ML20238E979

Application for Amend to License DPR-65,incorporating Changes in Limiting Condition for Operation 3.4.6.2(c) on Page 3/4 4-9 from 0.5 Gpm to 0.15 Gpm for Any One Steam Generator.Fee Paid

ML20238E979
Person / Time
Site:	Millstone
Issue date:	09/04/1987
From:	Mroczka E NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20238E981	List: B12648, Proposed Tech Specs,Changing Limiting Condition for Operation 3.4.6.2(c) on Page 3/4 4-9 from 0.5 Gpm to 0.15 Gpm for Any One Steam Generator ML20238E979
References
B12648, TAC-65852, TAC-66116, NUDOCS 8709150319
Download: ML20238E979 (5)

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.a m wum. c"* HARTFORD CONNECTICUT 061410270 k k J N.EIY$ NcC, (203) 665-5000 September 4,1987 Docket No. 50-336 B12648 Re: 10CFR50.90 U. S. Nuclear Regulatory Commission Attention: Document Control Desk i

Washington, D. C. 20555 Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Proposed Changes to Technical Specifications Primary to Secondary Steam Generator Leakage Limit Pursuant to 10CFR50.90, Northeast Nuclear Energy Company (NNECO) hereby proposes to amend its operating license No. DPR-65, by incorporating the attached changes into the Technical Specifications for Millstone Unit No. 2.

BACKGROUND During January 1987, Millstone Unit No. 2 was shut down to locate and repair a 0.15 gpm primary to secondary leak which had developed in one steam generator (SG). The leak was located in Tube Line 25, Row 19 in the SG 1 hot leg. Bobbin coil eddy current test (ECT) inspection of this tube showed a large volume indication at the top of the tubesheet. Further inspection using a rotating pancake coil (RPC) probe revealed that the large volume indication was circumferential!y oriented and extended approximately 2200 around the tube.

The ECT indications were interpreted as a possible circumferential crack which was through-wall over at least a portion of the 2200 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 structural limits could be met for a circumferential!y oriented crack. Based on calcula-tions which concluded that a circumferential crack of the size which would allow 0.15 gpm primary to secondary leakage was structurally acceptable, an adminis-trative reduction of the allowable leakage from 0.5 gpm to 0.15 gpm per SG was adopted.

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

! Millstore Unit No. 2.

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L U.S. Nuclear' Regulatory Commission B12648/Page 2 September 4,1987

'In a letter dated March 16,1987,II) the NRC Staff concurred with NNECO's

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evaluation that the structural integrity of the steam generator tubes appear adequate at the present. This conclusion was based upon NNECO's commitment to observe the administrative primary to secondary leakage limit, through any one steam generator, of 0.15 gpm until a formal Technical Specification change is issued by the NRC Staff.

DESCRIPTION OF CHANGE NNECO proposes to change Limiting Condition for Operation (LCO) number 3.4.6.2(c) on page 3/4 4-9 from 0.5 gpm to 0.15 gpm for any one steam generator. For consistency, NNECO would also change the Bases for the Steam Generator section 3/4.4.5 on page B 3/4 4-2a from 0.5 to 0.15 gpm in two places and would insert a paragraph on page B 3/4 4-3 in section 3/4.4.6.2 (Reactor Coolant System Leakage) that explains and justifies the change in the steam generator leakage limit.

NNECO is not proposing a change to the limit of I gpm total primary to secondary leakage through both SGs contained in Technical Specification 3.4.6.2(c). Although with the proposed limit of 0.15 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 at Millstone Unit No. 2. Since there have been no changes to the radiological considerations, NNECO believes it is prudent to leave this limit as it currently exists.

SAFETY ASSESSMENT The development of cracks in SG tubes is not a safety concern provided appropriate leakage limits me utilized and multiple tubes do not crack simulta-neously. Tube Line 25, Row 19 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. Multiple tubes will not crack simultaneously due to the nature of the postulated cracking phenomena.

The change in the leakage limit from 0.5 gpm to 0.15 gpm is based on a calculation that found that a tube which leaks at 0.15 gpm retains an acceptable level of structural integrity in accordance with Regulatory Guide 1.121. The calculation is based on tests and analysis. Rotating pancake coil eddy current i testing provided the size and orientation of the defect in Tube Line 25, Row 19 I in the hot leg of SG 1. The defect was found to be circumferentially oriented j and through-wall over a 400 segment. Its total length spanned a 2200 segment.

(1) A. C. Thadani letter to E. "I. Mroczka, " Steam Generator Tube Leakage at 1 Millstone Unit No. 2," dated March 16,1937.

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4 U.S. Nuclear Regulatory Commission B12648/Page 3 l, September 4,1987 The defect had a measured in-service leakage rate of 0.15 gpm. Laboratory testing provided independent confirmation of the results obtained above. Tests on similar tubes (test specimens were 3/4" x 0.043 inches wall thickness while Millstone Unit No. 2 tubes are 3/4" x 0.048 inches wall thickness) obtained leakage rates under normal operating conditions of 0.10 to 0.14 gpm for axial cracks (3 specimens) with 0.245 inch through-wall lengths. The 400 arc which is believed to be through-wall at Millstone Unit No. 2 has a length of 0.23 inches and a measured leakage rate of 0.15 gpm. Thus, the Millstone Unit No. 2 measured defect size and leakage rate correspond well with the laboratory defect size for similar leakage rates.

Structural integrity calculations were performed for the defect. It was found that the defect had structural margins to burst in accordance with Regulatory Guide 1.121 (see Attachment 2).

In addition, the leakage rate for this defect under accident conditions was estimated. It was found that the maximum total leakage under accident conditions would be 0.75 gpm which is within the previously analyzed value of I gpm. Thus, the previously analyzed radiological consequences for design basis accidents remain unchanged.

The observed defect which leaked at a rate of 0.15 gpm retained acceptable structural margins and would maintain accident condition leakage within previ-ously analyzed levels. Thus, this leakage limit is proposed to assure that any flaw of this type will be repaired before it becomes unacceptable.

NNECO has reviewed the attached proposed changes pursuant to 10CFR50.59 and has determined that they do not constitute an unreviewed safety question.

The probability of occurrence or the consequences of an accident or malfur'ction of equipment important to safety (i.e, safety-related) previously evaluated in the Final Safety Analysis Report have not been increased. The possibility for an accident or malfunction of a different type than any evaluated previously in the Final Safety Analysis Report has not been created. There has not been a reduction in the margin of safety as defined in the basis for any technical specification. These proposed changes will not result in physical changes to the plant, however, they will provide additional restrictions as to how the plant is operated. The more stringent leakage limit will ensure adequate structural margins for SG tubes. I SIGNIFIC ANT HAZARDS CONSIDER ATION 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:

1. Involve a significant increase in the probability or consequences of an accident previously evaluated. The proposed change would reduce the primary-to-secondary leakage limit from 0.5 gpm in any one steam gener-ator to 0.15 gpm. This will reduce the probability of occurrence of tube

U.S. Nuclear Regulatory Commission B12648/Page 4 September 4,1987 ruptures since the allowable leakage has been reduced. Consequences of the analyzed accidents are not increased since the reduced allowable leakage limit will ensure total accident condition leakage will remain below the 1 gpm limit.

2. Create the possibility of a new or different kind of accident from any previously analyzed. The proposed change lowers an existing leakage limit.

The reduction in the leakage limit clearly does not create the possibility of a new accident since no physical change has occurred. The more restrictive limit helps ensure an adequate margin of safety for the failure of a SG tube, an analyzed accident.

3. Involve a significant reduction in a margin of safety. Reduction in the leakage limit increases margins of safety. Further, structural integrity margins are retained at acceptable levels in accordance with Regulatory Guide 1.121.

l The Commission has provided guidance concerning the application of the standards in 10CFR50.92 by providing certain examples (51 FR 7750, March 6, 1986). Example (ii) most closely resembles this change, i.e., "a change that l

constitutes an additional limitation, restriction, or control not presently included in the technical specifications, e.g., a more stringent surveillance requirement."

The proposed reduction in allowable primary-to-secor.dary leakye to 0.15 gpm in any one SG has been evaNated. The proposed limit will ensure that acceptable structural margins are maintained in accordance with Regulatory Guide 1.121.

The Millstone Unit No. 2 Nuclear Review Board has reviewed and approved the attached proposed changes and has concurred with the above determinations.

Millstone Unit No. 2 is currently operating in accordance with the administrative limit of 0.15 gpm leakage per any one SG. Therefore, no specific schedule for issuance of the amendment is required.

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

Pursuant to the requirements of 10CFR170.12(c), enclosed with this amendment request is the application fee of $150.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY m&

E.3.A p6czka f Senior)Vice President

U.S. Nuclear Regulatory Commission B12648/Page 5 September 4,1987 Attachment cc: Kevin McCarthy Director, Radiation Control Unit Department of Environmental Protection Hartford, CT 06116 W. T. Russell, Region I Administrator D. H. Jaffe, NRC Project Manager, Millstone Unit No. 2 T. Rebelowski, Resident Inspector, Millstone Unit Nos. I and 2 STATE OF CONNECTICUT )

) ss. Berlin COUNTY OF HARTFORD )

l Then personally appeared before me E. 3. Mroczka, who being duly sworn, did state that he is Senior Vice President of Northeast Nuclear Energy Company, a Licensee herein, that he is authorized to execute and file the foregoing information in the name and on behalf of the Licensees herein and that the statements contained in said information are true and correct to the best of his knowledge and belief.

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