ML20101Q321
| ML20101Q321 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 11/21/1984 |
| From: | Mason C, Mcbride A, Selby D OAK RIDGE NATIONAL LABORATORY, SCIENCE APPLICATIONS INTERNATIONAL CORP. (FORMERLY |
| To: | NRC |
| Shared Package | |
| ML20101Q289 | List: |
| References | |
| REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR NUDOCS 8501070552 | |
| Download: ML20101Q321 (117) | |
Text
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A PRESSURIZED 'HIERMAL SHOCK EVALUATION OF ' DIE H. B. ROBINSON UNIT 2 NUCLEAR POWER PLANT Chapter 3. Development of Overcooling Sequences for H. B. Robinson Unit 2 Nuclear Power Plan t written by C. Nason A. McBride D. Olsen Science Applications, Inc.
and D. L. Selby Oak Ridge National Laboratory for The PTS Study Group of -
Engineering Physics and Mathematics Division Oak Ridge National Laboratory Date of Draft: November 21, 1984 l
NOTICE: This document contains information of a preliminary nature. It is subject to revision or correction and therefore does not represent a final report.
- Research sponsored by U.S. Nuclear Regulatory Commission under Contract No. DE-AC05-840R21400 with the Martin Marietta Energy Systems, Inc.
with U.S. Department of Energy.
8501070552 841217 PDR ADOCK 05000261 p PDR et es e r
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r A PRESSURIZED THERMAL SHOCK EVALUATION OF THE H. B. ROBINSON UNIT 2 NUCLEAR POWER PLANT List of Chapters Chapter 1 Introduction Chapter 2 Description of the H. B. Robinson Unit 2 Nuclear Power Plant Chapter 3 Development of Potential Overcooling Sequences for H. B.
Robinson Unit 2 Chapter 4 Thermal-Hydraulic Analysis of Potential Overcooling Sequences i for H. B. Robinson Unit 2 Chepter 5 Probabilistic Fracture-Mechanics Analysis of Potential Over-cooling Sequences for H. B. Robinson Unit 2 Chapter 6 PTS Integrated Risk for H. B. Robinson Unit 2 and Potential Mitigation Measures Chapter 7 Sensitivity and Uncertainty Analyses of Through-the-Wall -
Crack Frequencies for H. B. Robinson Unit 2 i
Chapter 8 Sammary and Conclusions l
l
.i
./ et * #
- 3. DEVELOPMENT OF OVERC00 LING SEQUENCES FOR H. B. ROBINSON UNIT 2 NUCLEAR POWER PLANT 057 3.1. Introduction 3.2. System State Trees 3.2.1. Reactor Vessel and Its Internals 3.2.2. Reactor Coolant System 3.2.3. Main Steam System 3.2.4. Feedwater and Condensate System 3.2.5. Auxiliary Feedwater System 3.2.6. Safety Injection System 3.2.7. Chemical and Volume Control System 3.3. Potential Initiating Events 3.3.1. Events Causing a Decrease in the Charging Flow Enthalpy 3.3.2. Events Causing Excess Steam Flow from the Steam Generators 3.3.2.1. Large Steam-Line Break 3.3.2.2. Small Steam-Line Break 3.3.2.3. Failed-Open STM PORVs or SDVs .
3.3.2.4. Main Steam-Line Safety Valves Open and Fall to Close 3.3.2.5. Reactor Trip 3.3.3. Events Causing a Decrease in the Feedwater Enthalpy 3.3.4. Events Causing Feedwater Overfeed 3.3.5. Inadvertent Safety Injection (SI) Events 3.3.6. Loss-of-Coolant Accidents (LOCAs) 3.3.7. Events Consisting of Pressurizer Pressure Control Failures l 3.3.8. Events Leading to Steem Generator Tube Rupture l 3.3.9. Sanmary 3 .4 . Initiator-Specific Event Trees l 3.4.1. Steam-Line Break at Hot 0% Power 3.4.2. Steam-Line Break at Full Power 3.4.3. Reactor Trip 3.4.4. Small-Break LOCA at Full Power 3.4.5. Medium-Break LOCA at Full Power 3.4.6. Small-Break LOCA at Hot 0% Power 3.4.7. Medium-Break LOCA at Hot 0% Power 3.4.8. Tube Rupture 3.4.9. Loss of Main Feedwater 3.5. Event Tree Quantification and Collapse 3.5.1. Reactor Trip 3.5.2. Large Steam-Line Break at Hot 0% Power
.i .. - a
2
- e. g 3.5.3. Small Steam-Line Break at But 0% Power
hj 3.5.4. Large Steam-Line Breal at Full Power 3.5.5. Small Steam-Line Break at Full Power 3.5.6. Small-Break LOCA at Full Power 3.5.7. Medium-Break LOCA at Full Power 3.5.8. Small-Break I4CA at Hot 0% Power 3.5.9. Medium-Break IACA at Hot 0% Power 3.5.10. Tube Rupture 3.5.11. Loss of Main Feedwater 3.5.12. Support System Failures 3.5.13. Sequence Summary J
- / am . ,
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HBR-3 .3 3.0. DEVELOPMENT OF OVERC00 LING SEQUENCES FOR H. B. ECBINSON UNIT 2 NUCLEAR POWER PLANT 3.1. Introduction The development of overcooling sequences that potentially could result in pressurized thermal shock (PTS) to a reactor vessel is difficult due to the complex interactions of the many systems comprising a nuclear power plant.
The first step in the development of these sequences for H. B. Robinson Unit 2 was the analysis of plant systems to determine possible system operating states, including failed states, which could affect an overcool-ing transient. The system state trees resulting from this analysis are presented in Section 3.2. The second step was the identification of specific initiating events which could lead to overcooling transients, fol-lowed by a review of the events to evaluate whether they need be considered i with respect to PTS. A summary of the initiators determined to be applica-
'ble to the H. B. Robinson Unit 2 PTS analysis is presented in Section 3.3.
l The third step in the development of the overcooling sequences was an exam-ination of the system operating states with respect to the initiating events and the development of initiator-specific transient sequences in an
( event tree format. In each case the event tree includes pertinent operator actions associated with each initiator that were determined from a review of plant operating procedures. The resulting event trees are presented in l
Section 3.4.
l Finally, as described in Section 3.5, the expected frequency of each event tree transient was calculated based on data from H. B. Robinson Unit 2 and
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HBR-3.4 l
generic failure data. The calculated frequencies and engineering judgement were then used to group the event tree sequences to develop a final list of sequences to be considered in subsequent thermal-hydraulics and fracture-mechanics analyses.
3 .2 . System State Trees Each of the systems discussed in Chapter 2.0 was examined to identify those system and subsystem functions which could have a significant effect on the
! temperature or pressure in the reactor vessel downconer region, and system state trees were then developed for the pertinent systems, he headings i
and the possible branches associated with these trees are described in this section, but for brevity the system state trees themselves are not i included.
i System state trees represent possible system operating states in response l to an unspecified initiating transient. Since the systems were analyzed on i a functional basis, the branching on the state trees may be more complex than simple binary success and failure branches. H is will be noted by qualifying conditions specified for some of the branches. ,
hermal-hydraulic " conditioning events" are also included on the functional system state trees. R ose events serve a dual purpose: (1) they limit the I samber of potential end states for a given system state tree that must be ,
I considered, and (2) they permit the compling between the various functional system state trees (due to the thermal-hydraulic lateractions). He term
" conditioning events" is used since subsequent system responses are ;
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HBR-3.5 /
considered conditional on the thermal-hydraulic parameters which typically comprise the event description.
3.2.1. Reactor Vessel and Its Internals The components of the first system examined consist of the pressure vessel and its internals, or, more specifically, the reactor core and its support structure. Since a reactor trip is assumed to occur following any initiat-ing transient considered in the PTS analysis, the only " action" expected of the reactor core is that it achieve subcriticality following the trip. The power generated by the core following the trip is a known function of time and past operation (i.e., it is not a function of an initiating event or the system failure), and thus no system state tree was developed for the pressure vessel and its internals.
3.2.2. Reactor Coolant System o
l As described in Chapter 2.0, the function of the reactor coolant system i
(RCS) is to remove heat from the reactor core and transfer it to the secon-dary system. This primary function is accomplished by two subfanctions:
(1) maintaining reactor coolant loop flow from the core to the steam gen-erators and (2) controlling the reactor coolant loop pressure to maintain the reactor coolant in a subcooled liquid state. Thus, there is a poten-tial need for two system state trees to describe this system. [Another subfnaction, control of reactor coolant inventory, is discussed in the sub-sequent sections on the safety injection system (SIS) and the chemical and volume control system (CVCS).]
L
.a.h a . d A rsvier cf r3cster ecolcat systco comp:nents rsyosicd the,t.ths r,esctor ~ ,y ,
I cos1 cat pumps (RCPs) compriso the cnly sat of cotivo compensnts rsq2 ired to maintain forced circulation of reactor coolant. For an overcooling event ,
of any consequence, the RCPs are expected to be manually tripped by the i operator,* an act that increases the potential for loop flow stagnation, ,
which, in turn, could lead to reduced downcomer temperatures. Hence, I failure to trip the pumps would improve the situation from the PTS point of view; however, as the procedures are presently written, this would consti-tute a failure of the operator to comply with procedures. Since credit should not be taken for a failure which could reduce the severity of a transient, the assumption was made that the RCPs would always be tripped a
within 30 seconds following a safety injection actuation signal (SIAS).
Thus, the operation of the pumps was not considered in the systen state tree.
As discussed in Section 2.3.4, the reactor coolant loop pressure is con-trolled by the pressurizer heaters, the pressurizer spray valves, two pres-suriter power-operated relief valves (PZR PORVs), and three pressurizer safety valves (PZR SVs).
- The operating mode of the pressurizer heaters has little effect on cooling sequences and was not included in the system state tree. For any overcool-ing event of significance, the pressurizer will drain and the heaters will automatically turn off. 'Ihis assumed proper operation of the heaters need not be addressed in the system state tree. Even if the heaters failed to turn off with low pressurizer level, their continued operation would not affect the RCS pressure (although heater damage could be expected).
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HBR-3.7 Restoration of pressurizer water level would permit the heaters to turn back on and function as required. The additional effect of the heaters is considered to be small, and, in any case, the assumption that they will operate as designed accounts for their effect.
The pressurizer spray valve operation was also eliminated from the system state tree, since tripping the reactor coolant pumps stops the normal spray flow regardless of spray valve position. H is leaves only the auxiliary spray from the CVCS. Even though the auxiliary pressurizer spray can have a significant effect on repressurization, it can be initiated only manu-ally, which makes it an operator action that is addressed on an event-specific basis on the event trees and not on the system state trees.
Thus, the system state tree for the RCS is limited to the control of the
~
coolant loop pressure, which, in turn, is limited to the potential states on of the PZR PORVs and the PZR SVs. He system state tree headings and the I
' potential branches for each heading are described in Table 3.1.
1 3.2.3. Main Steam System The main steam system was described in Section 2.3 as consisting of eight major subsystems: (1) the steam generators (SGs), (2) the main turbine stop valves and governor valves, (3) the steam dump valves (SDVs), (4) the steam power-operated relief valves (SIM PORVs), (5) the main steam-line isolation valves (MSIVs), (6) the main steam-line safety valves (SSVs),
(7) the steam-line flow restrictors, and (8) the azin steam check valves.
liLP.-3 . 8 Tchle 3.1. Description cf st:t tree headings and potential br:nches for reictor coolrt system pressure control 2 System State Heading Description Descriptions of Tree Heading and Discussion Conditional Branches Max RCS pressure This thermal-hydraulic The two branches required are:
< lift pressure parameter identifies the for PZR PORVs. need for components in (1) Pressure < PZR PORY lift set point.
this system to function. (2) Pressure > PZR PORV lift set point.
If the pressure < lift set point, no components in this system are re-quired to change state, if the pressure > lift set point, some components will be required to change state. Thus, two branches are required under this heading.
PZR PORVs open Given that the PZR PORVs If the RCS pressure < PZR PORV lift on demand. are required to open, set point, no branches are the potential exists for required under this heading.
one or both to fail to open. A failure for a PZR PORY to open could If the RCS pressure > PZR PORY lift
.e lead to the opening of a set point, three branches are PZR SV, which is not iso. required:
latable. The number of
(. i
- branches required depends (1) Both PZR PORVs open.
on the initial thermal. (2) One PZR PORY fails to open.
. hydraulic branching. (3) Both PZR PORVs fail to open.
Max RCS pressure This thermal-hydraulic If the RCS pressure < PZR PORY lift
< lift pressure parameter identifies the set point, it will be < PZR SV for PZR SVs. demand for PZR SVs. The lift set point, and no branches number of branches re- are required.
quired depends on the initial thermal. If the RCS pressure > PZR PORV lift hydraulic branching. set point, two branches are required:
(1) PZR SV demand exists.
(2) PZR SV demand does not exist.
PZR SVs open Given that the PZR SVs Four branches are required:
on demand. are required to open, i
t the potential exists (1) All three PZR SVs open. -
i for one, two or all (2) One PZR SV falls to open.
three to fail to open. (3) Two PZR SVs fall to open.
l (4) All three PZR SVs fall to open.
l l
PZR SVs close For those branches if only one PZR SV has oper.ed, on low pressure. involving the opening of two branches are required:
l the PZR SVs, the failure of the valves to close (1) PZR SV closes.
on low presstre must be (2) PZR SV fails to close.
considered. The number of branches reqrited is If only two PZR SVs have opened, determined by the number three branches are required:
of PZR SVs that opened.
(1) Both PZR SVs close.
(21 One PZR SV fails to close.
(3) Both PZR SVs fall to close.
If all three PZR SVs have opened, e four branches are required:
l l
(1) All three PZR SVs close.
( (2) One PZR SV falls to close.
(3) Two PZR SVs fall to close.
3 (4) All three PZR SVs fall to close. ,
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IIBR-3,9 Table 3.1. (Continued)
System State lleading Description Descriptions of Tree IIcading and Discussion Conditional Branches PZR PORVs close For those branches If only one PZR PORV has opened, on demand, involving the opening of two branches are required:
the PZR PORVs, the failure of the valves to close on (1) PZR PORY closes.
demand must be considered. (2) PZR PORY falls to close.
The number of branches required is determined if both PZR PORVs have opened. three by the number of PZR PORVs branches are required:
that opened.
(1) Both PZR PORVs close.
(2) One PZR PORY fails to close.
(3) Both PZR PORVs fail to close.
Block valves A block valve is provided if only one block valve is demanded, close. to isolate cach PZR PORV two branches are required:
if it fails to close auto-matically. The number of (1) Block valve closes.
branches is determined by (2) Block valve fails to close. j the number of valves !
demanded. If both block valves are demanded, three branches are required:
(1) Both block valves close.
(2) One block valve falls to close.
. (3) Both block valves fall to close.
- Acronyms used in this table are: RCS = reactor coolant system, PZR PORY = pressurizer power-operated relief valve, and PZR SV = pressurizer safety valve.
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i Of Th3 eight subsystems, the steam generators and the flow restrictors have passive functions and are not included on the system state tree. The sys-tem state tree headings used to define the condition of each of the remain- ,
e ing subsystems, together with descriptions of the possible branches for 7 each heading, are presented in Table 3.2.
3.2.4 Feedwater and Condensate System In Section 2.4 of this report the seven major subsystems of the feedwater and condensate system were identified as: (1) the condensate storage tank, (2) the condenser, (3) the condensate pumps, (4) the feedwater heaters, (5) the main feedwater (NFW) pumps, (6) the MFW control valves and bypass l
l valves, and (7) the MFW isolation valves.
l l
The condensate storage tank, the condenser, and the feedwater heaters have passive functions and thus are not considered in the system state tree.
'The active functions of the condensate pumps, the NFW pumps, and the MFW control and isolation valves provide feedwater flow in their operating (open) condition while stopping flow in their tripped (closed) condition.
l These component functions have been grouped under the heading of " main
\
i \
feedwater flow isolated on demand. "
Following any reactor trip, the NFW regulating valves are required to close l
and the bypass valves are opened (manually) to about 5% flow. This action is referred to as " main feedwater runback. " The question of whether run-
! back occurs must be addressed in the system state tree. ,
~ . . _ . . . . _ _ . . _ _ _ _ _ _ _ . _ _ . _ _ _ _ _ _ . _ _ _ . _ _ _ _ _ _ _ , _ _ _ _ . , _ _ . _ _ _ _ . _ . _ . . _ . _ , . .
HBR-3 ell Table 3.2. Description of state tree headings and potential
' branches for the main Steam system
- System State f(eading Description Descriptions of Tree Heading and Discussion Conditional Branches Turbine seep This step identifies whether The two branches required are:
enhes and the turbine trips on demand.
governer Closure of the turbme stop (I) All step valves er gerner sahes clone, val es or turbine governor enhes close.
valves is the function con. (2) One er more stop vehefs) and one sidered. Thus, two branches se store ge*ereur enhers) fail to are required under this close.
heading.
SDYs open, liigh T,., or high steam Sia branches are required:
pressurs thermal-hydraulic condnen could cause the (1) AR five SDVs opes.
SDvs to the condenser to (2) One SDV fails to opes.
open. (3) T=e SDVs fail to opes.
(4) nree SDvs fail to spee.
(5) Fear SDVs fail se opes.
(6) Au five SDVs fail to opee.
SDI PORVs opes, High T,., or high steam Four branches are required:
pressure shermal-hydraulic conditen could result io (1) AR three STM PORVs spee.
the steam PORVs opening. (2) One STM PORY fails se spee.
(3) Tee Snl POR)s fell to spes (4) AM three STM PORVs fad to open, steem pressure This thermal-hydraulic Only one branch is required:
< SRV hrt net functon opens the 12 SRVs point. (four on each of three (1) SRVs spea, lines), which lift in pairs .
at various pressures. It is assumed that even if some SRVs fail to open, one or more SRV(s) will eventually open on each line if the steam pressure > SSV hft pressure.
SRVs close Gi cn that one or more pairs Four branches are required-en demand. of SRVs open, the question of whether or not they close (I) As twelve SRVs close, on demand must be eaamined. (2) One er more SRVs fail to etene se Since both a single valve ese bne.
failure and multiple valve (3) One er more SRVs fail to close se failures are considered to be toe lines.
small steam-hne breaks, (4) One er mere SRVs fan to elene se they need not be treated au three lines.
indwulually.
STM PORVs Failure of a STM PORV to Four branches are required:
close se close is equivalent to a demand, small steam-hne break up. (1) AM three STM PORVs eleee.
stream of the MSIVs. (2) One STM PORY fails se elese.
(3) Tee STM PORVs fail to elese.
1 (4) An three STM PORVs fail se elene.
SDVs etene Failure of the SDVs to close bSia branches are required [
se demned. is equivalent to a steam.
i I line break downstream of the (1) AM five SDVs riese.
l MSivs. (2) One SDY fails to elene.
(3) Two SDVs fail to close.
(4) Three SDVs fail to etene.
t (5) Fear SDVs fail to eleee.
l (6) AR five SDvs fa3 se elese.
l MSIVs cleie Closure of the MSIVs en Four branches are required.
es demand. demand can isolate failed-opea SDVs. (1) AB three MSIVs close, w .. . e (2) One MSIV fails se elene.
(3) Tee MSIVs feu to etene.
(4) AB three MSIVs fall to elese.
l operated rc5cf valve, SRV = safety relief valve, and MSIV - main steam isolaten valve.
1 i
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HBR-3.12 l'
The coupling of components on a functional basis produces the system state /
tree headings and possible branches identified and explained in Table 3.3.
l 3.2.5 Auxiliary Feedwater System As described in Section 2.5, the principal active components of the auxili-ary feedwater (AFW) system are: (1) the AFW pumps, (2) the AFW control valves, and (3) the AFW block valves.
The control signals and functions of these components are used to construct ,
the system state tree headings and branches described in Table 3.4. It should be noted that the AFW system state tree is constructed to consider three flow conditions to the steam generators: maximum flow, normal flow, and no flow.
l 3.2.6 Safety Injection System 9
The safety injection (SI) system consists of three types of coolant injec-tion processes: (1) high pressure injection, (2) coolant injection from the accumulators, and (3) low pressure injection. (As noted in Chapter 2,
! two low pressure injection (LPI) pumps also serve as residual heat removal l (RHR) pumps.]
l On a first evaluation it appeared that failure of any of the injection processes would be more of an undercooling concern that an overcooling problem, and, therefore, the conservative perspective would be to assume ,
that all components would work when required and no system state tree would l
e . .-
HBR-3.13 Table 3.3. Description of state tree headings and potential branches for main condensate and feedwater system
- System State Heading Description Descriptions of Tree Heading and Discussion Conditional Branches MFW regulating Following a reactor trip, Four branches are required:
vahes close. the MFW system is required to run back to prevent a (1) All three MFW regulating valves close.
steam generat,r overfeed. (2) One MFW regulating valve fails to close.
The MFW regulating valves (3) Two MFW regulating valves fail to close.
will throttle to control the (4) All three MFW regulating valves fail to steam generator level In close.
addition, a reactor trip and low T will close the control valves. Rather than identify several branches to cover the various levels of runback possible, the branches under this heading bound the potential conditions by assuming that complete runback occurs (i.e.,
valves close) or that no run-back occurs (i.e., valves fail to close).
MFW pumps Upon occurrence of an SI Three branches are required:
trip. signal or a high SG level signal. the MFW pumps (two) (I) Both MFW pumps trip.
trip. This is a redundant (2) Only one MFW pumip trips.
mechanism to prevent steam (3) Both MFW pumps fail to trip.
generator overfeed.
MFW isolated Upon occurrence of an St Four branches are required:
- on demand. signal, the MFIVs close, stopping all flow in the MFW (I) All three MFW lines are isolated.
lines. (2) Two MFW lines are isolated.
(3) One MfW line is isolated.
, (4) No MFW lines are isolated.
SI signal The SI signal trips the MFW Two branches are required:
generated pumps. closes the MFIVs and on de=ad the MFW regulating valves, (I) SI signal is generated.
l and prevents the bypass (2) SI signal is not generated.
valves from opening.
' Acronyms ured in this table are: MFW = main feedwater, Si = safety injection, SG - steam generator, and MFIV - main feedwater isolation valve.
I l
i l
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HBR-3 44 - "
Table 3.4. Description of state tree headings and potential branches for auxiliary feedwater system
- System State Heading Description Descriptions of Tree Heading and Discussion Conditional Branches AFW pump This signal will start the The two branches required are:
breakers open. two motor-driven AFW pumps.
Two branches are required (1) AFW pump breakers open.
to describe this system (2) AFW pump breakers fail to open.
state.
Two of three A low-level signal of < 15% Two branches are required:
SGs give low- volume from any two of the level signal. three steam generators will (1) Signals from two SGs occur.
start the steam-driven AFW (2) Signals from two SGs do not occur.
pump.
One of three A low-level signal of < 15% Two branches are required:
SGs gives low- volume from any one of the level signal three steam generators will (1) Signal from one SG occurs.
start the motor-driven AFW (2) Signal from one SG does not occur.
pumps.
Motor-driven Given that the MFW pump Three branches are required:
AFW pumps breakers open or that a low.
3 operate. level signal from one SG (1) Both motor-driven AFW pumps start.
occurs, the two motor-driven (2) One motor driven AFW peep falls to start. i pumps should start and deliver (3) Both motor-drives AFW pumps fall to start.
water to the steam generators.
The potential for failure of the pumps to start must be considered.
l . Steam-driven Given that low level signals Two branches are required:
AFW pump from two SGs occur, the steam-operates, driven AFW pump should start (I) Steam-driven AFW peep starts, and deliver water to the steam (2) Steam-driven AFW peep fails to start.
generators. The potential for failure of the pump to start must be considered. !
Nomleal AFW For those sequences in which Two branches are required:
flow occurs. flow occurs, the level of flow must be considered. The flow (1) Nomleal flow occurs.
is controlled at each pump, (2) Overfeed occurs.
rather than to each steam gen-erator. Nominal now rate and overfeed are the only options considered. (A low flow can be considered as no flow and s treated with the case in which AFW flow does not occur;i.e.,
pumps do not start.)
' Acronyms used in this table are: AFW = auxiliary feedwater, and SG = steam generator.
l 8
i L
HBR-3.15 l
be necessary. However, further evaluation of an SI failure revealed two potential overcooling factors. First, an initial SI failure with recovery at some later time could affect the loop flow characteristics and the cool-down rate. Second, an SI failure during a loss-of-coolant accident (LOCA) could result in low pressure injection and accumulator tank flow at a con-siderably earlier time. This, coupled with a potential repressurization from the charging pumps and thermal expansion, could have PTS consequences.
Thus, an SI failure is considered on the system state tree. Although i
l failure of accumulators and low pressure injection would most likely be of greater concern for undercooling sequences than for overcooling sequences, failure of these functions is retained in the system state tree for com- e pleteness. This results in the tree headings described in Table 3.5.
,j 3.2.7. Chemical and Volume Control System i
Four system functions were considered for the chemical and volume control
' system (CVCS) state tree: (1) letdown isolation, (2) letdown flow control, (3) charging flow heating, and (4) charging flow.
1 Letdown isolation and letdown flow control can be coupled together as one function: letdown flow. A letdown isciation signal occurs whenever a low pressurizer level signal is generated and thus is expected to occur for any overcooling transient. When letdown isolation occurs, letdown flow is stopped. Failure of both isolation valves to close or the failure of the 4
signal will cause failure of letdown isolation. In this case the flow con-trol valves must be examined to identify the flow state. A low pressurizer level will cause the flow control valves to stop the flow. Failure of
- - . . - _ - - = _ _ - _ . - - .___ - - - - _ - _ - - - _ - _ . _. -
liBR-3.16 f
7 Table 3.5. Description of state tree headings and potential sequence branches for the safety injection system
- System State Heading Description Descriptions of Tree Heading and Discussion Conditional Branches RG pressure This is a thermal-hydraulic The two branches required are:
> IIPI pump test that determines whether discharge or not HPI can physically (1) RG pressure > 1500 psig.
pressure of occur. Two branches are used (2) RG pressure 41500 psig.
1500 psig. to examine this system state.
HPI occurs For those sequences in which Two branches are required:
on demand, reactor coolant pressure 4 1500 psig, the question as to (1) HPI occurs.
whether or not IIPI is acti- (2) IIPI fails to occur.
vated must be addressed.
RG This is a thermal. hydraulic Two branches are required:
pressure > test that determines whether accumulator the accumulator water can (1) RG pressure > 600 psig.
pressure of discharge into the RCS. (2) RG pressure 4 600 psig.
600 psig.
Accumulators For those sequences in which Two branches are required:
discharge. RCS pressure 4 600 psig. the question as to whether the (1) Accumulators discharge.
accumulators will actually dis- (2) Accumulators fall to discharge.
charge must be addressed.
. RG pressure This is a thermal-hydraulic Two branches are required:
> LPI pump test that determines whether discharge or not LPI water can enter the (I) RG pressure > 175 psia, pressure of RCS. (2) RG pressure 4175 psia.
175 psia.
LPI occurs For sequences in which the RCS Two branches are required:
on demand. pressure falls below the LPI pump discharge pressare, the (I) LPI occurs.
question as to whether or not (2) LPI falls to occur.
coolant is injected must be addressed.
' Acronyms used in this table are: RCS = reactor coolant system, llPI = high.
pressure injection, and LPI = low-pressure injection.
e
x -
c HBR-3.17 these valves to run back will result in the normal letdown flow continuing.
Any intermediate flow rate is considered to be small both in size and in conse quence . Thus letdown flow is not considered for system state descrip-tion.
Heating of the charging flow is performed by the regenerative heat exchanger. The heat source for this heat exchanger is letdown coolant downstream of the letdown stop valves. Thus, when letdown isolation occurs, this heat source is automatically lost. The regenerative heat exchanger is a passive component in either mode and is not considered on the system state tree.
The low pressurizer level signal which isolates letdown also causes all operating charging pumps to accelerate to full speed. Anything less than
~
full flow will result in less cold water entering the primary coolant sys-tem and a slower repressurization rate. Thus, failure of the charging pumps to start is not considered. However, runback of the charging flow Iste in the transient is very important since failure to run back would l result in higher RCS pressures. Therefore, runback of charging pump flow must be considered. But since this was the only heading to be addressed under the CVCS system, no system state tree was generated for the CVCS.
Instead, the following two assumptions were made which define the system for overcooling events:
l I
f I
~^
HBR-3.18 j (1) Letdown isolation will occur whenever a pressurizer low-level signal is generated.
(2) All operating charging pumps will accelerate to full speed and l
provide full flow whenever a pressurizer low-level signal is gen-ersted.
! Charging flow will be automatically controlled to maintain pressurizer level when it is recovered. Failure of this control function is addressed, l
as appropriate, in the initiator-specific event trees.
3.3. Potential Initiatina Events l
I In the preceding section a set of system state trees was identified to describe potential system responses to overcooling event initiators. In this section, specific initiating events considered to have a potential for l
l- ' causing significant cooling of the reactor vessel are identified and dis-cussed.
The first step in identifying potential initiating events was the examina-tion of the RCS to determine what events would reduce the temperature in the reactor vessel downconer region. In general, the temperature in the downcomer region can be reduced by the injection of cold water into the r
vessel inlet lines; by a not removal of energy from the RCS via the steam I
generators; or by a breach in the primary system, resulting in significant RCS depressurization [a loss-of-coolant accident (IACA)]. The initiating i events identified as potentially leading to one of these cooling mechanisms
t HBR-3.19 fall into eight classes as follows:
(1) Events causing a decrease in the charging water enthalpy.
(2) Events causing an excess steam flow from the steam generators.
(3) Events causing a decrease in the feedwater enthalpy.
(4) Events causing feedwater overfeed.
(5) Inadvertent safety injection (SI) events.
(6) Loss-of coolant accidents (LOCAs).
l (7) Events consisting of pressurizer pressure control failures.
t l
l (8) Events leading to steam generator tube ruptures.
l l These classes of events were examined and initiator events specific to l
H. B. Robinson Unit 2 were identified as described below.
l j 3.3.1. Events Causing a Decrease in the Charging Flow Enthalpy 1'
l The charging flow enthalpy can be reduced by: (1) stopping the heat source to the regenerative heat exchanger (that is, stopping the letdown flow), ,
(2) increasing the charging flow in excess of the letdown flow, or (3) both f.
l
HBR-3.20 isolating the letdown flow and actuating (manually) the three charging pumps.
'llte maximum enthalpy decrease would be caused by isolation of letdown and manual actuation of the three charging pumps, but since this event is l addressed separately in Section 3.3.5, it will not be discussed here.
1 With the normal charging flow of 45 gpm, a loss of the regenerative heat exchanger would result in a decrease of 363*F or more in the charging flow
- 'I temperature.' If it is assumed that perfect loop flow mixing (see Section 4.4) and a simple mass-energy balance exist, which is the normal assump-tion, the loop flow temperature would be reduced by ~1eF. This is clearly not an overcooling event and thus loss of the heat exchanger is not con-sidered to be an initiating event.
An increase in the charging flow from nominal to maximum would increase the
' flow rate from 45 syn to 105 spa. The resulting water temperature would be l at 279'F rather than at the nominal temperature of 493'F. Again, if per-l=
fact loop flow mixing and a simple mass-energy balance are assumed the .
loop flow temperature would drop by only ~1eF, which is not an overcooling event. Thus increasing the charging flow is not considered to be an ini-tlating event.
l
+
In summary, events decreasing the charging flow enthalpy will not lettd to overcooling transients in H. B. Robinson Unit 2.
)
' l:!.!:.n: ::: '!.!::::::: I:': 'si:::l'!:l.!!i:.':7'::::ri.::':::.11:.
in.J:t. .".;,:,,*. .: .J.:.:!L::: 'J.'.::.:::; it:,: 'I:'; .'!::.'"
.......... . .. . i. ...i.. .
. ., , , - , - . _ , . _ . . _ ~ . _ ~ . . , , _ _ _ _ . _ . , _ _ . , _ _ , . , , , , , _ . . - _ . - _ . _ _ . . . ., .__-m_., . ~ m._ . _ , . . , . . - , . . .
HER-3.21 . .. r-3.3.2. Events Causing an Excess Steam Flow from the Steam Generators Events causing an abnormally high steam flow from the steam generators result in the depressurization of the steam generator (s) and an increased energy removal rate from the primary system. This class of potential ini-tlating events includes the following: (1) a large steam-line break, (2) a small steam-line break, (3) the SDi PORVs or SDVs opening and f ailing to close, and (4) one or more main steam-line SVs opening and failing to close. In addition, after a reactor trip has occurred, the failure of some pieces of equipment could also result in an excess steam flow. Thus, an additional initiating event is (5) a reactor trip followed by the opening I
of the SBI PORVs or SDVs as required, but with one or more of the SDI PORVs or SDVs failing to close.
3.3.2.1. Large Steam-Line Break
~
Potential large steam-line break events are characterized by two vari- '
i ables: the location of the pipe break and the core decay heat level, which l is the primary heat source following the reactor trip accompanying all l
l steam-line pipe breaks.
1 The extent and duration of the steam blowdown depend on whether the break is upstream or downstream of the main steam check valves and the main a steam-line isolation valves (MSIVs).* Decause these valves are very close Q
l
/
together, the probability of a break between them is considered to be small I
compared to the likelihood of a break in the remainder of the steam piping.
, Thus when reference is made in this report to upstream or downstream of the l
MSIV, we are actually referring to upstream or downstream of both the MSIV ,,
and the check valve on a line.
A be..k .pst r. .f th. fl.w r..t ri.t.r ..s1 e.e.i t i. . .oue.h.t f e e t.r n! it;'.':t...
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g R-3022 The check valves are downstream of the MSIVs and are intended to prevent the backflow steam from the unbroken steam lines to a steam-line break inside the containment. A break upstream of the MSIV, however, is not isolatable and one steam generator will blow down completely. 'Ibe MSIVs are designed to prevent blowdown of more than one steam generator and to isolate the steam generators from breaks downstream of the valves.
i i
e
IGR-3.23 Ezrminatien cf ths pipa configuratien chewsd that pips welds, pips elbcws, extracticn linas, ets. vare cbcut equ211y distributed upstrse::n cud doin-stream of the MSIVs. Since these are considered to be the most probable pipe break locations, it was assumed that a pipe break was equally likely to be upstream or downstream of the MSIV.* ,
The core decay heat source following the reactor trip can impact the down-comer temperature in two ways:
(1) It can promote natural loop circulation and mixing of the SI and loop flows.
(2) It can increase the downcomer temperature. [Whenever loop flow exists, the reactor coolant heated in the core will be tran-I sported to the downconer (vessel inlet) region.] l
/*
j The magnitude of the core decay heat source over the two-hour analysis ,
g.
t period used in this study was determined by applying the ANS decay heat k/
curve shown in Figure 3.1.g The curve shows that immediately following a
.[
reactor trip, the decay heat power would be ~7% of the preshutdown power, ,/'
j decreasing to ~1.2% after two hours (7200 seconds). If it is assumed that the plant has been operating at full power (2300 MWt), then 161 MWt would be generated as decay heat immediately following a reactor trip and ~19 Nyt would be generated two hours af ter the trip (7200 seconds). Based on a review of the operating history of H. B. Robinson Unit 2 during 1980, 1981, and 1982, this decay heat production would apply to 98.1% of the opera-
- th. N$ty.
st .h.1.14 e..ld plys...et.d le..,th.t th. sr.d. .f pipt.:f.11.,e tyet..t!.1 ...e dos. th..tr...
th..dof.,.tr..e..f the NS!Y.. Nov..... .i... th. .t..e-IA.. pip. f.it. . ...h..l... ... ..t th. g r.d.. of pipi.s ... ..t
.f Ily d... teed. th. .f f..t o.f.f or.di f f....t
.ls.ti..lly q...tifi.d. n. . th. .... f !!... pr.h.hility i. . d s.
f e, ha t h .p.t,..e ..d de .t,..e .f th. MSIV..
f., .. . . ... di .... .. d i.
l ' g.,. gig i . ,. ,ied i . d.f i..d .. i.e he...
i . ,i t .. . s . : . . . . . i . f i . i i . ..'. ., e ,. . .., t ,i.. ,, i .,
- n...h.td.
t . . . .h. n. .Ir..t .f ..... thi. ..... ,.th. th.. .. e . .t ..-
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1 I _ _ __
BBR-3.24
,8 -
T 1
l j =7 -
o 2 '
a
& 6 -
o 4
- t S -
3 8
2 4 .
E
- a:
U
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E S
o -
i 0 ' ' ' f ' f i '
O.I i 10 io2 803 10
- 10 3
106 TIME AFTER SHuf 00WN (StConds) r
[,
Figure 3.1. Thermal power after reactor shutdown.
t l
1 4
4
-.v,-e--r- ,-. , ,-e r, ~.-c.--,--n.,-.,--,~- .ce---.g. . . . - - - . , . . ~ . , , , - _ - -
HBR-3.25 tional time of the plant (i.e. 98.1% of the time excluding cold shutdown) . ,
' Thus this condition was deemed one for which the effects of a large
> steam-line break should be considered.
For the remaining 1.9% of its operational time. H. B. Robinson Unit 2 is in a hot 0% power or startup condition. Decay heat associated with a hot 0%
power condition depends upon the length of time since the previous reactor 6
shutdown.* A review of the plant's history revealed that in most cases 1
('80% of the time) plant startups occur within four days (~100 hours) after a reactor trip has occurred. Figure 3.1 shows that at 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> the decay .
heat production would be ~8.3 NWt over a two-hour transient period.# 1his
\-
was considered to be a second decay heat condition for which the effects of a large ! steam-line break should be considered.
~
Finally, there are scheduled outages and major incidents for which the time between shutdown and startup would be as much as 100 days or more. The
' decay heat for this condition would be less than 1 NWt. Rather than per-form an analysis for a third decay heat condition, it was decided to exam-i ine the sensitivity of the downconer temperature to changes in decay heat i
for the hot 0% power decay heat condition at 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> after shutdown. The effects of potentially lower decay heat events would then be reflected as part of the uncertainty.
On the basis of the above. two large leteam-linebreakinitiating V events were selected for examination for their potential importance:
l I '
'!'.;i:.h.h..n'!.:.:.:.:.n".'.!:.
, . . . . . .u.....
!'::N .i:i':!!::.;'t ! :',!!!',:::t
'!!.!!.:':n;'.l':!. ::.!!"' '" '"""" " " '"" "'" "'
HBR-3.26
- A large steam-lire break at full power with decay heat pro-i duction followed during the two-hour analysis period.
- A large ' steam-line break at hot 0% power with the decay heat production based on the heat generated approximately 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> after shutdown.
1 1
3.3.2.2. Small Steam-Line Break i
As for the case of a large steam-line break, potential small steam-line break events resulting in excess steam flow are characterized by two variables: the location of the break and the core decay heat level.
Many of the same considerations for the large break also apply to the small break. -
The most probable small break locations are in the small steam extrac- ,,
' tion lines that come off of the main steam lines. At H. B. Robinson Unit 2, almost all of the steam extraction lines are in the 4- to 6-inch f range. He lines to the S'IM PORVs are 6 inches, as are those for the 12 SRVs. Breaks upstream and downstream of the NSIVs are assumed to be equally likely.
v For the same reasons discussed above for the largel break, two decay
- ~~
.~.
heat levels are important for small breaks. Aus the small steam-11ae break initiating events to be examined also fall in two categories:
, - - - . - - - - - . - - - . .-,-.-,-,--._,-.,y-, _ , . , - , , -- , _ _ , , - ~ _ _ . - - - . . .--,,,,_-,-g, , - , - - ...w,-,--n- ., . . - _ - - .,, - , . -
HBR-3.27
- A small steam-line break at full power with decay heat pro-duction followed during the two-hour analysis period.
- A small steam-line break at hot O'.' power with the decay heat ,
production based on the heat generated approximately 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> after shutdown.
! 3.3.2.3. Failed-Open SIM PORVs or SDVs i SIM PORVs and SDVs which open and fail to close are equivalent to small -
- steam-line breaks. Since their locations are already known, only the l, decay heat level must be determined. For these events, the two decay heat levels defined above were again assumed, that is, the decay heat level fol-I lowing full power operation and at hot 0% power.
If during operation the reactor is tripped, the turbine is also tripped,
'and this causes the SDVs and, possibly, the STM PORVs to automatically open for a brief period of time. Failure of one or more of these valves to sub-sequently close has the same effect as a valve or valves spuriously opering i -
st power, since the reactor is expected to trip soon after the valves i /
, p/
open.' Thus those events involving STM PORVs or SDVs which spuriously open [/
l and in which a reactor trip occurs have been grouped together with SIM PORV and SDV failures to close following a reactor trip. Thesi events are dis-cussed in Section 3.3.2.5 below.
l At hot 0% power, there is no requirement for the SIM PORVs to operate (to ,
open). However, they will open periodically to control pressure and "D;.i:'iu'4' J '.;:2.:.'0 !.;;,';;;" !!:J"!,t;:.;'::t'.!!3: '"
HBR-3.28 potentially could fall open. This event was treated as a small steam-line break initiator and was not analyzed separately.
3.3.2.4. Main Steam-Line Safety Valves Open and Fall to Close A steam-line safety valve (SSV) that fails to close cannot be isolated.
Thus, SSV failures of this type will behave the same as the small steam-line breaks upstream of the MSIV discussed in Section 3.3.2.2. As a result, SSV failures of this type were grouped into the small steam-
- line break category and were not examined separately. (Note: If multiple breaks occur, they may be grouped into the large- - steam-line break category.)
1 3.3.2.5. Reactor Trip l
I i Although as noted in Section 3.3.2.3, a reactor trip is not an overcooling
' initiating event by itself, a reactor trip causes a turbine trip, which, in turn causes the SDVs to open and may possibly cause the STM PORVs also to open. Failure of the valves to close would result in excess steam flow.
Thus, an additional potential initiating event selected for examination is:
I l
!
- A reactor trip from full power.
1 l
Failure of the main turbine to trip following a reactor trip (open path to ,
the condenser) is a special case of the reactor-trip-induced excess steam
HBR 3.29 flow event. Owing to functional similarity of this event to a large steam-line break occurring downstream of the MSIV at full power, the tur-bine trip failure was grouped with the large steam-line pipe break cases I
and was not examined separately.
3.3.3. Events Causing a Decrease in the Feedwater Enthalpy
}
Two initiating events can cause a decrease in the feedwater enthalpy:
(1) a loss of feedwater heaters, and (2) the initiation of auxiliary feed-water flow to the steam generators.
A loss of feedwater heaters does not appear to result in an overcooling event, since sufficient energy is stored in the feedwater heaters and pip-las to prevent a rapid decrease in main feedwater temperature following a reactor trip. This is exemplified by the fact that the steam supply to the i
feedwater heaters is isolated following every turbine trip and the result-
' ngi feedwater temperature change observed is small. R us, the loss of feedwater heaters is not considered to be an important initiating event.
However, the effects of the loss of steam supply to the feedwater heaters I which accompany other overcooling initiator events will be considered along with those initiator events.
Similarly, the effects of auxiliary feedwater flow will.be minimal. While the auxiliary feedwater temperature is lower than the main feedwater tem-perature and thus feedwater enthalpy will decrease whenever auxiliary feed-water flow is initiated, the auxiliary feedwater flow is small with respect to main feedwater flow or steam generator (liquid) volume. he effects of
_ _ ~ . _ . _ , _ . . _ . . _ _- ..~. _, _,. _ _ _ _ _ , _ _ _ . . . _ _ _ _ - _ _ . _ - _ . , _ _ _ _ . , _ _ . _ . _ _ _ . _ . . ~ . _ _ , _ . _ _ . . _ _ _ _ _ _ . _ _ _ . _ . _ _ _ . ,
-. HBR-3.30 auxiliary feedwater flow on the coolant temperature become more important I - when main feedwater flow is 1 cst and auxiliary feedwater flow is actuated.
Thus, another specific potential initiating evert to be considered is:
- Loss of mais feedvater flow.
i 1
! 3.3.4. Events Causing Feedwater Overfeed Two types of feedwater overfeed events are of interest as potential over-coollag initiating events: (1) main feedwater overfeed, and (2) auxiliary feedwater overfeed.
)
A main feedwater overfeed is not considered a significant overcooling event i
prior to a reactor trip; thus, only those main feedwater overfeed events that follow a reactor trip need be considered. This type of event can be characterized by an overfeed resulting from a failure of the feedwater sys-tem to run back following a reactor trip. The initiating event is a reac-tor trip and the failure associated with the initiating event is a failure of feedwater to run back on one or more lines.
l The relatively low temperature of the auxiliary feedwater makes an overfeed I
of anzi11ary feedwater potentially significant even though the maximum flow L rate is small compared to the main feedwater flow rate. Spurious auxiliary feedwater actuation is not considered as an initiating event. With a j
spurious actuation, the high main feedwater flow rate with its relatively high temperature and the large volume of water in the steam generator would l
r l
l
HBRS3.31 minimize t'.ae overcooling effects. Only those auxiliary feedwater overfeeds following a required actuation of auxiliary feedwater (isolation of main feedwater) will be considered.* In these cases, the steam generator level I will be low and the overfeed will have the potential to cause a higher cooldown rate.
The auxiliary feedwater overfeed condition can be reached only if some ini-tlating event which leads to auxiliary feedwater actuation has occurred.
The appropriate initiating events are a reactor trip and large and m.
small steam-line breaks, which in themselves are overcooling events v but which also result in auxiliary feedwater actuation.
3.3.5. Inadvertent Safety Injection (SI) Events With a maximum high pressure safety injection (HPI) pump discharge pressure of 1500 psia, an inadvertent safety injection (SI) actuation will not
, result in SI flow while the RCS is pressurized. The spurious signal will cause a reactor trip and consequential reduction in pressurizer level. In.
response to the reduced pressurizer level, the charging pump speed increases and the letdown line is isolated. The resulting pressure is expected to remain above the HPI flow pressure and thus the event will not l result in a significant decrease in the reactor coolant temperature (see l
Section 3.3.1). Therefore, the inadvertent SI alsnal is not considered an overcooling initiator.
l l
i
. .... ,,...u. ....,,.... .c .. ... m .,,r.....
% i.g.gi.. ' '
i l
1
_ _. . . -- - __ .. __-_~ -. ___ _ _ _ _ -
HBib-3.3 2 - ** *-
3.3.6. less-of-Coolant Accidents (LOCAs)
The categories of potential loss-of-coolant accidents (IDCAs) which lead to overcooling are the most difficult to define due to the potential for repressurization and the importance of loop flow stagnation. A review of potential thCA sizes was therefore considered in defining LOCA categories.
The first category was composed of those breaks for which HPI could fully compensate and thus the pressure would stabilize at some level slightly below the HPI shutoff head. In terms of size. this corresponds with breaks that are less than ~0.016 ft 2. It should be noted that single PZR PORV or SRV failures and reactor coolant pump seal failures
- are also included in ;
this category of "small-break LOCAs. " lj The second category of LOCA sizes includes those for which MPI can not keep up with the flow out the break but for which the pressure decrease is gra-dual owing to a partial compensation from the HP1 flow. Identified as
" medium-break LOCAs," these break sizes run from ~0.0162 f t to ~0.05 ft .*
.Il the most probable size appearing to be a break of one of the many 2-inch [/
lines which come off of the primary piping.' 'I1:1s corresponds to a break ,
^
size of f).02 f t . However. based on analyses performed by Westinghouse, .
I' I
J it appea.ed that a 2.5-inch break would result in early loop flow stagna-tion. 81 ace this condition was considered to be potentially important. the
\
- 1;".
. m1: ' I,n.. im ..id...'.:n,,.0:::"M:: ; .',::;'.!:!'i::t.!::'.". : 0*u 4 .
'D.:.;;:'#. '..'..:!! :::.it:':r 44'.: ':!!';!.:..:.:.:.::,':.n.'.:7.: :::'::.0.. ..
...................sn..n... .. .g, n.. n . e. ,...., ,...,, , .. ....
..i...... ......... m.. .... .. . ......i....
'!ittit::0::'::':!:nl:*::'!ni;i:::::!!!':::*::'*!!:ti
.. . ,. ... i... i... ,.,,..
HBR4.33 -
l '
/l break size was also considered in the analysis of this group.* ' '
The third category of LOCA sizes includes all breaks larger than 0.05 f t2 ,
Without isolation of the break, a rapid depressurization will severely limit the potential for a vessel failure. Thus the only concern for breaks j of this size is whether or not there is a break larger than 0.05 ft2 which i
at some later time can be isolated. A review of the H. B. Robinson Unit 2 system reveale,t several 4- and 12-inch lines, but no potential break loca-i tions that could be isolated were identified. Thus no LOCAs in this size j category were considered as PTS initiators.
In summary, it was determined that two LOCA sizes should be considered as initiating events, and, as is the case for steam-11ae breaks, they each must be considered for two power conditions. Thus, four IACA laitisting
- , events must be addressed as follows
l 6 Small-break LOCA at full power.
- Nedium-break LOCA at full power.
- Small-break LOCA at hot 0% power.
e Medium-break LOCA at het 0% power.
I i
'A. . i . .. . .. d i . h .p . . , . .. . m. : b,d,..i t . ... i g . i . .f .. . . .... . did
" '::'d:' ! 'il.';.!:tf1;;':i'is. l*;;'::tJ li :';U:: ....... !'t.!'"li".
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, ,41) n 3.3.7. Events Ca sistics of Pross:ritor Prosstro Cestrol Falleros The PZR PDRV control signal failures and PZR SV failures have already been identified. An additional pressure control failure of interest could be the spurious actuation of the pressurizer sprays, which would decrease the pressure and could eventually result in SI actuation and the tripping of the reactor coolant pumps. A loss of pressuriser spray flow would follow and the depressurization would be terminated. Thus, even though safety injection actuation occurred, the actual SI flow would not be alsnificant.
As a result, this is not considered a potential PTS event initiator.
3.3.3. Events Leading to Steam Generator Tube Rapture A rupture of a steam generator tube has many of the characteristles of a small-break LOCA that cannot be isolated. With normal operator action, or even without operator action, the effects of the rupture appear to be less severe than those of the LOCAs that were analyzed and the consequences associated with a steam generator tube rupture should be bounded by LOCA
,seguences. Nevertheless it was decided to address this event speelfically and the following was included as a potential initiating event to be analysed:
l 6 A steam generator tube rupture.
i 3.3.p. Summa ry i
In the preceding sections, 11 potential initiating events for overcooling have been identified i
EBR-3.35
. . .. e (1) A large- steam-line break at hot 0% power.
(2) A small steam-line break at hot 0% power.
(3) A large steam-line break at full power.
(4) A small . steam-11ae break at full power.
(5) A reactor trip from full power.
(6) Loss of main feedwater.
1 (7) A small-break LOCA at full power.
(8) A medium-break LOCA at full power.
l (9) A small-break LOCA at hot 0% power.
(10) A medium-break LOCA at hot 0% power.
(11) Steam generator tube rupture.
3.4. Initiator-Snealfin graal Igata Event trees have been developed for each of the laitiating events identi-fled in Section 3.3. This development involved the identifloation of applicable system inactional conditions and potential operator actions.
e
, The system state trees described la Section 3.2 were used to identify those
_ HBRI 3.36 systems or components that are required to function and whose failure will have a potentially adverse effect on overcooling transients. It should be noted as discussed earlier. that since these trees are developed on a functional basis, the branching on the trees associated with system or com-ponent actions may be more cor91ex than binary success and failure branches.
i 4
Operator actions were identified from a review of procedures associated with each specific initiating event. These operator actions were grouped e into two categories:8 k/
(1) Actions involving recovery of a failed system function. (Exam-ple: SI signal falls and the operator manually starts HPI injec-
- tion.)
i
! (2) Actions required by procedure following identification of an ini-
! tlating event. (Emample: Operator isolates APW from the low-pressure SG following a steam-line break.)
l l
Category 1 actions were examined on the basis of the time available for j recovery and the effects of recovery. The results of tLis analysis were f
- then used to adjust branch psobabilities. For example, if a PZR PORY l
fallare was isolated before SI actuation, the event would be very similar to a reactor trip event and would be created as such.
Category 2 actions were treated directly on the event tree. D ese operator
! *!!.' ::"t:!; li..'.th ::.'!,:';f..!:4..!.:.:' ..:u.'h.!.!.:.' ':
- i.'!:.:.::'.!:: O. i.!
i
.. u. . . . .... . a .,. ......n...,....
u .. .u . ... . ... ......,,.,. ... .
. . . u . i ..
i
- !!:!4' :::'.h: ;i!!:::. :"' "' '""'" '"""" " '""'"
i i _ . . _ _ _ _ - . . _ . _ , _ . _ _ . . . _ . ._ _ _ _ . . _ _ . _ . . _ _ _ . . . , _ _ . _ _ . _ . _ _ _ _ . _ _ .
HBR-3.37 actions were defined as being performed during some time frame following the procedural cues to perform the action.
T-3.4.1. Steam-Line Break at Hot 0% Power I
Although the frequencies of the small and large steam-line break .
events at hot 0% power are different, the event tree structures as shown in Figure 3.2 are the same.
j l
The first heading of the event tree is "SI signal generated on demand," the l
direct " demand" being an initiating event that is either high steam-line differential pressure or high steam flow coincident with either low steam Pressure or low T ,,. The high steam flow signal will close the MSIVs.
while the high differential pressure signal will not. If the steam-line break is upstream of the MSIVs, the only function of the MSIVs is to iso-late the bre,ak from the other steam lines. It is more likely, however, that the check valve on the ruptured steam 11ae will perform this function.
l It should be noted that neither an STM PORY f ailure nor an SDV f ailure was r
I considered for this initiating event. With the low steam-line pressures accompanying the event, these valves would not be required to function.
The next heading on the event tree, "MFW isolated on demand," comes from the main feedwater and condensat's system state tree and is concerned with f
stopping the main feedwater flow. Among other things, the SI signal will send a signal to trip the main feedwater pumps, run back the NFW control 1 l
valves,* close the NFW pump discharge valves, and prevent the NFW bypass ('
k ni::.: an;;u- - ~ ~ ~"
t 4
Figure 3.2. Event tree headings for steam-line breaks at hot 0% power.
pd Generated Isolated SGs Actuates Automatically to Low- Occurs Runs Back OA: AFW Rescats I on Demand on Demand Blow Dows en Demand Controlled Pressure SG en Demand on Demand Throttled on Demand ,"h 4 Branches: 2 Brancher 2 Brancher 2 Branches: 2 Branches- 2 Bramhes:
2 Brancher 4 Brancher 2 Branches: 2 Branches-(1) Signal is (1) Nelies (I) No SGs (I) AFW (1) Flow (I) Isolation (I) HPI (I) Rees back (I) Operator (l) PORY "'
generated. overfeeds. blow dows. acteates centrolled eccert occurs. es required. throtiles rescats.
(2) Signalis (2) One kne (2) One SG , * (2) A.! W at nominal (2) Isolation (2) IIPI (2) Fails to AFW flow. (2) PORY fails not generated. overfeeds. blows down. & es not rate. fails to fa:In to rea back. (2) Operator to rescat.
, (3) Two lines (3) Two SGs actuate. (2) Overfeed occur. ector. faits to
Iancs SGs.
overfeed blow does.
~~
-- .- -. - _ . ..= ..
s e
N s
, . . . e-HBR-3.39 valve s from opening. A second important signal is high water level in any steam generator, which will do all of the above except close the NFW pump discharge valves. The final signal is reactor trip coincident with low Taye, which only closes the MFW control valves.
The next heading, " SGs blow down," addresses the action of the main steam check valve on the ruptured line and the possible closing of the MSIVs.
This branch considers whether an MSIV closure signal would be generated owing to the break and whether the MSIVs would close if the signal is given. The net system response to the break and MSIV closures is presented in terms of the number of steam generators " blowing down."
The next three headings are associated with defining auxiliary feedwater flow conditions. The first, "AFW actuates on demand," defines whether the
~
auxiliary feedwater system is initiated. Once initiated, two potential
, conditions are considered under the heading
- AFW flow automatically con-trolled": (1) flow controlled at a nominal flow rate or (2) a failure to automatically control, resulting in abnormally high flow rates (overfeed).
i The third heading, "AFW isolated to low-pressure SG," identifies whether anxi11ary feedwater flow is isolated from the depressurized steam genera-I It should be noted that this requires an operator action and is very tor.
l l important in minimizing the RCS overcoo11mg.
The next branching, "HPI occurs on demand," addresses the initiation of SI flow as a result of an SI signal or an operator action.
Under the next heading, " Charging flow runs back on demand," control of ;
4
,- , ,w - . ._.,_.e,_,_.m.g. ,y..,_,,,-y ,. . , , , . . , .._..,m ._,_.y.y,_,,, ,,.m_..m.,,m._,...m,..m., _ , , . . ,+ . - , , ,,-. --
HBR-3.40 83 repressurization via charging pump flow runback is addressed. Charging flow is run back automatically when the pressurizer water level is restored. Failure to run back automatically would result in challenging the PZR PORVs. Because the charging flow is controlled on pressurizer level rather than on pressure, it is conceivable that overpressurization could occur with resultant opening of the PZR PORVs. At this point, the operator can shut off the charging flow and monitor the repressurization caused by the thermal expansion of the primary system water, but because this sequence is extremely unlikely, no operator action was considered.
The second operator action of importance, included under the heading AFW throttled," is controlling auxiliary feedwater to maintain the steam gen-erator level. Once the broken steam line is isolated, the initial cooldown will be limited to the blowdown of the steam generator inventory. When steam generator dryout occurs, the cooldown will then be dominated by the conditions in the intact steam generators and steam lines. If the operator f
' manually controls the auxiliary feedwater flow to maintain level, the pri-mary system temperature will begin to increase. If, on the other hand, flow is not controlled, auxiliary feedwater overfeed will occur, which could further reduce the primary system temperature.
I l
l De two operator actions, auxiliary feedwater isolation to a depressurized l
i steam generator and anzi11ary feedwater throttling, are related. H is cou-p11ag between the two actions is addressed in the event trees. If the operator falls to isolate the APW when required, it is assumed that he will also fall to control the APW flow, l
i l
I,
NBR-3.41 1
The final tree heading, "PZR PORY resents on demand. " is required because if the repressurization is not controlled (charging flow does not run back). the high pressure is assamed to lead to a PORV lift. Thus, the potential for a PORY failure to close must be examined. This failure to close includes mechanical failures to close and the failure of the operator l-to block the PORVs in a short period of time.' j 3.4.2. Steam-Line Break at Full Power J 1,.*
As shown in Figure 3.3. the event tree headings for the steam-11ae break at in11 power are the same as those for hot 0% power except that one branch has been added for the full power steam-line break and one has been modi-fled.~ The additional branch comes from the main steam system state tree *
+
and addresses the potential for a SDV failure to close following a small break in which a momentary T.,, increase occurs. The SDVs are not con-sidered to be of importance for large breaks because no increase in T,,,
'will occur prior to NSIV elosure.
h modified branch deals with the feedwater system runbeek and is takea from the main feedwater system state tree. (Rumbeek was not considered for the hot 0% power ease, because the valves are already closed.) All four I
I potential branches as identified in Table 3.3 are considered as potential i states.
The 8'Di PORVs are not espected to open during the initial phases of either C. '
y v a large or small steam-line break. Following break isolation and ,
u steam generator blowdown (if app 11eable), T.,, may ineresse to the normal i
%. u . . ns i !!!! !!.' e., .. . i, ..i . ll.'!::
- !:':!.:!u!!.' . .. ...d!!dt';;;0!!n!'U:.
.. . . . . .. o ...... .':. lj,l ':. '!:'
1:::::::';'
3.g.ig... ,. M,..':.l.:.,':!.!:::.l:.'::!:':.!*:.
.. ns ,.e, ,. n .. . .n i . .... ..lli.:.00!i::'..::::'!!.!..
i l
1 Figsse 3.3. Event tree headags for steam-Iime tweaks at feu power.
-- - ---- ~' z ; _ ___ . . . _ _ _ _ _ . _ _ _
3 2 3 4 3 4 2 8 9 89 II
~ Osam ' Gamesumed and Immimams SGs a- Aen e .ey se tee- Ossers pens Bad OA: AFW Rarets 2 Demand as Demand em Demand h Omme en Demand Cassvemed Presasse SG en Deussed en Destand Theartled en Demand ah 2W 4W 4h 2 Br* 2 Br* 2 Branchet 2 Drasches 2 Braectet 2 Brancher 2 Branches (1) AB Ene stnut (1) $gnet a (1) AB hams (1) DEe 3Ge (t) AFW (1) nem (t) M- (I) IIFt (3) Rees back (1) Operaser (1) PORY (2) Omatads .
i see bed tese esma, asemesa. emmasJud ecsees scrum as segesrod thresties semeats g as stsunt (2)Sgamle and teFW (2) One SG (2) AFW at emmenal (2) ledemme (2)ISPI (2) Fads se ATW flee. (2) PORY fads g
, (3) Tee End "
im mudased teses does, dans esa rest fads en fads to roe back. (2) Operaser sesacat I mas . W as semmt (2) One tee (1) Tee SGs - (2) O=erimme assur- escar. fasts se (45 Thema er emer8medL tese esseL assers alwertas a mese and (3) T=e amms (e) Aashsms Af W. 9J as sssmet musensi SGe (4) Tasse home tese esamt
% _ emeremmt __
Este *1he event tree heedtage for a remeter trip are the same es these eneopt (1) the heading
- 32*t POSTS close se h d
- should precede heading 1, and heading 3 abould be divided into taso testings that
- Test SFtf rumback and SWW isolattee seger&tely.
a e
w e
~R.;
, . .. ,+
NBR-3.43 L
hot 0% power level anless plant cooldown is initiated. In this case, the STN PORVs w!11 be required to modulate to remove decay heat. STM PORY ;
failures in this situation have not been considered.
J t
1 3.4.3. Reactor Trip t ,
i The event tree for a reactor trip initiator has the same basic structure as the event tree for a steam-line break at full power (see Figure 3.3): how-
- ever, since there is no initial steam-line break, the closure of the STN PORVs, in addition to the SDYs, must be ocasidered.
j In addition, whereas MFW raaback and isolation are combined in a slagle heading in Figure 3.3, they are treated as separate branchings in the event l tree for a reactor trip because the isolation signal will act necessarily i
occur. Also, many of the impliott branchings used for the steam-line break j
4 will be used only la conjunction with addittomal failures. For esemple, the NEIVs will not be commanded to elose following a remotor trip maless 4
there is an addittomal fe!!sre, such as SDVs falling to resent, which may eventually require closure of the NSIVs.
l t
3.4.4. Nue11-Break LOCA at Full Power
! Slase any oversoollas event of sisalfieases will involve a reestor trip, it is assnaed that a LOCA event will be followed by a reester trip. In this ease, the remotor trip event tree headings apply for the LOCA event tree qg .
with appropriate additions as shown la Figure 3.4. The additions are: g( '
- s turbine trip, seenssister discharge and low-pressure injestloa, PER PORY t
- -- e- rwm,.-a-e+y'--- e-----s---e-ry-m mmev + wee n- g----g-+-mmm-pev -yg- -w msy--11-P" =' FT'"- Y"F W -Nk"-7-^t
- Y'MNe"r-"""--F*f-'
e U- .
~
E'8".3.4 Emot tree headings for sameN-break LOCAs at fell power.
5 2 3 4 5 6 7 3 Teeme STM PORVs SDvs 58 Seese MFW Rams Back IIPt Tays Omme en AFW Omme se Generased and Isolaers Occers SGs en w Drased w Acessies en Desmand em Deansed em Demand Blow Do e en Demand 2 bra 4 Branchset 4 Br* 2 Braschen: 4 Breaches: 2 Branchest 4 Br*sches; (t) Tegs ee 2 Brancher (t) AB shsee stemL (I) AR eless.
w (I) Semelis (1) A5 haes (I)ItPI (1) Ne 5Gs (1) AFW (2) One fads (2) One fads greermees run back accert blev deos. acteates.
(2) Feas se se stima to cause. (2) Semelisest and blFW (2) IIPI faas (2) One SG (2) AFW knet (3) T=eled (3) T=e fat seeerased is imetaeed. se esser. bla.4ma, does mas to cases. se cImme. (2) One noe (4) Aa gad (3) Tee SGs ace ate.
(4) Thee er overfeeds ble= does to sanse, mere faa (3) Teehees (4) AB three is et e.e fa sG.
(4) Three bees blow dem E '
.( 7s t
_ Figure 3.4 (Cestimmed) i F, , I , se j g &
33 12 33 34 IS I -
- Censsesse Pesumuse 50 Dumherge h en Demead Theestled en Drmand 2 Br*- 2 Brancher 2 Br-h 2 Branches: 2 3rascher 2 3 rancher 2 Stascher (1) Flee (t) temiesame (1)* % - (1) Operaser (I) Rams back (I) Operaser (I)tPt i emmeseAnd accert discharge fads se as segeood thrustles access l $ es sammet (2) h when segment imagmas 2) Faas to AFW flee. as eequired.
gods se (2) a -** berett l
seet een hect (2) Operaser (2) tPt *
(2) OmarGed occur. fed se (2) Operaner fads se fads as escurt deckergt melsess thsettle accer.
hreat AFW flow.-
l - -- -
. +
note: The eeemt tree heedtags for other LOCAa are stallar to these eteept for the following:
l (1) For medium-break LOCA at fall power, delete Leadings 12 and 13 (2) For nasall-break LOCA at hot CS peerer, delete headings 1. 2, 3 and to and modify heading 5 to read "tTd isolated on demand.* (3) For medium-break LOCA at het c5 power, delete headings 1, 2, 3. 10. 12, and 14 aasd modify heading 5 to read "Ifts isolated en demand.'_ ._ - . ~ _ - _ _ _
{
l .A i
___-.m_ _ _ _ _ _ . . . . _ - _ _ _ _ _ _ . . - _-___.m. _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
. s. e
~
HBR-3.45 %
E resent and LOCA isolation. In addition, main feedwater runback and main feedwater isolation have been combined into a single branch.
An SI failure condition was considered for the LOCA event tree. However, this condition can be considered as an overcooling situation only if loop flow stagnation and subsequent recovery of SI flow occur.
3.4.5. Medium-Break LOCAs at Full Power The event tree for a medium-break LOCA at full power is identical to that for the small-break LOCA at full power except that the branches " Break not isolated" (No.12) and " Charging flow runs back on demand" (No.13) are deleted. Because the break cannot be isolated, control of charging flow is irrelevant.
3.4.6. Small-Break LOCA at Hot 0% Power The event tree for a small-break LOCA at hot 0% power was constructed from the event tree for a small-break LOCA at full power by deleting the head-l
! ings " Turbine trips on demand" (No.1), "STM PORVs close on demand" I
(No. 2), "SDVs close on demand" (No. 3), "SGs blow down" (No. 7), and 4AFW Isolated to low presure 80" (No.10) . In addition heading No, 5 should be modified to read "NFW isolated on demand. " (NFW rumback does not apply at hot 0% power, but NFW isolation is considered.)
i t
, . .. r-HBR-3.46 3.4.7. Medium-Break LOCA at Hot 0% Power
- The event tree for a medium-break LOCA at hot % power was obtained by deleting two branches from the tree for a small-break LOCA at hot 0% power:
" Break not isolated" and " Charging flow runs back on demand" (Nos.12 and 14 in Figure 3.4). The resulting event tree headings are summarized in the Section 3.5.
t e
i f
i i e s
4 4
T i
i
. .. r-HDR-3.47 pg ,
3.4.8. Tube Rupture
, The tube rupture event tree was developed based on a review of tube rupture I
procedures. It is composed of five branches:
(1) Steam Dumps Close on Demand - This branch is required to examine I the potential combination of a tube rupture and a small-pipe steam-line break.
i (2) OA: Number of Pressurizer PORY Lifts Performed - The Emergency Operating Procedures require the operator to use the pressurizer PORV to lower the primary system pressure. This adds an addi-tional cooling effect to the system. The question arises as to whether the initial PORY lif t is enough to keep the pressure at a lower level. There is at least some argument that a second manual opening of the PORV would be performed at some delayed time following the initial opening. This branch identifies
, whether one or two PORY openings are performed.
! (3) PORY Resent - Each time a PORY is opened, the potential for f ailure of the PORV to close must be examined. This branch determines whether closure is ef fected.
3 (4) OA: Close Block Valve - Each time a PORY falls to close, the 1
potential for operator isolation of the valve via the block valve ,
must be examined. This branch determines whether the operator
i HER-3.48 performs the action.
(5) OA: Terminate SI - This final branch addresses whether or no t the operator terminates SI. Failure to terminate SI will lead to a continuous feed and bleed situation where HPI feeds cold water into the system and warmer water flows from the primary to the secondary system.
3.4.9. Loss of Main Feedwater The loss of main feedwater event was also considered to be a potential overcooling initiating event because auxiliary feedwater flow will occur.
The effects of auxiliary flow and potential overfeed associated with other l
events such as stemn-line breaks, LOCAs, etc. are addressed by the event l
trees defined in the previous sections. However, the loss of main feedwa-ter followed by auxiliary feedwater flow and potential auxiliary feedwater
' overfeed has not been addressed. Since there are only a Itaited tamber of these cases, no event tree was developed for the case of main feudwater loss. Instead, each sequence is simply defined and quantified.
l i
HBR-3.49 a
3.5. Event Trag Quantification and Co11anse #
In this section probabilities are assigned to each of the branches of the event trees identified in Section 3.4 and the probabilities are then com-bined with the frequencies of the corresponding initiating events identi-fled in Section 3.3 to determine the frequency of each possible sequence on each event tree. The resulting frequencies are then screened and collapsed to determine which event tree sequences are important enough to undergo subsequent thermal-hydraulic and fracture-mechanics analyses. In addition, the importance of support system failures with respect to PTS events are examined and sequences initiated by such failures are selected for further analysis.
In determining the branch probabilities, the complete Licensee Event Report i (LER) data base for H. B. Robinson Unit 2 was reviewed for initiating events and system failures, as well as for a general overview of the per-i l formance of plant systems of interest. Although the H. B. Robinson data base did reflect some failures and unavailability of components, it did not reflect a significant number of failures on demand for the systems of l
interest. Therefore, in lieu of relying solely on H. B. Robinson informa-tion, Westinghouse-specific and PWR specific operational information was employed for the target event when available and when the H. B. Robinson operational experience did not provide an adequate data base for that event. Additional information was obtained from the national Reliability Evaluation Program Generic Data Base, the Nuclear Power Plant Operating Experience Summaries, and, when practical, from other sources. With the 1
constraints imposed by programmatic needs and the availability of
HBR-3.50 i
operational data, only simplified approaches to frequency and probability estimation were permitted, but these estimates were considered to be acceptable for use as screening estimates. The estimates developed, the rationale used, relevant information, and information sources are presented in Appendix B.
A somewhat simplified approach was used to quantify the failure rates for expected operator actions. The basis for this approach was a hierarchical l structure of performance shaping factors that was developed as part of the current program and has since been labeled the STAHR approach * (sco Appendix C). The structure used in the STAHR approach allowed the human error rate for a particular target event to be calculated from a network of related assessments by individuals who had some operational experience or had been involved in human reliability analyses on nuclear power plant transient analyses. Some error rates were conditional probabilities, while others reflected the weight of evidence concerning influences operating at this particular nuclear power station. Generally, influencing events were organized to reflect the potential effects of the operator's physical and i
social environment, as well as personal factors. Interactions among these factors were also modeled. Once operator failure rates were quantified, dependence or coupling factors taken from NUREG/CR-1278 were used to adjus t the operator action failure probabilities. These final probabilities were.
then applied to the event tree branchings as necessary. The development of these probabilities is discussed in Appendix D.
4 After the frequencies for all the sequences for each initiating event were obtained, a frequency of 10-7/yr or greater was used as a screening h!'i3t J't;;P:0!*'is';;f:::fta:. Jtu:h'id*:;;;;;ls '*
!;;!!!!"le -
have been steesssist for this application, the ese of this methodology saamet be.eendoned,fpr a more generJe usage at thine time. Even theagh the beste str'e state of the approach has serit, a more beste scientifie analysis is necessary to perfect a usable methodology.
HBR-3.51 criterion to identify those sequences which should undergo thermal-hydraulic and fracture-mechanics analyses on an individual basis. The remaining sequences were combined into a set of " residual" groups. These groups were then further examined to identify sequences that were similar enough to sequences above the 10-7 screening level that their consequences were bounded by the respective higher frequency sequences. Sequences fal-ling into this category were removed from the residual group and their fre-quencies added in with those of the appropriate bounding sequences. 'Ihe residual groups were also examined for additional sequences that should be specifically evaluated because the combination of their frequency and potential consequences identified them as being potentially important.
These were removed from the residual group and treated separately. ,
The basis for bounding residual consequences by other existing sequences is tied to thermal-hydraulic and system state considerations. In general,
- sequences were bounded under the following conditions. Sequences which involved the failure of the AW to actuate and with no subsequent recovery i
were considered bounded by sequences involving successful operation of AFW.
Sequences involving failure of the SI signal to generate were considered bounded by failure of the HPI to occur on demand, since HPI would not occur without an SI signal. For LOCA initiators at power, all sequences involv-i ing failure of the SI signal or HPI were grouped with the top sequence I
L involving failure of HPI to occur on demand, regardless of the events l
l occurring on the secondary side, since the RCS could not be repressurized
(
l without HPI. For steam-line break initiators, sequences with HPI failure 1
l were considered of less consequence from a repressurization and overcooling l
standpoint than their counterpart sequences with HPI success and were
,,
- em . e
HBR-3.52
[ .-
therefore bounded. Likewise, failure of LPI is of less consequence to PTS than successful IEI. On the reactor trip tree, sequences with MFW isola-tion failure but with runback success were considered to be similar to sequences with APT overfeed. Likewise, sequences with SI signal failure were considered to be siellar to AFW overfeed sequences because MFW isola-tion would not occur immediately without an SI signal. APT overfeed sequences were also considered to be siallar to sequences with one MFW line falling to run back.
4 For each event tree discussed below, three items are presented: a table i
summarizing the branch headings and describing the branch probabilities used; the event tree; and a table describing the sequences identified for ,
, thermal-hydraulic and fracture-mechanics analyses. Sequence numbers and associated sequences provided in the tables are consistent with those V) l Included in the INEL analysis
- and not necessarily consistent with the i
l l//
order of presentation of the tables. Sequences that have been combined with other sequences are indicated on the far right side of the event j trees.
It will be noted that event trees per se are not included for tube rupture I events or loss-of-feedwater (LOFW) events. However, potentially important sequences for these events are identified and quantified. In addition, as l
l noted earlier, sequences from the support system failures that tiere identi-I fled as potential PTS sequence initiators are quantified.
l l
f Sequemees C.
forD. the Fletcher, R. B. Robinson et st. Thermal Bydrastic Analysis tait 2 Pressurised of overcootlebraf 1)ersal Shock Stady ( t).
l Idaho Natiosa! Engineerlag Laboratory. Asgast 1984.
f ._
., .. - e
- - - + . . . . _ . . --....----.,..-..,,,.-,.---,,----.-,,-,n...- - , , - . - - . - - - - , - - , , , . . - - - , _ , , - - , , , . . - - - . - - . - . , . - -
HBR-3.53 3.5.1. Reactor Trip R.
i*-- -The frequency for a reactor trip as an initiating event is 8.7/yr (see
/
development of initiating frequencies in Appendix B). This frequency combined ; ,
with the branch tree probabilities given in Table 3.6 resulted in a total '
i i
, of 9773 sequences. Of this number,112 had a frequency of 10-7/yr or higher. The remaining 9661 residual sequences had a combined frequency of 3.63 x 10-6/yr. The 112 sequences and the residual sequences are all shown ,h' in Figure 3.5. (I The 112 sequences with a frequency of 10-7 or higher were investigated to determine whether selected sequences could be combined. Where it was found that the thermal-hydraulic RCS response of a sequence was similiar to and bounded by that of another, the sequences were combined. The frequency of, the bounding sequence was calculated as the sum of the constituent
, sequences. This process reduced the number of specific reactor trip l
l sequences from 112 to 95.
I 1 At about this time it was realized that a very important operator action was missing from the analysis. It had initially been assumed that when SDVs f ailed, the MSIVs would automatically close, thereby isolating the SDV f ailures (except, of course, in the case where the MSIVs malfunction and fail to close). However, the initial thermal-hydraulic analysis revealed that conditions necessary for automatic HSIV closure would not exist.
Thus, as stated in the procedures, the operator would be required to close the MSIVs. Some delay is anticipated since it was felt that once diagnosed l
l there would be some attempt at closing the SDVs manually before isolating
, the system by closing the MSIVs. Thus the time of closure was chosen to be i
30 minutes after reactor trip. This led to two sequences for each case i
- e9 * *
-. . . - . - - - , - ~ , - _.--. - ,..,. -._ _ ,~ ~ , .. .- -
.-..-m.,.-,..., _ - - - - . . . - - - - - , ,
HBR-3.54 s
Table 3.6. Branch probabilities for a reactor trip
- Tree Heading Branch Branch Probabihty STM PORVs close (1) All three STM PORVs close. 0.97981 on demand. (2) One STM PORY fails to close. I.8 X 10'I (3) Two STM PORVs fail to close. 1.7 X 10'3 (4) All three STM PORVs fad to close. 4 9 X 10'#
e SDVs class on (1) All five SDVs close. 0.99768 demand. (2) One SDY fads to close. l.6 x 10'3 (3) Two SDVs fail to close. 3.0 X 10~4 (4) Three or more SDVs fail to close. 4.2 X 10
- .. e l MFW runs back. (1) AD three knes run back. . 0.9999940 1 (2) One hne fads to run back.6 (3) Two lines fad to run back.6 5.3 XX10' 5.0 107 (4) All three Ignes fail to run back. l.4 3r 10'I SI signal gene- (1) Si signal is generated 0.99997 rated os demand. (2) SI signal is not generated. 3 X 10 -5 MFW isolated If au knes run back, on demand. (1) no has overfeeds. 1.0 If one hne fails to run back,
' (1) No kne oserfeeds. 0.99 (2) One hne overfe=ds. 1 X 10-2 If two haes fail to run back, (1) No hne overfeeds. 0.97906 (2) One hoe overfeedt 2.0 X 10-2 -
(3) Two knes overfeed. 9.4 X 10
If three hnes fail to run back.
(1) No hoe overfeedt 0.96639 (2) One Ime overfeeds. 3 0 X 10-2 (3) Two hnes overfeed. 2.8 x 10'3 (4) All three hnes everfeed. 3.1 X 10
SGs blow down. If one or two SDVs fail.
(1) All three SGs blow down. 1.0' If three or more SDVs fait, (1) No SGs blow down. 0.9908/
(2) One SJ blows down. 6 6 X 10*
(3) Two SGs blow down. 2.0 X 10*
(4) AU three SGs blow down. 5.3 X 10' "
If one, two. or three STM PORVs fad, then. respectively,
(!) One SG blows down. 1.0 (2) Two SGs blow down. 1.0 (3) Three SGs blow down. I.0 ff MSIV closure signalis not generated, (1) All three SGs blow down. 1.0 I AFW actuates (1) AFW actuates. 0.999 on demand. (2) AFW does not actuate. ! X 10'3 AFW flow (1) AFW flow is automaticany con.
automatically trolled at nommat rate. 0.9923 controlled. (2) Flow control failure leads to abnormally high AFW flow rate 7.5 X 10~3 (overfeeds).
OA: AFW iso. (1) AFW isolation occurt 0.9983 lated to low- (2) AFW isolaten fails to occur.
pressure SG 1.7 X 10'3 HPI occurs on If SI signal is generated, demand. (I) HPl occurs. 0.99939 (2) HPI fads to occur. 6.1 X 10
If SI signalis not generated, (1) Operstar manually starts HPL 0.99 (2) Operator fails to start HPl. I X 10-2 o
e~
y ,0 Fw
HBR-3.55
. Table 3.6. Branch probabilitics for a reactor trip" (cef,)
Tree lleading Branch Branch Probability t
Charging flow (1) Charging flow runs back, as l
runs back os required (repressurization demand. limited). 0.99 (2) Charging flow fails to run back (repressurization act hmited). I X 10-2 OA: AFW If operator isolates AFW, throttled. (1) Operator throttles AFW flow. 0.99 (2) Operttar fails to throttle AFW flow. I X 10-2 If operator fails to isolate AFW, (1) Operator fails to throttle AFW flow. 1.0 (2) Operator throttles AFW flow. o.O PZR PORY (l) PZR PORY rescats if charging rescats on flow fails to run back. 0.9988 on demand. (2) PZR PORV fails to rescat if charging flow fails to run back. 1.2 X 10~3
'The acronyms used is this table (;n the order of their appearance) are: STM PORY = steam power-operated rehef valve, SDV = steam dump valve, MFW =
maia feedwater, SI = safety injection, SG = steam generator, MSIV = main steam isolation valve, AFW = availiary feedenter, OA = operator action, HPI =
high-pressure injectson, and PZR PORV = pressurizer power operated rehef valve.
- includes failure of MFW regulating valves to run back and failure of one or both MFW pumps to trip to high levelin any steam generator.
'Only one branch is carried foe cit].cr one or two SDVt In the case of the failure of one SDV. it was felt that the operator would be very reluctant to close the MSIVs tur this amount of excess steam flow and probably would allow the system to cool down as the transient defines. Thus all three SGs would blow down slowly. For two SDV failures,it is assumed that the operator still would be reluctant to isolate the SGs, but more thas hkely he oculd close the MSIVs within 30 c But, since the operator action failure probabdity used for this case (I X )10-gnutes. is higher than the valve for failure of the MSIVs to class on demand, the MSIV failure branches are not considered. Thus, with respret to the event trees, two SDV fadures.are presented as all three SGs blow down since closure of the MSIVs by the operator is considered separate from the event tree.
- The probabilities presented here represent blowdown due to MISV failure to close. It is anticipated that there udl be times when a steam-line valve or pipe fadure would not pro-duce enough steam flow to cause automatic closure of the MSIVs. In this case, the operator would be required to manually close these valves. Failure to close the valves would result in the blowdown of all three steam generators. When apphcable. *A* and
- B* sequences are identified to designate whether or not the operator closes the valves.
Probabihties associated with failure of the operator to close the valves vary with the cir-cumstances and are discussed in Appendia D.
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Figure 3.5. (Continued)
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Figure 3.5. (Continued) w
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- I
HBR-3.64 involving a failure of SDV(s) to close: (1) SDV(2) fall and operator closes MSIV(s) at 30 minutes, and (2) SDV(s) fall and operator falls to close NSIV(s) in the two-hour time frame. The success and failure proba-bilities associated with this operator action were perceived to vary with conditions. (These probabilities are discussed in Appendix D.) The two sequences are designated "A" and "B" respectively.
He use of the "A" and "B" designation increased the number of reactor trip
.\
sequences to be analyzed from 95 to 110 (see Table 3.7). He bounding pro- 2' ce e performed on the residual sequences reduced the total frequency of the d' residual group to 2.7 x 10-6/yr. The remaining residual sequences were 4
very diverse with respect to consequences; therefore, they were divided into four different groups based on the nature of the event. He four recidual classes can be characterized as:
(1) Equivalent to small-break LOCA (PZR PORY failed open) .
(2) Equivalent to a small-break LOCA coupled with a small-pipe steam-line break (PZR PORY and SDV or STM PCRV failed open).
(3) Equivalent to a small steam-line break with unisolated main or l auxiliary feedwater flow.
(4) Equivalent to a small steam-line break with full RCS repressuri-zation (unthrottled charging flow).
HBR-3.65 Table 3.7. Sequences to be analyzed for reactor trip at full power
- STM PORVs SDvs MFW AFW Flo. OA: AFW Charging Sequence Clone Claes MFW lacious SGs Automaisally laaldto Flo. OA;AFW Frequency I No.* en Deand on Demand Runs Back on Demand Blow Does ControHed LP SG Reas Bact Throttled (yr-')
9.1 (0001) AE close All close AG hans NA NA NA NA NA NA 85 rua back -
9 2 (0177) AE class One fails AB hnes No has AB SGs Assomatstally NA Reas back Drottles I.3E- 2 to clois rua back overfeeds blos does contreDed as required pnor so SG bagh-level I alana 9.3 (0178) AE cime One fads AR lines No has All SGs A- "i NA Fans so 1.3E-4
- t. c, ru. m er, s b e .ow. c_r.d Russ as ..vback.
9 4 (0179) AE close One fads AD bees No hae ABSGs Assomaucally NA Feds to Drottles 1.4E-4 to close rus back overfeeds bloe dowe controuse run back pnor to SG bish-level alarm 9.5 (0181) Aa class One fads A3 knes Ne has AnSGs Automoucally NA Feds to Fails se 1.3E-6 to cloes rua back overfeeds blee does contreued rua back throttle 9 6 (0185) AE clone One fads AD bees No hae ABSGs Overfeeds NA Ross back Throttles 1.0E-4 to close run back overfeeds bios does as required pner to SG alarm 9.1 (0186) AB close One fads A5 lines No Irg ABSGs Overfeeds NA Runs back Fads to t.0E-6 to class run back overfeeds bios does run back throuls 9 8 10187) AE cloes One fails All knes No has ABSGs Overfeeds NA Fails to hrottles 3.0E-6 to close run back overfeeds bios does run back pnre to SG kigh-level lana 9 9A (0516) AB close Tee fad AE ben No has AE SGs Automauca!!y NA Russ back Drottles 2.7E-3 to close rua back overfeeds blow does enstraued as regured pnor to SG for 30 sua high isvel
{s em 9 9B (0516) An cime Twe rail AD lines Ne lias AR Son Assemancasy NA Rens back nrottles 17E-3
, to close rua back eestfeeds ble= does coeuolled as required pner to SG j bigh-level J. alam 9.10A (0517) AE cleos Tee fail AB Emes Ne line ABSGs AntemaucaDy NA Rees back Fails so 2.8E-5 es close res back overfeeds bloe down as requwed throttle for 4 aue 9.109 (0517) AE class Two fad AE lines No hae $3 SGs Automaucally NA Rees back Fails to 4.2E-6 to cloes rua back overfeeds bios does controhed as requesd throttis 9.llA (0518) AE close Tee fad AB hans Ne line ' AB SGs Aetomaucany NA Fans te nrottles 2.8E-3 to close rua back enesfeeds blow does contreued rue back pnar so SG for 30 mas high isvel alana e ,e 99
- 9
. HBR-3.66 Table 3.7 (Cont'd)
STE( PORVs SDVs MFW AFW Flow OA: AFW Charging Sequence Close Closs MFW Isolates SGs Automatically Isolated to Flow OA: AFW Fregi.ency Na* on Demand on Demand . Runs Back oc Demand Blow Down Controlled LP SG Runs Back Throttled ( yr- 8 )
9 113 (0518) As close Two fad AD hace W hae Aa SGs AetemaucaDy NA Faels to Throttles 18E-?
to close rus back oserfeeds blow dows cuatroned rua back pner to SG high-level alarm 9.12A (0520) AB close Two fad AD haes NoEne AB SGs AntesesucaDy NA Fasis to Fees to 2.9E-?
to close run back overfeeds blos do=e enetroued rea back thrustle .,
9.128 (0520) As class Too fad AH lines No S AeNatEally NA Fails to Fads to 4.4E-8 to class rua back overfeeds blee down conueued rue back throstas 9.13A (0524) AD close Too fad AG lines No bee ABSGs Overfeeds NA Rees back Throttles 10E~3 to close rua back overfeede We dows as required pnar to SG for 30 saae high-levet alarm 9.138 (0524) AE close Two fad AB bnes Nohas AnSGs Overfeeds NA Reas back Throttles 10E-7 se close rua back overfeeds blow does as required pnor to SG
, bish-level alarm 9.14A (0835) (lacluded in Sequence 919A) 9.14B (Ok5$) (lacinded is Sequence 9.193) 9.15A (0856) (locluded in Sequence 9.20A) 915B (0856) (locluded as
- 9203) 9.16A (0857) (lactoded in Sequenos 9.2] A) 9.14 8 (0857) (tecluded in Sequence 9 21B) 917A (0859) (lacauded sa Sequenos 9.22A) 9 178 (0459) (locluded is Sequence 9 228) 9.18A (0863) (locluded is Sequesca 9 23A) 9.18 B (0863) (l=h er Sequence 9 218) 9.19A (0855) An close > Three fail AE less No has AE SGs . Automatically NA Russ back Throttles 3.4E-3 to cloes rua back overfeeds blew does costreued as required pnar se 50 for 30 sua bagb-level alarne 919B (0835) Au close > Three fad AU haes No Gee ABSGs Aetomatically NA Rams back Throttles 7E-6 to class run back e=erfeeds blow dowa controlled as required pner to SG bish-level alare 9 20A (0856) As close > Three fad AB haas No lies ABSGs Automatically NA Rees back Fails to 15E-5 to close run back overfeeds
~
blow does sentroDed as required throttle far 30 mas 9.205 (0856) A3 close > Three fad AD hans Nohas AB SGs AminsnatuaDy NA Reas back Fails se 35E-6 to close run back overfeeds We dove controlled as required throttle 9 21 A (0857) AB close > nree fad AB haas No hae AESGs AutomaticaHy NA Fads to Throttles 3.5E-3 to close run back ouwfeeds blow dove soeuoued run back pnar so SG for 30 mia bagb-level alarm 9.218 (0857) AB cloes > Three fad AB ham No has AD SGs Automaucany NA Fans to Throttles 7E-8 to close rua back overfeeds bios dews eseuclied run back pner to SG bish-level
, alarm pq W' f
IIBR-3 e 67 e
Table 3.7 (Cont'd)
STM FORVs SDVs MFW AFWFhe OA;AFW Chargms j Segmence Clane Ckne MFW Inolates SGs Assomatzally Isotsied to Flow OA.AFW Frequency Na* es Demand on Demand Reas Back es Demand Rice Down Controlled LP SG Rams Back Throttled (yr")
9.22A (0859) AH clone > Three fad AE bees No has AESGs Automaucany NA Fada to Fads to 3.5E-7 to clase rua back overfeeds blow down contreued rua back throttle for 30 aus 9.229 (0859) AE close > Three fail AD haes No Ene AE SGs Automaucany NA Fa:ls to Fads to 3.5E - 8 to cloes rua back overfeeds blow dose controlled rua back throttle 9 23A (0863) As clase > nroe fad AD knes NoEne AE SGs Overfeeds NA Rams back Throttise 16E-5 to close run back overfeeds ble= down as requwed pnor to SG for 30 nun htsblevel alans 9.238 (0863) Au close > Three fad AE knes No kne ABSGs Overfeeds NA Rens back Drottles 5.2E-8 to clans rua back overfeeds bios does as requwed pner to SG high-levet alarm 9.24 (0875) An close > Three fad AB hans No hae One SG Assematically teolation Reas back nrottles 2.4E-5 to clone run back overfeeds bloes dowa controued encurs as required pner to SG b 8ble**l alarm 9.23 (2682) One fads AD cloes AE times Ne has One SG Aetamatically NA kaas back nrottles I.5E-l se class rua back overfeeds blows does sentroded as regered pner so SG bgblevel alarm 9 26 (2683) One fails All clone AB lines No hae One SG AutamaucaDy NA Raas back Fods to ISE-3 to clone rua back overfeeds blows does enetrolled as required throttle 9.27 (2684) One fads AR class AE hees N has One SG Assomaucany NA Rees back Fails to 1.5E-3 to cloes rua back overfeeds blows dows enetreued run back throttle
- 9.28 (2686) One fads AE close AB Enes No Ene One SG Assamatuany NA Fads to Fads to 1.5E-5 to close rua back overfeeds blows does contround rua back throttle 9.29 (2690) One fads As clase A8 lines NoEne One SG Overfeeds NA Reas back Throttles 1,IE-3 to close rua back overfeeds blows dose . as regested pnor to SG hisblevel
. alane 930 (2691) One fads AB close AB bees No has One SG Overfeeds NA Rees tack Fads to 1.2E-5 to class run back overfeoda , bloes dows as requsred throttle 9J1 (2692) AB lines Ne hae One 50 NA
- One fads AB close Overfeeds Fods to Throttles 3.2E-5 to close run back overfeeds blows doo run back pnor so SG bish-Isvol sJarm 9 32 (2694) One fads AE close AE hans No hae One SG Overfeeds NA Fads se Fods to I.2E-7 to skee rua back overfeeds bloes does rua back throttle 9.33 (5550) Too fad AE class AE hess No hoe Two SGs Antaraatzeny NA Rees back Drottles 3.4E-2 to class rua back overfeuds bios dowe oneuolled as rugswed pner to SG high. level l alarm l
9.34 (5551) Two fad Au clase A8 haes No hae Tee SGs Aetomaticany NA Rees back Fads to I.4E-4 is class rua back overfeeds blow dowe controlled as regered throttle 9 35 (5552) Two fad AH class AE haes No hae TeeSGs Automatrany NA Faas to Throttles 1.4E-4 to clone run back overfeeds bios does conuelled run back pner se 50 h gblevel em l
I 9.36 (5554) Tee fad As close As base No kne TeeSGs Automatmany NA Fods se Fads to 1.3E-6 i ne close run back overfends bios does soavened rua back throttle 9.37 (5558) Tee fad As clone AE bass No bae Two SGs Overfeeds NA Rees back Threstiss 1.1E-4 to class rua back overfeeds blow dose .4 as requared pner to SG bish-levet alarm I
. .. . a.
HBR-3.68 Table 3.7 (Cont'd)
STE PORVs SDVs MFW AFW Flow OA: AFW Charging Sequence Close close MFW .solates SGs Aniomatically Isolated to Flow OA: AFW Frequency Na* on Demand on Demand . Runs Back en Demand Blow Do.a Controlled LP SO Runs Back Throttico (yr-8) 9.38 ($359) T=e fad An close A5 hans No bee Tee SGs Overfeeds NA Runs back Fade to 1.l E -6 to class rua back oserfeeds Idee de=a as requwed throttle 9 39 ($$60) T=e fag AR class AB lines No has Two SGs Overfeeds NA Fails to Drottles 1.l E-4 to time rua back overfeeds blow dowe run back pnor se SG bigblevel alares 9.40 (Rm 165) Tee fad AE clase AE hees Ne line Tee SGs Overfeeds NA Feds to Faas se I.lE-I to class run back overfeeds bio = does rua back throttle 9.41 ($418) AMfad Au close A8 hees No has ADSGs Asteenatically NA Reas back Throttles 4IE-3 to clone run back overfeeds bio, do.e ooetrolled as reqmrod pnartoSG btgblegd alans 9.42 (8419) AE faa AB close AB bees No has AB SGs Automatscany NA Ross back Fadto l 4.2E - 5 es class rua back overfeeds blee down opetrolled rua back thrustis 9.43 (8420) AE faa A8 cloes AB lines No bee ABSGs Astomaucally NA Faas to Drottles 4 2E-3 to class rea back overfeeds blow de=a oestraded rua back enor to SG begblewel
, alarm 9 44 (3422) A5 faa AB clase AE hans Ne line AE SGs Antamatzany NA Fails to Fads to - 4.2E-?
se class run back overfeeds blos done rua back throttle ,
9 45 (8426) At fail An close An hans Ne hae AB SGs Overfeeds NA Rees back Tbrottles 3.lE-S se class rua back overfeeds blow down as required pner se 50 bigh-level alarm 9 46 (8427) AG fad AM close An hans No has AN SGs Overfeeds NA Rees back Fails se 3.2E-7 es close rue back overfeeds bios does as regured tbrostle 9.47 (8428) AU fad AB skes Ad hess N kne A5 SGs Overfeede NA 7 ads se nrottles 3lE-7 to class run back overfeeds blos do=e rue back pnar to SG bash-level 4Wra 9 48 (0002) A9 class Au close Onehas N bee Ne SGs Amtematmally NA Russ back Drostles 4.3E-$
i fads se overfeeds bie= dowe ensueued as regered pner se SG
- rua back best-level alarm 9 49 (0003) AR clone All close One has No hae No SGs Automaucany NA Russ back Fads no 49E-7 fads to everfeeds blow does aestroded as requand throttle rua bact 9.30 (0004) A8 close
- AR class One has No bee No SGs Automatically NA Feas to Drottles 49E-7 fads to overfeeds bio = dowe eseuolled rua back pnar to SG rue back -
bish-level alarm 9 31 (Res 2) AE close AM close One bee No has No SGs Aetematacally NA Fads to Fods no 4et-9 fads se overfeeds biee does annuelled sua back throttle run back 9.32 (0010) A3 clans
- A8 close One kne No Isme No SGe Overfeeds NA Rees back Drottles 3.7E-7 fads se overfeeds blow down as regered pnortoSG rue back besklevel alans e
,f ep.t * #
BBR-3.69 Table 3.7 (Conn)
STM PORVs SDvs MFW AFW Flow OA: AFW Charging Sequence Class Close MFW Isolates SGs Automatmany Isolated to Na*
Flow OA: AFW Frequency os Demand on Demand Runs Back on Demand Blow Dowa Controued LFSG Runs Back Throttled tyr-8) 9.53 (Res 4) AR close AH close One line No hne No SGs Onrfeeds NA Reas back Fads to 3.3E-9 fads to omrfeeds blow down as required throttle run back 9.34 (Res 3) AH cloes Au close One line No line No SGs Omrfeeds NA Fads to Throttles 3.3E-9 fads to overfeeds blow does run back pnor to SG run back hash-lewl alarm 9.33 (Res 5) All claw An close One line No line No SGs Omrfeed NA Fails to Fails to 3.3E-9 fads to overfeeds blow down run back throttle run back 9.56 (0022) AD close Au close One line One line No SGs Automaticany NA Raas back Throttles 46E-7 fails to overfeeds W edoes contreued as required pnar to SG run back bish-lent alarm 9.37 (Res de) AD close One fails One line No line AB SGs Automatmany NA Runs back Throttles 8IE-8 to close fails to ourfeeds blow down controlled as requsred pnor to 50 rua back bish level alarm 9.38 (Res e6) An close One fails One hne No has Au SGs AetomatmaRy NA Ross back Faas to <8 IE-8 to close fads to overfeeds blow dows coeuolled as required throttle rua back 9.59 (Res 46) All close One fails One hne No has AMSGs Automassaav NA Fails to Throttles <8 IE'- 8 to close fails to overfeeds blow dows controlled run back enor to 50 rua back bish level alana 9.60 (Res 46) Au close - One fads One line No line ADSGs Automataany NA Fails to Fads to < t.t E -0 to close fads to overfeeds blow does controued rus back throttle run back 9.61 (Res 46) AD ckne One fads One line No line AHSGs Overfeeds NA Runs back Throttles <8. l E - 8 to close fads to overfeeds blow dows as roquared pnor to SG run back bish-level alarm 9.62 (Res $7) AE cloes Two fail One line No line AB SGs AutoestacaGy NA Ross back Throttles 4.3E-8 to close fads to overfeeds W e down contrope# as required pnot to 50 rua back bish-level e ,, alarm 9.63 (Res $7) Au close Two faa One line No line Alt SGs Aetomatically NA Runs back Fads to <l5E-8 to close fads to overfeeds b u down controlled as required throttle rue back 9.64 (Res $7) Au close Two faa One line No line AHSGs AutomatmaRy NA Fails to Drottles <lSE-8 to cleos fads to overfeeds blow dows controlled rue back pnar to 50 rue back bish-level slann 9.65 (Res $7) Au close Two fail One line No line ADSGs Overfeeds NA Rees back Throutes < l.3 E- 8 to cloes fails to overfeeds blow does as requued ' to 50 run back ' h-level alorse 9.64 (0047) AH close AH close Two lines No line No SGs Aetomatmegy NA Rees back Throttles 4OE-6 fad to overfeeds blow does contround as required pner to 50 rue back bish level alarm O
y[ S = ' N
-c - _- _
HBR-3.70 R* AFT **
Table 3.7 (Cont'd)
ST5l PORVs SDvs htFW AFW Flow OA;AFW Charsms Sequence Close Close MFW isolates SGs Amunnatically Isolaiad to Flow OA: AFW Frequency Na* en Demand on Demand. Runs Back on Demand Blow Down Controlled I.P SG Runs Back Throttled tyr)
y e7 INa 14) Auche All awe Two len s No hae Ne m A,tomaticdy NA Rune hk Feels to 4. i k - a fad to overfeeds blow dews controlled as requwed thruitle run back 9 64 (Res 15) AG cloes All cloes Two knes No hae W SGs Automaamagy NA Fads to Tbrestles 4. l E - 8 fad to everfeeds blow does sentrolled run back pner to SG run back bish-level alarm 9.69 (Res 15) Au cloes AU cloes Two hnes No line NoSGs Automancany NA Fails to Fails to <4. l E- 8 fad to overfeeds blow does sontroDed run back throttle run back 9.70 (Res 17) AH cloes A5 close Two hnes No hae No SGs Overfeeds NA Runs back Throttles 3.lE-8 fad to overfeeds W e down as requued pnar to 50 run back bagh-level alarm 9.7I (Res 87) AR cloes Ar close Two lines No hae NoSCs Owrfeeds NA Runs back Fads to <3.l E - 8 fail to overfeeds blow down asrequwed throttle rua back 9.72 (Res 17) AR close AE close Two knes Nohne W SGs Owriseds NA Fails to Throttles <3. l E- 8 fad to overfeeds b dowe rua back pner to 50 run back bagh level ,
alare e
9.73 (Res 87) A2 cloes AH close Two lines Ne line NoSGs Overfeeds NA Fads to Fails to <3.l E- 8 fail te overfeeds W wdown rua back throttle rue back 9 74 (Res 19) All close All close Two hnes One line NoSGs AutomaticaRy NA Rees back Throttles I9E-8 fad to overfeeds blow down controlled as requued pnor to SG run back bish-level alarm .
9.73 (Res 46) Au close One fails Two lines W line AD $Gs Automaticany NA Runs back Tb ettes 8.l E - 8 to close fail to overfeeds blow dove controlled as requued pner to SG rue back high-levet saanu -
9.76 (Res 44) Au close One raits Too lines No line All SGs AutomatmaDy NA Reas beck Feils to <8.l E - 8 to close fad to overfeeds blow dowe controued as requued throttle run back 9.77 (Res 46) AH close One fads Two knes N has Au SGs Automataany NA Fails to Throttles <s.l E - 8 ,
to cloes fad to overfeeds blow down controlled rua back pner to 50 run back
- bish-level naarm 9.78 (Kes 46) AH cloes One fails Two lines Ne line AuSGe Overfeeds NA Rees back Tbrestles <t.lE-s to close fad to everfeeds blow down as required prior to 50 run back hach-level alarm 9.79 (Res 37) AH close Two fad Two lines Ne lies AR SGs AutomatmaRy NA Rees back Tbrestles <l.5 E - 8 to close fed to overfeeds blow dews aestreued as requued pner to 50 rua back bagh-level alarm
.i vw e e'
HBR-3e71 Table 3,7 (Cont'd)
STM PORVs SDVs MFW AFW Flow OA-AFW Charging Seoncace Close Close MFW Isolates SG Automatxally Isolated to Flow OA: AFW Frequency Na* on Demand on Demand Runs Back on Demand Blow Dowe Controlled LPSG Runs Back Throttled (yr")
9 80 (Res $7) All close Too fad Two haes Nohne AuSGs Overfeeds NA Runs back Throttles <l.5E-8 to close fad to overfeeds blow dows as required prior to SG run back high level alarm i
9 81 (0112) Au close Au close AD hnes No line No SGa Automaticany NA Runs back Drottles I.lE-6 fad to overfeeds blow does controlled as reqmrod prior to SG run back high-level alarm 9 82 (Res 24) All close Au close All knas No hne No SGs Overfeed NA Runs back Throttles 8.6E-9 fad to ourfeeda blow does as reqmred pnoe to SG run back high-level alarm 9 83 (Res 22) Au close AH close All lines No line No SGs Automaticany NA Fada to Throttles 1.l E - 8 fad to overfeeds blow down controlled run back pnor to SG run back bagh level alarm ,
9.84 (Res 22) Au close Au close All hnes No line No SGs Automatsauy NA Fails to Fails to <l.l E- 8 fad to overfeeds blow down controlled run back throttle run back 9 85 (Res 24) AH close Au close All knes No hne NoSGs Overfeeds NA Runs back Throttles 8 6E-9 fad to overfeeds blow down as reqmrod pnot to SG rua back high level alarm 9 86 (Res 46) AH close One fads All hnes No line Ad SGs Automatscally NA Runs back Throttles 8. l E - 8 to close fad to overfeeds blow done controined as required pnor to 50 run back bish level stann 9 87 (Res 57) AD close Two fad AU hnes No has All SGs Automatically NA Runs back Throttles < l.5 E - 8 to close fad to overf de Uso does controlled as reqmrod pnor to SG run back for 30 mia high-lent alarm 9 88 (0523) An close Two fad All haes Nohne All SGs Ourfeeds NA Runs back Fails to 1.9E-?
to close rua back ourfeeds blow dows as reqmrod throttle for 30 min 9 89 (0526) All close Two faal AD haes No line All SGs Owefeeds NA Fadato Throttles 2,3 E - 7 to close rua back overfeeds blow does run back pnar to 50 for 30 mia hisle-6evel alarm 9 to (0s64) All close > Dree fad Au lines No kne AD SGs Ourfeoda NA Runs back Fods to 2 6E-7 to cJose rua back overfeeds blow down as required throttle
. for 30 mia 9.91 (0865) Au close > Three fad All knes No has Alt *Gs
- Overfeeds NA Fads to Throttles 2.6 E - 7 to close run back overfeeds blo= does run back pnor to SG for 30 mia high-level
. alarm 9 92 10876) Au close > Three fail An hnes No hne One SG Automatically laolation Runs back Fails to 3E-7 to cices rua back overfeeds b'aws down' controlled occurs as required throttle 9 93 (0877) Au cloes > Three fad All lines No hne One 50 Automaticauy isolaten Fails to Throttles 2.3 E - 7 to close run back overfeeda , blows dowa' controlled occurs rua back pnar to SG bish Isul alarm 9 94 (098I) Au cloes > Three fail All haes No hae Two SGs Automatwally isolatma Rens back Throttles 7.2E-6 to close rua back overfeeds blow dews' controlled occurs as required pnot to SG bigh-level alarm 9 95 (0947) AD close > Three fad All knes No has All SGs Automatmally NA Rams back Throttles 1.9 E - 6 to close run back overfeeds blow does' somtrolled as reqmrod pnor to SG bish-level alana 9 96 Res dual (Equivslent to a small-break LOCA) 4.3 E - 8 9 97 Resedual (Eqmvalent to e small-break LOCA coupled with a small. pipe steam-hne break) 2.2 E - 6 9 98 Residual (Eqmvalent to e sman steam-hne break onb sostinued flow to break) 33E-8 9 99 Residual (Egmeslant to a small-pipe steam hne break with full pressortaation) 4 3E-7
'The branches entsled *SI Signal Generated on Demand,AFW Acteates on Demand.* *HPI Occurs on Demand.' sad "FZR PORV Ressats on Demand
- este sue.
cessful is all sequences hated Therefore, these headings de not opsmar in this table Taitre were other sequences for shach not all of the branches were sucseaafel, but they did act surnve the frequency screemag. These sequences are included sa the res. dual groups.
'As stated is the test, the letters *A* and 'Be followies the sequence number segmfy whether or aos the MSIVs are closed by the operator. la the *A* naquences the corrster is assumed to close alte valves 30 mimetse into the transeenL la the *3* sequences 6e es assumed that the MSIVs remain open for the 2-hour period.
'All steam generators blow down for 30 maastas; at this time, the operator closes the MSIVe, but one, two, er au three of them fel to closa
,o es *
- _ _ _ _ - - - . . ~ - - _ . - . . - - - . .-
HDR-3.72 he frequencies of each of these residual groups, calculated as the sum of the constituent sequence frequencies, are included in Table 3.7.
3.5.2. Large Steam-Line Break at Hot 0% Power i
j In Appendix B, the frequency for a large steam-line break as an initiator t
is given as 1.2 x 10-3/yr. This frequency covers both full power and hot 0% power conditions. The fraction of operating time spent at hot 0% pow er (1.9%) was considered as a weighting factor for determining the frequency j of occurrence at hot 0% power. With this weighting factor, the initiator frequency for this category was defined as (1.2 x 10~3/yr) x 0.019 = 2.28 x 10~0/yr.
A i
! C Combining the initiating frequency with the branch headings probabilities p.'
given in Table 3.8 produced a totsi of 508 sequences. Of these, nine -; -
! sequences, three of which are residual groups, were identified for ana- , b-lyses. The event tree for this initiator is shown in Figure 3.6, and the [ f l sequences are listed in Table 3.9. The bounding process did not reduce the I*'
I residual group frequency significantly.
l l
l The frequency associated with the residual group totaled approximately 2.3 x 10-7/yr. This total residual is indicative of the importance (or lack thereof) of the sequences which were not selected for thermal-hydraulic and fracture-mechanics analyses.
l
HBR-3.73 t
v Table 3.8. Branch probabilities for large. and small;~ team-line e
breaks at hot 0% power
- _
Branch Probabihty*
Large' Pipe Small' Pipe Tree lleading Branch Break Break Si signal (1) 51 signal is generated. 0.99997 generated (2) Si signal is not generated. 3 X 10-s on demand.
M F'W isolated (1) No line overfeeds. 0.99999 on demand. (2) One hne overfeedt' 9 0 X 10*'
- 13) Two knes overfeed? 8.4 X 10 4 (4) All three knes overfeed? 8.1 X 10~8 SGs blow If MSIV closure is generated,#
dows. (1) No SGs blow dows. 0.5 (2) One SG blows dows. 0.5 (3) Two SGs blow dows. 9.9 X 10**
(4) All three SGs blow down. 1.7 X 10-8 If MSIV closure is not generated #
(1) One SG blows doma. 0.5 (2) All three SGs blow down. 0.5 AFW actuates (1) AFW actuatet 0.999 on demand. (2) AFW does not actuate. I X 10-8 i AFW flow (l) AFW flow is setomatically j sutomatwally controlled at nominal rate. 0.9925 (2) flow control failure leads f controlled. to abnormally high AFW flow t raie (overfeed.).. 7.5 X 10'8 OA: AFW (1) AFW isolation occurs. 0.9977 0.9983 isolated to (2) AFW isolation fails to occur. 2.3 X 10*8 I.7 X 10-s .
low. pressure SG.
HPI occurs if 51 signalis generated, on demand. (I) HPl occurs. 0.99939 (2) liPI fads to occur. 6.1 X 10**
If SI signalis not generated, l
(1) Operator manually starts HPL 0.99 (2) Operator fads to start itPL I X 10-2 Charging flow (1) Charging flow runs back runs back as required (repressuri-on demand, antion hmitedh 0.9983 0.99 (2) Charging flow fails to run back (repressurization act hmited) 1.2 X 10*8 I X 10*8 OA: AFW If operator tsalaies AFW, throttled. (1) Operator throttles AFW flow. 0.99 (2) Operator fails to throttle AFW flow. I X 10*8 If operator fails to isolate AFW, (1) Operator fails to thractie AFW flow. 1.0 (2) Operator throttles AFW flow. 0.0 PZR PORY (1) PZR PORY rescats if charging rescats on flow fails to run back. 0.9933 demand. (2) PZR PORY fads to rescat if j charging flow fads to run back. l.2 X 10*8
- Acronyms used in this table (hsted in the order of their appearsace) are: SI = safety injection, MFW = main feeduster, SG = steam generator, MSIY = mais steam isola-tion valve, AFW = assihary feedwater, OA = operator action, HPI = high-pressure injection, PZR PORY = pressurizer powereperated reist valve, and MFIV = mais feedwater isolation valve.
6 Probabihties centered between the two columes apply to both break sizet
' includes failure of MFW regulating ealves to run back, failure of one or both MFW pumps to trip on high level in any SG, and fadure of MFIVs to close on SI signal The MSIY closure signal may or may not be generated for a large-pipe steam line break; it
=di mor be generated for a small-pipe steam hne break at hat 0% power.
,1 ew *
- ELR-3.74 Ii
' ' ' ~
Combined ud.G #40 ~ ~44 GM. A's L .;,4- C.W- i; -Fr'o n.T, 3' '%if"'
. Ym,' with
-c-
[ l*"" -
Sequence
- 1. l w 10 0C':1 I 1. l w l0 00';2
-7 1.1w10 00::3
';.2 , I i ' ..Fr c . .t. 1. 3* 10"*
.. w e: 7 1.l*10""
.'8Es.A. 6.9*10
. cool
..M.4.4 8. 5w l0"
.44.5 1.lwl0" oco 1.Iw10" 00;'l
' ! l.1*10 00; 2 1.Iw10 00;:3
' ' [ . 25.h 1.3*10" D- ' ' . Ets. 7 1.IwI0"
..ers s 6,9w10" co21
. . .tT4.1 2.S*10"
...W5 eo 8.5wl0"
.Ms.9. 1.Iw10" on:
.J C 'Z 2.6*10"
..RC#5 2.3w10"*
..RTA I4 6. 8* 10"*
I Figure 3.6. Event tree for large steam-line break at hot 0% power.
l l
I I
l l
l 1
an 1
1 HBR-3e75 s
Table 3.9e Sequences to be analyzed for small and large. steam-line breaks at hot 0% power" St Lgnal bit W AtW A)W OA.A>W Chargeg Sequemen Generated teolated SGs Actuates Automatecally laolated to HPI Occurs Flow OA: AFW Frequency Na em Demand on Demand Blo Do e ce Demand Comersaled LP SG on Demand Runs Beck Thrustled (yr")
names bewtJee arena 7.4 (0001) Sageal as No hae One SG AFW AutomancaDy Isolation HPt Rees back Throeiks 2 4E-3 generated overfeeds blows does acteates controlled occurs occurs as regured pner se SG higklevel sierm 7.2 (0003) Signal is No has One SG AFW Aetomatically Isolsues HPt Fads to Thresties 2 4E- $
peereied overfeeds biens de=e actnias eenerelled oncere escurs rue back peer to SG h gbievel elarm 7.3 (0002) Sagent a No has One SG AFW AetamoucaNy leoisioon HPI Rses bact Fa.is se 24E-S steerstad emerfeeds blows does actuates contretied occura sczare es reqwred thretite 7 4 (Res 4) Sassal is No hae One SG AFW AetamenzaDy Fada se HPl Rens back Throeines 0 o' generated overfeeds blows dows acteates samtreued ecrut escurs es required pnor to 50 bagblevel alarm 7.3 (Res 5) Segnal in No hae One50 AFW Automaucally Fads to HPt Fails to Throttles 4.2E -8 generated overfeeds blows down actuates sentreued accer scrues res back pner to SG higbaswel storm 7.6 (0009) Signal u No has One SG AFW AutomaucaDy Fads to HPI Rune back Fads to 4 2E-6 generated overfeeds blows dove actuates soeuelled eccer assure as requsred throttle 7.7 (0017) Sessai e No has One SG AFW Overfeeds lactation HPI Rees back Thrailles i SE-5 generated overfeeds biows do.e actuates escurs occare as requered pner se 50 higblevel alarm 7 8 (Res 10) Signal is No hae One SG AFW Overfeeds Fods to HP1 Rees back Threstles 3.2E-8 generated everfeeds bioes down acessies accur oorers as esquared pner to SG beg 41evel storm 79' (Semdar te ' 7.1) 7.10' (Semdar no Sequence 14) 7 ti' (Similar to Segoceae 7.I) 1 12 (0037) Sagnat es Ne bas AR $Gs AFW Autometzany NA # HPt Rans bect Throttles 2.4 E - 3 generated e=erfeeds bios done ecumies controlled eeeurs es regeered pner se SG bigblevel elarm 7 13 (0033) Segnal in No lies AB SGs AFW Automatzany NA HPt Rune back Fads to 15 E - S generated emerfeeds blow down actestes coeuoued occurs as required throttle 7.14 (0039) Signal in No has AtSGa AFW Autometzally NA HPI Fans se Thrasiles 14E-5 generated everfeeds bio = dows actuates eostrousd accure rua back preir se 50 her h level skrm l 7.35 (0048) S gnal is Ne has AB SGs AFW AssametzaDy NA HPI Feas to Fods le 2.$E-7 geacrated overfeeds blow does actuates costreued occurs run back threstle l
7 16 (0005) Signalis No has One 50 AFW AmtematmaDy leolaiana HPl Fans se Fads to 2.$E-7 i generated everfeeds blows dows actuates enetrelled escurs accurs rua back throttis
( 7.17 (0046) $ssaal is Ne hne AESGs AFW Overfeeds NA HPI Russ bect Fads ee 19E-7 generosed overfeeds bios does acasanes occare es required throttle 718 {00lt) Signal is Ne hae One SG AFW Overfeeds leolaties HPI Rees bact Fods te 1.9 E - 7 generated westfeede blows does actuees accurs escurs as regested threetis 7.19 (0019) Signal s No hee One SG AFW Overfeeds teolanoo HPl Fads se Theatiles i SE-7 generated overfeeds blows down actuates acents occurs run back pnar se SG highievel alarm 7.20 Residul Group 2.5E - 7 1
F
, ,e en
- e
BBR-3e76 Table 3e9. (Continued) 51 S gest MFW AFW AFW OA AFW Charging hequesco Gcecrated foulated $Go Acteates Amtemahcally ladated te flPl Dixers Ihre OA. AFW Fregocesy Na se Ucesed as Demeed Bhre Do=e se Demand Controlled 17SG en Demand Rees Beck Thrwiiod tyr")
targe- Seeee4Jee Brook e 1181021) bemol as Ne has One M3 AFW Aeteenstessily leutecome flPl lives best i hrdete. l it= $
generated eserfeeds blows dowe actestes centrolled encore occare es regewed prese to SG high-level alaren 8 2 (0023) Signal u No bee One SG AFW Assomassally leoistion HPI Fads se Theorace I.l k - 7 genereiad overfeeds blows dowe octuates coatteiled eccers scrura run back pnor so SG high-level elares e 3 (0022) Sassal es Ne bee One SG ADW Autometscelly isolatese llPl Rees back Dette se B.t h- ?
geestated esesfeeds blows dowe actosses emetteiled accors occare as regewed threnals 8 4 (Rm 9) Sagasi is No hee One SG AFW Aetometselly Fails to HPl Rese back Feds to 2 6E- 8 genereted overfeeds blows dose actestes controlled accer occare es regewed throttle 8 3 (Res 10) Signal u Ne line One SG AFW Overfeeds isolaison HPS Rens back Throtties 8.5E-8 genstated overfeeds blows down acemains occurs essors as regemed pnor se SG high-level alarm 8 6 (Ree 10) Sageal is No hoe One SG AFW Overfeeds Fails se HPI Rees bact Fails to <8.5E-8 generated eserfeeds blows dowe actuates escur escurs as required throttle 8.7 (0001) $4 seal is No line NoSGs AFW Aetomatically NA HPI Rees bect Threstles I.l E- S generated seerfeeds blow does acusates controlled occurs as requed pner to SG high-level alarra 8 8 (0002) Signal is Ne bee NoSGs AFW AssomaticaDy NA HPI Rees back Fails se 1.lE-7 generated eserfeeds blee does actuates coetrolled occurs es regewed throttle 8 9 (0003) Signal in No bee NoSGe AFW AutomataceHy NA HPI Fails to Throttles I.IE-7 generated everfeeds bio = does actuates controlled occurs rua back pner se SG ,
high-level alarm S ie Res. deal Group 2.3E-7
'PZR FORVs ressat for all segereces hated, therefore, the heading "PZR PORY Reseats se Demsed* does est appear as sabia. In some other necessaces the PZR PORVs did see resent, but these esquen as did not serweve the frequency screesses and era um:leded to the resideal group.
eBecause of the souphes factor imposed en the thtettling af the AFW, see the fadere se moiste the AFW, this segessos bas e frequency of 0 0; that es, ao credit is gives for throt-thog the AFW of the operaser faded to anotate the AFW.
'Segmences 7 9. 7.10. and 7.11 involved feelare of the SDvs se malste en demsed. Sebesquent analyms revealed that the SDvs probably would not opeo derms the sweet, thus.
faalere of the SDVg to close was not considered.
- NA = not applicebte i
r l
l
,/ or =
- r
HBR-3.77 3.5.3. Small Steam-Line Break at Hot 0% Power Historically, small steam-line breaks have involved single and multiple open valves. The initiating frequency given in Appendix B for small steam-line breaks independent of the reactor state is 2.0 x 10-2/yr. At hot 0%
power and during initial power increase, there is a constant need to match feed flow and steam flow. This transient condition was believed to increase the potential for a small break. The effect of this transient condition is demonstrated by the fact that ~25% of the observed scrams occurred during startup. Also, although the data base is small, one of the four observed small breaks occurred during a startup condition. Thus, based on this information, 25% of the small-break frequency was assumed to occur at hot 0% power. This results in an initiating event frequency of (2.0 x 10-2/yr) x 0.25 = 5.0 x 10 -3 /yr.
1 The branch headings and probabilities for the small break are presented in Table 3.8. The event tree developed from these probabilities and the 10-7 .
truncation frequency is presented in Figure 3.7. It shows that 19 h sequences (out of the 2.92) survived the 10-7 screening level. As shown in Table 3.9, the sequence bounding process reduced this number to 16. The frequency for the group composed of those residual sequences which are nei-ther specifically analyzed nor grouped with a specifically analyzed sequence is 2.5 x 10-7/yr.
3.5.4. Large Steam-Line Break at Full Power l
l l The initiating frequency of a large steam-line break at full power is based on the overall frequency for a large' steam-line break multiplied by the fraction of time at full power: (1.2 x 10~3/yr) x 0.98 = 1.18 x 10 ~3 /yr.
l l
,, p e.= . e l
l
HBR-3.78 Combined
~ ' ' '
g
.- . e.;, - ' - - - -
- o,. ;g;G A2,!, ; w ;- gtg J ;',., %s' '/4," ' ".%/ with Sequence 2.1 = 10 0001
! 2.4=.0* C00 2.i=1C' C003 Fes t. 2. 3 = 10' 2.5=10" C00".
. ses2 3. 0= 10*
- 1. 5= 1 C C007 opt
.. F.rs 3 1.5=lC" 8ca A 4.2=10" C005 1 . . f,*'4 C.C
' Mah 2 ..fass 1.2=10"
$<5 f. 2.S=1C' coo %
C017 1 1.SalC'.
a 1. 9= 10 , 0015
- 1. S= 1 C C01S r ! .. b1 2.2=10"'
.. /<S 8 . 1.9=1C'
. .FM . 1.1 = 1 C coi?
. 05 R 3.2=1C' 2.5=lC* C0 !" ****
1
. . fe 588 2.5=1C"
.f*MA 1. 5= 10 coo i 2.4=10" C037 5 2.0=10' CO33
. 1 2.1 = 10"..C033 j g . As l3 2. 3= 10,, .
i, '
2.5=1C C041
..Rntt 3. C= 1C" 1.5=10' C013 3o37
.. a ,c, j . ..k) U l.5=1C* o * *8 Br~dat 1.s=lc" CO*5 **37 l . 9- 10 001E
- 1. 9 = l C C047
^
I i
..Rel& 2.2=10" t
... .. Arsll 1.9=10
...S<416 1.1=1C" ocos 2.5=lC' C0s- co11 i
..Resl'l 2.5=1C"
..,.. ..Resa o 1. 5= lC 0037 i
..P,*stl C.C l
' f<s2a 5.0=lc'
..F<12 3 1. 5 = 10
Figure 3.7. Event tree for satell u steam line break at hot 0% power.
. , . a
HBR-3.79 0
/
This initiating event frequency was used, together with the branch headings '
j , \, ,
and probabilities given in Table 3.10, to produce the event tree shown in !- ."
Figure 3.8.
{' -
Figure 3.8 shows that 21 sequences (out of the 1763) survived the 10-7 screening level for the large steam-line break at full power. This was ,
- p .
ff reduced to the 15 sequences presented in Table 3.11 to be specifically con- /'
/l' sidered for further analysis. The frequency associated with the remaining residual group totaled 4.4 x 10-7/yr.
3.5.5. Small Steam-Line Break at Full Power The initiating frequency for small steam-line breaks at full power is based on the overall frequency multiplied by the fraction of time spent at full
, Power: 2.0 x 10-2/yr x 0.75 = 1.5 x 10-2/yr. The branch headings and pro-babilities are given in Table 3.10, and the resulting event tree developed f; I
for this initiating event is presented in Figure 3.9. >*
Table 3.11 presents the 29 sequences identified for thermal-hydraulic analysis. It should be noted that several of these are sequences which have frequencies less than 10-7/yr. Based on our initial frequency analysis, these sequences were supplied to INEL for thermal-hydraulic analysis, and thus temperature, pressure and heat transfer coefficient data were developed for these sequences. As a result, these sequences were l
analyzed individually in order to reduce the size of the residual group.
The remaining residual group has a frequency of 6.6'x 10-7/yr.
l
- er t
- P
IIBR-3.80
, . - - i Table 3.10. Branch probabilities for large and small ; steam-line I breaks at full power'
, Breach Probabshiy*
Larpe' Pipe Small bpe * .-
Tree Heading Branch Break Break SDvs close (1) All five SDvs close. N A' 0 99768 on demand (2) One SDV feels to cices. NA I 6 x 10" (3) Too SDvs fad to close. NA 3.0 X 10-*
(4) Three or more SDvs fad se close. NA 4.2 X 10-*
Si signal (1) 51 signal is generated. 0 99997 generated (2) Si signal is not generated. 3 X 10-s om demand, MFW runs back If $193nalis genereced. MFW a wl enolates liacs run back sad isolass:
on demand (i) All haes run back and MFW is isolated 0 9999997 (2)One bne overfeedt# 2.8 X 10" .
(3) Too knes overfeed # 1 $ X 10 }
(4) AH three bees everfeed.# 10 X 10-*
If Si ognal as not generated, rueback only occurs; it) An haes rua back. 0 9999940 (2)One has overfeedL' $.3 X 10-*
(3) Two haea surfeed' S.0 X 10" (4) AH three knes oserfeed.' l.4 X 10~'
SGs blow if MSIV classte signalis generated, doet (Il No SG blows dowit 0.3 (2) One SG bloes doet 0.3 (3) Two SGs bio doen. 99 X 10**
(4) AD three SGs blee dosa, l.7 X 10**
If MSiv closure signalis not generated, (1) One SG bloes down. 0.5 (2) AB three SGs ideo does. 0.5 AFW scinates (1) AFW actuates 0 999 en demand. (2) AFW does not a actuatt 1 X 10*8 AFW flee (1) AFW flow is automatically
- automaticaHy controlled at nominal flow contrelled rete. 0 9923 (2) Flow control failure leads le abnormally high AFW flow rate (overfeedsk 7.3 X 10~8 OA AFW fl) AFW isolation occurt 0 9977 0 9983 notated te (2) AFW isolation faala se occur. 2.3 X 10~ 8 17 X 10~8 low-preuere SG HPI occurs If $1 signalis generated, os demand. (Il HP1 occurs. 0 99919 (2) HPI fa la la accer. 61 X 10
If SI segnal is nos generstad.
Il) Operator manuahy starts HPl. 0 99 (2) Operater fads to start HPt. I X 10*8 Chargtag flee (1) Charging flow rues back as runs best required (receesserustana on demand hmesedh 0 99 (2) Charging flee i sds le run back (repressuriaanon not bened) 1 X 10*8 OA AFW ff operator hotates AFW, throttied. II)Orerator threities AFW flee. 0 99 (2) Operator fails to throttle AFW flow- I X 10'8 If operator fads to nelate AFW, (1) Operator fails to throttle AF W flow. 10 (2) Operator throttles AFW flow. 00 PZR PORY (I) PZR PORY ressats if chargies ressats os flow fads to run back. 0 9988 demand (2) PZR PORY fails to reisst af charging flow fads se run back. I 2 X 10* 8
- 4cronyms used ta the table (in the order of thew appearsace) are SDV = steam deep eel e, 51 = safety injectos. MFW = ansia ferdester, SG = ateam generator. MSIV = main sseam isolation volve. AFW = sesiliary feedeater, OA = oprator action. HPl = bigh.
pressere ejectson, PZR FORY = presserver power. operated res cf valve, and MFIV = meia feedesier notation estre.
- Probabehtes censered beteses the two colemas apply to beeh break esass
'NA = Not applicable i
- lacludes fadere of M FW regulating velves se ten back. fadere of one er both MFW pumps se trip en high level to say SG. and feelste of MFive to close es SI segnal.
' includes faduce of MF W regulating esives to rua back sad failure of MFW pumps to trip on lugh level se any SG.
p @
HBR-3.81
- "d l - - - ;::.;::,.
-"" f W ft,9 l;p..E faa a;,,. ;. m- gg .;;,., 2,.. . .g.,. ;
Sequence
- 5. 7 = 10 ' C00;
' 5. 6 = 10 ' COO; e .s '
- 5. 0= 1C ' CCO ft LS '. . 6.9 10 '
.00 k 5.E=1C
- 3. 5= 1 C 000 omi
- . s u . a sM. 3. 6-IC* coo 2-8% ,
- 1. 3 = 10 C00'
' . J t 5 'f. 1.1=1C'
..885T. 1.1=1C"
.ntsL 2,7= 3 n'*
- 5. 6 = 16' col .: ooot
' .. !s 53. 5. 9 = 1 C
9853 3. 6 = l C'"
l 5. 7 = 10 002:
5 5.6=lC* CO2: .
5.3=10' C02' r . F asi 6. 9= 10' '
. . F r.S.t
- 5. 6= 10'
- 3. 5= 16' 002:- oost
. lf ts # 3.6 16' oop I.3 1C
- CC2.
' ..AESt4 C.C All aovki .. 53 1.3=lO
- * .. P Lt.45 8. 2= 1 C"*
cbw 1.3=10' COT
' . . E t5.'.5 1.1=10'
' ..f t$ l' 1.1 10'
- . .f 45. 41 2.7=10' #W
. .Ft t.4 1.C=1C" 5.6=lC COT 00:1
. 755 0 5. 3 = 10 0021
. . 8 L5 2* 3. 6= 1 C"* oo2I 1.1=10' CGT l 1
..Mial 1.1=10' ,
- ' e ,, ass 32 3,2=3c'
? .
J se s .1 6
, . ats 2) 7.C=10'* 80 0 -
.... .fas st 2.7=10' l
.. ... 155.# 8.7=10' l J. . .PcsA6 1.2=10'- 88 f 7 1.3=10' C09' 5 .. F l.131 2.C=16' Ad Q,, ,
' . .. .8598 2. Ca l6' w .: ..a a s. st 3,2= g g" oo%
5 .... .. des. Se, 3,5= 3 c '
' . . . . . ..a as. ?' 2. Ca l C"* 80i'5
. . .ftS u 3. 3=10 "
. . . . .. Pts.M 3.5= l6' osat 9.l=10 Cils ooo i
' .f55.M 9.2=16' ooos
. .. rs. 31 9.t=lC* o co 3
. #4.2s 5,7=1c # eel No !d > i .
- "' I , .. r ts 31 2. 2 = l 0
, . . . .. itS SC. 7.1 = 10
'....A.. . , . . .. 8 4..M 9.1 = 10 " ooo l Figure 3.8. Event tree for large , steam-line break at full power.
(continued on next page, with overlap) 1 =e
- 9
I HBR-3.82
' , r
, 9.1 = 1 C Cit ,
ooo g
. FES H 9.2=10 ooog
, .. 4s M 9. 3 = 10 o oo 3 i' fes.h 5.7=10'" ocol
.. Fat3 7 2.2=1C
. stS %. 7.1 = 1 C
. . F t5 .M 9.1 = 10' " ooo g i g,, ,
, 9.1=10* C15 ooat g..., , ,
. AL5'4 8 9.2=1C ooa1
.Its 9 9. 3=10 ' o o 3 's
.fes t 5. 7=10'* oo2i
. 6 E.T .9 2.2 10 o'o s eg
. 4 a s y 7,3 = j c
..f 8.S .41 9.1=}C oons
.. FL517 1. 7= 1C '
. 83 3 'f 8 5. 3 10 "
. 885..'M 5.7=10'" ooal
, 1. 7= l C* CSS' sool
. fas so 1. 7 = 10 *o*2
- % 5 8 1. 7= 10 0003
. h 5.52 g.j=30 ooog
..P o.ss 1.C=lc A'S M 1. 3= 1C '
..Ra s rf 1, s 1C
- 0004 3 % ., ,
i 1.7=10, 003I g,,, ,
i
. #Es 5' l.7=1C] C32; Coal
.. A ss 61 1. 7 = 1 C ' ooD
. ,b ' .865:3 1.1 = 10'* 0021
. .w 1. C= i G - om
, . Fst 6e 1. 3 = 1 C ' -
. 8E% 4 6 1. S = 1 C'* cosi
. e. .
. . Pt 5. ' A 3. 2 = 1 C
.h 5.O IC.C=lC'"
. 6.s4 c.3 3. g = gn " oogi
' 2.1 = 1 C ' 132'. 0008
, FW G5 2.1 = 1 C
- oca3 Nets '
f O 68. 2.1=lG .
oco%
u, . .
.. Pts L1 1.5= la . ooof
. .it.5 4 5.7 10'* !
.. W5 41 1. 9= 10
.fts.Jo 2.5 10'* oool
) 3 m,, ' ,
, 2.1 = 10, 135: o03
. P 65 % 2.1 = 1 C ' 0032
. .ft t %.7 4. 2.1 = 10 003'5 d' *
. f 413 1. L= 10'
- 0021
. $a) Tt 5.7-30 CO 99
. 88.S.15 1. 9 1 C {
. F.5.S. 76 2.5=10'" O O 'Al
, . M "21 1.1 = 10
.. ItS 78 1.1 = 10 "
. FCS .71 1.5= lC " con i
l ,, Figure 3.8. (Continued) l 1
- ee.
I i
of e=
- f I
HBR-3.83 Table 3.11. Sequences to be an Iyred for sman- and large-pipe steam-line breaks at futi power
- MFW Runs SDVs Back and AFW OA: AFW Charsins i' Sequence Ckse isolates SGs Automancany Isolated to Flow OA: AFW Frequency Net on Den and on Demand Blow Down Controlled I.P SG Runs Back Throttled (yr")
SmaH-Pipe Steam Une Break I 5.1(0001) AH close Runs back One SG Automatwally isolation Runs back Throttles 7.3E- 3 and isoistes blows down controlled occurs as required prior to SG high level
- alarm 5.2 (0003) AH close Runs back One SG Automatsally isolatma Fails to Throules 7.3E-3 and isolatea blows down controued occurs rua back prior to SG bigh-level alarm 5.3 (0002) Au close Runs back One SG Automaticauy isolaten Runs back Fads to 7.3E-5 and isolates blows dowa controlled occurs as required throttle
> 5.4 (0005) Au close Runs back One SG Automatically Isolation Fails to Fails to
- 7.4 E- 7 l and isolates blows down controlled occurs run back throttle 1
5 AH close Runs back One SG Automatica!!y Fails to Runs back Throttles 0.0 8 I .5 (Res 4) and isolates blows down controlled occur as requued pnor to SG i bigh-level alarm l
5.6 (Res 6) All close Runs back One SG Automaticauy Fails to Fails to Throttles 0.0 8 and isolates blows down controlled occur rumback prior to SG bigh-level alarm 5.7 (0009) All close Runs back One SG AutomstmaDy Fails to Runs back Fails to 1.2E-5 and isolates blows down controlled occur as required throttle 5.8 (00ll) All close Runs back One SG Automatically Fails to Fails to f ails to 1.3E-7 j and isolates blows down controlled occur rua back throttle .
5.9 (0017) Au close Runs back One SG Overfeeds isolanon Runa back Throttles 5.5 E - 3 and snolates blows down occurs as requesd prior to SG high-level I alana 5.10 (0019) All close Runs back One SG Overfeeds laulation Fails to Throttles 5.5 E - 7 and isolates blows down occurn run back pnor to SG higblevel
. sierm 5.11(0018) All class Runs back One SG Overfeeds isolation Runs back Fads to 5.5 E - 7 and miates blows down occurs as required throttle 5.12 (Res ll) AH close R uri. back One SG Overfeeds Fails to Runs back Throttles 008 and molates blows down occur as required prior to SG i bigh level f alarm 5.13(Res!!) All close Runs back One SO Overfeeds Fails to Runs back Fads to 9.5 E - 8 and isolates blows down accur as required throttle 5.14 (0279) One fails Runs back AH SGs Automatecally NA' Runs back Throttles 2. 3 E - 5 to close and isolates blow dowa' controlled as required pnot to 50 high-level alarm 5.15 (0281) One fails Rens back All SGs Automatically NA Fa.!s to Throttles 2.4E-7 to close and isolates blow down' controhed run back pnot to SG high. level alarm 5.16 (0280) One fada Runs back All SGs Automatically NA Runs back Fads to 2.4 E- 7 to close and isolates blow down' controlled as required throttle 5.17' (included in Sequence 5.14) 5 18 (0287) One fads Runs back All SGs Overfeeds NA Runs back Throttles 1.8 E - 7 to close and isolates blow dows' as tsquired pnor to SG lugh level
.s ew *
- l' HBR-3,84 Table 3.11. (Continutd)
Table 3.11. (Contissed)
. MFW Runs
! SDVs Back and AFW OA AFW Charging Sequence Close Isolates SGs Automatically isolated to Flow OA: AFW Frequency Na ce Demand as Demand Blow Down Controlled 11 SG Runs Back Thrott!cd (yr")
{
i AH SGs Automatically NA Runs back Throttles 4.4 E- 6 5.19 (0382) Two fail Runs back W e dowa' controlled as required prior to SG to close and isolates bigh-level i alarm 5.20' (Included in Sequence 5.19)
Runs back All SGs Automatically NA Runs back Throttles 7.3E-3 5.21 (0037) Au close and isolates We dawa' controlled as required pnor to SG high-level alarm Runs back All SGs Automaticany NA Fails to Throttles 7.3 E- 5 5.22 (0039) All class and isolates blow down' controlled rua back pnor to SG bigh-level alarm I' Runs back All SGs Automaucally NA
- Runs back Fails to 7.3E-5 5.23 (0038) All close and isolates We down' controlled as required throttle l
Runs back All SGs Overfeeds NA Runs back Throttles 5.5E-5 5.24 (0045) All close and isolates W w dowa' as required pnor to SG high-level alarm Runs back All SGs Automaticany NA Fails to Fails to 7.4E-7
' 5.25 (0041) All close and isolates Ww dowa' controlled run back throttle Runs back All SGs Overfeeds NA Fails to Fails to 5.5 E-7
, 5.26 (0046) All close and isolates Ww down' run back throttle l
Runs back All SGs Overfeeds NA Fails to Throttles 5.5E-7*
5.27 (0047) Au close and isolates blow down' run back pnor to SG high. level alarm Automatically isolation Runs back Throttles 3 lE-6
>Three fail Runs back All SGs pnor to SG 5.28 (0485) controlled occurs as required to close and isolates blow do.a
! for 30 man /
bish-level
' alarm Isolation Runs back Throtties 3. l E - 6 Runs back One SG Automatically 5.29 (0521) >Three fail ocents as required prior to SG and isolates blows dows controlled to close bigh-level alarm 6.6E-7 5.30 Residual Group targe-Flpe Steam-l.Jee Break One SG Automatically isolation Runs back Throttics 5.7E-4 6.I (0021) All close Runs back controlled occurs as required prior to SG and isolates Wes down high-level
- alarm One SG Automatically Isolation Faits to Throttles 5.8E-6 6.2 (0023) All close Runs back prior to SG and isolates blows does controlled cocars rua back e
high-level alarm One SG Automatically Isolatma Runs back Fails to 5.8E-6 6.3(0022) All close Runs back blows down controlled occurs as required throttle and siolates Automatscany isolation Fails to Fails to 5.8 E- 8
,6.4 (Res 10) All close Runs back One SG blows down controlled occurs run back throttle and isolates 8
Automatically Fails to Runs back Throttles 0.0 6.5 (Res 12) Au close Runs back One SG controlled occur as required prior to SG and isolates blows down high level alarm 1
Automsticany Fails to Fa;1: to Fails to 1.3 E- 8 All close Runs back One SG 6.6(Res 83) controlled occur tua back thrott!c and inciates blows dows One SG Automatically Fails to Runs back Fails to I.3E-6 6.7 (0029) All close Runs back blows down controlled occur as required throttle and isolates Overfeeds isolation Runs back Throttles 4.3 E - 6 6.8 l0037) All close Runs back One SG blows down occurs as required prmr to SG and isolates high-level alarm of *=
- e
BMFT HBR-3.85 Table 3 II. (Continued) htFW Runs SDVs Back and Sequence Close AFW OA-AFW Chargung Isolates SGs ha on Demand on Demand Automatically isolated to Flow OA: AFW Blow Down Controlled Frequency LP SG Runs Back Throttled (yr)
t 6.9 (Re 18)
I AH close Runs back One SG Overfeeds Fails to .Rans back Fails to 1.0E- 8 and isolates blows down oa:ur f as required throttle 6.10 (0057) AH close Runs back Two SGs Automatically Isolation Runa back Throttles I.lE-6 and isolates blow does I controlled occurs as required prior to SG I- high level alarm 6.11 (0093) AH close Runs back All SGs Automatmally NA Runs back Throttles I.9 E- 7 and isolates blow down controlled as required prior to SG bigh-level
, alarm 6.12 (0001) All close Rans back No SGs Automatically NA ' Runs back Throttles 5.7E-4 -
and isolates blow down controlled as required prior to SG f' bigh-level alarm 6.13 (0002) All close Runs back No SGs AutomaticaDy NA Raas back Fails to 5.9E-6 and isolates blow down controlled as required throttle 6.14 (0003) All close Runs back NoSGs Automatically NA Fails to throttaa 5.t E- 6 and isolates blow down controlled run back pnor to 50 high-ieven alarm 6.15 (0009) All class Runs back No SGs Overfeeds NA Runs back Throttles 4.3E-6 and isolatea bbw down as required prior to SG high level alarm 6.16 Residual Group 4.4E.7 j 'The branches entitled *S1 Signal Generated on Demand.' 'AFW Actuates on Demand,' 'HPl Occurs on Demand.* and *PZR PORY Rescats on Demand
- were successful in all sequences hsted. Therefore, these headings do not appear in this table. There were sequences other than those melude in the table residual for which not all of the branches were successful, but they did not survive the frequency screening. These sequences are included in the groups.
- Because of the couphag factor imposed on the throttling of the AFW, given the failure to isolate the AFW thi is, no credit is given for throttling the AFW if the operator fails to isolate the AFW.
s sequence has a frequency of 0.0; that
'Foraamajor have small steam-hne impact on the results.break downstream of the MSivs. no credrt was taken for closure of MSIVs; this was used as a boundin NA = not apphcable.
' Sequence were blowing down.is no longer apphcable and does not appear on event tree, since operator would not be called upon to isolate All
/ steam generators blow dows for 30 minutes; at this time the operator closes the MStYs, but one, two, or a!! three of them fail
,f em
- HBR-3.86 4 = w
, . y Ed AU E a a y o Sy = 2 u
$E .?. 5. 5 S *$ b $ {m h .$
s.
o s
e !! os o e Es *e a s$ u=s e 65 g > e s *
~. 9
% d n 2nc & Uc eu n o
Cg k% e Mb es g c *
$ YE .h O k% hh o
.o 5 0 h *o g c.
SG n
00 5e k ac u o dy
- ~ 8.S *? E5 kb %2 CE
..k EW -
G. { Q c E
$c E=
}Q }G 5 ~ % E } @* } < 8 } *.E }O o }.2 g 2-} 8}c.My} .g Q}g~ Og 7.3=10" CCC.
7.3=10" CCC.
- 7. 3=1C ' CCC
' FE S ( g,3=gg"
- 7. i = 1 C CCC'.
' .Y.5 Z. . S. 9=10 "
' 1.5 10 CCC 0001
.3E S.}. . 1.5=10" Coot
' 1.2=10" CCC' E.E 5,4 C.C
' 1. 3 = 10 001;
> '. pts 5..l.5=10'*
st .?6 5 6.. C.C Do*H ~
0001
. $C5 ~i . 7. 7 = 10 '
- 5. 5 = 10 001:-
I 5.5=10" CClf
' 5. 5= 10 Col' 1 i
' . . .".5 8. . 6. 6 1C
. ..".S t. 5. F = l C '
. 9 f *. 3.1 = 10 ' cos"?
..E.5 ? 9. 5= 1C
- i 7.1=10 CGT cool i
. . . . 8.Ci l E. 7. 5 = 10 i
. ES.!I 1. 6 = 10 0 008 !
7.3=10" CGT '
I 7. 3 = 10 CCY 7.3=1C" CCY.
' . 9!.f.. S. 6 = 10
AL L son 7.1=10" 001; c6csr ' ets r5
- " " - S. 9= l C' *
' 1. 5 = 10 ' Cor 8037 22.4!.' 1.5=1C" 0033 fu@
. etaw ,
, cC1:
- 5. 5 = 10,
- coWH
' I
- 5. 5 = lc., CC1' j 1 5.5=1C CC1:
l i 1
' . ET5 '7 6. 7 = 10'*
..If 5..';7. 5. 6 = 1 C"
. :G.9. 3.1= 10 00 6 7.1=1C" CC5~ 003 7 i
. 4 578 7.5 1C"
...RFs 21 1,6=1C U.s2.3 C.C
, . 3 25 1.2=lC" 2.2=10' 016 Cool i
...Ws7h. 2.2=1C" oco2 i
. 285.tf 2. 2= lG ' 0005 e sc, 0"I'
. ns t? 2. 2= 10
e teos ers 77
- " 3. a = 10'" ON)
'.'.rrsi5 1. 7 = i C ooi7
. Pes .21 2. 2= l 0'
- 0o08
' 2. 2= 10 C22; oo37 i .s i
..Pe5 P. 2.2=10" cosa i oo31 er.5 .ti 2. 2 = i C
I .AMil ggg . . e. r. s. . 3 E. oM7' 3
- 2. 2= 10.
cow H .* .. EE S. II 3. 7= 1C , 0047 O's J+ 2. 2 = 1 C
- 0057 t , , . . Pf 5 35 2.7=l0"' t Figure 3.9. Event tree for small steam-line break at full power.
- -=
-(continued on next page, with overlap)
- - ~ ~ ~
( ., liBRT3W7
../
/ ... -
- 2. 2= 10 016'. Cool i
..F5 M. 2.2=1C* 0002 1
. .M.25 2. 2= 10 ' 0005 isG i
,,qs 9 2.2=lC' ~
000l Now*w' . . 205 77 3. s= 1c Oty
. . FIS. 28 1.1 = l C Cos7
, . .@..E . 2. 2= l6" 00o)
- 2. 2= l 6' C22, 0057 i
. .PC S. 33, 2.2 16' 0036
. . .r. e.s. . .u. . . . . . . = i n,', oo31 g 9.g .
6 Low CO M
.. N ..N 2.2=10 0037
, 26,5. II 1. 7 = 1 C ' ~.co45
..$.5. I . 2. 2= I 0 " oo37
.. . Rf 7. 55 2.7 10"'
2.1=10' C27 5
2.1 a 16' C23r
' 2.1=16' 025.
' .E(> 3.b . 2. 3 = 16
...ee 5.7 7 2.1 = 1 c
ML 56'5
. 2r$..? 9 1. 5= 3 6' 0277 15Dr 1 M**' DCM 3 ,3 = l c 02g:
'js[*i
[ i
. .RE.S 37 1. 5= 1C
. . 2CS 4o . 1.C=lC'
.. te.5 ,41 3, g = g g " 0287
..E S N 2. i a l C 0271
. . * %.43 s. s= li*
FES N. 7. 2=16" 1.1=16' 03S:
i
.. ..RES 4E 1.1= 10
g g., ,
i
. ..E.f.5 44 g.5=3='
. - w' g gpg , '
. . D. i7 stow powes . 2. 7=lC ,
- 0542.
MitTo
" *5 r
. . . ...N i.$. 3. in l6' s i
. .- . ...ersU 1. saic ' osaz
.. . . .e.E 5. so. i.3=ic i
. . ..ers.p.l.. 1.1 = i c os<t 3.1 = 10 ' C 1 S'.
i
..R5 57, 3. i = 16'
...*f$.34. 3.1 = 1C '
No sa's ,
..ers.s4 9=ic" oggy y,*[g . . ... ..EES.Sf 5.1 16' ;
. . . . . . . ..rcs.IL 2.1 = l c -
..rcs .s1 3. i min
- e4rs
- 3. l = 10 ' 052.
h 504 i '
. PF5 SS 3.p.16' i i
fast To '
~ 205 51 3 t =
- 1% 1
. .Ef 5 M j .,g=l6' l6' oggg'
- i*g,g' -
. ..'f 5. .'!. 5. 3 = 10 '
{
I
. . .ees 'e. 2.1=in" i
. . .. . 93 osti
+
..W.T 9 .h.7.3.1=i6'
. 3 = 10 '
- . . .. .fr5.t.?. 1.s=iC
. . . . . erM4. i . 9=ic - os2 ,
Figure 3.9. (Continued) 2
.f .a B
W . f .
I
HBR-3.88 3.5.6. Small-Break LOCA at Full Power 1
The small-break LOCA includes pressurizer PORY and SRV single failures, pump seal failures and small pipe breaks. The most probable failure is the PORY failure, but there is a very high probability of isolating the PORV 3 early in the transient.
The initiating frequency for this event at full power is based on a fro-quency of 8.9 x 10-3/yr for small-break LOCAs under all operating condi- :
r, tions times a factor of 0.91 to account for the fraction of full-power (?
9-operations. The resulting initiating frequency is 8.1 x 10-3/yr, which,
.'l /g when combined with the branch probabilities presented in Table 3.12, lead ,
6*
- c. .
to the event tree shown in Figure 3.10. Thirty-one sequences out of a I i total 6,938 sequences remained for further analysis after the screening 3
( process.* These are shown in Table 3.13. The frequency associated with h'
ff .p the residual group is 9.4 x 10-7/yr. J'
- j k
l 3.5.7. Medium-Break LOCA at Full Power t
The initiating frequency for a medium-break LOCA at full power is 9.8 x 10 ~4/yr, based on an overall estimate for a medium-break LOCA of 1.0 x 10-3/yr and 98.1% operation at full power. This event includes breaks equivalent to 2 or 2.5-in.2 lines which cannot be isolated. The branch i .
l headings and ,9tobabilities are shown in Table 3.12, and the resulting event p f*
tree is shown in Figure 3.11. Fourteen sequences out of a total of 6,824 p ',
j sequences had frequencies of J10-7/yr and 12 were retained for thermal-( hydraulle and fracture-mechanics analyses, as shown in Table 3.13. The l
l .
i r
.!!.:':Ptd'.:::MK:.:'.:.!!.;*!::'i:::i:!':.'i:!:f:f.'s!;:.'n';
...m.
HBR-3.89 l
t Table 3.12. Branch probabilities for nasall. and medium-break LOCAs a( full poww' Branch Probabsiny*
[ Small. Break Medium. Break Tree Heading Branch LOCA LOCA
- , . _ . . ~ .
Turtune trips (!)1'arbine inpa on seina. nit 099996 os demand. (2) Turbine fails to inp. 4 X 10*8 STM PORVs (1) All three STM PORVs close. 0 97981 l close on (2) One STM PORY fails to class. I8 x 10*8 1.7 x 10-s l W e (3)Too STM PORVs fad to close.
(4) Thres STM PORVs fail to close. 4 9 x 10**
1 l SDvs close (t) AH five SDYs class. 0 99768
' en demand. (2) One SDY fails to class. I 6 x 10*8 (3) Tee SDVs fail to close. 3 0 X 10**
, (4) Thrw or amore SDVs fast le close. 4.2 X 10**
Si signal (1) Si signal is generated. 0.99997 generated (2) Si signal is not generated. $ X 10*8 es demand.
hlFW runs back if Si signal is seurat4 MFW and isolates knes run back and suolate; on demand. (l) All hnes run back and MFW is isolated 09999997 (2) One has overfeeds! 23 x 10*'
(3) Two knes overfeed! l.$ x 10*'
(4) Three knes overfeed' l.0 x 10*
If SI signal is not generated, run back only occurs.
0 9999940
' (1) Alllines run back.#
(2) One has overfeeds. S.3 x 10**8 (3) Tee haes overfeed.# $1.40 xX10*
10*8 (4) Thrw knes overfeed.#
HPI occurs if $1 signalis generated, e
on demand. (1) HPl occurs. 0 99939 I (2) HPI fads to occur. 4.1 X 10**
If SI signalis not generstd
, (1) Operator manually starts HPL 0 99 i (2) Operator fails to start HPl. I x 10-3 SGs blow if one or more SDvs fail, doen. (1) Three SGs blos dome. 10 if thru or niore $DVs feel, (1) No SGs blos done. 099051 (2) One 50 blows doen. 46 x 10*8 (1)Two SGs bio = doen. 2.0 X 10*8 (4) All three SGs blow does. 3.3 x 10**
If one, too, er three $TM PORVs fail, then. respectreely, (19 One 50 blows done. 1.0 (1) Tee SGs blow dose. 1.0 (1) All thru SGs blos doen. 1.0 if MSIV closure signalis not generated, (1) All three SGs blos doen. 1.0 AFW ectuates (t) AFW ectuates. 0 999 on demand. (2) AFW does not actate. I x 10*8 AFWnow (1) AFW is notamatically controlled automatically at nominal rate. 09923 controlled. (2) Flow sentrol failure leads to elinormally high AFW flow rete 7.5 x 60*8 (overfeedak OA: AFW (1) AFW holation omirs. 0 9985 esclated to (2) AFW isolation fails to occur. 1.7 x 10*8 a
low.pressere 50.
6 e
es a 9 er
15 9
BBR-3.90 t
Table 3.12 (Cont'd)
Dranch Probabihip*
Sma'! Bruk Medium-treat g irve ttcad.no Branch LOCA LOCA OA: AFW (I) AFW isolation occurs. 09933 inulated te (2) AFW isolation fails to occur. 1.7 x 10*8 low. pressure -
50.
Accumulators (1) Accumulators desharge when discharge. requwed. 0.99999 (2) Aaumulators fail to discharge. 1 x 10*8 OA Break set (1) Break nos isolatable isolated.' or operator fails to inelate break. 0 9610 1.0 (2) Operator isolates break. 3.9 x 10*8 1.0 Charging flow (l) Charging flow ruas buk as runs back required (repressurisatsoa es demand.' hmatedh 0.99 NAf (2) Charging flow fails to run back (repressurueton met limited). I X 10-3 yr OA: AFW If operator isolates AFW, e throttled. (1) Operator throttles AFW flow. 0.99 (2) Operator fails to throttle Af W flow. 1 X 10*8
, If operator fails to teclate AFW, (1) Operator fails to throttle AFW flow I.0
. (2) Operator throttles AFW flow. 0.0 LPI occurs If Si signal is pnereied, en demand. (Il LPI accurs as required. 0 99973 (2) LPI fads to eccur. 2.5 X 10**
If 51 signalis nos generated, (1)Oprator manually starts LPL 0 99 (2) Operator fans to start LPl. I X 10*8 ft 58 signalis not ynerated sad if operator fails to start HPl.
(1) Operstar fails to start LPI IO (2) Operster manually starts LPl. 00
' Acronyms used la this lable ha the order of their appearance) are: STM PORY = steam power eparated rehef valve. SDY = steam pump valve, $1 = safety inrection, MFW =
main feedesser HPl = bigh-presse e injection, bG = steam generator AFW = ousihary i feedester, OA = operator actice. LPI = low. pressure injecten. and MFIV = main feed.
water anointon valve.
'Probabilettee centered between the Iwe solumns apply to both break siset
' includes failure of MFW regulating valves to run back, fasture of one er both MFW pumps le trip en high level in any 50, and fadere of MFive to close en SI segnal d lncludes fadure of MFW regulatang selves to run back, and fadere of MFW pumps to tr6p en
(
high level la any 50.
'These headiese apply only to emen-break LOCAs and not te misdies-breet LOCAa.
/NA = ese apphcable.
et we
- 9
Ru o E 1IBR-3.91l.
]
~ '
9 e s "v ? q .12 e !? l j 2 s illilli!!il$;lIl:siO!!ibbi!!!]/l[
Elf $k Ej 5 j Tg . O. ,g O 8, =
f
- 7. ',= 10 , CC
- 7. 5= 10' GC '2
', 3.0= 10' OC '3 x
3.0= 10' CC 't 3.C=10*OC'S e 6. ..M.l.. 3. i = 10 *
's',, ,
- 5. A=10
- CC ;7 i
G.7=10*00'S
- 2. 3 = 10
- CC :1 **e 1
.tt'i ..'t 2.3=10'
. .. .t E S.5.. 2.1=10*
- 7. G= 10 ' 00 3 +
I 3. =10* CC 4 eaa 1 si sev.
'. . . . . . ..Fil'l. 3.:=10*
- 4. 6= 10. OC 6 A ,
../DT. 1.t=10
- v. i s. '
. ... RIM. 4. G= 10
L'f' , "
l . S = 10* OC 'O
.7 6'l 1.3=10*
[ . . . .. .. AC5t. 4.c= 10
.A 4 1. 3.6=10*
. . . . . . . . ..An.&. 4.S=10* ** ' 6
. . ... . . .. . .. .Eill 2.2=10*
- 2. 2 = 10* 01 3 a'6 0.'f ' . .RSIA 2.2=10* .
'*** ' i' ...
. .. . . . ..M 13. 9. s =107
........,....At%Ii 1.G=10*
- i. . . . . . . . . . . . ...fD 17. 2.4=10"' **
.... . . . . . . . . . .. . . . .. RO lb. 2.1 = 10* as6
=- .. . . .. . . . . . . . . . . . . . . . . . .
. .. . .. ..m t1 i . 4 = iO:
1.2=10 ,03 15 I 1.2=10* 03 4 8
o"- 8' i ,
4.0=10* 03 ;7
'"*' 1
..... R ts .19.
. i ses > , 4. 9 = 10.'
- 4. a. > . .. . ... ... Ar*, .11 4. ")= 10 . .
l.
..W i . .. . . . . . .. . .. A E*+ A9. 9.5=10'
. . . . . . . . . . . . . . . . . . . . . . . . . . . ...#5.21. l.3=10* 0**s .
.. .... .. . . . . .... ......... . .... ... .. ....RD M 7.7=10* **'6[
.. . . . . . . . . . . . . . . .. ..M.9. 3. s = 10"' i l.. . . . . . . . . . . . .... ... . . . . .. ... ..REi A'I. 3. S = 10"' **'6
. . . . g 2.2=10* 0" :7 6 8'l 4'* ' ' . . .M511 2. 3=10* l Di '
.. . ... . ..RCS 4 Q.2=10* 8 8 *
! 'U. , < : . . . . . . . . .. . . . . . . . ......AttYl.l.S=10*
- m. .
.... ... .. .. ... .. ... ... . . .... 4 s u 2.4=iO' .m i
.R 4.M. 1.5=10* o.'c .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. Ars.M. s.7 =10'" l
.. .. . . . .. .. . . . . . . . . . . . . . . .. . . . . . . . . .. RC5 .31. 7. s = t o'" *a
- 3. =10* 01 '3
'. .. M4 34 3.1 10*
e s. 1.3 10* 09 1 e e* =i
7* a 1 >
t .... A D)J. 1. 3= 10*
s e=, 1 l.. .... .. .. ...M".J'l 1. J 10* *
)#* ' >
... . . . . . . . . . . . .. . . . . .. . . ... . . . . . W . 71 2. 's = 10*
"7' . .. . . . . . . . . . . . . . . .. .. . I.II" . D 3. 3* lU "
. . . . . ...............?..... . ...S O . M 3.0=10*4
. . . . . . . . . . . . . . . . . . ... .pts...31 . '
- 2.C=iO ocit
...Rb .37 0.4=10*
.......e......,.........
j ,,
Figure 3.10. Event tree for small-break LOCA at full power.
" -= -
(continued on next page, willi overlap)
\n-
. , - BBR-3.92
/ ., *
- 3. a =10* 09 3
. f15. 31 3.e=10*
- t ,, , '
- 1. 3 = 10 ' 01 1 * *= 9
. .. AES. 27 1. 3=10*
id '"', '
6
..ltC. 34. 1. 3= 10'
.. o~ ;
, .. AD 35. 2. ',= 10'
. . .lE5.3h 3.3=10 edi
.I .
. . 66. 37 3.0=10'
. 8L.%.. 3I 2.0=to' **'&
. .,REs.37 0.1=10**
.. AES..sjo. 10. 0= 10'" **
l .1 = 10" 20 2 I
1.i=10* 2C P.
- 5. 5 = 10 ' 20 1 i
'. .fM..Hl. 5.6 10'
,,_ .s . ..E..HA 5.Ra 10*
p y, ,
' 1.0=10* 2C S c i.. ,
...llh..W M .% 1.2=10 l.0=10]
' 1.1 = 10 20 :1 2aea i
...R.L5.45 1.i=10
. AEh. % 5. 7 = 10
UU. . 855 47 S. )=10' co't
. PJ.S..'il 1. : = 10 "
.. AES..M 1.1 = 10 ** .
- 2. 2= 10' 23 M o2*f mai ss, i
.. (Ei . 50 2.2=10*
3:~....,
i si,= ' ..RC5.. 51. 9.c=10
- r. ., '
.115. 5 4 1. 7=10
- r. . # '* #
. . . AE1.55 2. 3= t0'"
+; '*
. . Rth. 5'l 1.1= 10"'
. ..Cfl. 55 6. 9 10'"- ;
- . . .. ... . 05 5. 5 6 7. 0 = 10'" ***' -
. . -- . . . ..W5..Q l . 0= 10 4 l.3=10# 33 'O l 1.3=10 33 il s, c , , ,
5.2=10* 33 2
, 75f- J '
EES. 58 5.3 10" s ,
i.. . .ID.Sl. 5. 3=10' -
}
L i ..
..EE .. 60. 1, c = 10 '
.. RE5.. 6.l. 1.1 = 10' "** !'
..R5.63 S.1=10* **86
! . . . . R t. 6 1. 3.a=iO"' I i . .lES. 6 4. 1, 3 = 10"' **
, , , . ..F15 f.5. 3.2=10
- 3. 7 = 10 ' 15 :S a8*C
..K5.. .l f. 3. 'i= 10 '
1.5=10 % 'O osu1, e~' - i I
- ..REL.47 1. 5 = i O' y",, ,
. . ..NES.66 1.5=10'
~
- . ..REE 61. 3.0=iO' -
i
..RI,5. 70. 1.0=10 ' oter
. . . ...RD.."II. 2.1=10* **
. . . . . . ..RD..~ll 1.1 = 10 " f
..f,G.75 1.2=10"' **86
. . . . . . . . . . . fFa.74 9.2=10' ~
. 3.0= 10 ' 'A 'G
' n,. u, ,
...EE5.75 3. i = 10' d** , ' .
. . ..EU..7b 1.2=10' M* . ,
~i 8
. .. . .80.77. 2.1=10' *
[,4,,,
. . - . . . . . ...c,... ...LIS .7 3.2=10
- senj'
. . . .. ALV1 3.0=10*
. ..RIS 10 2. 0 = 10'" *=1&
. . . .. AS . f l. O . i = 10'"
.. c::, 8,2, 0. 7 = 10"' aoec Figure 3.10. (Continued) _
Table 3.13. Sequences to be analysed fee sasall- and medium-break MFW Runs STM PORVs Back and AFW Sequence Turke Trips Close OA: AFW Charging SDvs Close telates llPI Occurs SGs Automatically Isolates to Na* .on Demand on Demand OA: Break Flow OA: AFW Frequency on Demand on Demand ca Demand 91ow Down Controlled 11 SG Not Isolated' Runs Back' (yr ~ ')
Throttled SmaE-Break IJDCA s 1.1(0001) Trips All close AR close Rees back flPI
% No SGs Automatically NA# Fails to Runs back and isolates occurs Throttles 7.5E-3 W edows controlled isolate break as required prior to SG bish-level alarm 8.2 (0002) Trips AR close All close IIPI
[ Rees back and isolates occurs No SGs Wu dows Automaticany controlled NA Fails to isolate break Runs back as required Fails to throttle 7.5E-5 1.3 (0007) Trips AR close Au close Runs back llPI No SGs Overfeeds NA Fails to and isolates occurs Ww down Rana back hrottles 3.6E-5 isolated break as required prior to SG bigh-level alarm 1.4 (0000) Trips An close All close Rams back HPt NoSGs Overfeeds NA Fails to Runs back and isolates occurs Fails to 5.7E-7 blow down isolate break as required throttle 1.5(0305) Trips An close One fails Rens back IIPI All SGs Automatically NA Fails to Runs back to close and isolates occurs W wdown controlled Throttles I.6E-5 isolate break as required prior to SG high-level alarm I.6 (0627) Trips All close Two fait Runs back HPl An SGs Automatically NA Fails to Runs back to close and isolates occurs Throttles 2.2E-6 kw down controlled s isolate break as required prior to SG high-level g' alarm I.7(0949)' (lacluded in Sequence 1.8) f t
Trips
.o l.8(0949) AH close > Three fail Runs back HPI AR SGs MD to class AutomaticeDy NA Fails to Runs back Throttles 3.lE-6 8" and isolates occurs blow down controlled isolate break
' as required prior to SG for 30 min high-level alarm 5 i
I.9 (2012) Trips One fails AD close Runs back HPI One SG Automaticany NA Fails to Rens back to close and isolates acters Throttles 1.4E-4 blows down controlled isolate break as required prior to SG high level alarm 1.10 (20l3) Trips One fails Au close Rees back HPt One SG Automatically NA Fails to Runs back Fails to to close and isolates occurs Wws down controlled 1.4E-6 isolate break as required throttle 3.1I(2018) Trips One fails Au close Runs back HPl OneSG to close Overfeeds NA Fails to Rens back Throttles 1.0E-6 and isolates occurs blows down isolate break as required prior to SG high-level e alarm
- 1.12 (3300) Trips Two fail Au close Rses back HPI Two SGs Automatically NA Faits to Rens back to close .and isolates occurs W edown controlled Thrott): 1.3E-3 isolate break as required prior to SG .
high-level 7 alarm 1.t 3 (0001) (Included in Sequence I.If - -^-
I.14 (0002) (Included in Sequence I.2f 1.15 (0007) (Included in Sequence 8.37 I.16(0305) (Included in Sequence 1.57 1.17 (0001) (lacluded in Sequence I.If 1.18(0001) (Included _ in Sequence 1.If
i
% -. . ,, 1 el l.19 (0016) Trips AR close AH class Runs back Fails to No SGs AutomaticaDy NA Fails to Runs back g
and isolases occur Throttles $.0E-6
, blow down controlled isolate break as required prior to SG high-level alarm I.20 (0306) Trips Au close Au class Runs back flPI All SGs Automaticauy NA Fails to Rans back and isolates occurs Fails to 1.2E-7 blow down controlled isolate break as required throttle 1.21 (3308) Trips Two fail AB close Runs back IIPI Two SGs Automatically NA Fails to to close and isolates occurs blow down controlled Rans back Fails to I.3E-7
. isolate break as required throttle 1.22 (587p) Fadsto AN close AG close Runs back llPI No SGs AutomaticaDy NA Fails to e trip and isolates occurs Runs back Throttles 3.0E- 7 blow down controlled isolate break as required prmt to 50 bigh.ievel alarm II.I (0003) Trips Au close AR close . Runs back IIPI NoSGs AutomaticaDy NA Isolates Runs back Throttles 3.0E-4 and isolates occurs blow down coa. rolled break 9
- as required prior to SG high. level alarm 11.2 (0005) Trips AG class AU close Runs back !!PI No SGs Automaticauy NA Isolates Fails to and isolates oscurs blow dows controlled Throttles 3.0E-6 4
break rua back prmr to SG
, bigh. level @
p, alarm I II.3 (0003) (laciuded im Sequence II.If ta 11.4 (0005) (included in Sequence 18.27 to II.5 (0004) Trips AH close AR close Runs back IIPI No SGs AutomaticaDy NA Isolates Runs back and isolates occurs blow does controued Fails to 3.0E-6 break as sequired throttle II.6 (0020) Trips AR close AR class F.uas back Fails to No SGs 1 AutomaticaDy NA isolates Russ back Throttles and isolates occurs 1.8 E-7 blow down controlled break as isquired prior to SG bish-level alarm II.7 (0307) Trips Au class One fails Runs back itPI Au SGs 4
to close AutomaticaHy NA Isolates Runs back Brottles 7.2E-7 and isolates occurs blow down controned break as required
' prior to SG bish-level alarm 11.3(20l4) Trips One fails Au close Rans back IIPI One SG to close Automaticauy NA Isolates Runs back Throttles 5.5E-6 and isolates occurs blows down controlled break as required pnar to SG bish. level tiarm 11.9 (3302) Tnps Two fe:Is Au close R uns l'ack Two SGs lirl Automaticau) NA Isolates Runs back Throttles 5.2E-7
' to close and iscJates occurs blow down epatrolled break as requued pnar to SG bish. level
. alarm II.10 Residual Group 9.4E-7
Teble 3,13 (Cont'd) blFW Runs STM PORVs Back and AFW OA: AFW Sequence Terbine Trips Charging
.Che SDYs Che Isulates HPI Occurs SGs Automatically Isolates to OA: Break Flow Ned on Demand on Demand OA: AFW Frequency on Demand on Demand on Demand Blow Down Controlled LP SG Not isolated' Rune Back' Throttled (yr")
Medium-Break LOCA 2.1 (0001) Trips All che AN close Runs back HPI No SGs Automatically NA and isolates occurs
- - Throttles 9.4E-4 blow does controlled prior to SG
' high-level alare 2.2 (0003) Trips Arche All che Runs back HPI No SGs Automatically NA - - Fasis to 9.5E-6 and isolates occurs blow down controlled throttle 2.3 (0000 Trips All close All class Runs back HPI No SGs Overfeeds NA - - Throttles 7.lE-6 and isolates occurs blow down prior to SG
' high-level alarm 2.4 (Res 4) Trips AH close AR close Runs back HPI No SGs Overfeeds NA.
and isolates occurs
- - Fails to 7.2E-8 blow down throttle
. 2.5 (0325) Trips Au close One fails Runs back HPI
- All SGs Automatically NA - - Throttles 1.5E-6 to close and isolases occurs blow down controned prior to SG high-level alarm 2 6 (0665) Trips AR close Two fail Runs back HPI AB SGs Automatically NA - - Thmetles 2.8E-7 to skne and isolates occurs blow down controlled prior to SG high-level
' alarm 2.7 (1009) (lacloded in Sequence 2.8) 2.8 (1009) Trips All cloes > Three fail Rams back IIPI All SGs AutomaticaUy NA - - Throttles 3.9E-7 Ed to close and isolates occurs blow down controlled
- prmr to SG for 30 min high-level g
alarm 2.9 (1853) Trips AD close AR close Runs back ifPI One SG AutomaticaBy NA - -
Throttles I.7E-5 and isolates occurs blows down controlled prior to SG high-level starm 110 (1856) Trips AR close A5 clone Russ back HPI One SG AutomaticaDy NA and isolates occurs
- - Fails to I.7E-7 blows does controlled throttle 2.18 (3229) Trips AM close All close Runs back HPI Two SGs Automatica!!y NA and isolates occurs
- - Throttles
- 1.6E-6 blow does controned pnor to 50 high-level alarm 2.12 (4605) Trips Arche A5 close Rmas back HPI All SGs Automaticany NA - - Throttles 4.7E-7 and isolates occurs blow down controlled prior to SG ,
high-level alarm 2.33(0021) Tnps AR close All close Runs back Fails to No SGs Autornetically NA - -
Throttles 6.2E-7 and isolates occur blow down contround prior to SG high-level e alarm
- 2.14 Residual Group 2.1 E - 7
- The branches entitled *SI Signal Generated on Demand * *AFW Actuates on Demand,'
- Accumulators Discharge and *LPI Occurs on Demand
- were successful in all sequences listed. Therefore, these headings Jo not appar en this table. There were other sequences for which act all of the branches were successful, but they dsd not survive the frequency screening. These sequences are included en the resedeal groupt
'During the analysis of sequences by Idaho National F.ngineering Laboratory (INEL), the LOCAs in which the break could not be isolated =cre identified as Sequence Series ll. The enginal sequence numbers are maintasned here for easy cross reference.
'These headings apply only so sman-break LOCAs and not to medium-break LOCAL NA = not appiscable.
'These sequenses include the failure of ens feedwater regulating volve which suhncquently was found to have sure impact because of a feedwater pump trip.
HBR-3.96 i o .A 'tf au e W
a V g.a us Eo* 5
~ - .:
2 * ~y 9 a c # e e i< .8 e .iyi Erir}lkEir lEul e g ' u.;r j , 2 ] $ , b u l
o, & lj' r5 ul.b.
k : i so f .?e !j f '; *. ,j hg4e I c; E
! [! gls.l.
.3
=- E- u u
=
f
- lg 8 \
- 8ll g 8' l H~ cj l
- 8li".@Sj}~g[J .
8/Ts.s.Cjfga. a j jx ,y j f8Qgg :
9.1=iC' CC: .
2.1=1C CC:2 4008
.452 9.5 1C' No u 7. t alC' CC:3
, S'own amW ,
' ' . . .gs 3, g,g 3;" oco9
-. ...ET5 4. 7. 2= 1C'
. ...kT 5 7. 2= 10
Att i
' 9.6=lC CC; ' Ocol
' , Ff.1/= 2.1= 1C 0001 SDj, .s ..
. .J.c5.7. 9. 6= 10
5.7=1C" CC:: '
' . T2s #. 1.1= 1C'* 0011 ye g3 ,
' . ..f-T 1. 5.3=10" E'c4 Do*** . . . U 5. 5.SalC"'
. .U.5 81 1.1=10'
.. . . .. ...ff 8.!Z 5.6=1C"* 0021
. . .8C383. 2.7=10'*
.3.73.!.4 2.9=10' 0028 1.5=10' C3: .
l I
' ...Res.15 3. 5 = 1 C 0J21 Att SA
. . ...EF3 8'. 1.5 1C' m
c-e n u , 'em cowW ..M 5.! 2 1. 5= 10'"
- hv3 Iwy . .
- .- res is. 1.2i.10" ctose rAcu- 0311 cari . .. . ..05 1 1.5=10' 8
. . . ..?f3 2.?. 9.1= l C co28 f . .
..tts.g ,,3.ic"'
. ~ - .. ..
..wstt 4, s. g c"" oozy 2.S=lC C6f ;
1 '..us.2s, 7,3.gc"' oggg att go
' .. W . 2.9=1C*
..tr3 6 2, g.j c
I how poww pD,' . .. . . .. " 5.rt. 2.2=lC*
O f=?S cmr: ,
. ..Pf3 77 2.9= 1C"'
.. e s ts 3,s.gg
- pegg 1
...tes.q. 8.1 = l C'" l
-- . . . .. . . .E?S.?). 8. 7= l C"' Call l #
I 3.9 10 C: :
l
' ' Ci il. 9. $= 1 C'" iset tt: 32 i '
WW *~
- .m u.1 C. i:C=ul*'-
4,
.n::4 3.C=ic'
'** To : ,
' . ... . .. . ft 5 "3 1.C=lC'* I039
...tts Je 3,7=lC"
(
,,.??$ 51 2. C= l C'* 002l
.. .. . ..rfs l' !. =10"' !
. . . . ..?.fS M. 1. 2= 1 C'" 00Z1 l
l Figure 3.11. Event tree for medluni-break LOCA at full power, 1
f (continued on next page, with overlap) l j
l\
- o i ,, .. e HBR-3.97 3.1 10" 4C: '
. ' F:s fl., 3. golf" seet I" tt::t 1. C= l C
' r"Y.YM . Ef 8J. 1. Ca l *
y3gevs , r - #" i.. . 8"234 3.C=1C' sas To .
. . . ... . . Pts 4 1.C=1C'# #081
. . . . . . . . ..tts Je= 3. 7= l C
. ... Mi 57 2. C= 10 002)
I
. . . ..P*5 I8 1.1=1C
. . . . .. ..ff 5 J.I. 1. 2=1 C'" 0c11 1.7=1C' 15: -
' Rt3 M. 4. 3 1C' '1853 1.7=lf' 13'_;
' TIL 4l. 1. t = l C'" 13 51.
our w , . W.I 1. 7 = l C*
' s6.*2 0 0* ** 1.1=1C' l $E 18f3 s avum , 1
' tr$ 4
- 3. 3 = l C'" ggsJ mv '
FAitt, fg * . .
esose g
- 74gl .1= 1.
1 I.
C.'.a w
' i
. . . . .. W4 1.8 16' 3837
. ft:37 1.1=1C' 002l
. . ..PfS+$ 5.C=1C"'
. . . . es 41, 5. 3=lC"' ooti .
.. . . . . .. . . ..ns s 1.1 =le*
l 1.6 IC* 30:3
'950 4 .1. l (* 3111 l gwe gv3 "
i., ,.t:sy2
- 1. 5 1 C" tn.ow oowre . .. 9 83 1. 6= l f" a straw, ' '
j i
. . . . . .MII4 l . 2 = l C
mvi ' '. *
. . . . ..sT fi 1. 7 = l C 377f I
[NEi !
' I
. . . .. .. . . . . #U f~~ 1. C= lf' 'Ca2l
. . .. ". . . . . . . .k.O S?. 1. 7 = 10"'
. . .. . ... C CS 5. Calc'" 0011
. . . . .. .. . . ....M357 3.9=lC'
- s. 7.lc' <sa
'Ffs 'a 1. 0= 1(' 4 c5"
' ft; Ll
- 1. 3. l f' au t vs 1 . .
! , ' 6 Low Dov"e <
. EI 'I 1. S
- 10"'
Itsreg '
. . .. . ..M U 1. 9= 1 C
W' 4 .
. . . . ... . E% 9 4.$=1C'# 4.33 cNss .' I
. . . . . .. . .48' 2.9=1C"' 0c2l
. . . .. . . . . . . . . . 8ff 6'a 1.4=lC"' I
.. . El l*7. 1. 4 = 10 8021
. .. . . . . . . . . .. .. . Mt 41 1. 4 =lC'
. . . . . . . .. ..ffi.'l 3.1=lC Figure 3.11. (Continued)
S A* *U e
ph O= t
BBR-3.98 frequency associated with the residual group is 2.1 x 10-7/yr.
, 3.5.8. Small-Break LOCA at Not 0% Power An initiating frequency of 8.01 x 10-4/yr was used for this event based on the overall estimate for a small-break LOCA of 8.9 x 10~3/yr and a factor g;h i,
, of 0.09 to account for those occurrences at hot 0% power. D e branch head- f' . y ings and probabilities for the event are shown in Table 3.14, and the
/I
- p.
resulting event tree is shown in Figure 3.12. Out of the nine sequences I with frequencies of },10-7/yr (out of a total of 158 sequences), five g-sequences were identified for further analysis. These are shown in I-Table 3.15. He frequency associated with the residual group is 1.1 x ,,. l
- 10~7/yr.
l 3.5.9. Medium-Break thCA at Hot 0% Power ne initiating frequency used for a medium-break LOCA at hot 0% power was 1.9 x 10-5/yr, based on 1.9% operation at hot 0% power. De branch head-Angs and probabilities for the event are presented in Table 3.14, and the G 1.g resulting event tree is shown in Figure 3.13. Three sequences out of a f
total of 124 sequences survived the screening criterion of 10~7/yr. Two of these were selected for thermal-hydraulle and fracture-mechanics analyses as shown in Table 3.15. The residual group frequency totals 6.5 a 10~9/yr.
3.5.10. Tube Rupture Event tree branches for a steam generator tube rupture initiating event
.i .. - -
HBR-3e99 Table 3.14. Branch probabilities for samall- and medium break LOCAs at hot 0% power
- Branch Probabdety' Small Bresh Mediene Brook Tree Heading Stanch LOCA LOCA k Si segnal (1) 51 signal se pnerated. 0.99997
[ generated (2) $1 signal is not generated. 3 X 10*8 en demand, f M FW isolmed (1) Ne has overfeeds. 0 999,9 en demand. (2) One has everfeeds.' 9 0 X 10*0 (3) Tee haes everfeed.' 8 4 X 10*I (4) All three knes overfeed' 8.8 X 10~ 8 HPl occurs if $1 signalis generosed, en demand. (1) HPl occura. 099919 (2) HPl fals to occur, 4 t X 10**
If $1 signalis not generated, (1) Operater manually starts HPL 0 99 (2) Operster fede le start HPL l X 10*8 AFW actesses (t) AFW actemes 0999 en demand. (2) AFW does nos actuate. IX10*8 AFWnew (1) AFW flow is automatscally een.
setematwelly trelled as nominal rate. 0.9923 controlled. (2) Fke sentral fadere leads to abnormally high AFW flow rue ?.S X 10*8 (overfeeds).
4 Assumulators (l) Accumulators discharp whee discharge. required. 0 99999 (2) Accumulators faal to dia6harge. I X 10*8 OA Dryn net (1) Bruk not 6eoleieblo enolated. er operator faele le isoiste breek. 09410 10 (2) Opermer isolates break. 3 9 X 10*I 1.0 Charging fles (1) Charging fbe runs back u tune bash reevised (repressartaaties on demand.# limesed k 0 99 NA (2) Charging flow fade le rue bath (repreestel8ation not bmped). 1 X 10*I NA OA: AFW If operater isolates AFW, throttled (t)Orwester throttles AFW Row 0.99 (2) Operstar fade to throttle AFW Row. i X 10*8 If osereter fade le isolate AFW, (t) Operator fade to throttle AFW flow. 10 (2)Operater throttles AFW flee. 00 LPI ocevre if Si signalis generwei, en demand, (1) LPI escurs se required. 099919 (2) LPI fails to escue. 2.3 X 10 *
- If $1 signalis nos pnerated, (1)Operaer massally starts LPl. 0 99 (2)Operecer fede to seatt LPl. 1 X 10* 8 ff $1 signalis see enereted and it operesse fede se start HPI, (l) Opereier rmis se start LPl. 10 (2) Operster mesmally eterte LPl. 00
'Astonymt used id the table (based in the order elthew appearance) are $1 = ufmy ingeo.
laun, MFW = meia feedetter, HPl = hech pressure 6ajestion, AFW = esadiary feedeo-ter, OA = opermee esteen, LPI = low.pressute tapetan, and MilV = mas feedeetw 6eelsteen vePro.
I Probabdetese esotered hetweee the two celemne apply se both break e6see.
'insiedes relare of MFW regulatens selves le rue bak. fadere of one er teth MFW pumpe se trip en high level la eny SG, and fossere of MFIVe le elone en El signat 1hees heedene apply only to small breat LOCAe end noe se medium.brub LOCAs.
'NA = not oppheable.
.r *e *
- BBR-3,1oo y3g l Combined
- i;g j w G4- L'e-. W4. ' .tn 6, ii' GTG, . '.4- 4ff"
. ' W with Sequence i
i 7. S = 10.". OCC i 7.G=10 -
OCC2 3
1 3.0=10.l 3.1=10, OCC i 00C+
u i
- 3. !=10 GCC3
- .. ....M.. 3.1 10 .
5.7=10 ' oool
.... .M t 5.8=10, 000
- 2. 3=10* OCC) oco3 i [.. .... .... M . 2.3=10*
i t... .... ..... .... ..#61 2.3=10.'7 I
i 7. 7 = 10.g 001 3 ocol
- I
. . . . . . , . . . . . . . . . . . . . . . .... M . 3.l=10 *P i
, I 4.6=10 qg 001 3 cool
.......M 1. 2 = 10 o***
i i !...... ..At?. 4.7*10"
' ' ! ***S
, . .. . . . . . . . . . . . . . . .. A.s.
- 1.9=10" I i......... . . . . . . . . . . . . . . .. ...... M . 4.9 10"'
i
. . . . . . . . . . . . . . . . . . . . . . . . . . ..........fo /* 3. 7 = 10"
. . . . . . .. .. fo . k. 4. 9 = 10".,' ooo 3
- l '. s... . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . .
...,...........................k!& 7.9=10 t
oooa
, . . . . . . . . . . . ........................................................................A03.2.4=10" I
4 4
1 1
Figure 3.12. Ennt tree for small-break LOCA at twd 0% power.
l i
.o .. . e
. _ ._. - i L Table 3.15. Segmences to be analyzed for senaR- and neediame-beenk LOCAs at het 4% power SI Signal h0FW AFW AFW Charging Sequence Generased betased itPI Occurs Arseases AessmanecaNy Acremelmeer OA Break fle. 04: ATW LPt Occors Frequency 9 Pia
- en w em Demand en D ==ad en Demand Consreded Dacharge Not isolated
- Rees Back Thrertled em Demand (yr-')
e SammE-Break IDCA 13 (gest) Signal s Nehme HFt AFW AssametacaDy Net Feas te Essback est Throttles LFl eet 7.7E-4 grecrased emerfeeds eccess acteases senerelled h ==A=a isolate break regmund pner to SG regenrod higblevel
- ' l 32 (ce62) 5.geal e W hae HPt AFW Am ny Net Fails to Remback met Fails no LFI not 7.6E-6 generased eserfeeds accurs acteases centremed de= == dad mutase betek regewed throttle segewed 1.3 % as apphcablef 52.l (8005) 5 gmat is Ne hme HPt AFW Ae===wk=By Nat Isoleses Feels te Throttles LFl eet 3.IE-7 generased erfeeds escors acneanes assuoned demanded break rea back pnar to SG regewed bigblevet alare g
82 2 (e004) S gmat is Nehme HPt AFW A-he=My Net tentases Rees back Faits ee LPl aat ilE-7 generased overleeds accurs acteases coeuened demanded break as requeed threstle requered 113 (0e09) 5.gmal a Ne has HPt AFW Overfeeds Not Isotases Rens back Throttles LFl not 2.5E-7 Mt generased e.erseeds occurs acteases demanded break as regesed prior to SG has49esel required d
alarm w O
AFW Assommuca5y Not Isolates Rees back Thearties LPI not 3E-5 M B14 (0003) Signal is No has HPt generased everfeeds accors er+==a= centselled de= ==d=8 break, as reqewed pnar to SG requered hashlevel alarm 12 5 Resident Groep I.IE-7 besa a-arentimCA 4 I (0001) 5.geal is Ne hae HPt AFW ^-
M, Dacharges - - Throttles LPI accors I 9E-5 generased emerfeeds occurs acrasess canuemed when required pner se SG assogemed bigblevel alarm 42 (one3) S.gmal as Ne bee HPt AFW Ahd=Hy Descharges - - Fsas to LPI accurs I.9E-7 gemeenned emesfeeds accus accesses sueuened when regewed throttle as requered 43 Remedeal Gseno 6.5E-9
'Deres she analyes of ergereces by leaho N *===B Engineenes Laboraanry (INELL she LOCAs in obsch the break emeld be isolated mere identised as Sequence Senes 3 and the LOCAs in which she break caeld oss he notased were edewised as Segmence Screes 12. The engmal sequence W are ===*-==ad here for easy crees reference.
"Then heademos api d y only se sun 5-break LOCAs and est as siehbreak LOCAt
- ' A5 SDvs ase espected to sesmass closed ender hat 9% peace e==As==r Sequence 13 couered the passdday of the SDYs faihng to close, and thus it is not appiscable to thes senes It is included only l Ser crees referrau se the INEL senes l
l I
HBR-3.102 Um seM' :iteth 'OP' "sj
~ ~
g,g3 nde &~ esse 5.:#Ae s22nn ETGe **$"*d Sequence
- 1. 9w 10" 000 ;
I
. 6s 8.. 4.7*10" l 1. 9 w 10 000 3 l .-
. 4.7. 4.7x10'"
.4 1 1.9w10" I 1.4w10 000 3 oooI I I i I . 655.9 3. 5
- 10'"
. l
../4.1. 1. 4 w 10" A.!!. 1. 4 w 10"'
, . ..th1. 1. 9x 10" coa, s ..b. 8.. 1.2wl0" mi
. .. 45.1 1.9x10"*
. . . .. . . . . . . Ahh. 5. 7x l 0"* aoag Figure 3.13. Event tree for medium-break LOCA at hot 0% power.
., .. . a
HBR-3.103 were described in Section 3.4.8. A review of this tree revealed the sequence descriptions would be dominated by operator actions, which means
, that the timing of the operator actions would be very important. Thus it l
was felt that a series of tube rupture calculations would be more appropri-ate than an analysis of the event tree. This' led to the identification of (i five tube rupture sequences, each of which represents a type of tube rup- $- l
,.,.?
ture event. These five sequences are described in Table 3.16. It should /j - {
be noted that in the interest of bounding the consequences associated with the tube rupture sequences, all tube rupture calculations were performed from the hot 0% power (Iow decay heat) initial condition.
Comments on the five tube rupture sequences are as follows:
4 Sequence 10.1: h is sequence is representative of the nominal tube rupture sequence. The frequer.cy assigned to it is the tube rupture initiator fre '
i quency of 5 x 10-3/yr identifled'in Appendix B.
Sequence 10.2: nis sequence is identical to sequence 10.1, but the SDVs i
fall to close for 10 minutes after the subcooling requirement is met. For failure of any one of five valves to close on demand, Appendix B reports a frequency of 1.6 x 10-3 This frequency is used to represent one or more SDVs faillas to close. This gives a total frequency for this transient of
.8 x 10-6j7,,
Sequence 10.3: In this sequence a pressurizer PORY is assumed to stick open for 10 minutes following the first opening. A value of 0.054 (0.027 for each valve as presented in Appendix B) is used as the frequency for 1
of W.
- 9
, -, ,, . . ~ . - . - , - - , - , - ,,,-nn.-,,,._- --w_n_-,,,,.,-,,,v-----,,-- .-,,--..n_n.www-.,,,,,_,,,,,-n,--c.
r i er HBR-3.104
/
Table 3.16. Sequences to be analyzed for steam generator tube ruptures at hot 07o power" Sequence Frequency No. Description of Sequences (yr-8) 10.1 (1) If SIAS is generated, operator trips RCPs when 5 X 10-3 RCS pressure reaches 1300 psig.
(2) Operator throttles AFW flow to maintain 40% SG level.
(3) At 500 seconds, operator closes affected SG MSIV. -
(4) At 10 minutes, operator fully opens three SDVs and cools primary system to 45'F. (Core outlet temperature and saturation temperature in the affected SG secondary are used to measure subcooling.)
(5) When subcooling is attained, operator closes SDVs.
(6) After waiting 260 seconds following Event 5, operator opens one PZR PORV to depressurize primary system.
(7) When pressures of pressurizer and affected SG dome have equalized, operator closes PZR PORV.
(8) After waiting 500 seconds following Event 7 operator opens a second PZR PORV to depressurize primary system to 1000 psia.
(9) When depressurization is accomplished, operator
! closes the second PZR PORV.
I (10) After waiting 100 seconds following Event 8, operator secures HPI.
10.2 Same as Svjuence 10.1 'except that SDVs fail to close 8 X 10-'
for 10 minutes after subcooling has been achieved.
10.3 Same as Sequence 10.1 except that PZR PORV sticks open 3 X 10-4 for 10 minutes on first opening.
9 10.4 Same as Sequence 10.1 except that second PZR PORY 5 X 10-3
, fails to open and operator throttles HPI and charging j flow when pressurizer set point level is attained.
I 10.5 Same as Sequence 10.4 except that operator does not 5 X 10-4 throttle flow.
! ' Acronyms used in this table are: SIAS = safety injection actuation signal, RCP =
reactor coolant pump, RCS = reactor coolant system, AFW = auxiliary feedwater, SG = steam generator, MSIV = main steam isolation valve, PZR PORY -- pres-
- surizer power-operated relief valve, and HPI = high-pressure injection.
oq O WO O Y
HBR-3.105 either of two valves to fall to close once open. 7his gives a sequence frequency of 0.005 x 0.054 = 3 x 10-4/yr.
Sequence 10.4: There was some concern expressed by Westinghouse represen-tatives that ORNL's representation of a typical tube rupture (sequence 10.1) was incorrect and that only one PORY lif t might be more typical. To address the potential effects of the different assumptions, sequence 10.1 was analyzed without the second PORY lift. The frequency used for the sequence was the tube rupture initiating frequency of 5 x 10-3/yr.
Sequence 10.5: In this sequence, HPI and charging flow are not throttled.
This is an actio.1 performed by the operator in an attempt to stabilize pri- 3 mary and secondary system pressure. For screening purposes, a 0.1 failure // ,/.l/
frequency
- was assigned to this operation, resulting in a frequency of 5 x 10-4/yr for this sequence.
t 3.5.11. Ioss of Main Feedwater 4
As described in Section 3.3.4, a loss of feedwater (LOFW) with subsequent auxiliary feedwater overfeed can result in sequences that potentially could be of concern with respect to PTS, Event sequences are similar to those identified for a reactor trip followed by main feedwater isolation (caused,-
for example, by a high steam generator level feedwater trip or i.afety injection), although the sequence frequencies are different from those in
' the reactor trip event tree. Six LOFW sequences have been identified.
Utilizing a LOFW initiating event frequency of 0.3/yr and the branch proba-bilities given in Table 3.6 for "AFW automatically controlled," " Charging
'0*J::":!a:' J'ah'!:d:'0::.";:::::'.'*: 04,' :n:.'0'!!.'ll"/
- sohydrasiles of this event revealed that a senservative frequency estles-e -11 wa 1 k. r r he a wa ed
e flow runs back on demand," and "AW throttled" results in the LOW-related .
I
/
sequences and frequencies given in Table 3.17. j I,
3.5.12. Support System Failures Of the support system failures postulated in Chapter 2 (Section 2.9.3), 12 were identified as being of potential concern with respect to PTS. 'Ibese included loss of instrument sir; loss of component cooling waters loss of service water; and several electrical bus failures, most of which involved the 4KV bus 3 or the de power supplies. The plant responses to these sup-o port system failures are summarized in Table 3.18.
In this section, the selected support system failures are evaluated as ini-tlators in potential PTS sequences. Initiator and sequence frequencies were then developed for those failures considered to be important. The potential PTS sequences associated with the selected support system initia-tors are discussed below.
Initiators 7, 8, and 9 (from Table 3.18), which involve the failure of vital instrument buses while tied into the 4KV bus 3 for maintenance, are effective loss of feedwater (LOW) events. Main feedwater would isolate as a result of the SI actuation caused by the bus f ailure. The support system failure also results in charging flow runback. Sequences of potential PTS concern include an effective LOW with initiation of AW, successful or unsuccessful automatic control of A M , and failure of the operator to mann-ally throttle A W .
p h
- w -.e , , . . . . - _ _ _ - . . - - . , _ . . - - . , . . - . _ . _ , . _ . .--
HBR-3,107 Table 3.17. Sequences to be analyzed for loss of main feedwater Thermal Hydraulically AFW AFW Charging Equivalent Sequence Actuates Automatically Flow OA: AFW Frequency Reactor Trip No. on Demand Controlled Runs Back Throttled (yr-8) Sequence 13.1 AFW Automatically Runs back Fails to 3E-3 9.49 actuates controlled as required throttle 13.2 AFW . Automatica!!y Fails to Fails to 3E-5 9.51 actuates controlled run back throttle 13.3 AFW Overfeeds Runs back Throttles 2.lE-3 9.52 prior to SG actuates as required high-level alarm 13.4 AFW Overfeeds Runs back Fails to 2.!E-5 9.53 actuates as required throttle 13.5 AFW Overfeeds Fails to Throttles 2.lE-5 9.54 actuates run back prior to SG high-level alarm 13.6 AFW Overfeeds Fails to Fails to 2.1E-7 9.55 actuates run back throttle i
I e* em 6
- 9
,4 _ _
O l
1 h
,
- Table 3.18. . System /camponent responws to selected postulated support systern failures * - - - -
e System / Component Response Pressurizer Postulated and PZR STM MFW MFW Safety Charging letdown Na f ailure Reactor Turbine RCPs PORVs SDvs PORVs MSIVs luolation Runback AFW Injection' flow Pump flow Dectrical Syuem Failures
. I 125V de Trips Trips RCPsA PZR heaters Closed C hed Closed Isolated NA # Actuates Train B Operable Isolated panel A and and C off off; annihary actuates associated spray valve 4KV buses closed; RC-456 I and 2 fail' stays closed l 2 125v dc Trips Trips Operable PORVs fail A2 Operable C hed Isolated NA Actuates Train A Operable Isolated I
panet P ched; con- and B-3 (only one actuates fads trol heaters closed motor-g on driven '
pump gg avadabic) C1 3 125V de av uliary Operable Operable Operable RC-456 closed; auxiliary spray A 1, B-1, and B 2 Closed Closed Isolated '4A Operable Operable Operable Isolated 7 taa papel valve closed closed *
- DC" fails N 4 DC buses Trips O
immediate Cannot bs PORVs closed; Closed Closed Ched Isolated NA Not JIPI and Operable Operable 00 A and B turbine be tripped auxiliary spray operable LPI not fail trip fails off valve closed, operable PZR heaters faded on 5 4KV buses Trips Trips .RCP C RC-455C Ched Eventual Eventual Impi Operable Not No flow; Isolated 2 and 3 and off; ched; block Jf PI and closure' closure' isolated, operable LPI not pumps associated potential valves fail and eventual operable fail D/Cs fad seal open; RC-456 isolation fadure eventually of other closes' '
MFW loops' 6 4KV buses Trips Trips RCPs A and PZR heaters C hed Operable Operable impi Operable Operable Operable Operable, Operable I and 2 and C off off isolated but anociated discharge D/Gs fad throttle valve fails opea
~ ~
, Table 3.18 (Cont'd) l System / Component Response Pressuriser Postulated and P2R STM MFW MFW Safety Charsing Letdown No. Fadure Reactor Turbine RCPs PORVs SDvs PORVs MSIVs Isohtion Runback. AFW Injection
- Pump Flow Flow 7 4KY bus 3 Trips Trips Operable RC.455C Closed Closed / Operable imp 2 Operable Actuated
, Actuated 1sw flows isolated g with main- closed, block isolated (only one Si tenance sie valves fad pump avad-to instre- open able) ment bus 2 fads' 8 4KV bus ) Trips Trips Operable PORVs closed Closed . Closedf Operable Imp 3 Operable Actuated Actuated 14w flo=8 teolated with main- isolated (only one SI tenance tec pump avad-v to instru- able) ment bus 3 fads' 9 4KV bus 3 Trips Trips Operable PORVs closed Closed Closedf Operable Imps 2 and Operable Actuated Actuated Imw flow 8 Isolated with main- 3 isolated (only one Si lenance tse pump avail-to instru- abic) ment buses 2 5 s and 3 fad' Inwrument Air System 10 Loss of instrument Operable Operable Operable PORVs closed Operable Closed Closed Isolated NA Overfeed if turbine Operable Overfeed (loss of Isolated hyd air pump is speed con- I actuated trol and W throttle g valve open) o Component Coeling Weser System It Ims of Operable Operable ~ Potential ' Operable Operable Operable Operable Operable Operable Operable I:PI and St Pump seal Operable CCW
' RCP pump seal failure failure Servlee Water System
)
12 less of Operable Operable Potential PORVs closed' Operable Eventual Eventual Isolated NA Inoper. Si pumps Overfeed' isolated' SWS RCP closure' closure' able inoperable (loss of bearing speed con-failure trol and throttle valve open)
~ ~~ ~ ~~
- Acronynis used in this table are RCP = reactor' coolant pump,'PZR PORb~ pressurizer power-operated reisef salN, SDV'- steam'dsivalve STM PORY = steam power-operated relief valve. MSIV = main steam-line isolation valve, MFW = main feedwater, AFW = auxiliary feedwater, SI = safety injection, HPI = bigh-pressure injection. LPI = low-pressure injection, CCW = coolant water system; and SWS = service water system.
6 Accumulator discharge remains operable under all failures postulated. 4 l
' Includes unavailability of associated diesel generator.
- NA = not applicable.
' Failure results in loss of SWS, which can fail the instrument air compressors.
/STM PORVs only fail closed if load reject signal from PM-447 exists.
- Manual recovery may be required.
BBR-3.110 Initiator 1, loss of the 125V dc panel A, also results in main feedwater isolation and SI actuation; however, charging pump flow remains fully oper-able. Sequences of potential PTS concern include those that would be ini-tlated by an effective LOFT with the possibility of charging flow runback failure and failure of the operable pressurizer PORV to close.
Initiators 2, 3, 10, and 12 would also result in main feedwater isolation and, except for initiator 3, would also result in the pressurizer PORVs failing closed. Modeling of the PTS sequences of potential concern includes considering the closure of the pressurizer safety relief valves (which would be demanded if charging flow runback failed) in those i
sequences where the support system initiator would result in inoperability ,
of the PORVs.
The failure of 4KV buses 1 and 2 and. associated diesel generator (initiator
- 6) results in a reactor trip initiator with operable primary and secondary side PORVs, closed SDVs, and operable MFW, ' AFW, MSIVs, SI, and charging flow. The expected frequency of this support system failure, though, is orders- of magnitude smaller than that of an unspecified reactor trip.
Three of the support system initiators identified in Table 3.18 are con-sidered to be benign from a PTS standpoint. Initiator 4, loss of de buses l
A and B, could be modeled as a steam-line break initiator owing to the.
potential turbine trip failure induced. However, minimal cooldown would occur since the de bus failure would also cause MSIV closure and HPI and-AFW failure. Loss of 4KV buses 2 and 3 and associated diesels (initiator l
l 5) is siellar in that SI, AFW, and charging flow are inoperable while the I
l ., -. . ,
. ~ _ .. .. -- . ._.
RBR-3.111 o i
secondary side is isolated. Failure of the component cooling water system (initiator 11) could result in an RCP-seal-failure-type loCA via loss of seal water to the charging pumps. However, failure of all three charging pumps would be required, as well as failure of the operator to trip the
- Table 3.19 summarizes the support system initiators modeled and the sequences with estimated frequencies greater than 10-7/yr. The frequencies of most of the PTS sequences that could be initiated by these support sys-tem failures are bounded by the frequencies for sequences initiated by LOW and nonspecific reactor trip events. Of the support system failures evaluated, three sequences resulting from support system initiators could -
not be bounded in this manner. These sequences involve LOW resulting from failure of the instrument air system caused by failure of the service water-system. The sequences of con:arn require the normal recovery of service water but not the consequently failed instrument air, failure to throttle AM , and, in one case, failure to manually run back charging flow. From a thermal-hydraulics standpoint, the sequences are approximated by reactor l
, trip sequences 9.53 (for the sequences involving effective manual runback l
l of charging flow) and 9.55 (for the remaining two sequences). These sequences have been designated as sequences 14.1 and 14.2, respectively, for analysis purposes (see footnotes e and f in Table 3.19).
l l
3.5.13. Sequence Summary l
l The procedure described in this section to quantify and collapse the event tree sequences produced 209 sequences for which thermal-hydraulic and l ..e -. - #
l -- ,_ __ _ _ _ _ . _ . _ _ _ . - - _ _ _ _ . _ _ _ . _ _ _ _ . _ _ _ . . . . _ _ _ . _ .
Table 3.19. PTS sequence modeling of support system initiators
- Support System Initiator
! Sequences > 10-7/yr Estimated Frequency Frequency No.6 Description (yr-') Impact Description (yr-8) d i Loss of 125V de 1.8E-3 LOFW with AFW and SI Since no overcooling or pressurization is forced Bounded by LOFW panel A and actuat:d; SDVs closed; STM by the initiator beyond what would be typically sequences ~
associated 4KV PORVs closed demanded in resulting transients, the associated buses I and 2' sequences are bounded in frequency by those associated with LOFW.
2 Loss of 125V de 1.8E-3 LOFW with AFW actuated; PZR Same as No. I panel B PORVs fait closed; STM PORVs
, operable; MSIVs closed 3 Loss of 125V de 1.8 E-3 i,OFW with STM PORVs closed; Same as No. I auxiliary panel one PZR PORY operable; @
"DC" MSIVs closed; AFW actuated y 6 Loss of 3.5E-4 Reactor trip with Since no overcooling or pressurization is forced Bounded by
- 4KV buses STM PORVs and SDVs by the initiator beyond what would be typically reactor trip g I and 2 and closed demanded in resulting transients, the associated sequences u associated sequences are bounded in frequency by those of D/G the reactor trip event tree.
7 Loss of 4KV bus 3 4.l E-5 LOFW with AFW actuated; Same as No. I with maintenance STM PORVs operable; SDVs tie to instrument closed; charging flow bus 2' at minimum 8 Loss of 4KV bus 3 4.l E-5 Same as No. 7 Same as No. I with maintenance tie to instrument bus 3' 9 Loss of 4KV bus 3 4. l E-6 Same as No. 7 Same as No. I with maintenance tie to instrument ,
buses 2 and 3' A
i
Table 3.19 (Confd)
. Support System Initiator Sequences > 10-7/yr Estimated Frequency Frequency Description (yr-')
No.* Description (yr-') Impact 1.0E-4 LOFW with STM PORVs 10a. Initiator with operator manually running Bounded by LOFW 10 Instrument air back charging now but failing to throttle sequences system failure closed; MSIVs closed; AFW e auto-control failure; PZR AFW PORVs closed; loss of charging 10b. Initiator with operator failing to manually Bounded by LOFW run back chargmg flow but successfully sequences flow control (overfeed) throttling AFW 10c. Initiator with operator failing to manually Bounded by LOFW run back charging flow and failing to sequences throttle AFW LOFW with AFW inoperable; Initiator with recovery of service water but not 12 SWS 0.01 STM PORVs closed; MSIVs instrument air. Same three sequences as in 3
closed; loss of charging flow No.10 above, but with initiator frequency based on the SWS failure and a probabihty of 0.9 control (overfeed) for recovery of SSW; that is:
E 12a. Initiator with rator manually running 8. l E-4' back charging INw but failing to throttle [
'AFW 12b. Initiator with operator failing to manually 9.0E-4
/ h w
run back charging flow but successfully throttling AFW 12c. Initiator with operator failing to manually 9.0E-4' run back chargmg flow and failing to throttle AFW Note: Without recovery of SWS, the event is not an overcooling transient.
LOFW = loss of feedwater, AFW = auxiliary feedwater, SI = safety injection, SDV = steam dump valve,
- Acronyms used in this table are:PZR PORY = pressurizer power-operated relief valve, STM PORV = steam power-operated relief v SWS = service water system.
6 Failures 4,5, and 11 listed in Table 3.18 are considered to be benign.
' Includes unavailability of associated diesel generators. 4 d Read; 1.8 X 10-3
' Initiator 12a is subsequently identified as Sequence 14.1. g l nitiators i 12b and 12c are subsequently jointly identified as Sequence 14.2.
f
'AI y
fracture-mechanics analyses were performed. The number of sequences iden-tified for analysis for each initiator and the frequencies of the associ- ,3, 0 i'
ated residual groups are summarized in Table 3.20. 5-
/ .<
i
,p ** * #
^
- - , - . , - - - - - . - , . _ _ . - - - _ . - ..m., . ,._ __ . . . -- _ . , _ . .
HBR-3.115 DRAR Table 3.20. Summary of event tree sequence collapse Number of Sequences Residual Grou Frequency (yr~g)
Grouped with Other Sequences
- Sequence Initiator To Be la Event Before After Scrus No. (Event Tree) Analyzed Tree Above 10-'/yr Below 10/yr Analysis Analysis
- 1. Il Small-break LOCA* at full power 22 6938 8 27 1.3 X 10 9.4 X 10-'
2 Medium-break LOCA at full power 12 6824 2 32 2.6 X 10 2.1 X 10
b 3, 12 Small-break LOCA at hot 0% power $ 158 4 4 2 8 X 10*' l.1 X 10
4 Medium-break LOCA at hot 0% power 2 124 I 3 3 8 X 10 6.5 X 10-'
t 5 Sc all-pipe steam-line break at full power 29 923 6 28 9.1 X 10 6.6 X 10-' -
l 6 Large-pipe steam-line break at full power 15 1763 10 41 4.6 X 10 4.4 X 10*?
7 Small-pipe steam-line break at hot 0% power 16 292 4 7 3.8 X IO*' 2.5 X 10-' j
!8 Large-pipe steam-line break at hot 0% power 9 508 0 4 2 3 X 10 2.3 X 10-'
9 Reactor trip 90 9773- 54 174 31 X 10 2.7 X 10-6
'O Tube rupture 5 NA' NA NA NA NA 13 Less of feedwater 6 NA NA NA NA NA 14 Support sptem failure 3 NA NA NA NA NA
'A screening frequency of 10/yr was used to initially identify sequences which should be analyzed on an mdivufual basis.
'LOCA = loss-of-coolant accident
'NA = not applicable.
[
., -. . a