ML20248D801

Safety Evaluation Supporting Amend 32 to License NPF-39

ML20248D801
Person / Time
Site:	Limerick
Issue date:	09/28/1989
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20248D790	List: ML20248D785 ML20248D801
References
GL-84-15, NUDOCS 8910040406
Download: ML20248D801 (7)

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pyr' UNITED STATES '

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-8 NUCLEAR REGULATORY COMMISSION o

g-t 7, E-WASHINGTON, D. C. 20555 c

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR' REACTOR REGULATION n

SUPPORTING AMENDMENT NO.

32 TO FACILITY OPERATING LICENSE NO. NPF-39 PHILADELPHIA ELECTRIC COMPANY LIMERICK GENERATING STATION, UNIT l' DOCKET NO. 50-352 1.0. INTRODUCTION By letter dated September 9, 1988, as supplemented by letter dated August 11,.1989', Philadelphia Electric Company (the licensee) requested an amendment to Facility Operating License No. NPF-39 for the Limerick Generating Station, Unit 1.

The proposed amendment would revise the testing requirements in Sections 3.8.1.1 and 3.8.1.2 along with the associated BASES related to the onsite emergency diesel generators (EDG) in response to Generic Letter 84-15, " Proposed 3taff Actions to Improve and Maintain Diesel Generator Reliability" which was issued July 2,1984.

2.0 DISCUSSION

'On'a generic basis, the NRC has been and continues to be interested in achieving and maintaining a high reliability level for EDGs.

In 1975, an NRC technical report evaluated EDG failure experiences reported during the period of 1959-1973. During this period, EDG testing was conducted on a monthly basis and during refueling. This report concluded that one specific problem dominated.the failure experiences and identified it as the starting of the engine. This experience spawned the general j

perception that if the EDG could start, it would likely continue on to accept load and operate in a reliable manner.

1 In 1977, Revision 1 t6" Regulatory Guide 1.108 " Periodic Testing of Diesel Generator Units Used as Onsite Electrical Power Systems at Nuclear Power Plants" was issued. This revision of Regulatory Guide 1.108 was an effort to improve the routine testing schedule by relating the testing frequency. to the number of failures being experienced. With the emphasis ~

on EDG starts, Regulatory Guide 1.108 indicates that the EDGs be " cold fast start" tested at various intervals depending upon the total number of EDG failures. These " cold fast starts" demonstrate the starting capabilities fro:n ambient conditions with full electrical loads. An objective of this testing schedule was to encourage utilities with high failure rate EDGs to take major repair actions to avoid the costs of very frequent EDG tests.

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s t s Subsequent reviews of EDG failure experience from 1976 to 1978 indicated that engine starting was no longer the dominant failure mechanism.

Apparently industry efforts in this area were becoming effective.

However, in July 1982, the first EDG failure occurred that was clearly identified as being caused by testing. One of the Nordberg 3500 KW EDGs at the Brunswick Nuclear Station had failed. The licensee reported that the metallurgical examination determined the failure cause to be fatigue due to excessive starts.

Inspection of the other EDGs revealed that two of the three also had indications of similar fatigue. This reactor operating experience confirmed concerns expressed earlier that excessive tests would be detrimental.

In September 1982, a staff summary of EDG experience presented to the ACRS suggested that:

(a) routine test starts on a 3-day frequency should

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be eliminated; (b) testing should be focused on identifying unreliable EDGs, and then major repair action should be pursued, rather than just more testing; (c) when an EDG failure has occurred, an. initial test of redundant EDG(s) should be conducted with a followup test about every 3 days to provide increased assurance that a new failure has not occurred.

In 1983 as part of an investigation into Station Blackout, the NRC published NUREG/CR-2989, " Reliability of Emergency Onsite AC Power Systems at Nuclear Power Plants." This study, based upon data from 1976 to 1980, concluded that the industry average EDG failure rate was 2.5 x 10-2 per demand (an average reliability of 0.975). Major contributors to this failure rate were failures in EDG subsystems (e.g., failures of instrumentation and control components, failures of fuel system components such as injectors, failures in the air start motors, valves and controls, failures in switchgear components, failures in the lube oil system, etc.), or human error related and hardware related common mode failures, and cooling water unavailabilities. No one cause of EDG failures F

was dominant. The report recommended several actions that could be taken to improve EDG reliabilities. These varied from having the governor overhauled on a periodic basis, review of repeat failures to determine root causes, use of corrosion inhibitors in jacket water coolants and upgrading EDG-related procedures, to the installation of an additional EDG.

In July 1984, the NRC issued Generic Letter 84-15 which described changes in staff requirements to improve EDG reliability.

The Generic letter requested that Licensees take actions to reduce " cold fast starts,"

including encouraging them to propose TS changes. On April 25, 1985, the NRC issued Amendment 48 to Facility Operating License No. NPF-7 for the North Anna Power Station, Unit No. 2 (NA-2), reducing the required testing of the EDGs. The changes to the NA-2 TSs reduced the parameters for each test, reduced the number of tests and applied to both routine surveillance and special tests. These changes to the EDG TSs considered both the EDG manufacturer recommendations and-current regulatory guidance.

The changes which were approved for NA-2 subsequently became the standard used by the industry for surveillance test method and schedule revisions necessary to improve the reliability and availability of the EDGs.

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3.0 EVALUATION The Licensee has provided specific changes that will improve the

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reliability and availability of the EDGs based upon recommendation from

-the EDG manufacturer and the appropriate recommendations provided in Generic Letter 84-15.

(A) The licensee proposes to specify prelubrication and prewarming of EDGs prior to preplanned EDG starts as required by the TSs. The staff concluded in Generic Letter 84-15 that overall improvement in' diesel engine reliability and availability can be gained by performing diesel generator starts using engine prelube to reduce i

engine stress and wear. The staff also concludes that allowing prelubrication and prewarming increases the margin of safety by increasing the reliability / availability of the EDGs, thereby decreasing the risk of station blackout. This change is acceptable.

(B) The licensee propo'ses to provide for gradual acceleration and gradual electrical load increases to an indicated load range during EDG testing in accordance with manufacturer's recommendations in order to decrease the stresses inherent with rapid acceleration and sudden large electrical load changes. Gradual acceleration and gradual electrical loading of the generator decreases the stresses on both the generator and engine cnd therefore would be operationally advantageous, avoid premature wear, and lead to greater EDG availability. This change to TS is acceptable.

The licensee has proposed to delete the requirement in Sections 4.8.1.1.2.a.4 that every routine test start be a fast (10 second) start (i.e., acceleration to full engine speed, and generator voltage and frequency). The licensee is developing procedures, in consultation with the manufacturer,(that would have the engine start and accelerate to an initial setting idle speed) followed by a manual increase of the speed setting to synchronous speed over a period of 1 to 2 minutes. The proposed changes to allow gradual electrical loading of the EDG upon synchronization incorporates manufacturer's recommendations into the surveillance test requirements and are acceptable.

The licensee has proposed a Footnote

• on pages 3/4 8-3, 3/4 8-5, l

3/4 8-6, 3/4 8-7 and 3/4 8-7a to provide direction to perform surveillance tests in accordance with manufacturer recommendations regarding loading and shutdown in addition to previously discussed prelubrication and prewarming. The proposed change assures the EDGs are operated in accordance with manufacturer's recommendations during l-all planned testing in order to extend diesel life and improve reliability and is acceptable.

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The present TSs require that whenever one or more of the diesel generators or offsite power sources becomes inoperable, the remaining

' diesel' generators be started within certain time limits to demonstrate operability;of the units.

The licensee retained this requirement but also proposed that every planned EDG start be followed by a 60 minute-loaded run to at least its 60% continuous rating.

The staff advised the licensee that when a diesel generator is paralleled with an offsite power source in order to load it, this makes it vulnerable to perturbations in the offsite power system and creates a potential for losing both the diesel generator and offsite power source due to a common cause at a time when the number of offsite and onsite power sources to-the emergency buses has already been reduced by'the initial inoperabilities.

In the supplemented letter of August 11, 1989,-the licensee submitted revised TSs to conform to the staff's suggestion. 'The revised TSs deleted the proposed to perform a 60 minute loaded run when the diesels are started to demonstrate operability.

The revised TSs are acceptable.

The licensee has proposed changes to allow the EDGs to be loaded to a band of 2700-2800 kW rather than > 2850 kW to prevent routine overloading during the performance o_f the monthly and 184 days surveillance testing. The load value of 3135 kW for the 2-hour portion of the 24-hour test of Section 4.8.1.1.2.e.8 would also be changed to a band of 2950-3050 kW to prevent overloading the EDGs to greater than its 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> rating.

The staff believes that the open-endad language " greater than or equal to" has the potential for routine overloading of the diesel generators.

In view of this consideration, the staff finds these proposed changes to be acceptable.

(C) The licensee propoied changes to ACTION requirements a. and d. in Section-3.8.1.1 to test the remaining EDGs within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> if an EDG becomes inoperable due to any other cause than preplanned, preventative maintenance, modification or testing.

The purpose of testing the remaining EDGs is to assure that any unknown (or undiscovered) generic problem does not exist.

Since the inclusion of the word " modification" is not in the current Limerick 1 TSs or in the BWR Standard TSs (STS), the staff proposed to the licensee that the word " modification" be deleted.

The licensee accepted the staff's proposed change; the deletion was reflected in the revised submittal of August 11, 1989.

On this basis, the staff finds the licensee's proposed changes, as modified, to be consistent with the current STS and are acceptable.

The licensee proposed to add a Footnote

• on pages 3/4 8-1 and 3/4 8-la to ACTION requirements a. and d. to require the completion of l

testing regardless of when the inoperable EDG is restored to operability for failures that are potentially generic.

This is i

l consistent with the STS and is acceptable.

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.In Section 3.8.1.1, the licensee has proposed to include'in ACTION b, e

c, d, f, g, and h the time limits in Generic Letter 84-15 for performing surveillance when one or more EDGs or offsite power sources are not available.

However, the licensee has added the word "commenc-ing" to the surveillance requirements.

Since this would not be consistent with GL 84-15, the staff proposed that the word

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'" commencing" be deleted where it appeared in this Section.

The licensee agreed with the change and incorporated the suggestion in the revised TSs submitted with the August 11, 1989 letter.

The revised TSs are acceptable.

The licensee has also proposed to increase the one hour action time for the initial test of the remaining EDGs in ACTION requirements b.,

d.g. and h. of Section 3.8.1.1 to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> and ACTION f to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, respectively.

The rroquirement to test the EDGs every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter in Section 3.8.1.1 ACTION b., c., d., f., g. and h. has been deleted.

The proposed changes are consistent with Generic Letter

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(D) In Section 4.8.1.1.2.e., the licensee proposed to allow EDG maintenance inspections and testing to be performed at least once per 18 months while at power.

The staff feels that some EDG surveillance require-ments should not be performed while at power and recommended that the wording in this Section be changed to "At least once per each refdeling cycle" rather than "once per 18 months." The licensee agreed with the change and incorporated the revised wording in the August 11, 1989 submittal.

This is a change in wording and does not change the intent of the requirement.

Therefore, the TS change, as modified is acceptable.

(E) The licensee proposed a new Section 4.8.1.1.2.h. which requires at least once per 184 days a fast (10 second) staat of each EDG to full speed and loading to full load in 200 seconds.

This change is consistent with Generic Letter 84-15 and is acceptable.

(F) In Section 3.8.1.1 ACTION items b and h, the 1;censee had proposed to

" perform" certain surveillance requirements.

To clarify why these surveillance requirements were being performed, the staff proposed that the wording be changed to " Demonstrate the OPERABILITY of the remaining diesel generators by performing" the specified surveillance requirements. The licensee accepted the clarification and incorporated the revised wording in the August 11, 1989 submittal.

This was solely a clarifying phase that did not change the requirement.

(G) Table 4.8.1.1.2-1 addresses diesel generator surveillance testing frequency.

The present requirement bases the DG test frequency on the number of failures in the last 100 valid tests on a per nuclear unit basis. The licensee has proposed to base the testing frequency on the number of failures in the last 20 tests. In addition, the proposed test frequency is based on a per diesel generator rather than per nuclear basis.

This proposed change is consistent with Generic Letter 84-15 and is acceptable.

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In the no significant hazards consideration which was published in the Federal Register (54 FR 5171) on February 1,1989, the staff stated upfront that the proposed changes to the TSs were to conform to the recommendations in the Comission's Generic Letter 84-15.

The "model" TSs included with the generic letter were general guidance rather than proscriptive because of the wide variation in redundancies I

between plants. At Limerick, there are eight (8) diesel generators, l

four for each unit. At some two unit plants, there is only one diesel' generator per unit, with one " swing" DG. At Limerick, each unit is provided with separate and independent onsite Class 1E ac power systems. The Class 1E power system for each unit consists of four independent Class IE buses, powered by four independent diesel generators, which provide power to four divisions of Class 1E loads.

For Limerick, Units 1 and 2, the TS requirements for testing the DGs would be expected to be different than for a two unit plant without the redundancy and independence that exists at Limerick. These TS requirements are developed on a case by case basis between the licensee and NRC staff. As discussed above, there were some differences of opinion on the general guidance is Generic Letter 84-15. As noted in the licensee's letter of August 11, 1989, the revised TSs incorporated staff suggestions. Also, administrative clarifications and typographical corrections were made to the licensee's incoming technical specifications pages. The revisions do not change the intent of the original amendment request and are consistent with the staff's no significant hazards consideration notice.

4.0 ENVIRONMENTAL CONSIDERATION

This amendment involves a change to a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes to the surveillance requirements. The staff has determined 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 issued a proposed finding that this 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 51.22(c)(9). Pursuantto10CFR51.22(b),noenvironmentalimpact statement nor environmental assessment need be prepared in connection with the issuance of this amendment.

5.0 CONCLUSION

The Comission made a proposed determination that the amendment involves no significant hazards consideration which was published in the Federal Register (54 FR 5171) on February 1,1989 and consulted with the State of Pennsylvania. No public coments were received and the State of Pennsylvania did not have any coments.

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6'I The staff has concluded, based on the considerations discussed above, that: ~(1) there is reasonable assurance that the health and safety of'the

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public will not be endangered by operation in the proposed manner, and (2).such activities will be conducted in compliance with the Commission's-regulations ar,d the issuance of this amendment will not'be" inimical to the common' defense and the security nor to the health and safety of the public.

Principal. Contributor: Dick Clark, Om Chopra.

Dated:

September 28, 1989 e

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