ML20076D281

Relief from the Requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code

ML20076D281
Person / Time
Site:	Seabrook
Issue date:	03/17/2020
From:	James Danna Plant Licensing Branch 1
To:	Moul D Florida Power & Light Co, NextEra Energy Seabrook
Poole J, NRR/DORL/LPLI, 415-2048
References
EPID L-2019-LLR-0043
Download: ML20076D281 (9)

Text

March 17, 2020 Mr. Don Moul Executive Vice President, Nuclear Division and Chief Nuclear Officer Florida Power & Light Company NextEra Energy Seabrook, LLC Mail Stop: NT3/JW 15430 Endeavor Drive Jupiter, FL 33478

SUBJECT:

SEABROOK STATION, UNIT NO. 1 - RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE (EPID L-2019-LLR-0043)

Dear Mr. Moul:

By letter dated May 6, 2019 (Agencywide Documents Access and Management System Accession No. ML19127A259), NextEra Energy Seabrook, LLC (the licensee) submitted Relief Request PR-2 to the U.S. Nuclear Regulatory Commission (NRC) for relief from the requirements of the 2012 Edition of the American Society of Mechanical Engineers (ASME)

Code for Operation and Maintenance of Nuclear Power Plants (OM Code), at Seabrook Station, Unit No. 1 (Seabrook).

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee requested an alternative test plan that would increase the vibration alert range absolute limit in the ASME OM Code from 0.325 inches per second (in/sec) to 0.400 in/sec for the containment building spray pumps. The Seabrook fourth 10-year inservice testing interval begins on August 18, 2020, and ends in August 2030.

The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the licensee has demonstrated that the proposed alternative provides an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1).

Therefore, the NRC staff authorizes the use of Relief Request PR-2 at Seabrook for the fourth 10-year inservice testing program interval at Seabrook, which begins on August 18, 2020, and ends in August 2030.

All other ASME OM Code requirements for which relief was not specifically requested and approved remain applicable.

D. Moul If you have any questions, please contact the Seabrook Project Manager, Justin Poole, at 301-415-2048 or by e-mail to Justin.Poole@nrc.gov.

Sincerely,

/RA/

James G. Danna, Chief Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-443

Enclosure:

Safety Evaluation cc: Listserv

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST PR-2 ASSOCIATED WITH INCREASE OF VIBRATION ALERT RANGE ABSOLUTE LIMIT FOR ALL CONTAINMENT BUILDING SPRAY PUMP BEARINGS NEXTERA ENERGY SEABROOK, LLC, ET AL.*

SEABROOK STATION, UNIT NO. 1 DOCKET NO. 50-443

1.0 INTRODUCTION

By letter dated May 6, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19127A259), NextEra Energy Seabrook, LLC (the licensee) submitted Relief Request PR-2 to the U.S. Nuclear Regulatory Commission (NRC) for relief from the requirements of the 2012 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants (OM Code), at Seabrook Station, Unit No. 1 (Seabrook).

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee requested an alternative test plan that would increase the vibration alert range absolute limit in the ASME OM Code from 0.325 inches per second (in/sec) to 0.400 in/sec for the containment building spray (CBS) pumps. The Seabrook fourth 10-year inservice testing (IST) program interval begins on August 18, 2020, and ends in August 2030.

2.0 REGULATORY EVALUATION

The NRC regulations in Title 10 of the Code of Federal Regulations (10 CFR) paragraph (f)(4)(ii) state that inservice tests to verify operational readiness of pumps and valves whose function is required for safety, conducted during successive 120-month intervals, must comply with the requirements of the latest edition and addenda of the ASME OM Code incorporated by reference in 10 CFR 50.55a(a)(1)(iv) 12 months before the start of the 120-month interval (or the optional ASME Code Cases listed in NRC Regulatory Guide 1.147 or NRC Regulatory Guide 1.192, as incorporated by reference in 10 CFR 50.55a(a)(3)(ii) and (iii), respectively),

subject to the conditions listed in 10 CFR 50.55a(b).

The regulation at 10 CFR 50.55a(z) states that alternatives to the requirements of 10 CFR 50.55a(b) through (h), or portions thereof, may be used when authorized by the Director, Office of Nuclear Reactor Regulation, or Director, Office of New Reactors, as appropriate. Paragraph 50.55a(z) to 10 CFR states that a proposed alternative must be submitted and authorized prior to implementation. It also states that the applicant or licensee must demonstrate:

Enclosure

(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.

The NRC staff provides guidance in NUREG-1482, Revision 2, Guidance for Inservice Testing at Nuclear Power Plants (ADAMS Accession No. ML13295A020), for preparing proposed alternatives to ASME OM Code requirements.

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 authorize the proposed alternative.

3.0 TECHNICAL EVALUATION

3.1 System Description The CBS at Seabrook is designed to provide cooling to the containment in the event of certain accidents to prevent containment pressure and temperature from exceeding acceptable limits by discharging water through the containment spray nozzles. The CBS consists of two trains, with each train containing one motor-driven, horizontal, centrifugal CBS pump. The CBS pumps are designed to take suction from either the refueling water storage tank (RWST) or the containment recirculation sump, depending on mode-dependent alignment.

3.2 List of Affected Components 1-CBS-P-9A - Containment Building Spray Pump A 1-CBS-P-9B - Containment Building Spray Pump B 3.3 Applicable ASME OM Code Requirements The applicable ASME OM Code edition for the fourth IST program interval at Seabrook is ASME OM Code, 2012 Edition.

Paragraphs ISTB-5121(e) and ISTB-5123(e) of the ASME OM Code, 2012 Edition, state that:

All deviations from the reference values shall be compared with the ranges of Table ISTB-5121-1 and corrective action taken as specified in ISTB-6200.

Vibration measurements shall be compared to both the relative and absolute criteria shown in the alert and required action ranges of Table ISTB-5121-1.

Table ISTB-5121-1, Centrifugal Pump Test Acceptance Criteria, states that for Group A tests with pump speed greater or equal to 600 revolutions per minute (rpm), the alert range is:

>2.5Vr to 6Vr or

>0.325 to 0.7 in./sec (0.8 to 1.7 cm/s [centimeters per second]).

Note 1 of Table ISTB-5121-1 indicates that Vr is the vibration reference value in the selected units.

3.4 Licensees Proposed Alternative In its alternative request, the licensee states that, due to resonance amplification, 1-CBS-P-9-B pump bearing vibrations have exceeded the ISTB Table 5121-1 absolute limit, and 1-CBS-P-9-A pump bearing vibrations have approached the absolute limit. Therefore, the licensee is proposing to increase the vibration alert range absolute limit from 0.325 in/sec to 0.400 in/sec on the basis that the alternative will provide an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1).

3.5 Licensees Basis for Alternative The licensee provided the following basis, in part, for the proposed alternative:

The manufacturer (Sulzer Pumps) reviewed the historical hydraulic and vibration monitoring data for both pumps, including the pre-service testing. The discrete peaks found at 1X, 4X, and 8X were found to exhibit normal energy for this design of pump. Energy in the form of a raised floor is also present, which combines with the discrete frequencies and causes the overall vibration to exceed 0.325 ips [inches per second]. No indication of material degradation was identified in the review. This is supported by the surveillance data over the past 28 years, where the pumps have maintained stable vibration levels and hydraulic performance.

The pump design contributes to the discrete frequencies identified in the vibration spectral analysis. Both pumps have two volutes, offset 180 degrees to balance flow, and four impeller vanes. This combination increases the risk of amplification at 1X, 4X, and 8X, which explains the discrete frequencies present.

These discrete frequencies are low and acceptable.

The raised floor has existed since original installation. The energy was analyzed by the manufacturer and found to be acceptable for continued operation of the pumps. This is additionally supported by the manufacturer's internal guidance document that recommends 0.43 ips as the alert level for this pump type.

Internal recirculation leakage across wear parts was assessed and is acceptable.

If the wear part clearance was to increase, the degrading performance would be indicated as a declining hydraulic trend during IST testing. The historical hydraulic performance data has been analyzed and does not indicate degradation.

Both pumps vibration levels result in testing challenges due to the lack of any margin between the reference value and the ISTB Table 5121-1, Centrifugal Pump Tests Acceptance Criteria Alert Range absolute limit. Exceedance of the Alert limit results in additional testing. Reduced interval testing does not provide any compensating increase in the level of quality and safety. The pumps are infrequently run, on the order of 200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> for an 18 month cycle.

The manufacturer determined that both CBS pumps can operate with vibrations up to 0.430 ips and support a mission time of 30 days. Anything below this limit is considered acceptable vibration for continued operation. Increasing the ISTB Table 5121-1 Alert Range Absolute Limit from 0.325 ips to 0.400 ips for all of the pump bearing limits on both 1-CBS-P-9-A and 1-CBS-P-9-B, will provide adequate margin for test repeatability and will be within the manufacturers recommended limit.

As part of the Third Ten Year Interval PR-2 alternative testing, additional testing, trending, and diagnostic analysis were added to the Seabrook Station Predictive Maintenance Program. This includes Static Motor Testing using the Baker Advanced Winding Analyzer Series IV (AWAIV) equipment, Dynamic Motor Monitoring utilizing the Baker EXP3000 equipment, thermography inspections, and lube oil sampling and analysis. This enhanced Predictive Maintenance Program goes beyond the vibration monitoring and analysis required by ISTB.

Performance of these tests during the past testing interval yielded satisfactory results.

The Silica Removal Program periodically uses the CBS pumps to recirculate the RWST for the removal of silica. Because of this, the CBS pumps were reclassified from Group B to Group A pumps for the Third Testing Interval, resulting in vibration analysis performance during quarterly pump runs. The increased frequency of testing provided a larger sample of trend data that has been used to better monitor component performance.

Based on test history and review of pumps performance by the manufacturer an ISTB 5121-1 Alert Range Absolute Limit increase of the lower vibration limit from 0.325 ips to 0.400 ips for the pump vibration readings is warranted.

Increasing the ISTB Table 5121-1 Alert Range Absolute Limit from 0.325 ips to 0.400 ips for all of the pump bearing limits on both 1-CBS-P-9-A and 1-CBS-P-9-B, will provide adequate margin for test repeatability and will be within the manufacturers recommended limit.

The CBS Pumps will continue to be monitored using testing, trending, and diagnostic analysis as required by the Seabrook Station Predictive Maintenance Program. This program employs predictive monitoring techniques that go beyond the vibration monitoring and analysis required by ISTB. If measured parameters are found to be outside the normal operating range or determined to be trending toward an unacceptable degraded state, then appropriate actions will be taken. These actions include monitoring additional parameters, review of specific information to identify cause, and potential removal of the pump from service to perform necessary maintenance.

The past 28 years of surveillance data, along with PDM [predictive maintenance]

program results, supports stable and acceptable pump performance at the current vibration levels. This is supported by the manufacturers review and analysis of pump operation.

3.6 NRC Staff Evaluation Pursuant to 10 CFR 50.55a(f)(4)(ii), the Seabrook IST program will comply with the ASME OM Code, 2012 Edition, as incorporated by reference in 10 CFR 50.55a (or accepted ASME OM Code Cases), except where relief is granted or alternatives are authorized. Paragraphs ISTB-5121(e) and ISTB-5123(e) both require that all deviations from the reference values be compared with the ranges of Table ISTB-5121-1. Paragraphs ISTB-5121(e) and ISTB-5123(e) also require that vibration measurements shall be compared to both the relative and absolute criteria shown in the alert and required action ranges of Table ISTB-5121-1.

The licensee has proposed an alternative to the alert range requirements in the ASME OM Code, Table ISTB-5121-1, for its CBS pump 1-CBS-P-9-A and pump 1-CBS-P-9-B.

Specifically, the licensee is requesting to increase the alert range absolute limit from 0.325 in/sec to 0.400 in/sec for all bearings of the subject CBS pumps. The NRC staff has previously approved similar increases to the alert range absolute limits for the same CBS pumps at Seabrook in the past, including an approved relief request by letter dated June 3, 2010 (ADAMS Accession No. ML101380166), for the third 10-year IST program interval that increased the alert range absolute limit to 0.350 in/sec. The required action range high vibration limit remains unchanged at 0.7 in/sec.

The CBS at Seabrook is designed to remove the energy discharged to the containment following a loss-of-coolant accident or main steam line break to prevent the containment pressure from exceeding design pressure and to reduce and maintain containment temperature and pressure within acceptable limits. The CBS pumps are motor-driven, horizontal, Bingham-Willamette Type CD centrifugal pumps. The pump style is a double-suction, single-discharge, single stage pump, and the impeller is configured with a wide, flat discharge vane exiting to the discharge diffuser. Each train of the CBS at Seabrook includes one 100 percent capacity pump.

The NRC staff has reviewed the historical CBS pump vibration data provided by the licensee, which indicate that the vibration level trends are stable and have been stable for over 30 years.

The CBS pumps have operated satisfactorily at these higher vibration levels since initial plant operation, including during the pre-operational test (1986). No unusual wear or degradation has been detected during testing or inspections due to this consistently elevated vibration.

The licensee has been performing vibration spectral analyses of the CBS pumps at Seabrook, which show similar vibration levels and signature from 1999 to 2018. The predominant spectral peaks have occurred at expected intervals as a direct result of the vane pass frequencies and were validated by the manufacturer of the pump as acceptable. As the cause of the vibrations has been identified and the vibrations are stable, there is no indication of bearing wear or degradation.

The CBS pumps are susceptible to higher vibrations due to the necessary test conditions. The pumps are tested at approximately 63 percent of their best efficiency point flow, which increases pump internal recirculation flow. Pump internal recirculation flow increases the pump impeller vane pass vibration response.

The CBS pumps are also susceptible to higher vibration due to their design and the fact that they are installed on a raised floor. The licensees data analysis identified high pump vane pass spectral responses. In addition, pump casing resonance testing identified that the pumps have a resonance frequency similar to that of the pump vane pass. This condition results in

increasing vibration amplitude that is primarily responsible for the vibration magnitude. The pump vendor has evaluated the pump vibration and agrees with the licensees cause determination for the pump vibration and with increasing the pump vibration limits. The elevated vibration limit also remains below the manufacturers recommended limit of 0.43 in/sec.

In its alternative request, the licensee specifies the continued performance of condition-based monitoring techniques that have been used since 2003, including thermography, lube oil sampling and analysis, and vibration spectral analysis, which exceed the monitoring and analysis requirements in Subsection ISTB of the ASME OM Code.

Therefore, the NRC staff finds that the licensees proposal to increase the vibration alert range limit from 0.325 in/sec to 0.400 in/sec for all bearings of the subject CBS pumps will have an insignificant effect on the timely detection of pump degradation prior to component failure, and the staff finds the licensees proposal to provide an acceptable level of quality and safety.

4.0 CONCLUSION

As set forth above, the NRC staff determines that the licensee has demonstrated that the proposed alternative provides an acceptable 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)(1). Therefore, the NRC staff authorizes the use of PR-2 at Seabrook for the fourth 10-year IST program interval at Seabrook, which begins on August 18, 2020, and ends in August 2030.

All other requirements of the ASME Code,Section XI, for which relief has not been specifically requested remain applicable.

Principal Contributor: I. Tseng Date: March 17, 2020

ML20076D281 *by e-mail OFFICE NRR/DORL/LPL1/PM NRR/DORL/LPL1/LA NRR/DEX/EMIB/BC(A)* NRR/DORL/LPL1/BC NRR/DORL/LPL1/PM NAME JPoole LRonewicz TScarbrough JDanna JPoole DATE 03/17/2020 03/17/2020 03/11/2020 03/17/2020 03/17/2020