ML18318A334

Relief from the Requirements of the American Society of Mechanical Engineers Code

ML18318A334
Person / Time
Site:	Braidwood
Issue date:	01/17/2019
From:	David Wrona Plant Licensing Branch III
To:	Bryan Hanson Exelon Generation Co, Exelon Nuclear
Wiebe J
References
EPID L-2018-LLR-0036
Download: ML18318A334 (8)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, O.C. 20555-0001 January 17, 2019 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO) Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BRAIDWOOD STATION, UNITS 1 AND 2 -RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE (EPID L-2018-LLR-0036)

Dear Mr. Hanson:

By letter dated March 19, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18078A185), as supplemented by letter dated July 31, 2018 (ADAMS Accession No. ML18212A334), Exelon Generation Company, LLC (Exelon, the licensee), submitted relief request (RR) 14R-06 for the fourth 10-year inservice inspection (ISi) interval at Braidwood Station (Braidwood), Units 1 and 2. The licensee requested relief from the requirements of Title 10 of the Code of Federal Regulations ( 1 O CFR) 50.55a(b )(2)(xx)(B) and the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI, paragraphs IWA-4221 and IWA-4540(a)(2).

The licensee is proposing to use phased array ultrasonic testing as an alternative to the required radiographic testing. Specifically, pursuant to 10 CFR, Section 50.55a(z)( 1 ), the licensee requested to use the proposed alternative on the basis that it provides an acceptable level of quality and safety. The U.S. Nuclear Regulatory Commission (NRC or Commission) staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that Exelon has adequately addressed all of the regulatory requirements in 10 CFR 50.55a(z)( 1 ). Therefore, the NRC staff authorizes the use of RR 14R-01 for the fourth ISi intervals at Braidwood, Units 1 and 2, which started on August 29, 2018, and on November 5, 2018, respectively, or until the NRC approves Code Case N-831, or a later revision, in Regulatory Guide 1.147 or other document during the interval.

By its letter dated March 19, 2018, the licensee indicated that the fourth ISi interval for Unit 2 was scheduled to start on October 17, 2018, but also indicated that the start was subject to the allowable changes for inspection intervals in IWA-2430.

By letter dated October 4, 2018 (ADAMS Accession No. ML18284A445), the licensee indicated that the fourth inspection interval for Unit 2 was scheduled to start on November 5, 2018. All other requirements of ASME Code,Section XI, for which relief was not specifically requested and authorized by the NRC staff remain applicable, including the third-party review by the Authorized Nuclear lnservice Inspector.

B. Hanson If you have any questions, please contact the Project Manager, Joel Wiebe at 301-415-6606 or via e-mail at Joel.Wiebe@nrc.gov.

Docket Nos. 50-456 and 50-457

Enclosure:

Safety Evaluation cc: Listserv Sincerely, /)' 1*. ) <-)_/-l. (__' l 'i '--*-* David J. Wrona, Chief Plant Licensing Branch Ill Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 14R-06 REGARDING PHASED ARRAY ULTRASONIC TESTING EXELON GENERATION COMPANY. LLC BRAIDWOOD STATION, UNITS 1 AND 2 DOCKET NOS. 50-456 AND 50-457

1.0 INTRODUCTION

By letter dated March 19, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18078A185), as supplemented by letter dated July 31, 2018 (ADAMS Accession No. ML18212A334), Exelon Generation Company, LLC (Exelon, the licensee), submitted relief request (RR) 14R-06 for the fourth 10-year inservice inspection (ISi) interval at Braidwood Station (Braidwood), Units 1 and 2. The licensee requested relief from the requirements of Title 10 of the Code of Federal Regulations ( 10 CFR), Section 50.55a(b)(2)(xx)(B), and the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, paragraphs IWA-4221 and IWA-4540(a)(2).

The licensee is proposing to use phased array ultrasonic testing (PA-UT) as an alternative to the required radiographic testing {RT}. Specifically, pursuant to 10 CFR, Section 50.55a(z)( 1 ), the licensee requested to use a proposed alternative on the basis that it would provide an acceptable level of quality and safety.

2.0 REGULATORY EVALUATION

Regulation 10 CFR 50.55a(g)(4) states, in part, that in a pressurized-boiling water-cooled nuclear power facility, components that are classified as ASME Code, Class 1, Class 2, and Class 3, must meet the requirements set forth in ASME Code,Section XI. Additionally, 10 CFR Section 50.55a(b)(2)(xx)(B) requires that: "The NDE provision in IWA-4540(a)(2) of the 2002 Addenda of ASME Section XI must be applied when performing system leakage tests after repair and replacement activities performed by welding or brazing on a pressure retaining boundary using the 2003 Addenda through the latest edition and addenda incorporated by reference in paragraph (a)(1){ii) of this section." Paragraph IWA-4540(a){2) of the 2002 Addenda of ASME Code,Section XI. requires that the nondestructive examination method and acceptance criteria of the 1992 Edition or later of ASME Code, Section Ill, be met prior to return to service in order to perform a system leakage test in lieu of a system hydrostatic test. The licensee has requested relief from the requirements of ASME Code,Section XI, paragraphs IWA-4221 and IWA-4540(a)(2).

Section XI, paragraph IWA-4200, covers repair/replacement activities, and paragraph IWA-4221 requires that when the licensee replaces an existing item, Enclosure the replacement shall meet the requirements of the Construction Code to which the original item was constructed.

Regulation 10 CFR, Section 50.55a(z) states, in part, that alternatives to the requirements of 10 CFR 50.55a(b)-(h) may be used when authorized by the NRC, if: (1) the proposed alternatives would provide an acceptable level of quality and safety or (2) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request and the Commission to authorize the alternative requested by the licensee.

3.0 TECHNICAL EVALUATION 3.1 ASME Code Components Proposed alternative RR 14R-06 covers ASME Code,Section XI, ferritic piping butt welds requiring radiography during repair/replacement activities.

3.2 Applicable ASME Code Requirements Regulation 10 CFR, Section 50.55a(b)(2)(xx)(B) requires that "The NDE provision in IWA-4540(a)(2) of the 2002 Addenda of Section XI must be applied when performing system leakage tests after repair and replacement activities performed by welding or brazing on a pressure retaining boundary using the 2003 Addenda through the latest edition and addenda incorporated by reference in paragraph (a)(1)(ii) of this section." The fourth 10-year ISi interval of Braidwood, Units 1 and 2, uses the 2013 Edition ASME Code,Section XI. Paragraph IWA-4540(a)(2) of the 2002 Addenda of Section XI requires that the nondestructive examination method and acceptance criteria of the 1992 Edition or later of Section Ill be met prior to return to service in order to perform a system leakage test in lieu of a system hydrostatic test. Additionally, ASME Code,Section XI, paragraph IWA-4221, requires the owner to use the requirements of the construction code for repair/replacement activities.

The examination requirements for ASME Code, Section Ill, circumferential butt welds are contained in subarticles NB-5200, NC-5200, and ND-5200. The acceptance standards for radiographic examination are specified in subarticles NB-5300, NC-5300, and ND-5300. 3.3 Proposed Alternative and Basis for Use The licensee is proposing the use of encoded PA-UT in lieu of the ASME Code-required RT examinations for ferritic piping repair/replacement welds. The proposed alternative qualification program is based on ASME Code Case N-831 with some small changes in wording for clarification.

ASME Code Case N-831 was approved by the ASME Code Standards Committee on September 27, 2016, but is not NRC approved for general use. The encoded PA-UT procedures, equipment, and personnel will be qualified using performance demonstration testing. The flaw acceptance standards for the PA-UT tests will consider all flaws to be planar and be evaluated against the preservice acceptance standards of ASME Code,Section XI, paragraphs IWB-3400, IWC-3400, or IWD-3400, for ASME Code Class 1, 2, or 3 welds, respectively.

The basis for RR 14R-06 is the encoded PA-UT is equivalent to or superior for detecting and sizing planar flaws as compared to the required radiographic examination.

The examination procedure and personnel performing examinations are qualified via performance demonstration testing using representative piping conditions and flaws that demonstrate the ability to detect and size flaws that are both acceptable and unacceptable to the defined acceptance standards.

The ultrasonic testing (UT) techniques are being used throughout the nuclear industry for examination of dissimilar metal welds and overlaid welds, as well as other applications including ASME Code, 831.1, piping replacements.

3.4 Duration of Proposed Alternative The licensee is requesting that this proposed alternative be applied for the duration of fourth the 10-year ISi intervals at Braidwood, Units 1 and 2, which started on August 29, 2018, and November 5, 2018, respectively, or until the NRC approves Code Case N-831, or a later revision, in Regulatory Guide 1.147 or other document during the interval.

3.5 NRC Staff Evaluation The licensee is proposing to use encoded PA-UT in lieu of RT in RR 14R-06 for repair and replacement activities for the remainder of their current 10-year ISi intervals at Braidwood, Units 1 and 2. The UT, like RT, is a volumetric inspection technique that is commonly used to inspect welds in nuclear power plants and in other industries.

Ultrasonic examinations are not equivalent to radiographic examinations as they use different physical mechanisms to detect and characterize discontinuities.

These differences in physical mechanisms result in several key differences in sensitivity and discrimination capability.

The NRC staff has been assessing the effectiveness of the use of ultrasound in lieu of radiography since 2009, including literature reviews, detailed evaluations of previous relief requests and proposed alternatives, and confirmatory experimental work to validate the findings.

An assessment of the use of UT in lieu of RT by the NRC is described in the 2015 NUREG/CR-7204, "Applying Ultrasonic Testing In Lieu of Radiography for Volumetric Examination of Carbon Steel Piping" (ADAMS Accession No. ML15253A674).

This report included evaluation on the use of UT in lieu of RT for welded pipes and plates with thicknesses ranging from 0.844 inches to 2.2 inches thick. One conclusion from NUREG/CR-7204 is: Considering overall detections/non-detections for the piping specimens, as well as the Navy plates, it appears that phased array ultrasonic inspection (PA-UT), based on the techniques applied in this study, provides an equally effective examination for identifying the presence of fabrication flaws in carbon steel welds. The PA-UT parameters applied were shown to be more effective for planar flaws, but slightly less effective for small volumetric flaws, than RT. Based on this research the NRC staff finds that there is a sufficient technical basis for the use of UT in lieu of RT for ferritic steel welds. Given that UT in lieu of RT can be effective, the staff worked to determine if the proposed alternative applies UT in a way that provides reasonable assurance of finding structurally-significant flaws. Important aspects of this proposed alternative include: The examination volume shall include 100% of the weld volume and the weld-to-base-metal interface.

The electronic data files for the PA-UT examinations will be stored as archival-quality records. In addition, hard copy prints of the data will also be included as part of the PA-UT examination records to allow viewing without the use of hardware or software.

Ultrasonic examination procedures shall be qualified by using either a blind or a non-blind performance demonstration using a minimum of 30 flaws covering a range of sizes, positions, orientations, and types of fabrication flaws. The demonstration set shall include specimens to represent the minimum and maximum diameter and thickness covered by the procedure.

The flaw through-wall heights for the performance demonstration testing shall be based on the applicable acceptance standards for volumetric examination in accordance with IWB-3400, IWC-3400, or IWD-3400.

At least 30% of the flaws shall be classified as acceptable planar flaws, with the smallest flaws being at least 50% of the maximum allowable size based on the applicable a/I [height/length]

aspect ratio for the flaw. Ultrasonic examination personnel shall demonstrate their capability to detect and size flaws by performance demonstration using the qualified procedure.

The demonstration specimen set shall contain at least 10 flaws covering a range of sizes, positions, orientations, and types of fabrication flaws. All flaws detected using angle-beam ultrasonic inspections will be treated as planar flaws and will be evaluated against the preservice acceptance standards of ASME Section XI, IWB-3400, IWC-3400, or IWD-3400 for ASME Code Class 1, 2, or 3 welds, respectively.

A significant change from the use of ASME Code, Section Ill, radiography requirements is the use of Section XI flaw acceptance standards as opposed to Section Ill, subarticles NB-5330, NC-5330, and ND-5330, flaw acceptance standards.

Section Ill acceptance standards require the inspector to detect and determine the type of flaw (e.g., porosity, lack of fusion, slag, incomplete penetration).

While radiography is effective at discerning between different flaw types, it is less capable than UT at detecting planar flaws such as cracks and lack-of-fusion defects. While ASME Code,Section XI, paragraphs IWB-3400, IWC-3400, and IWD-3400, allow larger flaws than Section Ill, subarticles NB-5330, NC-5330, and ND-5300, the use of ASME Code,Section XI, acceptance standards has proven effective for piping welds for ISi intervals.

The NRC staff finds that the use of ASME Code,Section XI, acceptance standards is appropriate for the proposed alternative, as the proposed alternative is for repair/replacement activities, not new plant construction, and the favorable industry experience with the ASME Code,Section XI, flaw acceptance standards.

Based on the inspection and qualification requirements described in RR 14R-06 and the results of NUEG/CR-7204, there is reasonable assurance that the encoded PA-UT qualified as proposed by the licensee will provide an adequate level of quality and safety.

4.0 CONCLUSION

As set forth above, the NRC staff concludes that the licensee's proposed alternative to use UT in lieu of RT using encoded PA-UT provides reasonable assurance of structural integrity and leak tightness of Class 1 and 2 ferritic piping welds. Thus, UT using the procedure described in the submittals of the subject welds would provide an adequate level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)( 1 ). Therefore, the NRC staff authorizes RR 14R-06 for the fourth 10-year ISi intervals at Braidwood, Units 1 and 2, or until the NRC approves Code Case N-831, or a later revision, in Regulatory Guide 1.147 or other document during the interval.

All other ASME Code,Section XI, requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.

Principal Contributor:

S. Cumblidge Date of issuance:

January 17, 2019 B. Hanson

SUBJECT:

BRAIDWOOD STATION, UNITS 1 AND 2 -RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE (EPID L-2018-LLR-0036)

DATED JANUARY 17, 2019 DISTRIBUTION:

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