L-2024-106, Fifth and Sixth 10-Year Inservice Testing Interval Relief Request No. VR-02
| ML24225A100 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 08/12/2024 |
| From: | Rasmus P Florida Power & Light Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-2024-106 | |
| Download: ML24225A100 (1) | |
Text
l=PL.
U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington D C 20555-0001 RE:
Turkey Point Nuclear Plant, Unit 3 and 4 Docket Nos. 50-250 and 50-251 Subsequent Renewed Facility Operating Licenses DPR-31 and DPR-41 Fifth and Sixth 10-Year lnservice Testing Interval Relief Request No. VR-02 August 12, 2024 L-2024-106 10 CFR 50.55a Pursuant to 10 CFR 50.55a(z)(1 ), Florida Power & Light Company (FPL) requests approval of an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Operation and Maintenance of Nuclear Power Plants (ASME OM Code), for Turkey Point Nuclear Units 3 and 4 (Turkey Point). Specifically, FPL requests for the Turkey Point motor-operated isolation valves, MOV-864NB, located on the Refueling Water Storage Tank (RWST) outlet lines, and the motor-operated isolation valves, MOV-856NB, located on the RWST return lines, relief from the biennial leakage test requirement of ASME OM Code, Section ISTC-3630, on the basis that the proposed alternative would provide an acceptable level of quality and safety. FPL requests that the proposed alternative apply for the remainder of the Turkey Point 5th 10-Year lnservice Test (1ST) Interval, and for the duration of the Turkey Point 5th 10-Year 1ST Interval, which begins February 22, 2025 for Unit 3 and April 15, 2025 for Unit 4.
The enclosure to this letter provides FPL's evaluation of the proposed change. Because the subject valves were recently recategorized as Section ISTC-3630, Category A, approval is requested within the current biennial leakage test surveillance period which, with consideration for 25% grace, expires in June 2025.
This letter contains no new or modified regulatory commitments.
Should you have any questions regarding this submittal, please contact Mr. Kenneth Mack, Senior Manager, Licensing and Regulatory Compliance, at 561-904-3635.
Sincerely, General Manager, Regulatory Compliance Florida Power & Light Company cc:
USNRC Regional Administrator, Region II USN RC Project Manager, Turkey Point Nuclear Generating Station USN RC Senior Resident Inspector, Turkey Point Nuclear Generating Station Mr. Clark Eldredge, Florida Department of Health
Enclosure:
Florida Power & Light Company 9760 SW 344th Street, Homestead, FL 33035
Turkey Point Nuclear Plant Docket Nos. 50-250 and 50-251 Turkey Point Units 3 and 4 Fifth and Sixth 10-Year lnservice Testing Interval Relief Request Number VR-02 L-2024-106 Enclosure Page 1 of 5
- 1.
American Society of Mechanical Engineers (ASME) Code Components Affected ASME ISTC-1300 Valve Number Description Code Class Category MOV-3-856A HHS! Pump Recirculation to RWST Motor Operated 2
A Isolation Valve MOV-3-856B HHS! Pump Recirculation to RWST Motor Operated 2
A Isolation Valve MOV-3-864A RWST Motor Operated Suction Isolation Valve to 2
A HHS! & RHR Pumps MOV-3-864B RWST Motor Operated Suction Isolation Valve to 2
A HHS! & RHR Pumps MOV-4-856A HHSI Pump Recirculation to RWST Motor Operated 2
A Isolation Valve MOV-4-856B HHS! Pump Recirculation to RWST Motor Operated 2
A Isolation Valve MOV-4-864A RWST Motor Operated Suction Isolation Valve to 2
A HHS! & RHR Pumps MOV-4-864B RWST Motor Operated Suction Isolation Valve to 2
- 2.
Applicable Code Edition and Addenda
Turkey Point Applicable ASME OM Code Unit 3 Unit4 1ST Program Edition / Addenda Effective Date Effective Date 5th 10-Year Interval 2004 Edition through 02/22/2015 04/15/2015 2006 Addenda 5th 10-Year Interval 2020 Edition 02/22/2025 04/15/2025 and no Addenda
- 3.
Applicable Code Requirement
Subsection ISTC-1300, Valve Categories, specifies that valves within the scope of the Subsection shall be placed in one or more... categories.
Paragraph (a) of Subsection ISTC-1300 establishes as Category A, valves for which seat leakage is limited to a specific maximum amount in the closed position for fulfillment of their required function(s).
Paragraph (b) of Subsection ISTC-1300 establishes as Category B, valves for which seat leakage in the closed position is inconsequential for fulfillment of the required function(s).
Subsection ISTC-3630, Leakage Rate for Other Than Containment Isolation Valves, specifies that Category A valves with a leakage requirement not based on an Owner's 10 CFR 50, Appendix J program, shall be tested to verify their seat leakages within acceptable limits.
Turkey Point Nuclear Plant Docket Nos. 50-250 and 50-251 L-2024-106 Enclosure Page 2 of 5 Paragraph (a) of Subsection ISTC-3630 establishes a leakage test frequency of at least once every 2 years.
- 4.
Reason for Request
Turkey Point motor-operated valves (MOV) MOV-856A/B, and MOV-864A/B, function in the open position to provide unimpaired flow to and from their respective Refueling Water Storage Tanks (RWSTs) during normal and emergency operating conditions. As can be seen from the Unit 3 drawing below, valves MOV-3-856A and MOV-3-856B are 2-inch globe valves installed in series to isolate the high-head safety injection (HHSI) pump recirculation flow path back to their associated RWST. Valves MOV-3-864A and MOV-3-864B are 16-inch double-disk gate valves installed in series to isolate the HHSI, residual heat removal (RHR) and containment spray (CS) pump suction lines from their associated RWST. The same design and orientation applies to Unit 4 valves MOV-4-856A and MOV-4-856B, and to MOV-4-864A and MOV-4-864B.
.tFlllJlCW,l!Jl
$TC<<AC£ T>IIX UNT l IIlil In Reference 3, Turkey Point adopted the Alternative Source Term (AST) which required reanalysis of the large-break loss-of-coolant accident (LOCA) and an accounting for radioactive fluid back leakage to the RWST during the post-LOCA recirculation cooling alignment of the emergency core cooling system (ECCS) potentially releasing to the environment through the RWST tank atmospheric vent.
Prior to 2011, the Turkey Point LOCA analyses did not model the RWST as a radiological release pathway. The revised LOCA radiological consequences analysis for the AST assumed a back leakage rate of 0.1 gallons per hour (gph), based on the allowable dose contribution from the RWST atmospheric vent, to maintain the overall dosage below the regulatory limit.
In Reference 4, FPL obtained authorization to maintain the containment purge supply and exhaust isolation valves administratively closed and deactivated during MODES 1 through 4. This change prompted a revision to the LOCA radiological consequences analysis which applies the allowable dosage previously attributed to the containment purge penetrations to the RWST vent pathway resulting in an increased allowable back leakage rate of 1.7 gph. To assure RWST back leakage remains below the value assumed in the LOCA radiological consequences analysis, 50% of 1.7 gph, or 0.85 gph, would be the combined allowable leakage from MOV-856A/B and MOV-864A/B. Noteworthy is that the radiological analysis conservatively assumes that the back leakage will reach the RWST instantaneously, though realistically the leak rate and piping lengths prevent this from occurring in the first 30 days of the event.
MOV-856A/B, and MOV-864A/B were recently re-categorized as Category A of Subsection ISTC-1300, requiring seat leakage testing every two years, in response to the regulatory findings described in Reference 1. Turkey Point construction predated Information Notice (IN) 91-56 (Reference 2) whereby similarly located valves were determined to have a safety function in the closed position with respect to control room and offsite dose limits to prevent containment sump water back leakage to the RWST.
As a result, the systems in which the valves reside were not designed to accommodate seat leakage testing. More specifically, localized system isolation valves and test connections are not available to facilitate leakage testing in a manner compliant with the leakage test measurement requirements of
Turkey Point Nuclear Plant Docket Nos. 50-250 and 50-251 L-2024-106 Enclosure Page 3 of 5 Subsection ISTC-3630, Paragraph {c), or by reverse leakage testing similar to the referenced precedent in Section 4.0 of this evaluation. Establishing a leakage test boundary for MOV-856NB using the system as presently designed would require aligning eight boundary valves to provide a test pressure barrier. Establishing a test boundary for valves MOV-864NB using the system as presently designed would require aligning ten boundary valves to provide the test pressure barrier. If attempted online, these valve alignments would render large portions of the ECCS inoperable for periods that would challenge the allowable Technical Specification completion times (CTs), potentially requiring operations support center coverage around the clock and increasing online risk without a corresponding increase in safety.
During shutdowns, the required alignments could potentially delay fuel movement and planned maintenance requiring system drainage, scheduled system outages, etc. Moreover, the large test volume that would result from the boundary valve alignments would yield unreliable test results due to voids and external leakage from within the boundary and the cumulative leakage that would result from non-Category A valves comprising the boundary. As such, application of the test volume pressure decay or makeup methods of ISTC-3630, Paragraph (c) would not validate MOV-856NB and MOV-864NB leak tightness without additional and otherwise unnecessary repairs.
Installing the necessary localized isolation valves and test connections to accommodate seat leakage testing compliant with Subsection ISTC-3630, Paragraph (c), would require modifications to safety-related piping in accordance with the applicable construction code of record. Specifically, two new isolation valves and appropriate test connections must be installed to accommodate leakage testing for the MOV-856A, B globe valves. For the MOV-864A, B gate valves, safety-related test connections must be installed on each to pressurize and test between the double-disks. These modifications would require significant engineering and maintenance resources to facilitate cutting and welding into a safety system, procuring qualified isolation valves, test connections, and piping supports, as well as updating applicable stress analyses. Moreover, these additions would have to be maintained for the life of the plant, thereby diverting valuable resources from more safety significant activities. The benefits of these plant modifications must be weighed against the low likelihood of RWST back leakage during the first 30 days of an event and the operational measures that would be undertaken in such times to preclude the back leakage from occurring. In lieu of these equipment modifications, FPL believes the proposed alternative described below would provide an acceptable level of quality and safety.
- 5.
Proposed Alternative and Basis for Use As stated above, the current LOCA radiological consequences analysis assumes a back leakage rate of 1. 7 gph based on the allowable dose contribution from the RWST vent pathway to maintain the overall LOCA dose below the applicable regulatory limit. Due to physical limitations in system design which prevent leakage testing in accordance with Subsection ISTC-3630, FPL proposes as an alternative, inspection of the valve seating surface every three refueling outages via performance of a disk-to-seating surface blue check. Blue checks assure valve seating surfaces are free of scratches and defects that can contribute to leakage. The proposed alternative would tentatively begin the next scheduled Unit 3 outage in Spring 2026 and Unit 4 outage in Spring 2025 such that each of the subject valves would undergo at least one disk-to-seating surface inspection within three refueling outages.
Unsatisfactory blue check results would warrant seating surface repairs before returning the valves to operability and potentially subject the valves to more frequent inspections in accordance with the Turkey Point Equipment Reliability Program. The valves are unlikely to experience consequential deterioration of their associated seating surfaces during the six years that would elapse between the inspections since they are seldomly positioned in the closed direction except to accommodate motor operator diagnostic testing and otherwise to establish clearance boundaries for unrelated maintenance repairs.
No failures have occurred during inservice stroke testing or position indication testing or Generic Letter 89-10/96-05 Motor Operated Valve Program diagnostic testing in the previous ten years on the subject valves. Accordingly, FPL believes the proposed alternative would provide a commensurate level of quality and safety when compared to the seat leakage testing requirements of Subsection ISTC-3630.
Turkey Point Nuclear Plant Docket Nos. 50-250 and 50-251 L-2024-106 Enclosure Page 4 of 5 In addition to the proposed alternative, and to further assure the combined seat leakage from MOV-856NB, and MOV-864NB remains below the analytical back leakage rate assumed in the safety analysis, FPL has confirmed adequate seating force on the associated motor operators. Specifically, Seat leakage for the MOV-856A/B pathway has been minimized by increasing the disk seating force provided by the motor-operators to meet the seating force requirements for a Class V isolation/seal, which is the most stringent requirement for globe valves. ANSI/FCI 70-2-2006 (Reference 5) defines a Class V leakage rate as 0.0005 milliliter per minute (ml/min) of water per inch of port diameter per pounds-per-square-inch differential (psid). The results tabulated below assuming maximum differential pressure (L'i.Pmax) conditions yield an order of magnitude lower than the 1.7 gph RWST leakage pathway assumed in the Turkey Point LOCA dose analysis.
Valve No.
L'i.Pmax (psi)
Class V Leak Rate (gph)
MOV-3-856A 1865 0.031 MOV-3-856B 1801 0.030 MOV-4-856A 1490 0.025 MOV-4-856B 1658 0.027 Seat leakage across MOV-864NB is also maintained very low by controlling performance parameters for the motor-operator to assure a tight disk-to-seat seal. The Turkey Point MOV Program establishes performance requirements for the MOV-864NB operators such that when closed, sufficient seating thrust is provided with margin to wedge the disk into the seat and prevent system pressure from unseating the valve (i.e., hard seated). The motor operator closes against a 4.0 psi differential pressure and retains leak tightness against a differential pressure of 194 psid.
The double-disk design comprises two sealing surfaces (upstream and downstream disk faces),
both designed to provide shutoff flow, though only one is needed for leakage integrity. The seating surface consists of a wedge assembly designed to impart sufficient thrust to each disk to maintain acceptably low-pressure seat leakage. As the differential pressure across the disks increase, the seating load increases to maintain a leak tight boundary through the entire range of operating pressures. Since the disks are completely independent of each other and the design is essentially symmetrical, zero leakage can be maintained in either flow direction.
In addition to the proposed alternative to conduct inspections of the valve seating surface every three refueling outages via performance of a disk-to-seating surface blue check, and perform repairs as warranted, these additional, programmatic controls further assure cumulative leakage across MOV-856A, B and MOV-864A, B will not exceed the leakage quantities assumed in the safety analyses.
- 6.
Duration of Proposed Alternative FPL requests that the proposed alternative apply for the remainder of the Turkey Point 5th 10-Year lnservice Test (1ST) Interval, and for the duration of the Turkey Point 5th 10-Year 1ST Interval, which begins February 22, 2025 for Unit 3 and April 15, 2025 for Unit 4.
- 7.
Precedents
- 1.
USNRC letter to Constellation Energy Generation LLC,dated February 1, 2023, R. E. Ginna Nuclear Power Plant-Proposed Alternative to the Requirements Associated with lnservice Testing of Refueling Water Storage Tank Outlet Valve (EPID L-2022-LLR-0044) (ADAMS Accession No. ML2301 OA011)
Turkey Point Nuclear Plant Docket Nos. 50-250 and 50-251
- 8.
References:
L-2024-106 Enclosure Page 5 of 5
- 1.
USNRC letter to Florida Power & Light Company dated December 20, 2022, Turkey Point Units 3
& 4 - Design Basis Assurance Inspection (Programs) Inspection Report 05000250/2022011 and 05000251/2022011 (ADAMS Accession No. ML22353A077)
- 2.
USNRC Information Notice (IN) 91-56, Potential Radioactive Leakage to Tank Vented to Atmosphere, September 19, 1991 (ADAMS Accession No. ML031190264)
- 3.
USN RC letter to Florida Power & Light Company dated June 23, 2011, Turkey Point Units 3 and 4
- Issuance of Amendments Regarding Alternative Source Term (TAC Nos. ME1624 and ME1625)
(ADAMS Accession No. ML110800666)
- 4.
USN RC letter to Florida Power & Light Company dated October 20, 2020, Turkey Point Units 3 and 4 - Issuance of Amendments Nos. 293 and 286 Regarding Containment Atmospheric Radioactivity Ventilation Isolation and Leakage Detection System (EPI D L-2019-LLA-0240) (L-2019-192)
(ADAMS Accession No. ML20237F385)
- 5.
American National Standards Institute and Fluid Controls Institute (ANSI/FCI) 70-2-2006, Control valve seat leakage.