ML092300514

Relief Request 13R-04 for Reactor Vessel Bottom Penetrations Examination

ML092300514
Person / Time
Site:	Braidwood
Issue date:	08/27/2009
From:	Shawn Campbell Plant Licensing Branch III
To:	Pardee C Exelon Nuclear
david marshall NRR/DORL 415-1547
References
TAC ME0598, TAC ME0599
Download: ML092300514 (9)

Text

UNITED NUCLEAR REGULATORY WASHINGTON, D.C. 20555-0001 August 27, 2009 Mr. Charles G. Pardee President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville,IL 60555 BRAIDWOOD STATION, UNITS 1 AND 2 -RELIEF REQUEST 13R-04 FOR REACTOR VESSEL BOTTOM PENETRATIONS EXAMINATION (TAC NOS. ME0598 AND ME0599)

Dear Mr. Pardee:

By letter to the Nuclear Regulatory Commission (NRC) dated February 5, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML090370190), as supplemented by letters dated February 26, March 11, and March 26, 2009 (ADAMS Accession Nos. ML090580290, ML090710423, and ML090861006, respectively), Exelon Generation Company, LLC (the licensee) submitted Relief Request (RR) 13R-04 to request relief from the requirement of Title 10 of the Code of Federal Regulations, Section 50.55a, "Codes and standards," paragraph (g)(6)(ii)(E), Footnote 1, which would require the performance of a metal visual examination of the reactor pressure vessel bottom mounted instrumentation penetrations during the next refueling outage after January 1, 2009. The NRC staff has reviewed the licensee's submittal and determined that the alternative proposed in RR 13R-04 will provide an acceptable level of quality and safety. To support the licensee's outage schedule, verbal authorization of this alternative was granted on April 2, 2009. Pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the use of the proposed alternative until the 15 th refueling outages of Unit 1 and Unit 2 in the fall of 2010, and the spring of 2011, respectively.

All other American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI requirements, for which relief was not specifically requested and approved, remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.

The NRC staff's safety evaluation is enclosed.

Please contact Mr. Marshall David at (301) 415-1547 if you have any questions on this action. Sincerely, Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-456 and STN Safety cc w/encl: Distribution via UNITED NUCLEAR REGULATORY WASHINGTON, D.C. 20555*0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NO. 13R-04 EXELON GENERATION COMPANY, LLC. BRAIDWOOD STATION, UNITS 1 AND 2 DOCKET NOS. STN 50-456 AND STN 50-457

1.0 INTRODUCTION

By letter dated February 5, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML090370190), as supplemented by letters dated February 26, 2009, March 11, 2009, and March 26, 2009 (ADAMS Accession Nos. ML090580290, ML090710423, and ML090861006, respectively), Exelon Generation Company (EGC), the licensee for Braidwood Station (Braidwood), Units 1 and 2, submitted Relief Request (RR) 13R-04, which requested authorization to use an alternative to the initial bare metal visual examination requirements of Footnote 1 of Title 10 of the Code of Federal Regulations, Section 50.55a, "Codes and standards," paragraph (g)(6)(ii)(E).

The request for authorization to use the alternative was made pursuant to the provisions of 10 CFR 50.55a(a)(3)(i).

The American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) of record for the station's third 1 O-year inservice inspection (lSI) interval is the 2001 Edition through the 2003 Addenda. 2.0 REGULATORY REQUIREMENTS Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (inclUding supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection (lSI) of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components.

The regulations require that inservice examination of components and system pressure tests conducted during the first 120-month interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. Pursuant to 10 CFR 50.55a(a)(3), alternatives to requirements may be authorized by the Nuclear Regulatory Commission (NRC) if the licensee demonstrates that: (i) the proposed alternatives provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The licensee submitted the subject request for authorization of an alternative, pursuant to 10 CFR 50.55a(a)(3)(i), which proposed an alternative inspection method to the bare metal visual examination requirements of 10 CFR 50.55a(g)(6)(ii)(E).

Enclosure

-2 3.0 PROPOSED ALTERNATIVE 3.1 ASME Code Component Affected The ASME Code components affected by the licensee's proposed alternative are the 58 reactor vessel bottom mounted instrument (BMI) nozzles at each Braidwood unit. 3.2 ASME Code Requirements ASME Code Case N-722, "Additional Examinations for PWR Pressure Retaining Welds in Class 1 Components Fabricated with Alloy 600/82/182 Materials,Section XI, Division 1," was mandated by NRC as an augmented lSI requirement in 10 CFR 50.55a(g)(6)(ii)(E) on September 10,2008. ASME Code Case N-722 requires, in part, that bare metal visual inspection of BMI nozzles be performed every other refueling outage. Footnote 1 to 10 CFR 50.55a(g)(6)(ii)(E) requires that the initial BMI inspections be performed at the next refueling outage after January 1, 2009. 3.3 Licensee's Proposed Alternatives to ASME Code Case The licensee's proposed alternative is to take credit for ultrasonic (UT) and eddy current testing (ET) performed during the 13 th refueling outages of Braidwood, Unit 1, and Braidwood, Unit 2, in the fall of 2007, and spring of 2008, respectively.

These examinations were performed from the inside of the 58 BMI nozzles. The proposed volumetric and surface inspection is in lieu of bare metal visual examination of the nozzles from outside the reactor vessel. The examinations consisted of UT and ET inspection of each BMI nozzle above, over, and below the partial penetration weld between the penetration nozzle and the reactor vessel. 3.4 Duration of the Alternative EGC requested approval of this alternative for use until the 15 th refueling outages of Braidwood, Unit 1, and Braidwood, Unit 2, in the fall of 2010, and the spring of 2011, respectively.

3.5 Licensee's Basis for Alternatives to ASME Code Case N-722 EGC proposed to take credit for previous volumetric and surface examinations of the BMI nozzles performed using UT and ET techniques.

These techniques were demonstrated by the examination vendor (WesDyne) at the Electric Power Research Institute (EPRI) Nondestructive Examination (NDE) Center in Charlotte, NC. The demonstration of these techniques was documented in MRP-166, "Materials Reliability Program: Demonstration of Equipment and Procedures for the Inspection of Alloy 600 Bottom Mounted Instrumentation (BMI) Head Penetrations." The demonstration took place in 2004, and used BMI nozzle mockups located at the EPRI NDE Center. The UT technique was demonstrated to effectively detect BMI tube inside and outside surface initiated axial and circumferential flaws as well as to establish the location and orientation of those flaws with respect to the weld profile. The ET technique was used in the demonstration for examination of the nozzle inside surface to supplement the volumetric examination technique.

-3 3.6 NRC Staff's Evaluation of Proposed Alternative to ASME Code Case N-722 3.6.1 Demonstration Mockups and Process The examination techniques for the inspection of the BMI nozzles, for which the licensee proposed credit, were demonstrated on mockups constructed to simulate BMI nozzles in the field. The demonstration was administered by EPRI. WesDyne, the BMI inspection vendor at Braidwood, was one of the vendors that participated in the demonstration.

The demonstration process was broken up into two phases: an open phase and a blind phase. During the open phase of the demonstration, the vendors were allowed access to tubes and a partial-scale mockup with discontinuities in the tube and weld volumes for developing their UT procedures.

These open samples included configurations that represented the Westinghouse 3 and 4 loop plant designs. Braidwood, Units 1 and 2, are Westinghouse 4 loop plants. Data collected on the open mockups were reviewed by EPRI to determine if the vendor was prepared to continue with the blind phase of the demonstration.

The BMI head penetration mockups used during the blind phase of demonstration included a full-scale mockup for the Westinghouse 3 and 4 loop designs. The mockups had realistic weld geometries and distortion as caused by manufacturing the J-groove weld. The mockups were manufactured at the EPRI NDE Center using a combination of electrical discharge machining (EDM) and cold isostatic processing (CIP), which created tight cracks. These mockups contained flaws in both the axial and circumferential orientations.

The flaws were located in critical flaw locations from a structural and leakage integrity perspective.

Specifically, the flaws were located in the tube above, below, and over the partial penetration weld. The mockups contained flaws that originated from both the inside diameter (10) surface and the outside diameter (00) surface. The flaw lengths did not exceed 70 mm (2.76 inches) and the flaw depths ranged up to 100 percent of the wall thickness of the nozzle. The manufacturing process, whereby CIP-squeezed EDM notches are used to fabricate mockups, was previously demonstrated to deliver UT and ET responses similar to those of real flaws removed from service. As indicated by information in EGC's March 26, 2009, letter, and information in EPRI Report 1015143: "Nondestructive Evaluation:

Comparison of Field and Manufactured Flaw Data in Austenitic Materials," UT CIP notch responses have been compared to a primary water stress-corrosion cracking (PWSCC) flaw in a control rod drive mechanism penetration at the Bugey Nuclear Power Plant in France. Typically, the radius of the squeezed CIP EDM notch tips used in control rod drive mechanism nozzle mockups and BMI mockups are 10 microns, which is smaller than that required by ASME Section XI, Appendix VIII. When the UT CIP squeezed EDM notch responses were compared with a PWSCC flaw from the Bugey plant, they were found to give similar forward-scatter time-of-fJight diffraction (TOFD) UT responses.

The amplitude of the UT tip responses varied only slightly.

This was determined to be primarily due to minor variations in surface condition and ultrasonic coupling.

The noise ratios were also very similar. There was only a small difference observed between the echo-dynamic characteristics of the simulated and field-removed cracks.

Based on this information, the NRC staff concludes that the mockups that were used were sufficiently representative of reactor vessel BMI nozzles with potential PWSCC. The flaws built into the mockups represent the range of critical flaws that could challenge structural integrity of the penetrations.

The types of flaws used produce signals that are sufficiently representative of the response from actual PWSCC for the purpose of demonstrating the TOFD UT method. 3.6.2 TOFD UT and ET Inspection Techniques During the BM! head penetration performance demonstration, vOlumetric and surface inspection techniques were demonstrated.

Volumetric inspection techniques demonstrated by the inspection vendors were exclusively TOFD UT. The TOFD UT technique was used for length and depth sizing, locating the flaws with respect to the weld profile, and determining the orientation of the flaws. ET was used by the vendors in the demonstration for surface inspection of the tube ID. The ET technique was used for surface flaw detection, length sizing, and determining axial and circumferential flaw locations and orientations.

TOFD UT utilizes two transducers, a transmitting transducer and a receiving transducer, arranged so that their beams intersect in the region of interest.

Unlike conventional based UT that relies on detecting a signal reflected off the flaw, the TOFD method makes use of the diffracted waves that radiate from an insonified flaw tip. Flaw sizes are determined based on measuring the travel time of the diffracted signals from the tips of the flaws. From the known geometry of the probe set up and measured beam path lengths, the location of the flaw tips can be determined by geometrical calculations.

The TOFD data is displayed in a two-dimensional grey-scale image in which one axis represents time and the other axis represents the position of the probe. TOFD images are generally interpreted by first identifying those diffracted signals occurring between the surface (lateral) wave and the backwall signals that represent the section of the inspection volume. Diffracted signals from flaw tips are then recognized by their location and appearance in the image. ET was the primary tool for detection, length sizing, flaw location, and orientation of both axial and circumferential fD connected flaws. UT was the primary tool for flaw characterization information and thru-wall sizing. Both ET and UT were used in combination for detection of ID connected flaws. All base metal ID detection and sizing was a result of the two complimentary exams used in this demonstration.

The NRC staff considers the TOFD UT and ET inspection techniques to be appropriate for detecting potentiallD or OD initiated flaws in BMI nozzles. These techniques have been successfully used for inspection of control rod drive mechanism nozzles for a number of years. 3.6.3 Demonstration Results The 3 and 4 loop Westinghouse blind demonstration using an inspection system called the WesDyne Paragon system resulted in all flaws greater than 10 percent of the wall thickness being detected.

This included ID and OD connected flaws ranging to 100 percent through-wall extent. The Paragon system was demonstrated to be successful in determining the orientation of all flaws longer than 0.4 inch, but was inconsistent in determining the orientation of short flaws. The WesDyne Paragon system is the system that the licensee contracted for use at Braidwood.

-5 Section 3 of MRP-166 contains graphs that depict measured flaw depth and length versus actual flaw depth and length. These graphs indicate that the techniques demonstrate a higher capability to measure flaw length than depth. The NRC staff considers that the most important attribute for inspection of components susceptible to PWSCC is flaw detection.

Due to the high growth rate of PWSCC, any BMI determined to have PWSCC would most likely have to be repaired since it would be difficult to justify continued operation and the burden of successive inspections.

Given the short time frame of this Braidwood request for authorization and the actions that would be taken if a service-induced planar flaw is detected, the NRC staff has concluded that the results of the WesDyne Paragon system demonstration are acceptable, notwithstanding the limitations discussed above. 3.6.4 Reporting and Recording Criteria for Flaws The UT procedures used during the demonstration included instructions for differentiating service-induced flaws from fabrication defects. Fabrication flaws were not considered reportable but were characterized and recorded to allow comparison in future examinations.

Recordable indications that were fabrication flaws, including lack of fusion, were flaws that could be seen by both circumferential and axial TOFD UT and with the a-degree UT transducer.

They were classified as fabrication flaws by the procedure.

Recordable indications that are reportable are service-induced flaws that are typically planar in nature (i.e., detected by either axial or circumferential TOFD UT transducers) and cannot be seen by the a-degree UT transducers.

The NRC staff considers these criteria for distinguishing between service-induced and fabrication-induced flaws to be logical and appropriate.

The NRC staff also agrees with the provisions of the procedures that specify that service-induced flaws are reportable and fabrication flaws are recordable, since service-induced flaws would require licensee action and recording fabrication flaws allows comparison with future examination results. These criteria are consistent with criteria that the NRC staff has previously determined to be acceptable.

3.6.5 Personnel Training In light of the fact that a high degree of operator skill is required to correctly interpret TOFD UT inspection results, the licensee provided information to the NRC staff on the training and qualification requirements for personnel to carry out the TOFD UT data acquisition and analysis at Braidwood.

In accordance with WesDyne inspection procedures, all data acquisition (both UT and ET) are performed using Paragon computer operators under the direction

/ supervision of Level II or Level III qualified personnel.

WesDyne and their contractor NDE personnel are qualified to a written practice that meets WesDyne's Procedure WDP-9.2, "Qualification and Certification of Personnel in Nondestructive Evaluation," which is based on the requirements of ASNT TC-1A, CP-189, and ASME Section XI, as applicable.

Additional training for the BMI specific application is as follows:

• For 8MI Acquisition

-The requirement is for 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br /> of Paragon Operator Training for Reactor Vessel Examinations.

Included in this course is training on the basic TOFD

-6 theory, BMI acquisition procedure review, Paragon TOFO display setup, and acquisition responses from BMI tubes. For BMI Analysis -The Basic Paragon Operator Training is a pre-requisite for BMI analysis.

The requirement for a BMI analyst is for a 40-hour BMI specific course. The course covers additional BMI theory, TOFO calibration, data quality, acquisition and analysis procedure reviews and hands on with recent field inspection data. Although the NRC staff does not have specific requirements in the area of personnel certification and training for BMI nozzle examination, the certification and training provided to the WesOyne examiners performing the BMI nozzle examinations at Braidwood are comparable to the certification and training requirements for examinations of other safety-related components addressed by the ASME Code,Section XI. 3.6.6 Procedures The open mockup phase of the demonstration was used to develop the inspection procedures used during the blind phase of the demonstration.

The equipment and procedures that were demonstrated by WesOyne have remained largely unchanged since the time of the demonstration.

The changes that were made since the original demonstration are as follows: The Paragon system uses O-degree longitudinal wave and 45-degree shear wave scans, which assist in the detection and evaluation process. Following the demonstration, both the O-degree longitudinal wave and 45-degree shear wave transducers were modified to obtain a better signal-to-noise ratio, and the size and frequency of each transducer were optimized.

The transducer material was changed to a composite element. Following the demonstrations, the data was reanalyzed using the Paragon system with an analysis procedure that had been revised based on lessons learned from the initial demonstration and field applications of this procedure.

The reanalysis reduced false calls, and the Paragon system was considered acceptable for field use. These improvements to the Paragon system were demonstrated on mockups, but have not been demonstrated at the EPRI NOE Center because the improvements would not affect the ability of the system to detect all the 10 and 00 connected flaws in the 3 and 4 loop Westinghouse data. The BMI examination at Braidwood utilized the equipment and procedure changes noted above. Since these changes would not be expected to have affected detection and sizing, but would have enhanced data analysis and characterization, the NRC staff considers the implementation of these changes without an additional demonstration to be acceptable.

4.0 CONCLUSION

Based on the discussion above, the NRC staff concludes that the alternative proposed in RR 13R-04, to credit previous volumetric and surface inspections of the inside of the 58 BMI nozzles in lieu of bare metal visual examination of the nozzles from outside the reactor vessel as required by 10 CFR 50.55a(g)(6)(ii)(E), will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the alternative for performing volumetric and surface inspections of the inside of the 58 BM! nozzles at Braidwood,

-7 Unit 1, and Braidwood, Unit 2. This alternative takes credit for UT and ET performed during the 13 th refueling outages of Braidwood, Unit 1, and Braidwood, Unit 2, in the fall of 2007, and spring of 2008, respectively, and is authorized for use until the 15 th refueling outages of Braidwood, Unit 1, and Braidwood, Unit 2, in the fall of 2010, and spring of 2011, respectively.

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

Principal Edmund J. Sullivan, NRR Carol Nove, NRR Date: August 27, 2009 Mr. Charles G. Pardee August27,2009 President and Chief Nuclear Officer Exelon Nuclear. 4300 Winfield Road Warrenville, IL 60555 BRAIDWOOD STATION, UNITS 1 AND 2 -RELIEF REQUEST 13R-04 FOR REACTOR VESSEL BOTTOM PENETRATIONS EXAMINATION (TAC NOS. ME0598 AND ME0599)

Dear Mr. Pardee:

By letter to the Nuclear Regulatory Commission (NRC) dated February 5,2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML090370190), as supplemented by letters dated February 26, March 11, and March 26, 2009 (ADAMS Accession Nos. ML090580290, ML090710423, and ML090861006, respectively), Exelon Generation Company, LLC (the licensee) submitted Relief Request (RR) 13R-04 to request relief from the requirement of Title 10 of the Code of Federal Regulations, Section 50.55a, "Codes and standards," paragraph (g)(6)(ii)(E), Footnote 1, which would require the performance of a metal visual examination of the reactor pressure vessel bottom mounted instrumentation penetrations during the next refueling outage after January 1, 2009. The NRC staff has reviewed the licensee's submittal and determined that the alternative proposed in RR 13R-04 will provide an acceptable level of quality and safety. To support the licensee's outage schedule, verbal authorization of this alternative was granted on April 2, 2009. Pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the use of the proposed alternative until the 15 th refueling outages of Unit 1 and Unit 2 in the fall of 2010, and the spring of 2011, respectively.

All other American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI requirements, for which relief was not specifically requested and approved, remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.

The NRC staffs safety evaluation is enclosed.

Please contact Mr. Marshall David at (301) 415-1547 if you have any questions on this action. Sincerely, IRA! Stephen J. Campbell, Chief Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-456 and STN 50-457

Enclosure:

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