ML20211B571

Forwards Second 90-day Rept for Implementation of Voltage Based Repair Criteria at Prairie Island Unit 1.Rept Fulfills Requirements of Section 6.b of Attachment 1 to GL 95-05

ML20211B571
Person / Time
Site:	Prairie Island
Issue date:	08/19/1999
From:	Sorensen J NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20211B576	List: ML20211B571 ML20211B597
References
GL-95-05, NUDOCS 9908250034
Download: ML20211B571 (4)

Text

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Northern States Power Company i Prairie Island Nuclear Generating Plant 1717 Wakonade Dr. East Welch. Minnesota 55089 August 19,1999 Generic Letter 95-05 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Unit 1, Cycle 20 Steam Generator Tube Support Plate Voltage Based Repair Criteria 90-Day Report i

During the Unit 1 April 1999 Refueling Outage following operating cycle 19, the Voltage Based Repair Criteria for ODSCC at Tube Support Plates (TSPs) was used in '

accordance with the requirements of NRC Generic Letter (GL) 95-05 and the Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment Nos.

133 and 125 to Facility Operating License Nos. DPR-42 and DPR-60 for NSP's Prairie Island Nuclear Generating Plant, dated November 18,1997, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking." This SG tube repair criteria allows bobbin coil indications of less )

than 2 Volts at TSPs to remain in service providing the total leakage under postulated Main Steam Line Break (MSLB) conditions is less than 1.0 gpm at room temperature and provided the End of Cycle (EOC) conditional probability of burst is less than 1 X 10.

Tube pulls were not required for this inspection per GL 95-05, Section 4.a.

Based on the end of cycle 19 tube examination, one TSP intersection also included a l I zone of transgranular wastage separate from the intergranular attack within the crevice I

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region. Since it is not certain that the volumetric eddy current indications at tube l support plates are in compliance with Technical Specification 4.12.D.4.a the one new l tube with a volumetric indication not associated with qualified sizing techniques was i plugged. I,~ gaj l 0 f n .(i$

9908250034 990819 I PDR ADOCK 05000282 i P PDR (

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USNRC NORTHERN STATES POWER COMPANY August 19.1999 Page 2 Since the mixed mode degradation identified by a previous tube pull from Prairie Island was not explicitly evaluated in GL 95-05, Prairie Island achieved compliance for this outage by examination of all of the distorted tube support plate bobbin coilindications (DSis) with rotating coil probes. The intersection with volumetric indications is conservatively included in the leakage and burst calculations.

The maximum voltage DSis were 1.85 Volts in the 11 SG and 1.02 Volts in the 12 SG.

The combined population average voltage growth rate for cycle 19 was -0.018 Volts per EFPY.

The calculated leak rates under Main Steam Line Break conditions for the actual end of cycle 19 conditions are 0.021 gpm and 0.005 gpm for 11 and 12 steam generators, respectively. These rates are less than the allowable leak rate of 1 gpm and less than '

the predicted leak rates for end of cycle 19. All leak rates are at room temperature.

The calculated conditional probabilities of burst under MSLB conditions for the actual  !

end of cycle 19 conditions are 1.9X10-5 and 1.2X104 for 11 and 12 steam generators, respectively. These values are less than the allowable value of 1X10-2 and less than the predicted values for end of cycle 19.

i The predicted leak rates for end of cycle 20 under Main Steam Line Break conditions are 0.46 gpm and 0.44 gpm for 11 and 12 steam generators, respectively. These rates are less than the allowable leak rate of 1 gpm. All leak rates are at room temperature.

The predicted conditional probabilities of burst for end of cycle 20 under MSLB 4

conditions are 1.9X10 and 2.5X10 4for 11 and 12 steam generators, respectively.

These values are less than the allowable value of 1X10-2 ,

The analyses performed used the latest database, Addendum-2 to EPRI Report NP-7480-L, dated April 1998.

During the outage, none of the conditions of Technical Specification 4.12.E.5 (section 6.a of GL 95-05) arose which require notification of the NRC staff prior to returning the steam generators to service. That is:

a. The projected end-of-cycle leakage did not exceed the 1 gpm limit,

b. no circumferential crack-like indications were detected at the tube support plate intersections,

c. no indications extended beyond the confines of the tube support plate intersections,

d. no indications at the tube support plate elevations were attributable to primary water stress corrosion cracking,

e. the calculated conditional burst probability did not exceed 1X10-2 ,

1999 ul voltage based 90 day. DOC

USNRC NORTHERN STATES POWER COMPANY .

August 19,1999 i Page 3 I The Upper Repair Limit of 4.97 Volts used a cycle length of 598 EFPD, a growth rate of 30% per EFPY and an NDE measurement uncertainty of 20%.

The attached Westinghouse Report SG-99-07-006, dated July 1999, provides the second 90-day report for implementation of the voltage based repair criteria at Prairie Island Unit 1. This report fulfills the requirements of Section 6.b of Attachment 1 to Generic Letter 95-05.

In this letter we have made no new Nuclear Regulatory Commission commitments.

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

oel P. Sorensen Site General Manager Prairie Island Nuclear Generating Plant i c: Regional Administrator- Region ill, NRC l Senior Resident inspector, NRC l

NRR Project Manager, NRC J E Silberg

' Attachments: I

1. Westinghouse Report SG-99-07-006, " Prairie Island Unit 1 Cycle-20 Voltage- l Based Repair Criteria 90-Day Report."

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l l

l 1999 ul volt. age based 90 day. DOC l

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TRANSMITTAL MANIFEST NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT Unit 1, Cycle 20 Steam Generator Tube Support Plate Voltage Based Repair Criteria 90-Day Report Correspondence Date: August 19,1999 GL 95-05 l

USNRC: Westinghouse DCD (original) 1 W J Orga 1  ;

NRR, Tae Kim 1 S P Swigart 1 l Regional Admin lli 1 Resident inspector 1 Roger O. Anderson RSO-8 1 Mark McKeown RSQ-8 1 Pat Culbert RSQ-9 1 State of Minnesota George Miserendino GO-2 1 Steve Minn 1 Mike Wadley RSO-8 1 J E Silberg i K J Albrecht 1 Safety Audit Committee T E Amundson 1 A B Cutter 1 J O Hill 1 Gerard Goering i Bob Peterson 1 Mike Peckham 1 Terry Silverberg 1 Wayne Shamla RSO-8 1 Betty Underwood (SAC) 1 Joel Sorensen Pl 1 Ken Weinhauer 1 NL Administrative:.

Gene Eckholt 1 Extra Distribution: Jeff Kivi 1 Richard Pearson 1 Jack Leveille 1 Scott Wilson 1 Dale Vincent 1 NL File (original) 1 PIRecords Mgmt 1 USAR File No Commitment No Fire Protection No Design Change No Comments:

Manifest Date: August 20,1999 1

RMS- Doc Type ikg.)

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