ML20215M453

Safety Evaluation Supporting Amend 21 to License NPF-30

ML20215M453
Person / Time
Site:	Callaway
Issue date:	05/01/1987
From:	Office of Nuclear Reactor Regulation
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ML20215M445	List: ML20215M442 ML20215M453
References
NUDOCS 8705130248
Download: ML20215M453 (5)

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UNITED STATES

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0. 21 TO OPERATING LICENSE NO. NPF-30 UNION ELECTRIC COMPANY CALLAWAY PLANT, UNIT I DOCKET NO. 50-483 INTRODUCTION By letter dated September 29, 1986, Union Electric Company requested changes to the Technical Specifications for the diesel generators at the Callaway Plant.

A supplemental letter dated February 18, 1987 prov'ided additional changes to those requested in the September 29, 1986 letter. Union Electric Company has in general used the staff's guidance outlined in Generic Letter 84-15 and the technical specifications approved for the North Anna Power Station as a basis for the proposed changes to the diesel generator Action statements and Surveillance Requirements.

EVALUATION (a) Action statement 3.8.1.la deletes the requirement to demonstrate the diesel generators operable for loss of an offsite circuit provided they have been successfully tested within the past 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. We find this change reduces unnecessary testing and thereby the associated detrimental effects of fre-quent starts and is, therefore, acceptable. This change is also in accord with previously approved technical specifications on North Anna.

(b) Action statements 3.8.1.la,b,c and e expand the length of time allowed to demonstrate a diesel generator operable from 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> in all cases, to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> for the loss of two power sources (offsite or onsite) and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for the loss of one power source. The requirement to retest at least once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> is also eliminated. We find these changes provide sufficient time to perform an orderly start test on the DG's, reduce unnecessary testing and thereby the associated detrimental effects of frequent starts and are, therefore, acceptable. This change is also in accord with the guidance in Generic Letter 84-15 and with previously approved technical specifications on North Anna.

(c) Action statements 3.8.1.la,c and e add a footnote that says the automatic start and sequence loading of a diesel generator satisfies the testing re-quirements of Specification 4.8.1.1.2a.4 for this Action statement. Each of the Action statements involves the loss of at least one offsite power source. The purpose of the footnote is to provide clarification that an additional start of the diesel generator for test purposes only is not 8705130248 870501 PDR ADOCK 0500 3

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. required if the diesel generator has automatically started and loaded following the loss of the offsite power source to its. respective bus.

This clarification was pres.ented in the licensee's February 18, 1987 letter. This change is considered to be only a clarification of an already existing Technical Specification requirement and is, therefore, acceptable.

(d) Action statements 3.8.1.lb'and c add a footnote that requires that sur-veillance testing on a redundant diesel generator be completed regardless of when the inoperable. diesel generator is restored to operability. The footnote also eliminates the need to demonstrate the operability of a diesel generator when its redundant counterpart is declared inoperable to do preplanned preventive maintenance, testing, or maintenance to correct a condition which, if left uncorrected, would not affect the operability of the diesel generator. The clarification of this second part was discussed in the licensee's February 18, 1987 letter. We find that the first part of this footnote ensures that both diesel generators are tested for common-mode failures which may have caused the initial inoperability of the first DG and is, therefore, acceptable. The second part of the footntle reduces unnecessary testing and thereby the associated detrimental effects of frequent starts and is, therefore, also acceptable. Both changes are also in accord with previously approved technical specifications on North Anna.

(e)

In the Surveillance Requirements section the licensee has modified Sur-veillance Requirements 4.8.1.1.2a4), 4.8.1.1.2a.5), and the applicable footnote so that the new surveillances and footnote now describe a diesel generator start that includes prelube, gradual loading, and warinup procedures recommended by the manufacturer. The fast start and load from ambient conditions required every 184 days on the diesel generator is now incorporat3d as a new Surveillance Requirement 4.8.1.1.21 separate from the above Surveillance Requirements. The new Surveillance Requirement 4.8.1.1.21 also includes a footnote which allows prelubing of the diesel generator prior to the start. Prelubing the diesel prior to the 184-day start will not affect the validity or results of the test and will reduce the mechanical stress and wear on the diesel generator which should result i

in an overall improvement in diesel engine reliability and availability.

l The change on prelubing is therefore acceptable and has been approved by the staff on recent near term operating license reviews. The other l

changes described above do not result in any changes to the diesel generator i

testing requirements as they existed in the previous Technical Specification I

and are, therefore, acceptable.

(f) The modified footnote, referenced above, that applies to Surveillance Re-quirement 4.8.1.1.2a.4) has also been made applicable to all the diesel generator starts in the 18-month surveillances 4.8.1.1.2f.4), 5), and 6),

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and 10-year surveillance 4.8.1.1.2g.

The footnote reads: "This test shall be preceded by an engine prelube period and/or other wamup procedures t

l recommended by the manufacturer so that the mechanical stress and wear on the diesel engine is minimized." In Generic Letter 84-15, the staff

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3-stated that in its technical judgerent 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 procedures to reduce engine stress and wear. The staff concluded that the frequency of fast start tests from ambient conditions of diesel generators should be reduced. This proposed technical specification change follows that guidance and is, therefore, acceptable..

(g) In Surveillance Requirements 4.8.1.1.2a.5), 4.8.1.1.2f.7), and 4.8.1.1.2i, the diesel generator loading requirements have been specified as an indicated loading band which extends up to the continuous rating or overload rating as appropriate (i.e., "an indicated 6000 to 6201 kV" for the continuous rating and "an indicated 6600 to 6821 kW" for the overload rating). The diesel generator loading requirements in these surveillances were orioinally specified as " greater than or equal to 6201 kW" for the continuous rating, and " greater than or equal to 6821 kW" for the overload -

rating. A new footnote has also been added to the loading band specified in these Surveillance Requirements which reads: This band is meant as-guidance to avoid routine overloading of the' engine. Loads in excess of this band for special testing under direct monitoring or momentary variations due to changing bus loads shall not invalidate this test." The staff has e

found that the open-ended language " greater than or equal to" that exists i-in the present Technical Specification has the potential for routine overloading of the diesel generators. The open-ended load requirement creates a situation wherein operators will tend to operate the diesel generators at a load for which the meter indicates a value greater than the specified value in order to avoid an enforcement action for an invalid test if the meter indication should slip below the specified value.

Because routine overloading of the diesel generators should be avoided, and because the loading bands utilized are sufficiently narrow to ensure the machines are nominally loaded to their continuous and overload ratings.

the staff finds these changes acceptable. The staff has also approved this type of change on North Anna and on near-term operating license reviews.

i (h) With regard to the changes made in Table 4.8-1 titled " Diesel Generator Test Schedule " the first specific proposal is to change the basis for the testing schedule from a "per nuclear unit basis" to a "per diesel generator j'

basis." The second proposal is to reduce the test frequency for an indi-vidual diesel generator based on the number of failures from the present minimum interval of once per 3 days to a minimum of once per 7 days.

The objective of testing the diesels on a regular basis is to ensure the DGs' operability by timely failure detection and necessary corrective action. Such testing provides a degree of assurance of the DGs' avail-i ability during the periods between tests. Therefore, the existing and the previous DG testing concepts are that the above assurance has to be demon-strated with more frecuent testing as the number of DG failures increases.

t Thus, the existing and the previous TS require that diesels be tested so that the interval depends on the demonstrated DG perfomance, i.e., the i

interval shortens as the number of failures increases.

Furthemore, the i

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.c-previous test interval is established conservatively on a per-nuclear-unit basis, rather than on a per-diesel basis. Thus, improper diagnosis of a DG failure could potentially result in more frequent testing of all the

=DG's.'Also, test intervals that are tco short could have an adverse impact on DG reliability.

Past experience has shown that many licensees have been frequently testing their good DG's mainly to quickly get out of the frequent test cycles imposed by the TS. The staff and industry agree that current requirements for testing of good DG's do not improve reliability of the good DG's and may be a factor in potentially degrading them. Also, excessive testing may have negative effects on the overall expected. life of the DG's and, hence, such testing is not warranted. Therefore, the staff agrees with the licensee's prcposal to count DG failures on a per-DG basis rather than on a per-nuclear-unit basis and that the frequency of testing a DG will be based on the number of its own failures. This is consistent with the guidance provided in Generic Letter 84-15 on DG reliability. Thus, the staff finds that these proposed changes are acceptable because they improve DG reliability and are not detrimental to the health and safety of the public.

In addition, the staff has for sometime been evaluating the frequency of DG testing and the associated potential for severe degradation of engine parts due to frequent fast-start testing. The staff concludes that the test frequency can be reduced to minimize this potential without affecting the overall DG reliability. Therefore, the staff finds that the licensee's proposal to reduce the test frequency for an individual diesel generator, based on the number of failures, from the present minimum interval of once per 3 days to a minimum of once per 7_ days is acceptable. This is consistent with the guidance provided in Generic Letter 84-15 on DG reliability.

The final change proposed in Table 4.8-1 would provide an explicit direct incentive for the licensee to perform a thorough and comprehensive complete overhaul of the DG (the DG would be rebuilt to like-new conditions) that is approved by the DG manufacturer.

Following such an overhaul, the DG would become operable after it successfully passed the appropriate surveil-I lance tests one time. However, in return for the overhaul, the utility would receive the benefit of not being required to count previous failures on that DG if an acceptable reliability can be demonstrated. With "no previous failures" in the past 20 or 100 tests, the DG would re-enter the test schedule at the monthly test frequency. Accelerated testing (weekly) would not become required until either 2 failures in 20 tests or 5 failures in 100 tests occur. The staff finds that this change is acceptable because a thorough and complete overhaul of a DG, that has experienced excessive number of failures, would potentially provide for better reliability.

The proposed reliability criterion for the rebuilt DG is the successful completion of 14 consecutive tests, at least 4 of which would be " fast cold" starts. Statistically, the probability that a DG with-an actual reliability of less than 0.90 demand will satisfy this 14-test criterion

. is no greater than 20% and decreases rapidly with the actual reliability.

The probability that a DG with an actual reliability of less than 0.95 will satisfy the 14-test criterion is 42% or less. The staff, therefore, finds the proposed 14-test criterion to be acceptable. A note of caution should be added regarding repeated attempts to satisfy the 14-test criterion because in such a case the statistical situation changes.

If a DG passes the criterion on a second attempt, the probability that the actual reliability is 0.95 would be reduced to only about 25%. Therefore, if the 14-test criterion is not passed on the first attempt, the previous test failures could not be disposed of until some new criterion is negotiated with the NRC. This is specifically required as part of the reliability test criterion in the current Table 4.8-1 and is, therefore, acceptable.

ENVIR0hPENTAL CONSIDERATION This amendment involves changes in the use of a facility component located within the restricted area as defined in 10 CFR Part 20 or changes in surveillance requirements. The staff has detemined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Comission has previously published a proposed finding that the amendment involves no significant hazards consideration and there has been no public coment on such finding.

Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 651.22(c)(9). Pursuant to 10 CFR 951.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

CONCLUSION The staff has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will i

not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations and the issuance of this amendment will not be inimical to the comon defense and security or to the health and safety of the public.

Principal Contributors:

T. Alexion J. Lazevnick Date: May 1,1987 l

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