for galling during assembly.

CNS, as well as the domestic BWR fleet, has not observed any instances of SCC based on inspections performed to date. In summary, non-welded Type 304 stainless'steel material in the solution annealed condition has shown to be highly resistant to IGSCC initiation in BWR applications. Based on manufacturing process controls and inspection history, susceptibility to IGSCC is considered low for the CNS core plate bolts.