ML20064E903

Application for Amend to License DPR-72,submitting Tscr 198, Proposing Interim Rev to Repair Criteria Contained in OTSG Surveillance Program in TS 5.6.2.10.4.a

ML20064E903
Person / Time
Site:	Crystal River
Issue date:	03/04/1994
From:	Beard P FLORIDA POWER CORP.
To:
Shared Package
ML20064E908	List: 3F0394-02, Forwards TS Change Request 198,requesting Amend to License DPR-72,proposing Interim Rev to Repair Criteria Contained in OTSG Tube Surveillance Program in TS 5.6.2.10.4.a ML20064E903 ML20064E976 ML20064E993
References
3F0394-02, 3F394-2, NUDOCS 9403150080
Download: ML20064E903 (5)

Text

A - .n - - ,

U. S. Nuclear Regulatory Commission 3F0394-02 Page 4 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION IN THE MATTER )

) DOCKET N0. 50-302 FLORIDA POWER CORPORATION )

CERTIFICATE OF SERVICE P. M. Beard, Jr. deposes and says that the following has been served on the Designated State Representative and Chief Executive of Citrus County, Florida, by deposit in the United States mail, addressed as follows:

Chairman, Administrator, Board of County Commissioners Radiological Health Services of Citrus County Department of Health and Citrus County Courthouse Rehabilitative Services Inverness, FL 34450 1323 Winewood Blvd.

Tallahassee, FL 32301 A copy of Technical Specification Change Request No.198.

FLORIDA POWER CORPORATION M ,

P.M.. Beard, Jr.

Senior Vice President ,

Nuclear Operations SHORN TO AND SUBSCRIBED BEFORE ME THIS DAY OF MARCH, 1994 JOAn) 8vFE M k l ]M i Y NitWy Public (print) Notary Publi6-(tignature)

Notary Public, State of Florida at Large My Commission Expires: p.cf muay renue, mm e n onm. y 940315o080 94o3o4 " E'N N' "

l DR ADOCK 05ooo3o2 p

PDR .2

i

. \

l U. S. Nuclear Regulatory Commission  !

3F0394-02 l Page 5 j l

FLORIDA POWER CORPORATION  ;

CRYSTAL RIVER UNIT 3 i DOCKET NO. 50-302/ LICENSE NO. DPR-72  !

REQUEST NO. 198, REVISION 0 '

INTERIM OTSG TUBES REPAIR LIMIT LICENSE DOCUMENT INVOLVED: Technical Specification (TS) ,

PORTIONS: Technical Specification 5.6.2.10.4.a.

DESCRIPTION OF REQUEST:

Currently, the TS repair limit used as the criteria to remove steam generator tubes from service is 40% through-wall (TW). This criteria is based on a structural evaluation of a simplified model of tubes with uniform wall thinning.

Most degradation has substantially different morphology. The percent TW is typically measured by the " bobbin ceil phase angle method".

This proposal is an interim change cor:sisting of a method for selecting an alternate criteria to be used for repair of OTSG tubes utilizing the indications' signal-to-noise ratio, amplitude and axial /circumferential dimensions. The definitions of imperfection and degradation are being revised to add signal-to-noise ratio, voltage and axial /circumferential dimensions as defining parameters.

The proposed alternate criteria will be as follows.

Indications with bobbin coil signal-to-noise ratios > 5:1 will continue to be sized using the " phase angle" method. The repair limit will be equal to 40% of the nominal tube wall thickness.

Indications with a bobbin coil signal-to-noise ratio 5 5:1 and voltage-amplitude < two volts will remain in service.

Indications with a bobbin coil signal to noise s 5:1, voltage amplitude greater than two volts, axial extent 10.25 inches and circumferential extent s 120 degrees will remain in service. These physical characteristics will be measured by motorized rotating pancake coil (MRPC) probes.

These criteria apply to all regions of OTSGs A and B.

REASON FOR REQUEST:

During previous eddy current inspections, a significant number of small volume indications were identified. Due to the small signal amplitude associated with these indications, they can not be accurately sized by conventional bobbin coil phase angle. Therefore, FPC chose to develop other methods to disposition these small volume indications. FPC has determined that the proposed repair criteria described above is more accurate than the TW criteria currently used in the TS.

U. S. Nuclear Regulatory Commission 3F0394-02 Page 6 EVALUATION OF REQUEST:

The approach used by FPC to evaluate the proposed repair criteria is discussed in the " Regulatory Guide (RG) 1.121 Evaluation" submitted in conjunction with this amendment request (Attachment 1). The evaluation contains a methodology for demonstrating the adequacy of the proposed repair limit. FPC considers the essential elements for demonstrating the acceptability of the proposed repair criteria to be:

Structural adequacy of the tubing.

Section 5.0 of Attachment 1, discusses the results of the structural analysis performed by MPR and Associates Inc. The MPR structural analysis calculated the maximum allowable tube wall degradation for various types of damage mechanisms of the CR-3 OTSG tubing. The proposed repair limit provides considerable margin above the RG 1.121 allowable values for steam generators tube degradation.

Growth rate of tube flaws at CR-3.

Section 6.0 of Attachment 1, documents a review performed by the EPRI NDE Center to assess growth of 1GA indications observed in the first span of the B OTSG and a comparison of the last three eddy current inspections completed by BWNS. The objective of this comparison was to assess growth of tube flaws at CR-3. EPRI concluded that the IGA patches had not arown since they were detected. BWNS also found no significant growth for indications present at the free span or the support plates. However, the proposed repair criteria includes a 1 volt marain for conservatism.

Accuracy of detectability and sizing for CR-3 pit-like IGA.

Section 7.0 of Attachment 1, provides a discussion of EPRI's findings regarding eddy current sizing accuracy correlations. A linear regression and comparison of eddy current indications and actual metallurgical test results demonstrated  ;

that the bobbin coil phase angle method of sizing could not accurately size the l small volume indications found at CR-3. The proposed method of screening l indications will utilize a voltage limit to assess the need for a second level I evaluation of the indication prior to its disposition.

Conservatism of signal amplitude and dimensional plugging limits.

Section 8.0 of Attachment 1, provides the basis for the proposed signal amplitude i based screening limit of 2 volts and for the dimensional based repair limit of I indications with axial extent less than or equal to 0.25 inches and  ;

circumferential extent less than or equal to 120 degrees. Section 10.0 of the '

attachment discusses in detail the proposed methodology for dispositioning signal to noise (S/N) indications. Also, sections 10.0 and 7.5 of Attachment 1, discuss the conservatism of MRPC for sizing. The axial and circumferential limits selected within the range of interest (low S/N and >2 volts) reduces the significance of TW sizing since, the limits were developed assumina a 100% TW defect. CR-3's operating experience demonstrates there is a low probability for this to happen. .

I

U. S. Nuclear Regulatory Commission 3F0394-02 Page 7 Margin against tube rupture.

Section 5.0 of Attachment 1, summarizes the extensive investigation and burst testing performed by FPC as part of the Refuel 8 Tube Pull Project and burst testing performed on OTSG tubing with simulated flaws that envelope all known t OTSG damage mechanisms.

Leakage-considerations.

Section 9.0 of Attachment 1, discusses primary-to-secondary leakage rates under ,

normal operating pressure. Since CR-3 has not experienced significant tube 1 degradation, the current administrative limit of approximately 430 gallons per day is considered reasonable for assuring OTSG tubing structural adequacy and practical in terms of detectability.

l l

l

U. S. Nuclear Regulatory Commission 3F0394-02 Page 8 SHOLLY EVALUATION OF REQUEST:

Florida Power Corporation has reviewed the requirements of 10CFR50.92 as they -

relate to the proposed method for sizing steam generator tubing degradation and changes to the plugging / sleeving limits and considers the proposed change does not involve a _ significant hazards consideration. In support of this conclusion the following analysis is provided:

1. The proposed change will not significantly increase the probability or consequences of an accident previously evaluated because the structural integrity of the OTSG tubes will be maintained. Regulatory Guide 1.121 margins against tube burst are mafntained for normal and postulated accident conditions.

2. The proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated because the primary-to-secondary leakage flow through a postulated broken tube is not affected by this change. The proposed change does not affect other systems, equipment or failure modes previously evaluated.

3. The proposed change will not involve a significant reduction to the margin of safety because the structural margirs of the OTSGs for both normal and accident conditions are maintained.

The proposed change is an enhancement to the inservice inspection of OTSG tubing that will provide a higher level of confidence that tubes exceeding the allowable limits are repaired while sound tubes are left in service.