ML19325C605

Application for Amends to Licenses NPF-37,NPF-66,NPF-72 & NPF-77,changing Tech Spec 3/4.8.3.1, Onsite Power Distribution.

ML19325C605
Person / Time
Site:	Byron, Braidwood, 05000000
Issue date:	10/03/1989
From:	Chrzanowski R COMMONWEALTH EDISON CO.
To:	Murley T Office of Nuclear Reactor Regulation
Shared Package
ML19325C606	List: ML19325C605 ML19325C607
References
0308T:1, 308T:1, NUDOCS 8910170108
Download: ML19325C605 (10)

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J ' Commonweehh Edloon M 7I / 72 West Adams Street, Chcago, liknos

) KikFess Meply to; P/40ffiE3 B5Pi67-j

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(_/ - ONeago Ilknois 60690 0767 l

,;4 October 3, 1989 h '

l a Dr. Thomas E. Murle' y , Director l Office of Nuclear Reactor Regulation j U.S. Nuclear Regulatory Commission j Hashington, DC 20555  ;

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Subject:

Byron Station Units 1 and 2 j Braidwood Station Units 1 and 2 i i:

Application for Amendment to Facility Operating )

Licentes NPF-37, NPF-66, NPF-72, and NPF-77  !

, EC_ Docket Nos. 50-454/455 and 50-456/457 l

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Dear Dr. Hurley:

Pursuant to 10 CFR 50.90, Commoitwealth Edtson proposes to amend Appendix A, Technichi Specifications of Facility Operating Licenses NPF-37,  ;

NPF-66 NPF-72, and NPF-77. The proposed amendment requests changes to Specification 3/4.8.3.1, Onsite Power Distribution. The detailed description  ;

is contained in Attachment t.. The revised Technical Specification pages are -

contained in Attachment B.

- . The proposed changes have been reviewed and approved by both on-site '

zano off-site review in accordance with Commonwealth Edison procedures.

Commonwealth Edison has reviewed this proposed amendment in accordance with 10 ,

CFR 50.92(c) and has determined that no significant hazards consideration ,

~ exists. .This evaluation is documented in Attachment C.  ;

e Commonwealth Edison has evaluated the proposed amendment rith the

• requirements of 10 CFR 51.21. Attachment D contains the corresponding Enviror. mental Assessment Statement. ,

Commonwealth Edison is notifying the State of Illinois of our application for this amendment by transmitting a copy of this letter and its ,

' attachments to the designated State Official. >

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, Dr. Y.E..Murley- October 3, 1989 t

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, Please direct any questions regarding you may have this matter to .

this office.  !

Very truly yours,  :

c'W R. A. hrzanowski .

T Nuclear Licensing Administrator a i 1 5 Attachments l

l cc:L. Senior. Resident Inspector - Byron '

Senior Resident Inspector - Braidwood L.N. 01shan - Project Manager, NRR S.:P. Sands - Project Manager, NRR Regional Adelnistrator - Region III ,

Office of Nuclear Facility Safety - IDNS -

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ATIK9HLA DETAILED DESCRIPTION INTRODUCTION The Byron and Braidwood Stations Technical Specification 3/4.8.3.1 requires that each 120 VAC instrument bus be energized from its associated inverter connected to its ossociated DC bus during operation in Modes 1, 2, 3, and 4. An action statement allows the instrument bus to be de-energized for a period of up to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and not energized from its associated inverter "

connected to its av,sociated DC bus for a period of up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Failure to meet either of the action statement conditions would require the plant to be ,

in hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown within the  !

following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. This attachment supports a proposed amendment to the  !

Technical Specifications which would allow one 120 VAC instrument bus to be energized from its associated constant voltage transformer for a period of up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The proposed amendment will:

1. P, educe the hesitancy to allow planned outages on inverters for preventive maintenance to be performed due to the short 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> allowed out-of-service time currently permitted by Technical Specifications and, i

2. Allow sufficient time to troubleshoot, repair, test. tune, clean and inspect failed inverters before requiring a plant shutdown.

BACKGROURD 1 L _ The 120 VAC Instrumentation System suppl us a reliable source of regulated instrument and control power to equipment and systems which must remain in operation during a momentary or complete loss of AC power. These systems include the Reactor Protection System, the ESF Actuation System, Process Instrumentation System, and certain Safety Category II (non-safety

related) loads required to facilitate plant operation. Each of the Byron units has four 120 VAC instrumentation busses, supplyinn one of the four l Reactor Protection System channels.

L l Each of the two 480 VAC ESF Divisions sLpplies two of the 120 VAC l instrumentation busses. A 120 VAC instrumentation bus is capable of receiving power from its 480 VAC ESF busses by two means: 1) from its associated static inverter or 2) from its asscciated 480/120 Volt self-regulating constant voltage transformer. The inverter and transformer feeder breakers are l mechanically interlocked to prevent their simultaneous closure and subsequent paralleling of the inverter and the transformer power feeds. The inverter power supply frequency is much more regulated (60 Hz 10.51.) than the constant voltage transformer output and parallel operation might cause overheating of the inverter. The inverter is the normal and preferred source while the I l constant voltage transformer serves as a backup source when the inverter is out-of-service for maintenance or repair, i

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i The 7.5 KVA inverter provides additional redundancy in that it is i t capable of being powered from either the 480 VAC ESF bus or from a 125 VDC control power battery bus. The inverter produces a single phase, 60 Hz, 118 VAC output. The 480 VAC ESF bus is the normal source of pcver to the invertei with automatic transfor to the 125 VOC bus if the AC input tills. The .

three-phase, 480 VAC input to the inverter is first transformed then rectified to a DC output voltage. DC output voltage is adjusted so that it does not ,

exceed 140 VAC and is not less than the battery voltage. A blocking diode is -

installed in the battery input circuit. This blocking diode is normally reverse-biased, thus blocking the DC bus input. If the AC power supply falls,  ;

the diode will :onduct and automatically "bumplessly" transfer battery power to supply'the instrument bus through the inverter.

The 10 KVA constant voltaga transformer is classified as Safety Category I (Class IE) and is powered from its associated 480 VAC ESF bus. The transformer produces a single-phase 60 Hz, 120 VAC output. The transformer is the controlled ferro-resonant type and provlies output voltage regulation to wtthin 32% with +10% to -15% input variation. The constant voltage transformer is a reliable piece of equipment and no failures have occ1rred on Byron Units 1 and 2 based on a review of the Nuclear Plant Reliability Data ,

e System. In addition, a review of the Total Job Management data base te ntified that no maintenance activities have been regoired on these transformers as a result of any work requests. A sketch of the bus arrangements is provided in Addendum 1.

h Plant Response to a Complete Loss of an Instrument Bus  :

The complete loss of power to a 120 VAC instrument bus can interrupt the following safety related and nor-st.foty related power supplies depending on the particular bus de-energized:

l SALETY RELATEQ

1. NIS Channel Control Power

2. NIS Channel Instrument Power

3. Auxiliary Safeguards Re?ay Power

4. Safeguard Test Relay Power

5. Reactor Coolant Loop Stop Valve Protectior. System Power

6. Solid State Protection System Train "A" Input Channel Power ,

7. Solid State Protection System Train "B" Input Channel Power

~8. ESF Sequencing and Actuation Cabinet Power

9. Main Control Board ESF Power Supply

10. Process Instrumentation and Control Rack Channel Power Supply

11. Solid State Protection System Output Relay Power p.

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12. Process Instrumentation and Control Rack Channel Power Supply t

13. Main Control Board Instrument Channel Power Supply ,

It should be noted that en automatic transfer to reserve power separate from the 120 VAC instrument busses is provided for the process  ;

instrumentation and control cabinets identified in items 10 and 12 above. i Therefore on a loss of instrument bus power it is highly unlikely that the I process I & C cabinets would be de-energized. Additionally, the operator is required by procedure to select alternate control channels or defeat inoperable control chi.nnels and is provided with Abnormal Operating Procedures ;

j to identify which process instruments have been lost when a particular instrument bus is de-energized.

It should be noted that for each of the two ESF Divisions only one of i the two 120 VAC instrument busses on that division supplies power to its dedicated train Solid State Prc.wction Systerc. (SSPS) output relay cabinet. As '

such for Division 11 (21), only 120 VAC instrument bus 111 (211) supplies power to SSPS Train A output relay cabinets while bus 113 (213) does not. '

Similarly, for Division 12 (22), only 120 VAC instrument bus 114 (214) supplies power to SSPS Train B output relay cabinets while bus 112 (212) does ,

not. With instrument bus 111 (114) [211 (214)) on the Constant Voltage Transformer (CVT) and with a loss of offsite power concurrent with an SI 4 signal the shutdown sequencer and safety loads would sequence on the 4KV bus per design. There would be no reduction in the level of safety provided by an instrument bus fed from either its associated instrument inverter or from its associated CVT. No single failure during a loss of offsite AC power would prevent the automatic actuation of at least one division of safety, should it bt required. This is because of the inherent system design. When instrument bus 111 (114) [211 (214)) is deenergized the SSPS would process the SI signal up to the master relays. When the 4KV ESF bus 141 (142) [241 (242)] is reenergized the slave relays associated with the SI signal would be energized. The sequencing cabinet does not start sequencing until the undervoltage relay for the 4KV ESF bus has reset. The time for this reset is about 1.8 seconds. The average time for the SSPS to process an ESF signal is less than 0.5 seconds. Thus the automatic ESF System for the associated 4KV ESF bus will respond as designed under loss of offsite power with an SI signal upon the diesel generator (DG) for the associated 4KV ESF bus reaching rated l speed and voltage af which time the DG feed breaker to the associated 4KV ESF l- bus would close anri the loads would sequence on the 4KV ESF bus. The bus feed breaker from the 4KV ESF bus to the 480 VAC bus which feeds the CVT and the breaker from the 480 VAC bus to the CVT does not open on undervoltage. Thus the instrument bus would be reenergized when the DG feed breaker closes on the 4KV bus. Some control board indication would be lost until the DG feed breaker closed on the bus, but indication of plant parameters would be provided by the other instrument busses on their respective 125 VDC battery source through the inverter. There would be no delay in providing any protection required due to the instrument bus being fed from the CVT.

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r hG All ESF functions would respond as required on a loss of offsite AC if the Diesel Generator on the division not affected by the inverter outage were to fail.

Abnormal Operating Procedure 1/2 BOA ELEC-2, LOSS OF INSTRUMENT BUS provides the symptoms and required operator actions for a loss of any of the four 120 VAC instrument busses. While the procedure is written based on the loss of an instrument bus while on its associated inverter, it would also be applicable for loss of the bus while on the constant voltage transformer.

The control room indications following a loss of an instrument bus would include one or more of the following:

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1. Possible Reactor Trip and/or Safety Injection from logic coincide..ces made up by tripped bistables.

2. Tripped status lights for a particular channel indicate a tripped condition.

3. Abnormal _ main control board indications fed from the de-energized instrument bus.

4. Various main control board alarms.

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!, 5. Loss of instrument and control power to the channel of nuclear Instrumentation fed from the de energized bus.

6. . General Harning alarm from the Solid State Protection System Cabinet A or B.

Required operator actions consist of:

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1. Check Rod Control System in manual.

2. Check TAVE - TREF deviation is stable and within l'F.

3. Check that the following instrument control channels are operable:

L Pressurizer pressure

, Pressurizer level l Steam flow L Steam generator level Feedwater flow Turbine Impulse Pressure DhhaT 0308T:6

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4. Dttermine which instrument bus is de-energized by verifying instrument and control power is available to all NIS.

5. Restore power to affected instrument bus (ses) by checking inverter amps and voltage, verifying supply and individual load breakers are closed and i transferring to the constant voltage transformer if necessary.

6. Check that the instrument bus (ses) is(are) reenergized and available to.  !

all NIS.

Onsite Power Distribution Technical Specifications ,

The basis for the operability of the AC and DC power sources and -

associated distribution systems during operation ensures that sufficient electrical power will be available to supply safety related equipment required for: 1) the safe shutdown of the facility, and 2) the mitigation and control of accident conditions within the facility. The minimum specified AC and DC power sources and distribution systems satisfy the requirements of General Design Criteria 17 of Appendix A to 10CFR part 50.

r As mentioned above, Technical Specifications currently limit ,

operation with an inverter out-of-service to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> during which time the 120 VAC instrument bus is energized by its constant voltage transformer. If l during this time period transformer power becomes unavailable for any reason, one Reactor Protection System channel is lost and one train of ESF Protection  ;

nmy be lost and the degree of protection redundancy is potentially reduced.

The Technical Specification Bases do not present a discussion of the >

basis for the allowable out-of-service times for the power distribution system, but does state that the AC and DC source allowable out-of-service times for the power sources are b. sed on Regulatory Guide 1.93, " Availability of Electrical Power Sources", December 1974. For the lack of a more definitive guidance, the regulatory position as presented in Regulatory Guide 1.93 will be used as a reference for extending tha allowable out-of-service time with an inverter out-of-service from 24 to 72 hotrs durina which time the 120 VA; instrument bus is energized by the constant voltri: transformer.

Regulatory Guide 1.93 states that whenever the Technical

. Specifications allow power operation to continue with less than the required number of electrical power sources, such continued power operation should be contingent on: a) an immediate verification of the ava11at'111ty of the remaining sources, b) reevaluation of the availability of the remaining diesel-generators at a time interval not to exceed eight hours, c) verification that required maintenance activities do not further degrade the power system or in any way plant safety, and d) compliance with the additional  ;

conditions stipulated for each specified degradation level.  ;

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I Since Regulatory Guide 1.93 was intended to provide e basis for the allowable out-of-service times for power sources to the 4 Kv Esf busses ttrict i application of items a) through d) above is not deemed approptlate for power sources to the 120 VAC instrument busses. Each item and its application to the extension of the action time allowed for an A.C. instrument bus to be i energized from a source other than from the inverter connected to its  !

associated D.C. Bus is commented on below.

Item a) an immediate verification of the availability of the remaining sources.

There are two sources under consideration: 1) the sources supplying the instrument bus not eneraized from its associated inverter and 2) the sources supplying the titree instrument busses energized frc.n their associated inverters, l

For the instrument bus no LeDergized from its inverter the sources under consideration are the supplies to its associated Division 4 KV ESF bus and 125 VOC battery. Since the battery is not capable of supplying the instrument bus via the constant voltage transformer, the remaining sources are the associs.ted diesel generator and etrher units System Auxiliary Transformer (SAT) as prescribed in specification 3.8.1.1. Surveillance Requirement 4.8.3.1.2 has been added to meet the intent of this item. '

4.8.3.2 The 480-Volt A.C. ESF bus nergizing the affected 120-Volt A.C.

Instrument bus shall be determined energized in the required r..anner by verifying correct breaker alignment aim) indicated voltage on the associhted 4160-Volt and 480-Volt bu:,ses.

• For the three instrument busses ster.gited from their associated inverters the sources under consideration are the supplies to their associated 4 Ky ESF bus and 125 VDC battery. Surveillance Requirement 4.8.3.1.3 has been added to meet the intent of this item.

4.8.3.3 The three unaffected 120-Volt A.C. instrument busses shall be determined energized from an OPERABLE inverter by verifying correct breaker alignment and indicated voltage on the associated ESF and 125-Volt D.C. busses.

The current action statement does not require immediate verification of the availability of the remaining sources, but allows 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of operation on the constant voltage transformer. This is consistent with

• NUREG-0452 and in general with all stations whose Technical Specifications are based on NUREG-0452, Rev 4 and later. Insertion of the Regulatory Guide 1.93 requirement to immediately verify the remaining sources would make the action statement more restrictive than the current action statement since any variation in breaker alignment or indicated voltage on associated 480-Volt and e Kv busses could immediately force the plant into shutdown via specificatto.i 3.0.3.

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Based on the above the action statement has been modified to allow l 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of operation with the instrument bus not energized from its ,

associated inverter. Verification of correct breaker alignment and  ;

indicated voltage would be required within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and at least once i per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter. The choice of the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is consistent with the current industry practice of allowthg 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of operation on the  :

constant voltage transformer without verification of sources and consistent with the Regulatory Guide of requiring immediate verification l (after the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period) for the extension period. -

Item b) re-evaluation of the availability of the remaining diesel-generators at a time interval not to exceed eight hours. ,

The proposed amendment request does not specifically require that the availability of the remaining diesel-generators be reevaluated, but does require verification by Surve111ances 4.8.3.1.2 and 4.8.3.1.3 of correct breaker alignment and indicated voltage on the 4 Kv ESF busses. The term ,

verify as used in this context means to administratively check by examining logs or other infornation to determine if certain components are out-of-service for maintenante or other reasons and this would include the diesel generators. It is felt that these additional surveillances, and 1 with the requirements of ACTION C. of specification 3.8.1.1 if one diesel-generator were inoperable, are sufficient to meet the intent of .

this item. i Item c) verification that required maintenance activities do not  !

further degrade the pcwer system or in any way plant safety.  ;

This item will be covered by the performance of surveillance 4.8.3.1.2 and 4.8.3.1.3 above. Additionally, the station out-of-service procedurt BAP 330-1, Revision 4, dated December 20, 1989 states ti.e following: '

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1. Prior to taking a Technical Specification required component 005, the 4 rW9ndant train will be verified operable (item 2.a page 3) +

2.- The Shift Engineer or SR0 licensed assistant deterrines that the redundant train of Safety Related equibmant is operable by checking the Master 0ft ei ~;cvice board, prior to approving an outage on St.fety T, elated equipment.

Item d) compliance with the additional conditions stipulated for each specified degradation level.

There is only one degradation level under consideration, the instrument bus supplied for a period of time (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) by its constant voltage transformer instead of the inverter. Additional ccnsiderations are provided by the inodified action statement and the addition of surve10ance requirements.

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I Tte proposed Technical Specification changes are provided in l Attachment B. The proposed amendment will reduce the time pressures to complete repairs or 5!mit opnortunities for preventive maintenance on the inverters currently felt as k result of th3 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> limit. While a quantitative assessment of plant availability has not been conducted it is feP that it is good engineering practice to provide sufficient time for the connJ.t of both these repair / maintenance activities. The current 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> limit is insufficient when considering that: ,

1. It takes several hours to complete the required paperwork and eqolpment tag out process prior to any work being started.

Troubleshooting the inverters has historically taken 10 to 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> 2.

depending on the complexity of the circuit that has failed.

3. Once the falltd item is determined, a paper work change with accompanying repair work instructions and signatures must be cbtained prior to repair.

4. Following repair the inverter must be ten.porarily energized and loaded to verify proper operation and tuning.  ;

5. It can take several hours to clear the equipment tags and complete the required paperwork to return the inverter to service.

The total time for the above process outilne for a corrective action is in the range of 15 to 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> depending on the complexity of the failure.

This does not include any additional time for preventive maintenance actions

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~such as tuning the ferro-resonant transformer, capacitor change outs, cleaning the inverter, ascertation of electrical connection tightness and new part

" burn in" time.

1he inverter units need periodic inspections fo- dust and dirt buildup on electrical circuit comoonents and particularly on capacitors located in the ferro-resonant transformer. This requires that the normal paperwork and equipment tag out process described above be completed in order to disassembit and access the ferro-resonant transformer for cleaning. With the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> time clock operating, repair of all but minor problems would be limited.

It should be noted that the Regulatory Guide does not specify a particular time limit for allowed out-of-service time for this bus.

Additiona)1y, the instrument bus will be energized during this period from a very reliable 480 VAC ESF bus with increased surveillances on both the affected and unaffected busses. For these reasons and those discussed above, "

we believe it is acceptable to allow an instrument bus to be surplied via the 10 KVA constant voltage transformer for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to allow for sufficient time for the performance of both comprehen,1ve repair and maintenance actions in accordan;e with good engineering practices.

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