RS-21-035, Relief Request I4R-12 Relief from Code Examinations for 2B33-F060A and 2B33-F060B Repairs
| ML21068A442 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 03/09/2021 |
| From: | Demetrius Murray Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-21-035 | |
| Download: ML21068A442 (19) | |
Text
4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office RS-21-035 10 CFR 50.55a March 9, 2021 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 LaSalle County Station, Unit 2 Renewed Facility Operating License No. NPF-18 NRC Docket No. 50-374
Subject:
Relief Request I4R-12 Relief from Code Examinations for 2B33-F060A and 2B33-F060B Repairs
References:
- 1. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. NRC (Nuclear Regulatory Commission), "Relief Request I4R-12 Relief from Code Surface Examinations for 2B33-F060B Valve Repair," dated March 7, 2021 (ML21067A000).
- 2. Email from B. Vaidya (U.S NRC) to J. Taken (EGC), "LASALLE UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION (RAI) RE: Relief Request I4R-12 Relief from Code Surface Examinations for 2B33-F060B Valve Repair, (EPID-L-2021-LLR-0016)," dated March 9, 2021.
In Reference 1, Exelon Generation Company, LLC (EGC) requested NRC approval of a relief request associated with the fourth Inservice Inspection (ISI) interval for LaSalle County Station (LSCS), Unit 2 in accordance with 10 CFR 50.55a, "Codes and standards," paragraph (z)(2).
Specifically, the referenced letter requested authorization of alternative examination requirements for the repair of Unit 2 Reactor Recirculation flow control valve 2B33-F060B, currently in progress, in accordance with American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code (Code),Section XI, paragraph IWA-4000.
The fourth interval of the LSCS Unit 2 ISI Program is based on the ASME Code,Section XI, 2007 Edition through 2008 Addenda. The fourth ISI interval at LSCS began on October 1, 2017 and is currently scheduled to end September 30, 2027.
In Reference 2, the NRC requested additional information needed to complete its review of Reference 1. A clarification call was held between NRC and EGC on March 9, 2021 to ensure a common understanding of the questions. Attachment 3 to this letter contains the requests for additional information and EGC responses.
March 9, 2021 U.S. Nuclear Regulatory Commission Page 2 EGC has determined that the relief request in Reference 1 is also applicable to the current repair of Unit 2 Reactor Recirculation flow control valve 2B33-F060A. Additionally, EGC requests relief from performing required radiographic examinations based on hardship. to this letter provides a revision to relief request I4R-12 and includes supplemental information for Unit 2 Reactor Recirculation flow control valve 2B33-F060A and the additional request for relief from radiographic examination requirements. Attachment 2 to this letter provides the supplemental information associated with 2B33-F060A and 2B33-F060B.
EGC requests authorization of the proposed relief request for both 2B33-F060A and 2B33-F060B by March 12, 2021.
There are no regulatory commitments contained within this letter. Should you have any questions concerning this letter, please contact Mr. Jason Taken at (630) 657-3660.
Respectfully, Dwi Murray Sr. Manager - Licensing Exelon Generation Company, LLC Attachments:
- 1. Relief Request I4R-12 Associated with Alternative Examination Requirements for Repairs of Reactor Recirculation Flow Control Valves, Revision 1
- 2. Associated Figures
- 3. Response to Request for Additional Information cc:
NRC Regional Administrator, Region III NRC Senior Resident Inspector - LaSalle County Station NRC Project Manager, NRR - LaSalle County Station Illinois Emergency Management Agency - Division of Nuclear Safety
ATTACHMENT 1 Relief Request I4R-12 Associated with Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves 2B33-F060A and 2B33-F060B, Revision 1
ATTACHMENT 1 10 CFR 50.55a Relief Request I4R-12, Revision 1 Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves in Accordance with 10 CFR 50.55a(z)(2)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
Page 1 of 7
- 1. ASME Code Component(s) Affected LaSalle County Station (LSCS), Unit 2 valve 2B33-F060A ("A" Reactor Recirculation System Flow Control Valve).
LaSalle County Station (LSCS), Unit 2 valve 2B33-F060B ("B" Reactor Recirculation System Flow Control Valve).
2B33-F060A and 2B33-F060B valves are ASME Section XI, Class 1 (Section III 1971 Edition, Summer 1972 Addenda) components, and the valve bodies are ASME SA-351 Grade CF8M material.
The design temperature of the valves is 575°F and the design pressure of the valves is 1675 psig. The design pressure of the attached system is 1650 psig. The maximum valve operating temperature is 550°F with a maximum operating pressure of 1260 psig.
2. Applicable Code Edition and Addenda
The Code of Construction is ASME Section III 1971 Edition, Summer 1972 Addenda.
For LaSalle County Station Unit 2, the Inservice Inspection Code of Record and Interval Dates are:
Interval Section XI Edition/Addenda Interval Start Date Interval End Date Fourth 2007 Edition, through 2008 Addenda October 1, 2017 September 30, 2027
3. Applicable Code Requirement
ASME Section XI IWA-4411, "Welding, Brazing, Fabrication, and Installation," states in part:
Welding brazing, fabrication, and installation shall be performed in accordance with the Owners Requirementsand in accordance with the Construction Code of the item.
ASME Section III NB-2570, "Examination and Repair of Statically and Centrifugally Cast Products," contains NB-2571, "Required Examinations," which states in part:
Cast pressure-retaining materials shall be examined by radiographic methods, except cast ferritic steels shall be examined by either radiographic or ultrasonic methods or a combination of both methodsIn addition, all cast products shall be examined on all external surfaces and all accessible internal surfaces by either magnetic particle or liquid penetrant methods. Machined surfaces, except threaded surfaces, of a cast
ATTACHMENT 1 10 CFR 50.55a Relief Request I4R-12, Revision 1 Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves in Accordance with 10 CFR 50.55a(z)(2)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
Page 2 of 7 product shall be examined by either liquid penetrant of magnetic particle methods after machining.
ASME Section III NB-2573, "Radiographic Examination," contains NB-2573.1, "Extent, Methods, and Acceptance Standards," which provides the requirements and associated references for conducting radiographic examination.
ASME Section III NB-2578, "Elimination of Defects," states:
Elimination of defects shall be in accordance with NB-2538.
ASME Section III NB-2579, "Repair by Welding," states in part:
Repair by welding shall be in accordance with NB-2539.
ASME Section III NB-2538, "Elimination of Surface Defects," subparagraph (a)(3) states in part:
After defect elimination, the area is reexamined bythe liquid penetrant method in accordance with NB-2546 to assure that the defect has been removed or the indication reduced to an acceptable size.
ASME Section III NB-2539, "Repair by Welding," contains NB-2539.4, "Examination of Repair Welds," which states in part:
Each repair weld shall be examined bythe liquid penetrant method in accordance with the requirements of NB-2546. In addition, repair cavities, the depth of which exceeds the lesser of 3/8 in. or 10 percent of the section thickness, shall be radiographed after repair in accordance with NB-5110 and to the acceptance standards of NB-5320.
ASME Section III NB-2546, "Liquid Penetrant Examination," provides the requirements for conducting liquid penetrant examinations along with the Acceptance Standards.
ASME Section III NB-5110, "Procedures, Qualifications and Evaluation," and ASME Section III NB-5320, "Radiographic Acceptance Standards," provide the general requirements and associated acceptance standards for radiographic examination, respectively.
4. Reason for Request
In accordance with 10 CFR 50.55a(z)(2), relief is requested on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
ATTACHMENT 1 10 CFR 50.55a Relief Request I4R-12, Revision 1 Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves in Accordance with 10 CFR 50.55a(z)(2)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
Page 3 of 7
Background
In an effort to identify the source of the debris found in LSCS Unit 2 Reactor Pressure Vessel Jet Pumps during the previous refueling outage (L2R17) in February 2019, detailed inspections of the Reactor Recirculation (RR) system flow control valves were scheduled and performed during the current refueling outage (L2R18) in February 2021. Upon disassembly of the 2B33-F060A and 2B33-F060B valves, damage to each valve's internals and lower body was discovered. In order to restore the valves to an acceptable condition to allow the valve internals to fit into the valve body, activities in accordance with ASME Section III and ASME Section XI requirements will be employed.
Valve Details Drawings of the 2B33-F060A and 2B33-F060B valves are provided in Attachment 2.
Figures I4R-12-1 and I4R-12-3 are the drawings of the entire valve assembly, including the actuator for 2B33-F060B and 2B33-F060A, respectively. Figure I4R-12-2 is a close-up drawing of the area of the 2B33-F060B valve body in question. Figure I4R-12-2 is highlighted in orange for the lower guide plug, blue for the guide plug anti-rotation segment, and yellow as the estimated area of wear in the valve body where material is missing due to the lower guide plug impact on the valve body. Figure I4R-12-4 is a close-up drawing of the area of the 2B33-F060A valve body in question. Figure I4R-12-4 is highlighted in yellow as the estimated area of wear in the valve body where material is missing due to the lower guide plug impact on the valve body.
The drawings of the valves do not provide thickness dimensions of the valve bodies. At this point in the refueling outage, LSCS has been unsuccessful in obtaining direct thickness measurements of the valve body for 2B33-F060A and 2B33-F060B in their current conditions. Valve body thickness measurements were taken and documented in a 1976 report by the valve manufacturer after the valves were cast. Ultrasonic (UT) measurements were taken in several locations in the pocket area at the bottom of the valve close to where the work is being performed. The average of the thickness readings from this report for 2B33-F060A is 3.45 inches and for 2B33-F060B is 3.7 inches. This value is taken as the nominal sectional thickness of the valve body in this area. This same report documents the valve specified minimum sectional thickness for both valves as 2.418 inches.
LSCS has been unable to explicitly quantify or measure the material lost in 2B33-F060A and 2B33-F060B. This is due to the limited space of a person getting into the valve body and the radiological dose exposure internal to the valve body. Measurements have been obtained for the 2B33-F060B through contour gauge readings. This was done by taking a reading in an area where there was limited material loss and comparing it to another reading in a corresponding area where there was wall loss. Comparison of those readings shows the point where the most wall loss occurred for 2B33-F060B measures approximately 0.75 inches of material. These readings are compared to the nominal wall thickness to assess if the wall thickness had decreased below the minimum required wall thickness, and therefore into the required pressure boundary design area. The material loss on 2B33-F060A was
ATTACHMENT 1 10 CFR 50.55a Relief Request I4R-12, Revision 1 Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves in Accordance with 10 CFR 50.55a(z)(2)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
Page 4 of 7 visually determined to be less than the material loss on 2B33-F060B. Based on this approach, LSCS determined that the operational wear on the valve body did not result in wall thickness decreasing below the minimum wall thickness value.
However, during the maintenance activities to restore the valves to an acceptable condition, measurements determined that the maintenance performed on the valve body for surface conditioning encroached into minimum wall thickness of the valve. For 2B33-F060A, LSCS determined the surface conditioning extended approximately 0.135 inches below minimum wall thickness. For 2B33-F060B, LSCS determined that the surface conditioning extended approximately 0.095 inches below minimum wall thickness. These values below minimum wall thickness are not representative of the general condition throughout the valve body but are localized in one area of the lower valve body. As a result, these are defects that must be removed in accordance with NB-2538. In addition, weld repairs following defects removal must be radiographed in accordance with NB-2539.
NB-2538 requires a liquid penetrant (PT) examination to be performed following removal of the defect. NB-2539 requires that repair cavities the depth of which exceeds the lesser of 3/8 in. or 10 percent of the section thickness, shall be radiographed. After removal of the defect, weld buildup using the machine Gas Tungsten Arc Welding process will be performed in accordance with NB-2539 to restore the minimum wall thickness. Following weld build up and in accordance with NB-2539, a PT examination must be performed of the weld surface and a radiographic examination must be performed of the weld repairs.
The proposed alternative of enhanced VT-1 visual examination (EVT-1) will be performed as part of the repair activities. Following machining activities, and prior to welding, an EVT-1 will be performed to ensure surface quality. Welding activities will then be performed to restore the valves to above minimum wall thickness, followed by an EVT-1. The maintenance activity will continue with additional welding and machining to reestablish configuration of valve wall to support valve internals. This will be done to achieve the nominal wall thickness of 3.45 inches for 2B33-F060A and 3.7 inches for 2B33-F060B. The final EVT-1 will be performed following establishment of nominal wall thickness.
Radiological Hardship During the L2R18 refueling outage, significant radiological dose rates are being experienced both internally to the valves and in the external area surrounding the valves. Therefore, LSCS is employing several approaches to limit the personnel exposure during the valve repair activities (e.g., automatic welding is being used).
The internal dose rate at the bottom of valve 2B33-F060A is 8 R/hour, and the internal dose rate at the bottom of valve 2B33-F060B is 10 R/hour. The total combined exposure impact for performing surface examinations (PT) associated with both valve repairs is estimated at 11.6 person-Rem. The total combined exposure for performing a radiographic examination associated with both valve repairs is estimated at 11.8 person-Rem. This is based on stay time estimates for examiners to perform PT and
ATTACHMENT 1 10 CFR 50.55a Relief Request I4R-12, Revision 1 Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves in Accordance with 10 CFR 50.55a(z)(2)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
Page 5 of 7 radiographic examinations under the conditions described below. As a result of the significant dose rates, LSCS has evaluated alternatives to the required nondestructive examinations (NDE).
By comparison, performing the PT examination scope using the proposed alternative of EVT-1 approach discussed in Section 5, "Proposed Alternative and Basis of Use,"
would result in an estimated EVT-1 examination dose of 1.3 person-Rem, which represents an approximate radiological dose savings of 10.3 person-Rem. This substantial radiological dose reduction is due to the EVT-1 examination not requiring the NDE technicians to be inside the valve bodies when compared to the PT examinations.
Additionally, not performing the radiographic examination provides an additional radiological dose savings of approximately 11.8 person-Rem. Therefore, the total radiological dose savings associated with this relief request is approximately 22.1 person-Rem.
Physical Limitations Hardship The area of repair inside valves 2B33-F060A and 2B33-F060B is at the bottom of each valve which is approximately 42 inches from the main flange on the top of the valve body. Additionally, the valve throat opening is 18 inches in diameter. To perform PT examinations, NDE technicians have limited remote options available to support performing the PT surface examinations. Technicians must clean the examination surface prior to applying the dye penetrant. Although penetrant dye may be applied using a brush with an attachment piece to limit entering the valve body, the technician must enter the valve body to adequately remove excessive dye penetrant and to apply and remove developer.
To perform radiographic examinations, NDE technicians are challenged due to valve access restrictions to position the film inside the valve. With the current dose rates inside the valve between 8 to 10 R/hour, the ability to produce a quality radiographic examination film required by the ASME Code will be impacted due to exposure of the same type of gamma radiation. Placing the source for radiography from inside of the valve body and the film on the outside of the valve, presents an issue of being able to properly distance the radiography source to satisfy the ASME Code required geometric calculation. Lastly, the size and weight of the container for the Cobalt-60 source is 2'x3'x3' and nearly 800 pounds, which represents a physical challenge.
The significant radiological dose and physical limitations associated with the PT and radiographic examinations of 2B33-F060A and 2B33-F060B in accordance with the ASME Code would be contrary to the as low as reasonably achievable (ALARA) radiological controls program.
5. Proposed Alternative and Basis for Use
In lieu of the surface examination requirements of ASME Section III 1971 Edition, Summer 1972 Addenda and/or ASME Section XI 2007 Edition with 2008 Addenda associated with
ATTACHMENT 1 10 CFR 50.55a Relief Request I4R-12, Revision 1 Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves in Accordance with 10 CFR 50.55a(z)(2)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
Page 6 of 7 repair activities on valves 2B33-F060A and 2B33-F060B, EGC proposes to substitute the PT examinations with EVT-1.
The enhanced visual examination of the machined surfaces will be performed using methods and personnel qualified to the standards of ASME Section XI VT-1 visual examination requirements. The EVT-1 will be conducted using remote visual equipment such as a video probe or camera equipment. The acceptance criteria for the EVT-1 examinations will be consistent with NB-2546.3, "Acceptance Standards," from ASME Section III 1971 Edition, Summer 1972 Addenda.
EGC has performed a resolution demonstration, which is the process of demonstrating the ability of the remote visual examination equipment, equipment setup, inspection area environment, and inspection technique to resolve the appropriate 0.044-inch characters.
EGC has evaluated the resolution and examination capabilities of the EVT-1 and PT examination methods. A comparison between the two techniques demonstrates that the EVT-1 will provide the ability to detect a post-machining or post-welding flaw as the PT method with no loss of examination capability. Specifically:
Liquid Penetrant (and Magnetic Particle) acceptance criteria is required to identify an indication with dimensions greater than 1/16 inch (0.0625 inches).
Visual Examination, EVT-1 examination capabilities are demonstrated before and after the examination to dimensions down to 0.044-inch characters.
EVT-1 is a proven and accepted visual examination method and technique as described in Electric Power Research Institute (EPRI) Technical Report (TR) 3002007793, "Remote Visual Testing Round-Robin Study," published December 2, 2016 and NRC NUREG/CR 7246, PNNL-27003, "Reliability Assessment of Remote Visual Examination," published August 2018.
EPRI TR 3002007793 documented an approach that has been used throughout the nuclear industry for remote visual examination of various types of flaws, simulated cracks, electrical discharge machining (EDM) notches and actual cracks for its demonstration. In addition, EVT-1 examinations are routinely used for In Vessel Inspections (IVVI) under the boiling water reactors (BWR) Vessel and Internals Project (VIP) at BWR.
The NRC has approved EVT-1 as an acceptable alternative to PT examination previously as described in Section 7 below.
6. Duration of Proposed Alternative
Use of this proposed alternative is applicable only to L2R18 repair activities associated with 2B33-F060A and 2B33-F060B valves.
ATTACHMENT 1 10 CFR 50.55a Relief Request I4R-12, Revision 1 Alternative Examination Requirements for Repair of Reactor Recirculation Flow Control Valves in Accordance with 10 CFR 50.55a(z)(2)
--Hardship or Unusual Difficulty Without Compensating Increase in Level of Quality or Safety--
Page 7 of 7
7. Precedents
Braidwood Station, Units 1 and 2 - Relief from the Requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (EPID L-2018-LLR-0033), dated January 17, 2019 (ADAMS Accession No. ML18347B419).
ATTACHMENT 2 Associated Figures
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Figure I4R-12 2B33-F060A
Figure I4R-12-4, Closeup 2B33-F060A
ATTACHMENT 3 Response to Request for Additional Information
ATTACHMENT 3 Response to Request for Additional Information Page 1 of 2 Request for Additional Information By letter to the U.S. Nuclear Regulatory Commission (NRC) dated March 8, 2021, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21067A000 Exelon Generation Company, LLC (the licensee) proposed an alternative to certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),
Section III and Section XI, related to the repair of degraded Reactor Recirculation Flow Control Valve B at LaSalle County Station, Unit 2 (LaSalle Unit 2). The licensee submitted Relief Request No. I4R-12, for the proposed alternative Enhanced Visual testing (EVT) examination requirements in lieu of the required Penetrant Testing (PT) for the repairs.
The NRC has determined that the following additional information is necessary to complete its review and make a regulatory decision.
RAI-1: What acceptance criteria will be used to evaluate any possible flaws found during the EVT examinations?
EGC RESPONSE:
The acceptance criteria used to evaluate any possible flaws found during the EVT-1 examinations are consistent with NB-2546.3, "Acceptance Standards," from ASME Section III 1971 Edition, Summer 1972 Addenda.
RAI-2: What is the expected thickness of the repaired material beyond the required minimum wall thickness when the repairs are completed?
EGC RESPONSE:
EGC intends to restore the valve body thickness of both valves to their nominal thickness in almost all locations, as this is required to achieve the needed fit for the lower guide plug for the valve to function as designed. This nominal wall thickness of 3.45 inches for 2B33-F060A and 3.7 inches for 2B33-F060B are well above the minimum wall thickness of 2.418 inches for each valve. Material wear has been noted where weld buildup is not required to get the needed fit.
In these locations, the wall thickness has and will be maintained above the minimum wall thickness during the entire maintenance activity.
2B33-F060A and 2B33-F060B valves will require the addition of minimal weld material to get above the minimum wall thickness, as this will be accomplished with only a few weld passes.
The surface conditioning of 2B33-F060A extended approximately 0.135 inches below minimum wall thickness. In Reference 1, the depth value below minimum wall thickness for 2B33-F060B was described as 0.060 inches. Due to additional machining that was performed since Reference 1 was submitted, the surface conditioning of 2B33-F060B extended approximately 0.035 inches, resulting in a total of 0.095 inches below minimum wall thickness. All required machining below minimum wall thickness is complete, and no additional material will be
ATTACHMENT 3 Response to Request for Additional Information Page 2 of 2 removed as part of 2B33-F060A and 2B33-F060B valves repair activities. The accuracy of the machining tool used for surface conditioning is +/- 0.001 inches for axial and radial directions.
RAI-3: ASME Code Section III Paragraph NB-2539.4 requires that repair cavities greater than the lesser of 3/8 of an inch or 10 percent of the section thickness require a radiography examination. Will the radiographic examination be used to confirm the results of the EVT examination?
EGC RESPONSE:
Radiographic examination will not be used to confirm the results of the EVT-1 examinations.
Proposed relief to not perform radiographic examination is described in Attachment 1 in accordance with 10 CFR 50.55a(z)(2) due to the significant radiological dose associated with the radiographic examination.
References
- 1. Letter from D. Murray (Exelon Generation Company, LLC) to U.S. NRC (Nuclear Regulatory Commission), "Relief Request I4R-12 Relief from Code Surface Examinations for 2B33-F060B Valve Repair," dated March 7, 2021 (ML21067A000).