ML20237B011

Revised 871008 Application for Amends to Licenses NPF-35 & NPF-52,incorporating New Steam Generator Tube Plugging Criteria.Rev Clarifies Proposed Definition of F Distance. Revised Justification & Discussion of NSHC Encl

ML20237B011
Person / Time
Site:	Catawba
Issue date:	12/03/1987
From:	Tucker H DUKE POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20237B014	List: ML20237B011 ML20237B157
References
NUDOCS 8712150410
Download: ML20237B011 (8)

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Dunn POWEn GOMPANY P.O. BOX 33180 clLAHLOTrE N.O. 28242 l HALU. TUCKER TELEPHONE vws eBassioewt (704) 07&4M1 NUCLEAR PRODU(MON December 3, 1987 l U. S. Nuclear Regulatory Commission ,

Attention: Document Control Desk '

Washington, D. C. 20555

Subject:

Catawba Nuclear Station, Units 1 and 2 Docket Nos. 50-413 and 50-414 Technical Specification Amendment Steam Generator Tube Plugging Criteria - F*

Dear Sir:

{

1 l Attached is a revised justification and discussion of no significant hazards l consideration and a revised Technical Specification change request. These revisions are applicable to my letter dated October 8, 1987, concerning the Technical Specification amendmnnt request to incorporate the new steam generator tube plugging criteria - F*.

l In particular, this revision clarifies the proposed definition of the F* distance I to make the definition consistent with the discussion. The F* distance requested is to be changed to 1.60 inches versus 1.31 inches. This is conservative with respect to the original request and is consistent with F* distances previously j licensed for other nuclear plants. The alternate tube plugging criteria has been l

expanded to show that tubes with degradation within the F* distance do not fall  !

under this definition.

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i The revision to the Technical Specification changes affects only Insertion A for  !

page 3/4 4-16. As such, only this Insertion page is being provided. The remainder of the Technical Specification changes are as presented in the october {

j 8, 1987 letter. The justification and discussion of no significant hazards consideration has been revised to correct several typographical errors.

l This proposal involves a revision to a previous amendment request to Catawba's l

Technical Specifications. Accordingly, no license fee is required.

Pursuant to 10 CFR $0.91 (b) (1) the appropriate South Carolina State official is being provided a copy of this revision to the previous amendment request.

Very truly yours 4 -

Hal B. Tucker RWO/1013/sbn 8712150410 871203 3 Attachments DR ADOCK 050 k

U. S. Nuclear Regulatory Commission December 3, 1987 Page Two xc: Dr. J. Nelson Grace, Regional Administrator i U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. Heyward Shealy, Chief Bureau of Radiological Health l South Carolina Department of Health &

Environmental Control l 2600 Bull Street Columbia, South Carolina 29201 American Nuclear Insurers c/o Dottie Sherman, ANI Library The Exchange, suite 245 ,

270 Farmington Avenue Farmington, CT 06032 M&M Nuclear Consultants 1221 Avenue of the Americas New York, New York 10020 INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 Mr. P. K. Van Doorn NRC Resident Inspector Catawba Nuclear Station l

JUSTIFICATION AND DISCUSSION OF NO SIGNIFICANT HAZARDS CONSIDERATIONS This amendment request applies to the Catawba Unit 1, Wcatinghouse model D3 steam generators and assesses the integrity of the tube bundle for tube eddy current inspection indications occurring in the length of tubing located within the tubesheet.

Alternate plugging criteria have been developed for use in determining whether or not plugging of full depth roll expanded tubes is necessary for degradation which has been detected in the expanded portion of the tube which is within the tubesheet (WCAP 11581). Existing Catawba Unit 1 steam generator tube plugging criteria apply throughout the tube length but do not take into account the reinforcing effect of the tubesheet on the external surface of the tube.

plugging criteria have been developed for tube degradation in the tube expansion region below the transition of the expanded to unexpanded portions of the tube.

The elastic preload applied by tubesheet spring-back from the roll procedure and friction between the tube and the tubesheet due to the roll expansion provides the force required to resist pullout. The presence of the tubesheet acts to constrain the tube and complement its integrity in that region by essentially precluding tube deformation beyond its expanded outside diameter i.e., the resistance to both tube rupture and collapse is significantly strengthened by the tubesheet. In addition, the proximity of the tubesheet significantly affects the leak behavior of through wall tube cracks in this region.

The F* criterion, represents a length, designated F*, of continuous tube expansion in the tubesheet such that tube pullout would not occur during either normal operation or postulated accident condition loadings. The F* distance is measured from the bottom of the roll expansion transition or the top of the tubesheet if the bottom of the roll expansion is above the top of the tubesheet.

As neither tube burst nor collapse can occur within the tubesheet region, steam generator tube integrity has been assessed on the basis of both tube pullout and primary to secondary leakage considerations.

In order to evaluate the F* criterion concept for indications within the l tubesheet, it was postulated that a circumferential severance of a tube could occur, which is contrary to existing plant experience. Based on plant operation and laboratory experience the configuration of any cracks in the tubesheet roll region, should they occur, is axial. For axial indications in the tubesheet region, the tube end at the tube-to-tubesheet weld remains structurally intact minimizing any potential for tube pullout. Implicit in assuming a circumferential severance to occur in the development of the F* criterion is the consideration that degradation of any extent or orientation within the tubesheet is demonstrated to be acceptable during normal and postulated accident conditions below the F* location.

An evaluation consisting of analysis and testing programs of the Westinghouse steam generator tubes' roll expanded into the tubesheet was conducted to determine the length of roll expansion necessary to resist tube pullout forces during normal and faulted condition loadings. The required engagement length, F*, below the bottom of the roll expansion transition or the top of the tubesheet, whichever is lower, to preclude tube pullout under postulated accident conditions

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I JUSTIFICATION AND DISCUSSION OF NO SIGNIFICANT llAZARDS CONSIDERATIONS (Cont.)

was calculated with a safety factor of 1.43, to be 1.06 inches. The safety factor of 1.43 corresponds to an ASME Code safety factor of 1.0/0.7 for allowable stress for faulted conditions. The calculation for normal operation loading )

conditions with a safety factor of 3 results in a distance of 1.04 inches so the postulated accident loading condition value of 1.05 inches is limiting. The I engagement length determination method was derived from preload testing and was J verified as conservative by both tube pullout and hydraulic proof (pressure) testing. Specifically, the F* criterion was calculated from a derived preload force and an assumed conservative static coefficient of friction for tube to tubesheet contact. Both the tube pullout and hydraulic proof testing conducted on rolled joints provided support for the derived preload force as well as an indirect measurement of the actual static coefficient of friction. Also, in assessing the F* criterion, it is expected that the radial preload resulting from the roll expansion is sufficient to significantly restrict leakage during normal operating and postulated accident condition loadings.

Use of a conservative eddy current elevation location uncertainty increases the operational value of F* above that which has been calculated as the minimum J

required engagement length. The uncertainty value is based on previous experience and laboratory testing.

On the basis of this evaluation, it is determined that tubes with any tube I degradation within the tubesheet region below the operational F* pullout criterion (including allowance for eddy current elevation uncertainty) can be 3 left in service. Tubes with tube degradation which are located a distance of ]

less than F* below the bottom of the roll expansion transition or the top of the l tubesheet should be removed from service by plugging in accordance with Technical Specification requirements.

The criteria defined in this evaluation have been demonstrated to result in tube integrity considerations commensurate with Hegulatory Guide 1.121 criteria both analytically (tube preload) and empirically (tube pullout and proof testing and leakage testing). Therefore, implementation of the alternate tubesheet region I plugging criteria within the Catawba Unit 1 steam generators is determined not to l represent an unreviewed safety question as defined in 10 CFR 50.59 (a)(2). ,

j As required by 10 CFR 50.91 (a)(1) this analysis is provided to demonstrate that  !

a proposed license amendment to implement alternate tubecheet region tube plugging criteria for the Catawba Unit I steam generators represents no significant hazards consideration. In accordance with the three factor test of 10 CPR 50.92(c), implementation of the proposed license amendment was analyzed using the following standards and found not to: 1) involve a significant increase in the probability or consequences for an accident previously evaluated; or 2) create the possibility of a new or different kind of accident from any accident previously evaluated; or 3) involve a significant reduction in a margin of safety.

The amendment has been proposed to address potential eddy current indications of tube degradation in the roll expanded portion of the tubes within the tubesheet in the steam generators at Catawba Unit 1. These steam generators were fabricated

JUSTIFICATION AND DISCUSSION OF NO SIGNIFICANT HAZARDS CONSIDERATIONS (Cont.)

with a mechanical roll expansion of the tube the full depth of the tubesheet.

Using existing Technical Specification tube plugging criteria, many of the tubes which may be identified to exhibit these indications would have to be removed I from service. It can be shown that tube plugging is not required in many cases to maintain tube bundle integrity.  !

The proposed license amendment (Technical Specification change) addresses the action required when degradation has been detected in the roll expanded portion of steam generator tubes within the steam generator tubesheet. Existing plugging criteria, i.e., current applications of Regulatory Guide 1.121, do not take into account the effect of the tubesheet on the external surface of the tube. The presence of the tubosheet will enhance the integrity of degraded tubes in that region by precluding tube deformation beyond the expanded outside diameter.

Additionally, a portion of the roll expansion at the top end of the tube expansion is sufficient to preclude pullout of the tube during normal operation and postulated accident condition loadings if a tube were postulated to sever circumferentially during plant operations in the portion of the tube covered by the proposed amendment. Finally, the roll expansion of the tube into the tubesheet provides a barrier to significant leakage for through wall cracking of j the tube in the expanded region.

The proposed change designates a portion of the tube for which tube degradation  ;

does not necessitate remedial action except as dictated for compliance with tube l leakage limits as set forth in the Catawba Unit 1 Technical Specifications. As noted above, the area subject to this change is in the expanded portion of the tube within the tubesheet of the steam generators. The length of expansion-required to resist pullout for all postulated conditions, designated F*, has been determined to be 1.06 inches. Since the expansion of the tube above F* is sufficient to preclude pullout of the tube, use of the F* criteria does not depend on any determination of the condition of tube degradation in the portion of the tube below the F* distance. The addition of an eddy current elevation location uncertainty allowance results in an operational F* value which is t greater than the calculated minimum required engagement length of 1.06 inches.

The proposed amendment would modify Technical Specifications B 3/4.4.5 (Steam Generator Bases), and specifications 4.4.5.2, 4.4.5.4 and 4.4.5.5 (Steam Generator Surveillance Requirements) which provide tube inspection requirements and acceptance criteria to determine the level of degradation for which the tube may remain in service. The proposed amendment would add definitions required for the alternate plugging criteria and prescribe the portion of the tube subject to the criteria. The proposed Technical Specification changes accompany this analysis.

The proposed amendment would preclude occupational radiation exposure that would otherwise be incurred by plant workers involved in tube plugging operations. The proposed amendment would minimize the loss of margin in the reactor coolant flow through the steam generator in LOCA analyses. The proposed amendment would avoid loss of margin in reactor coolant system flow and therefore assist in assuring that minimum flow rates are maintained in excess of that required for operation at full power. Reduction in the amount of tube plugging required can reduce the length of plant outages and reduce the time that the steam generator is open to the containment environment during an outage.

JUSTIFICATION AND DISCUSSION OF NO SIGNIFICANT HAZARDS CONSIDERATIONS (Cont.)

10 CFR 50.92 states that a proposed amendment involves no significant hazards considerations if operation in accordance with the proposed amendruent would not:

(1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin of safety.

(1) Operation of Catawba Unit 1 in accordance with the proposed license amendment does not involve a significant increase in the probability or consequences of an accident previously evaluated.

The supporting technical and safety evaluations of the subject criteria (WCAp 11581, proprietary and WCAp 11582, non-proprietary, and SECL 87-389) j demonstrate that the presence of the tubesheet will enhance the tube integrity in the region of the hardroll by precluding tube deformation .

beyond its initial expanded outside diameter. The resistance to both tube rupture and tube collapse is strengthened by the presence of the tubesheet in that region. The result of the expansion of the tube into the tubesheet is an interference fit between the tube and the tubesheet. Tube rupture can not occur because the contact between the tube and tubesheet does not permit )

sufficient movement of tube material. In a similar manner, the tubesheet does not permit sufficient movement of tube material to permit buckling collapse of the tube during postulated LOCA loadings.

Additionally through analysis and testing, Westinghouse has demonstrated I that the roll expansion above the F* distance is sufficient to preclude pullout of the tube from the tubesheet. Even with the conservative assumption that a tube could completely sever circumferential1y below the F*

distance, test results demonstrate that pullout of the tube is precluded under normal and postulated accident condition loadings. This assumption is conservative as the degradation that has been observed in operating units has been typified as short and axially oriented. A conservative allowance is added for eddy current elevation location uncertainty to determine the )

operational value of F*.

Relative to expected leakage, the length of roll expansion above F* is sufficient to preclude significant leakage from tube degradation located below the F* distance. The existing Technical Specification leakage rate requirements and accident analysis assumptions remain unchanged in the unlikely event significant leakage from this region does occur. As noted above, tube rupture and pullout is not expected for tubes using the alternate plugging criteria. Any leakage out of the tube from within the tubesheet at any elevation in the tubesheet is fully bounded by the existing steam generator tube rupture analysis included in the Catawba Final Safety' Analysis Report. The proposed alternate tube plugging criteria do not adversely impact any other previously evaluated design basis accident.

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JUSTIFICATION AND DISCUSSION OF NO SIGNIFICANT HAZARDS CONSIDERATIONS (Cont.)

(2) The proposed license smendment does not create the possibility of a new or different kind of accident from any accident previously evalmated.

Implecientation of the proposed alternate tube plugging criteria does not introduce any significant changes to the plant design basis. Use of the criteria is a passive activity and does not provide a mechanism to result in a new or different accident outside of the region of the tubosheet expansion or below the F* length. Primary-to-secondary tube leakage as a result of l

degradation below the F* length would still be subjected to the limits for i leakage as defined in the Technical Specifications. Any hypothetical accident as a result of any tube degradation in the expanded portion of the tube would be bounded by the existing tube rupture accident analysis.

(3) The proposed license amendment does not involve a significant reduction in a margin of safety.

The use of the alternate tube plugging criteria has been demonstrated to l maintain the integrity of the tube bundle commensurate with the requirements of Regulatory Guide 1.121 for indications in the free span of tubes and the primary to secondary pressure boundary under normal and postulated accident l conditions. Acceptable tube degradation is any degradation in the tubesheet more than the F* distance and the strength of degraded tubes are consistent with the safety factors in the ASME Boiler and pressure Vessel Code useS in steam generator design. The F* distance has been verified by testing to be greater than tne length of roll expansion required to preclude significant leakage during normal and postulated accident conditions. The allowance used for eddy current elevation location measurement uncertainty hea been supported by previous experience and laboratory testing.

For axial or nearly axial indications in the tubesheet region, the tube end remains structurally intact further decreasing any potential for tube  ;

pullout. For tubes with axial or nearly axial cracks, the strength of the I tube relative to an axial load would not be reduced below the strength required to resist potential axial loads. In this case, leakage is the dominant consideration to determine the necessity of tube plugging. Again, based on testing, using the alternate plugging criteria would not be i 1

expected to result in significant leakage from throegh-wall cracks located  !

below the F* distance.

Implementation of the alternate tube plugging criteria will decrease the number of tubes which must be taken out of service with tube plugs. Tube plugs reduce t.a RCS flow margin, thus implementation of the alternate plugging criteria will maintain the margin of flow that would otherwise be reduced in the event of increased plugging. Based on the above, it is  ;

concluded that the proposed change does not result in a significant reduction in a margin of safety with respect to plant safety as defined in the Final Safety Analysis Report or the bases of the Technical Specifications.

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l JUSTIFICATION AND DISCUSSION OF NO SIGNIFICANT HAZARDS CONSIDERATIONS (Cont.)

l Based on the preceding analysis it is concluded that operation of Catawba Unit I l in accordance with the proposed amendment does not: result in the creation of an I unreviewed safety question, increase the probability of an accident previously evaluated, create the possibility of a.new or different kind of accident from any accident previously evaluated, nor reduce any margins to plant safety.

Therefore, the license amendment does not invrlve a Significant Hazards Consideration as defined in 10 CFR 50.92.

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