ML20046C506

Informs of Proposed Change 168,requesting to Increase EDG Reliability & Availability by Reducing Number of Fast Start Tests

ML20046C506
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	08/04/1993
From:	Reid D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20046C507	List: ML20046C506 ML20046C514
References
BVY-93-30, NUDOCS 9308110088
Download: ML20046C506 (9)

Text

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VERMONT YANKEE NUCL'EAR POWER CORPORATION

.. gh- Ferry Road, Brattleboro, VT 05301-7002

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) ENGINEERING OFFICE 580 MAIN STREET f GOLTON MA 01740 (508)779-6711 August 4,1993 BVY 93-30 United States Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

References:

a) License No. DPR-28 (Docket No. 50-271) b) Generic Letter 84-15, " Proposed Staff Actions to improve and Maintain Diesel Generator Reliability" c) Letter VYNPC to USNRC, FVY 84-126, " Response to Generic Letter 84-15, Diesel Generator Reliability" d) Letter VYNPC to USNRC, BVY 89-49, " Surveillance Testing of ECCS and SLC Equipment, Supplement 2 to Proposed Change No.85" e) Letter VYNPC to USNRC, BVY 92-133, " Submittal of Vermont Yankee Nuclear Power Corporation Third-Interval inservice Testing Program Plan and Safety Evaluation Responses"

Attachment:

Relief Request RR-V03, Rev.1

Subject:

Proposed Change No. 168 to the Vermont Yankee Technical Specifications- Auxiliary Electric Power System Technical Specifications and Associated Revision to the Vermont Yankee Inservice Testing Program

Dear Sir:

Pursuant to 10CFR Part 50.90 of the Commission's Rules and Regulations, Vermont Yankee Nuclear Power Corporation proposes the following modifications to Appendix A of the Operating License [ Reference a)]. Pursuant to 10CFR Part 50.55a of the Commission's Rules and Regulations, Vermont Yankee Nuclear Power Corporation also proposes the following modifications to the Inservice Testing Program [ Reference e)].

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vonmm nsu o wouan Powon coiwo uuos United States Nuclear Regulatory Commission August 4,1993 Page 2 PROPOSED CHANGES Replace pages 173 and 174 of the Vermont Yankee Technical Specifications with the i attached pages 173 and 174. Add new page 173a, also attached.

Replace Relief Request Number RR-V03 of the Vermont Yankee Inservice Testing Program with the attached revised Relief Request.

l This proposed change modifies the monthly periodic testing of the emergency diesel i generators to permit a slow start test in place of the existing requirement to perform a i monthly fast start test. A fast start test shall be performed every six months in lieu of the  !

slow start test. Both the monthly and the every sixth month test will require the engine be run at expected maximum emergency loading not to exceed the continuous rating for a minimum period of one hour. A note has also been added allowing all diesel generator starts to be preceded by an engine prelube and warmup procedures.

In addition, some rearrangement and rewording of the Technical Specification requirements is proposed to enhance usability. However. the only substantive change to the requirements of the Technical Specifications is that which is discussed above.

The proposed change also results in a revision to the testing methods for the emergency diesel generator starting air inlet and vent valves. This is further discussed in the attached revision to Relief Request Number RR-V03 of the Vermont Yankee Inservice Testing Program.

REASON FOR CHANGE The proposed change is requested to increase emergency diesel generator (EDG) reliability and availability by reducing the number of fast start tests. Fast starts have been shown by NRC and industry sponsored research to contribute to diesel generator engine wear and failure. The NRC has endorsed the reduction of fast starts in Generic Letter 84-15,

" Proposed Staff Actions to Improve and Maintain Diesel Generator Reliability" [ Reference b)).

Vermont Yankee has already taken the initiative to incorporate many of the recommendations contained in Reference b) in its maintenance and surveillance program.

Reference c) reported that Vermont Yankee has prelubricated the engine prior to required surveillance tests, and has also limited the rate of engine loading in all surveillance tests except for the once per cycle test which requires the simulation of actual loading. Vermont Yankee now performs a slow start test on maintenance and troubleshooting starts that are not performed to demonstrate operability as required by the Technical Specification.

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August 4,1993 Page 3 Vermont Yankee has also improved diesel generator reliability and reduced diesel generator engine wear by modifying Technical Specifications [ Reference d)] to eliminate fast ,

start alternate testing of the diesel generator that were required by Technical Specifications when emergency core cooling systems or related subsystems were declared inoperable. This proposed change will further reduce engine wear and increase diesel reliability by permitting the substitution of a slow start for most starts required by Technical Specifications.

By substituting a slow start for the currently required monthly start test, engine wear would be reduced and the engine would still be tested adequately. A " slow start" is considered a start in which the engine is prelubricated, has prewarmed oil and water circulating and reaches speed and load on a prescribed schedule that is selected to minimize stress and wear. The test demonstrates the ability of the diesel generator to start reliably, and to carry the required load. The capabilities of the cooling system and other support systems are also demonstrated.

A fast start test will be performed every six months in lieu of the slow start. During this test the engine will be prelubricated, and will have prewarmed oil and water circulating. A

" fast start" demonstrates the ability to start within the time required in the accident analysis.

1 in addition, both the monthly test and the six month test will require that the engine be loaded to expected maximum emergency loading not to exceed the continuous rating for a minimum period of one hour. Testing at Vermont Yankee has shown operation for a minimum of one hour ensures that proper cooling of the EDG system occurs and that stable conditions are achieved. In addition, testing for a minimum one hour period is consistent with NP.C guidelines [ Reference b)).

Once per operating cycle, the conditions under which the diesel generators are required to start automatically will be simulated. This test will demonstrate that EDGs will ,

start within 13 seconds and accept emergency loads within the specified starting time. i During this test actual automatic start conditions are simulated. Current practice is that the engine is not prelubricated.

SAFETY CONSIDERATIONS

• The revision of the Technical Specification and the Inservice Testing Program permits slow starts for most monthly periodic tests, and to only require fast starts once every six months. This change would bring Vermont Yankee's testing requirements into conformance with the latest NRC guidance [ Reference b)] to reduce fast st .;ts. Fast starts have been demonstrated to be a contributor to engine wear and premature failure. The revised testing wih still demonstrate that the EDGs are ready to perform their safety function and will I

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United States Nuclear Regulatory C ,mmission i August 4,1993 Page 4 ,

increase the reliability and availability of the EDGs. In addition, allowing all planned testing l to be preceded by a prelube period and warmup procedures reduces engine wear. -!

Therefore, approval of this proposed change enhances safety of the plant by reducing engine wear and tear; thereby improving the aval, ability and reliability of the EDGs and reducing the l

possibility of introducing test related failures in the diesel generators.

Additionally, changing the duration of the required test to a minimum period of one hour establishes specific criteria to determine test completion. Testing at Vermont Yankee i

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has shown that operation for a minimum one hour period demonstrates proper cooling of the EDG system. Vermont Yankee procedures for monthly testing currently require a test  ;

duration at maximum emergency loading of one hour followed by 7 additional hours of loaded  ;

run.  ;

SIGNIFICANT HAZARDS CONSIDERATIONS i The standards used to arrive at a determination that a request for amendment involves .

no significant hazards considerations are included in the Commission's regulations,10CFR l 50.92, which state that the operation of the facility in accordance with the proposed amendment would not:

• involve a significant increase in the probability or consequences of an  :

accident previously evaluated; or l

• create the possibility of a new or different kind of accident from any accident previously evaluated; or

• ir;volve a significant reduction in a margin of safety. l The following discussion addresses the proposed changes with respect to each of l these three criteria and demonstrates that the proposed changes do not constitute a  !

significant hazard consideration: l

1) The proposed change does not involve a significant increase in the probability  !

or consequences of an accident previously evaluated. The change only affects  !

diesel generator periodic testing. T'1e diesel generators are not accident initiators and the method of testing of the diesels cannot initiate an accident  !

and therefore will not increase the probability of an accident. This change to the diesel generator testing method does not impact any FSAR safety analysis.  !

The proposed surveillance will still provide assurance that the diesel generator  :

is available to mitigate the consequences of accidents previously evaluated. l We believe, as Reference b) states, that "an overall improvement in diesel l engine reliability and availability can be gained by performing diesel generator starts for surveillance testing using engine prelube and other manufacturer

vamou vmn .w a un rowen co u ..n mm United States Nuclear Regulatory Commission August 4,1993 Page 5 recommended procedures to reduce engine stress and wear." In addition, the i test duration of one hour is sufficient to demonstrate that during loaded 1 operation proper cooling of the emergency diesel generators occurs. Thus the l consequences of an accident previously evaluated are not increased.

2) The change does not create the possibility of a new or different kind of accident '

from any accident previously evaluated. The proposed change will only affect diesel generator periodic testing. The diesel generators are not accident initiators and the method of testing of the diesels cannot initiate an accident.

This change does not relieve the operation of the diesel generator from existing requirements and the diesel generator is still bounded by the assumptions in the accident analysis. The method of testing provides assurance that the diesel generators are available when needed. The proposed change does not involve any changes in Technical Specification setpoints, plant equipment, plant operation, protective functions or design basis of the plant. Therefore, change in the method of starting, load application and test duration during periodic testing would not create a different type of accident than previously evaluated.

3) The change does not involve a significant reduction in the margin of safety.

The proposed change is made to increase the reliability and availability of the EDGs thus enhancing the safety of the plant. Assurance that the diesel generators operate within limits determined to be acceptable continues to be provided. We believe, as Reference b) states, that "an overall improvement in diesel engine reliability and availability can be gained by performing diesel generator starts for surveillance testing using engine prelube and other manufacturer recommended proced.ures to reduce engine stress and wear."

In addition, the test duration of one hour is sufficient to demonstrate that during loaded operation proper cooling of the emergency diesel generators occurs.

Thus improvement in diesel generator reliability and availability c as not involve a reduction in the margin of safety.

Based on the above, Vermont Yankee concludes that the proposed change does not constitute a significant hazards consideration as defined in 10CFR50.92(c).

This proposed change has been reviewed by the Plant Operations Review Committee and the Vermont Yankee Nuclear Safety Audit and Review Committee.

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vnmosi ymix Nrur umow ui com oinuos United States Nuclear Regulatory Commission August 4,1993 Page 6 SCHEDULE OF CHANGE The proposed changes will be incorporated into Vermont Yankee Technical Specifications and Inservice Testing Program as soon as practicable following receipt of your approval.

We trust that the information provided above adequately supports our request.

However, should you have any questions in this matter, please do not hesitate to contact us.

Very truly yours, VERMONT YANKEE NU LEAR POWER CORP.

%dce Donald A. Reid Vice President, Operations DAR/gmf  ;

Attachments ,

cc: USNRC Region i Administrator USNRC Resident inspector - VYNPS USNRC Project Manager - VYNPS VT Department of Public Service STATE OF VERMONT )

)ss WINDHAM COUNTY )

Then personally appeared before me Donald A. Reid, who, being duly sworn, did state that he is Vice President- operations of Vermont Yankee Nuclear Power Corporation, that he is duly authorized to execute and file the foregoing document in the name and un the behalf of Vermont Yankee Nuclear Power Corporation, and that the statements therein are true to the best of his knowledge and belief.

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Votuosi hw..r Nrcu. An Powrn Coneon vuoN ATTACHMENT I RELIEF REOUEST Number: RR-V03, Revision 1 (Sheet 1 of 3)

SYSTEM: Diesel Generator Starting Air COMPONENTS: i OM Safety Dwg i Valve Number Cat Class Drawing Number Coor i

AS-24-1A B 3 G-191160 Sh 7 B-16 i AS-24-1B B 3 G-191160 Sh 7 B-03 AS-24-2A B 3 G-191160 Sh 7 B-17 l AS-24-2B B 3 G-191160 Sh 7 B-03 AV-24-1A B 3 G-191160 Sh 7 B-17  :

AV-24-1B B 3 G-191160 Sh 7 B-03 These valves are the Emergency Diesel Generator (EDG) starting air inlet and vent valves. They have safety functions, as a set, to provide starting air to the EDG, to prevent EDG and/or piping ,

damage after the EDG starts, and to prevent inadvertent EDG starts.

EXAM OR TEST CATEGORY:

Category B.

CODE REOUIREMENT: Part 10 Para. 4.2.1.1 " Exercising Test Frequency"  :

" Active Category A and B valves shall be tested nominally every 3 months, except as provided by paras. 4.2.1.2, 4.2.1.5, and 4.2.1.7."

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vunmsi m,u; Nnuan Powut Conemunos ATTACHMENT I RELIEF REOUEST Number: RR-V03, Revision 1 (Sheet 2 of 3)

CODE REOUIREMENT fcontinued): Part 10 Para. 4.2.1.3 " Valve Obturator Movement" "The necessary valve obturator movement shall be determined by exercising the valve while observing an appropriate indicator, such as indicating lights which signal the required change of obturator position, or by observing other evidence, such as changes in system pressure, flow rate, level, or temperature, which reflect change of obturator position."

REOUEST FOR RELIEF:

Relief is requested on the basis that compliance with the Code requirements is impractical and that the proposed alternatives would provide an acceptable level of quality and safety.

These valves do not have remote position indication. Measuring the stroke time of these valves by observing stem travel would require disassembly of the operator.

Testing of the inlet valves individually would require the lifting of the power leads to the other valve. Since the stroke timing of these valves is performed by the indirect indication of the respective EDG start time, to lift leads each quarter and perform the necessary EDG fast starts to verify each valve's stroke time would be an undue hardship. Because excessive EDG fast starts are a known contributor to decreased EDG reliability and owing to the criticality of the EDGs as part of the ECCS system, the overall impact of testing these valves in accordance with Code requirements would be an overall decrease in plant safety. Furthermore, since the air start system is not totally redundant (e.g. they share common piping, components and initiating logic), testing of these valves individually on a quarterly basis would not increase the quality and safety of the system.

ALTERNATE METHOD:

During EDG slow start testing performed each month, indirect indication that at least one of the two parallel air start inlet valves opens, and the vent valve closes, will be performed by ensuring the EDG starts.

Revision 5-104

venuost nsiar Nrcuan Powrn coiu oinuos ATTACHMENT I RELIEF REOUEST Number: RR-V03, Revision 1 (Sheet 3 of 3)

ALTERNATE METHOD (continued):

l During EDG fast start testing performed every six months, indirect measurement that at least one of the two parallel air start inlet valves opens promptly, and the vent valve closes promptly, will be performed by ensuring the EDG starts within the Technical Specification limit of 13 seconds. Measuring the EDG start time gives indication of possible valve degradation (as a pair) since any significant changes in valve stroke time will be identified by longer than normal EDG start times.

In addition, to further assess the operational readiness of each air start inlet valve, an independent operability test is performed once per operating cycle. This test will be accomplished by alternately lifting the power leads to one of the two air start l valves, and then measuring the EDG fast start time with the remaining valve in operation.

USNRC EVALUATION STATUS:

Revision 5-105