ML18026A242

Forwards Response to Generic Ltr 91-06, Resolution of Generic Issues A-30, 'Adequacy of Safety-Related DC Power Supplies.'

ML18026A242
Person / Time
Site:	Susquehanna
Issue date:	10/24/1991
From:	Keiser H PENNSYLVANIA POWER & LIGHT CO.
To:	Chris Miller Office of Nuclear Reactor Regulation
References
REF-GTECI-A-30, REF-GTECI-EL, TASK-A-30, TASK-OR GL-91-06, GL-91-6, PLA-3673, NUDOCS 9111010196
Download: ML18026A242 (94)

Text

ACCELERATED DTRIBUTION DEMONS~TION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR: 9111010196 DOC. DATE: 91/10/24 NOTARIZED: NO DOCKET FACIL:50-387 Susquehanna Steam Electric Station, Unit 1, Pennsylva 05000387 50-388 Susquehanna Steam Electric Station, Unit 2, Pennsylva 05000388 AUTH. NAME AUTHOR AFFILIATION KEISER,H.W. Pennsylvania Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION MILLER,C.L. Project Directorate I-2

SUBJECT:

Forwards response to Generic Ltr 91-06, "Resolution of Generic Issues A-30, 'Adequacy of Safety-Related DC Power Supplies.'" D DISTRIBUTION CODE: AOOID COPIES RECEIVED:LTR 7 ENCL / SIZE:

TITLE: OR Submittal: General Distribution

/

NOTES:LPDR 1 cy Transcripts. 05000387

~ 'PDR 1 cy Transcripts. 05000388 A 5:~~ 8~~r>> D RECIPIENT COPIES RECIPIENT COPIES i ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL D PDl-2 LA 1 1 PD1-2 PD 1 1 RALEIGH,J. 2 2 INTERNAL: ACRS 6 6 NRR/DET/ECMB 7D 1 1 NRR/DET/ESGB 1 1 NRR/DOEA/OTS B1 1 1 1 NRR/DST 8E2 1 1 NRR/DST/SELB 7E 1 1 NRR/DST/SICB8H7 1 1 NRR/DST/SRXB 8E 1 1 NUDOCS-ABSTRACT 1 1 OC/LF 1 0 OGC/HDS2 1 0 QE 1 1 RES/DSIR/EIB 1 1 F-Kl'SIC EXTERNAL: NRC PDR 1 1 NOTES: 2 2 R

D D

D NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE XVASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 26 ENCL 24

0 Pennsylvania Power 8 Light Company Two North Ninth Street ~Allentown, PA,18101-1179,~,215/774-5151 Harold W. Keiser Senior Vice President-Nuclear 1'CT 215/7744194 2 4 jtIQ)

Director of Nuclear Reactor Regulation Attention: Hr. C. L. Hiller, Project Director Project Directorate I-2 Division of Reactor Projects U.S. Nuclear Regulatory Commission Washington, D.C. 20555 SUSQUEHANNA STEAN ELECTRIC STATION RESPONSE TO GENERIC LETTER 91-06 Docket Nos. 50-387 LA- 3673 FILES R41-1D and 50-388

Dear Hr. Hiller:

Enclosed is our response to Generic Letter 91-06, "Resolution of Generic Issue A-30". In an effort to avoid confusion caused by extensive explanatory remarks provided for each DC system, our response is divided into four parts:

I ATTACHMENT ATTACHMENT ATTACHMENT II:

III:

24V DC SYSTEM 125V DC SYSTEM 250V DC SYSTEM ATTACHMENT IV  : DG'-E 125V DC SYSTEM Should you have any questions, please contact Hr. W. W. Williams, at (215) 774-7910.

Very truly yours, gl H. W. Keiser Enclosure 9111p1 01'96K 91102%

PDR ADOC p5ppp387 P

OCT 24 lg01 FILES A17-8/so-24 PLA-'3673 Mr. C. L. Miller cc: iiiLC D~ocumen. Control-Desk-(original.)P NRC Region I Mr. G. S. Barber, NRC Sr. Resident Inspector Mr. J. J. Raleigh, NRC Project Manager WWW:llr PLA/021. WWW

SUS UEHANNA S.E.S. ATTACHMENT I 24V DC SYSTEN Page 1 ENCLOSURE 1 The following information is applicable to either Unit 1 or 2 at Susquehanna SES.

l. Unit Sus uehanna S.E.S. Unit 1 or 2 24V DC

2. a ~ The number fty- l ddt f tll yl tl any separate Class lE or safety-related dc, such dedicated to the diesel generators.)

~t.(l of independent redundant divisions of Class lE or as any dc ld

b. The number of functional safety-related divisions of dc power yt ttl f ttd f tll ltd

3. Does the control room at this unit have the following separate, independently annunciated alarms and indications for each division of dc power?

a. Alarms

1. Battery disconnect or circuit breaker open?

No

2. Battery charger disconnect or circuit breaker open (both input ac and output dc)? No

3. dc system ground? No

4. dc bus undervoltage? No

5. dc bus overvoltage? No

6. Battery charger failure? No

...9111010196

C 4'

SUS UEHANNA S.E.S. ATTACHMENT I 24V DC SYSTEM Page 2

7. Battery discharge? No

b. Indications

1. Battery float charge current? No

2. Battery circuit output current? No

3. Battery discharge? No

4. Bus voltage? No

c. Does the unit have written procedures for response to the above alarms and indications? No

4. Does this unit have indication of bypassed and inoperable status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from its dc bus and the battery charger from its ac power source during maintenance or testing?

No See remark tl

5. If the answer to any part of question 3 or 4 is no, then provide information justifying the existing design features of the facility's safety-related dc systems.

• See note below.

See remark Ol

6. (I) Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one dc division to be unavailablet ~es and (2) do plant procedures prohibit maintenance or testing on redundant DC divisions at the same time'I ~es If the facility Technical Specifications have provisions equivalent to those found in the Westinghouse and Combustion Engineering Standard Technical Specifications for maintenance and surveillance, then question 7 may be skipped and a statement to that effect may be inserted here.

I

~YYS.E.S.

SUS UEHANNA T

ATTACHMENT Page 3

7. Are maintenance, surveillance and test procedures regarding station batteries conducted routinely at this plant? Specifically:

a. At least once per 7 days are the following verified to be within acceptable limits:

1. Pilot cell electrolyte level? Yes

2. Specify gravity or charging current? Yes

3. Float voltage? Yes

4. Total bus voltage on float charge? Yes

5. Physical condition of all cells? Yes

b. At least once per 92 days, or within 7 days after a battery discharge, overcharge, or if the pilot cell readings are outside the 7-day surveillance requirements are the following verified to be within acceptable limits:

l. Electrolyte level of each cell? Yes

2. The average specific gravity of all cells? Yes

3. The specific gravity of each cell? Yes

4. The average electrolyte temperature of a representative number of cells? Yes

5. The float voltage of each cell? Yes

6. Visually inspect or measure resistance of terminals and connectors (including the connectors at the dc bus)? Yes

SUS UEHANNA S.E.S. ATTACHMENT I 24V DC SYSTEM Page 4

c. At least every 18 months are the following verified:

1. Low resistance of each connection (by test)? Yes

2. Physical condition of the battery? Yes

3. Battery charger capability to deliver rated ampere output to the dc bus? Yes

4. The capability of the battery to deliver its design duty cycle to the dc bus? Yes

5. Each individual cell voltage is within acceptable limits during the service test? Yes

d. At least every 60 months, is capacity of each battery verified by performance of a discharge test? Yes

e. At least annually, is the battery capacity verified by performance discharge test, if the battery shows signs of degradation or has reached 85X of the expected service life? Yes

8. Does this plant have operational features such that following loss of one safety-related dc power supply or bus:

a. Capability is maintained for ensuring continued and adequate reactor cooling? Yes

b. Reactor coolant system integrity and isolation capability are maintained? Yes

c. Operating procedures, instrumentation (including indicators and annunciators), and control functions are adequate to initiate systems as required to maintain adequate core cooling? Yes

9. If the answer to any part of question 6, 7 or 8 is no, then provide your basis for not performing the maintenance, surveillance and test procedures described and/or the bases for not including the operational features cited.

• See note below.

N SUS UEHANNA S.E.S. ATTACHMENT I 24V DC SYSTEM Page 5

• Note: For questions involving supporting type information (question numbers 5 and 9) instead of developing and supplying the information in response to this letter, you may commit to further evaluate the need for such provisions during the performance of your individual plant examination for severe accident vulnerabilities (IPE). If you select this option, you are required to:

(1) So state in response to these questions, and (2) Commit to explicitly address questions 5 and 9 in your IPE submittal per the guidelines outlined in NUREG-1335 (Section

2. 1.6, Subitem 7), "Individual Plant Examination: Submittal Guidance."

c:iwp51idocsi24VDCSYS.PCD (18) 10/24/91 9:20am

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 1 REMARK 1:

1.0 The following indications and alarms for the 24V dc class 1E subsystem are provided. Justification for this design has been previously provided in PLA-959 to the NRC dated 11/6/81, regarding Control Room monitoring of Class lE dc power systems.

Each 24V dc subsystem consists of two 24 volt battery banks connected in series with a common ground bus connected to the common (center) point of the two battery banks. The ground bus is solidly grounded to the station ground grid. Each 24 volt battery bank is designated as either the positive or negative bus as referenced to ground. The alarms/indications in the following table and discussion are typical for each positive and negative bus.

, Location Alarm or Indication Local Control Room Notes Bus Undervoltage Alarm 1,2 Battery Monitor Alarm 1,2,4 Battery Charger Trouble Alarm 1,2,5 Bus Overvoltage Alarm 1,2 Bus Voltmeter Battery Charger Ammeter 3 Battery Charger Voltmeter DC System Trouble Alarm NOTES:

1. See Table 1 and Figure 2 for specific local alarm indication.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 2

2. These are locally indicated and actuate dc subsystem trouble alarm, see Table 1 and Figure 1.

3. Heters are provided locally. See Figure 3.

4. Battery monitor 'compares battery center point voltage with high and low threshold reference points of the high and low voltage comparators. The degraded cell conditions (such as a shorted cell) or an open circuit condition (such as an open fuse) are detected by the battery monitor.

5. Battery charger trouble alarm indication is provided for battery charger AC power failure, DC output breaker open, battery charger failure alarm operation.

6. One annunciator window for each 24V dc subsystem is provided.

(Includes inputs from either the positive or negative bus).

2.0 The monitoring scheme provided for the dc power subsystem is based on the degree of control provided to the control room operator. Since the dc power system equipment can not be remotely controlled, a single dc system trouble annunciator window for each subsystem is provided in the control room, consistent with the system level alarm criteria set forth in Section 8 of R.G. 1.47.

The SSES design is based on the general criteria that, if the operator can perform some corrective action in the control room in response to a specific input, that information is specifically provided. The dc power system equipment can not be controlled from the control room.

Annunciating specific inputs from the 24V dc system in the control room does not enhance the control room operators's ability to deal with the situation and it would not be consistent with SSES alarm design philosophy. However, if the only response required is to dispatch an operator to an area removed from the control room, then the only information required in the control room is general information with only the level of specificity required to direct that operator to the proper location. This method is faster and more reliable since abnormal

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 3 conditions are automatically alarmed. Furthermore, this approach is consistent with the human factors engineering goal to not over burden the operator with unnecessary information. 24V dc system instrumentation, locally provided, is in full compliance with the requirement of IEEE 308-1974 and Regulatory Guide 1.47.

The DC system general trouble alarms and specific local indicators in conjunction with the routine operator surveillance provide positive assurance that the Class lE dc power system are maintained in a steady state ready to perform-the required safety function.

3.0 Following is the justification for each alarm and indication listed in Generic Letter 91-06.

3. 1 Batter Disconnect or Circuit Breaker 0 en Alarm:

The Susquehanna S.E.S. (SSES) 24V dc subsystem utilizes fuses as the battery disconnect. This condition is detected by the battery monitor. The battery monitor utilizes a variable threshold circuit together with two comparators (high and low) to detect the loss of battery capability due to an open circuit (i.e., an open fuse or degraded cell condition). A variable threshold circuit accepts the battery charger voltage and develops two threshold voltages for use with the comparators. When the monitored voltages go above or below the thresholds, the battery monitor output relay contacts initiate a local battery monitor alarm which is reflashed to the control room as a 24V dc system trouble alarm.

This is consistent with the general design philosophy discussed in Section 2.0.

3.2 Batter Char er Disconnect or Circuit Breaker 0 en Both In ut AC and Out ut DC Alarm 3.2. 1 Battery Charger AC Input Disconnect or Circuit Breaker:

SSES utilizes a circuit breaker in the battery charger as a disconnect for the ac input power supply. An ac power

RESPONSE TO GENERIC. LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEN PAGE 4 failure alarm relay is installed internal to the battery charger to detect loss of ac input power. This condition could be caused by an open input circuit breaker or loss of the 120V ac power supply to the charger. The ac power failure alarm relay initiates a battery charger trouble alarm at the local reflasher panel, which is reflashed to the control room as a 24V dc system trouble alarm. This is consistent with the general design philosophy discussed in section 2.0.

3.2.2 Battery Charger DC Output Circuit Breaker SSES utilizes a circuit breaker in the battery charger as a disconnect for the dc output circuit. The circuit breaker is provided with an auxiliary position indicating switch. A switch contact which is closed when the circuit breaker is open is used to initiate a battery charger trouble alarm at the local reflasher panel. A dc system trouble alarm is reflashed to the control room by the local reflasher panel.

This is consistent with the general design philosophy discussed in Section 2.0.

3.3 DC S stem Ground Alarm The 24V dc subsystem is a solidly grounded system. Therefore, a system ground alarm is not required. A second ground on either the positive or negative bus will cause protective devices in the circuit to operate. This condition will be detected at the local reflasher panel by either the battery monitor alarm (for battery fuse open) or the battery charger trouble alarm (for battery charger DC output breaker open).

In either case, the local reflasher panel will reflash a 24V dc system trouble alarm to the control room annunciator. This is consistent with the general design philosophy discussed in Section'.0.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 5 3.4 DC Bus Undervolta e Alarm The 24V dc subsystem is provided with positive and negative dc bus undervoltage relays. Each relay is connected across the system buses (positive bus to ground, negative bus to ground). The relays are normally energized and, set to drop out at the specified setpoint. A positive bus or negative bus low voltage alarm at the local reflasher panel is initiated after the undervoltage relay drops out.

The local reflasher panel, in turn, reflashes the alarm to the control room annunciator as a dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3.5 DC Bus Overvolta e Alarm The 24V dc subsystems are provided with overvoltage relays. The relays are located inside the 24V dc distribution panels. Each relay is connected across the system buses (positive bus to ground, negative bus to ground) and set to pick up at the specified setpoint. A normally open contact of the over'voltage relay, when closed, initiates a positive bus or negative bus high voltage alarm at the local reflasher panel which in turn will reflash a dc system trouble to the control room annunciator. This is consistent with the general design philosophy discussed in Section 2.0.

3.6 Batter Char er Failure Alarm Each 24V dc subsystem battery charger is provided with a battery charger failure relay. This relay will detect the loss of the charger output current with the input and output circuit breakers closed.

This condition is indicative of a battery charger failure and it initiates a battery charger trouble alarm at the local reflasher

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 6 panel which in turn will reflash a dc system trouble alarm to the control room annunciator.

This is consistent with the general design philosophy discussed in Section 2.0.

3.7 Batter Dischar e Alarm The battery can only discharge when its .terminal voltage is less than the nominal open circuit voltage. This is indicative of a battery charger failure or system current in excess of the charger capability. A battery charger failure alarm is provided and its operation is discussed in Section 3.6. When system current exceeds battery charger capability, a dc system undervoltage condition will occur, and will be detected by the dc bus undervoltage relay (see Section 3.4). Charger failure and bus undervoltage initiate alarms at the local reflasher panel which in turn will reflash a dc system trouble alarm to the control room annunciator. This is consistent with the general design philosophy as discussed in Section 2.0.

3.8 Batter Float Char e Current Indication Under normal conditions, the battery float charge current is very small compared to battery discharge current. Measurement of this current requires a very sensitive ammeter. Shunt bypasses are employed to protect the ammeter movement from the much larger battery discharge current possible in this circuit. These shunts must be manually removed when reading normal small float current.

Thus this reading cannot be continuous and no automatic indication or alarms can be given.

Since the intent of indicating "Battery Float Charge Current" is to determine the battery condition, the method used to accomplish this purpose should not be important.

The bus undervoltage, battery monitor and battery charger failure

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 7 alarms (previously described) provide continuous monitoring to detect degradation of battery capability. These alarms will reflash the dc system trouble alarm in the control room, and an operator is dispatched locally to determine the cause of the condition and initiate corrective action.

Specific indication is provided on the local reflasher panel.

This response is exactly what would 'be achieved if an improper state of battery current were indicated on an ammeter in the control room.

This is consistent with the general design philosophy discussed in Section 2.0.

3.9 Batter Circuit Out ut Current Indication In normal condition when the battery charger is supplying the 24V dc power, the battery circuit (battery and the battery charger) output current is indicated by an ammeter located at the battery charger.

In the condition of a battery charger failure, the battery supplies the dc power. In this condition the battery circuit output current cannot be determined since an ammeter is not provided at the 24V dc distribution panels.

As indicated in Section 3.8, the intent of indicating "battery current" is to determine the battery condition, and therefore the method used to accomplish this purpose should not be important.

3. 10 Batter Dischar e Indication As previously discussed in Section 3.7, a battery discharge will occur as a result of a battery charger failure or system current in excess to battery charger capability. Since these conditions are automatically alarmed in the control room (via the system trouble alarm), an operator will be dispatched locally to

I RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 8 determine the cause of the condition and initiate corrective action. This response is exactly what would be achieved if battery discharge current was indicated on an ammeter in the control room.

3.11 Bus Volta e Indication The battery, the battery charger and the 24V dc distribution panel are located in close proximity of each other. The battery charger and the dc distribution panel are each provided with a voltmeter.

The purpose of a bus voltmeter at the control room would be to enable the operator to dispatch someone to take corrective action locally to correct abnormal bus voltage. At SSES bus undervoltage and overvoltage is monitored directly at the distribution panel.

The bus undervoltage and overvoltage conditions are annunciated as 24V dc system low or high voltage at the local reflasher panel. A dc system trouble alarm is reflashed to the control room annunciator by the local reflasher panel.

This design automatically alerts the control room operator to unusual voltage conditions without unnecessarily requiring his periodic attention and analysis. As a result, 24V dc bus voltage indication is not provided in the control room and has been provided on the front of the distribution panel where it provides useful information during surveillance and maintenance activities.

A voltmeter is located on the front of the battery charger panel.

With the charger output circuit breaker closed, the charger output and the bus voltages are essentially the same due to the close proximity of the charger to the load center. All abnormal voltage conditions of the battery charger are annunciated at the local reflasher panel which is reflashed to the control room as a dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEN PAGE 9

3. 12 Alarm Res onse Procedure Control room alarm response procedures for a 24V dc system trouble alarm direct the operator to respond to the local reflasher panel to determine the condition which caused the alarm.

Local alarm response procedures for the reflasher panel are provided to direct the operator to determine the cause of the condition and to initiate corrective action.

3. 13 Indication of B assed and Ino erable Status of Circuit Breakers or Other Disconnectin Devices Although indication of bypassed and inoperable status of circuit breakers or other disconnecting devices is not provided as a part of the Bypass Indication System, the 24V dc System Trouble Alarm in the control room is initiated for the following condition (which are disconnecting devices in the system):

Hain battery fuse open.

Battery charger ac input circuit breaker open.

Battery charger dc output circuit breaker open, or dc distribution panel feeder breaker open.

P RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

24V DC SUBSYSTEM PAGE 10 TABLE 1 24V DC S stem Ref lash Panel Indicators 1L610 (Typical for positive and negative buses)

l. 24V DC System Low Voltage

2. , 24V DC System High Voltage

3. Battery Honitor (indicates battery degradation or open battery fuses)

4. Battery Charger Trouble indicates (1) AC power failure, (2) DC output breaker open, or (3) battery charger failure C:KWP51%00CSK24VDCSS ~ PGO (18) 10/24/91 9:168AI

124 DC MULTIPLE ALARM INPUTS FROM %24V DC LOCAL REHASH PANEL POWER SYSTEM PER WITH INDICATION 1L670 TABLE 1 DC SYSTEM AlARM INPUTS FROM OTHER REFLASH PANELS (8MILAR TO ABOVE)

CONTROL ROOM PANEL 1C651 ANNUNCIATOR +24V DC SYSTEM TROUBLE 1L670 FIGURE 1

INDICATOR UGHI'ERASHER PANEL POWER FAILURE POSITIVE BUS NEGATIVE BUS BATlERY LOW HIGH CHARGER 41 VOLTAGE VOLTAGE TROUBLE 0

NEGATIVE BUS BATTERY BATIERY LOW POSITIVE CHARGER W VOLTAGE MONITOR TROUBLE 0

POSITIVE BUS BATlERY HIGH NEGATIVE VOLTAGE MONITOR 224V DC SYSTEM LOCAL REHASHER PANEL QYPICAO FIGURE 2

I BATIERY BANK 1 D670 I

+24 -24 I

96P

>0 CLQ

+24 VDC -24 VDC BA11ERY BA11ERY CHARGER CHAI&ER DC BKR DC BKR Qv Q~ QvQA 59 y 27 P

27 N y 69 N

AMP SPARE POS NEG SPARE COMP MPUIER OUTPUT VOLTS VOLTS OUTPUT

} NEG PROCESS SOURCE RNG. MON'S RADIATION INIERM RNG. MON'S MONITORS 1RIP. AUX, UNITS NOTE 1

+24V COMMON -24V NOTE 1: COMMON BUS GROUNDED 24 VDC SYSTEM OYPICAQ

SUS UEHANNA S.E.S. ATTACHMENT II 125V DC SYSTEM Page 1 ENCLOSURE 1 The following information is applicable to either Unit 1 or 2 at Susquehanna SES.

1. Unit SUS UEHANNA S.E.S. UNIT-1 or 2 125V DC SYSTEM

2. a 0 The number of independent redundant divisions of Class lE or safety-related DC power for this plant is See Remark 1 (Include any separate Class 1E or safety-related DC, such as any DC dedicated to the diesel generators).

b. The number of functional safety-related divisions of DC power necessary to attain safe shutdown for this unit is See Remark 2.

3. Does the control room at this unit have the following separate, independently annunciated alarms and indications for each division of DC power?

a ~ Alarms

1. Battery disconnect or circuit breaker open?

No

2. Battery charger disconnect or circuit breaker open (both input AC and output DC)? No

3. DC system ground? No DC bus undervoltage? No

5. DC bus overvoltage? No

6. Battery charger failure? No

7. Battery discharge? No

b. Indications

l. Battery float charge current? No

2. Battery circuit output current? No

3. Battery discharge? No Bus voltage? No

SUS UEHANNA S.E.S. ATTACHMENT II 125V DC SYSTEN Page 2

c. Does the unit have written procedures for response to the above

'alarms and indications? No I *,

I

4. Does this unit have indication of bypassed and inoperable'status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from its DC bus, and the battery charger from its AC power source during maintenance or tes'ting?

No See remark ¹3

5. If the answer to any part of question 3 or 4 is no, then provide information justifying the existing design features of the facility's safety-related DC systems. *See endnote.

See remark ¹3

6. (I) Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one DC division to be unavailablet ~es and (2) Do plant procedures prohibit maintenance or testing on redundant DC divisions at the same time? ~es If the facility Technical Specifications have provisions equivalent to those found in the Westinghouse and Combustion Engineering Standard Technical Specification for maintenance and surveillance, then question 7 may be skipped and a statement to that effect may be inserted here.

7. Are maintenance, surveillance and test procedures regarding station batteries conducted routinely at this point? Specifically:

a. At least once per 7 days are the following verified to be within acceptable limits:

I. Pilot cell electrolyte level? Yes

2. Specific gravity or charging current? Yes

3. Float voltage? Yes

4. Total bus voltage on float charge? Yes

5. Physical condition of all cells? Yes

SUS UEHANNA S.E.S. ATTACHMENT II 125V DC SYSTEM Page 3

b. At least once per 92 days, or within 7 days after a battery discharge, overcharge, or if the pilot cell readings are outside the 7-day surveillance requirements are the following verified to be within acceptable limits:

l. Electrolyte level of each cell? Yes

2. The average specific gravity of all cells? Yes

3. The specific gravity of each cell? Yes

4. The average electrolyte temperature of a representative number of cells? Yes

5. The float voltage of each cell? Yes

6. Visually .inspect or measure resistance of terminals and connectors (including the connectors at the DC bus)? Yes

c. At least every 18 months are the following verified:

Low resistance of each connection (by test)? Yes

2. Physical condition of the battery? Yes

3. Battery charger capability to deliver rated ampere output to the DC bus? Yes The capability of the battery to deliver its design duty cycle to the DC bus'? Yes

5. Each individual cell voltage is within acceptable limits during the service test? Yes

d. At least every 60 months, is capacity of each battery verified by performance of a discharge test'? Yes

e. At least annually, is the battery capacity verified by performance discharge test, if the battery shows signs of degradation or has reached 85X of the expected service life? Yes

8. Does this plant have operational features such that following loss of one safety-related DC power supply or bus:

a. Capability is maintained for ensuring continued and adequate reactor cooling? Yes

SUS UEHANNA S.E.S. ATTACHMENT II 125V DC SYSTEN Page 4

b. Reactor coolant system integrity and isolation capability are maintained7 Yes

c. Operating procedures, instrumentation (including indicators and annunciators), and control functions are adequate to initiate systems as required to maintain adequate core cooling7 Yes

9. If the answer to any part of question 6, 7, or 8 is no, then provide your basis for not performing the maintenance, surveillance and test procedures described and/or the bases for not including the operational features cited. *See Note below.

• Note: For questions involving supporting type information (question numbers 5 and 9) instead of developing and supplying the information in response to this letter, you may commit to further evaluate the need for such provisions during the performance of your individual plant examination for severe accident vulnerabilities (IPE). If you select this option, you are required, to:

1) So state in response to these questions, and

2) Commit to explicitly address questions 5 and 9 in your IPE submittal per the guidelines outlined in NUREG-1335 (section 2. 1.6, Subitem 7), "Individual Plant Examination: Submittal Guidance."

C:KIIP51I,docshadeqofsa.pgd (18) 10/24/91 8:57am

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEM PAGE 1 REMARK 1:

The Unit 1 Class 1E direct current, (dc) system consists of four independent 125 volt dc subsystems. These four subsystems are identified as channels A, B, C, and D. Each subsystem provides the control power for its associated class lE ac power load group consisting of: '. 16kV switchgear, 480V load centers, and a standby diesel generator. The 125V dc subsystems also provide dc power for safety feature valve actuation, diesel generator auxiliaries, and plant alarm and indication circuits.

REMARK 2:

Four separate and independent class 1E 125V dc subsystems supply control power for each of the class 1E load groups. Loss of any one of the subsystems does not prevent the minimum safety function from being performed (i.e., three out of four subsystems are necessary to attain safe shutdown for Unit 1).

REMARK 3:

1.0 The following indications and alarms for the 125V dc class lE subsystem are provided. Justification for this design has been previously provided in PLA-959 to the NRC dated ll/6/81, regarding Control Room monitoring of Class 1E dc p'ower systems.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEM PAGE 2 Location Alarm or Indication Local Control Room Notes Bus Undervoltage Alarm 1,2 Bus Ground Alarm 1,2 Battery Monitor Alarm 1,2,4 Battery Charger Trouble Alarm 1,2,5 Bus Ammeter Bus Voltmeter Battery Charger Ammeter Battery Charger Voltmeter DC System Trouble Alarm NOTES:

1. See Table 1 and Figure 2 for specific local alarm indication.

2. These are locally annunciated and actuate dc subsystem trouble alarm, see Table 1 and Figure l.

3. Heters are provided locally. See Figure 3.

Battery monitor compares battery center point voltage with high and low threshold reference points of the high and low voltage comparators. The degraded cell conditions (such as a shorted cell) or an open circuit condition (such as an open fuse) are detected by the battery monitor.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEM PAGE 3

5. Battery charger trouble alarm indication is provided for battery charger AC power failure, DC output breaker open, battery charger failure alarm operation, and bus overvoltage.

6. One annunciator window for the 125V dc subsystem is provided.

2.0 The monitoring scheme provided for the dc power subsystem is based on the degree of control provided to the control room operator. Since the dc power system equipment can not be remotely controlled, a single dc system trouble annunciator window for each subsystem is provided in the control room, consistent with the system level alarm criteria set forth in Section B of R.G. 1.47.

The SSES design is based on the general criteria that, if the operator can perform some corrective action in the control room in response to a specific input, that information is specifically provided. The dc power system equipment can not be controlled from the control room.

Annunciating specific inputs from the 125V dc system in the control room does not enhance the control room operators's ability to deal with the situation and it would not be consistent with SSES alarm design philosophy. However, if the only response required is to dispatch an operator to an area removed from the control room, then the only information required in the control room is general information with only the level of specificity required to direct that operator to the proper location. This method is faster and more reliable since abnormal conditions are automatically alarmed. Furthermore, this approach is consistent with the human factors engineering goal to not over burden the operator with unnecessary information. 125V dc system instrumentation, locally provided, is in full compliance with the requirement of, IEEE 308-1974 and Regulatory Guide 1.47.

The DC system general trouble alarms and specific local indicators in conjunction with the routine operator surveillance provide positive assurance that the Class 1E dc power system are maintained in a steady state ready to perform the required safety function.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEM PAGE 4 3.0 Following is the justification for each alarm and indication listed in Generic Letter 91-06.

3. 1 Batter Disconnect or Circuit Breaker 0 en Alarm:

The Susquehanna S.E.S. (SSES) 125V dc subsystem utilizes fuses as the battery disconnect. This condition is detected by the battery monitor. The battery monitor utilizes a variable threshold circuit together with two comparators (high and low) to detect the loss of battery capability due to an open circuit (i.e., an open fuse or degraded cell condition). A variable threshold circuit accepts the battery charger voltage and develops two threshold voltages for use with the comparators. When the monitored voltages go above or below the thresholds, the battery monitor output relay contacts initiate a local battery monitor alarm which is reflashed to the control room as a 125V dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3.2 Batter Char er Disconnect or Circuit Breaker 0 en Both In ut AC and Out ut DC Alarm 3.2. 1 Battery Charger AC Input Disconnect or Circuit Breaker:

SSES utilizes a circuit breaker in the battery charger as a disconnect for the ac input power supply. An ac power failure alarm relay is installed internal to the battery charger to detect loss of ac input power. This condition could be caused by an open input circuit breaker or loss of the 480V ac power supply to the charger. The ac power failure alarm relay initiates a battery charger trouble alarm at the local reflasher panel, which is reflashed to the control room as a 125V dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEN PAGE 5 3.2.2 Battery Charger DC Output Circuit Breaker SSES utilizes a circuit breaker in the battery charger as a disconnect for the dc output circuit. The circuit breaker is provided with an auxiliary position indicating switch. A switch contact which is closed when the circuit breaker is open is used to initiate a battery charger trouble alarm at the local reflasher panel. A dc system trouble alarm is reflashed to the control room by the local reflasher panel.

This is consistent with the general design philosophy discussed in Section 2.0.

3.3 DC S stem Ground Alarm The 125V dc subsystem is ungrounded and is provided with a ground detection circuit. It consists of a relay having a center tapped coil. The coil is connected across the positive and negative bus and its center point is grounded. The ground detection relay coil is not actuated during normal operation of the 125V dc subsystem when a ground is not present. A ground on either the positive or negative bus of the 125V dc subsystem causes one-half of the relay coil to be short circuited, thus providing sufficient voltage to the remaining relay coil half to pickup the relay. A normally open contact of the relay closes and initiates a 125V dc system.

ground alarm at the local reflasher panel. A dc system trouble alarm is reflashed to the control room annunciator by the local reflasher panel. This is consistent with the general design philosophy discussed in Section 2.0.

3.4 DC Bus Undervolta e Alarm The 125V dc subsystem is provided with a dc bus undervoltage relay. The relay is connected across the positive and negative bus of the 125V dc subsystem. The relay is normally energized and set to drop out at the specified setpoint. A 125V dc bus undervoltage alarm at the local reflasher panel is initiated after the undervoltage relay drops out.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEN PAGE 6 The local reflasher panel, in turn, r eflashes the alarm to the control room annunciator as a dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3.5 DC Bus Overvolta e Alarm The 125V dc subsystem is provided with an overvoltage relay. The relay is located inside the battery charger cabinet. It is connected across the positive and negative 125V dc bus of the battery charger and set to pick up at the specified setpoint. A normally open contact of the overvoltage relay, when closed, initiates a battery charger trouble alarm at the local reflasher panel which in turn will reflash a dc system trouble to the control room annunciator.

Since the battery, the battery charger and the dc load center are in close proximity of each other, the battery charger voltage is representative of the 125V dc bus voltage. This is consistent with the general design philosophy discussed in Section 2.0.

3.6 Batter Char er Failure Alarm The 125V dc subsystem battery charger is provided with a battery charger failure relay. This relay will detect the loss of the charger output current with the input and output circuit breakers closed.

This condition is indicative of a battery charger failure and it initiates a battery charger trouble alarm at the local reflasher panel which in turn will reflash a dc system trouble alarm 'to the control room annunciator.

This is consistent with the general design philosophy discussed in Section 2.0.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEM PAGE 7 3.7 Batter Dischar e Alarm The battery can only discharge, when its terminal voltage is less than the nominal open circuit voltage. This is indicative of a battery charger failure or system current in excess of the charger capability. A battery charger failure alarm is provided and its operation is discussed in Section 3.6. 'When system current exceeds battery charger capability, a dc system undervoltage condition will occur, and will be detected by the dc bus undervoltage relay. (See Section 3.4.) Charger failure and bus undervoltage initiate alarms at the local reflasher panel which in turn will reflash a dc system trouble alarm to the control room annunciator. This is consistent with the general design philosophy as discussed in Section 2.0.

3.8 Batter Float Char e Current Indication Under normal conditions, the battery float charge current is very small compared to battery discharge current. measurement of this current requires a very sensitive ammeter. Shunt bypasses are employed to protect the ammeter movement from the much larger battery discharge current possible in this circuit. These shunts must be manually removed when reading normal small float charge current. Thus this reading cannot be continuous and no automatic indication or alarms can be given.

Since the intent of indicating "Battery Float Charge Current" is to determine the battery condition, the method used to accomplish this purpose should not be important.

The bus undervoltage, bus ground, battery monitor and battery charger failure alarms (previously described) provide continuous monitoring to detect degradation of battery capability. These alarms will reflash the dc system trouble alarm in the control room, and an operator is dispatched locally to determine the cause of the condition and initiate corrective action.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEM PAGE 8 Specific indication is provided on the local reflasher panel.

This response is exactly what would be achieved if an improper state of battery current were indicated on an ammeter in the control room.

This is consistent with the general design philosophy discussed in Section 2.0.

3.9 Batter Circuit Out ut Current Indication.

In normal condition when the battery charger is supplying the 125V dc power, the battery circuit (battery and the battery charger) output current is indicated by an ammeter located at the battery charger.

In the condition of a battery charger failure, the battery supplies the dc power. In this condition the battery circuit output current is indicated by an ammeter located at the dc load center.

As indicated in Section 3.8, the intent of indicating "battery current" is to determine the battery condition, and therefore the method used to accomplish this purpose should not be important.

3. 10 Batter Dischar e Indication As previously discussed in Section 3.7, a battery discharge will occur as a result of a battery charger failure or system current in excess to battery charger capability. Since these conditions are automatically alarmed in the control room (via the system trouble alarm), an operator will be dispatched locally to determine the cause of the condition and initiate corrective action. This response is exactly what would be achieved if battery discharge current was indicated on an ammeter in the control room.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEM PAGE 9

3. 11 Bus Volta e Indication The battery, the battery charger and the dc load center of 125V dc subsystem are located in close proximity of each other. The battery charger and the dc load center are each provided with a voltmeter. The purpose of a bus voltmeter at the control room would be to enable the operator to dispatch someone to take corrective action locally to correct abnormal bus voltage. At SSES the bus undervoltage is monitored directly and the bus overvoltage conditions are monitored at the battery charger output. The bus undervoltage and the battery charger output overvoltage conditions are annunciated as 125V dc system low voltage or battery charger trouble at the local reflasher panel.

A dc system trouble alarm is reflashed to the control room annunciator by the local reflasher panel.

This design automatically alerts the control room operator to unusual voltage conditions without unnecessarily requiring his periodic attention and analysis. As a result, 125V dc bus voltage indication is not provided in the control room and has been provided on the front of the load center where it provides useful information during surveillance and maintenance activities.

A voltmeter is located on the front of the battery charger panel.

With the charger output circuit breaker closed, the charger output and the bus voltages are essentially the same due to the close proximity of the charger to the load center. All abnormal voltage conditions of the battery charger are annunciated at the local reflasher panel which is reflashed to the control room as a dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3. 12 ,

Alarm Res onse Procedure Control room alarm response procedures for a 125V dc system trouble alarm direct the operator to respond to the local reflasher panel to determine the condition which caused the alarm.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEH PAGE 10 Local alarm response procedures for the reflasher panel are provided to direct the operator to determine the cause of the condition and to initiate corrective action.

3. 13 Indication of B assed and Ino erable Status of Circuit Breakers or Other Oisconnectin Devices Although indication of bypassed and inoperable status of circuit breakers or other disconnecting devices is not provided as a part of the Bypass Indication System, the 125V dc System Trouble Alarm in the control room is initiated for the following condition (which are disconnecting devices in the system):

Hain battery fuse open.

Battery charger ac input circuit breaker open.

Battery charger dc output circuit breaker open or 125V dc load center input breaker open.

125V dc load center feeder breaker to 125V dc distribution panels open.

r (The undervoltage relay at the distribution panels initiates the distribution panel low voltage alarm at the local reflasher panel which is reflashed to the control room 125V dc system trouble alarm.)

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

125V DC SUBSYSTEN PAGE 11 TABLE 1 125V DC S stem Ref lash Panel Alarms 1L610

1. 125V DC System Low Voltage

2. 125V DC System Ground

3. Battery Monitor (indicates battery degradation or open battery fuses)

4. Battery Charger Trouble indicates (1) AC power failure, (2) DC output breaker open, (3) battery charger failure, or (4) bus overvoltage

5. 125V DC Distribution Panel 1D614 Low Voltage

6. 125V DC Distribution Panel 1D615 Low Voltage C:XWP51XDDCSX125VDCSS.PGD (18) 10/24/91 9:00am

CHANNEL A 125V DC MULTIPLE AIARM INPUTS LOCAL REHASH PANEL FROM 125V DC CHANNEL A WITH INDICATION POWER SYSTEM PER 1L610 TABK 1 DC SYSTEM ALARM INPUTS FROM OTHER REFLASH PANELS (SIMILAR TO ABOVE)

CONTROL ROOM PANEL 1C651 ANNUNCIATOR 125V DC SYSTEM TROUBLE 1L610 FIGURE 1

INDICATOR UGHT REFLASHER PANEL POWER NAMEPlATE FAILURE 125V DC SYSTEM BATTERY SPARE LOW VOLTAGE CHARGER 125V DC 125V DC DIST SYSTEM PANEL 10614 SPARE GROUND LOW VOLTAGE BATTERY 125V DC MONITOR PANEL 1D615 SPARE LOW VOLTAGE 125V DC SYSTEM LOCAL REFlASHER PANEL OYPfCAD FIGURE 2

BATTERY BANK BATTERY CHARGER 59 AMMETER BATTERY FUSE MONITOR VOLTMETER AMMETER Q VOLTMETER SYSTEM GROUND 27 INDICATORS DC LOAD CENTER LOADS LOADS SEE TABLE 1 FOR ALARMS 125V DC SYSTEM QYPICAD FIGURE 3

SUS UEHANNA S.E.S. ATTACHMENT III 250 DC SYSTEM Page 1 ENCLOSURE 1 The following information is applicable to either Unit 1 or Unit 2 at Susquehanna SES.

1. Unit Sus uehanna S.E.S. Unit-1 or 2 250V DC

2. ,The number of independent redundant divisions of Class 1E or safety-related dc power for this plant is ~2 two . (Include any separate Class lE or safety-related dc, such as any dc dedicated to,the diesel generators.)

b. The number of functional safety-related divisions of dc power necessary to attain safe shutdown for this unit is ~1 one

3. Does the control room at this unit have the following separate, independently annunciated alarms and indications for each division of dc power?

a. Alarms

1. Battery disconnect or circuit breaker open?

No

2. Battery charger disconnect or circuit breaker open (both input ac and output dc)? No

3. dc system ground? No

4. dc bus undervoltage? No

5. dc bus overvoltage? No

6. Battery charger failure? No

SUS UEHANNA S.E.S. ATTACHNENT III 250 DC SYSTEN Page 2

7. Battery discharge? No

b. Indications

1. Battery float charge current? No

2. Battery circuit output current? No

3. Battery discharge? No

4. Bus voltage? No

c. Does the unit have written procedures for response to the above alarms and indications? No Does this unit have indication of bypassed and inoperable status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from its dc bus and the battery charger from its ac power source during maintenance or testing?

No See remark ¹1

5. If the answer to any part of question 3 or 4 is no, then provide information justifying the existing design features of the facility's safety-related dc systems.

• See note below.

See Remark ¹1

6. (1) Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one dc division to be unavai1ablet ~es and (2) do plant procedures prohibit maintenance or testing on redundant dc divisions at the same time? ~es (See response from the site)

If the facility Technical Specifications have provisions equivalent to those found in the Westinghouse and Combustion Engineering Standard Technical Specifications for maintenance and surveillance, then question 7 may be skipped and a statement to that effect may be inserted here.

SUS UEHANNA S.E.S. ATTACHMENT III 250 OC SYSTEN Page 3

7. Are maintenance, surveillance and test procedures regarding station batteries conducted routinely at this plant? Specifically:

a. At least once per 7 days are the following verified to be within acceptable limits:

1. Pilot cell electrolyte level? Yes

2. Specify gravity or charging current? Yes

3. Float voltage? Yes

4. Total bus voltage on float charge? Yes

5. Physical condition of all cells? Yes

b. At least once per 92 days, or within 7 days after a battery discharge; overcharge, or if the pilot cell readings, are outside the 7-day surveillance requirements are the following verified to be within acceptable limits:

l. Electrolyte level of each cell? Yes

2. The average specific gravity of all cells? Yes

3. The specific gravity of each cell? Yes

4. The average electrolyte temperature of a representative number of cells? Yes

5. The float voltage of each cell? Yes

6. Visually inspect or measure resistance of terminals and connectors (including the connectors at the dc bus)? Yes

SUS UEHANNA S.E.S. ATTACHMENT III 250 DC SYSTEM Page 4

c. At least every 18 months are the following verified:

1. Low resistance of each connection (by test)? Yes

2. Physical condition of the battery? Yes

3. Battery charger capability to deliver rated ampere output to the dc bus? Yes

4. The capability of the battery to deliver its design duty cycle to the dc bus? Yes

5. Each individual cell voltage is within acceptable limits during the service test? Yes

d. At least every 60 months, is capacity of each battery verified by performance of a discharge test? Yes

e. At least annually, is the battery capacity verified by performance discharge test, if the battery shows signs of degradation or has reached 85K of the expected service life? Yes

8. Does this plant have operational features such that following loss of one safety-related dc power supply or bus:

a. Capability is maintained for ensuring continued and adequate reactor cooling? Yes

b. Reactor coolant system integrity and isolation capability are maintained? Yes

c. Operating procedures, instrumentation (including indicators and annunciators), and control functions are adequate to initiate systems as required to maintain adequate core cooling? Yes

9. If the answer to any part of question 6, 7 or 8 is no, then provide your basis for not performing the maintenance, surveillance and test

SUS UEHANNA S.E.S. ATTACHNENT III 250 DC SYSTEM Page 5 procedures described and/or the bases for not including the operational features cited.

• See note below.

• Note: For questions involving supporting type information (question numbers 5 and 9) instead of developing and supplying the information in response to this letter, you may commit to further evaluate the need for such provisions during the performance of your individual plant examination for severe accident vulnerabilities (IPE). If you select this option, you are required to:

(1) So state in response to these questions, and (2) Commit to explicitly address questions 5 and 9 in your IPE submittal per the guidelines outlined in NUREG-1335 (Section

2. 1.6, Subitem 7), "Individual Plant Examination: Submittal Guidance."

c:~sp51~docsQR106001.PGD (18) 10/24/91 9:06am

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 1 REMARK 1:

1.0 The following indications and alarms for the 250V dc class lE subsystem are provided. Justification for this design has been previously provided in PLA-959 to the NRC dated 11/6/81, regarding Control Room monitoring of Class 1E dc power systems.

Location Alarm or Indication Local Control Room Notes Bus Undervoltage Alarm 1,2 Bus Ground Alarm 1,2 Battery Monitor Alarm 1,2,4 Battery Charger Trouble Alarm 1,2,5 Bus Ammeter Bus Voltmeter Battery Charger Ammeter Battery Charger Voltmeter DC System Trouble Alarm NOTES:

1. See Table 1 and Figure 2 for specific local alarm indication.

2. These are locally indicated and actuate dc subsystem trouble alarm, see Table 1 and Figure l.

3. Meters are provided locally. See Figure 3.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 2

4. Battery monitor compares battery center point voltage with high and low threshold reference points of the high and low voltage comparators. The deg} aded cell conditions (such as a shorted cell) or an open circuit condition (such as an open fuse) are detected by the battery monitor.

5. Battery charger trouble alarm indication is provided for battery charger AC power failure, DC output breaker open, battery charger failure alarm operation, and bus overvoltage.

6. One annunciator window for each 250V dc subsystem is provided.

2.0 The monitoring scheme provided for the dc power subsystem is based on the degree of control provided to the control room operator. Since the dc power system equipment can not be remotely controlled, a single dc system trouble annunciator window for each subsystem is provided in the control room, consistent with the system level alarm criteria set forth in Section B of R.G. 1.47.

The SSES design is based on the general criteria that, if the operator can perform some corrective action in the control room in response to a specific input, that information is specifically provided. The dc power system equipment can not be controlled from the control room.

Annunciating specific inputs from the 250V dc system in the control room does not enhance the control room operators's ability to deal with the situation and it would not be consistent with SSES alarm design philosophy. However, if the only response required is to dispatch an operator, to an area removed from the control room, then the only information required in the control room is general information with only the level of specificity required to direct that operator to the proper location. This method is faster and more reliable since abnormal conditions are automatically alarmed. Furthermore, this approach is consistent with the human factors engineering goal to not over burden the operator with unnecessary information. 250V dc system instrumentation, locally provided, is in full compliance with the requirement of IEEE 308-1974 and Regulatory Guide 1.47.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 3 The DC system general trouble alarms and specific local indicators in conjunction with the routine operator surveillance provide positive assurance that the Class lE dc power system are maintained in a steady state ready to perform the r equired safety function.

3.0 Following is the justification for each alarm and indication listed in Generic Letter 91-06.

3.1 Batter Disconnect or Circuit Breaker 0 en Alarm:

The Susquehanna S.E.S. (SSES) 250V dc subsystem utilizes fuses as the battery disconnect. This condition is detected by the battery monitor. The battery monitor utilizes a variable threshold circuit together with two comparators (high and low) to detect the loss of battery capability due to an open circuit (i.e., an open fuse or degraded cell condition). A variable threshold circuit accepts the battery charger voltage and develops two threshold voltages for use with the comparators. When the monitored voltages go above or below the thresholds, the battery monitor output relay contacts initiate a local battery monitor alarm which is reflashed to the control room as a 250V dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3.2 Batter Char er Disconnect or Circuit Breaker 0 en Both In ut AC and Out ut DC Alarm 3.2. 1 Battery Charger AC Input Disconnect or Circuit Breaker:

SSES utilizes a circuit breaker in the battery charger as a disconnect for the ac input power supply. An ac power failure alarm relay is installed internal to the battery charger to detect loss of ac input power. This condition could be caused by an open input circuit breaker or loss of the 480V ac power supply to the charger. The ac power failure alarm relay initiates a battery charger trouble alarm at the local reflasher panel, which is reflashed to

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 4 the control room as a 250V dc system trouble alarm. This is consistent with the general design philosophy discussed in section 2.0.

3.2.2 Battery Charger DC Output Circuit Breaker SSES utilizes a circuit breaker in the battery charger as a disconnect for the dc output circuit. The circuit breaker is provided with an auxiliary position indicating switch. A switch contact which is closed when the circuit breaker is open is used to initiate a battery charger trouble alarm at the local reflasher panel. A dc system trouble alarm is reflashed to the control room by the local reflasher panel.

This is consistent with the general design philosophy discussed in Section 2.0.

3.3 DC S stem Ground Alarm The 250V dc subsystem is ungrounded and is provided with a ground detection circuit. It consists of a relay having a center tapped coil. The coil is connected across the positive and negative bus and its center point is grounded. The ground detection relay coil is not actuated during normal operation of the 250V dc subsystem when a ground is not present. A ground on either the positive or negative bus of the 250V dc subsystem causes one-half of the relay coil to be short circuited, thus providing sufficient voltage to the remaining relay coil half to pickup the relay. A normally open contact of the relay closes and initiates a 250V dc system ground alarm at the local reflasher panel. A dc system trouble alarm is reflashed to the control room annunciator by the local reflasher panel. This is consistent with the general design philosophy discussed in Section 2.0.,

3.4 DC Bus Undervolta e Alarm The 250V dc subsystem is provided with a dc bus undervoltage relay. The relay is connected across the positive and negative

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 5 bus of the 250V dc subsystem. The relay is normally energized and set to drop out at the specified setpoint. A 250V dc bus undervoltage alarm at the local reflasher panel is initiated after the undervoltage relay drops out.

The local reflasher panel, in turn, reflashes the alarm to the control room annunciator as a dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3.5 DC Bus Overvolta e Alarm The 250V dc subsystem is provided with an overvoltage relay. The relay is located inside the battery charger cabinet. It is connected across the positive and negative 250V dc bus of the battery charger and set to pick up at the specified setpoint. A normally open contact of the overvoltage relay, when closed, initiates a battery charger trouble alarm at the local reflasher panel which in turn will reflash a dc system trouble to the control room annunciator.

Since the battery,'he battery charger and,the dc load center are in close proximity of each other, the battery charger voltage is representative of 250V dc bus voltage. This is consistent with the general design philosophy discussed in Section 2.0.

3.6 Batter Char er Failure Alarm The 250V dc subsystem battery charger is provided with a battery charger failure relay. This relay will detect the loss of the charger output current with the input and output circuit breakers closed.

This condition is indicative of a battery charger failure and it initiates a battery charger trouble alarm at the local reflasher panel which in turn will reflash a dc system trouble alarm to the control room annunciator.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 6 This is consistent with the general design philosophy discussed in Section 2.0.

3.7 Batter Dischar e Alarm The battery can only discharge when its terminal voltage is less than the nominal open. circuit voltage. This is indicative of a battery charger failure or system current in excess of the, charger capability. A battery charger failure alarm is provided and its operation is discussed in Section 3.6. When system current exceeds battery charger'apability, a dc system undervoltage condition will occur, and will be detected by the dc bus undervoltage relay. (See Section 3.4) Charger failure and bus undervoltage initiate alarms at the local reflasher panel which in turn will reflash a dc system trouble alarm to the control room annunciator. This is consistent with the general design philosophy as discussed in Section 2.0.

3.8 Batter Float Char e Current Indication Under normal conditions, the battery float charge current is very small compared to battery discharge current. Measurement of this current requires a very sensitive ammeter. Shunt bypasses are employed to protect the ammeter movement from the much larger battery discharge current possible in this circuit. These shunts must be manually removed when reading normal small float charge current. Thus this reading cannot be continuous and no automatic indication or alarms can be given.

Since the intent of indicating "Battery Float Charge Current" is to determine the battery condition, the method used to accomplish this purpose should not be important.

The bus undervoltage, bus ground, battery monitor and battery charger failure alarms (previously described) provide continuous monitoring to detect degradation of battery capability. These alarms will reflash the dc system trouble alarm in the control

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 7 room, and an operator is dispatched locally to de'termine the cause of the condition and initiate corrective action.

Specific indication is provided on the local reflasher panel.

This response is exactly what would be achieved if an improper state of battery current were indicated on an ammeter in the control room.

This is consistent with the general design philosophy discussed in Section 2.0.

3.9 Batter Circuit Out ut Current Indication In normal condition when the battery charger is supplying the 250V dc power, the battery circuit (battery and the battery charger) output current is indicated by an ammeter located at the battery charger.

In the condition of a battery charger failure, the battery supplies the dc power. In this condition, the battery circuit output current is indicated by an ammeter located at the dc load center.

As indicated in Section 3.8, the intent of indicating "battery current" is to determine the battery condition, and therefore the method used to accomplish this purpose should not be important.

3.10 Batter Oischar e Indication As previously discussed in Section 3.7, a battery discharge will occur as a result of a battery charger failure or system cur rent in excess to battery charger capability. Since these conditions are automatically alarmed in the control room (via the system trouble alarm), an operator will be dispatched locally to determine the cause of the condition and initiate corrective action. This response is exactly what would be achieved if battery discharge current was indicated on an ammeter in the

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 8 control room.

3. 11 Bus Volta e Indication The battery, the battery charger and the dc load center of 250V dc subsystem are located in close proximity of each other. The battery charger and the dc load center are each provided with a voltmeter. The purpose of a bus voltmeter at the control room would be to enable the operator to dispatch someone to take corrective action locally to correct abnormal bus voltage. At SSES the bus undervoltage is monitored directly and'the bus overvoltage conditions are monitored at the battery charger output. The bus undervoltage and the battery charger output overvoltage .conditions are annunciated as 250V dc system low voltage or battery charger trouble at the local reflasher panel.

A dc system trouble alarm is reflashed to the control room annunciator by the local reflasher panel.

This design automatically alerts the control room operator to unusual voltage conditions without unnecessarily requiring his periodic attention and analysis. As a result, 250V dc bus voltage indication is not provided in the control room and has been provided on the front of the load center where it provides useful information during surveillance and maintenance activities.

A voltmeter is located on the front of the battery charger panel.

With the charger output circuit breaker closed, the charger output and the bus voltages are essentially the same due to the close proximity of the charger to the load center. All abnormal voltage conditions of the battery charger are annunciated at the local reflasher panel which is reflashed to the control room as a dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 9

3. 12 Alarm Res onse Procedure Control room alarm response procedures for a 250V dc system trouble alarm direct the operator to respond to the local reflasher panel to determine the condition which caused the alarm.

Local alarm response procedures for the reflasher panel are provided to direct the operator to determine the cause of the condition and to initiate corrective action.

3. 13 Indication of B assed and Ino erable Status of Circuit Breakers or Othe Disconnectin Devices Although indication of bypassed and inoperable status of circuit breaker's or other disconnecting devices is not provided as a part of the Bypass Indication System, the 250V dc System Trouble Alarm in the control room is initiated for the following condition (which are disconnecting devices in the system):

Main battery fuse open.

Battery charger ac input circuit breaker open.

Battery charger dc output circuit breaker open, or 250V dc load center breaker open.

250V dc load center feeder breaker to 250V dc motor control centers open.

(Each of the load center feeder breakers to the 250V dc MCC's is provided with an auxiliary position indicating switch which initiates an alarm on the local reflasher panel when the circuit breaker is open. A 250V dc system trouble alarm is reflashed to the control room by the local reflasher panel.)

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S.

250V DC SUBSYSTEM PAGE 10 TABLE 1 250V DC S stem Reflash Panel Indicators T ical

l. 250V DC System Low Voltage

2. 250V DC System Ground

3. Battery Monitor (indicates battery degradation or open battery fuses)

4. Battery Charger Trouble indicates (1) AC power failure, (2) DC output breaker open, (3) battery charger failure, or (4) bus overvoltage (Division I has 2 chargers, Division II has 1 charger)

5. Load Center Incoming Breakers Trip

6. RCIC & Isolation Valve Control Center 1D254 trouble

7. Turbine Bldg. Control Center 1D155 trouble

8. Computer UPS Supply Breaker Trip C:XMP51%00CSX250VDCSS.PGD (18) 10/24/91 9:08am

CHANNEL A 250V DC MULTIPLE ALARM INPUIS LOCAL RERASH PANEL FROM 250V DC CHANNEL A WITH INDICATION POWER SYStEM PER 1L650 TABLE 1 DC SYSTEM ALARM INPUTS FROM OTHER REFLASH PANELS (SIMILAR TO ABOVE)

CONTROL ROOM PANEL 1C651 ANNUNCIATOR 250V DC SYSTEM TROUBLE 1L650 FIGURE 1

INDICATOR UGHT REFLASHER PANEL POWER FAILURE BATTERY RCIC & ISO VLVS SYSTEM CHAIWER A CONTROL CENTER LOW VOLTAGE TROUBLE 1D254 TROUBLE 250V DC BATTERY TURB BU)G SYSTEM CHARGER B CONTROL CENTER GROUND TROUBLE 1D155 TROUBLE BATTERY LC INCOMING BKR COMPUTER UPS MONITOR 7245212/22 SUPPLY BKR TRIP TRIP 250V DC SYStEM LOCAL REFLASHER PANEL OYPICAO FIGURE 2

BATTERY BANK BATTERY CHARGER 59 AMMETER BATTERY FUSE MONITOR VOLTMETER AMMETER Q VOLTMETER SYSTEM GROUND 27 INDICATORS DC LOAD CENTER LOADS LOADS SEE TABLE 1 FOR ALARMS 250V DC SYSTEM OYPICAQ FIGURE 3

SUS UEHANNA S.E.S. UNIT-1 AND UNIT 2 ATTACHMENT IV DG-E 125V DC SYSTEM Page 1 ENCLOSURE 1 The following information is applicable to either Unit at Susquehanna SES.

Unit Sus uehanna S.E.S. Common to Unit 1 & 2 DG-E 125V DC SYSTEM

'a ~ The number of independent redundant divisions of Class 1E or safety-related dc power for this plant is see Remark l. (Include any separate Class 1E or safety-related dc, such as any dc dedicated to the diesel generators.)

b. The number of functional safety-related divisions of dc power necessary to attain safe shutdown for this unit is see Remark 1.

3. Does the control room at this unit have the following separate, independently annunciated alarms and indications for each division of dc power?

a. alarms

1. Battery disconnect or circuit breaker open? No

2. Battery charger disconnect or circuit breaker open (both input ac and output dc)? No

3. dc system ground? No

4. dc bus undervoltage? No

5. dc bus overvoltage? No

6. Battery charger failure? No

7. Battery discharge? No

0 SUS UEHANNA S.E.S. UNIT-1 AND UNIT 2 ATTACHMENT IV DG-E 125V DC SYSTEM Page 2

b. Indications

1. Battery float charge current? No

2. Battery circuit output current? No

3. Battery discharge? No

4. Bus voltage? No

c. Does the unit have written procedures for response to the above alarms and indications? No Does this unit have indication of bypassed and inoperable status of circuit breakers or other devices that can be used to disconnect the battery and battery charger from its dc bus and the battery charger from its ac power source during maintenance or testing? No See Remark 2

5. If the answer to any part of question 3 or 4 is no, then provide information justifying the existing design features of the facility's safety-related dc systems.

• See note below.

See Remark 2

6. (I) Have you conducted a review of maintenance and testing activities to minimize the potential for human error causing more than one dc division to be unavailablet ~es and (2) do plant procedures prohibit maintenance or testing on redundant dc divisions at the sama time? ~es If the facility Technical Specifications have provisions equivalent to those found in the Westinghouse and Combustion Engineering Standard Technical Specifications for maintenance and surveillance, then question 7 may be skipped and a statement to that effect may be inserted here.

SUS UEHANNA S.E.S. UNIT-1 AND UNIT 2 ATTACHMENT IV DG-E 125V DC SYSTEM Page 3

7. Are maintenance, surveillance and test procedures. regarding station batteries conducted routinely at this plant?'pecifically:

a. At least, once per 7 days are the following verified to be within acceptable limits:

1. Pilot cell electrolyte level? Yes

2. Specify gravity or charging current? Yes

3. Float voltage? Yes

4. Total bus voltage on float charge? Yes

5. Physical condition of all cells? Yes

b. At least once per 92 days, or within 7 days after a battery discharge, overcharge, or if the pilot cell readings are outside the 7-day surveillance requirements are the following verified to be within acceptable limits:

l. Electrolyte level of each cell? Yes

2. The average specific gravity of all cells? Yes

3. The specific gravity of each cell? Yes

4. The average electrolyte temperature of a representative number of cells? Yes

5. The float voltage of each cell? Yes

6. Visually inspect or measure resistance of terminals and connectors (including the connectors at the dc bus)? Yes

SUS UEHANNA S.E.S. UNIT-1 AND UNIT 2 ATTACHMENT IV DG-'E 125V DC SYSTEM Page 4

c. At least every 18 months are the following verified:

1. Low resistance of each connection (by test)? Yes

2. Physical condition of the battery? Yes

3. Battery charger capability to deliver rated ampere output to the dc bus? Yes t

The capability of the battery -to deliver its design duty cycle to the dc bus? Yes

5. Each individual cell voltage is within acceptable limits during the service test? Yes

d. At least every 60 months, is capacity of each battery verified by performance of a discharge test? Yes

e. At least annually, is the battery capacity verified by performance discharge test, if the battery shows signs of degradation or has reached 85X of the expected service life? Yes

8. Does this plant have operational features such that following loss of one safety-related dc power supply or bus:

a. Capability is maintained for ensuring continued and adequate reactor cooling? Yes

b. Reactor coolant system integrity and isolation capability are maintained? Yes f

c. Operating procedures, instrumentation (including indicators and annunciators), and control functions are adequate to initiate systems as required to maintain adequate core,cooling? Yes

SUS UEHANNA S.E.S. UNIT-1 AND UNIT 2 ATTACHMENT IV DG-E 125V DC SYSTEM Page 5 9 If the answer to any part of question 6, 7 or 8 is no, then provide your basis for not performing the maintenance, surveillance and test procedures described and/or the bases for not including the operational features cited.

• See note below.

• Note: For questions involving supporting type information (question numbers 5 and 9) instead of developing and supplying the information in response to this letter, you may commit to further evaluate the need for such provisions during the performance of your individual plant examination for severe accident vulnerabilities (IPE). If you select this option, you are required to:

(1) So state in response to these questions, and (2) Commit to explicitly address questions 5 and 9 in your IPE submittal per the guidelines outlined in NUREG-1335 (Section

2. 1.6, Subitem 7), "Individual Plant Examination: Submittal Guidance."

c:Xup51hdocshdg-e125v.pgd (18)10/24/91 8:48am

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 1 REMARK 1:

Diesel Generator E is an installed spare diesel generator capable of substituting as an emergency power source for any one of the existing emergency diesel generators (A, B, C, D). The Diesel Generator E 125V dc power subsystem is identified as Channel H and is dedicated to providing dc power to ESW valves for Diesel Generator E cooling, Diesel Generator E controls, and Diesel Generator E 4. 16 kV Switchgear. This equipment is all located in a separate Diesel Generator E building.

The Diesel Generator E 125V dc Subsystem is required only when this diesel generator is substituting for one of the existing diesel generators. It is in addition to, independent and isolated from the other four Class lE 125V dc Subsystems. Loss of any one of the 125V dc Subsystems does not prevent the minimum safety function from being performed.

REMARK 2:

1.0 The following indications and alarms for the DG-E 125V dc class lE subsystem are provided. Justification for this design is consistent with the design philosophy regarding Control Room monitoring of Class 1E dc power systems as previously provided in PLA-959 to the NRC dated 11/6/81.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 2 Location Alarm or Indication Local Control Room Notes Bus Undervoltage Alarm 1,2 Bus Ground Alarm 1,2 Battery Monitor Alarm 1,2,4 Battery Charger Trouble Alarm 1,2,5 Bus Ammeter Bus Voltmeter Battery Charger Ammeter Battery Charger Voltmeter DC System Trouble Alarm NOTES:

1. See Table 1 for specific local alarm annunciation.

2. These alarms are locally provided on DG-E annunciator/reflasher panel OC577E. A dc subsystem trouble alarm .is reflashed to the control room by this annunciator. See Table 1, Figure 1.

3. Heters are provided locally. See Figure 2.

4. Battery monitor compares battery center point voltage with high and low threshold reference points,,of the high and low voltage comparators. The degraded cell conditions (such" as a shorted cell) or an open circuit condition (such as an open fuse) are detected by the battery monitor.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 3

5. Battery charger trouble alarm indication is provided for battery charger AC power failure, DC output breaker open, battery charger failure alarm operation, battery charger high/low voltage and battery charger high voltage (shutdown).

6. One annunciator window for the DG-E 125V dc subsystem is provided.

2.0 The monitoring scheme provided for the dc power subsystem is based on the degree of control provided to the control room operator. Since the dc power system equipment can not be remotely controlled, a single dc system trouble annunciator window for each subsystem is provided in the control room, consistent with the system level alarm criteria set forth in Section B of R.G. 1.47.

The SSES design is based on the general criteria that, if the operator can perform some corrective action in the control room in response to a specific input, that information is specifically provided. The dc power system equipment can not be controlled from the control room.

Annunciating specific inputs from the 125V dc system in the control room does not enhance the control room operators's ability to deal with the situation and it would not be consistent with SSES alarm design philosophy. However,.if the only response required is to dispatch an operator to an area removed from the control room, then the only information required in the control room is general information with only the level of specificity re'quired to direct that operator to the proper location. This method is faster and more reliable since abnormal conditions are automatically alarmed. Furthermore, this approach is consistent with the human factors engineering goal to not over burden the operator with unnecessary information. 125V dc system instrumentation, locally provided, is in full compliance with the requirement of IEEE 308-1974 and Regulatory Guide 1.47.

The DC system general trouble alarms and specific local indicators in conjunction with the routine operator surveillance provide positive assurance that the Class 1E dc power system are maintained in a steady state ready to perform the required safety function.

e

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 4 3.0 Following is the justification for each alarm and indication listed in Generic Letter 91-06.

3. 1 Batter Disconnect or Circuit Breaker 0 en Alarm:

The Susquehanna S.E.S. (SSES) DG-E 125V dc subsystem utilizes a fused disconnect as the battery disconnect. This condition is detected by the battery monitor. The battery monitor utilizes a variable threshold circuit together with two comparators (high and low) to detect the loss of battery capability due to an open circuit (i.e., an open fuse or, degraded cell condition). A variable threshold circuit accepts the battery 'charger voltage and develops two threshold voltages for use with the comparators.

When the monitored voltages go above or below the thresholds, the battery monitor output relay contacts initiate a local battery monitor annunciator which is reflashed to the control room as a DG-E 125V dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3.2 Batter Char er Disconnect or Circuit Breaker 0 en Both In ut AC and Out ut DC Alarm 3.2. 1 Battery Charger AC Input Disconnect or Circuit Breaker:

SSES utilizes a circuit breaker in the battery charger as a disconnect for the ac input power supply. An ac power failure alarm relay is installed internal to the battery charger to detect loss of ac input power. This condition could be caused by an open input circuit breaker or loss of the 480V ac power supply to the charger. The ac power failure alarm relay initiates a battery charger trouble alarm at the local annunciator panel, which is reflashed to the control room as a DG-E 125V dc system trouble alarm.

This is consistent with the general design philosophy discussed in section 2.0.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 5 3.2.2 Battery Charger DC Output Circuit Breaker SSES utilizes a circuit breaker in the battery charger as a disconnect for the dc output circuit. The circuit breaker is provided with an auxiliary position indicating switch. A switch contact which is closed when the circuit breaker is open is used to initiate a battery charger trouble alarm at the local annunciator panel. A DG-E dc system trouble alarm is reflashed to the control room by the local annunciator

'anel. This is consistent with the, general design philosophy discussed in Section 2.0.

3.3 DC S stem Ground Alarm'he DG-E 125V dc subsystem is ungrounded and is provided with a ground detection circuit. It consists of a relay having a center tapped coil. The coil is connected across the positive and negative bus and its center point is grounded. The ground detection relay coil is not actuated during normal operation of the 125V dc subsystem when a ground is not present. A ground on either the positive or negative bus of the 125V dc subsystem causes one-half of the relay coil to be short circuited, thus providing sufficient voltage to the remaining relay coil half to pickup the relay. A normally open contact of the relay closes and initiates a 125V dc system ground alarm at the local annunciator panel. A DG-E dc system trouble alarm is reflashed to the control room annunciator by the local annunciator panel. This is consistent with the general design philosophy discussed in Section 2.0.

3.4 DC Bus Undervolta e Alarm The DG-E 125V dc subsystem is provided with a battery charger undervoltage relay. The relay is connected across the positive and negative bus of the 125V dc battery charger. The relay is normally energized and set to drop out at the specified setpoint.

A battery charger trouble alarm at the local annunciator panel is

RESPONSE TO GENERIC LETTER 91-06 SUS UEMANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTE PAGE 6 initiated after the undervoltage relay drops out.

The local annunciator panel, in turn, reflashes the alarm to the control room annunciator as a DG-E dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

In addition to the battery charger undervoltage relay, a bus undervoltage relay is provided to detect a loss of bus voltage.

The most probable cause of a DC system undervoltage condition is a result of a battery charger problem, which will be detected by the battery charger, failure alarm relay (see Section 3.6). The charger failure relay initiates a battery charger trouble alarm at the local annunciator panel, which in turn, reflashes a DG-E dc system trouble alarm to the control room annunciator. This is consistent with the general design philosophy discussed in Section 2.0.

3.5 DC Bus Overvolta e Alarm The DG-E 125V dc subsystem is provided with an overvoltage relay.

The relay is located inside the battery charger cabinet. It is connected across the positive and negative 125V dc bus of the battery charger and set to pick up at the specified setpoint. A normally open contact of the overvoltage relay, when closed, initiates a battery charger trouble alarm at the local annunciator panel which in turn will reflash a DG-E dc system trouble alarm to the control room annunciator.

Since the battery, the battery charger and the dc load center are in close proximity of each other, the battery charger voltage is representative of the DG-E 125V dc bus voltage. This is consistent with the general design philosophy discussed in Section 2.0.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT I AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 7 3.6 Batter Char er Failure Alarm The DG-E 125V dc subsystem battery charger is provided with a battery charger failure relay. This relay will detect the loss of the charger output current with the input and output circuit breakers closed.

This condition is indicative of a battery charger failure and it initiates a battery charger trouble alarm at the local annunciator panel which in turn will reflash a DG-E dc system trouble alarm to the control room annunciator. This is consistent with the general design philosophy discussed in Section 2.0.

3.7 Batter Dischar e Alarm The battery can only discharge when its terminal voltage is less than the nominal open circuit voltage. This is indicative of a battery charger failure or system current in excess of the charger capability. A battery charger, failure alarm is provided and its operation is discussed in Section 3.6. When system current exceeds battery charger capability, a dc system undervoltage condition will occur, and will be detected by the battery charger undervoltage relay (see Section 3.4). Charger failure and battery charger undervoltage initiate alarms at the local annunci ator panel which in turn will reflash a DG-E dc system trouble alarm to the control room annunciator. This is consistent with the general design philosophy as discussed in Section 2.0.

3.8 Batter Float Char e Current Indication Under normal conditions, the battery float charge current is very small compared to battery discharge current. Measurement of this current requires a very sensitive ammeter. Shunt bypasses are employed to protect the ammeter movement from the much larger battery discharge current possible in this circuit.'hese shu'nts must be manually removed when reading normal small float charge current. Thus this reading cannot be continuous and no automatic

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 8 indication or alarms can be given.

Since the intent of indicating "Battery Float Charge Current" is to determine the battery condition, the method used to accomplish this purpose should not be important.

The battery charger undervoltage, bus ground, battery m'onitor and battery charger failure alarms (previously described) provide continuous monitoring to detect degradation of battery capability.

These alarms will reflash the DG-E dc system trouble alarm in the control room, and an operator is dispatched locally to determine the cause of the condition and initiate corrective action.

Specific indication is provided on the local annunciator panel.

This response is exactly what would be achieved if an improper state of battery current were indicated on an ammeter in the control room.

This is consistent with the general design philosophy discussed in Section 2.0.

3.9 Batter Circuit Out ut Current Indication In normal condition when the battery charger is supplying the 125V dc power, the battery circuit (battery and the battery charger) output current is indicated by an ammeter located at the battery charger.

In the condition of a battery charger failure, the battery supplies the dc power. In this condition the battery circuit output current is indicated by an ammeter located at the dc switchboard.

As indicated in Section 3.8, the intent of indicating "battery current" is to determine the battery condition, and therefore the method used to accomplish this purpose should not be important.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 9 3.10 Batter Dischar e Indication As previously discussed in Section 3.7, a battery discharge will occur as a result of a battery charger failure or system current in excess to battery charger capability. Since these conditions are automatically alarmed in the control room (via the system trouble alarm), an operator'will be dispatched locally to determine the cause of the condition and initiate corrective action. This response is exactly what would be achieved if battery discharge current was indicated on an ammeter in the control room.

3.11 Bus Volta e Indication The battery, the battery charger and the dc switchboard of the DG-E 125V dc subsystem are located in close proximity of each other.

The battery charger and the dc switchboard are each provided with a voltmeter. The purpose of a bus voltmeter at the control room would be to enable the operator to dispatch someone to take corrective action locally to correct abnormal bus voltage. This condition will occur when a battery charger problem is present.

Undervoltage and overvoltage conditions are monitored at the battery charger, and are annunciated as battery charger trouble at the local annunciator panel. A DG-E dc system trouble alarm is reflashed to the control room annunciator by the local annunciator panel.

This design automatically alerts the control room operator to unusual voltage conditions without unnecessarily requiring his periodic attention and analysis. As a result, 125V dc bus voltage indication is not provided in the control room and has been provided on the front of the dc switchboard where it provides useful information during surveillance and maintenance activities.

A voltmeter is located on the front of the battery charger panel.

With the charger output circuit breaker closed, the charger output and the bus voltages are essentially the same due to the close

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 10 proximity of the charger to the load center. All abnormal voltage conditions of the battery charger are annunciated at the local annunciator panel which is reflashed to the control room as a DG-E dc system trouble alarm. This is consistent with the general design philosophy discussed in Section 2.0.

3. 12 Alarm Res onse Procedure Control room alarm response procedures for a DG-E 125V dc system trouble alarm direct the operator to respond to the local annunciator panel to determine the condition which caused the alarm.

Local alarm response procedures for the annunciator panel are provided to direct the operator to determine the cause of the condition and to initiate corrective action.

3. 13 Indication of B assed and Ino erable Status of Circuit Breakers or Other Disconnectin Devices Although indication of bypassed and inoperable status of circuit breakers or other disconnecting devices is not provided as a part of the Bypass Indication System, the 125V dc System Trouble Alarm in the control room is initiated for the following condition (which are disconnecting devices in the system):

Hain battery fused disconnect open.

Battery charger ac input circuit breaker open.

Battery charger dc output circuit breaker open or 125V dc switchboard breaker open.

RESPONSE TO GENERIC LETTER 91-06 SUS UEHANNA S.E.S. UNIT 1 AND UNIT 2 DG-E 125V DC SUBSYSTEM PAGE 11 TABLE 1 125V DG-E DC S stem Annunciator Panel Alarms

l. 125V DC System Low Voltage

2. 125V DC System Ground

3. Battery Honitor (indicates battery degradation or open battery fuses)

4. Battery Charger Trouble indicates (1) AC power failure, (2) DC output breaker open, (3),battery charger failure, (4) battery charger high/low voltage, or (5) battery charger'igh voltage (shutdown).

C:XQP51%00CS~RGL91-06.PGD (18) 10/24/91 8:35am

MULTIPLE ALARM INPUTS DG-E BLDG FROM DG-E 125V DC PANEL OC577E POWER SYSTEM PER TABlE 1 DG-E BLDG PANEL OC577E CONTROL ROOM PANEL OC653 DC SYSTEM TROUBLE ANNUNCIATOR FIGURE 1

BATTERY BANK BATTERY 7/59 CHARGER AMMETER 59 BATTERY FUSE MONITOR VOLTMETER AMMETER VOLTMETER SYSTEM GROUND 27 INDICATORS DC SWITCHBOARD LOADS LOADS SEE TABLE 1 FOR ALARMS DG-E 125V DC SYSTEM FIGURE 2