Information Notice 2013-21, Welding Problems During Fabrication of Reactor Plant Components
| ML13150A405 | |
| Person / Time | |
|---|---|
| Issue date: | 11/21/2013 |
| From: | Michael Cheok, Kokajko L Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Beaulieu D | |
| References | |
| IN-13-021 | |
| Download: ML13150A405 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001 November 21, 2013 NRC INFORMATION NOTICE 2013-21: WELDING PROBLEMS DURING FABRICATION
OF REACTOR PLANT COMPONENTS
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 who 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 early site permit, combined license, standard
design certification, standard design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants.
All contractors and vendors that supply basic components to U.S. Nuclear Regulatory
Commission (NRC) licensees under 10 CFR Part 50, Domestic Licensing of Production and
Utilization Facilities or 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear
Power Plants.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of examples of welding problems that occurred during the fabrication of reactor
plant components. The NRC expects that recipients will review the information for applicability
to their facilities and consider actions, as appropriate, to avoid similar problems. Suggestions
contained in this IN are not NRC requirements; therefore, no specific action or written response
is required.
DESCRIPTION OF CIRCUMSTANCES
Three instances are described below where welding problems which required significant repair
occurred during the fabrication of large reactor plant components. Weld repairs on reactor
coolant system components are generally undesirable due to the introduction of residual tensile
stresses, a contributor to primary water stress corrosion cracking (PWSCC).
Weld Defects in the Flamanville 3 European Pressurized Reactor (EPR) Vessel Head (France)
In November 2010, during fabrication inspections of the new Flamanville 3 EPR reactor vessel
head, AREVA detected defects in several reactor head penetration nozzle welds. In April 2011, the French Nuclear Safety Authority (ASN) issued an Information Notice outlining the location of
ML13150A405 the defects and the proposed corrective actions. In June 2011, during repairs of the penetration
nozzle weld defects, AREVA discovered that there was also insufficient buttering thickness for
some of the welds due to excessive grinding during nozzle weld repairs. See ASN Information
Notice 2012-13 for more details.
The design of the EPR vessel head includes over 100 penetrations. This relatively large
number of penetrations restricts access to the penetration welds which makes in-process
cleaning, nozzle welding, and weld repairs more difficult. Also, the welding process was
changed compared to previous (non-EPR) reactor head fabrication. Changes in welding
practices compared to manufacturing of previous vessel closure heads included filling the weld
in sequences of three layers instead of two layers, and cleaning operations at the end of the
welding sequences were performed by brushing instead of grinding. The combination of poor
accessibility to weld sites, and the changes in the weld cleaning process led to several weld
defects.
The removal of an excessive amount of buttering material during repair of the reactor head
welding defects was, in part, due to slight deformation of the vessel head which occurred during
the final heat treatment. This deformation is expected, but was not appropriately taken into
account when grinding was performed during penetration nozzle weld repairs. This resulted in
an excessive amount of buttering material being removed.
Lessons learned from the EPR reactor vessel head repairs have led to several improvements in
AREVA welding processes. These included making specific weld procedure acceptance criteria
more stringent, performing more frequent weld checks during welding operations, and
increasing the use of ultrasound inspections on nozzle adapter welds.
Vogtle Electric Generating Plant (Vogtle) Unit 3 AP-1000 Reactor Vessel Nozzle Weld Issues -
Doosan Heavy Industries, South Korea
After welding the Vogtle Unit 3 reactor vessel nozzles at Doosan Heavy Industries in the
Republic of Korea, ultrasonic testing revealed several indications in the Alloy 52M inlet
nozzle-to-safe end welds. Some indications were in excess of the allowable limits of the
American Society of Mechanical Engineers Boiler & Pressure Vessel Code,Section III, and
therefore were determined to be defects that required repair. The primary cause for the
indications was loss of weld shielding gas during welding operations due to the ventilation
configuration in the vicinity of welding. Corrective actions included revising procedures to better
control ventilation configurations to ensure that the correct weld shielding gas is maintained, repairing the welds by excavating the defects from the inside diameter, and re-welding.
Additional information appears in Southern Nuclear Operating Companys public meeting notes
presented to the NRC on October 4, 2012. They can be found on the NRCs public Web site in
the Agencywide Documents Access and Management System (ADAMS) under Accession No.
ML12277A349. Vogtle Electric Generating Plant Unit 3 AP-1000 Containment Vessel Weld Cracking
In April 2012, licensee contractors discovered cracks in four welds in the lower ring of the
Vogtle Unit 3 containment vessel. The cracks were located in the welds joining 1-7/8 inch
SA-738 grade B alloy steel plates. Corrective actions included modifying the fit-up procedure to
reduce fit-up stresses and modifying the post weld heat treatment procedure to distribute heat
during post weld heat treatment over a larger area.
Additional information appears in Southern Nuclear Operating Company Vogtle Electric
Generating Plant Units 3 and 4 - NRC Integrated Inspection Reports 05200025/2012-003, and
05200026/2012-003, dated August 2, 2012, on the NRCs public Web site in ADAMS under
Accession No. ML12220A476.
BACKGROUND
Related NRC Generic Communications
NRC IN 2010-08, Welding and Nondestructive Examination Issues, dated April 9, 2010,
alerted addressees to several instances of welding and nondestructive examination human
performance errors and ASME code non-compliances. (ADAMS Accession No. ML091670177)
NUREG-1425, Welding and Nondestructive Examination Issues at Seabrook Nuclear Station:
An Independent Review Team Report, dated July 28, 1990, describes lessons learned
regarding licensee radiographic and welding programs. (ADAMS Accession No.
DISCUSSION
This IN provides examples of recent welding issues that involved inadequate procedures to
control critical welding parameters, inadequate quality checks, or inadequate technical
evaluation of welding conditions. In each of the examples, the affected welds were removed
and completely re-welded, or the welds were repaired. However, weld repairs in contact with
reactor coolant are generally not preferred due to the introduction of residual tensile stresses on
the surface of the weld in contact with reactor coolant. This can potentially contribute to weld
degradation mechanisms such as PWSCC. The implementation of adequate procedures, training, and quality oversight is necessary to avoid these types of welding issues. Specifically,
10 CFR Part 50, Appendix B, Quality Assurance Criteria for Nuclear Power Plants and Fuel
Reprocessing Plants: (1) Criterion VII requires that measures be established to adequately
control contractor materials and services, and (2) Criterion IX requires a licensee to establish
adequate measures to ensure the control of special processes, including welding, heat treating, and nondestructive testing, and (3) Criterion XVI requires that measures be established to
assure that conditions adverse to quality be promptly identified and corrected.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contacts listed below or the appropriate Office of New Reactors (NRO) or
Office of Nuclear Reactor Regulation project manager.
/RA/ /RA Sher Bahadur Acting for/
Michael C. Cheok, Acting 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 Contacts: Robert Davis, NRO Phil OBryan, NRO
301-415-4028 E-mail: Phil.OBryan@nrc.gov
E-mail: Robert.Davis@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
ML13150A405 TAC MF0922 OFFICE PM:DCIP/NRO Tech Editor: DE/NRO BC:CIB/DE/NRO
NAME POBryan CHsu RDavis DTerao
DATE 05/31/13 e-mail 06/14/13 e-mail 05/31/13 e-mail 9/23/13 e-mail
OFFICE BC:IGCB/DCIP/NRO D:DE/NRO LA:PGCB/NRR
NAME BAnderson MShuaibi CHawes CMH
DATE 9/24/13 e-mail 10/29/13 e-mail 11/04/13 e-mail
OFFICE PM:PGCB/NRR BC:PGCB/NRR (A) D:DCIP/NRO D:DPR/NRR
NAME DBeaulieu SStuchell MCheok S. Bahadur for
LKokajko
OFFICE 11/04/13 11/4/13 11/8/13 11/21/13