ML22258A302
| ML22258A302 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/15/2022 |
| From: | James Holloway Dominion Energy Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NRA/SS RO, Serial No.22-256 | |
| Download: ML22258A302 (13) | |
Text
Dominion Energy Nuclear Connecticut, Inc.
~ Dominion 5000 Dominion Boulevard, Glen Allen, VA 23060 DominionEnergy.com
=--' Energy 0 September 15, 2022 U.S. Nuclear Regulatory Commission Serial No.22-256 Attention: Document Control Desk NRA/SS RO Washington, DC 20555 Docket No. 50-423 License No. NPF-49 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 PROPOSED REQUEST FOR ALTERNATIVE PUMP PERIODIC VERIFICATION TESTING PROGRAM FOR CONTAINMENT RECIRCULATION SPRAY SYSTEM PUMPS In accordance with 10 CFR 50.55a(z)(1 ), Dominion Energy Nuclear Connecticut, Inc.
(DENC) hereby requests Nuclear Regulatory Commission (NRC) approval of a proposed alternative for the Containment Recirculation Spray System (RSS) Pumps at Millstone Power Station Unit 3 (MPS3). Specifically, DENC proposes an alternative to the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants Code (OM Code), Mandatory Appendix V requirement to perform pump periodic verification (PPV) testing for applicable pumps at their highest design basis accident flow rate. In lieu of this requirement, DENC proposes a testing program that requires PPV testing to be performed at the highest design basis accident flow rate for two RSS pumps in one train, and at reduced flow rate (using pump recirc lines) for the two RSS pumps in the opposite train during each 24-month interval. The testing flow requirements will be alternated for the trains during subsequent intervals to ensure that all four RSS pumps are periodically tested at their design basis accident flow rate.
This request, which is being submitted on the basis that the proposed alternative provides an acceptable level of quality and safety, is provided in the attachment to this letter. The duration of the proposed alternative is requested for the remainder of MPS3's fourth 10-year inservice testing interval which ends on December 1, 2028.
NRC review and approval of the proposed alternative request is requested by September 30, 2023, to support the upcoming refueling outage scheduled to occur during the fall of 2023.
Serial No.22-256 Docket No. 50-423 Page 2 of 2 If you have any questions or require additional information, please contact Shayan Sinha at (804) 273-4687.
Sincerely, James E. Holloway Vice President - Nuclear Engineering & Fleet Support
Attachment:
Proposed Request for Alternative Pump Periodic Verification Testing Program for Containment Recirculation Spray System Pumps Commitments made in this letter: None cc:
U.S. Nuclear Regulatory Commission Region I 475 Allendale Road, Suite 102 King of Prussia, PA 19406-1415 Mr. Richard V. Guzman NRC Senior Project Manager - Millstone 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.22-256 Docket No. 50-423 ATTACHMENT PROPOSED REQUEST FOR ALTERNATIVE PUMP PERIODIC VERIFICATION TESTING PROGRAM FOR CONTAINMENT RECIRCULATION SPRAY SYSTEM PUMPS MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
Serial No.22-256 Docket No. 50-423 Attachment, Page 1 of 10 Pump Alternative Request Number P-07 Millstone Power Station Unit 3 Proposed Request for Alternative Pump Periodic Verification Testing Program for Containment Recirculation Spray System Pumps In accordance with 10 CFR 50.55a(z)(1)
Alternative Provides an Acceptable Level of Quality and Safety Dominion Energy Nuclear Connecticut, Inc. (DENC) proposes an alternative to certain requirements of American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants Code (OM Code), Mandatory Appendix V for Millstone Power Station Unit 3 (MPS3). Specifically, DENC proposes a testing program that requires pump periodic verification (PPV) testing to be performed at the highest design basis accident flow rate for two Containment Recirculation Spray System (RSS) pumps in one train, and at reduced flow rate (using pump recirc lines) for the two RSS pumps in the opposite train during the 24-month interval. The testing flow requirements will be alternated for the trains during subsequent intervals to ensure that all four RSS pumps are periodically tested at their design basis accident flow rate.
- 1) ASME Code Pump(s): 3RSS*P1A 3RSS*P1B 3RSS*P1C 3RSS*P1D System: Containment Recirculation Spray System Group: B Class: 2 Function: These pumps provide for containment structure depressurization during the recirculation mode for core heat removal. The pumps provide safety injection via the charging and safety injection pumps during recirculation.
- 2) Applicable Code Edition American Society of Mechanical Engineers Operation and Maintenance of Nuclear Power Plants, 2012 Edition, No Addenda.
Serial No.22-256 Docket No. 50-423 Attachment, Page 2 of 10
- 3) Applicable Code Requirement(s)
The requirements applicable to this request for relief in accordance with the requirements 10 CFR 55.55a include paragraph ISTB-1400 Part (d) which states that it is the responsibility of the Owner to establish "a pump periodic verification test program in accordance with Division 1, Mandatory Appendix V."
Mandatory Appendix V, V-3000 requires certain applicable pumps with specific design credited safety analysis (e.g., technical specifications, technical requirements program, or updated safety analysis report) to be included in this program, with testing performed at least once every 2 years. The MPS3 RSS pumps are included in the PPV program since all four pumps inject from the containment sump to the recirculation spray headers, for containment heat removal during a Loss of Coolant Accident (LOCA).
Mandatory Appendix V, V-2000 defines PPV as a test that verifies a pump can meet the required (differential or discharge) pressure as applicable, at its highest design basis accident flow rate.
- 4) Reason for Request System/Component Background The MPS3 RSS consists of two parallel redundant trains which feed two parallel 360-degree spray headers. Each train consists of two pumps and two heat exchangers.
The design of RSS is sufficiently independent so that an active failure in the recirculation spray mode, cold leg recirculation mode, or hot leg recirculation mode of the emergency core cooling system (ECCS) has no effect on its ability to perform its engineered safety function. In other words, the failure of one train does not affect the capability of the other train to perform its designated safety function of assuring adequate core cooling in the event of a design basis LOCA. As long as one train (or e of assuring core cooling and the other pump capable of removing heat from containment, the RSS system meets design requirements.
All four RSS pumps and motors are located outside the containment structure. The pumps are vertical deep well type, each mounted in a separate stainless steel well casing supported by the concrete containment structure mat. The pumps are located adjacent to the containment structure at an elevation sufficiently below the containment structure sump to ensure an adequate available net positive suction head (NPSH). Access to the motors for inspection and maintenance is provided.
The RSS pumps are started automatically on a refueling water storage tank (RWST)
Low-Low Level signal coincident with a containment depressurization actuation (CDA) signal. Each RSS pump has a design flow of approximately 3,950 gpm. An orifice is
Serial No.22-256 Docket No. 50-423 Attachment, Page 3 of 10 installed on the discharge of each pump. The orifice has been designed to limit pump flow to a maximum of 3,000 gpm. This maximum flow is based on avoidance of suction line flashing and RSS heat exchanger baffle plate load limitations.
recirc lines for RSS pumps P1A & P1B were included because these pumps could be subjected to deadhead conditions during the switchover from the injection phase to the recirculation phase. These recirc lines were installed with orifices to help perform SS pumps P1C & P1D are not subject to deadhead because they are dedicated to providing flow to the spray headers, but recirc lines (without orifices) for these pumps were included to perform flow testing at power, per previously applicable IST requirements.
PPV Background The vertical line shaft pump high flow test is identified as a variable flow system test.
For surveillance testing the flow is set between 2475 gpm and 2550 gpm, which exceeds the assumed design basis accident flow rate of 2144 gpm. Performing PPV testing of the RSS pumps in this flow range, requires aligning the pumps to the RWST through piping in the residual heat removal RSS pumps (3RSS*P1A & 3RSS*P1C) are aligned to the RWST by opening motor-operated RHR train cross-tie valve 3RHS*MV8716A and manual valve 3RHS*V43, B & 3RSS*P1D) are aligned by opening motor-operated RHR train cross-tie valve 3RHS*MV8716B and manual valve 3RHS*V43.
of RSS is interconnected to pump 3RHS*P1B). When RSS pump PPV testing is performed, the motor-operated discharge valve to the reactor coolant system (RCS) cold leg (3SIL*MV8809A or B) for the interconnected RHR pump must be closed. Thus, the RHR pump in the train associated with the tested RSS pump is unavailable. The motor-operated RHR train cross-tie valve in the train not being tested (3RHS*MV8716A or 3RHS*MV8716B) is closed to allow the associated RHR pump to supply flow to two RCS cold legs without diversion to the RWST, but the other two RCS cold legs cannot be supplied.
In modes 1 through 4, an RHR pump that only delivers flow to two RCS cold legs is considered inoperable per MPS3 Technical Specifications (TS) 3.5.2/3.5.3, since a rupture is postulated in one of the two RCS cold legs. As a result, performing the test in this configuration in modes 1-4 would violate existing TS 3.5.2/3.5.3 requirements by making both RHR pumps inoperable, which would mandate a unit shutdown in accordance with Limiting Condition for Operation (LCO) 3.0.3. The installed pump recirc lines cannot be used to meet the testing requirements of the ASME OM Code, because the required PPV test flow rate cannot be achieved.
Serial No.22-256 Docket No. 50-423 Attachment, Page 4 of 10 Reason for Proposed Alternative To comply with the applicable ASME OM Code and TS requirements, all four RSS pumps are currently tested each refueling outage (RFO). However, performing this testing during RFO shutdown modes can present challenges for MPS3 due to the RSS/RHR shared piping configuration. The MPS3 General Operating Procedure for Conducting Outages requires maintaining at least one protected train of plant safety-related components throughout the outage. One RHR pump is specifically required to be available during modes 5 and 6 due to th which influences the sequencing of RSS pump testing. RSS pump testing is also a competing priority with work on RHR trains and/or its support systems (such as component cooling water, service water, and electrical buses) in modes 5 and 6 or when the unit is defueled (mode 0). These considerations, combined with protected train windows, can cause RSS pump testing activities to be on or near outage critical path. The proposed alternative would support elimination of a safety train swap in the timeframe between the two reduced RCS inventory windows (i.e., before fuel offload and after fuel onload) in a baseline MPS3 RFO. This would essentially allow one train of RHR to remain dedicated for decay heat removal during this timeframe. The alternative testing program proposed by DENC would be beneficial for RFO planning and improve RHR availability, while continuing to provide adequate indication of RSS pump performance.
- 5) Proposed Alternative and Basis for Use Proposed Alternative In lieu of the requirements of Mandatory Appendix V (V-2000), DENC proposes an alternative PPV testing program for the MPS3 RSS pumps, as defined below:
All four RSS pumps shall be tested every 24 months, where two pumps in one train are tested at the highest design basis accident flow rate and the two pumps in the opposite train are tested at a reduced flow rate (using pump recirc lines) AND The two pumps tested at reduced flow in a given 24-month interval shall be tested at the highest design basis accident flow in the subsequent 24-month interval.
As an example, RSS pumps 1A and 1C are tested at the design basis accident flow rate, and RSS pumps 1B and 1D are tested at the reduced flow rate (using pump design basis accident flow rate, and RSS pumps 1A and 1C would be tested at the flow requirements for the trains during the subsequent 24-month intervals will ensure that all four RSS pumps are periodically tested at the design basis accident flow rate.
Serial No.22-256 Docket No. 50-423 Attachment, Page 5 of 10 Basis for Use Operating any of the four RSS pumps in recirc does not require aligning a return flow path to the RWST through RHR piping, and therefore does not affect RHR pump availability. A minimum flow rate of approximately 950 gpm for RSS pumps P1A &
P1B, and 1950 gpm for RSS pumps P1C & P1D can be achieved using the pump recirc lines. This equates to approximately 45% of the design basis accident flow rate for RSS pumps P1A & P1B, and approximately 90% of the design basis accident flow rate for RSS pumps P1C & P1D. These flow rates are sufficient to accommodate flow adjustment and maintain stable test flow conditions. Acceptable vibration levels will also be verified under the proposed alternative testing program, to satisfy MPS3 RSS pump comprehensive testing requirements per ASME OM Code ISTB-3430.
Testing at the design basis accident flow rate as a general practice is important for pumps with characteristic head-flow curves that are flat or gently sloping in the low flow region (little change in developed head with increasing flow). In the low flow region, increasing internal flows, usually due to wear, are difficult if not impossible to w flows should be tested at or near pump design flow to ascertain if increasing internal recirculation flows have degraded pump performance to the point where accident requirements cannot be met. This situation does not apply to the RSS pumps as the pump performance curves exhibit a relatively constant slope from no flow to design flow conditions (Figures 2 and 3). Testing at recirc flow rates will detect pump degradation because the pump curve is well sloped at this point on the curve. Also, the expected wear would be limited since the RSS pumps are typically only operated for testing purposes.
Testing over the last five RFOs has shown consistent performance for the four pumps with no signs of mechanical or hydraulic degradation, even when compared to the original vendor shop testing data. The MPS3 safety analysis basis assumes one train of RSS must be operable for the system to meet its design requirements. The proposed alternative continues to demonstrate performance capability for the pumps in one train at the design basis accident (PPV) flow during each 24-month interval.
The pumps in the other train not tested at the design basis accident flow rate under the proposed alternative will be tested at a flow rate that maintains the ability to detect potential degradation and failures.
If maintenance is performed on any of the RSS pumps while the proposed alternative is in effect, DENC will evaluate retesting requirements per the provisions of ASME OM Code, ISTB-3310. If required, a preservice test will be performed in accordance with ISTB-3100. At least one of the five required measurements for the preservice test will be taken at a flow rate that exceeds the design basis accident flow rate. If a preservice test is not required, either a Group A or comprehensive test run will be performed at reduced flow rate (using the pump recirc lines) or greater to assess whether the pump is operable.
Serial No.22-256 Docket No. 50-423 Attachment, Page 6 of 10 In addition to the requirements of ASME OM Code, the RSS pumps are included in the MPS3 Predictive Maintenance Program. This program currently employs predictive monitoring techniques such as:
Vibration spectrum analysis, Monitoring of motor electrical parameters, Periodic mechanical seal replacement, and Periodic motor oil replacement (the motors are the only pump components with oil lubricated bearings).
Preventive maintenance and performance monitoring efforts to date have been effective in maintaining RSS pump performance.
The review of past work orders for the RSS pumps over the last ten years did not identify any corrective repairs other than regular maintenance and minor oil leaks. One Condition Report was written in 2013 after a mechanical seal and O-ring inspection identified minor damage to the upper gland plate O-ring seating area for RSS pump P1B. The inspection concluded that the identified condition had no effect on the sealing capabilities of the shaft. Since being returned to service, the pump has not experienced any leakage or degradation of tested parameters. The shaft will be inspected again by no later than the spring 2025 RFO, as part of the MPS3 hanical seal and O-ring inspections.
RSS piping is drained when not in service to prevent corrosion. Inspections of the containment sump and RSS pump suction piping are also performed in accordance with MPS3 TS surveillance requirement (SR) 4.5.2.d.2. RSS pump suction piping internals and sump are inspected to ensure there is no evidence of structural distress, abnormal corrosion, or debris. The RSS pump suction inlet pipes are also inspected to ensure they are not restricted by debris. Operating the pumps for testing in either a full flow or recirc alignment will continue to ensure that the leak tightness of RSS piping (including pump suction and discharge) is periodically verified in accordance with MPS3 TS 6.8.4.a.
Conclusion The RSS system conditions, and limited usage of the RSS pumps help preserve the the successful past testing results.
Continued testing of the RSS pumps at either design basis accident flow rate or reduced flow rate on a 24 month interval will maintain the ability to detect potential degradation and failures. In addition to testing, the RSS pumps are also subject to predictive monitoring techniques. Therefore, the proposed alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1).
Serial No.22-256 Docket No. 50-423 Attachment, Page 7 of 10
- 6) Duration of Proposed Alternative This proposed alternative is requested for the remainder of the MPS3 fourth 10-year IST interval, which began on December 2, 2018, and will end on December 1, 2028.
- 7) Precedents A similar request for performing PPV at a reduced flow rate has been approved for Outside Recirculation Spray Pumps at North Anna Power Station Units 1 & 2 in Relief Request P-4 (ADAMS Accession No. ML20252A004).
Serial No.22-256 Docket No. 50-423 Attachment, Page 8 of 10 Figure 1: Simplified Diagram for MPS3 RSS/RHR Piping Interconnection
Serial No.22-256 Docket No. 50-423 Attachment, Page 9 of 10 MPS3 3RSS*P1A Shop Curve with IST Test Criteria 600 575 550 525 500 Total Developed Head (ft) 475 450 425 400 MPS3 3RSS*P1A 375 Shop Curve 350 DBA Flow 325 300 Recirc Test Flow 275 250 225 200 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Capacity (gpm)
MPS3 3RSS*P1B Shop Curve with IST Test Criteria 600 575 550 525 500 Total Developed Head (ft) 475 450 425 400 MPS3 3RSS*P1B 375 Shop Curve 350 DBA Flow 325 300 Recirc Test Flow 275 250 225 200 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Capacity (gpm)
Figure 2: MPS3 RSS Pump 1A/1B Curves
Serial No.22-256 Docket No. 50-423 Attachment, Page 10 of 10 MPS3 3RSS*P1C Shop Curve with IST Test Criteria 600 575 550 525 500 Total Developed Head (ft) 475 450 425 400 MPS3 3RSS*P1C 375 Shop Curve 350 DBA Flow 325 300 Recirc Test Flow 275 250 225 200 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Capacity (gpm)
MPS3 3RSS*P1D Shop Curve with IST Test Criteria 600 575 550 525 500 Total Developed Head (ft) 475 450 425 400 375 MPS3 3RSS*P1D 350 Shop Curve 325 DBA Flow 300 275 Recirc Test Flow 250 225 200 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Capacity (gpm)
Figure 3: MPS3 RSS Pump 1C/1D Curves