ML20155E495

Application for Amend to License DPR-65,incorporating primary-to-secondary Steam Generator Leakage Limit to Ensure Acceptable Structural Margins.Fee Paid

ML20155E495
Person / Time
Site:	Millstone
Issue date:	09/30/1988
From:	Mroczka E, Sears C NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20155E498	List: B13032, Proposed Tech Specs Pages 3/4 4-7,3/4 4-9,B 3/4 4-2a & B 3/4 4-3 Re Surveillance Requirements for RCS Leakage ML20155E495
References
B13032, TAC-69401, TAC-69557, NUDOCS 8810120317
Download: ML20155E495 (5)

Text

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NORTHEAST UTILITIES o n.,,,o mc.,,s,m.n si,,,i.e.,nn. Conn ,ci,co, 1 Ui7.$ E2$ISC P O. BOX 270

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.%, a . (203) 665-5000 September 30, 1988 Docket No. 50-336 EllQM Re: 10CFR50.90 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Propose ( Changes to Technical Specifications Primary-to: 4econdary Steam 1ggerator Qakane limit Pursuant to 10CFR50.90, Northeast Nuclear Energy Company (NNECO) hereby proposes to amend its Operating 1.icense No. DPR-65 by incorporating the attached changes into the Technical Specifications for Millstone Unit No. 2.

Backaroun_d During January 1987 Millstone Unit No. 2 was shut down to locate and repair a 0.15 gpm primary-to-secondary leak which had develboed in one steam generator (SG). The leak was located in tube line 25, row 19, in the hot la w side of SG #1 . Bobbin coil eddy current test (ECT) inspection of this tube showed a large volume indication at the top cf the tube sheet. Further inspection using a rotating pancake coil (RPC) probe revealed that the large volume indication was circumferentially oriented and extended approxituately 220 degrees around the tube. The ECT indi.;ations were interpreted as a possible circumferential crack which was through wall over at least a portion of the 220-degree circumferential extent.

Assessments of the safety significance of the leaking tube were performed and concluded that operation of the SG continued to be safe provided that struc-tural limits could be met for a circumferentially oriented crack. Based on I

calculations which concluded that a circumferential crack of the size which would allow 0.15 gpm primary-to secondary leakage was structurally acceptable, an administrative reductien of the allowable leakage from 0.5 to 0.15 gpm per SG was adopted.

A meeting with the NRC Staff was held en March 5, 1987 in Bethesda, Maryland, to discuss events leading up to, and actions taken as a result of. the steam I generator primary-to-secondary leak at Millstone Unit No. 2. NNEc0 informed the Staff that an administrative leakage limit of 0.15 gpm per steam generator had been established to ensure that acceptable structural margins wouid be maintained, and that a license amendment request would be submitted to the NRC Staff to change the Technical Specifications for Millstone Unit No. 2.

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U.S. Nuclear Regulatory Commission B13032/Page 2 September 30, 1988

In a letter dated March 16,1987,(I) the NRC Staff concurred with NNECO's l evaluation that the structural integrity of the steam generator tubes appeared i f

adequate for the present. This conclusion was based upon NNECO's commitment l to observe the administrative primary to secondary leakage limit, through any  ;

one steam generator, of 0.15 gpm until a formal technical specification change

• could be issued by the NRC Staff. This administrative limit was formaliz.3d as  ;

a change to the Hillstone Unit No. 2 Technicalgecifications by issuance of License Amendment No. 121 on November 13, 1987.

j During the January 1988 Millstone Unit No. 2 refueling outage, tube line 25,  ;

row 19, in the hot leg side of SG #1 was removed for destructive examination.

The observed circumferential crack was larger than the size which had been

, previcusly measured. Based on a more complete understanding of the cracking i phenomena, the structural implications of circumferential cracks were reevalu- l l ated and a new, lower, primary-to secondary leakage limit of 0.10 gpm was ,

1 administratively implemented prior to start-up from the 1988 refueling outage.

This leakage limit was implemented to better assure that any flaw of the type j discovered in the leaking tube will be repaired before the structural margin or accident condition leakage becomes unacceptable. Accordingly, this  ;

I proposed change formalizes that administrative limit.

l i Descriotion of Chamgg NNECO proposes to change limiting Condition for Operation (LCO) 3.4.6.2(c) on  !

page 3/4 4 9 from 0.15 to 0.10 gpm for any one steam generator. For consis- 1 1

tency, NNECO would also change the Bases for the Reactor Coolant System I Leakage Section 3/4.4.6 on page B 3/4 4 3 from 0.15 to 0.10 gpm. The 0.10 gpm I

limit assures that the structural integrity of the tube will be adequately

maintained even in the presence of a circumferentially oriented crack leaking ,

l at the allowable limit.

1 j The proposed change will also modify the requirements to perform eddy current

examinations when the unit is shut down to repair primary to secondL y  !

I leakage. The change will limit the required examinations to thuse necessary l to locate the leakage, investigate the cause and define appropriate corrective measures. Prior to restart, an evaluation will be performed to assure that  !

l structural integrity is adequate, f l Section 4.4.5.1.3(c)(1) would be changed to eliminate the requirement for l 1 unscheduled eddy current inspections in the case of primary to-secondary tube  :

i leaks in excess of the limits of Section 3.4.6.2; and a new Section  !

) (1) A. C. Thadani letter to E. J. Mrotzka, "Steam Generator Tube Leakage at ,

! Millstone Unit No. 2," dated March 16, 1987.  ;

D. Fl. Jaffe lette" to E. J. Mroczka, "Issuance of Amendment," dated 1

l (2)

! November 13, 1987.

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U.S. Nuclear Regulatory Commission B13032/Page 3 September 30, 1988 i

(4.4.5.1.3(d)) would be added to specify the examinations and evaluations conducted in the event of primary to-secondary leakage and to supersede the requirements of Section 4.4.5.1.2. For consistency, NNEC0 would also change the Bases for the Steam Generator Section 3/4.4.5 on page B 3/4 4 2a.

l NNECO is not proposing a change to the limit of I gpm total primary-to-l secondary leakage through both SGs contained in Technical Specifica-

' tion 3.4.6.2(c). Although, with the proposed limit of 0.10 gpm leakage per SG

< the 1 gpm total leakage would never conceivably be reached, the 1 gpm limit was established for radiological considerations following design basis events j at Hillstone Unit No. 2. Since there have been no changes to the radiologi' cal i considerations, NNEC0 believes it is prudent to leave this limit as it currently exists, j Safety Assessment

] The development of cracks in SG tubes is not a significant safety concern provided appropriate leakage limits are utilized. Physical examinations of

! tube line 25, row 19, and our technical evaluations have demonstrated that if a circumferential crack were to develop, the crack would penetrate through-

) wall and leak prior to reaching a condition which would burst the tube. The

change in the leakage limit from 0.15 to 0.10 gpm is based on new under-l standing of the defect.

1 The existing Technical Specification requires a random sample examination of the tube population in the event measured primary-to secondary tube leakage exceeds the allowible. The proposed change to the requirement for eddy l current examinations would redirect the scope of examinations to those neces-

sary to locate the leakage, investigate the cause, and define appropriate

! corrective measures. Prior to restart, an evaluation to assure adequate structural integrity would be required. In contrast, the existing Technical i Specification requires examinations which target the general level of struc-l tural integrity and does not address the specific cause of leakage or its j effect on structural integrity.

! In light of the above, NNECO considers the proposed change to be safer and i more practical than the existing Technical Specification requirement. The existing program could possibly miss a local problem, in that it does not l

require an investigation of cause, or a reassessment of structural integrity.

! In addition, the proposed changes are more conservative in that an inspection

is required regardless of whether the leakage limits are exceeded prior to

shutdown of the unit to repair primary-to secondary leakage.

j Sionificant Hazards Consideration l

i NNECO has reviewed the attached proposed changes in accordance with 10CFR50.92

( and has concluded that they do not involve a significant hazards consideration in that these changes would not:

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i U.S. Nuclear Regulatory Commission i B13032/Page 4 September 30, 1988 ,

1. Involve a significant increase in the probability or consequences of an

! accident previously evaluated. The proposed change would reduce the i

primary-to-secondary leakage limit from 0.15 gpm in any one steam gener-ator to 0.10 gpm. This will reduce the probability of occurrence of tube

ruptures since the allowable leakage has been reduced. Consequences of r

-j the analyzed accidents are not increased since the reduced allowable leakage limit will ensure that the total accident condition leakage will i remain below the 1 gpm limit.

! The change to modify eddy current inspection requirements formalizes the existing practices at the unit in the event the unit is shut down prior j to the leak exceeding the Technical Specification limits. Adequately t l

fulfilling the proposed requirements to locate the leak, regardless of  ;

t size, investigate the cause, and identify appropriate corrective actions i

) increases the probability that highly localized )roblems, as well as .

The addit'on of the requirement widespread problems, will be identified.

to evaluate the structural integrity prior to restart of the unit will

! increase the probability that all items of safety significance have been adequately addressed and will increase the overall safety of the unit. .

! 2. Create the possibility of a new or different kind of accident from any ,

j previously analyzed. The propcsed change lowers an existing leakage  :

i limit. The reduction in the leakage limit clearly does not create the [

] possibility of a new accident since no physical change has occurred. The t j more restrictive limit helps ensure an adequate margin of safety for the failure of an SG tube, an analyzed accident.

l Since the proposed change in eddy current inspection requirements does  !

a not alter the way the plant is operated, the potential for an unanalyzed

) accident is not created and no new failure modes are introduced. j i

i l 3. Involve a significant reduction in a ma,:.n. of safety. The reduction in i the leakage limit increases margins of safety. Further, structural '

l integrity margins are retained at acceptable levels in accordance with j Regulatory Guide 1.121. The proposed change to eddy-current inspection  !

j requirements is more conservative in that an inspection is required  ;

j regardless of whether the leakage limits are exceeded prior to shutdown  ;

of the unit to repair primary to secondary leakage, i The Commission has provided guidance concerning the application of the stan- ,

i dards in 10CFR50.92 by providing certain examples (51 FR 7750, March 6, 1986).

I Example (ii) most closely resembles this change; i.e., "a change that consti-  !

tutes an additional limitation, restriction, or control not presently included

! in the technical specifications, e.g., a rmre stringent surveillance require- i ment " because the allowable leakage is reduced and proposed post-leakage requirements focus the inspection examinations to more closely relate them to .

the cause of the leakage, j l

l The Millstone Unit No. 2 Nuclear Review Board has reviewed and approved the ,

! attached proposed changes and has concurred with the above determinations.

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i U.S. Nuclear Regulatory Commission '

B13032/Page 5 September 30, 1988 Millstone Unit No. 2 is currently operating in accordance with the ad.ninistra-tive limit of 0.10 gpm leakage per any one SG; therefore, no specific schedule ,

for issuance of the license amendment is required, t

l. In accordance with 10CFR50.91(b), we are providing the State of Connecticut with a copy of this proposed amendment, i

Pursuant to the requirements 10CFR170.12(c), enclosed with this amendment 3

request is the application fee of $150.

l Very truly yours, 1

NORTHEAST NUCLEAR ENERGY COMPANY l

l N..

E. J. Mroczka (Let4 Rtt.

M l Senior Vice President l

L, SV2__

l' By: C. F. Sears Vice President Attachment l cc: Mr. Kevin McCarthy i Director, Radiation Control Unit l Department of Environmental Protection i Hartford, CT 06116 I

i cc: W. T. Pussell, Reqinn 1 Administrator i D. H. Jaffe, NRC i'roject Manager, Millstone Unit Nos. 2 and 3 W. J. Raymond, Senior Resident inspector, Millstone Unit Nos.1, 2, and 3 STATEOFCONNECT!CVT) l ) ss. Berlin l COUNTY OF HARTFORD )

! Then personally appeared before me, C. F. Sears, who being duly sworn, did i state that he is Vice President of Northeast Nuclear Energy Company, a l Licensee herein, that he is authorized to execute and file the foregoing information in the name and on behalf of the Licensee herein, and that the l

l statements contained in said information are true and correct to the best of j his knowledge and belief.

l Yw % N.Lucla,e j Nottry Public i

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