Text

Draft, Evaluation of Effects of Calvert Cliffs Nuclear Power Station Electric Power,Compressed Air & Cooling Water Sys Failures on Pressurized Thermal Shock Event Sequences
	ML20084A333
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Site:	Calvert Cliffs
Issue date:	03/19/1984
From:	Mcbride A; SCIENCE APPLICATIONS INTERNATIONAL CORP. (FORMERLY
To:	; NRC
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References
	CON-FIN-B-0468, CON-FIN-B-468, REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR NUDOCS 8404240513
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DRAFT EVALUATION OF THE EFFECTS OF CALVERT CLIFF NUCLEAR POWER STATION ELECTRIC POWER, COMPRESSED AIR AND COOLING WATER SYSTEM FAILURES ON PRESSURIZED THERMAL SHOCK EVENT SEQUENCES

Art McBride Science Applications, Inc.

Systems Analysis Division Prepared for D. L. Selby-Oak Ridge National Laboratory e.a.

By acceptance of this article, the publisher or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty free , '

ncens. in .no to .ny copyrighi covering the article.

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Research sponsored by Nuclear Regulatory Commission (Fin #B0468, USDOE Interagency Agreement #41 33 55 04 1) for the Union Carbide Corporation-under Contract #W-7405-eng-26 with~the U.S.. Department of Energy.

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TABLE OF CONTENTS RAFy Section .P.AES.

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . ..... iv LIST OF FIGURES . . . . . . . . .. . . . . . . . . . . . . . . ..... iv ACRONYM DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . ..... v

1.0 INTRODUCTION

. . . . . . . . . . . . . . . . . . . . . . . ..... 1 2.0

SUMMARY

OF RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . 3

, . . . . . .. . . . . . . . . . _ . . . . . . ..... 5 30 METHODOLOGY 4.0 IDENTIFICATION, SELECTION AND DESCRIPTION OF SYSTEMS AND COMPONENTS AFFECTING PTS SEQUENCES . . . . . . . . . . . . ..... 6 4.1 Selection of Systems and Components Affecting PTS Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 l

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4.2 Description of Systems' and Components' Responses to Support Systems Failures . . . . . . . . . . . . . . ..... 6 4.2.1 Reactor Trip . . . . . . . . . . . . . . . . . . . . . . 9 4.2.2 Atmospheric Dump and Turbine Bypass Valves . . . . . . . 11 4.2 3 Turbine Trip System . . . . . . . . . . . . . ..... 11

4.2.4 Pressurizer Relief Yalve . . . . . . . . . . . . . . . . 12 4.2.5 RCP Shaft Seals . . . . . . . . . . . . . . . ..... 13 4.2.6 Main Steam Isolation Yalves . . . . . . . . . . . . .

14 14 4.2.7 Main Feedwater Regulating Valves . . . . . . . . . . . .

4.2.8 Main Feedwater Bypass Valves . . . . . . . . . . . . . . 16 f 4.2 9 Main Feedwater Isolation Yalves . .

- . . . . ... . . . . -16 4.2.10 Main Feedwater Pump Trip . . ..... . . . . . . . . . . . 17

- 4.2.11 Auxiliary Feedwater Systes . . . . . . . . . . . . . ._. 17 ii O

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i p TABLE OF CONTENTS (Continued)

Section h 4.2.12 High Pressure Safety Injection . . . . . . . . . . . . . 19 4.2.13 Chemical and volume Control System . . . . ... .. . . 20 4.3 Summary of Failure Mode Responses to Support System Failures ........................... 22 431 Responses to Electric Tower System Failures . .. . . . 22 4.3.2 Responses to Compressed Air System Failures ..... . 26

( 4.3 3 Responses to Cooling Water System Failures . . . . . . . 26

. 5.0 COM10N CAUSE SUPPORT SYSTEM FAILURES . . . . . .......... . 32 51 Calvert Cliffs support Systems Designs . ....... .... 32 5 1.1 Flectrical Power Systems . . . . . . . . . . . . . . . . 32 5.1.2 Compressed Air Systems . ............... . 35 5.1 3 Cooling Water Systems .......... ....... 37 5.2 Effects of Support Systems Failure Modes . .......... 38 5.2.1 Identification of Support System Failure Modes . .. . . . 39-5.2.2 Effects of Support Systems Failure Modes on PTS Sequences .......... ......... .. 45 66

6.0 REFERENCES

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LIST OF TABLES 2aa 2m1 RAFT Im 1 Systems and Components Identified in PTS Event Sequence Initiating Events . . . . . . . . . . . . . . . . . . . . . . . 7 2 Systems and Components Identified in PTS Event Sequence Branch Events . . . . . . . . . . . . . . . . . . . . . . . . . 8 3 Summary of System / Component Failure Modes . . . . . . . . . . . 10 4 Summary of System / Component Failure Modes in Response to Electric Power System Failures . . . . . . . . . . . . . . . 23 5 Summary of System / Component Failure Modes in Response to Compressed Air System Failures . . . . . . . . . . . . . . . 27 6 Summary of System / Component Failure Modes in Response e to Cooling Water Failures . . . . . . . . . . . . . . . . . . . 29 7 Initiating Support System Failure Modes . . . . . . . . . . . . 40 8 Interactive Failure Modes Among Support Systems . . . . . . . . 42 t

I 9 Support Systems Initiating Failures . . . . . . . . . . . . . . 43 10 Response of Identified Plant Systems and Components to Postulated Support Systen Failures . . . ... . . . . . . . . 46 11 Impact of Support Systems Failures on PTS Sequences . . . . . . 53 i

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LIST or rIonas t

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.r 1 Simplified Schematio of Calvert Cliffs Unit 1 AC Power Distribution . . . ............. ........33 l'

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i ACRORYM DEFINITIONS .

Aeronym Definition ADV Atmospheric Dump Valve AFAS Auxiliary Feedwater Actuation System AFS Auxiliary Feedwater System AFW Auxiliary Feedwater BG&E Baltimore Gas and Electric Co.

CCW Component Cooling Water q

CEDM Control Element Drive Mechanisms CSAS Containment Spray Actuation Signal CV Control Valve CVCS Chemical and Volume Control System EHC Electro-Hydraulic Control (Turbine Control)

, ERY Designation for Pressurizer Relief Yalves

, (ER7-402 and ER7-404)

ESFAS Engineered Safety Features Actuation Systen FSAR Final Safety Analysis Report

'. High Pressure Safety Injection

HPSI RfAC Heating, Ventilating and Air Conditioning I/P Current to Pneumatic (Transducer)

( KVAC Thousand Volta, Alternating Current LOCA Loss of Coolant Accident i LPSI Low Pressure Safety Injection MCC Motor Control Center MFIY Main Feedwater Isolation Yalve MFW Main Feedwater N07 Motor Operated Yalve t

e ACR0EYM DEFINITI0EiS (Continued)

Acronym Definition MSIV Main Steam Isolation Valve MT Mechanical Trip MTSV Haster Trip Solenoid Valve ORNL Oak Ridge National Laboratory PR7 Pressurizer Relief Valve I PTS Pressurized Thermal Shock i RC Reactor Coolant RCP or RC Pump Reactor Coolant Pump RCS Reactor Coolant System

,~ SCFM Standard Cubic Faet per Minute SG Steam Generator SGIS Steam Generator Isolation Signal SIAS Safety Injection Actuation Signal i

i SLB Steam Line Breaks TBf Turbine Bypass Valve YAC Yolts, Alternating Current ,

VCT Yolume Control Tank f--

VDC Yolts, Direct Current

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1.0 INTRODUCTION

4 An analysis of the Calvert Cliffs Nuclear Station is being performed by the Oak Ridge National Laboratory (ORNL) to assess the potential risk due to ;

Pressurized Thermal Shock (PTS). The PTS analysis consists of identifying and

, estimating the frequency of sequences of events leading to low temperature, high pressure conditions at the reactor vessel wall, estimating the thermal response to the reactor vessel wall to these conditions, and calculating the conditional probability of a through wall crack for the sequences of interest.

These analysis elements are ocabined to assess the overall risk due to PTS.

i I This report describes the response of key plant systems identified in PTS sequences to failures of required support systems. Support system failures can be of importance due to the potential for single support system failures

, I resulting in multiple failures of the systems comprising the PTS event sequences. Based on a review of the Calvert Cliffs systems' designs, the f, electric power, compressed air and cooling water systems have been identified as required support systems for the systems and associated control instrumentation comprising the Calvert Cliffs PTS event tree sequences.

1 i

In addition to these support systems, the necessity of the plant's heating,

ventilating and air conditioning (MAC) systems for continued plant operation was recognized. However, the effect of WAC failures on equipment performance is expected to be long ters with respect to the effects of failures of the l,, other identified support systems. In general, the effects of HVAC failures 1 '

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and severe equipment operating environments is considered to be beyond the

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scope of this analysis.

The electric power, compressed air and cooling water support systems have been

, j evaluated to specify potentially PIS adverse responses of the systems and j functions identified in the FTS event tree sequences to support system

. failure.

i The major results of the support system failure analysis are summarized in Section 2. In Section 3, the methodology used to identify and analyse the plant systems and components responses to support systems failures is i

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DRAFT described. Using this methodology, systems and components which may affect PTS sequences are identified and described in Section 4. The common cause failures adverse to PTS which could occur in response to support system failures are discussed in Section 5 3

The identification of support systems failures which could lead to multiple adverse PTS sequence events is the first step in evaluating their impact.

Although not assessed in this analysis, the frequency of each support system failure and associated events (including the effects of operator intervention) must be calculated and compared to the frequencies of equivalent sequences occurring independently to evaluate the overall impact of support system failures on the PTS sequences.

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2.0 Smet&RY OF RESULT 3 DRfp j ,.

f' The Calvert Cliffs systems and components identified in the PTS event trees 1'

have been analyzed to determine the effects of postulated initiating failures

[. of the electric power,. compressed air and cooling water support systems.

i Support system failure modes were selected based on two criteria: the failure

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node resulted in at least one system or component response adverse to PTS and

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the failure mode could be initiated by a single postulated failure in one of the pousible support system configurations (i.e., including non-randon f multiplo failures). Based on the identified support system failure modes, the responses of all systems and components identified from the PTS event trees to

{, each failure mode were analyzed to determine whether multiple, coupled responses existed.

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Four support system failure modes were identified which would result in

' multiple, coupled responses adverse to PTS:

'. 1. Failure of Vital Buses YO1 and YO2: This double vital bus

- failure would result in opening the pressurizer relief valves j

(an isolatable small LOCA) and delay of the initiation of High Pressure Safety Injection (HPSI) until manually initiated or r*

j' either of the vital buses was recovered.

l 2. Failure of 4 KVAC Buses 11 and 12: Failure of these two buses l l would result in termination of the cooling water flow to the RC-

! e i i Pump seals (RC pumps assumed to be running) and deenergizing the standby HPSI systen.- Failure of the operator to trip the

... RC pumps-under these conditions would lead to RC pump seal failure (a small LOCA) and subsequent delayed initiation of the HPSI.

3 Failure of Motor Control Centers (MCC's) 104R and 114R

I Failure of MCC's 104R and 114R would result in runback of the sain feedwater pumps, loss of the instrument air and plant- air compressors' control power (120 VAC buses YO9 and I10) and deenergizing the HPSI injection valve motors. The eventual.

depressurization of the instrument air pressure would result in

., isolation of cooling water to the RC pump seals. Failure of the operator to trip the RC pumps under these conditions would

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lead to RC pump seal failure and subsequent delayed initiation of the HPSI. Due to the probable early reactor and turbine

- trip resulting from the feedwater pump runback, the main L. feedwater regulating valves are expected to close prior to c.

instrument air depressurization. However, the feedwater bypass valves will open fully.

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4. Instrument Air Header Failure: A passive failure of the main f instrument air header results in freezing the main feedwater regulating valves in position (open) and isolating cooling water flow to the RC pump seals. Failure of the operator to

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trip the RC pumps would result in a coupled main feedwater overfeed of both steam generators and an eventual small LOCA.

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The four support system failure modes identified are low probability events.

! In addition, failure of the operator to take available remedial actions is required, in each case, to result in a transient adverse to PTS. The combined frequency of the support system failure and operator action failure should be determined and compared to the uncoupled PTS event tree failure frequencies to evaluate to potential impact on PTS.

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r- In addition to the coupled events described above, support system failures I

i- were identified as potential causes of single system and component failures

. adverse to PTS. These failures, and the coupled events, . are listed in Tables 10 and 11 and discussed in Section 5.

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30 METHODOLOGY j' The objective of this study is to identify common cause failures which result

l from failures in the electric power, compressed air or cooling water systems

,- and affect PTS sequence quantification.

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L The methodology used in this study is outlined below:

1. Identify plant systems and components potentially affecting the PTS event sequences.

[ 2. Identify the specific failure modes of these systems and components in response to electric power, compressed air or cooling water system failures.

3 Identify the failure modes which are " PTS Adverse" (i.e., make

,. the pressure-temperature response of the reactor coolant system i more severe from a PTS standpoint).

4. Identify failures in the electric power, compressed air or cooling water systems which result in one or more PTS adverse failure modes, t'

i Using the methodology outlined above, the common cause effects of support systems f ailure on PTS sequences can be evaluated. It should be noted that

> the results obtained are not necessarily applicable to non-PTS accident

. r sequences and have not considered the effects of common cause initiators such I

\ as operator errors, severe operating environments, severe natural phenomena or sabotage.

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4.0 IDENTIFICATION, SELECTION AED DESCRIPTION OF SYSTEMS AMD COMPONENTS AFFECTIEG PTS SEQUENCES

. . As discussed in Section 3, the initial tasks of performing the PTS common cause failure analysis involve the selection of systems and components

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potentially affecting PTS and defining their failure modes in response to support systems failures. In Section 4.1, the selection of Calvert Cliffs' i~ systems and components utilizing the previously developed PTS event sequences i

is discussed. The designs, interfaces and failure modes of the systems and components are discussed in Section 4.2. The failure modes of the systems and components in response to support systems failures are summarized in Section

. .3

,.. 4.1 SELECTION OF SYSTEMS AND COMPONENTS AFFECTING PTS SEQUENCES

[ The specific purpose of performing the common cause failure analysis is to determine whether one or more individual

branch events" of the PTS event sequences may occur due to a failure of the support systems. The principal source of information to select the systems and components affecting PTS 4 sequencet - +5e event sequence diagrams.1 The information contained in the

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event n 9 Jiagrams was supplemented by associated material used to

. develo, 11 uefine the event sequences.2 l

L The systems and components identified in the PTS event sequences are listed in I

Tables 1 and 2. Each system and component identified was evaluated briefly to determine whether a potential failure due to a support system failure was possible. Where no consequential failure was possible, the event need not be~

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considered further.3 The systems and components identified in the remaining

[ events are analyzed further as -discussed in Section 4.2.

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4.2 DESCRIPTION

OF SYSTEMS' AND COMPONENTS' RESPONSES TO SUPPORT SYSTEMS j

I. FAILURES

! The designs of systems and components identified in Tables 1 and 2 for which a support system interaction was possible were evaluated to determine the particular response to support systea failures. The evaluation of systems' and components' responses typically was performed as follows:

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l TABLE 1. SYSTEMS AND COMPONENTS IDENTIFIED l IN PTS ETENT SEQUENCE INITIATING EYENTS r

Systems and Components Identified Potential Initiation Due to in Sequence Initiating Events Support System Failure

1 4.

Reactor Trip (Reactor Protection System) Yes Y

Steam Line Breaks (SLB)

Small Breaks e

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Piping Failure No Safety Valves Fail Open No

... Atmospheric Dump Valves Fail Open Yes

,~ Turbine Bypass Valves Fail Open Yes k Large Breaks Piping Failure No f

i Failure to Trip Turbine Yes L.

Loss of Coolant Accidents (LOCA)

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Small LOCA Safety Valves Fail Open No E- Pressurizer Relief Valves Fail Open Yes Reactor Coolant Pump Shaft Seal Failures Yes Steam Generator Tube Rupture No 1

Isolable LOCA Other Than Pressurizer No l Relief Yalves A Piping Failure No Medium and Large LOCA's No j

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' Passive failure events, such as a pipe break, were not considered to occur due to a support system failure. At this level of screening, all "non-passive" events were considered to have a potential for an interaction.

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TABLE 2. SYSTEMS AND COMPONENTS IDENTIFIED.

IN PTS EVENT SEQUENCE BNANCH EVENTS t.

Systems and Components Identified Potential Response To e- in Sequence Branch Events Support System Failure i

Main Steam System

, Turbine Trip Yes Atmospheric Dump Valves Yes j Turbine Bypass Valves Yes ,

Main Steam Isolation Valves Yes 1

' J- Main Feedwater (MW) System MFW Control Valves Yes f

i MW Bypass Valves Yes MFW Isolation Valves Yes MW Pump Trip Yes

-b Auxiliary Feedwater (AN) System

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AW Control Valves Yes i i AN Isolation Valves Yes

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, High Pressure Safety Injection Systea Yes I

Chemical and Volume Control System Yes

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1. The components of systems potentially affecting system performance due to support system failures (e.g., automatic p valves, pump actors, etc.) were identified from system design documentation.

2. The support functions and supplying systems (e.g., 125 VDC Bus

[ 11) required for the operation of the identified components and their control instrumentation circuits were identified from available design documentation or requested from Baltimore Gas and Electric (BG&E) personnel.

j 3 Failures of identified support system components (e.g., bus at

0 volts, instrument air pressure at 0 psig, etc.) were

- postulated for each of the systems and components affecting PTS i sequences. The responses of the systems and components were identified from available design documentation or requested

{ from BG&E personnel.

i h The designs of the identified systems and components relating to their failure S.

modes in response to support systems failures are discussed below. Table 3 I

summarizes the responses to assumed complete failures of support functions.4 1

The specific failure modes of the support systems are discussed in Section 5.

. The systems and components discussed in Section 4 are described in the Calvert Cliffs Nuclear Power Plants 1 and 2 Updated Final Safety Analysis Report (FSAR). The FSAR information was supplemented by detailed design information provided by Baltimore Gas and Electric Co. (BG&E) as referenced throughout this report.

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! 4.2.1 Reactor Trin

\ The reactor is tripped by deenergizing each of the control element drive mechanisms (CEDM). The drive mechanisms are energized from either 480 YAC bus

... 1 or 2 via actor generator sets. The reactor is tripped by opening either trip circuit breaker in each of the four 240 YAC buses from the two actor

. generator sets.

The trip breakers open when the power from associated 125 YDC buses to their undervoltage coils is interrupted or is supplied to their. shunt coils. These

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i TABLE 3. semesaRY OF SYSTEN/CCIWOMENT FAILURE BEDES ;

i Potential Failure Mode of Svatem/P - nent Due to Support System Failure Instrument Instrument Electric Motive Electric Air Failure Cooling Water

> Power Failure Pouer Failure (Supply Piping Failure (Loss of ,

System / Component (Buaea at Zero Volta) (Buses at Zero Volta) Depressurized) Cooling Water Flow) '

6 ,

Reactor Trip Tripped Tripped N/A N/A Atmospheric Dump Valves Closed N/A Closed N/A Turbine Bypass Valves Closed N/A Closed N/A Turbine Trip Trip N/A N/A Eventual Trip ;

Pressuriser Relier Valves Opeg Clopd N/A N/A Reactor Coolant Pump (RCP) N/A N/A N/A Eventual Failure i Shatt Seals limin Steam Isolation Valvea Open N/A N/A N/A Main Feeduater (BWW) As Is3 ufa A 1. gfa

Regulating Valves - t g IWW Bypass Valves Closed N/A Open N/A ilWW Isolation Valves Open Open N/A N/A

.,0fW Pump Trip .

Fails to Trip Trip N/A Eventual Trip Auxiliary Feedwater ( AFW)

Electric Motor Driven Pump Off Off N/A High Speed N/A*

N/A

- AFW Steam Turbine Driven Pumps Off N/A AFW Control Valves closed N/A Open5 N/A AFW Isolation Valves Open N/A Open6 N/A

]; High Pressure Safety Injection Off Off N/A Eventual Failure j System -

Chemical and Volume Control Net Injection Off Net Injection Recirculation Mode l System I

IFailure of electric power to RCP motors or pump trip may prevent or delay seal failure on loss of cooling water.

2go,, of. Instrument Air or instrument power may lead to loss of cooling water to RCP seals.

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% oss of electric power to Instrument Air Solenoid valves leads to loss of Instrument Air to MW Control Valves.

No External Cooling Water System Required.

I l 5 Backup Accumulators to Compressed Air System Available.

b loss of cooling water to the CEDM can result in dropped rods and possibly eventual reactor trip.

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- actions are initiated by deenergi=ing trip circuit breaker relays normally supplied power from the 120 VAC vital instrument buses.

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The trip logic is arranged such that failure of any one 120 VAC, 125 VDC, 480 VAC bus or either motor-generator set will not result in reactor trip.

However, failure of any two 120 VAC buses, both 480 V AC buses or both motor ,

generator sets will trip the plant. Failure of any three or certain I combinations of two 125 VDC buses also will result in reactor trip.5 The CEDM's are cooled by the Component Cooling Water (CCW) systes.6 Cooling I

'.. water is required to maintain electric circuitry within its operating temperature range. Failure of the cooling water supply eventually will result in-degradation of the circuitry and release of the individual control rods

! (rod drop).

( 4.2.2 A*=ascher ie Dunn (ADY) and Turbine Evenss Valves (TB7) i Four TBY and two ADY are provided to release steam from the main steam line to k the condenser or atmosphere, respectively, following main turbine trip. These valves are pneumatically operated and designed to close upon loss of pneumatic i pressure.780

) Following turbine trip, the TBY and ADY are ' quick opened" by energizing _

solenoid valves via 125 VDC bus 11 which open to pneumatically pressurize the valve operators. The turbine trip relay (IKT-1194-1) which energizes these k

solenoids requires power from EHC Cabinet T11 to open the TBY and ADY.0

" The TBY and ADY any also be opened by manual or automatic signals pressurizing <

the valve-operators via I/P transducers. The manual control st.ation, reactor t i

! average temperature (Tav) or steam pressure signals require 120 VAC power from -

I buses YO1, YO2, T09 and/or T10 to open the TBY or ADY.0' ,

l 1 .

! 4.2 3 Turbine Trin system Turbine trip involves closure of the two main stop valves and two main control valves isolating steam from the high pressure turbine.9 Closure of the stop

' and control valves results from doenergizing the master trip ~ solenoid valves

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(MT57-A, MTSV-B) or energizing the mechanical trip solenoid (MT-5). During l

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- power operation the master trip solenoid valves are energized, from Turbine EHC Cabinet T11.10 EHC Cabinet T11 is energized from 120 V AC bus T09 or a p- permanent magnet generator operated off the turbine shaft.14 ,

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s. j Individual turbine trip conditions result in the Master Trip Bus being energized from T11. Some trip conditions energize the bus directly; others indirectly by energizing 125 VDC relays from 125 VDC bus 11. Energizing the ,

master trip bus energizes the master trip relays which doenergize the master trip solenoid valves.10 i i

" Loss of T11 directly deenergizes the master trip solenoids resulting in turbine trip. Loss of the 125 VDC bus 11 deenergizes a relay which will

. energize the master trip bus after a 30 second time delay.10

{ Loss of vital bus YO2 defeats the " reactor tripped" signal to the turbine trip logic.5 However, following reactor trip, turbine speed cannot be maintained f

and turbine is expected to trip on other turbine or generator parameters such

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4 as low speed.10 s

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Although loss of cooling water does not affect turbine trip directly, the I ' service water system does provide cooling water to many turbine, generator and feedwater systes components. Loss of service water is expected to result in eventual turbine trip.6 5

4.2.4 Pre ==m'imer Relief Yalva (PNV)

The two pressurizer relief valves (PHY) mounted on the pressuriser are designed to open at the high pressurizer pressure trip setpoint to prevent or I minimize the lifting of pressurizer code safety valves. PRV's ERV-402 and 404 ,

i h are opened by energizing their solenoids from 480 VAC actor control centers (MCC) 114R and 104R, respectively. Power is applied by closing contacts in the 480 VAC supply. The contacts are closed by energizing scienoids powered

! from 120 VAC auxiliary circuits supplied from the associated 480 VAC bus and 125 VDC bus 21.11,14 4

1 The RCS pressurizer pressure signals used to open the PRY's (energize the control relays) are obtained from the reactor protective system (RPS).

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Auxiliary pressurizer pressure trip-eenacts from the M8S are arranged in a 2 of 4 logic. When any two of the dux111sry coraticts' trip,' indicating high pressurizer pressure, the PR7 control' relaye wil'1 be jeergized and the PRV's opened. . When the pressurizer pressuro drogs below the setpoint the control relays are deenergized by the trip cont' acts and the PRY'a close.5 Failure of either the 480 VAC or the 125 VDC buses will' result in the PRV's f' closing or remaining closed. . Due to the 2 of.4. logic, failure of any one of the four 120 YAC vital buses supplying the RFS'will neither' ooen the PRY nor preYor.c them from being opened due to high presadrizer pressure. Failure of j, le any two vital buses, however, will result in both PRV's opening and remaining s

open until manually ^elosed from the cont?ol room or one or both vital buses 1

are reenergized.11,5 -

1 e 4.2.5 RCP ShaftM eals .

i i The reactor coolant pressure boundaries between the RCS and the,RCP shafts are '

l T maintained by four n'echanical face seals on e.:cE RCP shaf t. The seals are

(' located above the thermal barrier. These of the seals a?e rated for full RCS 4 pressure .and the fourth ~ is a low pressure vapor seal.12 j ,

t

(

For proper operation, the shaf t seal's requ" ire .a continuous small flow of l l_

coolant to lubricate and cool the seals and Lto equaliza the pressure drop across them. The coolant is reduced in temperature in integral pump heat exchangers prior to flowing past the seals. Irde heat exchangers are cooled by water from the CCW systbe. After the coolant flows past the three seals it is ,

directed to the Chemical- and Volume Control f.'9ystem (CYCS)Jor diverted to the I containment sump.12,6 ,

f

l. Failure of the CCW flev to the puas heat exchanger's will result in higher temperature coolant flowing past the . seals and inducing high thermal stresses in the seal faces. Atter five minut'es et operation seal damage could occur.12 However, pump operation without CCW flow for .a longer period of time is I expected before complete failure of the seals would occur. If the RCP were i tripped prior to seal damage, seal failure would.te delayed er prevented.

P 13 ,

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T 4.2.6 Main steam isointion valves (MsrV) '

The MSIV's (CV-4043 and cV-4048) are designed to isolate tho containment and r limit the release of steam from the steam generators following main steam line l break accidents. One MSIV is located downstream of the main steam safety valves outside the containment in the steam line from each steam generator.13 L

Each MSIV is closed by releasing hydraulic fluid from pressurized accumulators into the upper chamber of the valve's hydraulic actuator and releasing fluid from the lower chamber. The accumulators are designed to close the valve and hold it closed for at least one hour without external motive power

{

requirements. The hydraulic fluid is released to the actuator by opening either of two solenoid valves in the hydraulic flowpath. Either of the two

{ separate solenoid valves are opened to release the fluid from the lower chamber of the actuator.13 I

Each of the four pairs of solenoid valves on the two MSIV's hydraulic circuits are energized to open upon Channel A and Channel B steam generator isolation (SGIS) or Containment Spray Actuation signals (CSAS) from the ESFAS (cicaing l' the MSIV's). Since the two solenoid valves in each pair are redundant, failure of one vital bus (120 VAC bus YO1 (ZA) or' YO2 (ZB) or associated 125 l

t-VDC buses 11 or 21 will not prevent closure of either MSIY on demand. Failure I

a of buses YO1 and YO2 or 125 VDC buses 11 and 12 would prevent closure of both MSIT 's.5,14 i

[ L.

4.2.7 Main Feedvatar* Rennistine Valves

~

The main feedwater flowrate to each steam generator is controlled by a w.

pneumatically operated regulating valve in response to feedwater demand signals. Flow to steam generators 11 and 12 is controlled by regulating f! The feedwater demand signal for each valves CV-1111 and 1121, ' respectively.

regulating valve is developed based on steam generator steam and feedwater flowrate and downconer liquid level. The normal demand signals are overridden .

.by turbine tripped signals which close both regulat ngi va ves.

l The pneumatic p

supply to the regulating valves from the positioners is isolated automatically l by solenoid valves upon low pneumatic supply pressure or loss of power to the r control instrumentation. Isolation of the pneumatic supply holds the regulating valve in position.15,16 14

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r' 1 i t, .

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t Each valve is opened and closed by admitting pressurized air below or above the pneumatic actuator piston respectively. The air is directed by a c-( transducer / positioner responding to the feedwater demand signal. Steam generator downcomer level is monitored by four measurement channels and the signals combined in a two of four logic. Two or more high steam generator 4

i

,l .

level signals cause turbine trip which results in the feedwater regulating valves being closed.13 fr, i- The regulating valves are designed to remain in position upon loss of pneumatic pressure or control power. A pneumatic supply. pressure less than 70

- psig to one of the regulating valves' transducers will be detected and results in automatic closure of the regulating valve's three pneumatic supply solenoid valves. This action holds the regulating valve in its existing position.14,13 3

1 The control instrumentation positioning the regulating valves is powered

~

4 through 120 VAC panels C35 and C36'for valves CV-1111 and CV-1121

~

respectively. Panel C35 is supplied power via bus YO1 and an automatically i~ transferred backup bus YO9. . Panel C36 is powered via buses Yo2 and Y10.17 -

t Failure of panels C35 or C36 will result in the pneumatic supply' isolation valves being deenergized a'nd closing, thus holding the regulating valves in 7- position.16 LI_ '

f s

The -high SG 1evel ' input signals to the turbine" trip instrumentation.are powered from the vital 120 YAC buses. The high level signals are configured

. in' a 2 of 4 logic. A separate high. steam generator level signal is developed for each steam generator and combined with :the reactor tripped signal in a 1

[~ of 3 logic'to develop a. turbine trip signal. The 2' of 4 and 1 of 3 ESFAS U logic is powered from vital bus YO2 (ZB).5 I

Turbine trip' will result in Iontact signals being sent to tho' feedwater -

regulating valve control? instrumentation. These relays are ' powered from 24 l- l- VDC panel T11 (EHC Cabinet).10, l

t-

! Failure of vital bus T02 (ZB) will delay turbine trip and feedwater runback -

i 1.

i depending on the particular plant conditions.- Assuming a reactor trip, the

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turbine . is expected to trip on other resultpq parameters su.ch as underspeed.

Failure of panel T11 will cause turbine trip as previously discussed. In r either case, the normal feedwater controls will reduce feedwater flowrate t

s. directly in response to high steam generator level.

i 4 a 4.2.8 Main Feedvater Byeasa Valves i

h Feedwater bypass valves CV-1105 and 1106 are designed to regulate the g.,

i feedwater flow to steam generators 11 and 12, respectively, at low level :

conditions. During power operation the bypass valves are normally closed. At f low power conditions, the operator normally will manually position the bypass valves to regulate steam generator level. An automatic level control circuit j

also is available to the operator.13'14

[

Upon turbine trip, the main regulating valves will be closed and a signal 4 I, generated to open the bypass valve. The valves are positioned by the control i circuitry to maintain approximately 55 of the flowrate required at 1005 power.

t The bypass v.tives continue to maintain this flowrate until manually controlled l {

by the operator.13

( The control instrumentation for valves C7-1105 and 1106 is' powered from 120 VAC panels C35 and C36 respectively. Failure of these panels will produce a I zero amp signal' to the associated valve transducer and result in valve closure.15 Failure of T11 (EHC Cabinet) will result in the bypass valves t

L . remaining . closed and the main regulating valves modulating to control steaa

. generator level as previously discussed. Loss of instrument air to the bypass l

= valves will result in the valves opening.15 i.

l l

i 4.2.9 M=4n Feedvater Isolation Valves

-- p .

Main feedwater isolation valves M07-4516 and 4517 are designed to close and terminate main and bypass feedwater flow to steaa generators 11 and 12,

- respectively. The isolation ~ valves automatically close on a steam generator isolation signal (SGIS) or containment spray actuation signal (CSAS) from the ESFAS and may be manually closed by the operator.18 4

i 16 1 .

~

1 L, .

" The valve motors for MOV-4516 and 4517 and associated switchgear are powered from 480 V AC MCC-114R and 104R, respectively. MOV-4516 and 4517 each are c.

closed automat'ically by signals from ESFAS actuation channels A and B.18:14 i

During normal operation the isolation valves are open. Failure of the associated MCC or both ESFAS channel vital power buses will result in the j

valve remaining open. However, failure of the ESFAS signals will not prevent manual closure provided the 480 VAC power is ava11able.10 14 i.

, { 4.2.10 Main Feedvatar Pu=n Trin

!. l ' ESFAS steam generator isolation or containment spray actuation signals, in r

addition to closing the MSIV's and MFIV's, will trip the main feedwater,

' condensate and feedwater heater drain pumps. The pump trip signals are arranged such that the Channel A or Channel B signals will trip the three sets

, j of feedwater pumps. Failure of either channel power supply,120 VAC vital bus YO1 or T02, will not prevent pump trip on demand. Failure of 125 VDC bus 11 will' prevent tripping pump 11 and failure of 125 VDC bus 21 will prevent tripping pump 12. Failure of both vital buses will prevent steam generator

! isolation.14 Although the pump trips require vital power, the main feedwater and condensate booster pumps will trip if the normal power sources to the motor switchgear fail.14

!I In addition to automatic main feedwater pump trip, the speed of the main f - feedwater pump is regulated to maintain a constant pressure drop across the

{-

main feedwater regulating valves.13 Failure of the 120 VAC power supply to this instrumentation, bus YO9, results in-the pump speed being reduced to ,

idle, significantly reducing or terminating train feedwater flow.14 I Although loss of cooling water will not result directly. in a pump trip, loss of service water cooling to the pumpa' lube oil coolers will require eventual manual trip on high oil temperature.6,19 4.2.11 aurfitar v Feedvater system The auxiliary feedwater system is designed to provide feedwater to the steam generators-if the main feedwater system is incapable of asintaining a miniaua l steam generator level.

17 l

1 s

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f

.s The auxiliary feedwater system consists of two steam turbine driven, 700 gpa i P pumps and one motor driven 400 gpa pump. The discharge from the turbine I

- driven pumps are combined in a common header and then directed in separate

' . headers to the two steam generators. A pneumatic control valve in each steam

\

i1 generator header controls the flow to 200 spa. Two pneumatic isolation valves in each header are provided to isolate the flow to a steam generator upon low s ,

steam generator pressure via the ESFAS steam generator isolation logic. The flow from the single motor driven pump is directed to the two steam generators in separate headers each with a pneumatic control valve and two pneumatic

- .f - isolation valves. .As designed, the two pumps inject 800 spa to the two steam generators through four headers. The source of water to the three pumps is I condensate storage tank 12.13,20 b The four steam generator level signals from each steam generator are combined in the ESFAS auxiliary feedwater actuation system (AFAS) in a 2 of 4 logic producing Channel A and Channel B low stesa generator level actuation signals.

The Channel A signals start the actor driven pump, powered from 4 KVAC bus 11, I and open pneumatic steam supply valve C7-4070 from steam generator 11. The channel B signal opens steam supply valve CY-4071 from steam generator 12.

Valves CV-4070 and CV-4071 require 125 VDC power from DC buses 11 and 12, respectively, to open.14 The steam from either steam generator can drive either auxiliary feedwater pump . turbine. How ever, the steam supply to

{

L auxiliary feedwater pump turbine 12 is manually isolated to prevent automatic pump start. Downstream of. the steam supply valves, pneumatically operated turbine regulating valves are positioned to control turbine speed. The control circuitry is powered by vital bus Y02. Failure of the vital bus will result in maximum turbine speed.7 Following an AFAS initiation, one steam turbine driven and one motor driven pump will be automatically started.20,7 The auxiliary feedwater flowrate from the motor driven pump to each steam generator is controlled separately to 200 spa 'with a pneumatic control valve.

The flowrate control instrumentation in the motor driven pump flowpaths to the two steam generators is powered' from 120 VAC vital bus T01 -(ZA). . The flowrate from the steam turbine driven pump is controlled separately.in a similar manner with the flowrate control instrumentation powered from 120 7AC vital .

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i 18

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P bus YO2. In each case, loss of power will result in the associated Train A or Train B control valves closing.20 p,

i. Two pneumatic isolation valves are provided in each of the four flowpaths to the two steam generators. One of the isolation valves in each flowpath is y closed by an ESFAS Channel A SGIS signal and the other by a Channel B signal in the event of a steam line break. The ESFAS isolates a steam generator's p-.

auxiliary feedwater flow when its steam pressure is greater than 100 psi lower than the other steam generator's pressure.20 The twelve valves in the discharge lines and two valves in the steam supply lines are pneumatically operated. Each of these valves are designed to open on loss of instrument air. However, two accumulators are provided to position

. the feedwater control and isolation valves in the event of a loss of the instrumentation air supply. One accumulator supplies the feedwater control valve in the actor driven pump train and the second supplies the control valves in the steam turbine driven pump train. Each accuculator supplies one f of the two isolation valves in each discharge flowpath and one of the two i steam supply valves.20 The turbine speed regulating valves also are designed to open on loss of i pneumatic pressure.I However, these valves are not supplied by the accumulators.20 i

L The auxiliary feedwater pumps are designed to operate without external cooling water systems.20 4.2.12 N4eh Pressm e M aty Infaction The High Pressure Safety Injection (HPSI) system is designed to inject borated

water from the refueling water storage tank (RWT) to the reactor coolant system in the event of a loss of coolant accident (LOCA).

Borated water from the RWT flows to the three HPSI pumps in two headers which also supply . the LPSI and CS pumps. HPSI pumps 11 and 12 are supplied from one

header and pump 13 from the other. The three HPSI pumps feed a common header which supplies the main and auxiliary injection header. The main and 19

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auxiliary headers each inject into the four reactor coolant system inlet pipes t I through separate injection paths.21

t Electrically, the system is divided into two trains, ZA and ZB, each providing 4 KV AC, 480 V AC and 120 V AC power. HPSI pump 11 and the auxiliary header injectica valves are supplied Train ZA power (4 KV AC Unit Bus 11 and 480 V AC

)

MCC 114R), HPSI pump 12 and the main , header injection valves train ZB power (4 KYAC bus 14 and 480 VAC MCC 104R). HPSI pump 13 any be electrically connected to ZA or ZB power.21 The HPSI pump actor circuit breakers, in addition, require 125 VDC power from the associated 125 VDC bus 11 (ZA) or 125 VDC bus 12 (ZB).

1 l The HPSI is initiated by the Train A and B ESFAS safety injection action signals (SIAS) upon a coincidence of 2 of 4 low pressurizer pressure or I containment spray actuation signals. Train A signals start HPSI pump 11 and i open the auxiliary and main header injection valves. Train B signals start HPSI pump 12 and open the injection valves.5 HPSI pump 13 is automatically started if the HPSI pump (11 or 12) associated with the HPSI pump 13 Power

[ source fails to start (breaker fails to close).5

\

In addition to electric power, the HPSI pumps require cooling water from the e

Component Cooling Water (CCW) System. Cooling water for the HPSI pumps'

! (

bearing and seal coolers is provided from either CCW pump via either CCW heat e

exchanger.6,21 4.2.13 N =temi mad val - control svatam The Chemical and Volume Control System (CVCS) is designed to -remove, purity

[ and replace reactor coolant at a controlled floweste to maintain pressurizer I level during reactor operation. The system also is used to inject chemicals

. to control reactor coolant chemistry, collect and reinject the controlled bleed-off from the RC pump seals and provide high pressure injection of concentrated boric acid following accidents.22 The flowrate of letdown reactor coolant is controlled by the letdown flow

' control valve based on pressuriser level. The reactor coolant is cooled in the letdown heat exchanger and is passed through filters and ion exchangers.

l 20 l

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The flow from the ion exchanger to the volume control tank (VCT) is controlled f7-

, i. by a three-way valve based on volume control tank level. Normally the flow is

- routed to the VCT. When boric acid or domineralized water is added to the VCT for reactor coolant chemistry control, the excess flow from the ion exchangers is diverted to the liquid waste processing systes.22 I F i

,4 l

The coolant in the VCT is injected into the reactor coolant system by three t

positive displacement charging pumps. One pump is normally in operation. The

{- second and third pump are sequenced on automatically to maintain pressurizer l level.22

/. . .

The CVCS emergency mode of operation is initiated by the ESFAS SIAS. In this aode, letdown is isolated, a flowpath from the boric acid tanks to the charging pumps is initiated and the three charging pumps are started.22 i ,

g i

The C7CS requires instrument air and control power for valve positioning and motive power for the charging pumps to function. Loss of instrument air

' - results in closure of the letdown stop and regulating valves.6 Injection

. continues with a single charging pump in operation . Loss of 120 VAC

, { instrument power, bus Y10 or the selected YO1/T02 bus powering the pressurizer l :

_ level instritaentation results in a closure signal to letdown control valve CV-

! 110P and starting of the three charging pumps.23 i Failure of YO2 may affect the charging rate following ESFAS SIAS depending on the selection of YO2 for pressurizer level input.- Assuming that bus YO2 is t t.ot selected for pressurizer level control, a YO2 bus failure prevents SIAS 4

'- actuation of charging pump 12 (Note: charging pump 11 continuously operates

e and need not rely on an SIAS start signal).

l.

! Charging pumps 11 and 13 are powered fros- 480 VAC unit bre 11 A (Train ZA) and

! charging pump 12 from bus 14A (Train ZB).22 i

i I Cooling water for the letdown heat. exchanger is provided by the component cooling water system via ocaponent cooling heat exchanger 11. In the event of

' a loss of cooling water, the CTCS automatically transfers to the recirculation aode, bypassing the ion exchangers, radiation monitor and boron meter.22

- . - - - , , - . , __ _ _ . _ , ,,,. . _ . , _ _ ., , -, _ . . .~ .. ,.,_m ~ _ .,_,._c-,,-, -...-m, ,. -w__,. -m,-

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j 43

SUMMARY

OF FAILURE MODE RESPONSES TO SUPPORT SYSTEM FAILURES In Section 4.2, the responses of the systems and components potentially important to PTS sequences in response to support systems failures were described. These responses are summarized in Section 4 3 and the responses adverse to PTS sequences identified. The responses to electric power, F

b compressed air and cooling water failures are described in Sections 4 31, e

4 3 2 and 4 3 3 4.3 1 Ramoonses to Electric Power system r=41ures

The responses of the systems and components to electric power failures are a

summarized in Table 4. In addition to summarizing the response, an evaluation y

of the potential impact on PTS sequences was made. The responses of the systems and components potentially important to PTS sequences are itemised

[ below:

h 1. Pressurizer Relief valves will fail open following a concurrent r failure of two or more vital buses.

2. The main steam isolation valves will fail to close on demand following a concurrent failure of vital buses YO1 and Y02.

3 A main feedwater regulating valve will freeze in position following failure of its associated control power (Panels C35 f or C36). Both valves will freeze following a concurrent failure of the two panels.

]

4 The main feedwater isolation valves will fail to automatically

close and main feedwater train pump will fail to automatically i

- trip on demand following a concurrent failure of vital buses I_ YO1 and YO2. The isolation valves also will fail to close if their individual 480 V power supplies fail and the feedwater

'._ pumps will fail to trip if their individual 125 VDC power supplies fail.

5. The HPSI will fail to automatically initiate following a concurrent failure of vital buses YO1 and Y02. However, the concurrent failure will initiate the injection mode of the i CVCS.

t i

I

,_ 22

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. . . . .. . . .. . . . . - - - - , .~, -m - - ,

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l TABLE 4. SMSIARY OF SYSTEM /COHr0NENT FAILURE HDDES IN RESpouSE YO ELECTRIC POURE SYSTEM FAILURES . ,

t System / Component Failure Mode Response r Potential Impact on PTS Sequences ,

Reactor Trip Spurious trip will occur following- None. Reactor la expected to trip as two or more failures of redundant part of any PTS sequence of interest.

electric power supplies.

j Atmost heric Dump and Turbine ADV and TSV operate as dealgned or No adverse impact. Failure of valves 4

Bypass Valves fail closed following electric to open will result in a challenge te power failures. main steam safety valves.

Turbine Trip Turbine will trip as designed or Small or no adverse impact. Failure apuriously trip following most of EHC power results in spurious power supply failures. Failure of turbine trip and failure of " quick l vital instrument bua YO2 may result open" ADV/TBV feature which challengea l in a delayed turbine trip on demand steam safety valves. Turbine la (failure to trip on reactor trip expected to trip rapidly even $f t U signal). reactor trip input failed based on exceeding other trip setpoints auch as l j'

speed, j Pressurizer Relief Valves PRV's will operate properly or Impact on PTS sequences will depend on

close following any single electric relative frequency and duration of <

i bus failure. Failure of two (or double bus failures.

more) wital buses will open PRV's i (manual closure possible).

RCP Shaft Seala N/A No direct impact. However, loss of electric power can result in loss of ,

cooling water to the RCP seals.

, Main Steam Isolation Valves MSIV's will close on demand Impact on PTS sequences dependa on ,

J

following any single electric bus relative frequency of and duration of failure. Failure of buses YO1 and double bus failures, j YO2 wil-1 prevent closure on demand.

~

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TABLg 4. (Continued) ,

System / Component Failure Mode Response Potential Impact on PTS Sequences Main F-edwater Regulating Valves Failure of-the associated control Failure of a regulating valve to power (C35 or C36) will result in close can result in a steam generator one of the regulating valves overfill following reactor trip. EHC freezing in-position (As Is). power failure not expected to be l Failure of the EHC power results in significant.

i delayed valve closure based on high i steam generator level rather than 4 on turbine trip.

i l Main Feedwater Bypass Valves Failure of the associated control No adverse impact. Failure of the power will result in nne of the valve to open may result in auxiliary 4 bypass valves remaining closed, feedwater actuation. i Failure of EHC power results in the

, valve not being automatically 9 ! opened.

& i j Main Feedwater Isolation Valves Failure of associated instrument Impact of failure limited due to buses (YO1 and YO2) or motive power expected closure of regulating valve.

will prevent closure of one or both Flow through bypass valve continues.

MFIV on demand, f

Feedwater Pump Trip . Main feedwater, condensate booster Impact will depend on relative and heater drain pumps will trip frequency and duration of double bua

on demand or spuriously trip failures.

following single bus failures. .

Failure of busen YO1 and YO2 will cause failure to automatically trip the pumps following SGIS or CSAS 1 conditions. In addition, failure of 120 VAC bus YO9 will result in the main feedwater pump speed being reduoed to idle speed.

i 4

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TABLE 4. (Continued) .

System / component Failure Mode Response Potential Impact on PTS Sequences Auxiliary Feedwater System Failure of either bus YO1 or YO2 No adverse impact on PTS sequences. ,

will reduce the capacity of the system to 400 spa (from 800 gpm).

Failure of 4 KVAC bus 11 also i results in a reduction of capacity to 400 spa. Failure of both vital buses YO1 and YO2 results in a failure to initiate the auxiliary

, feedwater system. .

High Pressure Safety Injection Failure of bus YO1 or YO2 or Small or no adverse impact on PTS

failure of 4 EVAC bus 11 or 14 sequenoes. Impact will depend on E$ I reduces the capacity of the system relative frequency and duration of

, by half. Failure of the vital double bus failures, i power or motive power in both trains results in a failure to ,

initiate the HPSI on demand. ;

Chemical and Volume Control System Failure of the selected pressuriser Small impact. Initiation of the SIAS level power (YO1 or YO2) or control injection mode expected in all PTS power (Y10) results in spurious sequences of interest.

actuation of the three charging pump injection mode. Failure of non-selected pressuriser level power YO2 reduces the capacity of .

I the system to one pump in the SIAS .

3 mode. Failure of 480 VAC bus 11 A or 14A reduces the capacity of the system to one or two pumps.

1 i

)

l l

, I

a l-l_

ff In addition to the feedwater regulating valves freezing,in position and possibly contributing to a steam generator overfill, the concurrent failure of r, two vital buses has been identified as a small LOCA initiator. The importance of this initiator will depend, as noted, on its expected frequency and duration.

In several cases where the failure of electric power had no direct impact on a component response, the potential impact of electric power failures on other support systems has been noted for reference.

432 Ramoonman to ca-are--=d air swataa F.fiures E The responses of the systems and components to compressed air system failures are summarized in Table 5. The responses potentially important to PTS sequences are itemized below:

1. Both feedwater regulating valves will freeze in position and both feedwater bypass valves will open following a loss of instrument air pressure.

2. A passive failure of the 'B' AFS instrument air train will result in spurious initiation of the steam driven AFS pump and opening of the associated AFS control valves.

1 In addition to the direct response of the systems and component to instrument air failures, the impacts of instrument air failures on other support systems

[, affecting the ccaponents have been noted.

e 433 R==naa=== to coalia- untar svaten r.4tures The responses of the systems and components to cooling water failures are

{ summarized in Table 6. The responses potentially important to PT3 sequences I are itemized below:

r 1. Continued operation of the reactor coolant pumps following loss

4. of component cooling water would result in eventual seal failure and a small LOCA.

7 l 2. Operation of the NFSI pumps for periods of time greater than 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months following loss of component cooling water may result in eventual pump bearing failure.6 m

t s..

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TABLE 5. SmetaRY OF SYSTEN/CGIWOMENT FAILUBE IWDES IN RE3 ream TO Copenneten AIR SYSTEM FAIL 5e.ES ,-

System / Component Failure Mode Response Potential Impact on PTS Sequences Reactor Trip F/A No direct impact. Reactor expected to trip following loss of instrument air.

Atmospheric Dump and Turbine Bypass Loss of instrument air pressure No adverse impact. Failure of ADV and resulta in closure of all TBV and TBV to open on demand increases ADV. frequency of steam safety valve challenges.

Turbine Trip N/A No impact.

Pressurizer Relief Yalve N/A No impact.

RCP Shaft Seala N/A No direct impact. However, loss of o, instrument air resulta in isolation of

" cooling water flow to RCP seals.

Main Steam Isolation Valves N/A No impact.

Main Feeduater Regulating Valve.s Decrease in instrument air pressure Failure of the regulating valves to results in isolation of pneumatic close results in a steam generator supply to both regulating valves, overfill following reactor trip.

freezing them in position.

Main Feeduater Bypass Valves Failure of instrument air results Small impact with respect to response in the bypass valves opening. of feedwater regulating valve .

responae.

Main Feedwater Isolation Yalves N/A No impact.

Malm Feeduater Pump Trip N/A No impact.

TABLE 5. (Continued) ,-

System /f -.- r nt Failure Mode Response Potential Impact on PTS Sequences aum111ary Feedwater System Failure of the main fastrument air Small adverse impact. Depending on supply to the AFS will not cause an the effect of a pasalve failure on tto actuation nor prevent proper main instrument air pressure, the operation for approximately two spurious initiation of AFS may hours. A passive failure of the exacerbate a main feeduator overfill.

AFS Train B (som - later IIB) penumatic tubing will result in automatie start of the steam driven pump and operation with the control valves fully opea.

Nish Pressure Safety Ia M tion M/A No impact.

Chemical and Volume Control System Instrument air failure will result Small or no adverse impact.

la reactor coolant letdown isolatium and contiamed CUCS l u operation with one pump.

am t _

, _ . , _ _ , _, ~ . .

i l *-

N OF SYSTWCRIWSEENT FAILWEE 1E135315 EE350ESE Ve cans.Yan WAVER FAILEGES TABLE 6. .

System /f-- ::: rt Failure Mode Response Potential Impact on PTS Sequences l

Beactor Trip Loss of -pa==at cooling water to hall or no adverse impact. Reactor CED06 can result in CEDet damage and is expected to be tripped fo11 cuing potential release of control loss of cooling water.

l

. elements.

I Atmospheric Dump and Turbine N/A No direct impact. However, loss of Dypass Valves servios water may lead to loss of instrume at air and plant air

[ comprea ors.

Turbine Trip Loss of service water to the No adverse impact.

turbine and generator is expected to eventually require turbine trip. .

l Fressuriser Beller Valves N/A No impact.

U Loss of ecaponent cooling water to Chall LOCA initiator would result if BCP Shaft Seals seals may result in seal damage and the operator failed to trip the possible seal failure. reactor coolant pumps following a loss of oomponent cooling water. ,

i Nain Feeduater Regulating Valve N/A No direct impact. However, loss of service water may lead to lo.ss of '

instrument air compressors.

. i Bhia Feeduater Bypass Valves N/A No direct impact. However, loss of service water may lead to loss of instrument air compressors.

Itala Feedwater Isolation Valves N/A No impact. ;

. -- q -- - - - -

l .. o TAK E 6. (Continued) ,

System /evt Failure Mode Bosponse Potential Impact on PTS Sequences Main-Feedwater Pump Trip Loss of service water to main Small or no adverse impact. Trip of feedwater pump turbine and the main feedwater pumps will result condensate booster pump lobe oil la actuation of the auxiliary coolers is espected to require feedwater system.

eventual pump trip to prevent bearing damage.

4 Aemiliary Feedwater System M/A No impact due to external cooling water systems failure.

Nigh Freasure Safety Injeettom Loss of v =* cooling to the Sas11 adverse irspect. Failure of the l WPSI pumps during NPSI operation operating NPSI pumps may increase the g could lead to eventual pump likelihood of Safety Injectica Thak or failure. The BPSI pumps are Low Pressure Safety Injection in some designed to operate a minimum of PTS sequences. Impact will depend on l 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months following a complete loss relative frequency and durairion of I of W oooling water. multiple component cooling v.nter i system failures.

l Cheadel and Volume Control System Loss of Pt cooling water to No adverse impact. However, loss of letdous heat exchanger results in service unter may lead to loss of l automatic transfer to the instrument air compressors, rectroulation pode bypassing the baron and radiatica monitors and los exchangers. .

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As above, the potential impact of cooling water failures on other support systems affecting the systems and components have been noted.

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r 50 COISIDE CAUSE SUPPORT SYSTEM FAILURES i

i l The dependence of systems and components identified in the PTS sequences on electric power, compressed air and cooling water systems has been discussed in ,

, Section 4. In Section 5, the failure modes of the systems and components in t- response to specific failure modes of the support systems are identified and i , discussed. In Section 51, the designs of the Calvert Cliffs electric power, i

f. compressed air and cooling water systems are described briefly and the failure modes resulting in the important system responses itemized in Section 4 3 identified. The responses of the systems and components to these support I

system failure modes are described in Section 5.2 in a failure modes and effects format.

5.1 CALVERT CLIFFS SUPPORT SYSTEMS DESIGNS j The designs of the Calvert Cliffs electric power, compressed air. and cooling j water systems are described in Sections 5.1.1, 5.1.2 and 5.1 3 The

t.

interfaces with the system and components affecting PTS sequences and the I interfaces among the support systems are identified and support system failure modes defined.

5 1.1 Electrical Power Systans The Calvert Cliffs Unit 1 AC electric power distribution is shown in a i

simplified schematic diagram, Figure 1. The plant power requirements normally

[ are supplied from the switchyard' through 13 KY service buses 11 and 12. Bus

. 12 supplies the four reactor coolant pump buses and bus 11 supplies the 4 KY l , unit buses.24

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4 KY buses 11 and 14 supply the safety' related Channel ZA and ZB power

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requirements respectively. These buses are energized by two of the three

$ emergency diesel generators shared by the two Calvert Cliffs Units.24 a .

The 4 K7 buses supply the 480 Y buses through transformers. In particular, 4 i KV bus 11 supplies 480 7 buses 11 A and 11B; 480 Y bus 115 supplies 480 Y reactor MCC 114R. 4 KY bus 14 supplies 480 V buses 14 A and 148 and 480.7 bus

14A supplies 480 V reactor MCC 104R.24 4

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Plant DC loads are supplied by 125 VDC buses 11,12, 21 and 22, and 250 VDC f f

bus 13 which are shared between the two units. Each DC bus normally is fed by p

its associated battery charger (i.e., bus 11 fed by battery 11 and battery j j charger 11). The four 125 VDC battery chargers,11,12 and 21, are fed by I

j p 480 VAC unit buses 11 A, 14B, 21B and 24A respectively.24 4 -

3- 120 VAC instrument buses are fed from the DC buses through inverters or from

f. the 480 VAC MCC's through transformers. 120 VAC vital buses 11,12,13 and 14 are supported through their associated inverters from DC buses 11, 21, 12 and f 22 respectively. The vital buses may also be fed, by manual transfer, from :

I 120 VAC bus Y11. 120 VAC buses Y10 and Y11 are fed through their transformers ;

from 480 VAC MCC 104R. Bus YO9 is fed from MCC 114R.24 i

l~ . Electric bus failures can occur for a variety of reasons including isolation

- or failure of feeder buses or shorts which could occur during maintenance. ,

! r For purposes of this analysis, single unspecified failures have been postulated at various points in the power distribution circuitry. The failure has been assumed to deenergize the directly affected bus, buses only fed from A.

this bus ad possibly the feeder buses to the affected bus. In cases where a i maintenance tie between existed, failures affecting both normally isolated j - buses were considered.

+

f The 4 KY buses shown on Figure 1 have multiple sources of power (13 KY bus 11 i and the emergency diesel-generators). Thus, 4 KY bus failures were assumed due to postulated f aults on the 4 KY buses. This f ault results in j

' doenergizing lower voltage bus fed from the affected bus. Similar faults have

. been postulated on lower voltage buses. In addition, the existence of m

maintenance ties between 4 EV buses 11 and 14 and between McC's 104R and 114R

' were considered possible mechanians for propagating a single fault to both

.i -

buses or MCC's.24, 125 VDC buses 11, 12, 21 and 22 each have multiple independent power supplies and have no maintenance ties.24 Therefore, only faults affecting single

, buses were considered.

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n Each 120 VAC vital buses, YO1, 702, YO3 and YO4 is normally fed from a

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separate DC bus through an inverter. However, one or more vital buses may be

' (t: fed from 120 VAC bus Y11. Therefore, single and multiple vital bus failures I^

were considered.

l' i I t i Where either of two instrument buses supply a single instrument panel by I-

- - automatic selection, two failure modes were considered. A fault in the panel bj could result in both feeder buses being isolated from the panel. The feeder ,

! buses would continue to supply other loads in this case. The analysis also considered the possibility of a panel fault propagating to the primary supply f bus and subsequently propagating to the backup supply bus on automatic

, ! transfer. In this case, the two buses feeding the panel would be deenergized.

l.

1 l 1- 5.1.2 Comnreanad Air Svatana

- The 260 SCFM instrument air requirements of Calvert Cliffs Unit 1 are supplied g

by instrument air compressors 11 and 12, each rated at 470 SCFM. The I instrument air compressors are in intermittent operation to maintain pressure

, in their associated air accumulators. The instrument air compressors discharge into a common header upstream of the accumulators. Additional l i

cross-connecting headers are also installed upstream of the distribution- ,

1 piping to the plant components. In addition, the 616 SCFM plant air compressor 11 is aligned automatically to supply instrument air requirements i if the pressure in the instrument air header falls below a preset value.6 l l

f AC electrical motive power supplies for the three compressors are shown in

{ ! Figure 1.- Control power for instrument air ocapressor 12 and plant air <

l ocapressor 11 is supplied from 120 VAC bus Y10; control power for instrument

' 4 air compressor 11 is supplied by 120 VAC bus YO9. As shown, the compressors are supplied from independent electric power trains. The three ocapressors i are supplied cooling water from service water pump 11 and heat exchanger '11.

The cooling water supply is automatically isolated on SIAS signals, loss of l\ power to the isolation valve solenoids,125 VDC buses 11 and 21, or loss of ;

instrument air pressure to the isolation valves.

- Compressed air- systes failure (low pneumatic supply pressure), can be caused by a postulated passive failure of the pneumatic piping failure of the three 35 i 9

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,' compressors or their associated motive or control powec. Normal plant instrument air requirements can be satisfied by either instrument air

{^ compressor or the plant air compressor. Thus, failure of one or two of the compressors will not result in system failure. As shown in Figure 1, single

- bus failures will result in, at most, two of the three compressors. Failure 1

[- of service water pump 11 or isolation of service water to the compressors would lead, ultimately, to failure of the three compressors. The time jj required for the compressors to fail following a loss of service water is unknown. However, following a loss of cooling water, the operator may choose to trip the compressors rather than allowing them to run to f ailure.

Following loss of the compressors, the instrument air system is expected to i depressurize over a period of minutes. The operator has the option of L manually aligning the Unit 2 Compressed Air Systems.

la Auxiliary feedwater system pneumatic valves are supplied by two 55 f t3 accumulators in addition to the primary instrument air source. Failure of the

/ pneumatic supply to one train of auxiliary feedwater systen valves would require a passive piping failure in one of the two auxiliary feedwater systes pneumatic supply headers.'

The effects of low instrument air pressure on the systems and components

affecting PT3 sequences have been summarized in Table 5. Ezeluding the A effects on the auxiliary feedwater system, low pressure in the instrument air distribution piping will occur following a passive failure of the instrument air headers or failure of the compressors due to a single teilure of the.

service water supply combined with a failure of the operator to natus11y align an alternate instrument air supply.

Low instrument air pressure in either of the auxiliary feedwater supply headers will result in the control valves associated with that train opening.

> Failure of the "B' pneumatio train, in addition to opening the control valves, i

will result in the turbine driven pump starting and secolerating to nazimum i speed. Due to the two auxiliary feedwater system accumulators, this failure is expected to result in the near ters (<2. hours) only from a passive failure in the muziliary feedwater pneumatic piping. The postulated passive failure 4

would only affect one of the two auxiliary feedwater pneumatio trains.

36

I' .

i .If the postulated failure depressurizing the auxiliary feedwater pneumatic

% piping also depressurised the main instrument air system, the effects associated with failure of the instrument air system also would occur.

However, depressurization of the instrument air system due to a failure of

.r

. auxiliary feedwater instrument air branch tubing is considered highly

' unlikely.14 e-

}' 513 can11am vatar swataan f' Cooling water for normally operating and standby Calvert Cliffs components and

! systems is supplied by the component cooling water system and the service

, water system. These two closed loop systems reject heat to the open loop salt ,

,' water system. l l i r

The component cooling water systes consists of component cooling pumps 11,12 i

{

and 13, which feed ocaponent cooling heat exchangers 11 and 12 through a i

! 6 common discharge header. Normally one oosponent cooling water pump and heat l I" exchanger 11 are in operation. During normal operation the ocaponent cooling

< water system provides cooling water for the CEDM, the reactor coolant pump l

mechanical' seals and lube oil heat exchangers and the letdown heat exchanger.0 l l

Energency operation of the system is initiated by ESFAS Containment Isolation !

signals. Fuaps 11 and 12 are started, flow through component cooling heat I exchanger 12 and shutdown heat exchangers 11 and 12 initiated and cooling [

water for the reactor coolant pumps and CEDM isolated. In this mode of operation, cooling water from either component cooling heat exchanger can supply the shutdown heat exchangers and safety injection pumps' seals and coolers.0 The AC power sources for the component cooling water systes are l' - shown in Figure 1. Instrument air and solenoid power is required to position

.- systen valves. . Solenoid power for isolation valves CV-3832 and CV-3833 is i

t, supplied from 125 VDC buses 11 and 21, respectively. Loss of either instrument air or solenoid power results in isolation of cooling water to the l )" reactor coolant pumps and CEDM and opening the isolation valves in the component oooling and shutdown heat eschangere.

i 37 i ..

i..

[' The service water system consists of two independent loops. Pump 11 feeds

' ~

heat exchanger 11 and pumps 12 and 13 feed heat exchanger 12. Normally pumps

.r 11 and 12 are in operation and pump 13 is in standby. The cooling water from

- I- heat exchanger 11 supplies the instrument air and plant air compressors, the turbine electro-hydraulic oil and lube oil coolers. Heat exchanger 12 7-(. supplies the feedwater and condensate booster pump lube oil coolers, the generator coolers, spent fuel cooler and nitrogen compressor.6 s

1.

Emergency operation is initiated by ESFAS SIAS signals which start the service water pumps, isolate the turbine plant, spent fuel and instrument air cooling

{"

water and initiate flow to emergency equipment such as the containment coolers i and emergency diesel-generators.0 4.

Service water heat exobangers 11 and 12 are fed ocoling water via salt water p pumps 11 and 12 respectively. Service water AC power requirements are shown in Figure 1. Instrument air and solenoid power are required to position systen valves. Solenoid power for isolation valves CV-1600 and CV-1637 is supplied by 125 VDC bus 11 and for valves CV-1638 and CV-1639 by 125 VDC bus

21. Loss of either instrument air or either 125 VDC bus will result in isolating the cooling water to the turbine plant oosponents, air and nitrogen r compressors and the spent fuel cooler and initiating flow to the emergency

. equipment.0 The effects of loss of cooling water on the systems and components affecting FT3 sequences have been shown in Table 6.

52 EFFICTS OF SUPPORT SYSTINS FAILCRE HDDES The systems and components identified in the FTS event trees have been analysed to determine their individual failure mode responses to support system failures. The failure modes of potential significanoe to PTS sequences

( have been sussarized in section.4 3 In sootica 5 2, the combinations of failure mode responses of the systems and oosponents to particular failure f.

I ,

modes of the support systems are identified and evaluated.- In sootica 5J.1, i the specific support systes failure modes are identified and, in Section

- 5 2.2, the overall response of plant systems to these failure modes are determined.

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I 5 2.1 Ydantifiaatian of Sunnert Swataa Fafture Medan k The system and component failure modes judged to be potentially significant to PTS sequences in Section 4.3 were analyzed to identify specific initiating I failures of the electric power, compressed air or cooling water systems. The ;

'- initiating support systems failure modes are listed in Table 7 In addition to support system failures directly resulting in a system or g component failure affecting PTS, a failure of one support systen may result in j a failure of another. To evaluate this interactive effect, each of the support system failure modes listed in Table 7 was analysed to determine possible initiating failures in other support systems. The interactive support system failure modes are listed in Table 8.

f' . ,

i The initiating support system failure modes listed in Tables 7 and 8 have been sussarized in Table 9 This list of support systems failure modes consists of the failures for which at least one PTS adverse response has been identified.

Multiple system failure mode responses to each support system failure are s, identified and evaluated in Scotton 5 2.2.

Initiating electrical system failures were selected from those identified in f Tables 7 and 8, if they could result from a single doenergised bus or from a -

single postulated failure (e.g., short to ground) of a possible electrical connection. Multiple 120 VAC vital bus failures were selected, on this basis, f due to the common, manually oonaseted backup supply bus Y11. 4 KYAC buses 11 and 12 and 480 VAC MCC's 104R and 114R also say be manually connected. Panel C35 is supplied 120 VAC power from bus Y01 or Y09 by automatic transfer. The 7

double failure of these buses is postulated on this basis. A similar condition esists for buses Y02 and Y10 via panel C36.

i' Compressed air system failures selected were limited to single postulated piping f ailures. Multiple oospressor failures were considered only to the l

extent that they any be caused' by a common support system failure, b'

Component failures resulting from a loss of cooling water flow have been 7

considered. However, it is recognised that a significant period of time may

, 39 L

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TABLE 7. IEITIATIM 3GPPORT SYSYEM FAILORE BEEbES ,

Initiating Initiating Initiating Electrical Compressed Air Cooling Water Failed System / Component System Failures System Failures System Failures PEV Fail Open Vital Buses YO1 & YO2, None None ,

YG1 & YO3, YO1 & Yo4, YO2 & YO3, YO2 & YO4, YO3 & Yo4 BISIV Fail to Close on Demand Vital Buses YO1 & YO2 None None Bev Regulating Valve CV-1111 Panel C35, Yo1 & YO9 Failure of all compressors, None Freezes in Position (Open) passive instrument air line failure BEW Regulating Valve CV-1121 Panel C36, YO2 & Y10 Failure of all compressors, None Freezes la Position (Open) passive instrument air o line failure IWW Bypass Valves CV-1105 & 1106 None Failure of all compressora, None Fail Open passive instrument air line failure Igv Isolation Valve Be0V-4516 Buaea YO1 & YO2, 480 V None None Fails to Close on Demand itCC 1145, 480 V AC Bus 11B, 4 KV AC Bus 11 BEFW Isolation Valve Itur-4517 Buses YO1 & YO2, 480 V None None Fails to Close on Demand ItCC 104R, 480 VAC Bus 14 A, 4 EV AC Bus 12 IWW Pump 11 Fails to Trip on Buses YO1 & YO2, 125 VDC Mone None Demand Bus 11 DEW Pump 12 Fails to Trip on Busea YO1 & YO2,125 VDC Mone None h= M Bus 12

w. - . - _ . - - - . - _ . - . ,

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TABLg 7 (Continued) ,-

Initiating Initiating Initiating Electrical Compressed Air Cooling Water Failed System / Component 2 System Failures System Failures System Failuree Spurious Initiation of AFS Steam None Pasalve failure of AFS None

" Driver Pump Trat. -

instrument air line -

Train B HPSI Falla to Initiate on Buses YO1 & YO2, 4tV None Ikee* ,

Lemand Buses 11 & 12, 480 V HCC 104 & 114, 480 V Bus 11B

& 14A -

3CP Seal Failures pone -

Kone Fail.ure of operating ,

. 'CCW Pump 11, cloeuse-

& . 'f ' -

of CV-3832, closure a- ,

of CV-3833 -

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4 2

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O eMultiple failures or a pasalve failure of the CCW could be postulated which would stop cooling water flow to the NPSI pumps. Nouever, Icas of CCW does not prevent initiation or operation of the HPSI pumps for two hours or more. Delayed initiation of HPSI rather than long term failure la of concern to PTS sequences.

. . . . .- -, - .- .-- -. . , . . , .- .--~ - .. - -. .

TABLE 4. INTERACTIYE FAIIM BWDES ANDEG SOPPORT SYSTEBIS *-

Initiating Initiating Initiating Electrical- Compressed Air Cooling Water Failed System / Component System Failures System Failures System Failures Failure of Vital Buses . Failure of associated N/A N/A 125 VDC Buses 11, 12, 21, 22 or manual transfer to Y11 ard subsequent failure of Y11 Failure of All Instrument 4 KV Buses 11 & 12, MCC's N/A Failure of se:vice Air Compressors - 104R and 114R,120' VAC water pump 11, buses YO9 and Y10 closure of CV-1637, S

closure of CV-1639 Failure of CCW Pump 11 4 EV Bus 11, 480 Y Bus 11 A None None

, closure of CCW CV-3832 125 VDC Bus 11 Failure of all compressors, None N passive instrument air line failure Closure of CCW CV-3833 125 VDC Bus 21 Failure of all compressors, None passive instrument air line failure Failure of Service Water Pus.p 11 4 EV Bus 11 None None Failure of Service Water CV-1637 125 VDC Bus 11 Failure of all compressors, None passive instrument air line failure Failure of Service Water CV-1639 125 VDC Bus 21 Failure of all compressors, None passive instrument air line failure

r . -. .,

9

} TABLE 9 SUPPORT SYSYEMS IIITIAYING FAILURF.!

?'

Initiating Support System Failure Mode ' Comments r

i l- Electrical System Failures l' Multiple 120 VAC Instrument Bus Fai.ures l

1. YO1 and YO2 . Multiple vital bus failures have occurred due to improper maintenance actions. Y11 is a

{ common backup supply for buses YO1 - YO4.

2. Other double vital bus failure Multiple vital bus failures have occurred due to improper

/ maintenance actions. Y11 is a l', common backup' supply for buses YO1 - YO4. ,

,1 3 Yo1 and YO9 YO1 and YO9 supply panel C35

YO2 and Y10 supply panel C36.

4 - 4. YO2 and Y10

. I %

! 5. Panel C35 or C36 Deenergized Instrument buses supplying panels assumed to remain energized.

(, 6. 125 VDC Bus 11 Postulated single failure.

7. 125 VDC Bus 12 Postulated si gle' failure.

I- I- 4 E7AC Bus 11 Failure Postulated single failure.

8.

9 4 E7AC Buses 11 and 12 Fail Postulated fault while buses are i

electrically connected.

10. 480 VAC MCC's 104R' and 114R Fail - Postulated fault while MCC's are

,- k* ~ electrically connected.

l t ,

C^=ncessed Air System Failures'

[

I-

11. Passive Failure of Instrument Air Postul'a ted single failure.

-Header

-3 l

11 2 . . Passive Failure _ of Auxiliary Postulated single failure.-

l ~ Feedwater Instrument Air Header i

I 43.

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TABLE 9 (Continued) s, Initiating Support System Failure Mode Comments v*.,

[, Cooline Water System Failures 13 Failure, of CCW Pump 11 Postulated single failure, i

t i- 14. Closure of CCW CV-3832 or CV-3833 Postulated single failure.

\ ,.

15. Failure of Service Water Pump 11 Postulated single failure.

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16. Closure of Service Water CV-1637 Postulated single failure.

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or CV-1639 i

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l elapse prior to component failure. For this reason, only failures resulting in a complete loss of flow to a serviced component have been selected as

(* cooling water initiating failures (e.g., loss of service water flow to the air g

compressors). Failures of the salt water flow to the component cooling and

service water heat exchangers have not been selected since they do not result I' in a loss of flow to a serviced component.

r- .

1- 5 2.2 Effects of Succort Systems Failure Modes on PTS Secuences The responses of each of the systems and components identified from the PTS

[, event sequences to the sixteen postulated support system failures listed in Table 9 have been evaluated. The responses of each are summarized in Table i.

!. 10.

'l The responses listed in Table 10 describe the status of each system or i

- ::omponent in response to the postulated failure prior to possible remedial by

<- the operator. The responses listed include both direct responses to a 1

i postulated support system failure (e.g., a valve closes in response to a loss p of instrument air pressure) and indirect responses (e.g., instrument air

! pressure is lost due to air compressor cooling water failure which results in .

valve closure). The " operable 8 response is used to indicate that a system or component will respond as designed to plant conditions. Supplementary information concerning the particular " operable" responses of components or the status of manual controls for components responding to failed automatic controls has been added where possible.

k Detailed information concerning the responses of systems and components to 7

support systems failures has been provided in Section 4 and the interactive

{, responses of the support systems in Section 5.1.

!~ The overall-effects of the support systems failures depend on the potential 4 -

severity of the resulting transient and the availability of remedial actions to the operator. These factors have been evaluated, to the degree . possible, for each of the support systems failures to identify the support. systems failures of greater importance to the PTS sequence analysis. The frequency of i

. support system failure leading to multiple adverse PTS sequence events 'is to be calculated for ~ the support systems f ailures of greater importance in 45

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. TaaLE 10. RESPONSE OF IDEllTIFIED Pl. ANT SYSTEMS AND MMPOWENTS TO POSTM.ATEL SOPPORT SYSTEM PAILUBES System / Component Response IGN HIM Reactor Turbine RC Reg. Bypass Mk1 Vnitiating Failure Trap :ADV/TBV Trip Pumpa PW 's MSIV 's Valves Valves Pumpa IFIV AFS HPSI CVCS Electrical Syste d allurea 1... Buses YO1 & 102 Tripped Operable .Trippedes Operable Opene Opene Opera- Operable Opera- Opene orre orre 3-Pump ble, .

Ling, Injection closed pump follou- trip ing tur- failed bine trip Other Double Tripped Operable Tripped Operable Opene Operable Opera- Operable Operable Operable One or One or Operable 2.

. p, Vital Bus Failures ble, Both Both or 3-Pump Ch closed Trains Trains Injection Operable Operable Closede Opera- Operable Operable Operable CV-1811 CV-1105 Minimum operable operable operable operable 3 Buses Y01 & 109 Opera-or 3-Pump ble, . . or ble, . open, closed, speed, probable operable probable CV-Il21 CV-1106 pump Injection trip- trip operable, operable trip closed . operable

4. . Buses 102 & Y10 Opera- Closede' Probable operable Operable operable CV-1111 CV-1105 Opera- Operable Operable Operable 3-Pump ble, or Tripes opera- opera- bla. Injection probable operable ble, bl e, high trip closed, CV-1106- speed

CV-112) closed open

, . .. , e -- ~.---- ~ ~ . -, r- -'" - - , ---? - - -

M r -- % ~. --.

- -- 3, , . a ~.

) ,. . ,

TABt.E 10. (Continued)

System / Component Response IGV DeV Reactor Turbine RC Reg. Bypass HEY IIttiating Failure Trip .ADV/TBV Trip Pumps PNV's MSIV 's Valven Valves Pumps MFIV AFS HPSI CV CS 5 Panel C35 or C36 Opera- Operable Opera- Operable operable Operable CV-1111 CV-1105 Operable Operable operable Operable operable Deenergized ble, ble, or or eventual . eventual CV-1121 CV-1106 trip trip open, closed, other other valve valve closes . opens on un turbine e turbine ' trip N trip

6. 125 VDC Bus 11 opera- ' " Quick Trip Eventual Operable operable Opera- Operable opera- Operable One One Operable ble, Open" after failure ble, untti ting, Train Train until trip failed, 30 of. seals closed Instru- pump 11 Operable Operable Instru-after . auto sea unless ment Air trip ment Air 30 sec. con- tripped Pressure failed Pressure trolled is lost. lost.

on pres- Valves Letdoun sure or then then Tav will u111 be until open taolated Instru-ment Air Pressure loat.

Valves then close

^~

r - ~, , ,

re . -

_ . . ~ .% ,- ,. ., _ ,

- .{ ' . . . .

e

TABLE 10. (Continued)

System / Component Response itV MFW Turbine RC Reg. Bypesa MFW Reactor .

Pumps MFIY AFS NPSI CVCS Trip ADt/TBV Trip Pumpa PRV 's MSIV 's Valvea Valves 131 Listing Failure Operable Opera- Operable Opera- Operable Operable One Operable

-7 125 VDC Bus 21 Operable Operable Operable. Eventual closed ting. Train failure ble, until Operable of seala closed pump 12 Instru-unless trip sent Air tripped failed Pressure lost.

Valves then close

v. Operable Opera- Operable Min. Mat-4516 One Or.e Su-J 12 00 8. 4 EV AC Bue 11 Opera- Closeda Opera . Eventual ERV-402 closed, ble, speed, open, Train Train 6amra-ble, oc ble, failure pump Mut-4517 operable operable ting, probable operable probable of seals. BRW- %4 closed operable trip operable letdeun trip trip unless isolated tripped operable Ope.-able Min. Open One Off Off Opera- Closeda Opera- Eventual Closed Operable Opera-9 4 KV AC Busea 11 ble, speed. Train a 12 ble, ble, failure closed pump operable probable probable of seals trip trip trip unless tripped operable 9

, c ..- , , .- -

.. - .-- ~ . - - s ~~

- . e--- -M - -

1 .

+ .

TABLE 10. (Continued)

System / Component Response M WW Beactor Turbine RC Reg. Bypass Hrv Initt.*.ing Failure Trip ADf/TBV Trip Purpa PNV 's MSIV's Valves Valves Pumps WIV AFS HPSI CVCS

10. 480 V AC MCC's Opera- Closede Opera. Eventual Closed Operable Operable Operable Min. Open Operable Off, Pumps 104R & 114R ble, ble, failure until untti speed, isolated operating probable probable of seals Instru- Instru- pump from VCT trip trip unle ss ment Air ment Air trip water tripped Pressure Pressure operable source lost, lost, only valves valves p s then then e ,

remain open closed Comorassed Air Svstem Failures

11. Passive Failure -Opera- Closed Opera- Eventual Operable Operable Open Open Opera- Operable Operable Operable One Pump of Instrument ble, .

ble, failure ting at Injeo-Air Header probable probable of seals high Lion, trip trip unle ss speed letdown tripped taoisted

12. Passive Failure Operable Operable Operable Operable Operable Operable Operable Operable Operable Operable Train B Operable Operable of AF3 Instrument Initta-Air Header "B* ted Control

Valves open

..s r.. g_. _... _, .. __ _ , ; .. . , _ _ ,

~ . s * , o TABLE 10. (Continued)

System / Component Response ,

f MV Mtv Reactor Turbine RC Reg. Bypasa HFW Initiating Failure Trip ADV/TSV Trip Pumpa PRV 's MSIV's Valves Valves Pumps NFIV AFS HPSI CVCS Coolinn Water Sumten Failures

13. CCW Pump 11 Opera- Operable Opera. Eventual Operable Operable Operable Operable Operable Operable Operable operable Operable ble, ble, failure eventual eventual of seal trip trip unless tripped in

o. 14. Closure of CQi Opera- Operable Opera. Eventual Operable Operable Operable Operable Operable Operable Operable Operable Operable

, CV-3822 or ble, ble, failure CV-3833 eventual eventual of seal trip trip unless tripped

15. Failure of Servloe Opera- Even- Opera- Eventual Operable Operable Probably Operable Operable operable Operable Operable Operable Water Pump 11 ble, tually ble, taola- closed until untti eventual closed eventual tion of unless Instru- Instru.

trip on loss trip CCW on Instru- ment Air ment Air i of In- loss of ment Air pressure pressure strument Instru- Pressure la lost. la _ tost.

Air ment la lost Valves Lethoun s Air. prior to then then vill Eventual turbine will be seal trip open isolated failure unless tripped

. - - - ., . - . ;.---, -s - 3

_ , a .._ -. -

, ~ _ - , ,- <- - .,e a. . . - - .

' , t ,

TABLE 10 (Continued) i System / Component Response M M Reactor Turbine RC Reg. Bypass WW Initiating Fatture Trip ADV/TBV Trip Pumps PRV 's MSIV 's Valves Valves Pumps WIV AFS HPSI CVCS

16. Failure of Servloe Opera- Even- Opera- Eventual Operable Operable Probably Operable Operable Operable Operable Operable Operable Water 61-1637 or ble, tually ble, tecla- closed until until CV-1639 eventual closed eventual' tion or unless Instru- Instru-trip on loss trip CCW on. Instru- ment Air ment Air of In- loss of ment Air pressure pressure strument Instru- Pressure is lost. is lost.

Air meet is lost Valves Letdeun Air. prior to then- then will

. u be H Eventual turbine will seal trip open teolated failure unless tripped

' Manual Control Available. ;

e* Turbine will trip on low speed or other turbine related parameter. ;

i t

l t

. - . - ~ = - -- - - - ... .-. -- --- -

+ e . . .

v. .

subsequent analyses. The comparison of these frequencies with equivalent 4

independently occurring event sequence frequencios will be used to evaluate the overall importance of support system failures,

i. -

f Based on the system and component responses listed in Table 10, a brief I- description of the resulting plant transient and possible remedial actions i . available to the operator are presented in Table 11 for each of the sixteen

( postulated support system failures. In addition, an estimate of the potential severity has been made for each of the resulting transients. These responses

. to support systems failures are discussed below.

Electrical Syst==a Failures

, h 1.

t.

j Two postulated electrical systems failures resulted in a small LOCA coupled 1

with a f ailure to automatically initiate HPSI. These coupled events are of l potential importance to PTS sequences cue to the lower reactor coolant system

- temperatures which result during the repressurization phase of the transient

, ! following delayed initiation of the LPSI and HPSI.

Transient 1 (Table 11) consisted of a coincident failure of vital buses YO1 and YO2. Failure of these buses would result in a spurious high pressurizer pressure signal which opens tho' two PHY's _and would deenergize the two ESFAS actuation channels defeating SIAS actuation of HPSI. Following transient l' initiation, the operator can manually close the PRY's, start the HPSI or 1

' reenergize either of the vital buses. Recovery of either bus results in automatic closure of both PRY's and actuation of one HPSI and LPSI train.

l Coincident failure of 4 KYAC safety buses 11 and 14, Transient 9, would result in termination of cooling water to the RC pump seals and would doenergize the

- HPSI pumps' and. valves' actors. Coincident failure of MCC's 104R and 114R, l

Transient 10, also any result in an isolation of cooling water to the RC- pump sesis due to the loss of instrument air compressors' control power (120 YAC L buses YO9 and Y10) and loss of power to the HPSI injection valves. Tripping the RC_ pumps effectively would prevent seal failure and the possibly resulting

- small LOCA. If the RC pumps were not cripped and seal failure occurred, l .

recovery of ~ one of the .4 KY AC buses or 480 V MCC's would be required for recovery from Transients 9 and 10, respectively. -

52 l

i

, ,n- a - r 4 - .n, . - e~w,-n--e ,

m -n- -n.- - -

- . - . , - - ---e-., a---,,-,-,- -rw .-y -

. . . . .. ,- -, . . - , , . _ . . - . . ., ,_ ... _ ~ _. . . . . , .. , - _ . . . _ . , .

. , o a . > .

L TABLE 11. POTENTIAL IMPACT OF SUPPORT SYSTEMS FAILURES ON PTS SEQUENCge ,-

Estimated Impact

'nitiating Failure . Description of Transient Available Remedial Actions on PTS Sequences Electrical System Failures

1. Buses YO1 & YO2 Reactor trips and PRV's open Operator may manually close (a) With promptly instituted creating a small LOCA. PRV's or their isolation remedial actions, the

Turbine tripa on low speed. valves and start HPSI. Impact of this transient ESFAS actuation channels fail Recovery of either vital bus on PTS sequences is resulting in failure to results in automatic closure considered negligible, actuatc HPSI, AFS or isolate of PRV's and probable ESFAS steam generators. CVCS actuation. (b) Without remedial actions,

" fails" in the 3-pump a coupled small LOCA and injection mode. Main feed- failure to automatically water to steam generators start HPSI will occur.

regulated to 55 Automatic initiation of u CVCS injection moderates the effect of the HPSI initiation failure.

\ '

2. Other Double Reactor trips and PRV's open Operator may manually close A double vital bus failure is Vital Bus creating small LOCA. Turbine PRV's and recover vital a cause of an "isolatable" l

Failures 'will trip on reactor trip or buses. small LOCA. The impact of low speed depending on whether this transier.t on PTS YO2 la available. At least sequences is limited since it one. of two ESFAS actuation is not coupled to a failure channels available. to automatically initiate .

HPSI.

4 CImpact of support systems failures on PTS sequences will require a calculation of the frequency of the support system failures and the failures of the operator to take remedial actions. This calculation will be performed in '

subsequent analyses.

., __ _. . . . . . . - , , - - . , . _ . . . , . ~ , . . ,

TABLg 11. (Continued) . .

t Estimated Impact Initiating Failure Description of Transient Available Remedial Actions on PTS Sequences t

3. Buaea YO1 & YO9 HFW regulating valve CV-1111 Close HFIV NOV-4516 on Negligible impact on PTS freezea in position and MFW indicated high steam sequences, i pumpa runback to minimum generator level if required.

speed. Reactor and turbine trip on loss of feedwater flow and probable AFS ,

actuation. 3-pump CVCS operation may be initiated depending on selection of pressurizer level instrument j power. ;

4. Buses YO2 & Y10 HFW regulating valve CV-1121. Close HFIV Hot-4517 (or (a) With promptly initiated freezes in position. 3-pump trip HFW pumps) and regain remedial actions, the !

m

' CVCS operation initiated, control of CVCS. impact of this transient Reactor and turbine trip on on PTS sequences is high pressurizer level and considered negligible, steam generator 12 is overted. (b) Without remedial actions, a steam generator

< overfill transient will

! occur.

5. Panel C35 or C36 HFW regulating valve CV-1111 Close associated MFIV (a) With promptly initiated '

Deenergized or CV-1121 freezes in H0V-4516 or HOV-4517 (or remedial actions, the position. Eventual reactor trip HFW pumps). impact of this transient and turbine trip due to lack on PTS sequences is of feedwater control and considered negligible.

aubsequent overfeeding of i steam generator 11 or 12. (b) Without remedial actions, a steam generator overfill transient will s

occur.

4

, ..- . . . . - . _ - . = _. . - -_- .

. .. ~ -

.- ~. .- . -- , .

TantR 11. (Continued) +-

Eatinated Impact Initiating Failure Description of Transient Available Remedial Actions on PTS Sequences

6. 125 VDC Bus 11 Turbine and reactor trip Trip RC pumps on high (a) With promptly initiated after 30 sec. Service water controlled bleed-off remedial actions, the and CCW isolated to anon- temperature. It Unit 1 impact of this transient .

essential" components compressors must be tripped, on PTS sequences is including air compressors align Unit 2 compressors to considered negligible.

RC pump seals. Eventual supply Unit 1 instrument air failure of RC pump seals header. (b) Without remedial actions, 2 occurs unless pumps are a small LOCA due to RC l tripped. Long term operation pump seal failures would 1 of compressors without occur. The impact of cooling water an lead to this transient on PTS their failure. Houever, even sequences is limited if instrument air pressure is since the LOCA is not lost, MFW regulating valves coupled to a failure to U remain closed. automatically initiate l HPSI. (One HPSI train can be initiated automatically.)

k

TABLg 11. (Continued) .

Estimated Impact IIitiating Fa11uro Description of Transient Available Remedial Actions on PTS Sequences 7 125 VDC Bus 21 Service water and CCW Trip RC pumpa on high (a) With promptly initiated isolated to "non-easential" controlled bleed-off remedial actions, the components including air temperature. If Unit 1 impact of this transient compressors and RC pump compressors must be tripped, on PTS sequences is sealm. Eeactor and turbine align Unit 2 compressors to considered negligible.

expected to trip due to loss supply Unit 1 instrument air of cooling water to turbine header. (b) Without remedial actions, components. Eventual failure a small LOCA due to RC of RC pump seals occura pump seal failures would unless pumps are tripped, occur. The impact of Long term operation of this transient on PTS compressors without cooling sequences is limited water can lead to their since the LOCA is not failure. However, even if coupled to a failure to instrument air pressure is automatically initiate g lost, MFW regulating valves HPSI. (One HPSI train remain closed. can be initiated automatically.)

.-__ . _ _ _ _ ___ - _.~ --. . _ _ _ _ _ - _ _ ._ - . . _ . - _ . - . - ._ _ _ _ .

. > s . ,

TABLg 11. (Continued) , ,

[

i Estimated Impact t I itiating Failure Description of Transient Available Remedial Actions on PTS Sequences 8, 4 KV AC Bus 11 Service water pump 11 and Start CCW pump 12 and locally (a) With promptly initiated operating CCW pump stop open valves to supply service remedial actions, the !

, terminating flow to air water from heat exchanger 12 impact of this transient ;

compressors and RC pump to train 11 components. Trip on PTS nequences is i

. seals. Reactor and turbine RC pumps if the transient considered negligible.

expected to trip due to loss results in high controlled of cooling water to turbine bleed-off temperature. (b) Without remedial actions, components. Eventual failure a small LOCA due to RC of RC pump seals occura pump seal failures would i unless pumps are tripped. occur. The impact of Long term operation of this transient on PTS l compressors without cooling sequences is limited water can lead to their since the LOCA la not l failure. However, even if coupled to a failure to instrument air pressure la automatically initiate u lost, MFW regulating valves HPSI. (One HPSI train remain closed. can be initiated automatically.)

9. 4 KVAC Buses ' Reactor and turbine trip on Trip RC pumps on high (a) With promptly initiated

11 & 12 reduced feedwater flow or controlled bleed-off remedial actions, the other causes. CCW lost to RC temperature. Restore power impcot of this transient pump seals which are presumed to one or both 4 KVAC buses, on PTS sequences la -

to be running. Seal failure considered negligible. .

will result if RC pumps are !

not tripped. Auxiliary (b) Without remedial actions, reedwater initiated but HPSI a coupled small LOCA due i and CVCS are deenergized. to RC pump seal failures j (Loss of 4 KVAC buses and a loss of HPSI and initiated by loss of 500 KV LPSI injection capacity bus la of less interest to would occur until power i PTS ainee RC pumps are was restored.

deenergized and pump seal failure is not coupled directly to loss of_CCW.)

l

- .- _.,_ r _, -, . . , ..

j TABLE 11. (Continued) *2 Estimated Impact Initiating Failure Description of Transient Available Remedial Actions on PTS Sequences ;

10. 480 V AC MCC 104 R ' Reactor and turbine trip on Restore power to one or both (a) With promptly initiated j

& 114R reduced feedwater flow. McC's or align unit 2 air remedial actions, the f Letdown flow isolated and 3- compressors to unit 1 impact of this transient i j pump CVCS injection initiated.. Instrument air header. If on PTS sequences is Sources of water to VTC and unsuccessful, trip RC pumps considered negligible. l Chg. pumps remain isolated on high blecd-off temperature

and HPSI discharge valves re- and trip HFW pumps on high (b) Without remedial actions,

! main closed. Loss of control steam generator level. Trip a coupled small LOCA due t power to instrument air com- or deenergize Chg. pumps to RC pump seal failures ,

pressors may result in' a loss prior to draining VTC. If and a loss of HPSI and !

of instrument air pressure RC pump seal failure occurs LPSI injection capacity. I and isolation of CCW to the prior to restoration of would occur until power i RC pumps. Seal failure will electric power, open HPSI was restored or the HPSI/ ;

occur if RC pumps are not discharge valves manually, LPSI injection valves jg tripped. Feedwater bypass valves will open resulting in if possible, were opened manually.

i increasing steam generator

-levela. (Loss of MCC's due to lose of 4 KV bused dis- '

l oussed in transient 9, above),

< Comoressed Air System Failures

11. Pasalve Failure Both MFW regulating valves Trip RC pumps on high (a) With promptly initiated t of Instrument freeze in position and bypass controlled bleedoff remedial actions, the l Air Header valves open. CCW and service temperature and close MF1V's impact of this transient water to "non-essential" on high steam generator level, on PTS sequences la ;

components including RC pump considered negligible.

seals isolated. Following expected reactor and turbine (b) Without remedial actions, trip, both steam generators a coupled small LOCA due overfed and loss of CCW to RC to RC pump seal failures :

I pump seals will result in a and a steam generator small LOCA unless RC pumps overfill transient would are tripped. occur.

s ~~ -, .-. . ...., . _ ,

_ 7,

. . . .. , , , ~

i

~.3 .

TABLE 11. (Continued) l Estimated Impact I2itiating Failure Description of Transient Available Remedial Actions on PTS Sequences r

12. Passive Failure AFS Train B operation Close operable isolation Assuming the main instrument of AFS Instrument initiated with control valves valves in AFS injection paths air header remains Air Header "B" open. Failure not expected to both steam generators, pressurized, the impact of to depressurize main this transient on PTS instrument air header due to sequences is considered l available compressor negligible.

ca pacity. ,

Coolina Water System Failures 13 CCW Pump 11 CCW flow to RC pump seals, Start CCW pump 13 or 12. . (a) With promptly initiated CEDM's and letdown heat Trip RC pumpa on high remedial actions, the i

exchanger stops. RC pump controlled bleed-off impact of this transient seal failure will result if temperature if CCW flow on PTS sequences la y; CCW flow not restored or RC cannot be restored. considered negligible, pumps tripped.

(b) Without remedial actions, a small LOCA due to RC

. pump seal failures would occur. The impact of this transient on PTS nequences is limited since the LOCA is not coupled to a failure to, automatically initiate HPSI.

t

...a , . _ _ _ -- . - _- g_, ., , _, . __.

(-

TABLE 11. (Continued) 'l Estimated Impact Initiating Failure Description of Transient Available Remedial Actions on PTS Sequences

14. Closure of CCW CCW flow to RC pump seals Trip RC pumps if CCW (a) With promptly initiated

Valve CV-3832 and CEDH's stops. RC pump isolation valves cannot be remedial actions, the seal railure will result it rapidly opened. impact or this transient or CV-3833 CCW flow not restored or RC on PTS sequences is pumps tripped, considered negligible.

(b) Without remedial actions, a small LOCA due to RC pump seal failures would occur. The impact of this transient on PTS sequences is limited since the LOCA is not coupled to a failure to ;

c) automatically initiate HPSI.

e i

i 1

{

~

TARIR 11. (Continued) .y ,

Estimated Impact 4

Initiating Failure' Description of Transient Available Remedial Actions on PTS Sequences t

i

15. Service Water Service water flow to air Start service water pump 13 (a) With promptly initiated Pump 11 compressors and turbine or open valves in connecting remedial actions, the components ' atop. Turbine and piping from heat exchanger 12. impact of this transient reactor trip expected,. unless If cooling water to air on PTS sequences is i

service water flow restored. compressors cannot be considered negligible.

i Long term operation of the maintained, align Unit 2 air compressors without compressors to Unit 1 (b) Without remedial actions, service water may lead.to instrument air header. If CCW a small LOCA due to RC compressor failure and loss flow to RC pumps is isolated pump seal failures would '

' occur. The impact of of instrument air pressure on loss of instrument air (unless alternate compressors pressure, trip RC pumps, this transient on PTS are aligned). In the event sequences is limited

' of loss of instrument air since the LOCA is not pressure, CCW flow is coupled to a failure to automatically initiate

$ isolated from the RC pump HPSI.

seals, however, steam t generator overfeeding would not occur ' regulating valves j are closed). ,

t I

I !

t

-- ,_ r._ _ . . . , - _, - _, , _ . . , - . , . . _ . , . . ,

. . ~ .

. 3

~

< TABLE 11. (Continued) ~2 Estimated Impact Initiating Failure Description of Transient Available Remedial Actions on PTS Sequences

16. Closure of See Item 15 above, Service Locally reopen isolation (a) With promptly initiated Service Water Water Pump 11 valve it possible. If. valve remedial actions, the Valve CV-1637 cannot be reopened, align impact of this transient or CV-1639 Unit 2 compressora to Unit 1 on PTS sequences la instrument air header and conaldered negligible, trip Unit 1 compressors to prevent damage. If CCW flow (b) Without remedial actions, to RC pumps is isolated on a small LOCA due to RC loss of instrument air pump seal failures would pressure, trip RC pumps. occur. The impact of 1 this transient on PTS sequences is limited ;

since the LOCA la not ;

coupled to a failure to 9 automatically initiate l H PSI. ;

,i 2

i

~ , e.

1 1. -

e.

1 l

The three double bus failure transients are judged to be very unlikely.

I' However, the combined frequency of the double bus failures and failures of the

[l operator to take remedial actions should be eatincted and compared to the f

independent frequencies of a small LOCA and HPSI failure to evaluate the significance of transients 1, 9 and 10 to PTS.

I; Other electrical systems failures (Transients 6, 7 and 8) would result in r termination of cooling water to the RC pumps as shown in Table 11. However, m

they would not result in coincident loss of HPSI and therefore are considered less significant. Also, failure of control power to the MFW regulating valves (Transients 4 and 5) would result in a potential overfill of one steaa

! generator. However, other coincident, coupled events adverse to PTS were not identified.

2. Ca=nressed Air System Failures One compressed air system failure, a passive failure of the instrument air header, Transient 11, has been identified as potentially significant to PTS.

J Depressurization of the instrument air header would result in both MFW regulating valves freezing in position prior to turbine trip (open) and isolation of CCW flow to the RC pump seals and service water flow to the l turbine building equipment. The turbine and reactor are expected to trip on

! loss of cooling water to the generator or turbine resulting in overfeeding both steam generators. The steam generator overfeed may be terminated by the

{' operator by closing the MFW isolation valves or tripping the MFW pumps. In I

t addition to terminating the overfeed, MFW pumps and condensate pump trip is

,- required due to loss of service water to the pump bearing coolers.

j As discussed above, loss of CCW to the RC pump seals could result in seal failure, a coincident coupled small LOCA. The operator must trip the RC pumps on high controlled bleed-off temperature to prevent seal damage and possible failure.

The frequency of the postulated passive failure and failure of the operator to take appropriate remedial action should be estimated and compared to the 63 l

~ , e, p

frequency of coincident independent small LOCA and steam generator overfeed events to evaluate the significance of transient 11 to PTS.

j- -

The other compressed air system failure considered was a passive failure of an T

AFS instrument air header. This transient may result in the spurious

~

initiation of one AFS train; however, a coupled ' impact on the main instrument

[? air system is believed to be very unlikely due to the large compressor

'" capacity available.

, t' k Other support system failures would result in loss of air compressors due to loss of electric power or compressor cooling water (Transients 6, 7, 8, 9, 15 and 16). However, in each case, instrument air pressure would be lost after

! the MFW regulating' valves had closed in response to turbine trip. This action eliminates the coupling of a steam generator overfeed with other PTS adverse 4

responses. ,

3 Coali", water system r=<tures i

Cooling water system failure considered to be significant to PTS were not identified. Failure of the operating CCW pump (Transient 13) or closure of a CCW containment isolation valve (Transient 14) result in a loss of CCW to the I ! RC pump seals. However, additional, coupled responses adverse to PTS were not I

identified. Prior to tripping the RC pumps to protect the pump seals j following a CCW failure, the operator has the option of starting a standby CCW pump or reopening an inadvertently closed isolation valve. Other support j system failures which could lead to loss of CCW have been identified in ,

'~ Transients 6, 7, 8, 9 and 11.

.( Loss of service water pump 11 or closure of an isolation valve (Transients 15 and 16) would lead to loss of cooling water to the air compressors, and

turbine components. The operator has several remedial actions possible including initiating flow from service water heat exchanger 12 to service j water train 11 or reopening an inadvertently closed isolation valve. In the event air compressor cooling water cannot be restored, the operator has the

- option of aligning the Unit 2 air compressors to the Unit 1 instrument air

' header prior to Unit 1 compressor failures (or manual trip).

( 64

, L l

~. n t

_( . ~

1 .

I~

!, If service water is not restored, a turbine and reactor trip'is expected prior to loss of instrument air pressure. This results in the MFW regulating valves closing and preventing a coupled steam generator overfeed with other PTS

[

adverse events.

'~

Other support system failures which would result in a loss of service water flow to the air compressors have been identified in Transients 6, 7, 8, 9 and 11.

I' l'

l:

c l

L.

r i

i l

r T

4

+

65 u

n. ne 6.0 REFutENCES

1. Memorandum from D. L. Selby (ORNL) to Distribution, November 22, 1983

2. Letter Report from J. W. Minarick to D. L. Selby, " PTS Initiating Event f'

Frequency and Branch Probability Screening Estimates - Calvert Cliffs Nuclear Power Station," October 7,1983 l

i

, 3. At this level of evaluation, the events / systems eliminated were passive

! and no response to support system failure was considered possible.

4 The source of design information used to obtain these summary results is f identified in the individual systes/ component design discussions rather I thn on Table 3 for convenience.

1

5. Calvert Cliffs Nuclear Power Plants 1 and 2 updated Final Safety Analysis Reprt (FSAR), Chapter 7 t

i 6. FSAR, Chapter 9 1

7. "Significant Components Affecting PTS Sequences - Table 1,' C. Yoder (BGE).

i

8. "Calvert Cliffs Schematic Diagram, Turbine Steam Dump and Bypass

Controls," 61-061E, Rev. 8.

, 9 "Calvert Cliffs Piping and Instrument Diagram, Main Steam and Reheat,

! Unit 1, 60-225-E, Rev. 25

10. Calvert Cliffs Schematic Diagram, Turbine Auxiliaries, Turbine Alarms and Trips, 1E-74.

11. Calvert Cliffs Reactor Auxiliaries, Pressuriser Relief 1ER7-402 and 1ERV-404, 61-075-B, Rev. 3 i

12. FSAR, Chapter 4 66 I

l

ML20084A333

Contents

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1.0 INTRODUCTION

SUMMARY

6.0 REFERENCES

1.0 INTRODUCTION

4.2 DESCRIPTION

SUMMARY

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ML20084A333

Text

1.0 INTRODUCTION

SUMMARY

6.0 REFERENCES

1.0 INTRODUCTION

4.2 DESCRIPTION

SUMMARY

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