RA-13-063, Companys Response to Request for Additional Information - Proposed Alternative to Utilize Code Case N-786, Alternative Requirements for Sleeve Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping Section XI, Division 1

Companys Response to Request for Additional Information - Proposed Alternative to Utilize Code Case N-786, Alternative Requirements for Sleeve Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping Section XI, Division 1

ML13176A143
Person / Time
Site:	Dresden, Peach Bottom, Oyster Creek, Byron, Braidwood, Limerick, Clinton, Quad Cities, LaSalle, Crane
Issue date:	06/24/2013
From:	Jim Barstow Exelon Generation Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
N-786, RA-13-063, RS-13-179, TMI-13-094
Download: ML13176A143 (19)

Text

RS-13-179 RA-13-063 TMI-13-094 June 24, 2013 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461 Dresden Nuclear Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249 LaSalle County Station, Units 1 and 2 Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374 Limerick Generating Station, Units 1 and 2 Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353 Oyster Creek Nuclear Generating Station Renewed Facility Operating License No. DPR-16 NRC Docket No. 50-219 Peach Bottom Atomic Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-44 and DPR-56 NRC Docket Nos. 50-277 and 50-278 10 CFR 50.55a

Response to Request for Additional Information Proposed Alternative to Utilize Code Case N-786 June 24, 2013 Page 2

Subject:

Quad Cities Nuclear Power Station, Units 1 and 2 Renewed Facility Operating License Nos. DPR-29 and DPR-30 NRC Docket Nos. 50-254 and 50-265 Three Mile Island Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-50 NRC Docket No. 50-289 Response to Request for Additional Information - Proposed Alternative to Utilize Code Case N-786, "Alternative Requirements for Sleeve Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping Section XI, Division 1"

References:

1) Letter from M. D. Jesse (Exelon Generation Company, LLC) to U.S.

Nuclear Regulatory Commission, dated February 27, 2013

2) E-mail from J. Wiebe (U.S. Nuclear Regulatory Commission) to T. Loomis (Exelon Generation Company, LLC), dated April 30, 2013 In the Reference 1 letter, Exelon Generation Company, LLC (Exelon) requested a proposed alternative to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," 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. In the Reference 2 e-mail, the U.S. Nuclear Regulatory Commission requested additional information. Attached is our response.

There are no commitments contained in this submittal.

James Barstow Director - Licensing and Regulatory Affairs Exelon Generation Company, LLC Attachments: 1) Response to Request for Additional Information - Proposed Alternative to Utilize Code Case N-786

2) Revised Relief Request

Response to Request for Additional Information Proposed Alternative to Utilize Code Case N-786 June 24, 2013 Page 3 cc:

Regional Administrator - NRC Region I Regional Administrator - NRC Region III NRC Senior Resident Inspector - Braidwood Station NRC Senior Resident Inspector - Byron Station NRC Senior Resident Inspector - Clinton Power Station NRC Senior Resident Inspector - Dresden Nuclear Power Station NRC Senior Resident Inspector - LaSalle County Station NRC Senior Resident Inspector - Limerick Generating Station NRC Senior Resident Inspector - Oyster Creek Nuclear Generating Station NRC Senior Resident Inspector - Peach Bottom Atomic Power Station NRC Senior Resident Inspector - Quad Cities Nuclear Power Station NRC Senior Resident Inspector - Three Mile Island Nuclear Station, Unit 1 NRC Project Manager - Braidwood Station NRC Project Manager - Byron Station NRC Project Manager - Clinton Power Station NRC Project Manager - Dresden Nuclear Power Station NRC Project Manager - LaSalle County Station NRC Project Manager - Limerick Generating Station NRC Project Manager - Oyster Creek Nuclear Generating Station NRC Project Manager - Peach Bottom Atomic Power Station NRC Project Manager - Quad Cities Nuclear Power Station NRC Project Manager - Three Mile Island Nuclear Station, Unit 1 Response to Request for Additional Information -

Proposed Alternative to Utilize Code Case N-786

Question:

Response to Request for Additional Information Code Case N-786 Page 1 "1. Section 1 of the relief request states that the affected components are Class 2 and 3 moderate energy carbon steel piping systems. (1) Confirm that the relief request is not applicable to pumps, valves, flanges and flanged joints, socket welds (weldolets), expansion jOints, heat exchangers, tubing, and threaded connections that are associated with the subject piping systems. (2) The identified affected components do not appear to be limited by size. Identify the smallest piping diameter and thinnest pipe wall for which the relief request is applicable and discuss the potential problems with welding of the sleeve on the small bore piping."

Response

1) Reinforcing sleeves may not be applied to pumps, valves, expansion joints, vessels, heat exchangers, tubing, or flanges; and may not be applied over flanged joints, socket welded or threaded joints, or branch connection welds. This condition has been added to the Relief Request (see Attachment 2). The Code Case and Relief Request are not applicable to sleeve repair of weldolets and threaded connections; however, Type B reinforcing sleeves could include new integral branch connections (weldolet or socket-welded or threaded half-coupling) when required by design, such as for vent or fill connections for pressure testing, or to replace a degraded section of piping containing a branch connection.

2) The Code Case and Relief Request contain no lower limit of piping diameter that may be repaired using reinforcing sleeves. From a practical perspective, piping as small as 1 NPS XXS could readily be repaired using a sleeve made from 1-114 NPS XXS pipe.

The connecting weld would be about 3/16" in size/depth on a diameter of 1.315 inches, which would not be a difficult weld to make. As long as the Construction Code and Code Case requirements can be satisfied, including monitoring requirements, there is no technical reason to establish a minimum size.

Question:

"2. Piping containing radioactive fluid: (1) Discuss whether any Class 2 and 3 carbon steel piping covered under the relief request contains radioactive fluid (e.g., tritium) as part of its design functions. If yes, please identify these piping systems and the plant(s). (2) The relief request specifies that the monitoring frequency for the full structural Type B sleeve is every fourth refueling outage. Provide the technical basis for the monitoring frequency of every fourth refueling outage. Discuss whether this monitoring frequency is adequate for the buried piping systems that carry radioactive fluid and are repaired with the full-structural Type B sleeve. (3) If radioactive fluid leaks from the sleeve-repaired piping, discuss how the leakage can be detected and how soon the plant personnel would identify the leakage."

Response

1) There are no design or application restrictions on radioactive content of the piping system defined in Code Case N-786 or this relief request. Typical Class 2 and Class 3 carbon steel PWR piping systems that are expected to have radioactive fluid (e.g.,

tritium) and could potentially be repaired via Code Case N-786 include Condensate, Emergency Feedwater, and Closed Cooling Water. Typical Class 2 and Class 3 carbon

Response to Request for Additional Information Code Case N~ 786 Page 2 steel BWR piping systems that are expected to have radioactive fluid (e.g., tritium) and could potentially be repaired via Code Case N~ 786 include Fuel Pool Cooling, Containment Spray, Core Spray, Reactor Water Clean-Up, Reactor Building Closed Cooling Water, Residual Heat Removal, and Shutdown Cooling.

2) The relief request requires a complete base-line mapping at the time of installation (see §6(b) of the Code Case). This mapping requires measuring and recording the thickness of the partial penetration attachment weld (Figure 2 of the Code Case) and the added (new) reinforcing sleeve around the full circumference of the repair. The base metal thickness beneath the fillet is not measurable, but that portion of base material is beyond the amount needed to provide full load transition from the pipe to the sleeve which is s = 0.75~Rtnom' Hence, measurement of the base metal beneath the fillet is excluded from monitoring in paragraph 6(b). After the initial baseline thickness mapping, a similar follow~up examination is required at each of the next two refueling outages.

Combining all of these data will establish 3~point curves from which the maximum actual degradation rates at the sleeve and partial penetration attachment welds can be determined. Subsequent thickness monitoring examinations will be scheduled based on the maximum rates observed over those two cycles, such that the required design thicknesses will not be infringed upon before each subsequently scheduled thickness monitoring examination. In no case may the examination frequency be longer than every fourth refueling outage even if it appears that the degradation has ceased. The monitoring frequency is based on observed degradation rates that are verified by actual measurements taken at the repair location; therefore, the developed monitoring frequency will be adequate and appropriate for that location in that piping system regardless of system content.

3) Radioactive fluid leakage will be monitored and detected in accordance with the standard plant monitoring practices for all buried piping containing radioactive fluids.

Exelon's commitment to NEI 07~07, "Industry Ground Water Protection Initiative ~ Final Guidance Document," dated August 2007, combined with the additional monitoring required by Code Case N~ 786 provides monitoring in excess of non~repaired piping.

Question:

"3. Three types of sleeve designs were proposed to repair the affected components~~Type A, partial~structural Type B, and full~structural Type B. Page 2, 2nd to the last paragraph alluded to a situation where the Type B sleeve design would be used, however, without specifics. Explain the process for selecting the type of sleeve to be used, including the extent of degradation, wall thickness, and operating conditions (e.g., temperature and pressure)."

Response

Type A reinforcing sleeves would be used for structural reinforcement of thinned areas which are not expected to penetrate the wall and cause leakage before the next refueling outage (see Code Case §3.1 (a>>. Type B full~structural reinforcing sleeves would be used in cases where the pipe is experiencing substantial structural degradation in addition to infringement on pressure integrity. In this case, the sleeve is designed to accommodate all pressure loads plus axial and circumferential design loadings at the location of the repair, taking no credit for any of

Response to Request for Additional Information Code Case N-786 Page 3 the degraded piping beneath the sleeve (see Code Case §3.1 (b)(1 >>. Type B partial-structural reinforcing sleeves would be used in moderately degraded areas (e.g., pitted or very localized degradation) where partial structural credit can be taken for the degraded section based on predicted degradation until the next refueling outage, but pressure integrity needs to be restored (see Code Case §3.1 (b)(2>>. In all cases, system operating conditions cannot exceed 200°F or 275 psig.

Question:

"4. The proposed alternative was submitted pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(a)(3)(ii), which permits alternative to the ASME Code requirements if compliance with the specified ASME requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

However, the licensee has not provided sufficient evidence to support its argument regarding hardship, unusual difficulty and the compensating increase in the level of quality and safety. Discuss fully the regulatory basis of the relief request in terms of hardship or unusual difficulty and the lack of a compensating increase in the level of quality and safety associated with the required ASME Code repair."

Response

This Relief Request permits the installation of technically sound temporary repairs in the form of Type A or partial-structural Type B reinforcing sleeves where there is inadequate time for evaluation, design, material procurement, planning and scheduling of an appropriate permanent repair or replacement, due to the impact on system availability, maintenance rule applicability, or availability of replacement materials. Additionally, this Relief Request permits installation of technically sound long-term repairs configured to permit on-going degradation monitoring, equal to or exceeding the level of quality and safety associated with permanent Code repairs or replacements. The alternative in some cases could necessitate extending Technical Specification Actions to install a permanent repair/replacement, putting the plant at higher safety risks than warranted compared with the short time necessary to install a technically sound sleeve repair. Without the use of this Code Case in some situations, it may be necessary to shut the plant down in order to perform a code repair/replacement activity; however, this results in an unnecessary plant transient and the loss of safety system availability as compared to maintaining the plant online. The Relief Request has been revised to clarify hardship or unusual difficulty without a compensating increase in the level of quality or safety as shown in.

Question:

"5. Page 3, 4th paragraph of the relief request states that "... A baseline thickness examination will be performed for completed full-structural Type B reinforcing sleeves, attachment welds, and surrounding areas, followed by thickness monitoring during the first two refueling outages after installation and at least every fourth refueling outage thereafter... ". (1)

Discuss whether a baseline thickness examination will be performed for the completed Type A and partial structural Type B sleeves. If not, provide justification. (2) Sections 6 and 8 of Code Case N-786 reference the Construction Code and ASME Code,Section III for volumetric examinations. However, the code case is not clear regarding to which ASME Code requirements the volumetric and thickness examinations will be qualified. Reference the ASME Code sections and subarticles for which the volumetric and thickness

Response to Request for Additional Information Code Case N~ 786 Page 4 examinations of the subject pipes are qualified. (3) Discuss the acceptance criteria for in-service thickness monitoring of the installed full~structural Type B sleeve. That is, after placing in service, under what condition would the full~structural Type B sleeve be considered degraded and be required to be removed?"

Response

1) Baseline thickness examinations will not provide meaningful information for partial~

structural Type B and Type A reinforcing sleeves because they completely encompass the degraded areas, preventing baseline or on~going thickness monitoring of the underlying portions of piping. Ultrasonic Testing (UT) can detect the condition of the base metal beneath a partial penetration attachment weld on a full~structural sleeve (see Figure 2 of the Code Case), but cannot detect the condition of the base metal beneath the sleeve (the ultrasonic signal will not transmit through the interface between the rolled plate of the sleeve and the underlying base metal), or fillet weld. The shape of the fillet weld precludes meaningful measurement of the base metal beneath it. As a result, these sleeves are designed to accommodate maximum predicted degradation, are monitored visually for leakage on a monthly basis, and must be removed entirely at the next refueling outage.

2) The applicable ASME Section III paragraphs for volumetric examination are NC/ND~5200 and ~5300, and these references have been added to the Relief Request as shown in Attachment 2. Ultrasonic thickness measurement is not an ASME Code volumetric examination per IWA~2230, but is accomplished in accordance with plant procedures that comply with ASME Section V. The examinations are performed with either: 1) a straight~beam UT evaluation, using a pulse echo ultrasonic scanning device with CRT type readout, or; 2) a "D~Meter," calibrated for the particular material and thickness, which uses a straight beam ultrasonic method to accurately measure material thickness. For thickness measuring and monitoring, either method is acceptable.

3) A full structural Type B reinforcing sleeve is required to be removed prior to infringing upon the minimum design thicknesses as required by the Construction Code or Section III either in the sleeve or in the attachment welds including the underlying base metal beneath the attachment welds. See Code Case §8(b).

Question:

"6. Page 3, ih paragraph, of the relief request states that "... When used on buried piping, the area of full~structural Type B reinforcing sleeves will need to be physically accessible for the examinations required by the Code Case, which could necessitate installation of removable barriers at the repair location in lieu of backfilling the pipe at that location.... " (1) Discuss how the exposed pipe segment of a buried pipe will be supported at the excavation location after sleeve installation to minimize pipe sagging. (2) Discuss how soil erosion at the excavated location can be minimized so that the soil support for the non~repaired buried pipe segment in the vicinity of the repair will not be compromised."

Response

Exelon design procedure CC~AA~102 requires the engineer to determine and provide information to assure that operability of the systems, structures or components located

Response to Request for Additional Information Code Case N~ 786 Page 5 underground will not be affected as part of the design change process. Installation of removable barriers after sleeve installation is an option that may be implemented in lieu of burying the repaired piping. This option would eliminate excavating down to the repair area during subsequent refueling outages in order to perform the required on-going thickness monitoring. If it is decided to install removable barriers, then support and erosion prevention are two of the many design considerations that would be routinely addressed by the design engineer in their design, which would be dependent upon the actual conditions existing at the repair location. It is not possible to predict those conditions or propose solutions on a generiC basis, but if practical means to ensure proper support of the pipe were not viable, then the designer would likely choose to have the pipe buried, necessitating excavation at future outages.

Question:

'7. Code Case N*786 allows the repair on piping systems that experience internal wall thinning from cavitation. The wall thinning rate for severe cavitation can be difficult to determine and predict. (1) Discuss whether cavitation will be mitigated after the sleeve is installed. If not, provide justification. (2) If cavitation cannot be mitigated after sleeve installation, discuss compensatory measures to ensure the structural integrity of the pipe at the repaired location. (3) If a full-structural Type B sleeve is installed on a pipe that experiences cavitation which cannot be mitigated, justify the adequacy of the proposed monitoring frequency of every fourth refueling outage or propose a shorter monitoring frequency that can be justified."

Response

1) Mitigation of cavitation and its justification is handled through each plant's corrective action program, depending on the conditions existing at each location of cavitation; therefore, generiC solutions cannot be predicted or proposed.

2) The existing plant conditions, observed rates of erosion at the repair location, general material condition, changes in system operation, are a" typical conditions that the design engineer must consider in designing the reinforcing sleeve. In addition, without mitigation, the new sleeve must initially be assumed to erode at twice the same rate as experienced by the underlying piping. All of these factors will have a bearing on establishing the thickness, length, and type of sleeve ultimately selected to ensure that structural integrity is maintained for each specific location.

3) Monitoring consists of a complete baseline thickness inspection that is repeated at each of the next two refueling outages. The data collected from the initial and following two inspections is used to calculate the maximum degradation rates (in./yr) in a" areas of the sleeve repair. Subsequent monitoring is dictated by the results of those inspections, but according to the Code Case, no less frequently than every fourth refueling outage even if cavitation is mitigated (see also the reply to Question 2). However, recognizing the concern and uncertainties associated with cavitation erosion, the following condition has been added to the Relief Request as shown in Attachment 2:

"For degradation caused by cavitation, thickness monitoring is required to be performed at a minimum of every refueling outage for the life of the repair."

Question:

Response to Request for Additional Information Code Case N-786 Page 6 "8. Paragraph 2(b) of Code Case N-786 states that "... The dimensions of the surrounding area to be evaluated shall be determined by the Owner, based on the type and rate of degradation present..." Provide guidance on how the surrounding area will be determined based on the type and rate of degradation to establish a consistent methodology across the fleet."

Response

The extent and rate of degradation in the piping shall be evaluated to ensure there will be no other unacceptable locations within the surrounding area that could affect the structural integrity of reinforced areas for the life of the repair. The extent of the surrounding area to be evaluated is dependent on the pipe material and system operating conditions at each specific location, the size and type of reinforcing sleeve selected by the design engineer, and the design loadings within the system at that location. Therefore, a common or consistent methodology cannot be proposed for all cases. However, in each situation the applicable design code loading criteria, special considerations, as well as general design rules and specific design rules of the applicable construction code will be applied to the design of the repair. The original design code or other code as allowed by ASME Section XI, IWA-4221, will be used to evaluate the sleeve installation (including adjacent pipe and attachment welds as applicable). Typical design code requirements expected to be applicable are ASME Section III (e.g., NC-3000 and ND-3000),

ASMElUSAS 831.7 (e.g., Chapter 2-11 and Chapter 3-11), ASMElUSAS 831.1 (e.g., Chapter II),

and AWWA M11.

Question:

"9. Paragraph 3.1(b)(1) of Code Case N-786 states that "... Full-structural reinforcement is designed to accommodate pressure plus axial and circumferential design loadings at the location for the design life of the repair... " Discuss how the design life of the repair is derived. Even though the reinforcement sleeve is installed, the original pipe metal is continuously being corroded and the corroded area will expand in the lateral direction. The sleeve may fail if the corroded area becomes larger than the size of the sleeve. In addition, the reinforcement sleeve may corrode over time also. Discuss the how the corrosion rate is calculated and provide the reference. Discuss how the corrosion of the pipe base metal and the sleeve is being considered in the design life."

Response

Full structural reinforcement is designed to replace the entire original pipe beneath the sleeve.

The design life of the new sleeve would initially be based on the conservative assumption that the sleeve rolled plate material would begin degrading immediately at a minimum of two (2) times the maximum rate observed at that location, or if unknown, four (4) times the estimated maximum degradation rate for that or a similar system for the same degradation mechanism.

This requirement has been added to the Relief Request as shown in Attachment 2. One can then determine expected life by applying this maximum rate to the material thickness selected for the sleeve.

Response to Request for Additional Information Code Case N-786 Page 7 To measure the degradation rate at a specific location requires mapping the degraded area (using ultrasonic equipment) a minimum of two (2) times with a distinct time interval between each mapping. Specific time intervals are not defined as they depend on the rate and extent of degradation, but they would need to be sufficient to measure discernible changes in thickness.

Measured point degradation rates would equal the change in thickness at various pOints within the mapped area divided by the time interval, revealing a predictable change in configuration of the area over time. Two (2) times this rate of change in configuration will be assumed in the design to establish the minimum size of the reinforcing sleeve (four (4) times system maximum, if data is not available for the specific location of the repair). This is consistent with the existing Exelon raw water corrosion program for application of degradation rates in design.

Thickness monitoring examinations at the first two refueling outages will validate or cause adjustment to that degradation rate. In addition, the thickness monitoring of the base metal beneath the attachment welds will detect any lateral growth of degradation into the base material beneath the sleeve attachment welds. On-going monitoring frequency will be established based on the actual measured results of those inspections, but at a minimum of every fourth refueling outage (every refueling outage if cavitation is involved).

For components with multiple direct examinations applicable to the degraded location the degradation rates are calculated per the Exelon Underground Piping Procedure ER-AA-5400-1002 as follows:

CR = (t measl - t meas2) X SF / time Where: t measl = minimum measured value from the first examination t meas2 = minimum measured value from the second examination SF

=Safety Factor (recommend at least 10%) = 1.10 time = length of time between inspections Normally a 110% Safety Factor is used in establishing degradation rates; however, for sleeve repairs a 200% Safety Factor will initially be applied.

It is recognized that the wall loss rate for cavitation may not be predictable on a generic basis. If multiple UT wall thickness readings over time at the repair location are available, then two (2) times this rate will be applied for determining wall loss rates. If multiple UT wall thickness readings are not available, then the as-found measured remaining wall thickness will be compared to the initial nominal wall thickness at the time at which a system parameter or component change can be identified that supports the start of cavitation damage. Two (2) times this rate will be applied to design of the sleeve. If no start of cavitation time can be identified through system operational reviews, then four (4) times the worst cavitation rate observed for that or similar systems will be applied to the design.

Question:

"10. Section 8(b) of the code case states that "... The owner shall prepare a plan for thickness monitoring of full-structural reinforcing sleeves and their attachment welds using ultrasonic or direct thickness measurements... The frequency and method of monitoring shall be determined based on an evaluation of the degradation mechanism. Monitoring activities shall be performed during the first two refueling outages after installation and at least

Response to Request for Additional Information Code Case N-786 Page 8 every fourth refueling outage thereafter... " (1) Discuss the exact nondestructive examination that will be used to verify the thickness of the sleeve and the underneath pipe base metal. (2) Clarify how the direct thickness measurements can be used on the reinforcing sleeve or pipe base metal. (3) Discuss whether the wall thickness of the pipe base metal in the vicinity of the sleeve will also be examined by ultrasonic testing to verify that the corroded pipe area underneath the sleeve has not expanded beyond the area that is covered by the sleeve. If this area will be examined, discuss the specific area of pipe wall where thickness readings will be taken. If this area will not be examined, provide justification. (4) Discuss how the fillet welds at the sleeve will be examined because ultrasonic testing will not be possible. (5) Explain how the evaluation of the degradation mechanism will provide the frequency and method of monitoring. For example, explain how the thickness monitoring frequency of every fourth refueling outage is derived. (6)

Clarify the "monitoring activities" in the above Section 8(b) statement (is this an inspection activity or monitoring activity? Please explain any difference.). Describe the exact activities that will be performed during the first two refueling outages and every fourth refueling outage, thereafter."

Response

1) For clarification, the Relief Request has been revised to read "... the Owner shall prepare and implement a plan for thickness monitoring... " This thickness monitoring is accomplished by measurement of the sleeve plate base metal beneath the partial penetration attachment weld, and base metal beneath the attachment weld using a straight-beam ultrasonic measurement process that accurately determines the thickness of the metal from the exterior surface at the ultrasonic transducer, or probe, to the under surface of the plate or pipe. The process measures the speed with which the sound waves reflect back from the opposite surface, then factors in the speed of sound in that material, and renders an accurate measurement of the thickness. As stated in our response to Item 5(2), this is accomplished in accordance with Exelon procedures using techniques compliant with ASME Section V.

2) Direct thickness measurement of internal degradation can only be achieved by applying a profile gage or a pit gage against the interior of the pipe or sleeve and referencing the result to a point of known through-wall thickness measurement in the area of concern.

Of necessity, it requires internal access to the piping in order to gain this information. As such, it is the least preferred method of measurement, and is unlikely to be used instead of ultrasonics except in a case where a particular configuration is not conducive to measurement by ultrasonic examination.

3) The wall thickness of the pipe base metal beneath the partial penetration attachment welds is ultrasonically monitored to verify that the degraded pipe area underneath the sleeve does not expand beyond the area that is covered by the sleeve, or infringe upon the structural integrity of the base metal beneath the attachment weld. If infringement does occur, it will be noted by reduced thickness readings of the original pipe beneath the interface between the partial penetration attachment weld and the sleeve rolled plate.

Response to Request for Additional Information Code Case N-786 Page 9

4) The fillet welds (Le., tapered edges adjacent to the partial penetration attachment welds) will not be examined, as they merely form a stress-reducing transition between the partial penetration weld and the pipe surface. As such, they are excluded from monitoring in paragraph 6(b) of the Code Case.

5) See responses to Questions 2,7 and 9.

6) Monitoring consists of a complete baseline thickness inspection that is then repeated at each of the next two refueling outages. The data collected from these inspections is used to calculate the maximum degradation rate (in./yr) in all areas of the sleeve repair.

Subsequent thickness inspections are then scheduled such that there will be no infringement on minimum design thicknesses before the next inspection activity, based on the maximum observed degradation rates. In no case shall monitoring inspections be performed less frequently than every fourth refueling outage (every refueling outage for repairs involving cavitation). See reply to Question 2.

Revised Relief Request

10 CFR 50.55a RELIEF REQUEST Revision 1 (Page 1 of 5)

Request to Use Code Case N-786 in Accordance with 10 CFR 50.55a(a)(3)(iI)

1. ASME Code Component(s) Affected:

All ASME Class 2 and 3 moderate energy (i.e., less than or equal to 200°F (93°C) and less than or equal to 275 psig (1.9 MPa) maximum operating conditions) carbon steel piping systems.

2. Applicable Code Edition and Addenda

PLANT INTERVAL EDITION START END Braidwood Station, Third 2001 Edition, through 2003 July 29, 2008 July 28, 2018 Units 1 and 2 Addenda October 17, 2008 October 16, 2018 Byron Station, Third 2001 Edition, through 2003 January 16, 2006 July 15, 2016 Units 1 and 2 Addenda Clinton Power Station, Third 2004 Edition July 1,2010 June 30, 2020 Unit 1 Dresden Nuclear Power Fifth 2007 Edition, through 2008 January 20, 2013 January 19, 2023 Station, Units 2 and 3 Addenda LaSalle County Stations, Third 2001 Edition, through 2003 October 1, 2007 September 30, 2017 Units 1 and 2 Addenda Limerick Generating Third 2001 Edition, through 2003 February 1, 2007 January 31, 2017 Station, Units 1 and 2 Addenda Oyster Creek Nuclear Fifth 2007 Edition, through 2008 January 15, 2013 January 14, 2023 Generating Station Addenda Peach Bottom Atomic 2001 Edition, through 2003 Power Station, Fourth November 5, 2008 November 4, 2018 Units 2 and 3 Addenda Quad Cities Nuclear 2007 Edition, through 2008 Power Station, Fifth April 2, 2013 April 1, 2023 Units 1 and 2 Addenda Three Mile Island Nuclear Fourth 2004 Edition April 20, 2011 April 19,2022 Station, Unit 1

3. Applicable Code Requirement

ASME Code,Section XI, IWA-4400 of 2001 Edition through 2003 Addenda, 2004 Edition, and 2007 Edition through 2008 Addenda provides requirements for welding, brazing, metal removal, and installation of repair/replacement activities.

4. Reason for Request

10 CFR 50.55a RELIEF REQUEST Revision 1 (Page 2 of 5)

In accordance with 10 CFR 50.55a(a)(3)(ii), Exelon Generation Company, LLC (Exelon) is requesting proposed alternatives from the requirement for replacement or internal weld repair of wall thinning conditions resulting from degradation in Class 2 and Class 3 moderate energy carbon steel piping systems in accordance with IWA-4000. Such degradation may be the result of mechanisms such as localized erosion, corrosion, cavitation, and pitting, but excluded are conditions involving any form of cracking. IWA-4000 requires repair or replacement in accordance with the Owner's Requirements and the original or later Construction Code.

One reason for this request is to permit installation of technically sound temporary repairs, in the form of Type A or partial-structural Type B reinforcing sleeves, to provide adequate time for evaluation, design, material procurement, planning and scheduling of appropriate permanent repair or replacement of the defective piping, considering the impact on system availability, maintenance rule applicability, and availability of replacement materials.

The other reason for this request is to permit installation of long-term repairs, in the form of full-structural Type B reinforcing sleeves, for locally degraded portions of piping systems. The design, construction, and inservice monitoring of such sleeves provide a technically sound equivalent replacement for the segment of degraded piping that is encompassed.

5. Proposed Alternative and Basis for Use

Exelon proposes to implement the requirements of ASME Code Case N-786, "Alternative Requirements for Sleeve Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping Section XI, Division 1," for repair of degradation in Class 2 and 3 moderate energy carbon steel piping systems resulting from mechanisms such as localized erosion, corrosion, cavitation, or pitting, but excluding conditions involving any form of cracking. These types of defects are typically identified by small leaks in the piping system or by pre-emptive non-code required examinations performed to monitor the degradation mechanisms. Code Case N-786, which is included as part of this relief request, is attached.

This code case invokes the design requirements of the original Construction Code or ASME Code,Section III. Reconciliation and use of editions and addenda of ASME Section III will be in accordance with ASME Section XI, IWA-4220, and only editions and addenda of ASME Section III that have been accepted by 10 CFR 50.55a may be used. The Code of Record for the specific 10-year lSI interval at each nuclear unit as identified under Section 2 above, will be used when applying the various IWA paragraphs of Section XI unless specific regulatory relief to use other editions or addenda is approved.

The alternative repair technique described in Code Case N-786 involves the application of Type A and Type B full encirclement sleeve halves welded together with full penetration longitudinal seam welds to reinforce structural integrity in the degraded area. In the case of Type B reinforcing sleeves, the ends are also welded to the piping in order to restore pressure integrity.

This repair technique will be utilized when it is determined that this repair method is suitable for the particular defect or degradation being resolved without flaw removal. Use of this repair method will be limited to pipe and fittings: as a result the following condition shall apply to the application of Code Case N-786:

10 CFR 50.55a RELIEF REQUEST Revision 1 (Page 3 of 5)

Reinforcing sleeves may not be applied to pumps. valves, expansion joints, vessels, heat exchangers, tubing, or flanges; and may not be applied over flanged joints, socket welded or threaded joints, or branch connection welds. Installed Type B sleeves may have new welded or threaded branch connections when reguired by design and permitted by the applicable Construction Code.

The Code Case requires that the cause of the degradation be determined and that the extent and rate of degradation in the piping be evaluated to ensure that there are no other unacceptable locations within the surrounding area that could affect the integrity of the repaired piping. The area of evaluation will be dependent on the degradation mechanism present. If the cause of the degradation is not determined, the maximum permitted service life of any reinforcing sleeve shall be the time until the next refueling outage. In addition, the following condition shall apply to the application of Code Case N-786:

The initial degradation rate selected for design of the sleeve shall be egual to or greater than two times the maximum rate observed at that location; or if unknown, four (4) times the estimated maximum degradation rate for that or a similar system for the same degradation mechanism.

"Full-structural Type B" means that the sleeve and attachment welds alone maintain full capability to withstand structural (mechanical) and pressure loading for which the piping is presently designed without need for additional support or reinforcement, and without reliance on any piping that is encased by the sleeve. Type A and partial-structural Type B sleeves rely on the encased underlying piping to provide some structural (mechanical) and/or pressure retaining integrity.

Type B reinforcing sleeves may be applied to leaking systems by installing a gasket or sealant between the sleeve and the pipe as permitted by the Code Case, and then clamping the reinforcing sleeve halves to the piping prior to welding. Residual moisture is then removed by heating prior to welding. If welding of any type of sleeve occurs on a wet surface, the maximum permitted life of the sleeve shall be the time until the next refueling outage.

The Code Case reguires that the Owner shall prepare and implement a plan for thickness monitoring by inspection of full-structural reinforcing sleeves and their attachment welds. To accomplish this, a baseline thickness examination will be performed for completed full-structural Type B reinforcing sleeves, partial penetration attachment welds, and surrounding areas, followed by similar thickness monitoring inspections during the first two refueling outages after installation and at least every fourth refueling outage thereafter, except that for degradation caused by cavitation, the following condition shall apply to the application of Code Case N-786:

For degradation caused by cavitation, thickness monitoring by inspection is reguired to be performed at a minimum of every refueling outage for the life of the repair.

Combining all of these data will establish 3-point curves from which the maximum actual degradation rates at the sleeve and partial penetration attachment welds can be determined.

Subseguent thickness monitoring examinations will be scheduled based on the maximum rates observed over those two cycles, such that the reguired design thicknesses will not be infringed upon before each subseguently scheduled thickness monitoring examination.

10 CFR 50.55a RELIEF REQUEST Revision 1 (Page 4 of 5)

Partial-structural Type B reinforcing sleeves and Type A reinforcing sleeves completely encompass the degraded areas. These sleeves are designed to accommodate predicted maximum degradation and must be removed at the next refueling outage. Accordingly, the Code Case does not require inservice monitoring for these sleeves. However, because of NRC concerns discussed in the May 10, 2012, NRC Safety Evaluation Report for the Exelon Generation Company, LLC sites concerning the approval to apply Code Case N-789 (ML12121A637), the following condition shall apply to the application of Code Case N-786:

Type A reinforcing sleeves and partial-structural Type B reinforcing sleeves shall be visually observed at least once per month to monitor for evidence of leakage. If the areas containing these sleeves are not accessible for direct observation, then monitoring will be accomplished by visual assessment of surrounding areas or ground surface areas above such sleeves on buried piping, or monitoring of leakage collection systems, if available.

When used on buried piping, the area of full-structural Type B reinforcing sleeves will need to be physically accessible for the examinations required by the Code Case, which could necessitate installation of removable barriers at the repair location in lieu of backfilling the pipe at that location. For Type A and partial-structural Type B reinforcing sleeves installed on buried piping, the monitoring will be based on visual assessment as discussed above.

Type A reinforcing sleeves and partial-structural Type B reinforcing sleeves shall have a maximum permitted service life of the time until the next refueling outage, when a permanent repair or replacement must be performed. Neither the Type A nor the partial-structural Type B reinforcing sleeve may remain in service beyond the end of the next refueling outage after they are installed, unless specific regulatory relief is obtained. This means that if such a repair is performed in mid-cycle (e.g., one month before the scheduled refueling outage) the reinforcing sleeve would be removed no later than the upcoming refueling outage (e.g., in one month) unless specific regulatory relief is obtained. Even if removal during the next scheduled refueling outage becomes challenging (e.g., it is installed on a system required to be functional during the refueling outage), it would still need to be removed when the system is not required to be functional and prior to the conclusion of the next scheduled refueling outage after it was installed.

A similar situation exists with common COOling lines that require a dual unit outage in order to remove them from service. Unless a full-structural Type B reinforcing sleeve is installed, specific regulatory approval would need to be obtained in order to defer removal of a Type A or partial-structural Type B reinforcing sleeve beyond the next upcoming refueling outage of either unit.

Full-structural Type B reinforcing sleeves will be removed and an IWA-4000 repair or replacement will be performed prior to the time that inservice monitoring indicates that structural integrity could be impaired based on measured degradation between monitoring activities.

Additional requirements for design, installation, examination (including volumetric examination in accordance with NC-5200 and NC-5300. or NO-5200 and NO-5300), pressure testing, and inservice examination of reinforcing sleeves are provided in Code Case N-786.

All other ASME Section XI requirements for which relief was not specifically requested and authorized by the NRC staff will remain applicable including third party review by the Authorized Nuclear Inservice Inspector.

10 CFR 50.55a RELIEF REQUEST Revision 1 (Page 5 of 5)

Performing code repair/replacement in lieu of implementing this Relief Reguest would in some cases necessitate extending Technical Specification Actions to install a permanent repair/replacement, putting the plant at higher safety risks than warranted compared with the short time necessary to install a technically sound sleeve repair. Without the use of this Code Case in some situations, it may be necessary to shut the plant down in order to perform a code repair/replacement activity; however, this results in an unnecessary plant transient and the loss of safety system availability as compared to maintaining the plant online.

Based on the above, the use of Code Case N-786 for full-structural Type B reinforcing sleeves and for Type A and partial-structural Type B reinforcing sleeves will apply when compliance with the specified Code requirements of ASME Section XI would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Code Case N-786 was approved by the ASME Board on Nuclear Codes and Standards on March 24, 2011 ; however, it has not been incorporated into NRC Regulatory Guide 1.147 "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," and thus is not available for application at nuclear power plants without specific NRC approval. Therefore, Exelon requests use of the alternative repair techniques described in the Code Case via this relief request.

6. Duration of Proposed Alternative

The proposed alternative is for use of the Code Case for the remainder of each plant's 1 a-year inspection interval as specified in Section 2. Installation of reinforcing sleeves in accordance with this request cannot take place after the end of the 1 a-year lSI interval for the unit. Any Type A and partial-structural Type B reinforcing sleeves installed before the end of the 1 a-year inservice inspection interval will be removed during the next refueling outage, even if that refueling outage occurs after the end of the 1 a-year lSI interval.

7. Precedent:

A similar Exelon relief request, for Code Case N-789 (Reinforcing Pads for Class 2 and Class 3 Moderate Energy Raw Water Systems) was approved by NRC Safety Evaluation dated May 10, 2012, ADAMS Accession No. Ml12121A637.