ML20044A315

Proposed Tech Specs Revising Requirements Governing Operability of Emergency & Vital Busses Ac Distribution to Make Reenergization & Power Source Requirements More Specific

ML20044A315
Person / Time
Site:	North Anna
Issue date:	06/26/1990
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML20044A310	List: ML20044A309 ML20044A315
References
NUDOCS 9006280327
Download: ML20044A315 (16)

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,, l Attachment 1 i

l Proposed Technical Specification Changes North Anna Power Station Unit 1 a

b Virginia Electric and Power Company 9006280327 900626 PDR ADOCK 05000338 P PDC

i Ft FOTRICAL POWER SYSTEMS 3!4.81 ONSITE POWER DISTRIBUTION SYSTEMS ,

l A C. DISTRIBUTION OPERATING LIMITING CONDITION FOR OPERATION _

3.8.2.1 The following A.C. electrical busses shall be OPERABLE and energized with tie breakers open between redundant busses:

a. H A.C. Emergency Busses consisting of:

1. 4160 volt Emergency Bus # 1H

2. 480 voit Emergency Busses # 1H,1H1

b. J A.C. Emergency Busses consisting of:

1. 4160 voit Emergency Bus # 1J

2. 480 voit Emergency Busses # 1J.1J1

c. 120 voit A.C. Vital Bus # 1 1 energized from its associated inverter connected to D.C. Bus # 1 l*

d. 120 voit A.C. Vital Bus # '; Il energized from its associated inverter connected to D.C. Bus # 1 It'

e. 120 volt A.C. Vital Bus # 1 Ill energized f rom its associated inverter connected to D.C. Bus # 1 111'

f. 120 volt A.C. Vital Bus # 1 IV energized from its associated inverter connected to D.C. Bus # 1 IV' APPLICABILITY: MODES 1,2,3, and 4 ACTION:

a. With one of the required A.C. Emergency busses not fully energized, re energize within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or be in at least 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 />.

b. With one A.C. Vital Bus not energized, re energize the A.C. Vital Bus within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> or be in at least 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 />.

c. With one A.C. Vital Bus either not energized from its associatod inverter, or with the inverter not connected to its associated D.C. Bus, re energize the A.C. Vital Bus from its associated inverter connected to its associated D.C. Bus within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in at least 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 />.

'Two inverters may be disconnected from their D.C. Busses for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> as necessary, for the purpose of performing an equalizing charge on their associated b3ttery banks provided (1) their vital busses are energized, and (2) the remaining vif;11 busses are eteergized from their associated inverters and connected to their associated D.C. Basses.

NORTH ANNA UNIT 1 3/4 8 6

i El ECTRICAL POWER SYSTEMS l A C. DISTRIBLfTION OPERATING EM4 i AhU Amt IREMNT i i

i 4.8.2.1 The specified A.C. busses shall be deterrnined OPERABLE with tie breakers open between redundant busses at least once per 7 days by verifying correct breaker alignment and indicated power avaliability. l J

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• I NORTH ANNA UNIT 1 3/4 8-6a

, t Attachment 2 l

i Proposed Technical Specification Changes l

North Anna Power Station Unit 2 l Y l

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y Virginia Electric and Power Company

El ECTRICAL POWER SYSTEMS 3!4.8.2 ONSITE POWER DISTRIBUTION SYSTEMS A C. DISTRIBUTION OPERATING LIMITING CONDITION FOR OPERATION ,

3.8.2.1 The following A.C. electrical busses shall be OPERAPLE and energized with tie breakers open between redundant busses:

a. H A.C. Emergency Busses consisting of:

1. 4160 voit Emergency Bus # 2H

2. 480 voit Emergency Busses # 2H,2H1

b. J A.C. Emergency Busses consisting of:

1. 4160 voit Emergency Bus # 2J

2. 480 voit Emergency Busses # 2J,2J1 1

c. 120 voit A.C. Vital Bus # 21 energized from its associated i inverter connected to D.C. Bus # 2 l* i

d. 120 volt A.C. Vital Bus # 2-11 energized from its associated i inverter connected to D.C. Bus # 2-11' l

e. 120 volt A.C. Vital Bus # 2111 energized from its associated l Inverter connected to D.C. Bus # 2111'

f. 120 volt A C. Vital Bus # 2 IV energized from its associated inverter connected to D.C. Bus # 2 IV' APPLICABILITY: MODES 1,2,3, and 4.

ACTION:

a. With one of the required A.C. Emergency busses not fully energized, re energize within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or be in at least 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 />,

b. With one A.C. Vital Bus not energized, re-energize the A.C. Vital Bus within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> or be in at least 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 />,

c. With one A.C. Vita l Bus either not energized f rom its associatod inverter, or with the inverter not connected to its associated D.C. Bus, re-energize the A.C. Vital Bus from its associated inverter connected to its associated D.C. Bus within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in at least 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 />.

'Two inverters may be disconnected from their D.C. Busses for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> as necessary, for the purpose of performing an equalizing charge on their associated battery banks provided (1) their vital busses are energized, and (2) the remaining vital busses are energized from their associated inverters ano connected to their associated D.C. Busses.

NORTH ANNA UNIT 2 3/4 8-11

4 Ft FCTRICAL POWER SYSTEMS A C. DISTRIBUTION - OPERATING i

afwaI enFun aEMENT l 4.8.2.1 The specified A.C. busses shall be deterrnined OPERABLE with lie breakers open between redundant busses at least once per 7 days by verifying correct breaker alignment and indicated power availability.

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NORTH ANNA UNIT 2 3/4 811a I

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i Attachment 3 i

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l Discussion of Proposed Changes j t

North Anna Power Station Units 1 and 2 i

l Virginia Electric and Power Company

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Discussion of Pronosed Technical Snecification Changes Introduction This proposed change to the North Anna Units 1 and 2 Technical Specifications revises the operability requirements of the emergency and vital busses of AC distribution. The list of busses in the operability section of the specification and the action statements are both made more similar to the Standard Speci0 cation for Westinghouse Pressurized Water Reactors. Action statements for the vital busses and the inverters are separated for clarity. In the current specification, the invener requirement is not :learly stated. This change adds the requirement to have the 120VAC vital busses powered from the inverters and provides actions when an inverter is not in service. The change requires n:-energization of a vital bus in less time than the current specification,2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> versus 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, and requires restoration of the inverter as the source of power to the vital bus within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. ,

i The proposed requirement will not reduce vital bus or inverter reliability. l Rather, reliability for the vital busses will be enhanced because of the more strict re-energinttion requirement and the more strict requirement to have the inverters as the source of vital bus power. The change is already reflected in our March 15,1990 MERITS proposed change.

llackuround l The vital AC power system provides a highly reliable source of 120VAC power for safety-related instruments and equipment, ensuring proper i action when vital power is required. The vital AC power system consists of four separate vital bus panels, each fed independently from an associated 125VDC/120VAC single phase static inverter. The inverters are connected i to batteries that are continuously float charged by the battery chargers.

Therefore, the effective power sources for the inverters are the 480VAC emergency buses. Should the effective power source to any battery charger fail, the inverter is automatically fed from its associated station battery without disturbing the vital bus voltage or frequency. Thus, an uninterruptible power source is provided for the vital AC busses.

interruptible voltage regulating transfomiers fed from the 480VAC emergency busses are provided to supply power to the vital bus in the event the respective inverter fails or is undergoing maintenance. A manual switch is provided for each vital bus to transfer the load to an inverter or to a voltage regulating transfomier. The vital bus panels 1-1 and 1-111 Page 1 of 6

.,e supply 120VAC power to ie safety system trains A and B, respectively.  :

All four vital bus panels 1-1,1-11,1-111, and 1-IV supply 120VAC power i to the safety system channels I, II, Ill, and IV, respectively. Please see the attached one-line drawing for an overview of the system.

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Description of the Pronosed Change This proposed amendment would revise Technical Specifications 3.8.2.1, AC Distribution - Operating, for North Anna Power Station Units 1 and 2, which govern the operability of the 4160VAC and 480VAC emergency busses and the 120VAC vital busses, to more closely n:semble the wording  ;

contained in the Standard Technical Specification 3.8.3.1. The major change is the addition of the requirement that an operable 120VAC vital bus be energized from its associated inverter in tum connected to its i associated 125VDC bus. This proposed change is consistent with the Standard Technical Specification with the following exceptions:

1) The requirement for the 125VDC busses is not contained in this specification because it is contained in the current specification  !

3.8.2.3.

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2) The Standard Technical Specification Action Statement "b" has been split into two action statements in order to clarify the allowed out-of-service times for two different but associated components. The proposed Action Statement "b" applies to the 120VAC vital busses.

The proposed Action Statement "c" applies to the 125VDC/120VAC single phase static inverters.

• This proposed amendment would also add the allowance that two inverters may be disconnected from their DC bus for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for the purpose of performing an equalizing charge on their associated battery bank provided that their vital busses are energized and that the remaining vital busses are energized from their associated inverters and connected to their associated DC bus. This allowance is in the Standard Technical Specifications. This allowance is reasonable because in a possible equalizing charge lineup the inverters are merely disconnected to protect the inverters from an overvoltage from the battery chargers. They are not taken out of service for maintenance. All other components in the DC and AC Vital system remain capable of perfomiing their design function. The system as a whole,indeed all four vital AC busses, can be quickly restored to being capable of performing their design function by switching the battery chargers back to normal and reconnecting the inverters.

The proposed amendment adds operability requirements for the 120VAC vital bus inverters. It would require that the 120VAC vital busses be powered from their associated inverters. This change is proposed because of recent NRC concerns about the 120VAC vital bus operability requirements at Beaver Valley, which has power distribution and associated Technical Specifications similar to those of North Anna. At Beaver Valley, the current NRC definition of an Page 4 of 6

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.0 operable 120VAC vital bus requires that the bus be powered from a seismically qualified source such as the inverters. Another design consideration is tnat the vital busses be powered from the batteries, not the 480VAC busses, in order to  :

ensure that no bistables in the vital protection systems downstream are adversely affected. With such an interpretation, the current Beaver Valley Technical Specification, and thus also that for North Anna, requires an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Action Statement be imposed whenever an inverter is unavailable for service. This proposed amendment for North Anna would change the current 8-hour Action Statement to a 2-hour Action Statement for a de-energized 120VAC vital bus and a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Action Statement for an inoperable inverter. The current 8-hour Action Statement is more restrictive than the allowed outage time permitted by the Standard Technical Specifications. However,8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> is insufficient time to perform troubleshooting, corrective maintenance, and post maintenance testing.

Because the respective 2-hour and 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Action Statements for a de energized 120VAC Bus and an inoperable inverter are consistent with the Standard Technical Specifications, and because this change essentially imposes additional operability n:quirements to minimize the outage time of the 120VAC busses and the inverters, this proposed amendment is conservative to the existing Technical Specification. It is also conservative in that it prohibits operation with more than one of the busses listed in Technical Specification 3.8.2.1 inoperable. Currently the specification only addresses "less than the above compliment" which would mean with multiple inoperable busses,8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> is allowed in which to restore the busses. The proposed Technical Specification is more restrictive.

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l Discussion of Pronosed Technlent Snecification Chnnees Cont'd.

Safet y Analysis The applicable accident analysis in the Updated Final Safety Analysis Report is Loss of Offsite Power to the Station Auxiliaries, found in section 15.2.9. The accident sequence includes the vital instruments being first supplied by emergency power sources, next by the batteries, then by tim emergency diesel generators.

The vital power system has sufficient capacity to supply vital equipment necessary for safe operation and shutdown of the reactor while maintaining the acceptable .

fuellimits and containment integrity. The system has independence and redundancy of components to ensure the performance of safety functions despite a single failure. For this reason, the Technical Specifications allow for one vital bus to be inoperable for a short period of time and then restored. This proposed change involves neither an increase in the number of inoperable busses nor an increase in time of inoperability. Rather it includes a reduction in the allowed time a single vital bus is de energized to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and it includes the requirement that the class IE inverters must be the source of power to the vital bus within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> where no such requirement was previously made. Therefore, the accident analyses are not affected by the proposed Technical Specification change.

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Attachment 4 i

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l 10 CFR 50.92 Evaluation j North Anna Power Station Units 1 .nd 2 i

e Virginia Electric and Power Company ,

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10 CFR 50.92 Sinnificant Hazards Considerations Analysis The proposed changes do not involve a significant hazards consideration as defined in 10 CFR 50.92 based on the following: i

1. Accident Probabilliv or Conscouence Increase. The I proposed changes have no adverse impact on accident  !

probability or consequence. No equipment or procedure being l currently used is changed in any way that increases accident probability or consequence. No new or unique accident precursors are introduced by these changes nor do these changes alter the conditions or assumptions of the accident analysis or the bases of the current Technical Specification.  !

The probability of a vital bus being de-energized pmventing  !

its function in the event of an accident is decreased because this change requires re-energization of the vital bus within less time than the current specification and it requires the ultimate restoration of a power source which is seismically qualified and will not adversely affect the bistables of the vital protection systems.

i This change does not increase the number of vital busses which may be inoperable at any time nor increase the time of l

inoperability. Therefor; all the possible configurations of the system are still within the bounds of the accident analyses contained in the Updated Final Safety Analysis Report ,

(UFSAR). Thus, the consequences of an accident are unchanged by this amendment.

2. Accident Probability Creation.The proposed changes require no alteration in the facility nor additional tests or experiments. The only procedural change is to reduce the restoration time of a vital bus and to require a more reliable ultimate power source. Nothing new is added or done. No conditions or assumptions of the accident analysis or bases of the current specification are altered. No accident which is l new or different from any previously identified is created.

l Therefore, no further accident probability is emated which has not already been evaluated in the USFAR.

3. Safety Margin Reduction. The results of the accident analyses documented in the USFAR continue to bound

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operation under the proposed changes. The analyses allow for I a single failure of vital bus. Compliance with this proposed specification change ensures restoration of one inoperable vital bus in less allowed action time than current specifications and i ensures ultimate restoration of the seismically qualified inverters as the vital power source. This change does not alter the conditions or assumptions of the accident analysis or the bases of the current Technical Specification. Therefore, there is no reduction in the safety margin.

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