Text

Forwards Amend Application 189 to License DPR-13 Requesting Mod to Tech Specs 3.5.1,3.7.1,4.1.1 & 4.4 Re Safeguards Load Sequencing Sys & ECCS
	ML13310A266
Person / Time
Site:	San Onofre
Issue date:	09/28/1990
From:	Ray H; SOUTHERN CALIFORNIA EDISON CO.
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML13310A267	List: ML13310A266; ML13331A494;
References
	NUDOCS 9010040254
	Download: ML13310A266 (69)
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PROBABILISTIC RISK ASSESSMENT OF UNIT 1 VITAL BUS TRANSFER SINGLE FAILURE PURPOSE Evaluate the risk associated with continuing plant operation with the present vital bus automatic transfer capability.

As part of that evaluation, determine the annual probability of core damage and/or containment failure resulting from failures of vital 120 VAC buses 1, 2, 3, 3A, and 4. The evaluation addresses a single failure susceptibility in the 120 VAC system concerning automatic transfer between the two power sources for the Train A vital buses. This single failure susceptibility was identified in the recently completed SONGS 1 emergency core cooling system single failure analysis (Reference 1).

BACKGROUND Vital buses 1, 2, 3, 3A, and 4 (hereafter referred to as the Train A vital buses) are normally powered through inverters 1, 2, 3, and 4 from DC Bus #1 (Reference 2).

Vital 120 VAC buses 5, 6 and the Containment Spray Actuation System (CSAS) inverter bus (hereafter referred to as the Train B vital buses) are normally powered through inverters from DC Bus #2.

The vital 120 VAC buses provide power to safety-related and non-safety related instrumentation, control circuits, and solenoid valves.

The vital 120 VAC buses are reliable power sources for essential plant instrumentation and controls.

The random failure rate of the vital 120 VAC buses during normal operation is dominated by low probability events such as inverter failures, DC bus failure, and bus shorts.

The Train A vital buses also provide power for unqualified loads for components that are located inside containment or near the main steam/feedwater lines outside containment.

A loss of coolant accident (LOCA) or main steam/feedwater line break (MSLB/MFLB) could cause shorting of these environmentally unqualified loads and challenge bus integrity.

The primary power source for the Train A vital buses is DC Bus #1 via four inverters. Each inverter is current limited.

Single or multiple shorts on the Train A vital buses can cause a voltage drop on the buses that is sufficient to prevent the protective circuit breakers and fuses on the shorted loads from tripping and isolating the bus from the shorted loads. Upon detection of low voltage on a vital bus, the auto-transfer switch for that bus will rapidly transfer to the backup power source (480 volt motor control center no. 2).

The backup power source has sufficient current capacity to trip/isolate the shorted loads on the 120 VAC vital buses.

Although all four Train A vital buses will automatically transfer from the primary to the backup source, the auto-transfer switches for vital buses 1, 2, 3, and 3A are not designed to automatically transfer back to the primary source should the backup source fail.

The vital buses can be manually transferred back to their primary source by the operator in the control room.

Table 1 provides a listing of essential ECCS loads supplied from the Train A vital buses. The Train A vital buses may automatically transfer to the backup source during a LOCA or MSLB/MFLB event due to shorts of environmentally unqualified loads. Since the backup source is non-redundant, the ECCS single failure analysis identified the Train A vital buses as non-single failure proof.

This probabilistic risk assessment (PRA) estimates the annual probability of core damage or containment failure occurring during a design basis LOCA, MSLB, or MFLB due to failures of the Train A vital buses.

The initiating events for which the Train A vital bus failures were evaluated include large LOCA, small LOCA, MSLB, and MFLB. Conditional loss of off-site power was considered for each of these events.

ASSUMPTIONS The following assumptions were made in the analysis:

1. The mission time for uninterrupted supply of 120 VAC power from the vital buses is assumed to be 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

After that time, brief losses of power (e.g., for manual retransfer back to the primary source) would be acceptable since all actuation signals and valve positioning operations would have been completed by that.time.

2. Each environmentally unqualified load on the vital buses is fed through an individual overcurrent protection breaker and fuse.

The protection breaker and fuse design is such that the non-safety related loads are coordinated to isolate on overcurrent without tripping safety-related loads or bus feeder breakers.

To be of sufficient magnitude to affect the power source, a short circuit must exceed the trip ratings of both the individual load circuit breakers and the bus circuit breaker. The probability of a low voltage protection breaker failing to trip on overcurrent is 4 x 10-4 per demand (Reference 3, page 119).

The probability of a low voltage fuse failing to blow on overcurrent is considered to be negligibly low (Reference 4).

Therefore, the probability of a shorted load failing to isolate from a 120 VAC vital bus (when connected to its backup power supply) is assumed to be negligible.

3. If multiple, simultaneous shorts were to occur on a 120 VAC vital bus, the bus current may exceed the backup source feeder breaker overcurrent protection limit before the individual load breakers and/or fuses isolate the shorted loads. However, the likelihood of such multiple, simultaneous shorts is assumed to be negligible.

4. Environmentally unqualified loads on the vital 120 VAC buses are assumed to be unaffected by containment conditions following a small LOCA event having a break diameter of 3/8 inch or less.

5. Shorting of environmentally unqualified vital bus loads is assumed to begin within several seconds of a small LOCA, large LOCA, MSLB, or MFLB.

6. Instrumentation and equipment necessary for generation of a safety injection actuation signal or a containment spray actuation signal are powered from the affected Train A vital buses. However, these components are required to operate only for several seconds after a large LOCA or MSLB/MFLB.

It is unlikely that the vital buses would be disabled at such an early point in the accident.

The probability of shorts occurring that require bus transfer in the first several seconds is assumed to be 0.01.

The Train B logic was assumed to fail with a probability of 1.0.

This assumption results in a large conservatism in the evaluation of safety injection signal (SIS) actuation failure.

In any case, the contribution of the SIS actuation failure scenarios to the total core damage probability is negligible.

7. Vital bus 4 is assumed to be adequately protected from failure caused by shorting of environmentally unqualified loads. The inverter for that bus has sufficient capacity to clear faults. The auto-transfer switch for vital bus 4 is also designed to automatically switch back from the backup power source to the primary source upon loss of the backup source.

8. A shorted load on a vital bus is assumed to clear if the bus power supply has sufficient current capacity.

Failure to clear a load would require the concurrent failure of two breakers, and in most cases, at least one fuse.

The probability of multiple breaker/fuse failures is considered negligible.

9. Vital buses 1, 2, 3, and 3A are each assumed to immediately fail if the associated auto-transfer switch fails to connect the respective bus to its backup source.

The bus inverters (the primary power supply) are assumed not to have sufficient current capacity to clear a fault and may fail after a brief time in the current limited condition.

10. Environmentally unqualified loads are assumed to short in a sequential manner throughout the accident. This assumption maximizes the number of demands upon the bus transfer switches.

It is also assumed that each transfer switch will be challenged once for every three environmentally unqualified loads on each bus.

11. For small break LOCA scenarios, the operators will have sufficient time to manually initiate safety injection and containment spray to prevent core damage and containment failure. Small LOCAs do not require immediate safety injection system actuation to prevent core damage.

Existing operating procedures and operator training provide assurance that these systems would be manually activated in the unlikely event that the automatic initiation circuits fail.

12. Failure to automatically actuate containment spray is assumed to lead to containment failure.

This assumption was made even though the SONGS 1 safety analysis demonstrates that the pressure rise in the containment due to failure of containment spray would not be significantly above the design limit. Short-term loss of containment spray is unlikely to result in a loss of containment integrity.

13. Following a small break LOCA, MSLB, or MFLB natural circulation continues in the Reactor Coolant System for a period of 30 minutes.

This allows sufficient time for operator action to initiate steam generator makeup via the Auxiliary Feedwater System (AFWS)

(i.e., to start the dedicated safe shutdown (DSD) diesel and power AFWS pump GlOW from the DSD diesel in the event of a loss of normal power to pump GlOW).

14. The following quantities of environmentally unqualified loads are powered from the Train A vital buses:

Vital Bus #1:

2 loads for LOCA 3 loads for MSLB/MFLB Vital Bus #2:

4 loads for LOCA or MSLB/MFLB Vital Bus #3:

6 loads for LOCA and 3A 9 loads for MSLB/MFLB ANALYSIS The sequences described below were considered for a large and small LOCA, MSLB, and MFLB events. The sequences are based upon the essential ECCS loads fed from the Train A vital buses (Table 1) which potentially may fail during an accident.

Each sequence is developed and quantified via an event tree (Figures 1 through 4).

Large LOCA:

LL1:

Large LOCA with subsequent SIS and containment spray failure (due to vital bus failure at the start of the accident).

Core damage is assumed to occur due to delayed initiation of safety injection flow.

LL2:

Large LOCA with high flow containment spray failure caused by closure of valve CV-517 (due to vital bus 3/3A failure) and independent failure of valve CV-518.

High flow containment spray is assumed to be required for one hour following a LOCA. This sequence does not result in core

damage, but potentially may result in radioactive releases due to containment failure.

LL3:

Large LOCA with long-term recirculation cooling failure caused by loss of two of three flow indications of cold leg injection flow rate (due to vital bus 3/3A failure).

Small LOCA:

SL1:

Small LOCA with AFWS failure to provide secondary heat removal caused by loss of Train A AFWS (due to loss of vital bus 3/3A) and concurrent failure of the Train B AFWS.

SL2:

Small LOCA with long-term recirculation cooling failure due to loss of two of the three cold leg injection flow rate indicators (similar to sequence LL3).

Main Steam Line Break:

MSLB1:

MSLB with SIS and containment spray failure at the beginning of the accident (similar to sequence LL1).

MSLB3:

MSLB with high-flow containment spray failure (similar to sequence LL2, except that high-flow spray is required for 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months post-MSLB).

Main Feedwater Line Break:

MFLB1:

MFLB with immediate containment spray failure (similar to the MSLB1

sequence, except that this sequence results only in containment failure).

MFLB2:

MFLB with AFWS failure to provide secondary heat removal (similar to sequence MSLB3).

The fault trees developed to support the quantification of the event trees are provided in Figures 5 through 14.

The component failure rates used in the fault trees were obtained from the SONGS 1 Partial PRA (Reference 4), except as noted otherwise.

The frequency of MSLB and MFLB initiating events were extracted from the Oconee PRA (Reference 5) since those accidents were not analyzed in the SONGS 1 Partial PRA.

RESULTS The fault trees and event trees for this analysis were solved using the PRA software (REBECA) being used to conduct the SONGS Individual Plant Examinations.

Minimal failure combinations (i.e., cutsets) were calculated for each fault tree and event tree sequence.

A truncation limit of 1 x 10-8 was used for the solution of each fault tree. A truncation limit of 1 x 10-10 was employed for each event tree sequence.

The results of the quantification of the event trees are provided in Tables 2 through 21.

Table 2 summarizes the overall results of the analysis.

The annual probability of core damage from failure of the Train A vital buses is estimated to be 5.5 x 10-7.

The annual probability of containment failure, without core damage exceeding design basis, is estimated to be 4.2 x 10-7.

The annual probability of core damage with containment failure is estimated to be 5.8 x 10-8.

The dominant cutsets contributing to core damage and/or containment failure for each sequence are identified (in order of importance) in Tables 9 though 21.

The dominant cutsets leading to core damage are comprised of failures of the vital bus 3 transfer switch and AFWS pump GlOW, and failures of diesel generator B and DSD diesel given a loss of off-site power. These cutsets lead to core damage from a failure of AFWS supply to the steam generators.

The dominant contributors to containment failure are comprised of failures of diesel generator B given a loss of off-site power leading to containment spray failure.

CONCLUSIONS This PRA estimates that the annual probability of core damage due to the loss of the Train A vital buses is less than 6 x 10-7 per year.

This contribution to the overall core damage frequency (estimated to be approximately 2 x 10-4per year) is quite low, accounting for less than 0.3% of the total.

The annual probability of containment failure with core damage is estimated to be less than 5 x 10-7 per year. This contribution to design basis containment failure probability (estimated to be 1 x 10-4 per year) is low (0.5%).

Also, there is large conservatism in the assumption that failure of containment spray will lead to containment failure.

The annual probability of core damage with containment failure is estimated to be less than 6 x 10-8 per year. This contribution to significant radioactive release probability is less than 6% of the NRC goal of 1 x 10-6 per year. As indicated above, there is large conservatism in the estimation of containment failure probability due to failure of containment spray.

REFERENCES

1. SONGS 1 Emergency Core Cooling System Single Failure Analysis, M41383 Rev. 0.

2. SONGS 1 One-line Diagram 5102174-46.

3. IEEE Std. 500-1984, "IEEE Guide to the Collection and Presentation of Electrical, Electronic, Sensing Component, and Mechanical Equipment Reliability Data for Nuclear-Power Generating Stations," Institute of Electrical and Electronic Engineers, 1983.

4. SONGS 1 Partial PRA, July 1987.

5. NSAC/60, "Oconee PRA, A Probabilistic Risk Assessment of Oconee Unit 3,"

Nuclear Safety Analysis Center and Duke Power Company, June 1984.

0 TABLE 1 Critical ECCS Loads on Train A 120 VAC Vital Buses For First 6 Hours Post-Accident Vital Bus Load Impact of Loss on ECCS Performance 1

PT-430 If lose 2 of 3 channels near front end of large break LOCA or MSLB, then would not get SI in sufficient time if train B SI lost.

1 CV-517 Lose hi flow containment spray for large break LOCA or MSLB during injection mode if CV-518 fails or train B vital 120 VAC buses lost.

1 CS Control A Lose auto containment spray actuation signal for large break LOCA, MSLB, or MFLB if CS control power B and train B

containment spray also lost.

2 PT-431 If lose 2 of 3 channels near front end of large break LOCA or MSLB, then would not get SI in sufficient time if train B SI is lost.

3/3A PT-432 If lose 2 of 3 channels near front end of large break LOCA or MSLB, then would not get SI in sufficient time if train B SI lost.

3/3A CS Control B Lose auto containment spray actuation signal for large break LOCA, MSLB, or MFLB if CS control power A and train B containment spray also lost.

3/3A FT-2114B/C Lose 2 of 3 cold leg recirculation flow indicators for large and small break LOCA

[note: FT-3114A on train B vital 120 VAC bus 5, however, may need more than one leg of flow indication].

3/3A AFWAS A Lose AFW auto-initiate and flow control for small break LOCA, MSLB, and MFLB if AFWAS B on train B vital 120 VAC bus 5 is also lost.

TABLE 1 (continued)

Vital Bus Load Impact of Loss on ECCS Performance 4

FY-1115A-F Lose all cold leg recirculation flow control for large and small break LOCA if train B controllers on CSAS inverters also lost.

Page 1 TABLE 2 09-23-1990 Event Tree Accident Class Report for then VBT Series Accident Class Sequence Probability Core Damage 5.53E-07 Containment 4.23E-07 Failure (no Core Damage)

Containment 5.77E-08 Failure w/

Core Damage

Page 1 TABLE 3 09-23-1990 Event Tree Dominant Sequences Report for then VBT Series Top Event Probability: 9.761E-07 Sequence Title Sequence Probability Sequence Importance MS*C2 3.23E-07 3.31E-01 S*LV 1.76E-07 1.80E-01 I*LV 1.76E-07 1.80E-01 MS*LV 1.28E-07 1.31E-01 L*CH 9.79E-08 1.OOE-01 MS*C2*LV 4.88E-08 5.OOE-02

TABLE 4 Page 1 09-23-1990 Event Tree Summary Report for the VBT Series Top Event Probability:

9.761E-07 Event Tree Event Tree Title Event Tree Number 95 Percentile Name Probability of Median Run Date& Time Sequences 5 Percentile MS CORE DAMAGE DUE TO VITAL BUS FAILURE DURING MSLB 5.02E-07 5

09-23-1990 11:23:06 SL CORE DAMAGE DUE TO VITAL BUS FAILURE DURING SMALL LOCA 1.85E-07 3

09-23-1990 11:24:53 MF CORE DAMAGE DUE TO VITAL BUS FAILURE DURING MFLB 1.79E-07 4

09-23-1990 11:19:39 LL CORE DAMAGE DUE TO VITAL BUS FAILURE DURING LARGE LOCA 1.10E-07 5

09-23-1990 11:17:02

TABLE 5 Page 1, Sequence-Level Event Tree Report for VBTLL Data File 09-23-1990 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING LARGE LOCA Top Event Probability:

1.102E-07 This file was created on 09-22-1990 at 17:50:44 95 Percentile Sequence Sequence Title

Cutsets Probability Accident Class Cull Limit Median Number Run Date Time File Name 5 Percentile 2

L*R 1

2.79E-09 CD 1.00E-10 09-23-1990 11:14:53 VBTLLO2 3

L*CH 7

9.79E-08 CTMT FAIL 1.OOE-10 09-23-1990 11:15:42 VBTLLO3 4

L*CH*R 3

8.74E-09 CD/CTMT FL 1.OOE-09 09-22-1990 20:23:21 VBTLLO4 5

L*KS 2

7.35E-10 CD 1.00E-10 09-23-1990 11:16:58 VBTLL05

TABLE 6 Page 1-Sequence-Level Event Tree Report for VBTSL Data File 09-23-1990 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING SMALL LOCA Top Event Probability:

1.852E-07 This file was created on 09-22-1990 at 17:52:03 95 Percentile Sequence Sequence Title

Cutsets Probability Accident Class Cull Limit Median Number Run Date Time File Name 5 Percentile 2

S*R 2

9.18E-09 CD 1.OOE-10 09-23-1990 11:23:52 VBTSLO2 3

S*LV 55, 1.76E-07 CD 1.00E-10 09-23-1990 11:24:44 VBTSLO3

TABLE 7 Page 1 Sequence-level Event Tree Report for VBTMS Data File 09-23-1990 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING MSLB Top Event Probability:

5.022E-07 This file was created on 09-22-1990 at 17:51:31 95 Percenti e Sequence Sequence Title

Cutsets Probability Accident Class CuLL Limit Median Number Run Date Time File Name 5 Percentile 2

MS*LV.

34 1.28E-07 CD 1.OOE-10 09-23-1990 11:20:26 VBTMSO2 3

MS*C2 8

3.23E-07 CTMT FAIL 1.OOE-10 09-23-1990 11:21:19 VBTMSO3 4

MS*C2*LV 24 4.88E-08 CD/CTMT FL 1.OOE-10 09-23-1990 11:22:11 VBTMSO4 5

MS*KS 2

2.37E-09 CD 1.OOE-10 09-23-1990 11:23:02 VBTMS05

TABLE 8 Page 1 Sequence-Level Event Tree Report for VBTMF Data File 09-23-1990 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING MFLB Top Event Probability: 1.785E-07 This file was created on 09-22-1990 at 19:35:49 95 Percentile Sequence Sequence Title

Cutsets Probability Accident Class Cutt Limit Median Number Run Date Time File Name 5 Percentile 2

I*LV 55 1.76E-07 CD 1.OOE-10 09-23-1990 11:17:50 VBTMFO2 3

I*KC 2

2.37E-09 CTMT FAIL 1.OOE-10 09-23-1990 11:18:44 VBTMFO3 4

I*KC*LV 1

1.77E-10 CD/CTMT FL 1.OOE-10 09-23-1990 11:19:35 VBTMF04 0

TABLE 9 Page 1 Sequence-Level Cutset Report for VBTLLO2 Data FiLe 09-23-1990 Top Event: VBTLLO2 Top Event Probability:

2.790E-09 This file was created on 9-23-1990 at 11:14:54 Cutset Cutset Rank Importance Probability 1 1.OOOE+00 2.790E-09 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' R-HUREPRE--U 1.OOOE OPERATORS FAIL TO SET RECIRC FLOW CONTROLLERS PER PROC U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

TABLE 10 Page 1 Sequence-Level Cutset Report for VBTLLO3 Data File 09-23-1990 Top Event: VBTLLO3 Top Event Probability: 9.793E-08 This fiLe was created on 9-23-1990 at 11:15:44 Cutset Cutset Rank Importance Probability 1 5.603E-O1 5.487E-08 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 2 1.899E-01 1.860E-08 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 3 1.425E-O1 1.395E-08 I-SYINSTAIR 5.OOOE INSTRUMENT AIR FAILS INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 4 2.849E-02 2.790E-09 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE IVBTLL' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 4 2.849E-02 2.790E-09 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' U-C212CO2--P 3.OOOE BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 4 2.849E-02 2.790E-09 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 5 2.184E-02 2.139E-09 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' U-DGB----1HR 2.300E DIESEL GENERATOR B FT RUN FOR 1 HOUR U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

TABLE 11 Page 1 Sequence-Level Cutset Report for VBTLLO4 Data File 09-23-1990 Top Event: VBTLLO4 Top Event Probability:

8.742E-09 This file was created on 9-22-1990 at 20:23:22 Cutset Cutset Rank Importance Probability 1 6.277E-01 5.487E-09 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' R-HURECIRC 1.OOOE OPERATORS FAIL TO CONTROL RECIRC W/O FLOW INSTRUMENTS U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 2 2.128E-01 1.860E-09 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' R-HURECIRC 1.OOOE OPERATORS FAIL TO CONTROL RECIRC W/O FLOW INSTRUMENTS U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 3 1.596E-01 1.395E-09 I-SYINSTAIR 5.OOOE INSTRUMENT AIR FAILS INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' R-HURECIRC 1.OOOE OPERATORS FAIL TO CONTROL RECIRC W/O FLOW INSTRUMENTS U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

TABLE 12 Page 1 Sequence-Level Cutset Report for VBTLL05 Data File 09-23-1990 Top Event: VBTLLO5 Top Event Probability: 7.347E-10 This file was created on 9-23-1990 at 11:17:00 Cutset Cutset Rank Importance Probability 1 7.468E-01 5.487E-10 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE IVBTLL' KSSHORTVB 1.OOOE VITAL BUSSES FAIL DUE TO SHORTS IMMED. FOLLOWING ACCIDENT U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 2 2.532E-01 1.860E-10 INIT-L---LL 9.300E INITIATING EVENT L FOR EVENT TREE 'VBTLL' KSSHORTVB 1.OOOE VITAL BUSSES FAIL DUE TO SHORTS IMMED. FOLLOWING ACCIDENT U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

TABLE 13 Page 1 Sequence-Level Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:17:52 Cutset Cutset Rank Importance Probability 1

1.887E-01 3.330E-08 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG1OW---M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 2 1.530E-01 2.700E-08 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-SX3-3 ---- N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 2 1.530E-01 2.700E-08 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG10W---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 3 1.003E-01 1.770E-08 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-00CONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 4

5.537E-02 9.770E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 5 5.100E-02 9.OOOE-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-SV3110---J 1.OOOE SOLENOID VLV 3110 FT DEACTUATE ON DEMAND U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 6 3.400E-02 6.OOOE-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.000E CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 2 Sequence-level Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:17:52 Cutset Cutset Rank Importance Probability 7 2.550E-02 4.500E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-XVG10WM--X 5.OOOE NO MINIFLOW - ONE OF 5 MANUAL VALVES LEFT CLOSED U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 8 2.346E-02 4.140E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 9 1.877E-02 3.312E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 10 1.530E-02 2.700E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12014 FT CLOSE ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 11 1.295E-02 2.285E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 12 1.020E-02 1.800E-09 INIT-1---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE IVBTMFI U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 12 1.020E-02 1.800E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE IVBTMF' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12CO2 FT REM CLOSED 6 HOURS U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL

Page 3' Sequence-tevel Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event Probability:

1.765E-07 This fiLe was created on 9-23-1990 at 11:17:52 Cutset Cutset Rank Importance Probability 12 1.020E-02 1.800E-09 INIT-I---MF 3.00OE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-XVG10WL--X 2.OOOE NO LUBE OIL COOLING 1 OF 2 MANUAL VALVES LEFT CLOSED U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 12 1.020E-02 1.800E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-AV3110---M 2.OOOE CV-3110 CLOSED DUE TO MAINTENANCE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 13 1.003E-02 1.770E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 13 1.003E-02 1.770E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-MXB42 ---- V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 14 9.181E-03 1.620E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG10W-6HR 1.800E MTR-DRIVEN PP GlOW FT RUN FOR 6 HR U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 15 8.446E-03 1.490E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE *VBTMF' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-SX3-3--- -N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 16 6.620E-03 1.168E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGOSO ---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 4 Sequence-Leve Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event ProbabiLity:

1.765E-07 This file was created on 9-23-1990 at. 11:17:52 Cutset Cutset Rank Importance Probability 17 5.631E-03 9.936E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMFI U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS 17 5.631E-03 9.936E-10 INIT-I---MF 3.OOOE INITIATING EVENT I.FOR EVENT TREE 'VBTMF' U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 18 5.100E-03 9.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE IVBTMF' U-C212CO2--P 3.OOOE BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 18 5.100E-03 9.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM 0

U-DGDSD----V 1.000E-O1 - OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 18 5.100E-03 9.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF L-CV387----P 1.OOOE CHECK VLV 387 FT OPEN ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 18 5.100E-03 9.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMFI L-XVG1OWS--X 1.OOOE INSUFFICIENT FLOW TO PUMP GlOW DUE TO MANUAL VALVE CLOSURE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 18 5.100E-03 9.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-XV389----X 1.OOOE MANUAL VLV 389 LEFT OPEN POST-MAINT U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

Page 5.

Sequence-level Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:17:52 Cutset Cutset Rank Importance Probability 19 3.711E-03 6.549E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG10W--- M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 20 3.400E-03 6.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------M 2.000E DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 20 3.400E-03 6.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 21 3.009E-03 5.310E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG10W--- S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 21 3.009E-03 5.310E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 22 2.815E-03 4.968E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 22 2.815E-03 4.968E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212CO2--P 3.OOOE BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

. Page 6, Sequence-level Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:17:52 Cutset Cutset Rank Importance Probability 23 2.346E-03 4.140E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 23 2.346E-03 4.140E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 24 2.244E-03 3.960E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGOSO ---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 25 1.548E-03 2.732E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGOSO----M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 26 1.530E-03 2.700E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 26 1.530E-03 2.700E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 27 1.258E-03 2.220E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMFI L-MPG10W--- M 3.700E PUMP G1OW OUT OF SERVICE DUE TO MAINTENANCE U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 0

Page 7 Sequence-Level Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event Probability:

1.765E-07 This fiLe was created on 9-23-1990 at 11:17:52 Cutset Cutset Rank Importance Probability 28 1.020E-03 1.800E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 28 1.020E-03 1.800E-10 INIT-I---MF 3OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG10W--- S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-DGB------M 2.000E DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 28 1.020E-03 1.800E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 28 1.020E-03 1.800E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 28 1.020E-03 1.800E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 28 1.020E-03 1.800E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO-ALIGN PP GlOW TO BUS A4 U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 29 1.01OE-03 1.782E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGOSO ---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-sX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

Page 8, Sequence-level Cutset Report for VBTMFO2 Data File 09-23-1990 Top Event: VBTMFO2 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:17:52 Cutset Cutset Rank Importance Probability 30 1.003E-03 1.770E-10 INIT-1---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE IVBTMF' L-SV3110---J 1.OOOE SOLENOID VLV 3110 FT DEACTUATE ON DEMAND U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 31 8.681E-04 1.532E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG10W--- M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 32 7.039E-04 1.242E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-MPG10W---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 32 7.039E-04 1.242E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' L-AV3110---P. 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 33 6.732E-04 1.188E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE IVBTMF' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGOSO ----

M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE 33 6.732E-04 1.188E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' U-DGOSO----M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS

TABLE 14 Page 1 Sequence-leveL Cutset Report for VBTMFO3 Data File 09-23-1990 Top Event: VBTMFO3 Top Event Probability: 2.370E-09 This fiLe was created on 9-23-1990 at 11:18:46 Cutset Cutset Rank Importance Probability 1 7.468E-01 1.770E-09 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' KSSHORTVB 1.OOOE VITAL BUSSES FAIL DUE TO SHORTS IMMED. FOLLOWING ACCIDENT U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 2 2.532E-01 6.OOOE-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' KSSHORTVB 1.OOOE VITAL BUSSES FAIL DUE TO SHORTS IMMED. FOLLOWING ACCIDENT U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

TABLE 15 Page 1 Sequence-Level Cutset Report for VBTMF04 Data File 09-23-1990 Top Event: VBTMF04 Top Event Probability:

1.770E-10 This file was created on 9-23-1990 at 11:19:36 Cutset Cutset Rank Importance Probability 1 1.OOOE+00 1.770E-10 INIT-I---MF 3.OOOE INITIATING EVENT I FOR EVENT TREE 'VBTMF' KSSHORTVB 1.OOOE VITAL BUSSES FAIL DUE TO SHORTS IMMED. FOLLOWING ACCIDENT U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

TABLE 16 Page 1 Sequence-Level Cutset Report for VBTMSO2 Data File 09-23-1990 Top Event: VBTMSO2 Top Event Probability:

1.281E-07 This fiLe was created on 9-23-1990 at 11:20:29 Cutset Cutset Rank Importance Probability 1 2.600E-01 3.330E-08 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG10W---M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-SX3-3---- N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 2 2.108E-01 2.700E-08 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 2 2.108E-01 2.700E-08 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE aVBTMSI L-MPG10W---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-SX3-3 ---- N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 3 7.026E-02 9.OOOE-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-SV3110---J 1.OOOE SOLENOID VLV 3110 FT DEACTUATE ON DEMAND U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 4 3.513E-02 4.500E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-XVG10WM--X 5.OOOE NO MINIFLOW - ONE OF 5 MANUAL VALVES LEFT CLOSED U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 5 3.232E-02 4.140E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 6 2.108E-02 2.700E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-SX3-3--- -N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

Page 2-Sequence-Level Cutset Report for VBTMSO2 Data File 09-23-1990 Top Event: VBTMSO2 Top Event Probability:

1.281E-07 This file was created on 9-23-1990 at 11:20:29 Cutset Cutset Rank Importance Probability 7 1.784E-02 2.285E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 8 1.405E-02 1.800E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL 8

1.405E-02 1.800E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 8 1.405E-02 1.800E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-XVG10WL--X 2.OOOE NO LUBE OIL COOLING 1 OF 2 MANUAL VALVES LEFT CLOSED U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 8 1.405E-02 1.800E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-AV3110---M 2.OOOE CV-3110 CLOSED DUE TO MAINTENANCE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 9 1.265E-02 1.620E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG10W-6HR 1.800E MTR-DRIVEN PP GlOW FT RUN FOR 6 HR U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 10 1.163E-02 1.490E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

Page 3 Sequence-Level Cutset Report for VBTMSO2 Data File 09-23-1990 Top Event: VBTMSO2 Top Event Probability:

1.281E-07 This fiLe was created on 9-23-1990 at 11:20:29 Cutset Cutset Rank Importance Probability 11 7.756E-03 9.936E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12CO2 FT REM CLOSED 6 HOURS U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS 11 7.756E-03 9.936E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN.6 HOURS 12 7.026E-03 9.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-XV389----X 1.OOOE MANUAL VLV 389 LEFT OPEN POST-MAINT U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 12 7.026E-03 9.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE *VBTMS' L-XVG10WS--X 1.OOOE INSUFFICIENT FLOW TO PUMP GlOW DUE TO MANUAL VALVE CLOSURE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 12 7.026E-03 9.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS L-CV387----P 1.OOOE CHECK VLV 387 FT OPEN ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 13 3.232E-03 4.140E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS, U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 13 3.232E-03 4.140E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP G10W TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 4-Sequence-Level Cutset Report for VBTMSO2 Data File 09-23-i990 Top Event: VBTMSO2 Top Event Probability:

1.281E-07 This file was created on 9-23-1990 at 11:20:29 Cutset Cutset Rank Importance Probability 14 2.133E-03 2.732E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGOSO ---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 15 2.108E-03 2.700E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 15 2.108E-03 2.700E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 16 1.405E-03 1.800E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE VBTMS' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 16 1.405E-03 1.800E-10 INIT-MS--MS 3.OOOE-03'- INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 16 1.405E-03 1.800E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 16 1.405E-03 1.800E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS

Page 5 Sequence-Level Cutset Report for VBTMSO2 Data File 09-23-1990 Top Event: VBTMSO2 Top Event Probability:

1.281E-07 This fiLe was created on 9-23-1990 at 11:20:29 Cutset Cutset Rank Importance Probability 17 1.391E-03 1.782E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGOSO ----

M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-SX3-3--- -N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 18 1.196E-03 1.532E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' L-MPG10W--- M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-DGB----6HR 1.380E DIESEL.GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 19 9.695E-04 1.242E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG10W--- S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 19 9.695E-04 1.242E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 20 9.274E-04 1.188E-10 INIT-MS--MS 3.000E INITIATING EVENT MS FOR EVENT TREE IVBTMS' U-C212CO26HO 6.000E BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGOSO----M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE 20 9.274E-04 1.188E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGOSO ----

M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-TIAUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 0

TABLE 17 Page 1 Sequence-LeveL Cutset Report for VBTMSO3 Data File 09-23-1990 Top Event: VBTMSO3 Top Event Probability: 3.230E-07 This file was created on 9-23-1990 at 11:21:21 Cutset Cutset Rank Importance Probability 1 5.480E-01 1.770E-07 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 2 1.858E-01 6.OOOE-08 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 3 1.393E-01 4.500E-08 I-SYINSTAIR 5.OOOE INSTRUMENT AIR FAILS INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 4 4.273E-02 1.380E-08 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB ----2HR 4.600E DIESEL GENERATOR B FT RUN FOR 2 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 5 2.787E-02 9.OOOE-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 5 2.787E-02 9.OOOE-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212CO2--P 3.000E BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 5 2.787E-02 9.000E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 6 5.573E-04 1.800E-10 C-SV3518-2HL 2.OOOE SOLENOID VLV 3518 ACTS/DE-ACTS SPUR W/I 2 HOURS INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

TABLE 18 Page 1 Sequence-Level Cutset Report for VBTMS04 Data File 09-23-1990 Top Event: VBTMS04 Top Event Probability: 4.879E-08 This file was created on 9-23-1990 at 11:22:13 Cutset Cutset Rank Importance Probability 1

3.628E-01 1.770E-08 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 2 2.002E-01 9.770E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 3 1.230E-01 6.OOOE-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 4

6.788E-02 3.312E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 5 3.628E-02 1.770E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 5

3.628E-02 1.770E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 6 2.394E-02 1.168E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGOSO ---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 2' Sequence-LeveL Cutset Report for VBTMS04 Data File 09-23-1990 Top Event: VBTMS04 Top Event Probability: 4.879E-08 This fiLe was created on 9-23-1990 at 11:22:13 Cutset Cutset Rank Importance Probability 7 1.845E-02 9.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212CO2--P 3.OOOE BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 7 1.845E-02 9.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 8 1.342E-02 6.549E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE IVBTMS' L-MPG10W-- -M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 9 1.230E-02 6.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP G10W TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 9 1.230E-02 6.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSI.TE POWER GIVEN TURBINE TRIP 10 1.088E-02 5.310E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG1OW---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 10 1.088E-02 5.310E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT'TREE 'VBTMS' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.000E CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 3, Sequence-level Cutset Report for VBTMS04 Data File 09-23-1990 Top Event: VBTMSO4 Top Event Probability:

4.879E-08 This fiLe was created on 9-23-1990 at 11:22:13 Cutset Cutset Rank Importance Probability 11 1.018E-02 4.968E-10 INIT-MS--MS 3.OOOE-03 INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212CO2--P 3.OOOE BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 11 1.018E-02 4.968E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 12 8.116E-03 3.960E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' U-DGB------m 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGOSO----M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 13 4.550E-03 2.220E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG10W ---M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 14 3.689E-03 1.800E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG10W---S 3.OOOE MTR-DRIVEN PP G10W FT START ON DEM U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 14 3.689E-03 1.800E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 15 3.628E-03 1.770E-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-SV3110---J 1.OOOE SOLENOID VLV 3110 FT DEACTUATE ON DEMAND U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 4, Sequence-LeveL Cutset Report for VBTMS04 Data File 09-23-.1990 Top Event: VBTMS04 Top Event Probability:

4.879E-08 This file was created on 9-23-1990 at 11:22:13 Cutset Cutset Rank Importance Probability 16 3.412E-03 1.665E-10 I-SYINSTAIR 5.OOOE INSTRUMENT AIR FAILS INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG10W--- M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-SX3-3 ---- N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 17 2.767E-03 1.350E-10 I-SYINSTAIR 5.OOOE INSTRUMENT AIR FAILS INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 17 2.767E-03 1.350E-10 I-SYINSTAIR 5.OOOE INSTRUMENT AIR FAILS INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' L-MPG10W---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

TABLE 19 Page 1 Sequence-LeveL Cutset Report for VBTMS05 Data FiLe 09-23-1990 Top Event: VBTMSO5 Top Event Probability:

2.370E-09 This file was created on 9-23-1990 at 11:23:04 Cutset Cutset Rank Importance Probability 1 7.468E-01 1.770E-09 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' KSSHORTVB 1.OOOE VITAL BUSSES FAIL DUE TO SHORTS IMMED. FOLLOWING ACCIDENT U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 2 2.532E-01 6.OOOE-10 INIT-MS--MS 3.OOOE INITIATING EVENT MS FOR EVENT TREE 'VBTMS' KSSHORTVB 1.OOOE VITAL BUSSES FAIL DUE TO SHORTS IMMED. FOLLOWING ACCIDENT U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 0III 0II

TABLE 20 Page 1 Sequence-Level Cutset Report for VBTSLO2 Data File 09-23-1990 Top Event: VBTSLO2 Top Event Probability:

9.177E-09 This file was created on 9-23-1990 at 11:23:54 Cutset Cutset Rank Importance Probability 1 9.807E-01 9.OOOE-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL R-HUREPRE--U 1.OOOE OPERATORS FAIL TO SET RECIRC FLOW CONTROLLERS PER PROC U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 2 1.929E-02 1.770E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSL' R-HUREPRE--U 1.OOOE-03 -.OPERATORS FAIL TO SET RECIRC FLOW CONTROLLERS PER PROC U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 0

TABLE 21 Page 1' Sequence-Level Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 1 1.887E-01 3.330E-08 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSL' L-MPG10W-- -M 3.700E PUMP G10W OUT OF SERVICE DUE TO MAINTENANCE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 2 1.530E-01 2.700E-08 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-SX3-3 ----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 2 1.530E-01 2.700E-08 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSL' L-MPG1OW---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 3 1.003E-01 1.770E-08 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-00CONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 4 5.537E-02 9.770E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 5 5.100E-02 9.OOOE-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE *VBTSLI L-SV3110---J 1.OOOE SOLENOID VLV 3110 FT DEACTUATE ON DEMAND U-SX3-3----N 3.000E TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 6 3.400E-02 6.OOOE-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-00CONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 2' Sequence-LeveL Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 7 2.550E-02 4.500E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-XVG10WM--X 5.OOOE NO MINIFLOW - ONE OF 5 MANUAL VALVES LEFT CLOSED U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 8 2.346E-02 4.140E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 9

1.877E-02 3.312E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 10 1.530E-02 2.700E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSLI U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 11 1.295E-02 2.285E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 12 1.020E-02 1.800E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSL' U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 12 1.020E-02 1.800E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGDSD----V 1.000E OPERATOR FAILS TO START DSD DIESEL

Page 31 Sequence-LeveL Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This fiLe was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 12 1.020E-02 1.800E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-XVG10WL--X 2.OOOE NO LUBE OIL COOLING 1 OF 2 MANUAL VALVES LEFT CLOSED U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 12 1.020E-02 1.800E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-AV3110---M 2.OOOE CV-3110 CLOSED DUE TO MAINTENANCE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 13 1.003E-02 1.770E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP G10W TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 13 1.003E-02 1.770E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-MXB42 ---- V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 14 9.181E-03 1.620E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSLI L-MPG1OW-6HR 1.800E MTR-DRIVEN PP GlOW FT RUN FOR 6 HR U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 15 8.446E-03 1.490E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSL' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES A A 16 6.620E-03 1.168E-09 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM

.U-DGOSO--- -M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 4 Sequence-Level Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 17 5.631E-03 9.936E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS 17 5.631E-03 9.936E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 18 5.100E-03 9.OOOE-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212CO2--P 3.OOOE BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 18 5.100E-03 9.OOOE-10 INIT-S---SL 3.OOOE-03.- INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM U-DGDSD----V 1.OOOE OPERATOR FAILS TO START DSD DIESEL U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 18 5.100E-03 9.OOOE-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSLI L-CV387----P 1.OOOE CHECK VLV 387 FT OPEN ON DEM U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 18 5.100E-03 9.OOOE-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-XVG10WS--X 1.OOOE INSUFFICIENT FLOW TO PUMP GlOW DUE TO MANUAL VALVE CLOSURE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 18 5.100E-03 9.OOOE-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-XV389----X 1.OOOE MANUAL VLV 389 LEFT OPEN POST-MAINT U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

Page 5.

sequence-Level Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 19 3.711E-03 6.549E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-MPG10W---M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 20 3.400E-03 6.OOOE-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 20 3.400E-03 6.OOOE-10 INIT-S---SL 3.0000E INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 21 3.009E-03 5.310E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-MPG10W---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 21 3.009E-03 5.310E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSL' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 22 2.815E-03 4.968E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSL' U-C212C15--N 3.OOOE BKR (CNTL) 4160V 12C15 FT CLOSE ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 22 2.815E-03 4.968E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212CO2--P 3.OOOE BKR (CNTL) 4160V 12C02 FT OPEN ON DEM U-DGDSD--1DR 5.520E DIESEL GENERATOR DSD FT RUN FOR 24 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP

Page 6 Sequence-Level Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 23 2.346E-03 4.140E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP G10W TO BUS A4 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 23 2.346E-03 4.140E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE IVBTSLa U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 24 2.244E-03 3.960E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-DGOSO ----

M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 25 1.548E-03 2.732E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-DGOSO ---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 26 1.530E-03 2.700E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 26 1.530E-03 2.700E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSLI U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES 27 1.258E-03 2.220E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-MPG10W--- M 3.700E PUMP GlOW OUT OF SERVICE DUE TO MAINTENANCE U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 0

Page 7-Sequence-LeveL Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 28 1.020E-03 1.800E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGDSDSW--V 1.OOOE OPERATOR FAILS TO ALIGN PP G10W TO BUS A4 28 1.020E-03 1.800E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-MPG10W---S 3.OOOE MTR-DRIVEN PP GlOW FT START ON DEM U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 28 1.020E-03 1.800E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB------M 2.OOOE DIESEL GANERATOR B OUT OF SERVICE DUE TO MAINTENANCE U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 28 1.020E-03 1.800E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-MXB42 ----

V 1.000E OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 28 1.020E-03 1.800E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-MXB42----V 1.OOOE OPERATOR FAILS TO OPERATE MANUAL SWITCH B42 U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 28 1.020E-03 1.800E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGDSDSW--V 1.000E OPERATOR FAILS TO ALIGN PP GlOW TO BUS A4 U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS 29 1.010E-03 1.782E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212C14--N 3.OOOE BKR (CNTL) 4160V 12C14 FT CLOSE ON DEM U-DGOSO---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-SX3-3----N 3.OOOE TRANSFER SWITCH 3 FAILS TO TRANSFER 3 TIMES

Page 8 Sequence-LeveL Cutset Report for VBTSLO3 Data File 09-23-1990 Top Event: VBTSLO3 Top Event Probability:

1.765E-07 This file was created on 9-23-1990 at 11:24:47 Cutset Cutset Rank Importance Probability 30 1.003E-03 1.770E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-SV3110---J 1.OOOE SOLENOID VLV 3110 FT DEACTUATE ON DEMAND U-DGB------S 5.900E DIESEL GENERATOR B FT START ON DEM U-OOCONLDOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 31 8.681E-04 1.532E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-MPG10W ---M 3.700E PUMP G10W OUT OF SERVICE DUE TO MAINTENANCE U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 32 7.039E-04 1.242E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-MPG10W---S 3.OOOE MTR-DRIVEN PP G10W FT START ON DEM U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 32 7.039E-04 1.242E-10 INIT-S-.--SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' L-AV3110---P 3.OOOE AIR-OPERATED VLV 3110 FT OPEN ON DEM U-DGB----6HR 1.380E DIESEL GENERATOR B FT RUN FOR 6 HOURS U-OOCONLOOPZ 1.OOOE CONDITIONAL LOSS OF OFFSITE POWER GIVEN TURBINE TRIP 33 6.732E-04 1.188E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-C212CO26HO 6.OOOE BKR (CNTL) 4160V 12C02 FT REM CLOSED 6 HOURS U-DGOSO---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE 33 6.732E-04 1.18E-10 INIT-S---SL 3.OOOE INITIATING EVENT S FOR EVENT TREE 'VBTSL' U-DGOSO ---- M 6.600E DSD DIESEL DOWN DUE TO MAINTENANCE U-T1AUXC-6HI 6.OOOE >4160V XFMR AUXC LOW/NO OUTPUT WITHIN 6 HOURS

FIGURE 1 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING LARGE LOCA LARGE LOCA SIS/CSAS HIGH FLOW RECIRC A

SF N

C E

FAILURE CONT. SPRAY FAILURE U

c E

m I SEQUENCE L

0 FAILURE IN BIDA EU 8DE S I GN ATIO0N DS E

1 HOUR E

ES NE L

KS CH R

T ECV SL SAFE 2

L-A Co 2.79E-09 3

L-CH CTMT FAIL 9.79E-0B 9.30E-04 4

L-CH-R CD/CTMT F 8.74E-09 5

L-KS CD 7.35E-10 REBECA (C) ERIN Engineering and Research, Inc.

Version 1.

Filename:

VBTLL Date:

09-22-90 Total Probability: 1.10E-07

FIGURE 2 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING SMALL LOCA SMALL LOCA AFW FAILURE RECIRC A

S N

C ER FAILURE U

CC L

E m

SEQUENCE IL U

DESIGNATION E

E N

CN S

LV R

T EC Y S

SAFE 2

S-A CD 9.18E-09

3. OOE-03 3

S-LV Co

. 76E-07 REBECA (C) ERIN Engineering and Research. Inc.

Version i.1 Filename:

VBTSL Date:

09-22-90 Total Probability: 1.85E-07

FIGURE 3 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING MSLB MAIN STEAM SIS/CSAS HIGH FLOW AFW FAILURE A

SF N

CE LINE BREAK FAILURE CONT. SPRAY UC C

E M EGENE L

UQ FAILURE IN BE A

u DESIGNATION 0 S EE 2 HOURS E

E 5 NN MS KS C2 LV T

EC w SSAFE 2

MS-LY CD 1.28E-07 3

XS-C2 CTMT FAIL 3.23E-07 3.OOE-03 4

N5-C2-LV CD/CTMr F. 4.88E-08 5

MS-KS CO 2.37E-09 REBECA (C) ERIN Engineering and Research, Inc.

Version 1.1 Filename:

VBTMS Date: 09-22-90 Total Probability: 5.02E-07

FIGURE 4 CORE DAMAGE DUE TO VITAL BUS FAILURE DURING MFLB MAIN FEED CSAS FAILURE AFW FAILURE A

SF N

C c EE LINE BREAK U

CC E

m SEQUENCE IL 0U E DESIGNATION DS EE N

C N KC LV T

EC Y

S1 SAFE 2

I-LY CD 1.75E-07

3. OOE-03 3

I-KC CTMT FAIL 2.37-09 4

[-KC-LY CO/CTMT Fl. i.77E-ID REBECA (C) ERIN Engineering and Research, Inc.

Version 1.1 Filename: VBTMF Date: 09-22-90 Total Probability: 1.79E-07

FIGURE 5 SIS/CSAS FAILURE DUE TO VITAL BUS LOSS SHORT-TERM 09-22-1990 SIS 0R CSAS FAILURE IN SHOAT-TERM POST LOCA OR MSLB KS 01 SIS FAILURE CSAS FAILURE

-KS-0N-02 KC-01-01 KC T REE PAGE 01 VITAL BUSSES FAIL FAILURE OF 2 VITAL DUE TO SHORTS IMMED BUS SUPPLYING FOLLOWING ACCIDENT SIS INPUTS l KSSHRTVS

) KS-01-03 l

2 K/N 1.00E-02 IMMEDIATELY IMMEDIATELY IMMEDIATELY KS-0\\-04KS-01-05 0,

OR OR, TRASFR WICH1 ACUPPOERFALS TRANSFER SWITCH 2

BACKUP POWER FAILS TRANSFER SWITCH 3

BACKUP POWER FAILS FAILS TO TRANSFER WITHIN ONE MINUTE FAILS TO TRANSFER WITHIN ONE MINUTE FAILS TO TRANSFER WITHIN ONE MINUTE ONE TIME ONE TIME ONE TIME KSSXifil----

N Ul 0-01-01l KSSX2-2I----

N u1-01-01 KSSX3-2I---N 01-01-01 1.00E-03 t TREE PAGE 01 1.00E-03 Ul TREE PAGE 01 1.00E-03 U1 TREE PAGE 01.

PAGE 1 REBECA (C)ERIN Engineering and Research. Inc.

Version 1.1

FIGURE 6 FAILURE OF THE CSAS SIGNAL -SHORT-TERM 109-24-1990 CSAS1 FAILURE OCCURS WITHIN 1 MINUTE l

KC-01-01 VITAL BUSSES FAIL FAILURE OF VITAL DUE TO SHORTS IMMED.

.BUSSES I A ON 3/3A FOLLOWING ACCIDENT

-KS5HORTVB I-KCS01-02 1 00E-02 VITAL BUS I FAILS VITAL BUS 3/3A FAILS WITHIN 1 MINUTE WITHIN 1 MINUTE ENKC-01-03T C-01-04 0OR O

TR ANSFER SWITCH 1 BACKUP POWER FAILS TRANSFER SWITCH 3 BACKUP POWER FAILS FA ILS TO TRANSFER WITHIN ONE MINUTE FA ILS To TRANSFER WITHIN ONE MINUTE ONE TIME 2

1ONE T IME KSSXI-il----

N lUl-01-01 l

KSSX3----N u1-01-01 1.00E-03 UTREPG011.00E-03 UTEEPAGE 01 PAGE 1 REBECA (CERIN Engineering and Researcn, Inc.

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FIGURE 7 FAILURE OF RECIRCULATION DUE TO VITAL BUS FAILURE O9-23-1990 iRECIRC FAILURE DUE TO V ITAL BUS FAILURE I RX-01-01 I

FAILURE OF VITAL OPERATORS FAIL TO BUS 3/3A WITHIN 6

SET RECIAC FLOW HOURS CONTROLLERS PER PROC AX-01-02

) -HUREPRE--Ul OR i.00E-03 TRANSFER SWlTCH 3

BAKPPWRFAILS FAILS TO TRANSFER WITHIN 6 HOURS l U-5X3---- N U 6-01-01 0

A 3.00E-03 U6 TREE PAGE 01 PAGE I1 RE8ECA (C)ERIN Engineering and Research. Inc.

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FIGURE 8 FAILURE OF HIGH FLOW CONTAINMENT SPRAY WITHIN 1 HOUR 109-22-1990 FAILURE OF HIGH FLOW CONTAINMENT SPRAY WITHI N I HOUR CH-01-01 AND CV-517 CLOSES OUE TO CV-518 FAILS CLOSED i VITAL BUS 3/3A TRANSFER SWITCH 3 BACKUP POWER FAILS INSTRUMENT AIR SOLENOID VLV 351B OC BUS 02 LOW/ND AIR-OPERATED VLV S1B FAILS TO TRANSFER WITHIN ONE HOUR FAILS ACTS/DE-ACTS SPUR OUTPUT W/I I HOUR FT REM OPEN I H 3 TIMES

/I 1 H l

-S3----NlI UA-01-01

(

CH-01-04 C-V581LlU-BYDC2--IHI CA5S_~

3.00E-03 UA TREE PAGE 01 1.00E-05 1.00E-05 4.17E-06 INSTRUMENT AIR CONDITIONAL LOSS OF FAILS OFFSITE POWER GIVEN TURBINE TRIP I

I-SINSTIA

)U-00CONLOOPZ 5.00E-03 1.00E-03 PAGE 1 REBECA (C)ERIN Engineering and Research. Inc.

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FIGURE 9 FAILURE OF HIGH FLOW CONTAINMENT SPRAY WITHIN 2 HOURS 109-22-1990 FAILURE OF HIGH FLOW CONTAINMENT SPRAY WITHIN 2 HOURS cI1-01 -0 1l A N)

CV-517 CLDSES DUE TO

.CV-518 FAILS CLOSED V ITAL BUS 3/3A.

FAILURE CI-01-02 c-10 TRANSFER SWITCH 3

BACKUP POWER FAILS INSTRUMENT AIR SOLENOID VL-V 3518 DC BUS #2 LO /ND AIR-0PERATEO VLY 518 FAILS TO TRANSFER WITHIN TW0 HOURS FAILS

.ACTS/DE-ACTS SPUR OUTPUT W/I 2 HOURS FT REM OPEN 2 HOURS 3 TIMES W/I 2 HOURS IU-SX3-3 N

lU2-01-01 lCI-01-04 l-V51-H U-BYDC2--2HI l C-AV51B--2HQ 0oOn 3.00E-03

,U2 TREE PAGE 01 2.00E-05 2.00E-06 8.34E-06 INSTRUMENT AIRA CONDITIONAL LOSS OF FAILS DFFSITE POWER GIVEN TURBINE TRIP II-SYINSTAIR I U-00CONLOOPZ 5.00E-03 1.00E-03 PAGE1 REBECA (CERIN Engineering and Research, Inc.

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FIGURE 10 BACKUP POWER FAILS WITHIN ONE MINUTE 09-24-1990 BACKUP POWER FAILS WITHIN ONE MINUTE NO POWER GIVEN OFF-LOSS F OFFSITE SITE POWER is POWER AND 0G B AVAILABLE FAILS Ut-01-02

)

U-1-03 CLSE FULiMNT

>4160V XFMR AUXC BKA (CNTL) 4160V 8KR (CNTL) 4160V 4150V-480V XFMR 55T2 FAILURE OF BIESEL 80CO ITIONAL LOSS OF LOW/ND OUTPUT WITHIN 12C02 FT REM CLOSED 12C0 FT REM CLOSED OLOW/NO OUTPUT O/

GENERATOR B

OFFSITE PO ER SMINUTE 24 H 0N.017 H

GIVEN TURBINE TRIP U-1AXCtM lU-C212CO21MO U-2211OlU-T2SST2-1MI U1-01l-04 U-0CONLOOPZ 1.70E-08 i.70E-08 1.70E-08 1.70E-08 1.00E-03 DIESEL GENERATOR B

BKR (CNTL) 4160V BKA (CNTL) 4160V FT START ON DEM 12C15 FT CLSE ON 12C02 FT OPEN ON OEM DEM l U-DGB ------

S IU-C212C15--N l

I U-C212602--P 416V BS 2 SHRT KR (CNTL) 480V 1202 8KR (CNTLI 480V 1218 TRANSFER SWITCH 759E0 0-330E0 CIRCUIT W/1.017 H FT REM CLOSED.017 H FT REM CLOSED.017 H FAILS TO REMAIN CLOSED FOR I MINUTE I -B2C-lM )

IU-C31202-lMO

-311-M U-SX7 ----

IMO DIESEL GA INERATOR B

DC BUS I2 LOW/NO1 OUT OS ERVCOUE DUTPUT W/I.017H 1.70E-08 1.70E-08 1.70E-0B 1.70E-08 U-DGB-t-----M U-BYOC2--IMI 480V-120V XFMA VBBAC 480V 8US SWGR2 SHORT LOW/ND OUTPUT W/I CIACUIT /I1.017 H

.017 H

lU-T3VB8AC1MI U-83SWGR21MA 1.70E-08 1.70E-08 iPAGE 1

RE8ECA (C)ERIN Engineering and Research. Inc.

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FIGURE 11 BACKUP POWER FAILS WITHIN ONE HOUR 09-22-1990 BACKUP POWER FAILS WITHIN ONE HOUR NO POWER GIVEN OFF-LOSS OF OFFSITE SITE POWER IS POWER AND 0O 8 AVAIABLEFAILS UA-01-02 l-UA-01-03 0A AND

>4160V XFMA AUXC BKR (CNTL) 4160V BKR (CNTL) 4160V 4160V-480V XFMR SST2 FALUE OEE C

T LLOSS LOW/NO OUTPUT WITHIN 12CO2 FT REM CLOSED 12C10 FT REM CLOSED LOW/ND OUTPUT WI NERATOR OFFSITE POWER 1 HO I HOUR 1 HOUR HOUR GIVEN TURBINE TRIP U-T C-IHl U-C21201H l-2122100 U-T2SST2-1H U-0CONLOOPZ OU OFIZC-H SERVICEH DU FTq I

R UNFR1HU UPTHI1HU TO MAINTENANC I.O0E-06 1.00E-06 1.00E-06 1.00E-06 1.OO E-03 DIESEL FENERATOR 8

BKR (CNTL) 4160V BKR (CNTL) 4160 FT START ON DEM 12C15 FT CLOSE ON 12C02 FT OPEN ON DEM OEM l

-OB----

l lU-C212C15--N U-2CO2 4160V BUS 2C SHORT BKR (CNTL) 480V 1200 8K CTI40 23 TASE WTH75.90E-02 3.00E-03 3.00E-03 CILCUIT W/I O

HOUR FT REM CLOSED 1 HOUR FT REM CLOSED I HOUR FAILS TO REMAIN CLOSED FHO 1 HOUR UA2C--H

-C3100-1HO

.U-B31WA2230lUSX---H U-B22 ---IHA I U-31tO-IHODIESEL GA

.EAATOR B

DIESEL GENERATOR B

DC BUS #2 LOWN0 OUT OF SERVICE OUE FT RUN FOR 1 HOUR OUTPUT W/I I HOUR 0

TO MAINTENANCE 1.00E-06 1.00E-06 1.00E-08 1.00E-06 lUDB---U-G--1RlU-8YOC2--tHI 2.00E-02 2.30E-03 1.00E-06 E480V-120V XFMR V88AC 4OV BUS SW 2 SHORT SLOW/NO OUTPUT W/I CIRCUIT W/I 1 HOUR 1 HOUR (U-TVBBA1HIU-B3SWGR21HA 1,00E-08 1.00E-06 PAGE 1 REBECA (C)ERIN Engineering and Research, Inc.

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FIGURE 12 BACKUP POWER FAILS WITHIN TWO HOURS 09-22-1990 BACKUP POWER FAILS WITHIN TWO HOURS I U2-01-01

-OR NO POWER GIVEN OFF-LOSS OF OFFSITE SITE POWER IS POWER AND DG B 0-2U2-01-02 l

U2-01-03 0R AND 4160V XFMR AUXC BKR (CNTL) 4160V BR (CNTL) 400VD 460V-40WS FR 5T 2 F

LOC/NO OUTPUT WITHIN 1202 FT REM CLOSED 12CDR FT REM CLOSED LOWFO OUTPUT WI GENERATOR B

OFFSITE POWER 2 HOURS TW HOURS COE O

OR 2UTOURSR2CHOURSTRUHOURS 2 HOURS GIVEN TURBINE TRIP U -T C U-C212CO22HO l U-C210C102H0O U-T2ST2-2HI l2-0 U-O0CONLOOPZl 2.00E-06 2.00E-04 2.00E-06 2.00E-06 1.00E-03 DIESEL GENERATO B

BKA (CNTL) 4160V KR (CNTL) 4160V FT START ON DEM 12Ci5 FT CLOSE ON 12C02 FT OPEN ON DEM.

OEM U-0GBt-----

l I U-C2t2C15--N 2

4160V BUS I2C SHORT BKR (CNTL) 4BOV 1200 BK CTJ40 23 TASE WTH75.90E-02 3.00E-03 3.00E-03 CIRCUIT W/I 2 HOURS FT REM CLOSED FOR FT REM CLOSED FOR FAILS TO EAIN 2 HOURS TWO HOURS CLOSED FDA 2 HOURS I U-B22C 2HA l

-3202O)U-C31223-2HO U-SX7- -2HQ DIESEL GANERATOR B

DIESEL GENERATOR B

DC BUS f2 LOW/NO OUT OF SERVICE DUE FT RUN FOR 2 HOURS OUTPUT W/I 2 HOURS 2.00E-06 2.O0E-06 2.00E-08 2.00E-06 lU-0G8------M IU-GB---2HA l U-8YDC2--2HI 2200E-02 4.60E03 2.00E-06 R4V-120V XFMR VEBAC ng480V BUS SWGR2 SHORT LOW/NO OUTPUT W/I CIRCUIT W/I 2 HOURS 2 HOURS U-T3BBACHI l

U-B3SWGR22HA 2.00E-06 2.00E-06 PAGE 1 RE8ECA (C)ERIN Engineering and Research.Inc.

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FIGURE 13 BACKUP POWER FAILS WITHIN SIX HOURS 09-22-1990 BACKUP POWER FAILS WITHIN SIX HOURS U6-01-01 OR NO POWER GIVEN OFF-LOSS OF OFFSITE SITE POWER IS POWER AND 05 8 AVAILABLE FAILS U6-01-02 3

U6-0-03 OR AN 4160V XFMR AUXC.

BKR (CNTL) 4 4150V80V XFMR S5T2 FAILURE OF DIESELCHA S

LOWND UTPUT WITHIN 1202 FT REM CLOSED 12C0 FT REM CLOSED LOW/O OUTPUT N/I GENERA OFFSITE POWER 6 HOURS 6 HOURS 6 HOURS 6 HOURS GIVEN TURBINE TRIP l-TIUC-HI U-C212C26HO lU-C12106Hl U-T

-6H l

U6-01-04 U-00CONLOOPZ 6.00E-06 6.00E-06 8.00E-08 6.00E-08 1.00E-03 DIESEL GENERATOR B

DESEL 60V ABR (CNTL)U4160V FT START ON EM 1215 FT CLOSE ON 1202 FT OPEN ON EM OEM U-DG8G-------S l-U-C22C-5HR U-C212-2--P 5.0-02 3

I.E-3 3E-02 0 4160V BUKR (CNTL) 480V 1200480 V 1223 SWI CLRC IT W/I 6 HOURS FT RE

/

CLOSEO FOR FT REM CLOSED FOR FAILS To REMAIN 6 HOURS SIX HOURS CLOSED FOR 6 HOURS I U-B22C-U-30 H

U-C31223-6HO IU-SX7--HO D

OUT OF SERVICE DUE FTI RUN FOR 5 HOURS OUTPUT W/I 6 HOURS 0

0 0TO MAINTENANCE 6.00E-06 6.00E-05.

6.00E-06 8.00E-06l U-DGB-----M I U-0G8----6HR

-YC2-H 2.00E-02 i.38E-02 6.00E-06 480V-120V XFMR VB8AC 480V BUS SW6R2 SHORT LOW/NO OUTPUT WI CIRCUIT W/I 6 HOURS..

6 HOURS U-T3VBBAC6HI lU-83SWGR26HA 6.00E-06 6.00E-06 PAGE I

REBECA (C)ERIN Engineering and ResearchInc.

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FIGURE 14 FAILURE OF AFW DUE TO VITAL BUS FAILURE 109-22-1990 AFW FAILS WITHIN 6 HOUS DE TO V ITAL

BUS, FAILUE LV-01-01 AND VITAL BUS 3/3A TO PROVIDE TO ALL 3 FAILUR STEAM GENERATORS LV-01-02 L-10 OR AD TRANSFER SWITCH 3 BACKUP POWER FAILS NO AFW FLOW TO NO AFW FLOW TO NO AFW FLOW TO FAILS TO TRANSFER WITHIN 6 HOURS STEAM GENERATOR A STEAM GENERATOR 8j STEAM GENERATOR C 3 TIMESIf IU-SX3-3----

N l

6-01-01 LV-02-01 l

LV-03-01 L-4O 3.00E-03 U6 TREE PAGE Of PAGE 02 PAGE 03 PAGE 04 FPAGE 1 REBECA (C)ERIN Engineering and Research, Inc.

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FAIL UR EN-OFY F

OED TO VI A

-U FA LU E

0V2 19 2.No

-04 FLOW-TO SETEAA GENERATO EniernAn eer.Cc eso.

FAI LURE OF AFW DUE TO VITAL BUS FAILURE

--709-22-1990 NO AFW FLOW TO STEAM GENERATOR 8

LV-03-01 on STEAM GENERATOR B

ATOR 8

FLOW PATH CHECK VLVS F OW PATH MNL VLVS NOT PEN GIOW TRAIN FAIL TO OPEN -3 VLYS LEFT CLOSED

- 2 VLVS L-CVStB P

I L-XVS68 X

0-0 -02 0-8-01 on 3.OOE 2.OOE-04 PAGE 05 FCI 013 OAOI CLOI, DUE OPE R CLOSES FLOW CNTLR 33008 INTENA RAT?3 LOW/NO UTPUT W/I 6 E

ICV 3008 n

H L-FC3300 6HI I L-AV3!008--M L-HU3 'DOB--V 7

1v 2.OOE-04 I.OOE-03 2.50E-05

-TPA G E 3, REBECA (C)ERIN Engineering and Research.Inc.

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FAILURE OF AFW DUE TO VITAL BUS FAILURE 709-22-1990 NO AFW FLOW TO STEAM GENERATOR C

I LV-04-01 STEAM GENERATOR C STEAM GENERATOR C FC-30 0SNO FLOW FROM PUMP FLOW PATH CHECK VLVS FLOW PATH MNL VLYS NOT OPEN GIOW TRAIN FAIL TO OPEN -3 VLYS LEFT CLOSED - 2 VLYS I L-CVSC ----

P (L-XVSC----

X LV0-2LV-05-01 3.00E-04 2.00E-04 PAGE 05 FCV-3300C CLOSED DUE OPERATOR CLOSES FLOW CTLR 3300C TO MINTNANE FV-3000 LOW/ND 0UTPUT W/I 6 TO MINTEANCE FCV-300C T

H L-AV300C--

L-HU33DOC--V L-FC3300C6HI O

O 2.00E-04 1.00E-03 2.50E-05 PAGE 4 REBECA (C)ERIN Engineering and Research, Inc.

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FAILURE OF AFW DUE TO VITAL BUS FAILURE NO FLOW FROM PUMP G1OW TRAIN LV-05-Of OR INSUFFICIENT FLOW INSUFFICIENT FLOW CHECK VLA 387 FT CV-3110 FAILS TO TO PUMP GIOW DUE TO FROM PUMP G1OW OPEN ON OEM OPEN MANUAL VALVE CLOSURE OL-XVGi0WS--X LV-05-02 L-CV3 0 ----

P OR

.00E-04 N.00E-04 PUMP 10 W FAILS MANUAL VL 389 LEFT CV-310 CLOSED DUE H OPEN POST-MAINT TO MAINTENANCEACUT ONDM D310F OPN N E LV-05-04l L-XV39---X AVt ---M L-AV3110 ---P OR 1.00E-04 200E-04E-PAG 08E PUMP GCW EUT OF MTR-RRVNPngRVNP And CPWeTOIILn-OE NOL IOLN SERVICE DUE TO FT START ON DEM FT RUN FOA 6 HR Pp 810w 5 MANUAL VALVES LEFT 1-OF 2 MANUAL VALVES MAINTENANCE CLOSED LEFT CLOSED I L-MPGtow

--- M l

I L-MPGI0W--SI LMP 0-6R5LXV 0W -XL VG W-Xl 3.70E-03 3.00E-03 1.80E-04 5.00E-04 2.00E-04 2C OS DOIESEL LV-05-05

)LV-07-01 PAGE 07 BKR (CNTL) 4160V DC US#2 O NO NO POER. ON BUS 2C 12M1 FT CLOSE ON OUTPUT W/I 6 HOUR UIG 6 OR PR OEM U-C212C14--N )

U-8YOC2--5HI l

L-60 F

4, L-P:

0 F7 F= W A EB C -F A -T M 50LEN-.10C VLVA 3-10T FTr-AIR0-0PERATED

-GVLY FAILUFRE OF)I AFgneASn an ACTUATIONc VeIGNAn AFE.GN1E

FAILURE OF AFW DUE TO VITAL BUS-FAILURE 09-22-1990 NO POWER ONBS2 0ITHIN 6 HOURS LV-06-01 0n NPOESIVEIN OFF-LOSS OF OFFSITE SITE POWER AVAILABLE 1 POWER AND DIESEL GENERATOA B FAILS

.LV-06-02 LV-06-03 OR AND BKR (ClNTL) 416l0V

>4160V XFMR AUXC

.DIESEL GENERATOR CONOITIONALLO55 OF 102 FT, REM COED LOW/NO OUTPUT WITHIN B FAILS GOFFST OE 8HOURS 6 HOURS IVEN TURBINE TRIP U-C212CO26HO

.l U-T1AUXC-6HIP OR i.80E-02 6.00E-06 I.00E-03 DIESEL GENERATOR B

DIESEL GENERATOR 8

DIESEL GANERATOR B

BKA (CNTL) 4160V BKR (CNTL) 4lSOV DC BUS #2 LOW/N0 FT START ON DEM FT RUN FOR 6 HOURS OUT OF SERVICE DUE 12C15 FT CLOSE ON 12CO2 FT OPEN ON DEM O0UTPUT WI 6 rHOURS SU-DG8n ----

S U-0GU---HR M

U-C212C15--N l

-22o-P(

]U-BYDC2--6HI 5.90E-02 1.38E-02 2.00E-02 3.00E-03 3.00E-03 6.00E-06 PAGE 6 REBECA (C)ERIN Engineering and Research, Inc.

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FAILURE OF AFW DUE TO VITAL BUS FAILURE

.109-23-1990 NO POWER FROM OSO DIESEL OR 0S0 OIESEL OPERATOR FAILS DIESEL GENERATOR ISO 410 BUS A4 OPERATOR FAILS TO 40V BUS B30 di0V-40V XFMR X56 OPERATOR FAILS TO DOWN DUE TO TO START FT RUN FOR 24 SHORT CIRCUIT ALIGN PP GIOW TO SHORT CIRCUIT LOW/NO OUTPUT OPERATE MANUAL MAINTENANCE DSOD DIESEL HOURS W/T 24 H BUS A4 A/I 24 H SIGNAL MI 24 H SWITCH 042

-OGOSO---M lU-OGOSD----V U-DGDSO--iDR U-B2A4--IOA U-08DSDSW--V U-B3B30--10A U-T2X--I U-4---

6.60E-03 1.00E-0l 5.52E-02 2.40E-05 1.OE-02 2.40E-05 2.40E-05 1.00E-02 PAGE 7 REBECA (C)ERIN Engineering and Research. Inc.

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ML13310A266

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