OMB Control No.: 3150-0011 

ML15169A543 

UNITED STATES 

NUCLEAR REGULATORY COMMISSION 

OFFICE OF NUCLEAR REACTOR REGULATION 

OFFICE OF NEW REACTORS 

WASHINGTON, DC 20555-0001 

March 23, 2016 

NRC REGULATORY ISSUE SUMMARY 2016-02 

DESIGN BASIS ISSUES RELATED TO TUBE-TO-TUBESHEET JOINTS 

IN PRESSURIZED-WATER REACTOR STEAM GENERATORS 

ADDRESSEES

All holders of an operating license or construction permit for a nuclear power reactor under 

Title 10 of the Code of Federal Regulations (10 CFR) Part 50, “Domestic Licensing of 

Production and Utilization Facilities,” except those that have permanently ceased operations 

and have certified that fuel has been permanently removed from the reactor vessel. 

All holders of and applicants for a power reactor combined license, standard design approval, or 

manufacturing license under 10 CFR Part 52, “Licenses, Certifications, and Approvals for 

Nuclear Power Plants.” All applicants for a standard design certification, including such 

applicants after initial issuance of a design certification rule. 

INTENT

The U.S. Nuclear Regulatory Commission (NRC) is issuing this regulatory issue summary (RIS) 

to clarify the design requirements for tube-to-tubesheet welds in pressurized-water reactor 

steam generators and that changes to the tube-to-tubesheet joint design basis should be 

evaluated in accordance with 10 CFR 50.59, “Changes, tests, and experiments.” 

Tube-to-tubesheet welds designed in accordance with the American Society of Mechanical 

Engineers Boiler and Pressure Vessel Code (ASME Code) as pressure boundary (structural) 

welds must follow the requirements of NB-3000, “Design,” in Section III, “Rules for Construction 

of Nuclear Facility Components.” For pressure boundary welds, conformance with ASME Code, 

Section III, NB-4350, “Special Qualification Requirements for Tube-to-Tubesheet Welds,” and 

NB-5274, “Tube-to-Tubesheet Welded Joints,” is not sufficient. This RIS requires no action or 

written response on the part of an addressee. 

BACKGROUND INFORMATION

On October 30, 2014, a licensee determined1 that the tube-to-tubesheet welds for their 

replacement steam generators were characterized as seal welds, not as pressure boundary 

(structural) welds. AREVA designed and manufactured these replacement steam generators, 

which were installed in 2007. AREVA evaluated and qualified the tube radial expansion against 

the tubesheet bore to serve as the tube-to-tubesheet joint pressure boundary by demonstrating 

 

1 St. Lucie Plant - NRC Integrated Inspection Report 05000335/2014005 and 05000389/2014005, January 30, 2015, 

Available at Agencywide Documents Access and Management System (ADAMS) Accession No. ML15030A323 
RIS 2016-02 

Page 2 of 5 

that the friction between the tube and tubesheet was sufficient to resist axial loads in the tube. 

The ASME Code, Section III, does not contain design limits that apply specifically to an 

expansion joint. 

The tube-to-tubesheet welds in the original steam generators were designed to the 

requirements of NB-3000; thus, they were originally qualified as structural welds, taking no 

credit for the ability of tube expansion against the tubesheet bore to resist axial loads in the 

tube. The licensee determined that evaluations performed in support of the steam generator 

replacement project in accordance with 10 CFR 50.59 did not specifically identify and address 

this change to the design basis because the change to the joint design basis was not included in 

the design technical report reviewed by the licensee. The licensee has placed this issue into its 

corrective action program. 

There are five units (Saint Lucie Plant, Unit 2; Salem Nuclear Generating Station, Unit 2; Prairie 

Island Nuclear Generating Plant, Units 1 and 2; and Callaway Plant) with replacement 

recirculating steam generators designed by AREVA that are potentially affected by this issue. 

The licensees for these five units are aware of this issue, as confirmed by the NRC through 

discussions with the industry. 

On February 12, 2015, the Electric Power Research Institute (EPRI) Steam Generator Task 

Force (SGTF) met with the NRC staff to discuss various steam generator topics, including 

tube-to-tubesheet welds. In addition to the issue discussed above, an EPRI representative 

reported2 that there is a difference in interpretation among steam generator 

designers/manufacturers for those units that consider the tube-to-tubesheet welds to be 

pressure boundary (structural) welds. The difference in interpretation is whether the welds must 

be analyzed in accordance with ASME Code, Section III, NB-3000. The alternative 

interpretation was that if the tube-to-tubesheet weld satisfied the requirements of NB-4350 and 

NB-5274, then all ASME design requirements for tube-to-tubesheet welds in a Class 1 

component were satisfied. 

On August 19, 2015, the EPRI SGTF met with the NRC and reported3 that the EPRI SGTF sent 

an inquiry to the ASME Code Section III Standards Committee to determine whether this 

alternative interpretation was correct. In response to the inquiry, the ASME Standards 

Committee concluded4 that the alternative interpretation was not correct, and that 

tube-to-tubesheet welds that are serving a pressure boundary function must meet the 

requirements of NB-3000, in addition to NB-4350 and NB-5274. 

This latter issue (i.e., tube-to-tubesheet welds intended to be pressure boundary (structural) 

welds, but not designed to NB-3000) affects 13 of 15 units with replacement steam generators 

supplied by Babcock & Wilcox Canada. The tube-to-tubesheet welds at these 13 units 

were either not evaluated, or were only partially evaluated, to the requirements of NB-3000. 

The 13 units are: 

 

 

2 February 12, 2015, Summary of Category 2 Public Meeting with the Steam Generator Task Force to Discuss 

Steam Generator Issues, Available at ADAMS Accession No. ML15068A400 3 NRC/EPRI Steam Generator Task Force Meeting - August 19, 2015, Available at ADAMS Accession No. 

ML15231A575 4 ASME BPVC, Section III, Division 1, Article NB-3000 (1983 Edition through 2013 Edition) – May 15, 2015, 

Available at ADAMS Accession No. ML15243A060
RIS 2016-02 

Page 3 of 5 

• Braidwood Station, Unit 1 

• Byron Station Unit 1 

• Calvert Cliffs Nuclear Power Plant, Units 1 and 2 

• Catawba Nuclear Station, Unit 1 

• Donald C. Cook Nuclear Power Plant, Unit 1 

• McGuire Nuclear Station, Units 1 and 2 

• Oconee Nuclear Station, Units 1, 2, and 3 

• R.E. Ginna Nuclear Power Plant 

• St. Lucie Plant, Unit 1 

The tube-to-tubesheet welds for the remaining 2 of 15 units (Millstone Power Station, Unit 2, 

and Davis-Besse Nuclear Power Station, Unit 1) were previously fully evaluated to the 

requirements of NB-3000 at the request of the respective licensees. The licensees for these 13 

units are aware of this issue, as confirmed by the NRC through communication with the 

industry. 

SUMMARY OF ISSUE 

This RIS addresses regulatory compliance issues related to the tube-to-tubesheet joint for both 

replacement and new steam generators. These regulatory compliance issues relate to the 

requirements of the ASME Code, Section III; the regulations of 10 CFR Part 50.55a, “Codes and 

standards;” 10 CFR 50.59, “Changes, tests, and experiments;” and 10 CFR Part 50, 

Appendix B, “Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing 

Plants,” Criterion III, “Design Control”. The NRC staff determined that five units with AREVA 

replacement recirculating steam generators have a tubesheet joint that relies on the tube radial 

expansion against the tubesheet to function as the tube-to-tubesheet joint pressure boundary. 

At least one of those five units (i.e., St. Lucie Plant, Unit 2) had original steam generators with 

tubesheet joints that relied on the tube-to-tubesheet welds to function as the pressure boundary 

and did not include this change to the design basis in the 10 CFR 50.59 evaluation for the 

replacement steam generators. The NRC staff further determined that 13 units with 

replacement steam generators designed by B&W Canada may have tube-to-tubesheet welds 

that were intended to be pressure boundary (structural) welds but were either not evaluated, or 

were only partially evaluated, to the requirements of ASME Code, Section III, NB-3000. The 

NRC staff concluded that these tube-to-tubesheet joint issues have limited risk significance 

because redundant load paths (i.e., the tube-to-tubesheet weld and the expansion joint) in the 

tube-to-tubesheet joint resist axial loads in the tubes. The NRC staff recommends that affected 

licensees ensure compliance with regulatory requirements, as clarified in this RIS for 

replacement and new steam generators. The licensees for all affected units are aware of this 

issue. 

BACKFITTING AND ISSUE FINALITY

This RIS requires no action or written response. This RIS does not present any new or changed 

NRC position or interpretation with respect to ASME Code, NB-3000, “Design,” in Section III, 

“Rules for Construction of Nuclear Facility Components,” ASME Code, Section III, NB-4350, 

“Special Qualification Requirements for Tube-to-Tubesheet Welds,” or NB-5274, 

“Tube-to-Tubesheet Welded Joints.” Consequently, the staff did not perform a backfit analysis. 

 
RIS 2016-02 

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FEDERAL REGISTER NOTIFICATION

A notice of opportunity for public comment on this RIS was not published in the Federal Register 

because it is informational and pertains to a staff position that does not represent a departure 

from current regulatory requirements and practice. 

CONGRESSIONAL REVIEW ACT

This RIS is not a rule as defined in the Congressional Review Act (5 U.S.C. §§ 801-808). 

PAPERWORK REDUCTION ACT STATEMENT

This RIS does not contain any new or amended information collection requirements subject 

to the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.). Existing collection 

requirements under 10 CFR Part 50 were approved by the Office of Management and Budget, 

control number 3150-0011. 

Public Protection Notification 

The NRC may not conduct or sponsor, and a person is not required to respond to, an 

information collection unless the requesting document displays a currently valid OMB control 

number. 

 
RIS 2016-02 

Page 5 of 5 

CONTACT

Please direct any questions about this matter to the technical contact listed below or the 

appropriate Office of Nuclear Reactor Regulation (NRR) project manager. 

/RA/ /RA/ 

Michael C. Cheok, Director Lawrence E. Kokajko, Director 

Division of Construction Inspection Division of Policy and Rulemaking 

 and Operational Programs Office of Nuclear Reactor Regulation 

Office of New Reactors 

Technical Contact: Kenneth Karwoski, NRR 

 301-415-2752 

 E-mail: Kenneth.Karwoski@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, 

http://www.nrc.gov, under NRC Library. 
RIS 2016-02 

Page 5 of 5 

CONTACT

Please direct any questions about this matter to the technical contact listed below or the 

appropriate Office of Nuclear Reactor Regulation (NRR) project manager. 

/RA/ /RA/ 

Michael C. Cheok, Director Lawrence E. Kokajko, Director 

Division of Construction Inspection Division of Policy and Rulemaking 

 and Operational Programs Office of Nuclear Reactor Regulation 

Office of New Reactors 

Technical Contact: Kenneth Karwoski, NRR 

 301-415-2752 

 E-mail: Kenneth.Karwoski@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, 

http://www.nrc.gov, under NRC Library. 

ADAMS Accession No.: ML15169A543 *Concurred by e-mail TAC No. MF6204

OFFICE NRR/DE/ESGB Tech Editor NRR/DE BC:NRR/DE/ESGB 

NAME AJohnson* JDougherty* KKarwoski* GKulesa* 

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NHilton 

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TDonnell* LHill* 

DATE 9/24/15 10/5/15 9/29/15 9/23/15 

OFFICE OGC (NLO) D:NRR/DORL LA:NRR/PGCB PM:NRR/PGCB 

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OFFICE 3/2/16 3/22/16 3/9/16 3/23/16 

OFFICIAL RECORD COPY