L-PI-03-095, 2003 Unit 2 Steam Generator Category C-3 Inspection Results 30-Day Report

2003 Unit 2 Steam Generator Category C-3 Inspection Results 30-Day Report

ML033210114
Person / Time
Site:	Prairie Island
Issue date:	11/07/2003
From:	Solymossy J Nuclear Management Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-03-095
Download: ML033210114 (4)

Text

Commid tdPraie Island Nuclear Generating Plant Committed to Nudarelen Operated by Nuclear Management Company, LLC L-PI-03-095 November 7, 2003 Technical Specification 5.6.7.3 U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT DOCKET 50-306 LICENSE No. DPR-60 2003 UNIT 2 STEAM GENERATOR CATEGORY C-3 INSPECTION RESULTS 30-DAY REPORT In accordance with Technical Specification 5.6.7.3 this special report due to Category C-3 inspection results of the Unit 2 steam generator tubing is provided for the information of the NRC Staff.

The results of the inspection of 21 Steam Generator and 22 Steam Generator were classified as Category C-3 in accordance with Technical Specification 5.6.7.3 because more than 1% of the inspected tubes in each Steam Generator were defective. The NRC Staff was informed of the Category C-3 classification by telephone on September 22, 2003. In accordance with Technical Specification 5.6.7.3, the 30-day special report on the Category C-3 steam generator inspection results is provided as Attachment 1 to this letter.

Inthis letter, we have made no new Nuclear Regulatory Commission commitments.

Please contact Jeff Kivi (651-388-1121) if you have any questions related to this letter.

Joseph M.Solymossy Site Vice President, Prairie Island Nuclear Generating Plant CC Regional Administrator, USNRC, Region IlIl Project Manager, Prairie Island Nuclear Generating Plant, USNRC, NRR NRC Resident Inspector - Prairie Island Nuclear Generating Plant Attachment 1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121

ATTACHMENT I NUCLEAR MANAGEMENT COMPANY, LLC PRAIRIE ISLAND NUCLEAR GENERATING PLANT DOCKET 50-306 November 7, 2003 PRAIRIE ISLAND UNIT 2 STEAM GENERATOR CATEGORY C-3 TUBE INSPECTION SPECIAL REPORT 2 pages follow

PRAIRIE ISLAND UNIT 2 STEAM GENERATOR CATEGORY C-3 TUBE INSPECTION SPECIAL REPORT Purpose This report fulfills the special reporting requirements of Prairie Island Technical Specification 5.6.7.3. This report is required whenever the steam generator tube inservice inspection finds more than 10% of the total tubes inspected are degraded tubes or more than I % of the inspected tubes are defective. This report summarizes the inspection results, the investigation into causes of major tube degradation and corrective measures. Corrective measures to prevent recurrence of Category C-3 inspections are discussed. Steam generator inspection results continue to exceed the category C-3 limits, so corrective measures do not prevent recurrence. However, careful inspections and repairs coupled with chemistry controls and low operating temperature provide assurance of safe and reliable operation of Unit 2 steam generators.

Summary of Inspection Results The inservice inspection for Unit 2 Steam Generators occurred from September 17, 2003 through October 1,2003. The inservice inspection consisted of inspection of 100% of the full length of tubing with the bobbin coil (except rows 1 through 4 u-bends),

100% of the hot leg tubesheet region, 25% of the hot leg Inconel 690 roll plugs, 25% of the cold leg tubesheet region and the rows 1 through 11 u-bends with mechanical rotating probes with +PointTM coil.

As a result of the eddy current inspections, 5.2% (165 of 3165) of the inspected tubes in 21 Steam Generator contained defects requiring repair. Seven of these tubes were plugged and the remaining 158 tubes were left in service using the F* and EF* repair criteria.

As a result of the eddy current inspections, 2.9% (92 of 3148) of the inspected tubes in 22 Steam Generator contained defects requiring repair. Ten of these tubes were plugged and the remaining 82 were left in service using the F* repair criteria.

Investigation into Causes of Major Tube Degradation There are two major causes of tube degradation in Unit 2 steam generators:

• Secondary side intergranular attack and stress corrosion cracking and

• Primary water stress corrosion cracking.

Secondary side intergranular attack and stress corrosion cracking (IGA/SCC or ODSCC) is occurring in the hot leg tubesheet crevice region and at the top of the hot leg tubesheet.

This was confirmed by metallurgical examination of three tube samples removed from Steam Generator 12 in January 1985. This was also confirmed by examination of a parent tube section removed during the sleeve pulls in Steam Generator 12 in 1996. In 1

PRAIRIE ISLAND UNIT 2 STEAM GENERATOR CATEGORY C-3 TUBE INSPECTION SPECIAL REPORT addition, three tubes were removed from Unit 1 for GL 95-05 Voltage Based Repair Criteria in 1997 and ODSCC was confirmed at the hot leg tube support plates.

Primary water stress corrosion cracking (PWSCC) at the roll transition region has been confirmed by metallurgical examination of one roll transition zone removed during sleeve pulls in Steam Generator 12 in 1996.

Corrective Measures Prairie Island participates in utility funded research on steam generator related issues.

Corrective measures to reduce and/or prevent tube degradation due to primary water stress corrosion cracking and secondary side IGASCC have been used by the industry with limited success. Prairie Island corrective measures include:

Chemistry Control: Prairie Island follows both the original equipment manufacturer's water chemistry guidelines and the EPRI secondary water chemistry guidelines.

The PWSCC degradation appears to be relatively independent of chemistry and occurs in regions of high residual stress.

High Hydrazine Control: Prairie Island maintains a hydrazine control band of 100 to 125 ppb as measured in the feedwater system.

Molar ratio control to reduce secondary side corrosion: Molar ratio control has been attempted by adjustments to steam generator blowdown resin ratios.

Conduct Crevice Flushing Operations with Boric Acid: Prairie Island employed crevice flushing from 1986 to 1999.

On-line addition of Boric Acid: Prairie Island began on-line addition of boric acid to Unit 1 steam generators in 1987.

Use of other chemical inhibitors: Titanium chelate has been added since January 1994.

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