ML20215D152

Application for Amend to License NPF-49,changing Tech Spec 4.3.4.2a to Increase Main Turbine Control Valve Testing Interval from Weekly to Monthly Per GE Recommendations.Fee Paid

ML20215D152
Person / Time
Site:	Millstone
Issue date:	06/10/1987
From:	Mroczka E NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20215D154	List: B12550, Proposed Tech Spec 4.3.4.2a,increasing Main Turbine Control Valve Testing Interval from Weekly to Monthly ML20215D152
References
B12550, NUDOCS 8706180415
Download: ML20215D152 (5)

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NORTHEAST UTILITIES cenerei Orrice. . seioen sireet. Beriin. connecticut THE COPeht cTQlf L@*? AND DOMP COMPANY l auum. wawav*ets nac'ac coua*= P.O. BOX 270 m ..na.owac" '*

HARTFORD CONNECTICUT 06141-0270 L L j ['"'*8]""77%^,*,

, ,, (203) 665-5000 June 10,1987 i Docket No. 50 423 B12550 Re: 10CFR50.90 i U. S. Nuclear Regulatory Commission Attn: Document Control Desk I Washington, D. C. 20555 I Gentlemen:

Millstone Nuclear Power Station, Unit No. 3 Proposed Revision to Technical Specifications Turbine Overspeed Protection Pursuant to 10CFR50.90, Northeast Nuclear Energy Company (NNECO) hereby proposes to amend its Operating License, NPF-49 by incorporating the attached proposed change into the Technical Specifications of Millstone Unit No. 3.

Specifically, the proposed change to Technical Specification Section 4.3.4.2a will increase the main turbine control valve testing interval from weekly to monthly in' accordance with the turbine manufacturer's (General Electric Company) recommenda tions.

Discussion Periodic valve testing and inspections provide assurance that the control valves will close when the turbine is tripped to prevent the turbine from reaching a destructive overspeed. Avoiding destructive overspeed is essential to minimizing the probability of the generation of turbine missiles which could impact and damage safety-related components, structures and equipment.

Justification for increasing the testing interval is based on accumulated operating experience of in-service nuclear units which show considerably lower valve failure than those values from fossil unit service upon which the weekly recommendation was originally based. General Electric turbine valves have demonstrated excellent reliability at Millstone Unit Nos. I and 2. In over 26 unit-years of operation, no valve failures to close have occurred and no incipient problems have been detected that might prevent a valve closure. Increased test intervals also reduces the number of plant load reductions from four per month j to one per month thereby minimizing the likelihood of system upsets, including i plant trips that might occur during plant load reductions.

Based on past in-service experience with nuclear turbine steam valves, General Electric has determined that turbine steam inlet valve reliability and testing 8706180415 870610 . g0 t i dl 46 d Ip l6 PDR ADOCK 05000423 Lg yd 6gt p tPDR i 4

U. S' Nuclear Regulatory. Commission B12550/Page 2 June 10,1987 intervais are no longer the major contributing factors in determining hypothetical turbine missiles. The overall probability of a hypothetical missile is therefore increased only a negligible amount by .increasin interval. The increased control valve test interval (monthly)g has the beenvalve used test in General Electric's probabilistic turbine missile analyses (basis for recommended surveillance testing and inspections), which demonstrate the adequacy of the' General Electric turbine design in maintaining an acceptably low probability of turbine missiles.

Safety Evaluation NNECO has reviewed the attached proposed change pursuant to 10CFR50.59 and has determined that it does not represent an unreviewed safety question. '..The basis for this determination is discussed below.

Effect on Design Basis Accident:

The proposed change increases the stroke test interval on the turbine control valves which negligibly increases the probability of control valve closure failure.

Such a failure by itself would not lead to a destructive turbine overspeed event.

A coincident failure of the turbine stop valve would have .to occur in conjunction with a demand for turbine overspeed protection before destructive overspeed could be reached. With an increase in the stroke test interval from weekly to monthly on the turbine control valve, the probability of significant plant damage caused by a turbine missile willincrease from 1.9 x 10-10 per year to 6.3 x 10-10 per year. This represents a neg!!gible increase in the probability value and this probability value is more than two orders . of magnitude lower than the j acceptable probability of significant damage as specified in Regulatory Guide ~

1.115. Therefore, this change yields an acceptable probability for turbine misslie damage due to overspeed. In addition, this proposed change will minimize the likelihood of a plant trip due to the plant load reduction for.the control valve testing since tests will be done once per month instead of the current four per j month. Based upon the above discussion, the proposed change does not impact the consequences of an accident caused by a turbine missile.

Potential for Creation of an Unanalyzed Accident The proposed change does not modify plant response to the point it may be l considered a new accident. As discussed above, the proposed change produces a I negligible effect on control valve reliability while reducing the likelihood of plant trip as the result of the valve testing. Therefore, it does not create the ,

possibility of an accident or malfunction of a different type than any evaluated- ]

previously in the safety analysis report.

Effect on the Margin of Safety l

Since the proposed change only modifies the testing interval for the turbine '

control valve, there is no impact on the basis of the technical specification.

Therefore, the change does not reduce the margin of safety as specified in the basis of any technical specification.

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4 U. S. Nuclear Regulatory Commission' B12550/Page 3 June 10,1987 1

Summary and Conclusions i

Based on the foregoing assessment, the change proposed herein is considered safe  !

and does not represent an unreviewed safety question as defined in 10CFR50.59  ;

since it does not: i I

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1. Increase the frequency of occurrence or the consequences of an accident or j malfunction of equipment important to safety previously evaluated in the j safety analysis report; _ .i 1

2.- Create the possibility of an accident or malfunction of a different type )

than any evaluated previously in the safety analysis report; y

3. Reduce the margin of safety as defined.in the basis for any technical specification.

Significant Hazards Consideration  ;

I In accordance with 10CFR50.92, NNECO has reviewed the attached proposed  !

change and has concluded that it does not involve a significant hazards consideration. The basis for this conclusion is that the three criteria of 10CFR50.92(c) are not compromised; a conclusion which is supported by our determinations made pursuant to 10CFR50.59. The proposed change does not involve a significant hazards consideration because this change would not:

1.

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Involve a significant increase in the probability or consequences- of an accident previously evaluated. . As stated above, with an increase in the l control valve test interval from' weekly to monthly, there will be. a negligible increase in the probability of significant plant damage caused by a turbine missile. The new value is more than two orders of' magnitude lower than the acceptable probability of significant plant damage specified in Regulatory Guide 1.115. In addition, the proposed change will minimize the likelihood of a plant trip due to load reductions for control valve testing since the tests will be done once per month instead of the current four per month. Therefore, the proposed change does not impact the consequences of an accident caused by a turbine missile.

2. Create the possibility of a new or different kind of accident from any previously evaluated. The proposed change produces a negligible effect on control valve reliability while reducing the likelihood of plant trip as the result of valve testing. Therefore, it does not cr.eate the possibility of an accident or malfunction of a different type than any evaluated previously in the safety analysis report. No design changes have been made to the turbine system; therefore, no new failure modes are introduced.

3. Involve a significant reduction in a margin of safety. As stated above, the proposed change only modifies the testing interval for the turbine control i valve and has no impact on the basis of the technical specification.

Therefore, the proposed change will not reduce the margin of safety as specified in the basis of any technical specification, i

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B12550/Page 4 June 10,1987 Moreover, the Commission has provided guidance concerning the application of standards in 10CFR50.92 by providing certain examples (March 6,1986, FR,7751) of amendments that are considered not likely to involve a significant hazards consideration. The change proposed herein is enveloped by example (vi), a change that either results in some increase to the probability or consequences of .

a previously analyzed accident or may reduce in some way a safety margin, but l where the results of the change are clearly within all acceptable criteria with respect to system or components specified in the Standard Review Plan. As stated above, with an increase in the control valve test interval from weekly to l monthly, there will be a negligible increase in the probability of significant plant damage (increases the probability from 1.9 x 10-10/ year to 6.3 x 10-10/ year) caused by a turbine missile. This new probability value is more'than the two orders of magnitude as specified lower in Regulatory than1.115 Guide the accep(tance probability i.e. less than 1 x 10- perof sig,nificant year). In damage addition, this proposed change will minimize the likelihood of a plant trip due load reduction for the control valve testing. Therefore, the proposed change would not involve a significant hazards consideration.-

Based upon the information contained in this submittal and the NRC final environmental assessment for Millstone Unit No. 3, NNECO has concluded that pursuant to 10CFR51, there are no significant radiological or non-radiological impacts associated with the proposed action and that the proposed license amendment will not have a significant effect on the quality of the human environment.

The Millstone Unit No. 3 Nuclear Review Board has reviewed and approved the attached proposed revision and concurs with the above determinations.

In accordance with 10CFR50.91(b), NNECO is 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 $150.00.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY

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Nr A/

E. pro'czka g/

Senror Vice President cc: Mr. Kevin McCarthy Director, Radiation Control Unit Department of Environmental Protection Hartford, Connecticut 06116 W. T. Russell, Region I Administrator

3. T. Shediosky, Resident Inspector, Millstone Unit No. 3 R. L. Ferguson, NRC Project Manager, Millstone Unit No. 3 i

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U. S. Nuclear Regulatory Commission

- B12550/Page5' '

June 10,1987 '

STATE OF CONNECTICUT )

./dj l9 ? 7f COUNTY OF HARTFORD. ) - ). ss. Berlin

. 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 -Lis : authorized to execute .!and file .the foregoing Information in the name' and on behalf of the Licensees herein and th'at the statements contained in said information are true and correct to the best of his

. knowledge and bellef.

Y1%'

Notary Public

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' MY COMMISSION EXPIRES MARCH 31,iM

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