ML16013A066

Summary of 11/9 and 12/30/15 Conference Calls with STP Nuclear Operating Company to Discuss the Fall 2015 Steam Generator Tube Inspection Activities (CAC No. A11018)

ML16013A066
Person / Time
Site:	South Texas
Issue date:	01/14/2016
From:	Lisa Regner Plant Licensing Branch IV
To:	South Texas
Regner L
References
CAC A11018
Download: ML16013A066 (5)

Text

LICENSEE: STP Nuclear Operating Company FACILITY: South Texas Project, Unit 1

SUMMARY

OF NOVEMBER 9 AND DECEMBER 30, 2015, CONFERENCE CALLS WITH STP NUCLEAR OPERATING COMPANY TO DISCUSS THE FALL 2015 STEAM GENERATOR TUBE INSPECTIONS (CAC NO. A11018)

On November 9 and December 30, 2015, the U.S. Nuclear Regulatory Commission (NRC) and representatives of STP Nuclear Operating Company (STPNOC, the licensee) participated in conference calls to discuss the steam generator (SG) tube inspection activities at South Texas Project, Unit 1. The summary of the conference calls is provided in the Enclosure.

During the fall 2015 SG inspections for refueling outage 19, eddy current examination identified one volumetric indication in SG 1D. While the indication did not meet tube plugging criteria, the licensee stated that subject tube was plugged as a precautionary measure. An evaluation of the indication is estimated to be complete by June 30, 2016. Upon completion of the evaluation, STPNOC stated it would provide the results to the NRC.

Please direct any inquiries to me at 301-415-1906 or lisa.regner@nrc.gov.

Sincere.' l yy/ '

(\_.* ti,.

1~/f\ll .~-'-

1--I vr usa M. Regner, Senior Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-498

Enclosure:

Summary of Conference Call cc w/encl: Distribution via Listserv

SUMMARY

OF CONFERENCE CALLS REGARDING THE FALL 2015 STEAM GENERATOR TUBE INSPECTIONS STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT, UNIT 1 DOCKET NO. 50-498 On November 9 and December 30, 2015, the U.S. Nuclear Regulatory Commission (NRC) staff participated in conference calls with STP Nuclear Operating Company, Inc. (STPNOC, the licensee), regarding the steam generator (SG) tube inspection activities at South Texas Project (STP), Unit 1. SG inspection activities occurred during refueling outage 19 for STP, Unit 1 (1RE19) in accordance with its technical specifications (TSs).

STP, Unit 1 is a 4-loop pressurized-water reactor with Westinghouse Model Delta 94 SGs.

Each recirculating SG contains 7,585 thermally treated Alloy 690 tubes with a nominal outside diameter of 0.688 inches and a nominal wall thickness of 0.040 inches. The tubes are supported by a number of stainless steel tube support plates and anti-vibration bars. The tubes were hydraulically expanded at both ends for the full depth of the tubesheet. In addition, the U-bend region of the low row tubes were stress relieved prior to operation.

November 9, 2015, Conference Call During the fall 2015 SG inspections for 1RE19, eddy current examination identified a volumetric indication in the tube located in row 30 column 78 (R30C78) in SG 1D. The prior inspection of this tube was in 1RE16 in the spring of 2011.

The indication initiated on the outside diameter of the tube, about 0.2 inches above the hot-leg tubesheet. The volumetric indication was sized at 12 percent through-wall and was approximately 0.1-inch long by 0.1-inch wide.

There was a hard sludge collar about 1-inch high around the tube. The subject tube was in the central portion of the hot-leg, in a region commonly referred to as the "kidney region." There are approximately 100 tubes in the "kidney region," and the sludge pile in this region varies from approximately 1/8-inch deep at the periphery, to approximately 1-inch in the center. All tubes within the "kidney region" were inspected from 6 inches above to 3 inches below the top of the tubesheet in all four SGs. No additional indications were found within this region.

A loose part, possibly a piece of stainless steel flexitallic gasket, was observed embedded in the hard sludge, near the tube with the volumetric indication, but the licensee did not determine if the indication was on the same side of the tube as the gasket material. A review of previous eddy current inspection data showed that the indication was discernable, but not reportable, when the tube was last inspected in 1RE16. A review of photographs from 1RE 16 did not show the flexitallic gasket, but the licensee stated that sludge lancing performed during the Enclosure

1RE19 outage might have removed sludge and exposed the gasket, because the licensee had used improved sludge lancing equipment.

The licensee also inspected the tube with a Ghent probe and a magnetically biased +Point' probe. These probes confirmed the indication. An ultrasonic probe was not used.

The licensee posed four possibilities for the cause of the volumetric indication: loose part wear, corrosion, a false call due to spalling of the hard sludge collar, or a surface blemish created during manufacturing. The licensee did not believe the manufacturing blemish was feasible since the indication was not present in eddy current data prior to 2011.

The licensee had no plans to pull the subject tube during the current outage, but said it might in a future outage depending on its conclusion for the cause of the indication. The licensee noted that due to the indication's location on the tube, pulling the tube could damage the indication.

At the time of the call, the subject tube had been plugged, all four SGs were re-sealed, and the reactor coolant system was being pressurized. The licensee recorded the indication in its corrective action program, but did not have an expected completion date for the review of the volumetric indication. The outage was expected to complete in 7 to 9 days.

The licensee discussed the range of loose part wear and pitting eddy current technique specification sheets used in assessing the depth of the volumetric indication. The licensee also clarified that for the top-of-the-tubesheet inspections, STPNOC usually inspects 100 percent of the tubes in the periphery of the SG and the no-tube lane, and an additional 20 percent of the remaining tubes in the interior of the bundle. During 1RE19, STPNOC inspected 100 percent of the "kidney region" tubes.

The NRC staff asked the licensee to provide a copy of the eddy current data for independent analysis, and the licensee agreed to provide it.

December 30. 2015, Follow-up Conference Call The licensee stated that the causal evaluation was estimated to be complete by June 30, 2016.

Upon completion of the causal evaluation, the licensee stated it would provide the results to the NRC.

The licensee clarified that if the causal evaluation concluded that the volumetric indication in the tube in R30C78 was due to a corrosion or pitting mechanism, it would conduct a degradation assessment assuming that the mechanism was existing. In performing the degradation assessment, STPNOC would assume the Alloy 690 tubing has the same propensity for pitting as Alloy 600 material.

STP, Unit 1, has nitrogen-16 monitors installed that are capable of detecting primary-to-secondary leakage as low as 1-gallon per day and the detectors alarm in the control room. The licensee stated that primary-to-secondary leakage was not expected this operational cycle, and that STP currently meets all Electric Power Research lnstitute's guidelines concerning SG leakage monitoring. The indication in the tube in R30C78 had an estimated growth rate of 1 percent per effective full power year. Additionally, for an indication of this size, the

through-wall depth would have to be approximately 95 percent before primary-to-secondary leakage would be expected.

The NRC reviewed the eddy current data provided by the licensee in November 2015 and noted three additional indications in tubes in R70C140, R84C22, and R84C24. The licensee clarified that all three of these indications were caused by foreign objects that had been removed in previous outages.

• ML16013A066 *via memo dated 1/5/16 OFFICE NRR/DORL/LPL4-1/PM NRR/DORL/LPL4-1/LA NRR/DE/ESGB/BC*

NAME LRegner JBurkhardt GKulesa DATE 1/11/16 1/13/16 1/5/16 OFFICE N RR/DORL/LP L4-1 /BC NRR/DORL/LPL4-1/PM NAME RPascarelli LRegner DATE 1/14/16 1/14/16 LICENSEE: STP Nuclear Operating Company FACILITY: South Texas Project, Unit 1

SUMMARY

OF NOVEMBER 9 AND DECEMBER 30, 2015, CONFERENCE CALLS WITH STP NUCLEAR OPERATING COMPANY TO DISCUSS THE FALL 2015 STEAM GENERATOR TUBE INSPECTIONS (CAC NO. A11018)

On November 9 and December 30, 2015, the U.S. Nuclear Regulatory Commission (NRC) and representatives of STP Nuclear Operating Company (STPNOC, the licensee) participated in conference calls to discuss the steam generator (SG) tube inspection activities at South Texas Project, Unit 1. The summary of the conference calls is provided in the Enclosure.

During the fall 2015 SG inspections for refueling outage 19, eddy current examination identified one volumetric indication in SG 1D. While the indication did not meet tube plugging criteria, the licensee stated that subject tube was plugged as a precautionary measure. An evaluation of the indication is estimated to be complete by June 30, 2016. Upon completion of the evaluation, STPNOC stated it would provide the results to the NRC.

Please direct any inquiries to me at 301-415-1906 or lisa.regner@nrc.gov.

Sincere.' l yy/ '

(\_.* ti,.

1~/f\ll .~-'-

1--I vr usa M. Regner, Senior Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-498

Enclosure:

Summary of Conference Call cc w/encl: Distribution via Listserv

SUMMARY

OF CONFERENCE CALLS REGARDING THE FALL 2015 STEAM GENERATOR TUBE INSPECTIONS STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT, UNIT 1 DOCKET NO. 50-498 On November 9 and December 30, 2015, the U.S. Nuclear Regulatory Commission (NRC) staff participated in conference calls with STP Nuclear Operating Company, Inc. (STPNOC, the licensee), regarding the steam generator (SG) tube inspection activities at South Texas Project (STP), Unit 1. SG inspection activities occurred during refueling outage 19 for STP, Unit 1 (1RE19) in accordance with its technical specifications (TSs).

STP, Unit 1 is a 4-loop pressurized-water reactor with Westinghouse Model Delta 94 SGs.

Each recirculating SG contains 7,585 thermally treated Alloy 690 tubes with a nominal outside diameter of 0.688 inches and a nominal wall thickness of 0.040 inches. The tubes are supported by a number of stainless steel tube support plates and anti-vibration bars. The tubes were hydraulically expanded at both ends for the full depth of the tubesheet. In addition, the U-bend region of the low row tubes were stress relieved prior to operation.

November 9, 2015, Conference Call During the fall 2015 SG inspections for 1RE19, eddy current examination identified a volumetric indication in the tube located in row 30 column 78 (R30C78) in SG 1D. The prior inspection of this tube was in 1RE16 in the spring of 2011.

The indication initiated on the outside diameter of the tube, about 0.2 inches above the hot-leg tubesheet. The volumetric indication was sized at 12 percent through-wall and was approximately 0.1-inch long by 0.1-inch wide.

There was a hard sludge collar about 1-inch high around the tube. The subject tube was in the central portion of the hot-leg, in a region commonly referred to as the "kidney region." There are approximately 100 tubes in the "kidney region," and the sludge pile in this region varies from approximately 1/8-inch deep at the periphery, to approximately 1-inch in the center. All tubes within the "kidney region" were inspected from 6 inches above to 3 inches below the top of the tubesheet in all four SGs. No additional indications were found within this region.

A loose part, possibly a piece of stainless steel flexitallic gasket, was observed embedded in the hard sludge, near the tube with the volumetric indication, but the licensee did not determine if the indication was on the same side of the tube as the gasket material. A review of previous eddy current inspection data showed that the indication was discernable, but not reportable, when the tube was last inspected in 1RE16. A review of photographs from 1RE 16 did not show the flexitallic gasket, but the licensee stated that sludge lancing performed during the Enclosure

1RE19 outage might have removed sludge and exposed the gasket, because the licensee had used improved sludge lancing equipment.

The licensee also inspected the tube with a Ghent probe and a magnetically biased +Point' probe. These probes confirmed the indication. An ultrasonic probe was not used.

The licensee posed four possibilities for the cause of the volumetric indication: loose part wear, corrosion, a false call due to spalling of the hard sludge collar, or a surface blemish created during manufacturing. The licensee did not believe the manufacturing blemish was feasible since the indication was not present in eddy current data prior to 2011.

The licensee had no plans to pull the subject tube during the current outage, but said it might in a future outage depending on its conclusion for the cause of the indication. The licensee noted that due to the indication's location on the tube, pulling the tube could damage the indication.

At the time of the call, the subject tube had been plugged, all four SGs were re-sealed, and the reactor coolant system was being pressurized. The licensee recorded the indication in its corrective action program, but did not have an expected completion date for the review of the volumetric indication. The outage was expected to complete in 7 to 9 days.

The licensee discussed the range of loose part wear and pitting eddy current technique specification sheets used in assessing the depth of the volumetric indication. The licensee also clarified that for the top-of-the-tubesheet inspections, STPNOC usually inspects 100 percent of the tubes in the periphery of the SG and the no-tube lane, and an additional 20 percent of the remaining tubes in the interior of the bundle. During 1RE19, STPNOC inspected 100 percent of the "kidney region" tubes.

The NRC staff asked the licensee to provide a copy of the eddy current data for independent analysis, and the licensee agreed to provide it.

December 30. 2015, Follow-up Conference Call The licensee stated that the causal evaluation was estimated to be complete by June 30, 2016.

Upon completion of the causal evaluation, the licensee stated it would provide the results to the NRC.

The licensee clarified that if the causal evaluation concluded that the volumetric indication in the tube in R30C78 was due to a corrosion or pitting mechanism, it would conduct a degradation assessment assuming that the mechanism was existing. In performing the degradation assessment, STPNOC would assume the Alloy 690 tubing has the same propensity for pitting as Alloy 600 material.

STP, Unit 1, has nitrogen-16 monitors installed that are capable of detecting primary-to-secondary leakage as low as 1-gallon per day and the detectors alarm in the control room. The licensee stated that primary-to-secondary leakage was not expected this operational cycle, and that STP currently meets all Electric Power Research lnstitute's guidelines concerning SG leakage monitoring. The indication in the tube in R30C78 had an estimated growth rate of 1 percent per effective full power year. Additionally, for an indication of this size, the

through-wall depth would have to be approximately 95 percent before primary-to-secondary leakage would be expected.

The NRC reviewed the eddy current data provided by the licensee in November 2015 and noted three additional indications in tubes in R70C140, R84C22, and R84C24. The licensee clarified that all three of these indications were caused by foreign objects that had been removed in previous outages.

• ML16013A066 *via memo dated 1/5/16 OFFICE NRR/DORL/LPL4-1/PM NRR/DORL/LPL4-1/LA NRR/DE/ESGB/BC*

NAME LRegner JBurkhardt GKulesa DATE 1/11/16 1/13/16 1/5/16 OFFICE N RR/DORL/LP L4-1 /BC NRR/DORL/LPL4-1/PM NAME RPascarelli LRegner DATE 1/14/16 1/14/16