2CAN069805, Application for Amend to License NPF-6,providing Range of Acceptable Values for 4160 Volt Bus Loss of Voltage Values, to Be Consistent W/Requirements Set Forth in NUREG-1432,rev 1

Application for Amend to License NPF-6,providing Range of Acceptable Values for 4160 Volt Bus Loss of Voltage Values, to Be Consistent W/Requirements Set Forth in NUREG-1432,rev 1

ML20236G548
Person / Time
Site:	Arkansas Nuclear
Issue date:	06/29/1998
From:	Hutchinson C ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20236G550	List: 2CAN069805, Application for Amend to License NPF-6,providing Range of Acceptable Values for 4160 Volt Bus Loss of Voltage Values, to Be Consistent W/Requirements Set Forth in NUREG-1432,rev 1 ML20236G563
References
RTR-NUREG-1432 2CAN069805, 2CAN69805, NUDOCS 9807060291
Download: ML20236G548 (8)

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S. * -e Entzrgy operrtions,Inc.

14485R 333 ROME. AR 72801 Td 501-8584389 C. Randy Hutchinson Vce Presrwt Operdtms ANO

.I' June 29,1998 2CAN069805 U. S. Nuclear Regulatory Commission .

De=aat Control Desk l Mail Station OPI-17 Washington, DC 20555 I

Subject:

Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Proposed Technical Specification Change Concerning the 4160 Volt Bus Loss of Voltage Settings {

Gentlemen Attached for your review and approval is a proposed change to the Arkansas Nuclear One Unit 2 Technical Specifications to provide a range of acceptable values for the 4160 Volt bus loss of voltage values. - The present Technical Speci6 cation Table 3.3-4, item 7.a provides a l

single value for both the trip and the allowable values for the 4160 Volt bus loss of voltage requirements. These table entries do not include an acceptable range or an explicit infeation of the allowed tolerance that the actual setting is allowed to vary from the indicatea value.

l The proposed change replaces the specific trip value with an explicit range of acceptable

- allowable values. The associated tolerance is consistent with the applicable safety analyses for loss of voltage protection while providing additional protection from unnecessary actuations during system transients. The application of the tolerance values and the removal of the trip /

value from the technical specifications is consistent with Revision 1 of NUREG-1432, /

" Standard Technical Specifications for Combustion Engineering Plants."

The proposed change has been evaluated in accordance with 10 CFR 50.91(a)(1) using j criteria in 10 CFR 50.92(c) and it has been determined that this change involves no significant i hazards considerations. The bases for these determinations are included in the attached submittal.

Entergy Operations requests that the effective date for this change be during the next ANO-2 raMag outage (2R13) currently scheduled to begin on January 8,1999. 2R13 will be the next expected calibration of the associated loss of voltage channels. Although this request is neither exigent nor emergency, your prompt review is requested.

.i0 9807060291 990629 PDR ADOCK 05000368 p PDR

. , . U, S. NRC . i June 29,1998 2CAN069805 Page 2 Very truly you ,

// f CRH/rde Attachments To the best of my knowledge and belief, the statements contained in this submittal are true.

SUBSCRIBED AND SWORN TO before me a Notary Public in and for N/dA)

County and the State of Arkansas, this dV/dday of d/w/> ,1998./

/

TV) / 2'#Y/$)A40 Notary Public /

My Commission Expires f//h/ // Addd f /

l cc: Mr. Ellis W. Merschoff l Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 l

l NRC Senior Resident Inspector Arkansas Nuclear One l

P.O. Box 310 London, AR 72847 l

Mr. William D. Reckley NRR Project Manager Region IV/ANO-1 & 2 U. S. Nuclear Regulatory Commission NRR Mail Stop 13-H-3 One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. David D. Snellings Director, Division ofRadiation Control and Emergency Management Arkansas Department ofHealth 4815 West Markham Street

' Little Rock, AR 72205 l

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9 4 ATTACHMENT IQ 2CAN069805 PROPOSED TECHNICAL SPECIFICATION l

AND RESPECTIVE SAFETY ANALYSES IN THE MATTER OF AMENDING LICENSE NO. NPF-6 ENTERGY OPERATIONS. INC.

ARKANSAS NUCLEAR ONE. UNIT TWO DOCKET NO. 50-368 l

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. Attesmant to 2CAN069805 Page1 of5 DESCRIPTION OF PROPOSED CHANGES 4 Technical Specification Table 3.3-4, " Engineered Safety Feature Actuation . System ,

Instrumentation Trip Values," item 7, " Loss of Power," includes item a, "4.16 kv Emergency Bus Undervoltage (Loss of Voltage)," with a trip and allowable value of 3120 volts. Each of these table entries is modified by table note (4) which reads: " Inverse time relay set value, not a trip value. The zero voltage trip will occur in 0.75

• 0.075 seconds."

l This proposed change removes the trip value from this table and modifies the allowable value table entry to "2300 i 699 volts with a 0.64 i 0.34 second time delay." In addition, table 3.3-4, note'(4) will be revised to read "The trip value for this function is listed in the

surveillance test procedures. The trip value will ensure that adequate protection is provided I when all the applicable calibration tolerances, channel uncertainties, and time delays are taken l

into account." Note (4) will no longer be applicable to the allowable value for the lou of voltage functional unit.

BACKGROUND Two levels of undervoltage protection are provided for the on-site power system. Two inverse-time undervoltage relays on each of the 4160 Volt (V) safety buses are provided to detect lou of voltage, isolate the safety buses, initiate load shedding, and start the associated emergency diesel generator. The undervoltage relays will initiate load shedding and the starting of the associated diesel generator within approximately one second of a total loss of  !

voltage. The isolation of the safety related buses will be delayed approximately two seconds (for a total of approximately three seconds) to permit the off-site power to supply the safety related loads in the event of a failure of a fast transfer. j

The 4160 V bus loss of voltage system is supported by a second level of undervoltage l protection circuitry with two undervoltage relays on each safety related 480 V vital bus for l " degraded voltage" conditions. This second level of undervoltage protection is not affected j by this requested change.

l The 4160 V unde voltage protection system is designed to protect against a loss of off site power as described in Safety Analysis Report (SAR) Section 8.3.1.1.8.8. The system consists of four 4160 V buses; 2A1,2A2,2A3, and 2A4. The non-vital 4160 V buses (2A1 and 2A2) supply power to auxiliaries which are not engineered safety features (ESF) and to safety buses 2A3 and 2A4. The vital 4160 V ESF buses (2A3 and 2A4) supply power to the ESF equipment essential for safe shutdown and accident mitigation. These vital buses are capable l

of being supplied from either the Unit Auxiliary Transformer, Startup Transformer #2, or

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Startup Transformer #3 via buses 2A1 and 2A2. Each vital 4160 V bus is also capable of being supplied by its associated emergency diesel generator. The alternate AC diesel generator is also capable of supplying 4160 V buses 2A1 or 2A3/2A4 for ANO-2.

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. Attachment to 2CAN069805 Page 2 of 5 l

l ESF buses 2A3 and 2A4 are designed with loss of voltage relays 127-2A3/A,127-2A3/B,

' 127-2A4/A, and 127-2A4/B to monitor the voltage condition of the buses. If a loss of voltage on bus 2A3 or 2A4 is sensed by the associated loss of voltage relays, at 3120 V (approximately 78 percent of motor rated voltage), all loads except the 480 V ESF load L centers 2B5 and 2B6 will be shed, the feeder breakers for off-site power supply to the 2A3 l and 2A4 buses from 2A1 and 2A2 will open (after a short time delay), and the associated emergency diesel generator will automatically start. When the emergency diesel generator has

!- attained rated speed and voltage (within 15 seconds), it will be tied to its associated bus and the required ESF loads will be connected automatically per the specified sequence.

The loss of voltage relays identified above are connected .in parallel, two per bus. Operation of either relay will isolate its associated bus from its off-site power source. This prevents the

! possibility of a single relay failure resulting in a failure to isolate the safety bus from off-site i power. Additional auxiliary relays initiate the actual safety functions ofisolating and stripping i the bus, starting the associated emergency diesel generator, and closing the emergency diesel i generator output breaker.  !

The 4160 V bus trip and allowable value entries for Technical Specification Table 3.3-4, item 7.a, are unchanged from the original issuance of the ANO-2 Operating License in 1978.

These values were based on the Combustion Engineering (CE) . Standard Technical Specifications (STS) at that time, NUREG-0212, which also included a single value. The l current CE STS, NUREG-1432, provides for an allowable value voltage range with a

! corresponding time delay range without a specified trip setpoint. This change removes the trip value from Table 3.3-4, item 7.a, and provides for an allowable value voltage range with a corresponding time delay range consistent with NUREG-1432.

Entergy Operations, Inc. has determined through operating experience that such single values do not allow for normal deviation from the desired setpoint due to manufacturer's recognized relay tolerances, etc. Also, the proposed setpoint provides improved protection from unnecessary actuation during potential system transient events. Further, recently completed design calculation revisions indicate that a substantial range of values will provide the

!- necessary safety function for loss of voltage protection, and protect the unit from spurious actuations.

DISCUSSION OF CHANGE The 4160 V system design includes loss of voltage protection relays which sense a loss of off-site power as a loss of bus voltage on a 4160 V vital bus and generates a diesel generator start signal. Specifically, two loss of voltage inverse time delay relays are provided on each 4160 V safety bus. The present loss of voltage relay setting is a single value based on 78% of the motor base voltage of 4000 V. As indicated above, recent evaluations have indicated that the present setting provides marginal protection from unnecessary actuations during certain limited potential system transient events. Additionally, recently completed design calculations indicate the setpoint can be reduced to allow a range of values that will continue to provide I

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Attachment to l 2CAN069805 )

Page 3 of 5 l 1

the necessary safety function for loss of voltage protection, and improve the unit protection

' from ' spurious actuations. These lower settings and the expanded relay time delays do not ,

affect the safety function since there is no appreciable time difference in reaching the lower setpoints during a loss of voltage event. The maximum proposed time delay setting is within those used in the ANO-2 safety analysis. The minimum proposed time delay setting provides adequate time to allow the preferred fast transfer of the associated buses to an alternate power source.

l The specific value in Technical Specification. L4.3.2, Table 3.3-4, item 7.a, under the trip i value column is proposed to be removed and replaced by note (4) for this table. Note (4) indicates that the trip value is maintained in the surveillance test procedures and that the setpoint provides adequate protection for a loss of power event while accounting for the w - y calibration tolerances, channel uncertainties, and time delays. The allowable value for this table is proposed to be revised from 3120 volts to "2300 i 699 volts." Additionally, an allowable value range for the time delay of 0.64 i 0.34 seconds is also proposed. The time delay setting was previously located in note (4).

The proposed setting for the loss of voltage channels provides a range of acceptable values based on a maximum setting which is below the lowest allowed motor terminal momentary voltage of 75% of motor voltage rating, plus further reductions to include channd uncertainties, calibration tolerances, and margin. In addition, the loss of voltage protection settings are chosen to protect the plant from spurious, unnecessary trips caused by off-site power system transients. This is made possible by the inverse voltage time characteristics of the relays used. A complete loss of off-site power will result in approximately a one second delay in initiating the diesel generator actuation signal. The relay time delay setting is also proposed to be revised to provide a range of acceptable setting values based on the delay i n==== y to prevent actuation during a normal fast transfer of power sources, and includes j channel uncertainties, calibration tolerances, and margin.

i DETERMINATION OF NO SIGNIFICANT HAZARDS CONSIDERATION

An evaluation of the proposed change has been performed in accordance with l 10 CFR 50.91(a)(1) regarding no significant hazards considerations using the standards in l

10 CFR 50.92(c). A discussion of these standards as they relate to this amendment request follows:

( Criterion 1 - Does Not involve a Significant Increase in the Probability or Consequences of an Accident Previously Evaluated.

The two 4160 Volt (V) vital bus loss of voltage protection relays that are provided on each of the 4160 V safety buses are provided to detect loss of voltage, isolate the safety buses, initiate load shedding, and start the associated emergency diesel generator. This safety function is unchanged by the proposed setpoint revisions. The revised settings for the loss of voltage protection relays will continue to provide the safety function with no appreciable additional

- ' Attehmar,t to i 2CAN069805 f' Page 4 of 5 time delay. The proposed time delays are within those assumed in the ANO-2 safety analyses.

Additionally, the lower voltage settings will prevent unnecessary isolations from the off-site power sources which will contribute to reducing the probability of a loss of off-site power due to off-site power system transients.

The ANO-2 technical specifications will continue to require the 4160 V loss of voltage functions to be surveillance tested at their present frequency without changing the modes in which the surveillance is required or the modes of applicability for these components. The technical specifications will continue to require the same actions as currently exist for the inoperability of one or more of the 4160 V loss of voltage channels. Therefore, this change does not involve a significant increase in the probability or consequences of any accident previously evaluated.

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! Criterion 2 - Does Not Create the Possibility of a New or Different Kind of Accident froni any Previously Ev? Justed.

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l The proposed change introduces no new modes of plant operation or new plant configuration. 1 l The 4160 V vital bus loss of voltage protection relays are required to operate following a complete loss of off-site power to initiate the bus power source transfer to on-site power, i.e.,

the emergency diesel generators, to prevent a loss of all AC power. This safety function is unchanged by the proposed setpoint revisions, and the proposed setpoints continue to provide the required actions consistent with the ANO-2 safety analysis. Therefore, this change does agt create the possibility of a new or different kind of accident from any previously evaluated.

l Criterion 3 - Does Not Involve a Significant Reduction in the Margin of Safety.

The two undervoltage relays located on each 4160 V safety bus are provided to detect loss of voltage, isolate the safety buses, initiate load shedding, and start the emergency diesel generators. This safety function is unchanged by the proposed setpoint revisions.

. The lower loss of voltage values do not affect the safety function since there is no appreciable time difference in reaching the lower setpoints during a loss of voltage event. The maximum proposed time delay setting with the minimum loss of voltage relay setting is within those l

used in the ANO-2 safety analysis. The revised settings for the relays will continue to provide the safety function with no appreciable additional time delay.

Removal of the trip value from the technical specifications is consistent with that which is presented in NUREG-1432, " Standard Technical Specifications for Combustion Engineering Plants." The current ANO-2 technical specifications and NUREG-1432 both indicate the.t if the setpoint is outside the allowable value column, the associated channel is declared inoperable. This approach is consistent with this proposed technical specification change.

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Attachment to 2CAN069805 Page 5 of 5 The trip and allowable values listed in the technicel specifications for the loss of voltage protection for the 4160 V buses are presently the same. With these values being the same, if I the trip value is exceesed, the allowable value will also be exceeded. This change pmvides a l range of acceptable allowable values for these relays. By relocating the trip values in the surveillance test procedures, the procedural limits for the voltage and time delay settings can be adjusted to ensure margin to the allowable values. Additionally, the lower voltage settings will help to prevent unnecessary isolation from the off-site power sources due to off-site perturbations in the electrical grid, and thus contribute to increasing the margin of safety.

Therefore, this change does nat involve a significant reduction in the margin of safety.

Therefore, based upon the reasoning presented above and the previous discussion of the amendment request, Entergy Operations has determined that the requested change does nat invc,1ve a significant hazards consideration.

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