L-2017-034, Turkey Point, Unit 4, Response to Request for Additional Information Regarding Steam Generator Tube Inspection Report

Turkey Point, Unit 4, Response to Request for Additional Information Regarding Steam Generator Tube Inspection Report

ML17090A432
Person / Time
Site:	Turkey Point
Issue date:	03/14/2017
From:	Summers T Florida Power & Light Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-2017-034
Download: ML17090A432 (5)

Text

U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555-00001 Re: Turkey Point Unit 4 Docket No. 50-251 Response to Request for Additional Information Regarding Steam Generator Tube Inspection Report

Reference:

MAR 1 4 2017 L-2017-034 10 CFR 50.36 1. Florida Power & Light Company letter, L-2016-178, "Turkey Point Unit 4, Docket No. 50-251, Steam Generator Tube Inspection Report," October 18, 2016 (ML 16298A391)

2. NRC E-mail, RAI for Turkey Point 4 RF029 SGTIR Review -MF8523," February 10, 2017(ML17044A205)

By letter dated October 18, 2016, Florida Power & Light Company (FPL) submitted the Turkey Point Unit 4 Cycle 29 Refueling Outage Steam Generator Tube Inspection Report (Reference

1) in accordance with Technical Specification 6.8.4.j, Steam Generator (SG) Program. On February 10, 2017, the NRC requested additional information regarding Reference

1. Attachment 1 to this letter provides FPL's response to the request for additional information (Reference 2). Should there be any questions, please contact Mr. Mitch Guth, Licensing Manager, at (305) 246-6698.

Regional Vice President

-Southern Region Turkey Point Nuclear Plant Enclosure cc: Regional Administrator, Region II, USNRC. Senior Resident Inspector, USNRC, Turkey Point Plant Florida Power & Light Company 9760 SW 344 St Homestead, FL 33035 L-2017-034ATTACHMENT1 Response to Request for Additional Information Regarding Unit 4 Steam Generator Tube Inspection Report NRC RAI # 1: Attachment 1 to L-2017-034 Page 1of3 Beginning on page 11 of 14 of the report, the licensee discusses a 77 percent through-wall foreign object wear indication reported during RFO 29 (2016) in SG B in a tube at row 17, column 71 (R 17C71) at the 01 H tube support structure.

The staff notes that wear was detected in a tube close to this location in 2012. Given that there was no detected degradation or possible loose part indication in R17C71 in 2012, and the wear indication was sized at 77 percent through-wall in 2016, the staff requests the licensee to discuss the operational assessment performed to justify operation until the next planned inspection in 2019. FPL Response for RAI #1: The justification of continued operation until the next inspection in 2019 was based on the condition monitoring (CM) and operational assessment (OA) performed for the 2016 inspection.

The CM and OA for foreign object degradation followed the guidance of EPRI SG ISPT guidelines, Rev. 4, EPRI SG IA guidelines, Rev. 3, and Turkey Point engineering procedures for evaluation of secondary-side foreign objects. The volumetric indication in R17C71 at 01 Hin SG B detected in 2016 by the bobbin coil was attributed to foreign object wear. The subsequent rotating +Point coil examination revealed no associated foreign object at the wear indication location, and tubes surrounding R17C71 showed no tube damage. Tube R17C71 in SG B was removed from service by plugging with stabilization.

The indication.

at 01 H in tube R 17C71 had a measured depth of 77% TW with an axial length of 0.35 in. and circumferential extent of 0.51 in. using EPRI +Point technique 27904.1 (tapered round hole calibration standard).

The same indication was sized at 27% TW using EPRI +Point technique 27905.1 (flat wear calibration standard).

The +Point volts peak-to-peak for the indication was 0.67 volts. Subsequent line-by-line depth sizing with EPRI +Point technique 27904.1 gave a maximum depth of 72% TW. The depth sizing profile further indicated the shape of the flaw is relatively flat and indicates that sizing with technique 27904.1 is conservative for CM and OA purposes.

the tapered round hole standard for technique 27904.1 has a drill-hole diameter <0.14 in. at the reported depth size. The axial/circumferential extent for the wear indication (0.35 in. by 0.51 in.) is much larger than that for a tapered hole. This suggests that the actual depth of the indication is most likely closer to the 27% TW size reported with technique 27905.1. The profile conservatively sized with technique 27904.1 was evaluated for tube integrity and the calculated burst pressure at 95-50 lower bound met the SIPC margin requirement of 4542 psi (3xNOPD), with margin. The depth of a flaw to cause possible leakage under a postulated limiting accident event (i.e., through-wall penetration due to remaining ligament pop-through failure), including analysis uncertainties at the 95-50 limits, was not exceeded for the detected indication.

Therefore, the AILPC leakage margin requirements at 1xLAPD (2550 psi) for the past operating period were satisfied.

In support of the CM calculations, the voltage screening limits in the EPRI ISPT guidelines were also evaluated for this indication.

Comparison of the measured voltage and length sizes with the exemption criteria was performed.

Applying the voltage screening methods in accordance with Attachment 1 to L-2017-034 Page 2 of 3 the EPRI ISPT guidelines concluded that the wear indication is exempt from proof (burst) testing (Vpp s 2 volts and length s1 in.) and exempt from leakage testing (Vpp s 1.6 volts, axial length s 0.5 in. and circumferential angle s 90°). This includes accident-induced bending stresses up to 27.7 ksi, which bounds the bending stress calculated at tube support plates for the Turkey Point steam generators for faulted loads. Therefore, the voltage-based screening criteria were met, with margin, for both leakage and structural requirements for R17C71 and ISPT was not required.

For the OA, two possible scenarios were considered:

1) the loose part affecting R17C71 is a new foreign object, and 2) the loose part is the same foreign object that affected R17C74 in 2012 and had migrated three tubes over to R17C71. For the OA performed at EOC 28, foreign object wear was evaluated under the assumption that the foreign object was new and would migrate to another location in Cycle 29 (Scenario 1). The likely source for new foreign objects in SG B is metal fragments generated from a SG feed pump suction strainer failure in 2013. A foreign object evaluation was performed by Turkey Point Engineering on the most likely metal fragments arising from the strainer failure. A list of credible debris was determined based on strainer construction, historical debris trapped in the strainer, and the parts of the strainer(s) that were retrieved after the failure. Using credible part configurations residing in a stable captured position and exposed to full gap velocity, the operating periods to reach the minimum allowable tube wall thickness were evaluated.

The resulting limiting inspection interval was calculated as 3.68 EFPY to reach the minimum allowable tube wall thickness.

This interval exceeds the planned inspection interval (Cycles 29 and 30), which is 2.84 EFPY. This limiting calculation supports a 2-cycle inspection interval to EOC 30. As a check on the above assessment and to address Scenario 2, the next inspection interval of 2.84 EFPY was compared to the last inspection interval of 2.15 EPFY in conjunction with the CM evaluation for R 17C71. The next inspection interval is -3% longer than the previous one (2.84/2.75

= 1.03). Under the assumption that the suspected loose part will migrate to another: location and is in direct contact with a tube, and the expected depth and shape of the resulting wear at EOC 30 will be similar to the indication in R17C71 observed at EOC 28, the minimum burst pressure and leakage potential were calculated and compared to the SIPC and AILPC margin requirements.

Given the established condition that the indication in R17C71 met CM margin requirements in 2016 (both analytically and voltage-based) with margin, a postulated indication under the same scenario from the past operating period as described above, having again been conservatively sized using technique 27904.1, will satisfy the CM margin requirements at the next inspection in 2019.

NRC RAl#2: Attachment 1 to L-2017-034 Page 3 of 3 Regarding the channel head, upper steam drum, and in-bundle tube support visual inspections, the staff requests the licensee to confirm that the descriptions of no anomalies/abnormalities means that no degradation was observed.

If this is not the case, the staff requests the licensee to describe the degradation it observed.

FPL for RAI #2: Channel Head Visual Inspections The Steam Generator (SG) Tube Inspection Report stated that no anomalies were observed in any of the three SG channel heads. For the channel head visual inspections, no degradation was detected in any of the three SG channel heads. In-Bundle Tube Support Visual Inspections With regards to the in-bundle tube support visual inspection (only performed in SG A) the report stated that no abnormal conditions were observed.

For the in-bundle tube support visual inspections, no degradation was detected.

Upper Steam Drum Visual Inspections During the inspection of the feedring and J-tubes, a few instances were noted where the J-Tube to feedring interface (on the inside diameter of the feedring) shows some minor erosion. This is not new degradation and does not appear to be changing over time. There was no new degradation in any of the steam drum components.

Acronyms AILPC CM *EFPY EOC EPRI IA ISPT LAPD NOPD OA 01H SG %TW SIPC Vpp psi ksi Induced Leakage Performance Criteria Condition Monitoring Effective Full Power Years* End of Cycle Electric Power Research Institute Integrity Assessment In Situ Pressure Test Limiting Accident Pressure Differential Normal Operating Pressure Differential Operational Assessment First (lowest) Broached Supp,art plate on the Hot-Leg side of the SG Steam Generator Percentage through the tube wall Structural Integrity Performance Criteria Voltage Peak-to-Peak pounds per square inch kilo pounds per square inch