ML19312B840

Proposed Tech Spec 3.7 Re Limiting Conditions for Transmission Line Paths & Monitoring Operations

ML19312B840
Person / Time
Site:	Oconee
Issue date:	10/13/1976
From:	DUKE POWER CO.
To:
Shared Package
ML19312B837	List: ML19312B836 ML19312B840
References
NUDOCS 7911250050
Download: ML19312B840 (8)

Text

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3.7 AUXILIARY ELECTRICAL SYSTEMS Applicability Applies to the availability of off-site and on-site electrical power for station operation and for operation of station auxiliaries.

Objective To define those conditions of electrical power availability necessary to provide for safe reactor operation and to provide for continuing availability of engineered safety features systems in an unrestricted manner and to prescribe safety evaluation and reporting requirements to be followed in the event that the auxiliary electric power systems become degraded.

Specification 3.7.1 Except as permitted by 3.7.2, 3.7.3, 3.7.4, 3.7.5, and 3.7.6, the reactor shall not be heated above 2000F unless the following conditions are met.

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(a) At least two 230 kV or 525 kV transmission lines, on separate towers, shall be in service.

(b) Two startup transformers shall be operable and available to the unit's 4160 volt Main Feeder Buses No. 1 and No. 2.

(c) One operable Keowee hydro unit shall be available to supply power through the underground feeder bus, transformer CT-4 and the 4160 volt standby buses No. 1 and 2 to the unit's 4160 volt Main Feeder Buses No. 1 and 2.

(d) One of the following conditions shall be met.

1. The second Keowee hydro unit shall be available to supply power automatically through a startup transformer to the units 4160 volt Main Feeder Buses No. 1 and 2.

2. The 4160 volt standby buses shall be energized by one of the Lee gas turbines through the 100 KV transmission circuit which shall be electrically separate from the system grid and non-safety related loads. [

(e) The two 4160 volt Main Feeder Buses shall be energized.

(f) The three 4160 volt Engineered Safety Features switchgear buses shall be energized.

- (g) Three 600 volt load centers plus the three 600 volt-208V Engineered Safety Features MCC Buses shall be energized.

(h) For etch 'mit, all 125 VDC instrunentation and control batteries with their respective chargers huses, diode monitors, and diodes supplying the unit's vital instrumentation and the four instru-nentation and control panel boards shall be operable.

3.7-1

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- - (1) Tha l'25 VDC switching etetion battarisa with thair rszpsetiva

, , chargers, buses, and isolating diodes shall be operable.

/j) The Keowee batteries with their respective chargers, buses, and isolating diodes shall be operable.

(k) The level of the Keowee Reservoir shall be at least 775 feet above sea level.

3.7.2 During hot standby or power operation, provisions of 3.7.1 may be modified to allow any one of the following conditions to exist:

(a) One of the two required startup transformers may be removed from service for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> proviaed it is expected to be restored to service within 48 tours and the other required startup transformer is available for automatic connection to the unit's main feeder bus.

(b) If two Keowee units had been operable and one Keowee unit should become unavailable for test or maintenance (corrective or preventative), the reactor may remain critical for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided the remaining Keowee hydro unit is connected to the underground feeder and is verified operable within one hour of the loss ano every eight hours thereafter.

(c) If one Keowee unit had been available and a Lee gas turbine was in operation and the Lee gas turbine should become unavaila-ble, the reactor may remain critical for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided the Keowee hydro unit is verified operable within one hour of the loss and every eight hours thereafter.

(d) If one Keowee unit had been available and a Lee gas turbine was in operation and the Keowee unit should become unavailable, the reactor may remain critical for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

(e) The underground feeder circuit may be inoperable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for test and maintenance.

(f) In each unit, the following items may be inoperable for periods not exceeding 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />s:

1. One 4160 volt main feeder bus.

5 2. One complete single string of any unit's Engineered Safety Features 4160 volt switchgear bus, 600 volt load center - 600V-208V MCC and their loads.

3. One complete single string of any unit's 125 VDC instrumentation and control batteries, chargers, buses, and all associated isolating and transfer diodes.

4. One 125 VDC instrumentation and control panel board and/or its associated loads.  !

(g) One complete single string of the 125 VDC switching station batteries, buses, chargers, and the related diode assemblies may be de-energized for test or maintenance for periods not exceeding 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

3.7-2

. (h) One complete single string of the Keowee batteries, chargers, buses, and isolating diodes may be de-energized for test or maintenance for periods not exceeding 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> on the operable Keowee unit.

(1) One 4160 volt standby bus may be inoperable for test or maintenance for periods not exceeding 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

3.7.3 In the event that the conditions of Specification 3.7.1 are not met within the time specified in Specification 3.7.2, except as noted below in Specification 3.7.4, 3.7.5, 3.7.6, and 3.7.7, the

, reactor shall be placed in a hot shutdown condition within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

If the requirements of 3.7.1 are not met within an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, the reactor shall be placed in the cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

3.7.4 In the event that all conditions in Specification 3.7.1 are met except that the underground feeder circuit to the standby buses is unavailable for longer than the test or maintenance period of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, the reactor shall be permitted to remain critical provided the following restriction is observed.

(a) Continued power operation is permitted provided within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> j of the determination that the underground feeder will be in-operable greater than the test or maintenance period of 72 l hours, the 4160 standby buses shall be energized by one of the Lee gas turbines through the 100 KV transmission circuit.

The Lee gas turbine and the 100 KV transmission circuit shall be electrically separate from the system grid and non-safety-related loads.

3.7.5 In the event that all conditions of Specification 3.7.1 are met except that all 230 KV transmission lines are lost, the reactor shall be permitted to remain critical or be restarted provided the following restrictions are observed:

(a) Prior to the restart of a shutdown reactor or within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> l

of losing all 230 KV or 525 KV transmission lines for an operating reactor, the 4160 volt stendby buses shall be ener-gized by one of the Lee gas turbines through the 100 KV trans-mission circuit. The Lee gas turbine and the 100 KV transmis-sion circuit shall be completely separate from the system grid and non-safety-related loads.

(b) The reactor coolant Tavg shall be above 5250F. Reactor coolant pump power may be used to elevate the temperature from 5000F to 5250F in the case of a restart. If Tavg decreases below 5000F, restart is not permitted by this specification.

3.7.6 In the event that all conditions of Specification 3.7.1 are met, both Keowee units may be made unavailable for planned tests or maintenance and the reactor shall be permitted to re=ain critical 3.7-3

for p2rioda not to exessd 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> providtd tha 4160 volt otendby

, - . buses are energized by one of the Lee gas turbines through the

, 100 KV transmission circuits. The Lee gas turbine and the 100 KV transmission circuit shall be completely separate from the system grid and non-safety-related loads.

3.7.7 Any degradation beyond Specification 3.7.2, 3.7.4, 3.7.5, or 3.7.6 above shall be reported to the Office of Inspection and Enforcement, Region II, within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. A safety evaluation shall be performed by Duke Power Company for the specific situation involved which justifies the safest course of action to be taken. The results of this evaluation together with plans for expediting the return to the unrestricted operating conditions of Specification 3.7.1 above shall be submitted in a written report to the Office of Nuclear Reactor Regulation with a copy to the Office of Inspection and Enforcement, Region II, within five days.

Bases The auxiliary electrical power system are designed to supply the required Engineered Safeguards loads in one unit and safe shutdown loads of the other two units and are so arranged that no single contingency can inactivate enough engineered safety features to jeopardize plant safety. These systems were designed to meet the following criteria:

" Alternate power systems shall be provided and designed with adequate independency, redundancy, capacity and testability to permit the functions required of the engineered safety features of each unit."

The auxiliary power system meets the above criteria and the intent of AEC Criterion 17. The adequacies of the AC and DC systems are discussed below as are the bases for permitting degraded conditiona for AC power.

Capacity of AC Systems The auxiliaries of two units in hot shutdown (6.0 MVa each) plus the auxiliaries activated by ESG signal in the other unit (4.8 MVa) require a total AC power capacity of 16.8 MVa. The continuous AC power capacity available from the on-site power systems (Keowee Hydro Units) is 20 MVa (limited by transformer CT4) if furnished by the underground circuit or 30 MVa (limited by CTl or CT2) if furnished through the 230 kV off-site transmission lines. Capacity available from the backup 100 kV off-site transmission line (Lee Station Gas Turbine Generator) is 20 MVa (limited by CTS).

Thus, the minimum available capacity from any one of the multiple sources c' AC power, 20 MVa, is adequate.

3.7-4

4 Capacity of DC Systems Normally, for each unit AC power is rectified and supplies the DC system buses as well as keeping the storage batteries on these buses in a charged state. Upon loss of this normal AC source of power, each unit's DC auxiliary

systems important to reactor safety have adequate stored capacity (ampere-hours) to independently supply their required emergency loads for at least

, one hour. One hour is considered to be conservative since there are redundant sources of AC power providing energy to these DC auxiliary systems. The loss of all AC power to any DC system is expected to occur very infrequently, and for very short periods of time. The following tabulation demonstrates the margin of installed battery charger rating and battery capacity when compared I to one hour of operation (a) with AC power (in amps) and (b) without AC power (in ampere hours) for each of the three safety-related DC systems installed at Oconee:

A. 125 VDC Instrumentation and Control Power System

Charger XCA, XCB, or XCS a. 600 amps each Battery ICA and 1CB Combined Capacity b. 698 ampere-hours (X = 1, 2, or 3)

Actual active loads on both 125 VDC a. First min. - 1371 amps I & C buses XDCA and XDCB next 59 min. - 568.5 amps during 1st hour of LOCA b. 581.9 ampere-hours (X = 1, 2, or 3)

B. 125 VDC Switching Station Power System Charger SY-1, SY-2, or SY-S Rating a. 50 amps each Battery SY-1 or SY-2 Capacity b. 14.4 ampere-hours 9

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Actual active load per battery a. First min. - 130 amps during ist hour of LOCA next 59 min. - 10 amps

b. 12 ampere-hours C. 125 VDC Keowee Station Power System Charger No. 1, No. 2 or Standby Rating a. 200 amps each Battery No. 1 or No. 2 Capacity b. 233 ampere-hours Actual active load per battery a. First min. - 1031 amps i

during ist hour of LOCA next 59 min. - 179.4 amps

b. 193.6 ampere-hours Redundancy of AC Svstems There are three 4160 engineered safety feature switchgear buses per unit.

Each bus can receive power frem either of the two 4160 main feeder buses per unit. Each feeder bus in turn can receive power from the 230 kV switchyard through the startup transformers, through the unit auxiliary transformer by backfeeding through the main step-up transformer, or from the 4160V standby bus. Another unit's startup transformer serving as an alternate supply can 1 be placed in service in one hour. The standby bus can receive power from the i Hydro Station through the underground feeder circuit or from a combustion turbine generator at the Lee Steam Station over an isolated 100 kV trans-mission line. The 230 kV switchyard can receive power from the on-site-Keowee Hydro station or from several off-site sources via transmission lines which connect the Oconee Station with the Duke Power system power distribution network.

J Redundancy of DC Systems A. 125 VDC Instrument and Control Power System i

l All reactor protection and engineered safety features loads on this system can be powered from either the Unit 1 and Unit 2 or Unit 2 and Unit 3 or Unit 3 and Unit 1 125 VDC Instrument and Control Power Buses.

The units' 125 VDC Instrument and Control Power Buses can be powered from two battery banks and three battery chargers. As shown above, one battery (e.g., ICA) can supply all loads for one hour. Also, one battery charger can supply all connected ESF and reactor protection loads.

B. 125 VDC Switching Station Power System i

There are two essentially independent subsystems each complete with an AC/DC power supply (battery charger), a battery bank, a battery charger bus, motor control center (distribution panel). All safety-related equipment and the relay house in which it is located are Class I (seismic) design. Each subsystem provides the necessary DC power to:

a. Continuously monitor operations of the protective relaying,

b. Isolate Oconee (including Keowee) from all external 230 kV grid faults, 3.7-6 7/19/74

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c. Connect on-site power to Oconee from a Keowee hydro unit or,

d. Restore off-site power to Oconee from non-faulted portions of the external 230 kV grid.

Provisions are included to manually connect a standby battery charger to either bactery/ charger bus.

i C. 125 VDC Keowee Station Power System l There are essentially two independent physically separated Class I (seismic) subsystems, each complete with an AC/DC power supply (charger) i a battery bank, a battery / charger bus and a DC distribution center. Each subsystem provides the necessary power to automatically or manually start, control and protect one of the hydro units.

l An open or short in any one battery, charger or DC distribution center l cannot cause loss of both hydro units.

i The 230 KV and 500 KV sources, while expected to have excellent availability, are not under the direct control of the Oconee station and, based on past experience, cannot be assumed to be available at all times.

t j The operation of the on-site hydro-station is under the direct control of the Cconee Station and requires no off-site power to startup. Therefore, an on-site backup source of auxiliary power not subject to failure from the same cause as off-site power is provided in the form of twin hydro-electric turbine generators powered through a common penstock by water taken from Lake Keowee. The use of a common penstock is justified on the basis of past hydro plant experience of the Duke Power Company (since 1919) which indicates that the cumulative need to dewater the penstock can be expected to be limited to

] about one day a year, principally for inspection, plus perhaps four days every 1 tenth year.

l l In instances in which extended maintenance is required for one Keowee hydro

] unit, the remaining hydro unit will be available for service through the i underground feeder circuit and the Lee gas turbine will be in operation i through the isolated 100 kV transmission circuit.

l In the event that only one hydro unit is available to backup the off-site power sources, continued power operation is acceptable since the operability  !

of the remaining Keowee unit is immediately verified and verified periodically l thereafter. If the hydro unit is unavailable longer than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, the Lee

, gas turbine will be placed in operation on the isolated 100 kV transmission circuit to assure a ecntinued supply of shutdown power in the event that an i external event should cause loss of all off-site power. i In a similar manner, in the event that none of the sources of off-site power 4

are available and it is considered important to continue to maintain an Oconee Unit reactor critical or return it to criticality from a hot shutdown condition, a Lee Station gas turbine can be made available as an additional

backup source of power, thus assuring continued availability as an auxiliary power to perform an orderly shutdown of a unit should a problem develop requiring shutdown of both hydro units.

3.7-7

,, . a Infrequent instances exist in which both Keovee hydro units must be removed from service for short periods of time to perform inspections or maintenance.

These are controlled evolutions in which the Lee gas turbine will be in operation prior to the removal from service of the hydro units. Additionally, availability of the 230 kV and 500 kV offsite power sources, startup transformers, and weather conditions will be evaluated prior to commencement of the inspection or maintenance.

In the rare occasion where both hydro units are unexpectedly lost there may be compelling reasons to maintain the Oconee reactors critical or return them to criticality from hot shutdown conditions for a specific period of time rather than require it to remain suberitical or be shut down. Factors to consider in justification of such a rare, limited period of criticality without the hydro station available would include number of off-site 230 kV and 500 kV power sources available, availability of the other unit's startup transformer, availability of the Lee gas turbine, weather conditions and all other factors which could bear on potential for loss of these power sources.

Also, the evaluation should show that reactor safety will not be compromised if during operation under such further degradation, an additional loss .

• AC power should be suffered.

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