ML20352A334
| ML20352A334 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/17/2020 |
| From: | Mark D. Sartain Dominion Energy Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 20-391 | |
| Download: ML20352A334 (21) | |
Text
Dominion Energy Nuclear Connecticut, Inc.
5000 Dominion Boulevard, Glen Allen, VA 23060 Dominion Dominion Energy.com Energy December 17, 2020 U.S. Nuclear Regulatory Commission Serial No.20-391 Attention: Document Control Desk NRA/SS RO Washington, DC 20555 Docket Nos. 50-336 50-423 License Nos. DPR-65 NPF-49 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNITS 2 AND 3 PROPOSED ALTERNATIVE REQUESTS RR-05-04 AND IR-4-02, USE OF ALTERNATIVE PRESSURE/FLOW TESTING REQUIREMENTS FOR SERVICE WATER SYSTEM SUPPLY PIPING Pursuant to 10 CFR 50.55a(z)(2), Dominion Energy Nuclear Connecticut, Inc. (DENG) requests use of an alternative for Millstone Power Station Unit 2 (MPS2) and Unit 3 (MPS3) for meeting certain examination and testing requirements of Section XI of the 2013 American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. Specifically, DENG requests approval of alternative methods for performing the VT-2 visual examination as required by ASME Section XI, Table IWD-2500-1 and IWD-5220 for the piping segments of the Service Water System located in the confined space of the intake structure bays. The proposed alternatives for MPS2 and MPS3 are provided in Attachments 1 and 2, respectively. These alternative requests were approved by the NRC for the previous ten-year inservice inspection interval at MPS2 and MPS3.
If you have any questions regarding this submittal, please contact Shayan Sinha at (804) 273-4687.
Sincerely, Mark D. Sartain Vice President - Nuclear Engineering and Fleet Support
Serial No.20-391 Docket No. 50-336/423 Page 2 of 2 Attachments:
- 1. Millstone Power Station Unit 2, Alternative Request RR-05-04, Use of Alternative Pressure/Flow Testing Requirements for Service Water System Supply Piping for the Fifth Ten-Year lnservice Inspection Interval
- 2. Millstone Power Station Unit 3, Alternative Request IR-4-02, Use of Alternative Pressure/Flow Testing Requirements for Service Water System Supply Piping for the Fourth Ten-Year lnservice Inspection Interval Commitments made in this letter: None cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08-C 2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No.20-391 Docket No. 50-336 ATTACHMENT 1 ALTERNATIVE REQUEST RR-05-04 USE OF AL TERNATE PRESSURE/FLOW TESTING REQUIREMENTS FOR SERVICE WATER SYSTEM SUPPLY PIPING FOR THE FIFTH TEN-YEAR INSERVICE INSPECTION INTERVAL MILLSTONE POWER STATION UNIT 2 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
Serial No.20-391 Docket No. 50-336 Attachment 1, Page 1 of 9 Alternative Request RR-05-04 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(2)
-- Hardship Without a Compensating Increase in Quality and Safety --
References:
ASME Section XI, Tables IWD-2500-1 and IWD-5220 Examination Category: D-B, All Pressure Retaining Components Items Number: D2.10
Description:
Millstone Power Station Unit 2 (MPS2) piping segments consist of two trains of 24" Service Water System (SWS) supply piping located in the intake structure bays. This piping material consists of spools that are A-106, Grade B Carbon Steel, spools that are 6% Molybdenum Stainless Steel (UNS N08367), also known as AL6XN.
Components: The applicable piping line numbers are identified as 24"-
JGD-1 and 24"-KE-1 (Reference Piping & Instrumentation Drawing (P&ID) 25203-26008, Sheet 2).
Note: Excerpts of P&ID 25203-26008, Sheet 2 and Piping Isometric Drawings 25203-20150, Sheet 679 and 25203-20150, Sheet 1080 are provided for information only, with the subject piping clouded for identification.
2. Applicable Code Edition and Addenda
ASME Section XI, 2013 Edition [Reference 8.1]
3. Applicable Code Requirements
The 2013 Edition of American Society of Mechanical Engineers (ASME)Section XI, Tables IWD-2500-1, Examination Category D-B, and IWD-5220 require, for Class 3 piping, a VT-2 visual examination be performed during a system leakage test conducted at the pressure obtained while the system is in-service and performing its normal operating function or at the system pressure developed during a test conducted to verify system operability. The system leakage test is required to be performed once each inspection period.
Serial No.20-391 Docket No. 50-336 Attachment 1, Page 2 of 9
4. Reason for Request
Dominion Energy Nuclear Connecticut, Inc. (DENC) requests approval of alternative methods for performing the VT-2 visual examination as required by ASME Section XI, Tables IWD-2500-1 and IWD-5220 for the "A" and "B" train piping segments of the MPS2 SWS located in the normally inaccessible confined space of the intake structure bays. The performance of the Code-required VT-2 visual examinations for these piping segments is considered a hardship with respect to both personnel and plant safety. This determination is based on the following factors and considerations.
The three SWS pumps discharge to the header 24"-JGD-1 that is divided into "A" and "B" trains and transitions into the downstream 24"-KE-1 pipe segments. There are seven bolted flange connections associated with the "A" train and four bolted flange connections associated with the "B" train of the affected pipe segments.
There are no valves within the affected pipe segments.
The piping was upgraded to 6% molybdenum stainless steel (UNS N08367), also known as AL6XN, as a result of preemptive mitigation measures in the fourth ten-year interval. Periodic internal visual inspection and system flow testing confirm there has been no degradation in the affected pipe segments since the upgrade.
The nominal wall thickness of the 24"-JGD-1 piping is 0.375 inches. The nominal wall thickness of the 24"-KE-1 piping is 0.410 inches. The normal operating pressure is 45 pounds per square inch gauge (psig). The normal operating temperature range is 33°F to 80°F.
The subject "A" train piping segment runs vertically through the floor of the SWS pump cubicle for a distance of 7.5 feet and then travels horizontally through four intake structure bays for a distance of approximately 69 feet until it passes through the outer wall of the intake structure, where it continues underground to the turbine building. Approximately 10.5 feet of this piping has been upgraded to AL6XN. The remaining piping in the intake structure bay is approximately 64.5 feet of A-106, Grade B carbon steel.
- The subject "B" train,_ piping segment runs vertically through the floor of the SWS pump cubicle for a distance of 8 feet and then travels horizontally through one intake structure bay for a distance of approximately 14 feet until it passes through the outer wall of the intake structure, where it then continues underground to the turbine building. This piping has been upgraded to AL6XN.
The carbon steel piping in the "A" train is internally lined with a cured in-place pipe, epoxy-impregnated material (lnsituform), and externally coated with an epoxy coal tar material (Carbomastic 14), in order to enhance long-term life. There is no coating or lining on the inside or outside surface of the SWS piping that has been
Serial No.20-391 Docket No. 50-336 Attachment 1, Page 3 of 9 upgraded to AL6XN, because the material is a highly corrosion resistant material and well suited for the environment inside the intake structure and bays.
The VT-2 visual examination of this piping requires entry into each of the four intake structure bays (A, B, C, and D) that are designated as confined spaces. There is limited access to each bay from an access hatch that is in the intake structure floor.
Personnel entry into the confined spaces of the intake structure bays, with equipment operational, is considered a personnel safety hazard; therefore, equipment is required to be removed from service and tagged-out prior to entry to perform the Code-required VT-2 visual examination.
Additionally, due to the physical configuration of the intake structure bays, each of the four bays require scaffolding to be erected to access the piping to perform the VT-2 visual examination. There are no platforms located in the bays. Erecting the scaffolding is difficult because of safety risks associated with moving personnel and materials into the confined space of the bay areas. Two of the bays (B and C) contain structural steel that can support erection of scaffolding over the water in the bays, but due to personnel safety concerns, the SWS pumps will still have to be taken out of service. The remaining two bays (A and D) require scaffolding to be erected from the floor of the bays up to the subject piping which requires each bay to be completely isolated and drained. Draining these bays also requires equipment to be taken out of service to preclude damage to the SWS pumps that could occur with the bays drained. Unavailability of safety-related SWS pumps puts MPS2 at a greater operational risk since it removes redundancy of available equipment, introducing a reduction in the safety margin of the plant.
The required VT-2 visual examinations would continue to be performed on the remaining accessible portions of piping lines 24"-JGD-1 and 24"-KE-1 not covered by this alternative request, when conducting the system leakage test in accordance with ASME Section XI, IWD-5000 and IWA-5244(b)(2) for buried components within this piping line.
Therefore, placing the plant in a condition where the safety-related SWS is out of service for an extended period results in increased operational risk, and performing the VT-2 visual examinations on the subject piping requires activities that present safety hazards to plant personnel. Thus, compliance with the specified requirements is considered a hardship without a compensating increase in the level of quality and safety.
5. Proposed Alternative and Basis for Use
5.1 Proposed Alternative Pursuant to 10 CFR 50.55a(z)(2), DENG proposes to use, as an alternative to the requirements of IWD-5220, a verification of unimpaired flow with an additional internal visual inspection to be performed every other refueling outage on each train.
Serial No.20-391 Docket No. 50-336 Attachment 1, Page 4 of 9 Periodic flow testing will be performed in accordance with lnservice Test (1ST)
Program (Reference 8.2) surveillance procedures. These surveillance procedures require flow to be measured, recorded and compared to established acceptance criteria to provide assurance that flow is not impaired during operation. The parameters of the flow test are described in Section 5.2.
In addition to flow testing, alternating internal visual inspections are performed on the "A" and "B" train piping segments considered to be inaccessible per this request.
The internal visual inspections will be performed on an alternating basis each refueling outage, thus each train is inspected every other outage at approximately 3-year frequencies. If during the performance of the internal visual inspections, any identified conditions such as erosion, corrosion, microfouling, biofouling, or other degraded piping and/or lining material conditions are identified, they will be evaluated by Engineering for acceptance or corrective action, as needed.
The required VT-2 visual examinations would continue to be performed on the remaining accessible portions of piping lines 24"-JGD-1 and 24"-KE-1 not covered by this alternative request, when conducting the system leakage test in accordance with ASME Section XI, IWD-5000 and IWA-5244(b)(2) for buried components within this piping line.
The proposed alternative consists of an unimpaired flow test and an internal visual inspection of the subject piping that will be used in lieu of the Code-required VT-2 visual examination for this inaccessible piping.
5.2 Basis for Use Flow Testing: Unimpaired flow testing of the three MPS2 SWS pumps is performed quarterly and uses an established minimum flow rate specified in the 1ST procedures as the acceptance criteria for the pressure testing of the subject associated SWS pipe segments of this request. The minimum flow rate per pump is currently specified as 10,400 gallons per minute (gpm).
During testing of a SWS pump, flow rate is measured using a single flow instrument, located in the turbine building, for measurement of total flow1 If the flow instrument is not available or does not meet accuracy requirements, the flow is measured using a combined total flow rate measurement from four heat exchanger flow instruments.
During the test, the flow rate is set to 10,500 gpm nominal (10,400 gpm minimum acceptable flow rate), stabilized, and observed for two minutes. Pump vibrations are then measured. Pump discharge and suction pressures arf:3 also measured and used to determine differential pressure. This measurement has an accuracy of roughly 200 gpm. Leakage flow is unmonitored, because the flow meters are downstream of the intake structure. However, leakage that is greater than or equal to 200 gpm during a test would result in a deviation between expected and measured differential pressure across the SWS pump (for a given measured flow rate). Such deviations would be entered into the Corrective Action Program (CAP) and investigated to determine the cause. Operators are in the vicinity of the SWS
Serial No.20-391 Docket No. 50-336 Attachment 1, Page 5 of 9 pumps during the testing. Any significant flow from leakage in the inaccessible piping would likely be audible to the operators during the testing. Flow rate is required to be held constant for two minutes before readings are taken. During that time, conditions are observed by the operators and any out-of-ordinary conditions are noted. The pumps are centrifugal, and performance follows a typical centrifugal pump curve. If a leak occurs, as indicated above, it would be unmonitored flow and observed as reduced differential pressure across the SWS pump and would be entered into the CAP and investigated to determine the cause.
Flow testing is performed in conjunction with quarterly testing of the SWS pumps. If the pump failed to meet the acceptance criteria during the 1ST surveillance, and a condition report would be initiated in accordance with the CAP. Investigation to determine the cause of the flow reduction would be identified as part of the CAP resolution plan. Additional corrective actions such as maintenance of the pump and system walkdowns, etc. would be initiated, as necessary, to restore the pump and/or system to operable status. Leakage identified during system walkdowns of accessible piping and components not covered in this request would be evaluated and repaired, as necessary. If during the investigation, it is suspected that there may be leakage occurring from the subject piping addressed by this request, the necessary actions would be taken to gain access to this normally inaccessible piping for visual inspection, as necessary. It should be noted that the most recent flow testing results have not identified an increasing trend for leakage in the inaccessible piping.
For normal operation, there are no indication alarms in the control room to monitor for reduced flow. However, during normal operation the total service water header flow indication for each train is available in real-time from the plant process computer in the control room. Additionally, the intake structure is walked down once each shift during plant equipment operator rounds. Any significant leakage would likely be audible to the operators during these rounds.
Internal Visual Inspection: The entire inside surface of each train of 24"-JGD-1 and 24"-KE
- 1 is visually inspected on an alternating basis each refueling outage.
Therefore, each train is inspected at an approximately 3-year frequency. The internal visual inspection is performed remotely using a robotic crawler unit fitted with. a high-resolution pan and tilt camera (or equivalent). Any identified conditions such as erosion, corrosion, macrofouling, biofouling, or other degraded piping liner material conditions are evaluated by Engineering for acceptance or corrective actions., as necessary. Inspections performed over the last two MPS2 refueling outages identified no unsatisfactory conditions.
Based on the history of the internal visual inspection results, the inspection frequency has been determined to be adequate to ensure structural integrity of the subject piping. The internal inspection frequency is consistent with the frequency that would be required for the ASME Code leakage test.
Serial No.20-391 Docket No. 50-336 Attachment 1, Page 6 of 9 Therefore, performance of the VT-2 visual examination during the system leakage test on the inaccessible portions of service water piping discussed in this alternative request does not provide a compensating increase in the level of quality and safety when compared to performing the proposed unimpaired flow test and internal visual inspection of this piping As noted above, the benefit accrued in performing the Code-required VT-2 examination is not deemed commensurate with the hardship, personnel hazards, and operational risk in taking safety-related equipment out of service and preparing each of the four bays for personnel entry to conduct the VT-2 visual examination.
Based on the use of 1ST to verify that flow through the subject piping is unimpaired in conjunction with the periodic internal visual inspections, this alternative provides reasonable assurance of operational readiness and continued structural integrity.
6. Duration of Proposed Alternative
This alternative is requested for the duration of MPS2's fifth ten-year ISi interval, which began on April 1, 2020, and ends on March 31, 2030.
- 7. Precedent A similar request for the MPS2 fourth ten-year ISi interval was approved by the NRC on January 23, 2013 (ADAMS Accession Number No. ML13011A158).
- 8. References
- 1. ASME Boiler and Pressure Vessel Code,Section XI, Rules for lnservice Inspection of Nuclear Power Plant Components, 2013 Edition.
- 2. DENC Letter 18-001, "Millstone Power Station Units 2 and 3, In-Service Testing Program for Pumps, Valves, and Snubbers, Fifth and Fourth 10-Year Interval Updates for Units 2 and 3," dated March 1, 2018 (ADAMS Accession No. ML18066A078)
Serial No.20-391 Docket No. 50-336 Attachment 1, Page 7 of 9
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Serial No.20-391 Docket No. 50-423 ATTACHMENT 2 ALTERNATIVE REQUEST IR-4-02 USE OF ALTERNATE PRESSURE/FLOW TESTING REQUIREMENTS FOR SERVICE WATER SYSTEM SUPPLY PIPING FOR THE FOURTH TEN-YEAR INSERVICE INSPECTION INTERVAL MILLSTONE POWER STATION UNIT 3 (MPS3)
DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
Serial No.20-391 Docket No. 50-423 Attachment 2, Page 1 of 8 Alternative Request IR-4-02 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(2)
-- Hardship without a Compensating Increase in Quality and Safety --
References:
ASME Section XI, Tables IWD-2500-1 and IWD-5220 Examination Category: D-B, All Pressure Retaining Components Items Number: D2.10
Description:
Millstone Power Station Unit 3 (MPS3) "B" train, 30" Service Water System (SWS) supply piping located in the intake structure bays. The piping material is SB-127 (Monel).
Components: The applicable piping line number is identified as 3-SWP-030-3-3 [Reference Piping & Instrumentation Drawing (P&ID) 25212-26933, Sheet 1].
Note: Excerpts from P&ID 25212-26933, Sheet 1 and Piping Isometric Drawing 25212-21041, Sheet 9 are provided for information only, with the subject piping clouded for identification.
2. Applicable Code Edition and Addenda
ASME Section XI, 2013 Edition [Reference 8.1]
3. Applicable Code Requirements
The 2013 Edition of American Society of Mechanical Engineers (ASME)Section XI, Tables IWD-2500-1, Examination Category D-B, and IWD-5220 require, for Class 3 piping, a VT-2 visual examination be performed during a system leakage test conducted at the press_ure obtained while the system is in-service performing its normal operating function or at the system pressure developed during a test conducted to verify system operability. The system leakage test is required to be performed once each inspection period.
Serial No.20-391 Docket No. 50-423 Attachment 2, Page 2 of 8
4. Reason for Request
Dominion Energy Nuclear Connecticut, Inc. (DENC) requests approval of alternative methods for performing the VT-2 visual examination, as required by ASME Section XI, Tables IWD-2500-1 and IWD-5220, for the piping segment of the MPS3 SWS located in the confined space of the intake structure bays. The performance of the Code-required VT-2 visual examinations for the piping segment is considered a hardship with respect to both personnel and plant safety. This determination is based on the following factors and considerations.
The subject piping of this request is the common "B" train SWS header piping which is part of the 3-SWP-030-3-3 piping line that runs vertically through the floor of the "B" SWS pump cubicle for a distance of 11 feet. It then travels horizontally through five intake bays at the top of the bays for a distance of approximately 88 feet in this normally inaccessible area until it enters and then passes through the accessible area of the intake structure chlorine room. The portion of the piping inside the chlorine room is accessible for examination from the outside diameter and is not part of this request because the required VT-2 examination of this portion of the piping line can be performed without restriction. The piping then becomes inaccessible again as it leaves the intake structure chlorine room and continues underground to the auxiliary building where the examination requirements of ASME Section XI, IWA-5244(b)(2) apply.
There is no coating or lining on the inside or outside surface of the "B" SWS header piping. The material is SB-127 (Mone!) which is a highly corrosion resistant material and well suited for the environment inside the intake structure and bays. There are no bolted joints or valves in this piping section.
No repairs or upgrades to this piping section have been performed and the service history of this piping has shown no significant degradation. In the early 1990s, minor internal pitting was observed due to mussel growth issues which were resolved during that timeframe. The pitting has not progressed any further since that time.
The nominal wall thickness of the subject piping is 0.375 inches.
- The normal operating pressure is 44 pounds per square inch gauge (psig). The normal operating temperature range is 33°F to 80°F.
Visual examination of this piping requires entry into each of the five intake structure bays. There is limited access to each bay from an access hatch located in the intake structure floor. Personnel entry into the confined space of the intake structure bays with equipment operational is considered a personnel safety hazard; therefore, equipment is required to be removed from service and tagged-out prior to entry.
Serial No.20-391 Docket No. 50-423 Attachment 2, Page 3 of 8 Additionally, due to the physical configuration of the intake structure, each of the five bays requires draining to erect the scaffolding needed to access these bays to perform the visual examination of the piping. There are small platforms located at the base of the intake bay access ladders, but they are not sufficient to adequately perform the examination without the erection of scaffolding. This scaffolding has to be erected in each bay to conduct this examination, in order to provide the examiner with a safe means to closely access the piping. Erecting the scaffolding is difficult because of safety risks associated with moving personnel and materials into the confined space of the bay areas. Due to the physical arrangement of the intake structure, the scaffolding in each bay has to be erected from the floor of the bay up to the subject piping, which requires each bay to be completely isolated and drained.
Draining the bays also requires equipment to be taken out of service, since operating with the bays drained could damage the SWS pumps. Unavailability of safety-related SWS pumps puts MPS3 at a greater operational risk since it removes the redundancy of available equipment, introducing a reduction in the safety margin of the plant.
The required VT-2 visual examinations would continue to be performed on the remaining accessible portions of piping line 3-SWP-030-3-3 not covered by this alternative request, when conducting the system leakage test in accordance with ASME Section XI, IWD-5000 and IWA-5244(b)(2) for buried components within this piping line.
Therefore, placing the plant in a condition where the safety-related SWS is out of service for an extended period results in increased operational risk, and performing the VT-2 visual examinations on the subject piping requires activities that present safety hazards to plant personnel. Thus, compliance with the specified requirements is considered a hardship without a compensating increase in the level of quality and safety.
5. Proposed Alternative and Basis for Use
5.1 Proposed Alternative Pursuant to 110 CFR 50.55a(z)(2), DENC proposes to use, as a'n alternative to the requirements\ of IWD-5220, a verification of unimpaired flow with an additional internal visual inspection to be performed every other refueling outage. Periodic flow testing will be performed in accordance with lnservice Test (1ST) program (Reference 8.2) surveillance procedures. These surveillance procedures require flow to be measured, recorded and compared to established acceptance criteria to provide the assurance that flow is not impaired during operation. The parameters of the flow test are described in Section 5.2.
Serial No.20-391 Docket No. 50-423 Attachment 2, Page 4 of 8 This proposed alternative utilizes the quarterly SWS flow testing to detect any significant through-wall leakage if present in the applicable piping segments in line 3-SWP-030-3-3. In combination, the periodic internal visual ins'pection of the line 3-SWP-030-3-3 segments would be performed every other refueling outage, using a robotic crawler unit fitted with a high-resolution pan and tilt camera (or equivalent). If any identified conditions such as erosion, corrosion, microfouling, biofouling, or other degraded piping material conditions are identified, they will be evaluated by Engineering for acceptance or corrective actions, as necessary. Therefore, performance of the VT-2 visual examination during the system leakage test on the piping segments that are considered to be inaccessible, does not provide a compensating increase in the level of quality and safety when compared to performing the proposed unimpaired flow test and internal visual examination of this piping.
The required VT-2 visual examinations would continue to be performed on the remaining accessible portions of piping line 3-SWP-030-3-3 not covered by this alternative request, when conducting the system leakage test in accordance with ASME Section XI, IWD-5000 and IWA-5244(b)(2) for buried components within this piping line.
The proposed alternative consists of an unimpaired flow test and an internal visual inspection of the subject piping that will be used in lieu of the Code-required VT-2 visual examination for this inaccessible piping.
5.2 Basis for Use Flow Testing: Flow testing of the four MPS3 SWS pumps is performed quarterly and uses an established minimum flow rate specified in the 1ST procedures as the acceptance criteria for the pressure testing of the subject SWS pipe segments of this request. The flow rate for each pump is currently specified as 8910 gallons per minute (gpm). This flow testing is performed in conjunction with quarterly testing of the service water pumps. The flow testing is performed by throttling flow through one of the two heat exchangers to obtain the reference flow conditions of 891 0 to 9180 gpm. Total flow is measured based on the sum of several branch line flow indicators (depending on which heat exchangers are in service). Flow is throttled until the* reference conditions are reached and then stabilized for two minutes. Flow and pump discharge pressure are recorded. Suction pressure is calculated based on water height in the pump bay. Pressure is measured at the pump discharge. A total flow indicator is not installed. Flow rates measured in the individual downstream branch lines are summed to determine the total flow. Because flow is throttled to a repeatable reference value, a specific leak rate is not available. If the flow rate cannot be achieved or the associated differential pressure at reference conditions is not achieved, the pump test would be considered unsatisfactory. The Corrective Action Program (CAP) would be used to determine the cause of the deviation. The minimum acceptable flow rate is 8910 gp*m.
Serial No.20-391 Docket No. 50-423 Attachment 2, Page 5 of 8 During the 1ST surveillances, if the minimum flow rates cannot be achieved, a condition report would be initiated in accordance with the CAP. Investigation to determine the cause of the flow reduction would be identified as part of the CAP resolution plan. Additional corrective actions such as maintenance of the pump and system walkdowns, etc. would be initiated, as necessary, to restore the pump and/or system to operable status. Leakage identified during system walkdowns of accessible piping and components not covered in this request would be evaluated and repaired, as necessary. If during the investigation, it is suspected that there may be leakage occurring from the subject piping addressed by this request, the necessary actions would be taken to gain access to this normally inaccessible piping for visual inspection, as necessary. It should be noted that the most recent flow testing results have not identified an increasing trend for leakage in the inaccessible piping.
For normal operation, there are no indication alarms in the control room to monitor for reduced flow. However, during normal operation the total service water header flow indication for each train is available in real-time from the plant process computer in the control room. Additionally, the intake structure is walked down once per shift during plant equipment operator rounds. Any significant leakage in the inaccessible piping would likely be audible to the operators during these rounds Internal Visual Inspection: Internal visual inspection is performed on the subject piping periodically during plant refueling outages to ensure the piping is not experiencing unacceptable degradation. The internal visual inspection is performed on an alternating basis each refueling outage for each train using a robotic crawler unit fitted with a high-resolution pan and tilt camera (or equivalent). Therefore, the "B" train is inspected at a frequency of approximately 3 years. If any identified conditions such as erosion, corrosion, microfouling, biofouling, or other degraded piping material conditions are identified, they will be evaluated by Engineering for acceptance or corrective actions, as necessary. Inspections performed over the last two MPS3 refueling outages identified no unsatisfactory conditions.
Based on the history of the internal visual inspection results, the inspection frequency has been determined to be adequate to ensure structural integrity of the subject piping. The internal inspection frequency is consistent with the frequency which would be required for the ASME Code leakage test.
Therefore, performance of the VT-2 visual examination during the system leakage test on the inaccessible portion of the 'B" service water piping discussed in this request does not provide a compensating increase in the level of quality and safety when compared to performing the proposed unimpaired flow test and internal visual inspection of this piping.
As noted above, the benefit accrued in performing the specified VT-2 examination is not deemed commensurate with the hardship, personnel hazards, and operational risk in taking safety-related equipment out of service and preparing each of the five
Serial No.20-391 Docket No. 50-423 Attachment 2, Page 6 of 8 bays for personnel to conduct the VT-2 visual examination. Based on the use of 1ST to verify flow through the subject piping is unimpaired, in conjunction with periodic internal visual inspections, this alternative provides reasonable assurance of operational readiness and continued structural integrity.
6. Duration of Proposed Alternative
This alternative is requested for the duration of MPS3's fourth ten-year ISi interval, which began on February 23, 2019, and ends on February 22, 2029.
- 7. Precedent A similar request for the MPS3 third ten-year ISi interval was approved by the NRC on January 23, 2013 (ADAMS Accession Number No. ML13011A158).
- 8. References
- 1. ASME Boiler and Pressure Vessel Code,Section XI, Rules for lnservice Inspection of Nuclear Power Plant Components, 2013 Edition.
- 2. DENC Letter 18-001, "Millstone Power Station Units 2 and 3, In-Service Testing Program for Pumps, Valves, and Snubbers, Fifth and Fourth 10-Year Interval Updates for Units 2 and 3," dated March 1, 2018 (ADAMS Accession No. ML18066A078)
Serial No.20-391 Docket No. 50-423 Attachment 2, Page 7 of 8 I
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