ML20023B378
| ML20023B378 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 02/19/2020 |
| From: | Undine Shoop Plant Licensing Branch II |
| To: | Moul D Florida Power & Light Co |
| Jordan N | |
| References | |
| EPID L-2019-LLR-0074 | |
| Download: ML20023B378 (10) | |
Text
February 19, 2020 Mr. Don Moul Vice President, Nuclear Division and Chief Nuclear Officer Florida Power & Light Company Mail Stop: NT3/JW 15430 Endeavor Drive Jupiter, FL 33478
SUBJECT:
ST. LUCIE PLANT, UNIT NO. 2 - SAFETY EVALUATION FOR RELIEF REQUEST RR-16, ALTERNATE REPAIR OF 2B BORIC ACID MAKEUP PUMP REVISION FOR THE FOURTH 10-YEAR INSERVICE INSPECTION INTERVAL (EPID L-2019-LLR-0074)
Dear Mr. Moul:
By letter dated August 9, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19221B307), Florida Power & Light Company (the licensee) submitted Relief Request RR-16 to request relief from certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, IWB-3142.3, at the St. Lucie, Unit 2 facility. Specifically, the licensee is proposing an alternative to allow continued operation with a degraded 2B boric acid makeup pump (BAMP) on the basis that complying with the ASME Code,Section XI would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The U.S. Nuclear Regulatory Commission (NRC or the Commission) staff reviewed the submittal and, as supported by the enclosed safety evaluation, concludes that granting relief pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(g)(6)(i) is authorized by law, will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Therefore, the NRC staff grants this relief request for the fourth 10-year inservice inspection interval at St. Lucie Plant, Unit No. 2.
D. Moul If you have any questions regarding this issue, please contact the project manager, Mr. Natreon Jordan, at (301) 415-7410 or by e-mail at Natreon.Jordan@nrc.gov.
Sincerely,
/RA/
Undine Shoop, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-389
Enclosure:
Safety Evaluation cc: Listserv
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST RR-16 FOURTH 10-YEAR INSERVICE INSPECTION INTERVAL FLORIDA POWER & LIGHT COMPANY ST. LUCIE PLANT, UNIT NO. 2 DOCKET NO. 50-389
1.0 INTRODUCTION
By letter dated August 9, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19221B307), Florida Power & Light Company (the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, IWB-3142.3, at the St. Lucie, Unit 2 facility.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee submitted Relief Request RR-16 proposing an alternative to allow continued operation with a degraded 2B boric acid makeup pump (BAMP) on the basis that complying with the ASME Code,Section XI would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
On August 9, 2019 (ADAMS Accession No. ML19221B674), the Nuclear Regulatory Commission (NRC or the Commission) staff verbally authorized the use of Relief Request RR-16 at St. Lucie, Unit 2. The NRC staff determined that the proposed alterative is technically justified and provides reasonable assurance of structural integrity of the affected 2B BAMP.
This safety evaluation documents the technical basis for the NRC's verbal authorization.
2.0 REGULATORY EVALUATION
The regulations at 10 CFR 50.55a(g)(4) require that, throughout the service life of a boiling or pressurized water-cooled nuclear power facility, components classified as ASME Code Class 1, 2, and 3 components meet the requirements, except the design and access provisions and preservice examination requirements, set forth in Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(a)(1)(ii), subject to the conditions listed in 10 CFR 50.55a(b)(2).
Pursuant to 10 CFR 50.55a(g)(5)(iii), a licensee may request relief from an ASME Code requirement if it determines that conformance with the requirement to be impractical at their facility. Additionally, pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee must notify the NRC and Enclosure
submit, as specified in 10 CFR 50.4, information to support the determination. Requests for relief made in accordance with 10 CFR 50.55a(g)(5)(iii), must be submitted no later than 12 months after the expiration of the initial or subsequent 10-year inspection interval.
Pursuant to 10 CFR 50.55a(g)(6)(i), the Commission will evaluate determinations of impracticality under 10 CFR 50.55a(g)(5). After its evaluation, the Commission may grant relief and may impose such alternative requirements as it determines are authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Based on the above and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request the relief and the staff to authorize it. The regulations at 10 CFR 50.55a(g)(4) state, in part, that ASME Code Class 1, 2, and 3 components will meet the requirements, except the design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI.
Paragraph 10 CFR 50.55a(z) states, in part, that [alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate: (1) Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.]
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request the use of an alternative and the NRC to grant relief and the use of the proposed alternative.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Components Affected
The affected component is the ASME Code Class 2, 2B BAMP, which is subject to the inservice inspections of ASME Code,Section XI, Table IWC-2500-1, Category C-H, Item C7.10. The 2B BAMP casing is made of type 316 cast austenitic stainless steel (CASS) and the material specification is ASME SA351 CF8M.
The 2B BAMP is one of two redundant pumps that support boron injection to the reactor coolant system (RCS). The availability of one BAMP is required to satisfy the Technical Specification, Section 3.5.2 requirement to provide for an emergency boration flow path through the charging pump to the RCS. During normal operation, the pump is run quarterly for a 15-minute in-service testing run to monitor pump performance, and weekly for a 30-minute run to support chemistry sampling.
3.2 Applicable Code Edition and Addenda The Code of Record for the St Lucie, Unit 2 fourth 10-year in-service inspection interval is the 2007 Edition through the 2008 Addenda of the ASME Code,Section XI, as modified by
10 CFR 50.55a. The fourth in-service inspection interval began on August 8, 2013 and ends on August 7, 2023.
3.3 Applicable Code Requirement ASME Code,Section XI, Subsection IWC, Subparagraph IWC-3113 states, in part, that a component with flaws that exceed the acceptance standards of Table IWC-3410-1 is acceptable for continued service if the component is corrected by a repair/replacement activity.
3.4 Reason for Request On August 6, 2019, the licensee performed a boric acid follow-up walkdown and found dry boric acid residue at a previously identified and programmatically tracked location on the St. Lucie, Unit 2 2B BAMP casing. Subsequently, the licensee performed a dye penetrant (PT) examination with inconclusive results. The licensee did not identify any indications; however, water weepage was observed through the developer in the area of the boric acid residue. To further investigate, the licensee ran the pump for one hour and observed a 1/32-inch diameter deposit of boric acid in the same area of the pump. The licensee declared the pump inoperable because of the through-wall leakage. The licensee also discovered similar indications on the St. Lucie, Unit 2 2A BAMP casing, which was simultaneously declared inoperable. These declarations resulted in entry of Action a.2 of Technical Specification, Section 3.5.2, which requires that with one Emergency Core Cooling System (ECCS) subsystem inoperable, the licensee needs to restore the inoperable subsystem to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or in accordance with the Risk Informed Completion Time Program, or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
The licensee stated that subsequent visual examination at 10X magnification of the 2B BAMP casing characterized the area as having a roughly 1/32-inch rounded indication with no branching or crack-like characteristics.
The licensee stated that the 2007 Edition through 2008 Addenda of the ASME Code,Section XI, Table IWC-3410-1 indicates that for pressure-retaining components (examination Category C-H), the acceptance standard is IWC-3516. IWC-3516 refers to IWB-3522.
IWB-3522 refers to IWB-3142 for corrective actions. Article IWB-3142 specifies that a component with a relevant condition is unacceptable for continued service unless the requirements of IWB-3142.2, -3142.3 or -3142.4 have been satisfied.
The licensee indicated that it has three options to resolve the issue based on the provisions of IWB-3142.2, -3142.3 or -3142.4. IWB-3142.2 is related to acceptance by performing supplemental examinations. This option is about sizing of defects for comparison to ASME acceptance criteria to allow leaving a flaw in service. The licensee stated that this option is not applicable to a through-wall flaw. IWB-3142.4 is related to accepting a flaw for service by analytical evaluation. The licensee stated that this option is not possible because the ASME Code,Section XI does not provide a methodology to analyze the subject flaw and flaw characterization is limited.
The licensee stated that of the three options, a repair/replacement per IWB-3142.3, is the only viable option for addressing the current observed condition. However, the licensee explained that repair of the 2B BAMP casing is not considered a viable option, as repair of CASS material is problematic. The licensee also noted that a replacement part is not readily available.
Therefore, the licensee requested relief and proposed alternative as discussed below.
3.5 Proposed Alternative The licensee proposed to temporarily accept the as-found relevant condition (through-wall flaw) to allow continued service instead of performing immediate flaw correction by a repair/replacement activity described in the ASME Code,Section XI, IWC-3142.3.
To monitor the condition of the 2B BAMP, the licensee proposed to take actions similar to those required by the NRC-approved ASME Code Case N-513-3, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping,Section XI, Division 1, for flaws without a growth rate analysis. These actions are:
- 1. The licensee shall observe and measure the flaw leakage rate and record a value in a retrievable format during each weekly sampling run and quarterly in-service test run to ensure early detection of an increased leak rate and to ensure the assumptions used in the component operability evaluation remain valid. The licensee notes that the current leakage rate is immeasurable, and the leakage rate will be documented as such until it can be measured in a drops/minute format.
1.a. Per the Updated Final Safety Report Table 12.2-39, the maximum allowable leakage rate is 6.12 gallons per day, or conservatively assumed to be approximately 16 drops per minute. The licensee stated that as a conservative measure, the relief request will only be considered valid for leakage rates of up to 8 drops per minute.
- 2. The licensee will conduct a visual examination every 30 days at 10X magnification of the flaw location to identify any change in flaw characterization (from rounded to linear) until the component is replaced.
The primary purpose of the visual inspection is to ensure no crack-like formations occur.
- 3. The licensee will take ultrasonic thickness measurements every 30 days.
Any measured wall loss greater than the error of the measurement device will be trended to ensure the minimum design thickness is maintained for the duration of relief.
3.6 Basis for Use The proposed alternative is based on:
(1) the licensees determination that there is reasonable assurance that the as-found condition of the 2B BAMP casing has adequate structural integrity under all licensing basis conditions, and (2) the licensee implementing appropriate surveillance activities to provide reasonable assurance that the condition of the 2B BAMP casing will continue to have adequate structural integrity throughout the period of the proposed alternative.
Regarding the structural integrity of the 2B BAMP, the licensee concluded that the observed degradation would not compromise the structural integrity of the pump casing because, based
on operating experience, the licensee had reasonable confidence that the observed degradation was due to fabrication defects in the pump casing having linked up from over 30+ years that the pump had been in service to provide for a leak path to the outside surface. The rounded nature of the indication on the surface of the pump casing is consistent with casting voids or porosity defects, and CASS material is generally resistant to inservice degradation mechanisms (e.g., stress corrosion cracking). Given the expected rounded nature of the fabrication defects, they would also be less challenging to the structural integrity of the pump casing than a sharp, crack-like (linear) defect.
The licensee stated that Type 316 stainless steel has excellent general corrosion resistance to the boric acid solution that is the process fluid for this pump. The licensee reported that the general corrosion rate in the process fluid is too small to measure based on testing done for Electric Power Research Institute [2012 EPRI Technical Report: Materials Reliability Program:
Boric Acid Corrosion Guidebook, Revision 2: Managing Boric Acid Corrosion Issues at PWR Power Stations, MRP-058, Revision 2]. The other internal parts of the pump are made from cast or wrought Type 316 stainless steel. The licensee stated that Type 316 stainless steel, either cast or wrought, is not susceptible to pitting or stress corrosion cracking in this environment. In addition, the licensee explained that cast Type 316 stainless steel is not susceptible to thermal aging at the low temperature at which this pump operates.
The licensee noted that mechanical loads due to normal operation, include pump vibration, are low and would not be anticipated to result in significant service induced flaw growth over the period of the requested alternative. The licensee noted that based on vibration data taken during in-service testing, the 2B BAMP has low vibratory loads, with no negative trends. The infrequent operation of the pump also results in a minimal impact of vibratory loads. The licensee specified that the operating conditions of the subject pump are not expected to cause the pin hole to grow because, for the 2B pump, the operating temperature is 120 OF at discharge and at suction, and the operating pressure is 150 psig at discharge and 0 - 9 psig at suction.
The licensee stated that the remaining reasonable explanation for leakage is that there is a leakage pathway via small voids, or porosity, originally present in the cast material. The licensee noted that such small imperfections do not significantly affect structural integrity of the component. The licensee stated that absence of an active degradation mechanism also shows that the currently observed leak rate will remain nearly constant for the duration of this relief request. The licensee concluded that there are no active aging degradation mechanisms for the pump that would cause the known rounded defect to initiate the growth of a planar flaw.
Regarding the monitoring of the structural integrity of the pump casing, the licensee stated that the relief will no longer be valid, and any applicable action statements will be declared if any of the following occurs:
- 1. The measured leak rate exceeds the condition of 1.a above.
- 2. Visual examination identifies a change in flaw characteristics (rounded to linear).
- 3. Trending of measured wall loss concludes the minimum design thickness of the casing will not be maintained for the duration of relief.
The licensee has proposed that implementation of the monitoring activities with acceptance criteria above will ensure that the structural integrity of the 2B pump casing will be maintained throughout the period of the proposed alternative. As such, the licensee reported that ultrasonic thickness measurements of the pump casing in the leak location showed thickness readings of 0.282, 0.289, and 0.292 inches. The licensee noted that per the vendor technical manual, this exceeds the design required minimum wall thickness of 0.25 inches. The licensee calculated a Code-required minimum wall thickness of 0.051 inches for the pump casing wall per the Construction Code, ASME Code, Section Ill, NC-3324 (1974 Edition). The licensee noted that the actual pump casing wall thickness has margin as compared to the design wall thickness, and has significant margin as compared to the ASME Code required minimum wall thickness.
Regarding hardship justification, the licensee stated that compliance with the applicable code requirement would result in a hardship without a compensating increase in the level of quality or safety, as it would result in an extended un-planned shutdown of the unit resulting in thermal stress cycling of plant components and emergent equipment issues that incur during shutdown and startup evolutions.
3.7 Duration of Proposed Alternative The licensee requested this relief to be effective for the 2B BAMP upon approval and until the 2A BAMP is returned to service. The licensee stated that this duration is bounded by the potential need for fabrication of a new pump, which is not expected to extend beyond December 2020.
4.0 NRC STAFF EVALUATION The NRC staff reviewed the following key aspects of the relief request: structural integrity of the subject pump casing, monitoring of the defect location for the duration of the alternative, and the licensees hardship justification.
Regarding structural integrity of the subject pump casing, the NRC staff finds that it is reasonable to conclude that the leak was caused by the linking of porosity to form a small leak path in the subject pump casing. The NRC staff based this conclusion on operating experience, which demonstrates that CASS material has favorable resistance to general corrosion, stress corrosion cracking, and other inservice degradation mechanisms. The NRC staff finds that a leaking flaw of 1/32 inch opening is small as compared to the size of the pump casing. The leak is not from a planar crack; therefore, crack propagation is not likely to occur. The NRC staff finds that the small flaw by itself will not significantly affect structural integrity of the pump casing. The low operating temperature and pressure and low vibrational loads due to occasional pump operation will not cause stresses to drive the pin hole to grow significantly during the duration of the relief request. As such, the NRC staff determined that the small flaw is not expected to grow to challenge the structural integrity of the pump casing.
The NRC staff independently calculated an ASME Code-required minimum wall thickness of 0.051 inches. The NRC staff confirmed that the measured pump casing wall thickness at the leaking location is acceptable and provides structural integrity for the pump because it has sufficient margin as compared to the ASME Code-required minimum wall thickness.
Regarding monitoring, the NRC staff finds that the licensees proposed pump wall thickness measurement and a visual examination at 10X magnification every 30 days are appropriate because the pump casing does not experience active degradation mechanisms that require
monitoring of the pump more frequently than every 30 days. In addition, the NRC staff finds the acceptance criteria specifying a leak rate of 8 drops per minute, a change in flaw characteristics, and a minimum wall thickness to be acceptable because these criteria will ensure that the structural integrity of the 2B pump will be maintained.
Regarding hardship, the NRC staff determined that performing the repair/replacement activity of the 2B pump in accordance with the ASME Code,Section XI is a hardship because it would result in an extended un-planned shutdown of the unit resulting in thermal stress cycling of plant components and emergent equipment issues that occur during shutdown and startup evolutions without a compensating increase in the level of quality and safety.
5.0 CONCLUSION
The NRC staff determined that the proposed alternative provides reasonable assurance of structural integrity of the 2B BAMP. The NRC staff finds that complying with the requirements of the ASME Code,Section XI would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(2). Therefore, the NRC authorizes the use of Relief Request RR-16 at St. Lucie Plant, Unit 2 until one of the following occurs: the 2A BAMP is restored to an operable condition, the allowable leak rate exceeds 8 drops per minute, a change in flaw characteristics is observed, or the December 2020 date is reached.
All other requirements in the ASME Code,Section XI, for which relief was not specifically requested and approved in this proposed alternative remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: John Tsao, NRR/DNRL/NPHP Date: February 19, 2020
ML20023B378 *by e-mail OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NPHB/BC* NRR/DORL/LPLII-2/BC NAME NJordan BAbeywickrama MMitchell UShoop DATE 01/23/2020 01/29/2020 12/02/2019 02/19/2020