ML20071A461

Rev 1 to Recirculation Sys, Draft Chapter to PRA

ML20071A461
Person / Time
Site:	Indian Point, 05000000
Issue date:	04/17/1981
From:	PLG, INC. (FORMERLY PICKARD, LOWE & GARRICK, INC.)
To:
Shared Package
ML20071A408	List: ML20071A429 ML20071A431 ML20071A433 ML20071A435 ML20071A438 ML20071A443 ML20071A447 ML20071A454 ML20071A461 ML20071A467 ML20071A484 ML20071A488
References
FOIA-82-626 PRA-810417-05, NUDOCS 8302240150
Download: ML20071A461 (117)

Text

{{#Wiki_filter:. INDIAN p0 INT PRA

     'Iginted,Lewc:and.Garrick,'Inc.                                                     REV 1
      . srj,1117, 1981 MK 6I               ~i
                                                      ' INDIAN POINT 3 g[g.

RECIRCULATION SYSTEM { , - . , ' .! 4.

s. E.

          ..          A. ~SUltMARY.                             ,,
                    'A.1 -INTRODUCTION The recirculation phase is evaluated in the context of a loss of coolant d'                     accident (LOCA). This phase calls for the combined operation of several systems' and components--the _ residual heat removal system (RHRS), the
                     - containment sump,- the recirculation sump and. pumps, the safety injection For ease of reference, we system (SIS), .and containment spray nozzles.

call this group the recirculation system. This system-is initiated by the operators when the water level in the refueling water storage tank (RWST) is at " low level" alam point. The function of this system is to e provide long-tem core cooling and containment spray for a LOCA of any break size. For core cooling, the system can be operated in three different modes: high pressure, low pressure, and hot leg recirculation. The analysis is carried out under the follcwing conditions: e Reactor trip has been successful (small LOCA). e 'njection phase has been completed successfully. e System is analyzed for 24 hours. e' One heat exchanger can provide sufficient cooling. e Success of the low head recin:ulation is defined as one 1cw pressure

                            -pump supplying cooling water to the core for 24 hours.

e Success of the high head recin:ulation is . defined as one, safety injection pump supplying cooling to the core for 24 hours. l e Success of the containment spray recirculation is defined as one 1cw head pump supplying water to one. spray header. l e Success of the hot leg recirculation is defined as one safety l- injection pump supplying water to one hot leg. I A.2 RESULTS . L In a small LOCA, core cooling recirculation via the safety injection H (SI) pumps (hi-head recirculation) should.be available. The other - l-functions (containment spray, lo-head, and hot leg recirculation) are not necessary. Hi-head recirculation is analyzed under several conditions depending on the availability of fan coolers, the component cooling water system (CCS), and necessary electrical pcwer supplies. The component cooling system provides the cooling water for the residual heat removal (RHR) heat exchanger. If the CCS is unavailable, the

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8302240150 830113 ' PDR FOIA BLUM82-626 PDR ' 1 ,' l L 1271 A042081/1

                                                                                                 .      l; containment fan ecolers would recove the decay heat by condensing the steam generated in the core

• Table 1 surr.arizes the boundary conditions

            , and the results. For some respresentative cases a list of dominant contributors follows :
             -Hi-Head Recirculation (Small LOCA)        ,

o With Pcwer On A11' Buses, Fan Coolers Unavailable, and Component Cooling Available Mean Operator Error 3.90 x 10-4 (10%)

                   -    All .three SI pumps ~ fail during       3.11 x 10-3 (76%)

the 24 hours e With Power on Bus 5A lost, Fan Coolers Unavailable, and Cocoonent ' Cooling Available Single Failures Mean

                   -     MOV 1802B fails to open                1.5 x 10-3 (13;)
                   -    MOV 822B fails to open-                 1.5 x 10-3 (13%)

w Double Failures

                   -     Both SI pumps (32 and 33) fail during the 24 hours                  7.1 x .10 (62%)                          ,

In Table 1 the WASH-1400 results are cuoted for cocparison. Mcwever, their high pressure recirtulation system (HpRS) is cuite different frca the hi-head recirculation system analyzed here. The following functions should be available in a large LOCA: core cooling recirculation via the low pressure headers, containment spray, and hot leg recirculation. Part of the recirculation flow is directed

             ~into the hot legs (24 hours after the accident) in the hot leg recirculation mode. These functions are analyzed under several conditions similar to those analyzed for the hi-head recirculation,

f.e., availability of fan coolers, CCS, and electric power. Tables 2 l through 4 summarize the results for each case. Similar to Table 1, the l WASH-1400 results are quoted for comparison. For some representative

! cases, a list of dominant contributors follows: Low-Head Recirculation (Large or Medium LOCA) e }Iith Power On All Buses, Fan Coolers Unavailable, and Conponent Cooling Available Mean Operator Error 1.5 x 10-3 (995) 2 - 1271 A042081/1  :

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e With Power On Bus 5A Lost, Fan Coolers Unavailable, and Concorent Coolina Available Mean Operator error 3.9 x 10-2 80%)

                       -     Recirculation pump 31 fails            1.4 x 10-3 ((3;)

to start

                        -    MOV 1802A fails to open                1.5 x 10-3 (3%)
                       -     MOV 822A fails to open                 1.5 x 10-3 (3%)

Containment Soray Recirculation (Large or Medium LOCA) e With Power On All Buses

                       -     Operator error                         1.5 x 10-3 (995) e    With Power On Bus SA Lost
                        -    Operator error                         1.5 x 10-3 (50%)   -
                        -    MOV 889B fails to open                 1.5 x 10-3 (50%)

Hot Leg Recirculation (Large or Mediua LOCA) e With Power On All Buses MOVs 856B and 856G fail 2.6 x 10-5. (100 ) to open . ( e ' With Power On Bus 5A Lost

                        -    MOV 856B fails to open                 1.5 x 10-3 A.3 CONCLUSI0HS Operator error in activating the recirculation phase was found to be an important contributor in ainost all cases that are analyzed here.

Failure to initiate switchover is the main component of this failure mode. Hi-head recirculation is an exception, because the unavailability of the SI pumps due to hardware failures dominate system unreliability. In all cases the unavailability of electrical bus SA (or 6A) has significant impact on system unreliability. However, in most cases, the simultaneous loss of both electrical buses 2A and 3A leads to a slight I increase in system unreliability. Also, in most cases, the effect of l fan cooler availability is insignificant. c . 4

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t . B. SYSTEM DESCRIPTION B.1 PURPOSE OF THE SYSTEM The function of the recirculation sys. tem is to provide long-tern core cooling and containment spray after a loss of coolant accide'nt (LOCA) of any break size. It recirculates the sump water back into the core and/or spray nozzles after cooling it in the RHR heat exchangers. B.2 SYSTEM DIAGRAMS Figures 1 and 2 show a block diagram and a piping and instrumentation diagram (P&ID) of this system. The P&ID is simplified, i.e., branching pipes with 1.ess than half the diameter of the originating pipe, such as-miniflow lines, are not shorn because loss of flow into these lines-would not cause insufficient flow in the system. , B.3 SYSTEM CONFIGURATION AND OPERATION B . 3.1 System Conficuration The recirculation system is the combination of several systems and components. These include the RHRS, the containment sump, the recirculation sump and pumps, and the SIS. The recirculation sump is covered with gratings, screens, and baffles to clear the water of debris (particles greater than 1/4-inch) and reduce water velocity to minimi:h debris carryover. Water level in the sump is monitored in the control room on the safeguards panel. A drainage trench also carries the water s to the sumps. The containment sump is separate from the recirculation sump and is located inside the missile barrier. The two recirculation pumps are of vertical, centrifugal type with 3,000 gpm capacity at approximately 150 psig. The pumps are driven by 350 hp electric motors which have air-to-water heat exchangers. The motors are more than 2 feet above the highest anticipated water level. The water to these heat exchangers is supplied by the auxiliary component cooling pumps (booster pumps) or the main component cooling loop. The booster pumps are started by the safety injection si.gnal in order to protect the-motors of the recirculation pumps from possible damage caused by moisture or high temperature from containment conditions prior to, and following, the switchover to recirculation. The RHR heat exchangers are of the vertical shell and U-tube design. The shell side contains the cooling medium (component cooling water) and the tube side the recirculated fluid. Each heat exchanger is capable, at accident conditions, of cooling 1.4 million pounds of water per hour i from.2130F to 1350F. There are a total of four pumps that can take suction from the sumps. The two recirculation pumps (located inside the containment) take suction from the reci.rculation sump, and the two RHR pumps (located - outside the containment) take suction from the containment sump. The 4 - 1271 A041681/1

configuration of components in the recirculation system is such that the 3 tad pumps (i.e. , recirculttion or RHR pumps) take suction from a sunp and pass the coolant through the RHR heat exchangers. One out of four pumps can provide sufficent coolant flow to cool the core and simultaneously spray the containment. Depending on the operator decision and the pressure in the reactor coolant system (RCS) and in containment, the flow is routed for core cooling or containm4nt spray, or both. Priority is given to core cooling. -

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The RHR heat exchangers cool the ump water. Their secondary side is connected to the conponent cooling system (CCS). The latter is cooled by the service water system (SWS) which is drawn from the ultimate heat sink (Hudson River). The component cooling outlet valves for each heat exchanger (822A and 822B) are opened by the safeguards actuation signal. If heat exchanger cooling is not available, the fan coolers can remove the . heat by condensing the steam generated in the core. Twenty minutes after accident initiation, three out, of five fan coolers are ' sufficient for a large LOCA. Fmm the heat exchangers, ficw can be directed in four different directions. The core and containment conditions determine which flowpath should be chosen. The path for icw pressure cold leg injection is opened by the safeguards actuation signal. If the RCS pressure is above the shutoff head of the low pressure pu=ps (477 feet for the recirculation pumps and 372 feet for the RHR pumps), the flow is

 ,       directed toward the suction line of the SIS pumps. The third path leads to the containment spray headers. Hot leg recirculation is also possible (hi-head only). The isolation valves to.the hot legs are nomally closed and deenergized. If one heat exchanger train is                     e unavailable, it is possible to align the other train for simultaneous core cooling and containment spray recirculation. Al so, if hi-heac injection is required and the connecting line between the RHR heat exchangers and the SIS pumps is closed or failed, then the RHR pump flow can be realigned (by opening M0Y 883 and manual valve 1863, and closing manual valve 846 and MOV 882) toward the suction side of the SIS pumps.

The heat exchangers are bypassed in this situation and containment spray recirculation is not possible. Therefore, this mode of recirculation in11 be successful if the containment fan coolers can remove the heat generated in the core. B.3.2 System Operation The operators activate the recirculation system when they receive a " low level" signal from the RWST (a one-out-of-two system). For a large LOCA, if all pumps are running, this is about 22 minutes after the initiation of the accident. This time period could be much longer depending on the number of pumps taking suction from the refueling water storage tank. The operators also check the sump level. The suitchover from the injection phase to the recirculation phase is done by eight switches (referred to as the "eight-switch secuence"). Following switchover, one spray pump is left operating until the RWST is empty. Core cooling has the first priority. Containment spray recirculation is activated later, manually; its operation depends on containment pressure. 5 1271 A041681/1

i- , The operators turn the recirculation switches to the "on" position, one at a time, starting with switch 1. There is a light associated with each switch which indicates that the recuired automatic operations are completed. If a particular switch operates on a deenergi:ed component, the function complete light would not turn on. These are centioned in the procedure at the related instruction. Operators would check the status of components that are affected by these switches. If some functions are not' completed, 'they would accomplish the operations manually according to the procedure to obtain the desired actions. Switch 1 trips SI pump 32 (if all three are running), spray pump 32 (if both pumps are nJnning) closes HOVs' 887A and 8879 (if SI pump 32 is stopped), and closes the discharge MOV; 866A and 866B (these are not shown in Figure 2) of the containment spray pump that has been stopped. Switch 2~ activates one additional nonessential service water pump in the conventional header and one component cooling pump. Both RHR pumps are-stopped and RHR suction and discharge valves (882 and 744) are closed by switch 3. Both valves are deenergized; therefore, a plant operator must energize them before they can be closed from the control room. One of the recirculation pumps is started and both discharge valves (1802A and 18028) are opened by switch 4. Switch 5 causes the heat exchanger discharge valves 746, 747, 899A, and 8998 to close and the SI pump ' suction valves 888A and 888B to open. It also closes the safety injection line valves 842 and 8A3, and closes the RHR mini flow line MOVs 743 and 1870 and ams the SI pump suction header low pressure alam . (these are not shown in Figure 2). At switch 5, the operator has to decide whether hi-head or lo-head recirculation is recuired. If hi-head If is recuired, then he continues, lo-head is reouired, he continues  ; with switch 5 and ships switch 6. with switch 6. Switch 6 trips all running safety injection pumps. If three diesels or offsite power are available, switch 7 would start a second service water pump. If this is successful it would start a second component cooling pump also. If both are successful, the second recirculation pump is started also. Switch 8 clases spray pump test line valve 1813 and SI pump suction valve 1810 (suction from RHST; it is - nomally deenergized). Containment spray recirculation is activated manually. After switchover to core cooling is completed, the operators trip the running spray pump (when the RWST is empty) and close the isolation valves. In lo-head j recirculation, the isolation valves 889A and 889B (at the RHR heat ' exchanger discharge) are opened and the throttle valves, 638 and 640, are adjusted until spray flow is established. In hi-bead recirculation, the operator opens HOVs 889A and 8898 and verifies 1300 spo flow to the I spray rings. At this time, Cold leg recirculation is maintained for 2a hour.s . according to the procedure, the operator realigns the system for combined hot and cold leg recirculation. The'two hot leg connections are associated with the safety injection discharge headers, which are isolated by normally deenergized and closed valves. Therefore, a plant operator's assistance is needed to open these valves (i.e., unlock and i o V close the appropriate MCC breakers for these valves). f - i < l 6 - ! 1271 A041781/1 *

     ,    . Several parameters relevant to system operation are nonitored on the control boerd. There are redundant level indicators for both sumps.

Coolant flow is also indicated _ for lo-head discharge headers, the containcent spray headers, and the two discharge pipes downstrean of the SI pumps. Low pressure at the safety injection pumps suction header is annuciated in the control room. B.4 SUPPORT SYSTEMS . This system is a composition of two emergency core cooling systems--the residual heat .recoval system and the safety injection systen. It also uses the same piping and spray rings as the containment spray system. The plant operator is essential for the activation of this system. Electric power is necessary to run pumps and operate valves. Table 5 gives the power sources- to the pumps and valves of this systen. The component cooling system cools the sump water in the RHR heat exchangers. Punp cooling is essential for the recirculation pumps. If the component cooling system is not available, the booster pumps (component cooling) can provide sufficient cooling flow. Cooling of SI pumps is acconplished by a shaft drain booster pucp using component cooling water to cool the oil system. RHR pumps can function for several hours without cooling. B.5 TEST RE0VIREIENTS . The various emergency core cooling systens employed in the recirculation systen are tested periodically. The description, frequencies, and nanes of tests perforced on each component are listed in Table 6. All pump's, e except for the recirculation pumps, are tested at least every conth. The latter are tested at every refueling outace. TFe valves are tested at different intervals; also, portions of the systen are used during heatup and cooldown. Table 6 shows the detail. The level indicators of the two sumps are tested for operability et every refueling ou; age. The recirculation switches are also tested during refueling (PT-R3A). B.6 1%INTENANCE REQUIRE!ENTS Under normal operating conditions, generally speaking, there is no maintenance on the recirculation pumps, and all the valves .inside the containment. At any given time, only one of the following components coul'd be unavailable due to naintenance: RHR pumps, SI pumps, auxiliary component cooling pumps, and HOVs 888A, 888B, 885A, and 8858; and they cannot be out of service for more than 24 hours. All valves are included in a preventive maintenance program. One spare SI pump and one spere RHR pump and associated parts are naintained in inventory to acconnodate expeditious exchange or repair when an installed pump is found to be inoperable. o ('

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B.7 TECHNICAL SPECIFICATION 5 The reactor should be maintained at cold. shutdown unless at least cae refueling rater storage tank low level alarm is operable; one residual

      -     heat removal pump, and one heat exchanger, together with the associated piping and valves are operable; or one recirculation pump together with with its associated piping and valves are operable.' Similarly, the reactor should be shut down if at least one safety injection pump remains out of service for more than 24 hours, one residual heat r~emoval pump remains out of service for more than 24 hours, one residual heat exchanger remains out of service for more than 48 hours, or one refueling water storage tank low level alara remains inoperable for more than 7 days.

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C. GENERAL REPARKS ON LOGIC,MODELS AND QUANTIFICATION C.1 LOGIC MODEL There are two modes of operation for.this system: core cooling

     ~       recirculation only, and containment spray recirculetion. System configuration for core cooling recirculation depends on the, type of LOCA. Only the availability of high pressure recirculation is questioned in a small LOCA. For medium and large LOCAs, low pressure, containment ' spray, and hot leg recirculation functions must be available. If icw pressure recirculation fails, then cor.tainment spray and bot leg recirculation are failed also. Thus, four distinct states for the system are defined and discussed separately. These are:

1. High pressure recirculation when injection phase is successful,

2. Low pressure recirculation when injection phase is successful.

3. Containment spray recirculation when low pressure recirculation is avail abl e.

4 Hot leg recirculation when core cooling recirculation is available. Each state is analyzed in a separate section. A fault tree and its minimal cutsets are given first. Then the fault tree is quantified under different conditions which are transferred from the event trees. These conditions include the avalability of the fan coolers, the conponent cooling system, and the electric buses. Tables 1 through 4 sur:rnarize the results.

• r Fault trees are constructed including the RHR heat exchangers. For sequences in which three out of five fan coolers are operating, the RHR heat exchangers are not required for successful recirculation system operation. Sufficient heat is removed by the fan coolers to prevent core damage. The effect of the fan coolers will be shown in the quantification sections.

e L The~ possibility of using line 190 (contains MOV 883 and manual l valve 1863) is not considered in the fault trees. Its impact on the l availabiliy of the system will be shown in the quantification sections. The conditions conmon to all fault trees are: l e A LOCA has occurred. l e The reactor has been scranraed successfully. l e . The injection phase has been successful. l- e At least 20 minutes has passed from accident initiation. 1 g 1271 A041681/1 '

e The water in the RWST is at 1cw-level alarm point (at least 96,000 gallons remain in the tank). e One RHR pump, or one recirculation pump, can provide sufficient flow for both core cooling and containment spray. e One RHR heat exchanger can provide enough cooli~ng. ' e The component cooling system can provide sufficient cooling to the recirculation pumps when the booster pumps are unavailable. e Mechanical fe.ilures in the heat exchangers are not considered. Their failure mode is very similar to pipe failures. Therefore, any significant damage in the heat exchangers would be detected within one day. The specific conditions are given later as each fault tree is described. Test and meintenance contributions are not shown in the fault tree.. However, they are considered in the sections on quantification. C.2 FAULT TREE CODING Table 7 is' a partial list of basic events, their failure modes, and the - corresponding codes. C.3 QUANTIFICATION 9 In the quantification sections, the unreliability of the system in 24 hours is assessed. The important factors and scne unavailability - values unique to this system are discussed in this s?ction. Time is an important factor. It appears under two different contexts; first, the total time of successful operation, and second, the available time for restoration after system failure. Success is defined as adequate core cooling and/or containment pressure control over a 24-hour period. The restoration time' is very important to system activation because it defines the available time for an operator to switch over to recirculation phase. We will refer to this as a " time window" and define it as 7(t) = t' - t; where t is the time when the top event occurs and t' is the time of core damage after t. For switchover, t is considered the time when the RWST water level reaches the low-level alarm point. Switchover to the recirculation phase is a dynamic task where the operators interact with the displays on the control board. The low

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level alarm from the RWST is a cue for initiating this process. Flow levels are checked to determine if the desired ~ flowpath is establishec. 10 -

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c The " Human Reliability Handbock"* is used in this study as a guide .to quantify the contribution of human error under accident conditions to system unavailability. For the quantification of each human-related

           . event we take the following steps:

1. We identify-the failure modes of human error that would lead to adverse situations. We break .down system failure to detailed bunan e'rror failute modes. Although the state of knowledge on the frequencies of human error under accident conditions may not warrant this detailed quanitification effort, we judge that this enables us to obtain'a clear picture about the role of human performance on system function. The handbook gives the following reasons in defense of a detailed ~ analytical approach (p. 21-11):

                  "a. The exercise of outlining all plausible modes of operator-             .

action decreases the probability of overlooking some important failure path.

b. Due to the lack of error probability data for nuclear power plant tasks, it is necessary to break down operator actions to a level at which existing data can be used.

c. The detailed approach nakes it easier for analysts making independent estimates to check on the source of any

                       ' disagreement and to resolve it."

2. We establish the basic human error rate based on our judgment and frequencies of similar tasks suggested by the handbook (see the chapter on " Human Error Rates" for a definition 'for Basic Human C Rate).- The most important factor influencing cur judement is the stress level in a particular accident. Skill and control board layout are also important. All the operators at theindian Point 3 station are trained on a simulator which is similar to the control

                ' board at the plant. Also, the lice'nsed operators practice accident mitigation (especially large LOCA) on this simulator at least once a year. The controis and instrumentation for switchover are in one general area on the control board.

3. Dependencies among the operators are established in this step (see the chapter on " Human Error Rates" for the definitions).

4. We compute the frequency of error for the team of operators using the conditicaal frequencies suggested by the Handbook (see the chapter on ' Human Error Rates").

5. We take the results of step 4 as the median frequency. To express our uncertainty in that frequency we assign an error factor that shows the span from 95th percentile to th'e median. We take the

       ,    " Swain, A.D. and H.E. Guttman, " Handbook of Human Reliability,"

NUREG/CR-1278, Sandia Laboratcries, Albuquerque, New Mexico,

 ,   g. October 1980.                                        ,

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t g. distribution as legnormal and compute the mean and variance. See the chapter on " Human Error Rates" for the reasons for choosing this distribution. In Table 7, several events are entered under the title of "Noncomponent Events" . for which data is not given i'n Section . These events are discussed hereafter. . . e ECNTSUMP or ERECSUMP . The two sumps (containment or recirculation) could be plugged by debris during a LOCA. This is deemed to be very remote because the strainers take a large area and more than one screen has to be plugged. We choose 10-6 (judgmentally) as the median and 100 for the err 6r factor; then the mean and variance of lognomal distribution become: a Mean: 5.0 x 10-5 Yariance: 6.4 x 10-6, . e HDISCHDN The safety injection (SI) part of the system is treated as an entity in one of the fault trees. This event is the failure of the SI system to align to the proper position for hi-head injection. From the section on "High Pressure Injection System" we obtain the follcwing mean (combination of supercomponents B, C, and D in that section): Mean: 1.1 x 10-5 i Yariance : 1. 2 x 10-8,- e .ELOHDDIS

The low pressure injection system is treated similarly to the SIS.

The failure here is unsuccessful alignment of the discharge paths for' low-press ure. injection. The section on the low pressure injection system gives the mean ( EF in that section): l Mean: 2.36 x 10-8, C.4 PIPING ANALYSIS l'- Table 8 shows the pipe failure analysis. There is no single pipe section failure that would totally disable one of the functions. In - most' cases the pipe failure can be detected through RWST level ! indicators . If pipe 361 (the connecting line between the RHR beat exchangers and lo-head injection headers) fails, the SI pumps could be used after the broken line is isolated. If pipe 60 fails, then the return line around the RHR pumps can be used. For this, MOY 883 and ( l - l I' 12 - 1271 A042081/1

nanual talve 1863 would be opened and MOV 882 and manual valve 846 vreuld be closed. Fan cooler availibility-is essential in this' node because

                . the heat exchangers are bypassed. If pipe 359 fails then lo-head recirculation via'lo-herd discharge headers vould not be possible.
                - Heuever, the broken pipe can be isolated by 899A and B valves and tne SI punps can be .used for core cooling recirculation.             ,     ,

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i . O 4 D. HIGH PRESSURE RECIRCULATION 0.1 FAULT TREE The fault tree is shown in Figures 3 through 12 and 20 through 24. The top event is "High Pressure Recirculation Fails to Provide 300 gpm for 24 Hours." Yhe fault tree is based on the following conditions in addition to those mentioned in Section C: e Small LOCA has occurred. e High pressure coolant injection has been completed successfully by the SI pumps; therefore, only pump failures are considered. Thi s means that inadvertent blockage of flow is discounted. e One hi-head pump is sufficient for adequate core cooling. e If M0Y 744 is needed, it should be opened from a closed position. The minimal cutsets with one and two basic events, and with the house events treated as basic events, are shown in Table 9. Failure of . pipe 60 (HPPLN60E) will fail the hi-head recirculation. This is because, in this fault tree, we have not allowed for heat exchanger bypass through line 190. However, in quantification the effect of this - line is taken into consideration. The failure of the component cooling system fails beat exchanger cooling. This fault tree is quantified under several conditions depending on t'he ( availability of fan coolers, the component cooling water system, and three electrical divisions. Table 1 gives all possible combinations of these conditions. D.2 QUANTIFICATION D. 2.1 All Electric Buses and Conoonent Cooling Available: Fan Coolers Unavailable Table 10 gives the cause table. Each item in this table is discussed hereafter. D . 2.1.1 Human Error Contributions The frequency of cperator failure to establish high pressure ! recirculation is evaluated here. In a small LOCA, the time for switchover to the recirculation phase is definitely greater than 2 hours after the accident. More likely, it is around 10 hours. The time windou for switchover is at least 60 minutes. This is relatively large and would allow the operators to take corrective actions in case of component failures'and human error. This is particularly true for the RHR pumps, which can be aligned for containment sump recirculation. Also, the stress level on the operators should be moderate. That is (', higher than for normal operating conditions but significantly less than the stress level in a large 1.0CA. . l 2 14

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    .        s Four pecple would be in the control room by this time. Two of the four ere control board operators and at least ore of them has a senior reactor overator's -(SRO) -license. The remaining two are the shift supervisor (SS; has SRO license) and shift technical advisor (STA). The latter does not have an operating license, but has been trained in the mechanics of accident control and plant response characteristics.

The two oper.ators would be doing the switchover. dne would be reading the procedures and the other would be manipulating the controls. The shift supervisor would be monitoring the process while checking other parts of the c'ontrol bnard. The shift technical advisor would not be involved in the detail. He is supposed to form an independent interpretation of the instrumentation readout._ Three Mile Island scenario (i.e., many people in the control room and frequent outside telephone calls) would not be experienced again because of special corrective actions candated by the Nuclear Regulatory Commission. We define three steges for the switebover process. In the first stage the operators follow the RWST level. This stage ends when decision is made to initiate the switchover. Errors at this stage (i.e., failure to' decide to initiate switchover) may fail the system and should be attributed to all four operators. At the second stage the _switchover is' performed. Here, errors would be due to the two operators at the control board. The third stage starts when switchover is cocpleted. . All four operators would be looking at the indicators to see if the switchover was successful . Errors can be discovered and corrected at this stage. Two operator-related events'are identified that coul'd lead to system failure. These are: e Failure to initiate switchover. e Switch 6 is turned to "on" position and no corrective actions are taken. Three things help the operators to recognize that switchover should be l initiated. First, operator' training will condition them to recognize switchover requirements. Second, the procedures would lead the operators to switchover. Third, the RWST low level alarm would alert the operators. ( l A small LOCA may impose a moderately high stress level. The handbook i suggests that the stress level may even become very high. We quote from l that source (p.17-18): i "A LOCA is a special case. Presumably a smal1 or slowly developing l LOCA should not be accompanied by nore than a moderately high level l of stress for most people. Of course, in some incidents involving small LOCAs, the initial stress level may not be very high, but

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subsequent events may raise the stress level. For example, some operating personnel in the THI accicent, which involved a small G 15 1271 A041681/1 -

i

   .      s LOCA, were considered sub' ject to high levels of stress at various times by the interviewers on the Kemery Commission (Kemeny,1979) and Rogovin Special Incuiry Group (Rogovin and Frampton,1980)."
        -     The basic human error frecuencies must' be estimated totally ,

judgmentally, because there is no statistical data. The handbook acknowledges this and suggests some adjusting facto'rs. We quote (p. 17-10) :

                    "We can find no objective data from which to derive the factors to apply to human error probabilities (HEPs) and uncertainty bounds for the condition of a moderately high level of stress. On the basis of judgment, we multiply the HEP and uncertainty bounds for step-by-ster, rule-based tasks perfomed under optimal stress levels by 2, and for tasks recuiring dynamic interplay between the operator and system indications, we use a cultiplier of 5."                           ,

For errors of omission (the first event is of this kind) the handbook makes the following suggestions (Table 20-15, page 20-33): Human Error Frequency -- Best TASK Estimate (lower bound "to" upper bound Omit an item when preparing a .003 ( .001 to .01 ) list of values or set of tags. Failure to carry out a specific .001- ( .0005 to .005) e oral-instruction to change or restore a valve. Failure to initiate level 1 .001 (.0005 to .005) tagging. Failure to follow established .01 (.005 to .05) procedure or policies in valve changes or restoration. In light of these arg'uments Section C.3 we choseasg the x 10 gndforsuggestions median the basic human and frequency and 1 x 10- and 3 x 10-2 as the 5th and 95th percentiles. error those give The dependencies among the operators are: high dependence (HD) between the two reactor operators, moderate dependence (MD) between the SS and

 -             the first two, and moderate dependence between the STA and the rest.

The two reactor operators would be interacting closely and possibly one of them is a novice, thus high dependence between the two. The shift supervisor (an SRO) is less dependent on the first two, because he may not become involved in the detail. The dependency level of the STA is ' not clear. He may be highly dependent on the rest because he is part of the term and would follow the same line'of thought. On the other hand, 16 ~ 1271 A041781/1 t

since he does not have to become involved in the detail, he may interpret the indicators rather independently. We judge that an average STA would be moderately dependent (MD) on the rest of the team. Using the fomulas recomended by the handbook, error frequency of the four-person team for this task (initf 3 tion of switchover) would be: 2 6.0 x 10-3 x [1 + 6 x 6 x 10% x 1 + 6 x 10 = 6. 6 x 10-5 ( 7 j 2 We assign an error factor of 20. - The mean and variance become: Mean: 3.46 x 10-4 Variance': 3.19 x 10-6, For the second event, the operators erroneous'ly turn switch 6 to "on" ' position which stops all the SI pumps. However, it is possible to restore these pumps from the control board. The former may occur due to the error of two operators, that is, one reading the procedure and the othe manipulating the controls. This error may be discovered by the SS or STA while the switchover is in progress or by the whole team after switchover is completed. We judge that it is more likely that the first two operators would not discover their cwn error. Also, the SS and STA would be highly dependent on each other. A point value for the frequency of turning switch 6 and not recovering the error is: a [ no recovery, i fr ,

                         .tch (swi.on.         6)x   fr i    SI pumps not    i

( ) (startedmanually)

                = 16.0 x 10-3      x    1 + 6 x 10% [ 6.0 x 10-3 ,1 + 6 x 10%

( 2 )( 2 /

= 9.0 x 10-0 .

11e take this as the median and assign an error factor of 20. The mean and variance for a lognomal distribution become: 1 ' ~ Mean: 4.72 x 10-5 Variance: 5.93 x 10-8, Hi-head recirculation may also fail due to a combination of human error - and other causes. At least one recirculation pump may fail due to human error (during maintenance) on manual valves 753A, 753F, 753G, 753H, 753J, or 753K, and 752A, 752F, 752G, 752H, 752J, or 752X. The RHR pumps have to be aligned manually (from the control room) to provide the - recirculation flow when the recirculation pumps are not available. 17 - 1271 A041681/1 a i

The booster pumps are flow-checked after maintenance or every month. Therefore, the position of canual valves 753A, 753F, 753G, 753H, 753J, or 753K, and 752A, 752F, 752G, 752H, 752J, or 752K is checked regularly. One of these valves in the closed position would result in the failure of one recirculation pump. - Under normal operating conditions, these valves are never manipulgted. The unavailability of these valves should be on the order of 10-0 or less. . The operators can switch to RHR pumps and establish the recirculation flow from the containment sump if there is no flow fron the recirculation pumps. The median frequency of failure for one operator to recognize this mode of operation is judged to be 0.1. Stress level could be high for this action because of cultiple failures in the recircul stf on pump section. With high and moderate dependencies among' the operators, SE, and STA, we obtain: point value: 0.1 x

                                                + 6 x 0.1 f1+

x 2

                                                                        =  .9 x 10  .

This is taken as the median. An error factor of 20 reflects our d' egree of uncertainty. The mean and variance for the resulting lognormal distribution are: Mean: 1.52 x 10-2 . Variance: 6.16 x 10-3, In case of failures in heat exchanger 31,110Vs 746 and 747 should be" q opened by the operators to establish flow from heat exchanger 32 to the suction side of the SI pumps. We assign the frequency distribution of failure to switch to aHR pumps to this failure mode also. D. 2.1. 2 Single Hardware Failures . The only single element cutset is: e HPPLN60E: pipe 60 rupture. - The failure of pipe 60 would fail hi-head recirculation. The maximun time that this failure may stay unnot From Section , pipe failure rate (mean) is 4.5 x 10-{ced is 1Then, per hour. week.failure frequency of line 60 is: liean: 8.6 x 10-10 x 24 x 7 x 1/2 = 1.44 x 10-7 Variance: (1/2 x 24 x 7)2 x 6.0 x 10-17 = 4.2 x 10-13 D.2.1.3 liultiple Hardware Failures The double and triple failure contributions are computed by the computer code PAS. This ccde orders minical cutsets (liCS) according to their degree of contribution to the frequency of the TOP event. We take the 18 .- 1271 A041681/1 i

     . s                                                                             -

first few cutsets that contribute more than 90% to the frequency of the T0p event and check for repeated component types. The contribution of human error to partial system failure is also included. Some hardware failure frequencies are adjusted to reflect these errors. In case of failures in the recirculation pump section, the operators would use the RHR pumps. The frequency of failure to switch to RHR pumps due to operator error is computed in Section D.2.1.1.* The mean and variance are: Mean: 1.52 x 10-2 Yariance: 6.16 x 10-3, This frequency is assigned to check valve 741 in the input to RAS. The meen frequency of the cutsets with repeated component types is adj usted. The following minimal cutsets contained such events: e EPitRC22S EP!!RC215 ECY-741C , If both recirculation pumps fail and ' operators fail to switch to RHR-pumps (represented by ECV-741C), then the system will be unavailable. The unreliability of one recirculation pump is the sum of two contributors--failure during operation and failure to start. - The mean and variance become: liean: 1.97 x 10-5 x 24 + 1.36 x 10-3 = 1.83 x 10-3 C Variance: 1.70 x 10-7 x (24)2 + 1.22' x 10-6 g,91 x 10-5, The mean of the frequency of both recirculation punps failing is: flean: (1.83 x 10-3}2 + g,91 x 10-5 = 1.02 x 10-4 Operator failure frequency is assigned to ECV-741C. The mean of the frequency of this minimal. cutset becones: [ Mean: 1.02 x 10-4 x 1.52 x 10-2 = 1.56 x 10-6, j e HPitSI215 HPMSI22S HPHSI235 The unreliability of one SI pump is equal to the sum of t'he i frequencies of pump failure while running (in 24 hours) and pump failure to restart. QSI = 051s + (1 - exp (-ASIt))(1-Osts).

QsIs + (1 - exp (-ASIt))

n

   . O                                                        ,

j . l - 19 !' 1271 A041681/1 ' J

                    ,,he re 05 I3: SI Pump failure to restart;
         .                        a = 1.36 x 10-3, p2 = 1.22 x 10-6 ASI:    SI pump failure rate given it has started;  -

a = 2.31 x 10-3/hr g2 = 7.47 x 10-5/hr2 . t: 24 hours Using DPD arithmetic the mean and variance of QSI is obtained

• Mean: 3.77 x 10-2 Yariance: 4.35 x 10-3 The frequency of system failure due to hardware failures in all three SI pumps is obtained from Q=Q SI* '

     -             Using DPD arithmetic the mean and variance of Q is computed:

Mean: 3.11 x 10-3 4 Variance: 1.67 x 10-4 e HitV888AQ HitV8888Q The mean and variance of the.fracuency of failure of an MOV to opc . are (from Section ): Mean: 1.51 x 10-3 .

                         .Yariance: 2.64 x 10-6, The mean and variance of both valves failing are:

Mean: (1.51 x 10-3)2 + 2.64 x 10-6 = 4.88 x 10-6 Yariance: 5.03 x 10-10, This is a conservative measure because the valves can be opened manually

• within the available time window. We inspected the system diagram and concluded that MCSs with four or more elements do not contribute significantly to the top event. The results of this section are sumarized in Table 10. -

( 20 1271 A041681/1

D . 2.1. 4 Maintenance Contribu-ion Section C.1 gives the list of' components that could be unavailabla due to maintenance when the system is activated. Only SI pumps are main contributors here. This is because the unavailability of RHR-related cor.ponents due to cperator error is riuch. larger than the - maintenance-related unavailability. Also, the auxiliary component cooling pumps do not appear in any of the minimal cutsets because the component cooling system is available. The mean and variance of the unavailability of the SI pumps due to maintenance are (from Section ): Mean: 8.13 x 10-4 Yariance: 6.22 x 10-8 System failure occurs if all' three pumps are unavailable. The < unaveilability of two SI pumps due to hardware failure is computed by applying DPD arithmetic on: 0=Ofg where SI is defined .in Section D.2.1.3. (he mean and variance of Q are: Mean: 7.14 x 10-3 Yariance: 6.43 x 10-4 9 System failure frequency due to SI pump maintenance beccmes: Mean: 3 x 8.13 x 10-4 x 7.14 x 10-3 = 1.74 x 10-5,

0. 2.1. 5 Other Causes The system does have several minimal cutsets in one compartment. The effects of external causes, fire or flood, are discussed in separate studies.,

Other causes such as errors in manufacturing, installation, and design are deemed to be of low frequencies because most of the system has been tested fre We use the S-factor to express these causes. We choose 10 guently.to 5 x 10-2 as the range for a g which yields a mean and variance of: Mean: 1.4 x 10-2 Yariance: 6.1 x 10-4 We use the same S-factor for valves and pumps. The frequency of all three SI pumps failing (using S-factor) is: Mean: 1.4 x 10-2 x 3,77 x 10-2 = 5.28 x 10-4

                                                                                              ~

21 ' 1271 A041681/1

The frequency of both MOVs 888 or both MOVs 822 failing to open (using S-factor) is: Mean: 1.4 x 10-2 x 1.51 x 10-3 = 2.10 x 10-5, The frequency of both recirculation pumps or ~both MOVs 1802 failing to operate (using S-factor) is: .

/

Mean: 1.4 x 10-2 (1.83 x 10-3 + 1.51 x 10-3) = 4.66 x 10-5, System failure will occur if RHR pumps are not realigned also. Then: Mean: 4.66 x 10-5 x 1.52 x 10-2 7,09 x 10-7,

0. 2.1. 6 System Unreliability Table 10 shows the results that have been derived for the mean values of the contributors to hi-head recirculation unreliability when the fan

'                          coolers are unavailable, and component cooling and all electric buses are available. Only the main contributors are used here for uncertainty analysis. The cathematical expression for the unreliability of the system is written in tems of unreliabilities or unavailabilities of

' dominant contributors. The human error distributions share the same state-of knowledge. Therefore, they are expressed in tems of a ' constant times a distribution. 3 2 30 SI

• 8IO SI + 20ggy)

O OHI-HEAD " OH1 + 0.1360g ) + 037 + 2030Y +SIM - e where Og ): Human error, failure to initiate switchover; a = 3.46 x 10-4, # =2 3.19 x 10 -6 , OMOY: MOV fails to operate:

                         -             a = 1. 51 x 10-3 , E2= 2.64 x 10-6                 ,

Q37: Unreliability of an SI pump in 24 hours: l see Section D.2.1.3 l 03;g: Maintenance on SI pumps: a = 8.13 x 10-4, $ 2= 6.22 x 10-8, B: S-factor: a = 1.4 x 10-2,$2 = 6.1 x 10-4 . Using DPD arithmetic, we find for OHI-HEAD'

   .         t-                                                                             ,

22 , 1271 A041681/1 . vs, -,- - , ,

                                                 =r      ww---m ---e ,e v _e-e---
                                                                          -          --~r

Mean: 4.10 x 10-3 Variance: 1.68 x 10-4 5th Percentile: 4.70 x 10-5 95th Percentile: 6.40 x 10-3 , , liedian: 4.70 x 10-4

0. 2. 2 Fan Cooler and Electric Bus SA Unavailable: Component Coolino and Electr'c Buses 2A, 3A, and 6A Available loss of electric bus 5A before safeguards actuation causes the failure of SI pump 31, recirculation pump 31, MOYs 888A, 822A, 885A, and 1802A.

Sin e 885A is inoperable, recirculation via the RHR pumps is not possible unless this valve is opened manually. Table 11 gives the cause table. Each item in this table is discussed hereafter. D.2.2.1 Human Error Contributions . The frequency of operator failure to establish hi-head recirculation is' evaluated in Section D.2.1.1. The same results apply here also. Loss of electric bus SA would not have significant effect on operator error rates because of a long time window.

• 0.2.2.2 Single Hardware Failures The dominant single element cutsets are: *

( e HPPLN6CE: pipe 60 rupture; mean = 1.44 x 10-7 i e JBS336BD: MCC bus 368 failure; mean = 2.00 x 10-6, e MOV 18028 fails to open; mean = 1.51 x 10-3, e. Manual valves 753A, F, Gtotal mean = 6 x 9 x 10-8.H, J, or K in closed position; e MOV 822B fails to open; mean = 1.51 x 10-3, D.2.2.3 !!ultiple Herdware Failures l The following multiple' failures would lead to system failure: e Recirculation pump 22 fails to run (mean 1.83 x 10-3) and - operators fail to open liOV 885A and align the RHR pumps for recirculation cooling. ' e 110V 888B fails to open (mean = 1.51 x 10-3) and operators fail to open one of the 110Vs 688A or 8880 manually. t., s Both SI pumps fail. . o l l' l l 23 l 1271 A041681/1 l -

The frequency' of human er_ror" portions of the first two events is judged to be lognomally distributed with the median at 0.1 and the error-factor at 3. The mean and variance are:

    -              -Mean:        1.25 x 10-1            e Variance: 8.78 x 10-3 Thus, the mean frequency of the first event is:

Mean: 1.83 x 10-3 x 1.25 x 10-1 = 2.29 x 10-4 The mean frequency of system MOV failure due to 888B failure and recovery ist Mear.: 1. 51 x 10-3 x 1.25 x 10-1 = 1.88 .x 10-4 , The frecuency of the event, that is the failure of both SI, is conputed in Section D.2.1.4. The mean and variance.are: Mean: 7.14 x 10-3 The contribution of .other multiple hardware failures to system unavailability is very small. D.2.2.4 Maintenance Co'ntribution If one SI pump is under maintenance and the other failed due to hardware i failures, hi-head recircul.ation muld be unavailable. The mean for system unavailability becomes (see Section for data): Mean: 2.00.x 8.13 x 10-4 x 3.77 x 10-2 = 6.13 x 10-5, D.2.2.5 Other Causes The discussions given in Section D.2.1.5 do not apply here; except for the SI pumps, because only one train of all the redundant trains is available. The resulting mean of the frequency of both SI pump failures due to other causes becomes': Mean: 1.40 x 10-2 x 3.77 x 10-2 = 5.28 x 10-4 D.2.2.6 System Unreliability - Table 11 shows the results that have been derived for the mean values of the contributors to hi-head recirculation unreliability when the fan coolers and electric bus 5A are unavailable and component cocling and - electric buses 2A, 3A, and 6A are available. Only the main contributors are addressed in the uncertainty analysis. The mathematical expression for the unreliability of the system in tems of the unreliabilities or ' unavailabilities of dominant contributors is: d

                                                                                             ~

24 ~ 1271 A041681/1

O g + 0.136 )g ~ 20MOV + ORCO H2 + OMOV 0 HI-HEAD =O) H2 + OSI

                         + 20373031 + B037 The tems are defined in Section D.2.1'.6 except for:           '

ORC: Unreliability of a recirculation pump in 24 hours;

                   ? = 1.83 x 10-3, g2 = g,91 x 10-5, OH2:      Human Error in Opening MOY 885A naqually and shifting to RHR pumps: a = 0.125; g2 = 8.78 x 10-3 The results of a DPD arithmetic for the unreliability of hi-head recirculation are:

a Mean: 1.15 x 10-2 Yariance: 6. 50 x 10-4 5th Percentile: 1.10 x 10-3 95th Percentile: 1.80 x 10-2

4. 20 x 10-3, Median:

0. 2. 3 Fan Coolers and Electric Bus 6A Unavailable and Conconent Cooling q and Electric Buses 2A, 3A, and 5A Available loss of electric bus 6A causes _the failure of SI pump 33, recirculation pump 32, RHR pump 32, MOVs 8888, 8223, 747, 885B, and 1802B. The cc,ditions here are similar to those of Section D.2.2. Therefore, the same results apply here also.

D.2.4 Fan Coolers and Electric Buses 2A and 3A Unavailabley Conoonent Cooling and Electric Buses 6A and 6A Available Loss of ' electric buses 2A and 3A at or before safeguards actuation cause the failure e' SI pump 32 and RHR pump 31. The situatinn here is very-similar to t in Section D.2.1. The only differences in the results are introduced through the SI pump unavailability due to nultiple hardware failures and maintenance plus hardware failure. Table 12 gives the cause table. The mean and variance of the frequency of hardware failure of both SI ' pumps,31 and 33 are (see Section D.2.1.4): Hean: 7.14 x 10-3 Yarfance: 6.43 x,10-4

                                                                                             ~

25 ' 1271 A041681/1 i

The mean of the unavailability of both SI~ pumps due to maintenance and hardware failure becomes: tiean: 2.00 x 8.13 x 10-4 x 3.77 x 10-2 = 6.13 x 10-5, System terns of unreliability the dominant is contributors computed by(the following see Table 12):expression which is in 2 OHI-HEAD " OH1 + 0.1360 3 ) + Q33+20jov+2031,3331+B(03g t + 20tiOVI - The terms are defined in Section D.2.1.6. Using DPD arithmetic, we find for OHI-HEAD

• liean: 8.18 x 10-1 Yariance: 6.39 x 10-4 5th Percentile: 1.20 x 10-4 .

95th Percentile: 1.60 x 10-2 Median: 9.00 x 10-4 D.2.5 Fan Coolers and Electric Buses 2A, 3A, and 5A (or 6A) Unavailablek conoonent Cooling and Eiec ric Bus 6A (or 5A) Available The components that may remain available under these. conditions are the 4 same as those given in Section D.2.3 except for SI punp. 31 (or 32) and RHR pump 31 (or both) . The mathematical expression for system unreliability becomes: QHI-HEAD " QH1 + 0.1360g) + QRC + 3Qn0y + Ost + Ostg. Credit is not given to manual valve manipulation because of high stress conditions (caused by bus failures). Compare this with that.given in Section D.2.2.6. All the terms are defined in Sections D.2.1.6 and D.2.2.6. Using DPD arithmetic on this expression, we find: Mean: 4.52 x 10-2 , Variance: 4.37 x 10-3

                            .Sth Percentile:    5.00 x 10-3 95th Percentile: 0.12 Median:             2.40 x 10-2 0         ( ,-                                                              .

G , , 1271 A041681/1 i-

D.2.6 Other Conditions When Fan-Coolers Are Unavailable If the electric buses SA and 6A, or ZA, 3A, EA, and 6A are unavailable, . then system failure is a certainty. Also, the same is true when cooponent cooling is unavailable.. D.2.7 . Fan Coolers, All Electric Buses, and Cocoonent Cooli_no Available The only. difference between this case and that of Section D.2.1 is that heat exchanger availability is not addressed here. Then component cooling affects the systecithrough the recirculation pumps only. Table 13 gives the cause table. D . 2. 7.1 Human Error' Contributions The frequency of operator failure to activate high pressure recirculation is given in Section D.2.1.1. Fan cooler availability does not have any effect on this probability distribution. D.2.7.2 Single-Hardware Failures . The only single element cutset is HPPLN60E. The mean and variance of - the frecuency for-this cutset was obtained in Section D.2.1.2: . Mean: 1.4 x 10-7 - Yariance: 4.2 x 10-13, If line 190 is opened and line'60 is isolated, the failure of the latter -C tculd be bypassed. This switchover requires opening of a canual valve. Our judgment is that the median frequency of failure is about 0.1 and the error factor is 3. Then, the mean and variance becoce: Mean: 0.12 . Variance: 8.80 x 10-3 The mean and variance of system failure due to a failure in line 60 is. obtained: Mean: 1.4 x 10-7 x 0.12 = 1.7 x 10-8 Yariance: 1.0 x 10-14 D . 2. 7. 3 11ultiple Hardware Feilures In Section D.2.1.3 a method is given for identifying the main contributors to cultiple hardrare failures. The sace approach is used here also. Similarly, operator error in switchover to RHR pumps (when recirculation punp's are failed) is incorporated in the input- data to the

          ,      RAS code, and the frequency of cutsets with repeated components is
  .    ( .-                                                            .-                                  .

27 1271 A041681/1

corrected. The significant 6.inical cutsets are given in Table 13. The frequency of one itCS is adjusted to incorporate the possibility of using line 190. e HMV88SAO. HMV8888Q , In Section 0.2.1.3, the mean and variance of the frequency lof two valves failing to open were obtained: Mean: 4.88 x 10-6 Yariance: 5.03 x 10-10, This failure. is sin.lar to failure of pipe 60; therefore, we should give credit to the fact that it may be bypassed through line 190. In Section D.2.7.2, we concluded that the mean .and variance of the ~, frequency of failure in using line 190 are: Mean: 0.12 Yariance: 8.80 x 10-3, The frequency of system failure yields: Mean: 0.12 x 4.88 x 10-6 = 5.86 x 10-7 D.2.7.4 liaintenance Contribution This case is similar to Section D.2.1.4 where only two sets of cocponents are the nain contributors: the SI purps and it0Vs 88SA and 8883. The mean frequency of system failure due to maintenance on SI pumps is the same as that obtained in Section D.2.1.a: Mean: 1.74 x 10-5, 0.2.7.5 Other Causes - The results of Section D.2.1.5 apply here also, except that only one pair of valves should be considered in this case. D. 2. 7. 6 System Unreliability The mathematical expression for hi-head recirculation unreliability when fan coolers, component cooling, and all electrical buses are available .. is written here in terms of the dominant contributors (see Table 13): 7HI-HEAD *O H1 + 0.1360g ) + Qfy + O$0V t OH4 + 3 OSIti 0 I+BQSI

                               +BO!!0V OH4.                                             -

28 - 1271 A041681/1

S fe The variables are defined in 5ection D.2.1.6 except for: Og4: Failure to establish recirculation ficw through line 190. a = 0.12; $2 = 8. 8 x 10-3, , DPD arithmetic on OHI-HEAD gives: - Mean: 4.05 x 10-3 Variance: 1.68 x 10-4 5th Percentile: 3.50 x 10-5 95th Perc'entile: 6.30 x 10-3 Median: 4.30 x 10-4 ' D.2.8 Electric Bus 6A Unavailable; Fan Coolers, Cenconent Cooling, and Electric Buses 2A, 3A, and 5A Available loss of electric bus 6A at or before safeguards actuation causes the failure of SI pump 33, recirculation punp 32, MOVs 8888, 8858, 747,

• and 1802B. This is similar to the conditions in Section D.2.2 except that the availability of MOVs 822A or 8228 does not affect the top event. Table 14 gives the cause table. It is very similar to Table 11.

The mathematical expression for system unreliability in terns of the a main contributors is: O HI-HEAD *OH1 + 0.136QH1^OMOV + ORC0 H2

• OMOVH2+OfI 0

                                 + 20SItt OSI + 80sI The results of a DPD arithmetic on this expression are:        ~

ltean:. 1.00 x 10-2 Yariance: 6.48 x 10-4 i Sth Percentile: 7.90 x 10-4 95th Percentile: 1.60 x 10-2 Median: 2.90 x 10-3, . D.2.9 Electric Bus EA Unavailable; Fan Cool' ers, Conconent Cooling, and Electric Buses 2A, 3A, and 6A Availeble 9 e 29 - 1271 A041681/1

less of electric bus'5A at.or before safeguards actuation causes the failure of SI pump 31, recirculation pump 31, MOVs 888A, 885A, 746, and 1802A. This is very. similar to the conditions of Section D.2.8. Table 15 gives the cause table for this case. System unreliability is also given in Section D.2.8.- D. 2.10 Electric Buses 2A and 3A Unavailable; Fan Coolers,-Component Cooling, and Electric Buses 5A and 6A Available Section D.2.4. discusses a similar case with the fan coolers unavailable. Table 12 applies here also except that heat-exchanger-related entries should be taken out and the possibility of using line 190 should be -incorporated. Table 16 is the result. The mathematical expression for system unreliability. is: 2 OHI-HEAD = Ogj + 0.1360H* OV Og4+037 + 20373 037 + B037

                                  + B0ft0V Og4 The tems are defined in Section D.2.1.6 and D.2.7.5.       Using DPD arithmetic we obtain:

Mean: 8.13 x 10-3 Variance: 6.45 x 10-4 5th Percentile: 1.00 x 10-4 C 95th Percentile: 1. 40 x 10-2 Median:- 8.70 x 10-4 D. 2.11 Other Conditions When Fan Coolers and Cocoonent Cooling Are Available If electric buses SA and 6A or 2A, 3A, 5A, and 6A are unavailable, then system failure is a certainty. . If electric buses-2A, 3A, and 6A (or electric buses 2A, 3A, and SA) are unavailable then fan coolers cannot be available. D. 2.12 Component Cooling Unavailable; Fan Coolers Available~ When the fan coolers are available, component cooling appears only in relation to the recirculation pump cooling. The auxiliary component cooling pumps act as a backup to the main (CCW) loop. The failure frequencies are given in Section . The ciean and variance of the unreliability of one pump in 24 hours are:

         ,            Hean:       1.65 x 10-5 x 24 + 1.36 x 10-3 = 1.76 x 10-3 Variance:   2.22 x 10-8 x (24)2 + 1.22 x 10-6     1,40 x 10-5,

, .. ( , . , C

                                                                                               ~

30 - 1271 A041681/1

The mean and variance of the unreliability of two pumps become: (1.76 x 10-3)2 + 1,40 x 10-5 = 1,71 x 10-5,

                                                           ~

11ean: This unreliability is due to hardware failu.res. For causes other than this, the S-factor approach is applied (see Section D.2.1.5 for detail s) . The mean of this contribution becomes: - Mean: 0.014 x 1.76 x 10-3 = 2.42 x 10-5, These frequencies are an order of aagnitude less than the total frequencies given in Section D.2.1.2 for the failure of one recirculation puap'. Therefore, the effect of component cooling availability can be dropped from the analysis when the fan coolers are. available. D 9 C e 6 e e t .' ' e 31 - 1271 A041681/1

E. LOW PRESSURE RECIRCULATICN E.1 FAULT TREE The top event is " Low Pressure Recirculation Fails to Provide 600 gpm

    ~

for 24 Hours." Figures 14 through 167 6 through 12, and 20 through 24 show the f ault tree for this event. The fault tree is constructed for the following conditions in addition to those centioned in Section C.1: e large or medium LOCA has occurred. e low presssure coolant injection has been comp 1'eted successfully; therefore, at least one of the four discharge headers is open. e Heat exc' hanger cooling is necessary. e Two out of three SI pumps can provide sufficient cooling if the < lo-head discharge headers are unavailable. e MOV 744 would not be closed on switch 3. In the event tree of large or medium LOCA, this event is coded as H. Table 17 gives the minimal cutsets (MCS) with one and two basic events when the house events are treated as basic events. The only single element cutset is the component cooling system. This fault tree is quantified under several conditions depending on the

• state of fan coolers, component cooling water system, and electric pcrer. The possibility of switchover to SI pumps due inability to establish containment spray recirculation, is not addressed here because core cooling takes priority. In case of failure of hi-head recirculation the two modes of opera'. ion (lo-head and containment spray recirculation) can be activated intermittently. Table 2 gives all possible combinations from these conditions. Also, it refers to the quantification section, the cause table, and the mean and variance of the frequency of the- top event.

E.2 OUANTIFICATION E.2.1 Fan Coolers Unavailable; Cocoonent Cooling and All Electric Buses Available The minical cutsets and the cause tables are given in Tables 17 and 18, respectively. E . 2.1.1 Human Error Contributions - In a large LOCA, the level in the RWST would drop to the low level alarm point in about 20 minutes. At this point, the tine vdndow is 20 minutes. Four operators (similar to small LOCA) would be in the control room by this ' time. They would still be recovering from the e 32 - 1271 A041681/1 .

l

          . initial very high stress conditions created by the LOCA. Similar to_a small LOCA, the two control beard operators would be doing the switchover. The SS would be checking other parts of the control ' board, and because' of the seriousness of the accident, he would be monitoring
          -the process of switchover closely. .The STA would not be involved in the specific detail; however, he rould be' monitoring the overall plant parameters.                                                -
                       ~

The three stages defined for a small LOCA apply here also. However, the timing is much shorter in this case. Operator related events are discussed in two parts: first, events that lead to system failure; second, events that lead to partial failures. Two operator-related events are identified that would lead to system failure. These are: e Failure'to initiate switchover. e Switch 5, in addition to switch 6, is turned to "on" position and no' ' corrective actions are taken within the available time. Three things help the operators to recogni::e that switchover should be initiated. First, operators would remember about the switchover from training. Second, the procedures would lead the operators to switchover. Third, the RUST low level alarm would alert the operators. A large LOCA is considered a high stress situation for the operators. The handbook equates this to emergencies in the military. It used the test results from simulated emergencies. It gives 0.25 as the point estimate for human error frequency. We interpret this as the frequency of error in one well-defined task for one operator. .The suggested g 5th and 95th percentiles are 0.03 and 0.75, respectively. The handbook suggests that human error frequency within a half-hour after a large LOCA decreases from unity to 0.1 (a point estimate) given that all automatic recovery systems function noma 11y. It would decrease to 0.25 (the human error frequency discussed earlier) if some systems do not function properly. It should be mentioned here that; switchover to the recirculation phase has always been initiated by the trainees on the simulator. Also, operators have extensive training on the simulator in coping with a large LOCA. Because of this, for switchover initiation only, ee divide the basic human error by half; 0.1/2 = 0.05. The dependencies among the operators are very much similar to that in a small LOCA. Using the dependency formulas, a point value for the frequency of. failure to initiate switchover becomes: 2 0.05 x 1 + 20. 05 x h + 6 x 0.05 7

                                                      = 9.1 x 10'# .

, 5 / We take this as the median and assign an error factor of 20. For lognomal distribution the mean and variance become: Mean: 4.75 x 10-3 Variance: 6.00 x 10-4 ' e 33 - 1271 A041681/1

The 5th and 95th percentiles are 4.55 x 10-5 and 1.82 x 10-2, re spectively. Note that this range includes other dependency levels; e.g. , if STA has zero dependence with the rest of the operators, the point value beccmes: 0.05 x 1 +.0.05 2 x 1 + 6 x 0.05 x 0.05 = 2.4 x 10-4.~ 1 In the second. event, the operators turn switch 5 to the "on" position which closes 110Vs 746 and 747 and later they turn switch 6 and trip the

                  .SI pumps. It is possible to restore these valves from the control board. The error may occur due to various reasons, e.g., errors by the operator at the control board in interpreting the instructions read to-

, him, or the operator that reads the instructions skips some lines. Thi s would be discovered when the flow to the cold legs is checked. The basic frequency of human error is 0.1. Using the dependence relationships a point value for the frequency of occurrence becomes: 0.1 I^ '1 = 0.055. 2 , This error may be discovered by all four operators within the remaining time window. In this case, it is assumed that the STA bas low ' dependence with the rest of the team. Thus a point estimate for the frequency of the first event becomes: 0.055 x 0.10 x 1 + 0.10 1 + 6 x - 0.10 x 1+ig20.1

• 2 x

7 to

                                                                                                  = 1. 00 x 10-4    .

We take this as the median and assign an error factor of 20. The legnormal distribution yields: Mean: 5.26 x 10-4 Yariance: 7.36 x 10-6, The 5th and 05th percentiles are 5.01 x 10-6 and 2.01 x 10-3, respectively. Note that this range inclues other dependency or basic error rates. For example, if STA is moderately dependent and the basic human error rate for recovery is 0.25, the point estinate becomes: 0.055 x 0.25 x 1 + f 25 x +6 x 0.25

                                                                                = 1.10 x 10-3   ,

Lo-head recirculation may also fail due to a combination of human error and other causes. The failure of the recirculation pumps due to human error is discussed in Section D.2.1.1. This has small impact on system unreliability. Human error on RHR pumps is significant. They have to be aligned manually (from the control room) to provide the recirculation flow when the recirculation pumps are not available.

  .     (,'

• 34 O

  '                1271 A041681/1

The operators can switch to the RHR pumps and establish the recirculating flow from the containment sucp. They have to reset the recirculation switch 3, also. k'e believe that, since the stress level would be very high due to failures in the recirculation pumps, the error rate for one operator is about 0.5 and the dependency among all four operators is very high. (HD). Then, a point value for the operators to fail to switch to the RHR pumps is: . .

                                   +

0.5 x 2

                                                = 0. a .

An error factor of 3 is chosen for this frequency. The mean and variance of lognornal distribution become: Mean: 0.26 Yariance: 3.9 x 10-2, E . 2.1. 2 Single Hardware Failures - There are no single element minimal cutsets. E . 2.1. 3 11 alt.iple Hardware Failures . The approach taken here is very similar to that explained in Section D. 2. ' .3. Table 18 enumerates the main contributors. They are: e Both recirculation pumps fail and operators fail' to switch to RHR punos. The mean of the unreliability of both recirculation pumps is found in Section D.2.1.3: liean: 1.02 x 10-4 The frequency of operator error is computed in Section E.2.1.1. Then systen failure frequency yields: liean: 1.02 x 10-4 x 0.26 = 2.65 x 10-5; e Both 110Ys 1802A and 18028 fail to open and operators fail to switch to RHR pumps. The mean and variance of the frequency of failure of two 110Vs are found in Section D.2.1.3: Mean: 4.88 x 10-6 Yariance: 5.03 x 10-10, Systen failure frequency yields: Mean: 4.88 x 10-6 x 0.26 = 1.27 x 10-6,

      ". e     110Vs 822A and 8223 fail to open. This failure node causes total

., t,. loss of cooling in the heat exchangers. . e 35 ., 1271 A041681/1

                   .       . . _ .       ,    -    _ . . , , . . . . . , _   m._ , , .     , . _ _ , - ,       . _a__   _
                                                                                                                          .m

E . 2.1. 4 Maintenance Contribu" tion Only the SI pumps are the main contributors here. The contribution of RHR-related components is dominated by operators' failure to switch over. The cutsets that are affected by maintenance consist of two-o'ut-of-three SI pumps.,one.of either MOV 747 or 638, and either M0Y 746 or 640. Section D.2.1.3 gives the unreliability of one SI pump due to hardware failure: Mean: 3.77 x 10-2 Variance: 4.35 x 10-3, and due to maintenance: ,, Mean: 8.13 x 10-4 Variance: 6. 22 x 10-8, Unreliability of two out of three SI pumps becomes: . Mean: 3 ( 3.77 x '10-2 x 8.13 x 10-4) = 9.20 x 10-5, The frequency for one MOY transfer closed (see Section ) yields: Mean: 9.15 x 10-8 c Yariance: 1.01 x 10-14 Mean of the frequency of two valves out of two pairs of valves failing to open is: Mean: 4 (9.15 x 10-8)2 + 1,01 x 10-14 = 7.35 x 10-14 Thus, the mean frequency for system failure due to maintenance is much less than 10-10, E . 2.1. 5 Other Causes The disc'ussions given in Section D.2.1.5 apply here also. The same S-factor can be used. The failure of all SI punps and both MOVs 888 does not cause the top event here. However, if both recirculation pumps . or both MOVs 1802 fail and RHR pumps are not realigned, then system failure would occur. The same is true if both MOVs 822A and 8223 fail to open. The frequency of both recirculation pumps or both MOVs 1802 failing to operete (using #-factor) is computed in Section D.2.1.5: Mean: 4.66 x 10-5, , 36

               ,1271 A041681/1

     ^

The:cean of system failure freuency is:

                                                                                                   ~

Mean: - 4.66 x 10-5 x 0.26 = 1. 21 x 10-5 4 The frequency of two MOVs (822A and 8223 in this case) failing to open is computed in Section D.2.1.5 (usingf_-factor). The mean is: Mean: 2.10 x 10-5, . E . 2.1. 6 System Urreliability - Table 18 shows the results that have been derived for the mean values of the contributors' to lo-head recirculation unavailability _ when'the fan coolers are unavailable and component cooling and all electric buses are availabl e. Only the main contributors are used here for uncertainty analysis. The mathematical expression for the system unreliability in terms of the dominant contributors is: < 2 O OLO-HEAD

• OH1 + 0.mgQ ) +Q AC H3+Of0VOH3 + 0 OY

                                                                      + B(ORC + OMOV   IOH3 + BOMOV where                                                                                                                  *
   ,                                           Og): Human error, failure to initiate switchover; a = 4.75 x 10-3, g2 = 6.0 x 10-4 e

ORC: Recirculation pump unreliability; a = 1.83 x 10-3, g2 , g,91 x 10-5 OH3: Human error, failure to switch to RHR pumps; a = 0. 26, g2 = 3.9 x 10-2 i . ! OM0y: MOV fails to operate; a = .1.51 x 10-3, g2 = 2. 64 x 10-6 B: #-factor; a = 1.4 x 10-2, $2= 6.1 x 10-4 Using DPD arithmetic, we find for Qto HEAD

• Mean: 5.32 x 10-3 l~

Va,riance: 1.43 x 10-4 I 5th Percentile: 5.00 x 10-5 l 95th Percentile: 1 40 x 10-2 Median: 2.10 x 10-3, - 37 -

l. ,

1271A041681/1 '  : l .

     .m ,   4 . - , - - -y -.vv      y--,r---             -is       . .-,m-1 m                       , , - - m._,.   . _ . - , . . -           , e

r E.2.2 Fan Coolers and Electric Bus 6A Unavailable; Comoonent Coolino and f.lectric Buses ZA, 3A, and 5A Available

                        ' Loss of electric. bus 6A at or before safeguards actuation causes the failure of recirculation pump 32, RHR. pump 32, SI pump 33, MOVs 88ES, 822B, 8858, and 1802B. Since 885B is electrically inoperable, recirculation via the RHR pumps is assumed not possible. Hewever, it may be opened manually within the.available time.- Table 19 gives the cause table. Each item in this table is discussed hereafter.                           j E . 2. 2.1 ~ Human Error Contributions The frequency of operator failere to establish lo-head recirculation is evaluated in:Section E.2.1.1. _ The discussions there apply to this case also. Loss of electric bus 6A would have some effect on operator error rates. The handbook increases the human error frequency to 0.25. We cuote from p.17-19: "if the automatic recovery systems function nomally to instigate the effects of the accident the error rate is 0.1. Otherwise, the error probability will- not decrease below 0.25 but will remain at that:value as long as the highly stressful conditions persist."                                                                   .

The discussions on human error in Section E.2.1.1 apply to this ' case also. Bus failure would probably occur at safeguards actuation. The . operators would immediately attempt to restore the bus from the control room. -In case of failure operation personnel would be dispatched to restore the bus locally. Only one, operator would be occupied with bus ' restoration for the first few minutes. By the time of switchover c initiation all four operators would be in positions'similar to those described in Sections E.2.1.1 except that the SS would be receiving telephone calls regarding the failed bus. The levels of dependency are taken as identical to those in Section E.2.1.1. Similarly, the' basic human error rate is halved for failure to initiate switchover. A point value for the frecuency of failure to initiate switchover becomes: 0.125 x 1 + p125 x O C 6 x-0.125 f = 4.4 x 10-3 ,

n. (- 7 j We take this as the median and 20 for the error factor. The lognomal distribution yields :

Mean: 2.31 x 10-2 Yariance: 1.42 x 10-2 Error on switch 5 is discussed in Section E.2.1.1. The same arguments apply here also, except that the basic human error frecuency is 0.25 in this case. Moderate dependence is given to STA. A point value for the' conditional frecuency of error on switch 5 is:

,            y                                                                .

S 38 . . '1271 A042081/2

I+ *6 O.25 'x 2

                                       = 0.156.

A point value for _the conditional frequency of failure to discover the error is: 0.25 x 1 + 0.25 x[1+6x0.25}2 = 1.99 x 10-2 , 2 \ 1 j Then a. point value for the unconditional frequency of error on switch 5 is: 0.156 x 0.0199 = 3.11 x 10-3, Taking this as the median and assigning an error factor of 20 for a lognomal distribution we obtain: Mean: 1.63 x 10-2 Variance: 7.10 x 10-3, . E.2.2.2 Other Causes The only single event cutsets that have some impact on system , unreliability are: Mean 9 e Recirculation pump 31 = 1.83 x 10-2' e MOV 1802A = 1.50 x 10-3 s MOV 822A = 1. 50 x 10-3, Unavailabilities of the components due to naintenance (see Section D.2.1.5 for details) do not contribute significantly because l they are at least two orders of magnitude smaller than the total l contribution of human error. ( .E.2.2.3 System Unavailability l DPD arithmetic is used to sum the distributions given in Sections E.2.2.1 and E.2.2.2. The mathematical expression used for system unreliability is: OLO-HEAD " OH2 + 0.7060g+ ORC + 20110V ,

         .~

l. . c- -

I _ 39 1271 A041681/1

where OH2 = Human Error, failure to initiate switchover; a = 2.31 x 10-2 ,

                                 # 2= 1,.42 x 10-2  ,                              ,

The other terms are defined in Section E.2.1.6. The unreliability of lo-head recirculation in 24 hours after a large or medium LOCA has the following parameters: Mean: 4.42 x 10-2 Yariance: 5.12 x 10-3 5th Percentile: 1.90 x 10-3 95th Percentile: 0.11

                          !!edian:             2.30 x 10-2, E.2.3 Fan Coolers and Electric Bus SA Unavailable; Component Cooling and Electric Buses 2A, 3A, and 6A Available                        .

Loss of electric bus SA causes the failure of recirculation pump 31, RHR pump 32, SI pumps 31 and 32, and 110Vs 888A, 822A, 885A, and 1802A. The situation here is almost identical to that described.in Section E.2.2-vtere bus 6A is unaveilable. The same discussions and results apply to 5 this case also. See Section E.2.2.3 for the distribution of system unavail ability. E.2.4 Fan Coolers and Electric Buses 2A and 3A Unavailable; Cocoonent Cooling and Electric duses 5A and 6A Available loss of electric buses 2A and 3A causes the failure of SI pump 32 and RHR pump 31. The situation here is very similar to that described in Section E.2.1 because these pumps (SI 32 and RHR 31) have little impact on system unavailability. Hoeever, this event would affect the operators. The results of Section E.2.2.1 apply here also. Then the system unreliability is the sum of the two dependent distributions defined in that section because other causes do not contribute significantly. The results are: Mean: 3.94 x 10-2 Yariance: 7.53 x 10-3 , 5th Percentile: 2.60 x 10-4 95th Percentile: 0.1 06

                                                  ~
    . s,-             Median:             7. 50 x 10-3,              ,

0

   -                1271 A041681/1

    .    .. E.2.5 Fan Coolers and Electric Buses 2A, 3A, and 6A (or SA)

Unavailable; Cononnent Coolina and Electric Bus 5A (or 6A) Available The components that would be inoperable are the same as those given in Sections E.2.2 and E.2.3 (or E.2.4). The stress level on the operators would be very high. We judge that the frequency distributions given in Section E.2.2.1 are sufficiently conservative and ' apply to'this case also. See Section E.2.2.3 for the results. E.2.6 Other Conditions When Fan Coolers are Unavailable If electric buses SA and 6A or 2A, 3A, SA, and 6A are unavailable, then system failure is a certainty. The same is true when component cooling is unavailable. E.2.7 All Electric Buses, Fan' Coolers, and'Cocoonent Cooling Available The only difference between this case and that of Section E.2.1 is that heat exchanger cooling availability is not questioned here. Table 19 gives the cause table. It is derived from Table 18 (heat exchanger-related events are deleted). The impact of MOVs 822A and 8 to systen unreliability is minimal. The mean frequency of two 110Vs inoperable is (see Section 0.2.1.3): liean: 4.88 x 10-6, This is auch smaller than the mean unreliability of the system. Then, the results of Section E.2.1.6 apply to this case also. C E.2.8 Other Conditions When Fan Coolers Are Available For different combinations of electric bus availability, the systen has already been analyzed in Sections E.2.2 through E.2.5 und .. the conditions of fan cooler unavailability and component cooling availability. In Section E.2.3, we can see that M0V 822A has very small inpact on systen unreliability. Then, the results of Sections E.2.2 i through E.2.5 apply to this case (i.e., fan coolers available) also. I When electric buses SA. and 6A are unavailable, system failure is a certainty. If component cooling is unavailable, then recirculation pump. cooling is , conpletely dependent on auxiliary component cooling pump

i. unavail ability. In Section D.2.13, we found that the mean of the l reliability of two of these pumps is:

Hean: 1.84 x 10-5, N

  . Q                                                          .

41 1271 A041681/1 t

4

    '       *           ~

l' The.-saae failure mode may oc6ur'due to comon cause. Using S-factor, we obtained -(see Section D.2.13): Mean: 2.42 x 10-5, These are much smaller than the human error. contribution. Therefore, the effect of component cooling availability can be dropped from the analysis .when the fan coolers are available. , 4 J f + . F ( . A O s i l-I t 4 5 O 42 1271 A041681/1

        ,:      ...           ~ F.

CONTAINMENT SPRAY RECIRCULATION-F.1 FAULT TREE The fault tree for the failure of containment spray recirculatio n-is shown in Figures 13, 5 through 12, and 20 through

                               " Failure to Establish Containment Spray Recirculation "' The f

24. . The is based Section C: on the following conditions in -ddition to aultthose tree mentip n'

e Containment spray has been completed successfully, e Fan would coolers are unavailable (because otherwisery not be necessary). containment h - e Component cooling is available. e Backflow into the containment spray system is not considered ~ In the event tree of large or medium LOCA, this event is ' coded a . This sequence mode of. operation is activated manually after the eight-switc is completed. - HOVs 638 and 640. Operators open MOVs- 889A and 8898 and throttle-Table 20 gives _the minimal cutsets (MCS) with one sand and two eleme all house events treated as basic events. electrical buses 6A, 36A, and 36B are single Similarly, This leads elem g recirculation is not available.to the failure of containment However oolingspray rec recirculation can only be caused by compo,nents upstream of the hea exchan phase (gers because core cooling has been successful during the infectio i.e., at least one path from the heat.exchangers to the cold l is available). The components located upstream of the heat'exchangers are sharedspray). containment between these two modes of operation (core coolf'ng and leads to the failure of containment spray recirculation.Therefor The availability of core' cooling recirculation means that there is sufficient and substantially subcooled (relative to the pressure in containmentThus, exchangers. atmosphere) if one of MOVs flow in the outlet of one of the heat i spray recirculation is a success. 889A or B is opened then containment flow in the spray nozzles (sump water not cooled), the containm pressure vill not rise substantially.

- provides more cooling than core heat generation.The available heat exchanger Therefore, subcooled water would be discharged into the sump. Hot flow into the nozzles ca occur.when the other trainone losesofcooling MOVscapability. 889A or 8 fail to open and the heat exchange electric buses SA, 6A, 36A, or 368. This can be caused by is the simultaneous failure of HOVs 889A and B.Thus, the only minimal cutset here discounted because of low frequencies of failure. Nozzle failures are 43 .

1271A041681/1

The system is quantified under two conditions only, namely, both electrical buses are available and one electric bus EA or SA is available. Under other conditions system status can be determined with certainty . Table 3 summarizes the results for all the cases. F.2 QUANTIFICATION - F.2.1 All Electric Buses Available Table 21 gives the cause table. Each item of this table is discussed hereafter.- F.2.1.1 Human. Error Contributions Containment spray recirculation is' aligned inmediately after core cooling recirculation alignment is completed successfully. This (the successful realignment) may have a reassuring effect on the operators and reduce their error rates. The handbook suggests 0.1 for the error rate of one operator 30 minutes after a large LOCA. In Section E.2.1.1, the dependencies among the operators are given. Two events must occur for the operators to ignore containment spray recircul ation. First, two of the operators (HD) do not follow the procedure beyond the core cooling switchover. Second, all four operators do not recognize the need for containment spray reci rcul ation. The frequency of the first one is: 0.1

                                     =  0.055.

1 '2 The conditional frequency of the second event, given that the first one has occurred, is judged to be 0.01. Then, a point value 'for the , frequency of system failure would be: 0.055 x 0.01 = 5.5 x 10-4 We take this point estimate as the median value and assign an error factor of 10 for the spread. For lognormal distribution, the mean and variance become: Mean: 1.5 x 10-3 Variance: 1. 3 x 10-5, F . 2.1. 2 Single Hardware Failures Tiere are no single element cutsets. . F . 2.1. 3 Hultiple' Hardware Failures The staultaneous f ailure of MOVs 889A and 8898 is the dominant s*. contributor when hardware failures are considered. The mean and ): variance of one valve f ailing to open are (data from Section d 44 . - 1271 A041681/1

l Mean: 1. 50 x 10-3 Variance: 2.63 x 10-6, The mean frequency for both valves failing to open becomes: Mean: (1. 50 x 10-3)2 + 2.63 x 10-6 = 4.88 x 10-6, , The remajning contributors are at least an order of magnitude smaller than 10 . F . 2.1. 4 Maintenance Contribution liaintenance does not have any effect on this event because MOVs 889A and 889B do not undergo maintenance during nomal operation. Maintenance on other components would affect. core cooling recirculaton, which is available when the availability of containment spray recirculation is questioned. F . 2.1. 5 Other Causes - The discussions given in Section D.2.1.5 apply to this case also. . The ' S-factor method can be used for the pair of tiOVs mentioned in Section F.2.1.3. For one pair of t10Vs, from Section D.2.1.5, we find: . Mean: 2.10 x 10-5, F. 2.1. 6 System Unavailability , t Table 22 shows the results that have been derived fcr the mean values of the contributors to containment spray recirculation unavailability when the fan coolers are unavailable and component cooling and all electric buses are available. Only the main contributors are used here for uncertainty analysis. The mathematical expression for the

              - unavailability of the system in tems of the unavailabilities of the dominant contributors is:

OCS " OH1 + O!!OV

• B QMOV vhere:

OH1 : Human error, failure to intitiate containment spray recirculation; a = 1.50 x 10-3, g2 = 1.30 x 10-5 Ot10V: MOV fails to operate - a = 1. 51 x 10-3, g2 = 2.64 x 10-6 B: S-factor; a = 1.40 x 10-2, p2 = 6.10 x 10-4 . c.-

• m 45 .

1271 A041681/1

                        ,   ,   , . . - _ _ _ . _          e rw -

Using DPD arithmetic we find f-or Ocs: Mea'n : 1.50 x 10-3 Variance: 1.31 x 10-5 - 5th Percentile: 5.50 x 10-5 95th Percentile: 5.50 x 10-3 , Median: 5.50 x 10-4 F.2.2 Electric Bus SA f or 6A) Unavailable Loss of elect?ric bus SA (or 6A) causes inoperability in MOVs 889A and 822A (or MOVs 889B and 8223 for 6A). System availability is dependent on one train only. Table 22 gives the cause table. , F.2.2.1 Human Error Contributions In Section E.2.2.1 operator error rates are increased because some of their attention would be drawn toward restoring the lost bus. We think that this increase does not apply to error rates-on containment spray , recirculation because core cooling recirculation is established successfully and it has some reassuring effect on the operators. Then we can use the results of Section F.2.1.1 for this case also. F.2.2.2 Single Hardware Failures c The dcainant single element cutset is the failure of MOV 8893 (for 6A it - would be MOV 889A). The frecuency of MOV failure to operate is given in Section . _F.2.2.3 Hultiple Hardware Failures All multiple hardware contributors to the unavailability .of TOP

                                                                               "    event are of the order 10-b or lower.

F.2.2.4 ' Maintenance Contribution Maintenance does not have any effect (see Section F.2.1.4). F.2.2.5 Other Causes The discussions given in Section F.2.1.5 do not apply here because only one train of the redundant trains is available. . F.2.2'.6 System Unavailability Table 22 shows the results that have been derived for the mean values of the contributors to containment spray recirculation unavailability wh,en the fan coolers and electric bus SA are unavailable and component 1 46 ] 1271 A041781/1 ', f .

cooling and electric buses' EA, 3A, and 6A are available. Only the main contributors are used here for uncertainty analysis. The_ results of a DPD arithmetic for the unavailabilty.of hi-head recirculation are: 11ean: - 3.00 x 10-3 Variance: 8.90 x 10-5 , 5th Percentile: g4'. 00 x 10-4 ' . 95th Percentile: 7.00 x 10-3 Median: 2.00 x 10-3, F.2.3 Other. conditions

             -See Table 3 for the effect of other conditions.                                ,

9 t G e e k S e 4 l e 47 , , i 1271 A041681/1

G. HOT LEG RECIRCULATION The fault tree for this event is given in Figures 18 through 26 and 7 through 12. The top event is " Failure to Establish Hot Leg Recirculation." The fault tree is constructed based on the following conditions in addition' to those of Section C.1: e large or medium LOCA has occurred. e RCS pressure is below 170 psig. e One SI pump.can provide sufficient coolant flow. e SI pumps have to~ restart. e Contairnent spray is not necessary. e At least one sump is not blocked. Hot leg recirculation is questioned only when core cooling recirculation has been successful. This means that recirculation flow up to the suction side of the SI pumps is available. Then, the MCS should include the SI pumps, MOVs 856B, 856G, 888A, and 8888,. The time to initiate hot leg recirculation is very flexible. Therefore, it is believed that conponents outside the containment can be restored (if they fail) without great delay in switchover to hot leg recirculation. Thus, the only failure that we should be concerned with is failure of MOVs 856B and 856F to open. The frequency of two valves f ailing to operate is obtained in Section D.2.1.3. The mean is: . Mean: A.88 x 10-6, The valves may fail due to causes cornon to both, such as errors in

                          -procedures, manufacturing, installation, and design.

In Section 0.2.1.5, the frequency of two MOVs failing is computed using S-factor. The mean is: Mean: 2.10 x 10-5 Unavailability of hot leg recirculation is the sum of these two '. distributions. Using DPD arithmetic, we obtain: Mean: 2.'57 x 10-5' Variance: 2.00 x 10-9 5th Percentile: 5.30 x 10-7 95th Percentile: 6.90 x 10-5 Median: 8.10 x 10-6, , If one of electric buses SA or 6A is unavailable, then system success is l based on one MOV only. Table 4 shows sy' stem unavailability for these Cases. ( . t. , *. , l

                                                                                                               ~

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o. TABLE I (continued)

SUMMARY

'0F Tile RESULTS FOR llI-ilEAD RECIRCULATION (SMALL LOCA) t ns ansfe '
                              ,     q gree                     Data on Systee Unreliability in 24 llours Section lio. Tahle glo.
                                                                                                                      ~ 14ain Contributors         for             for Av i     le?    Ava a le7                   Ilean       Variance        5th           fledian      95tli                         Quantification 'Cause.lable fes             .            2A, 34,  1.00 a 10-2   6.48 a 10-4 7.9 a 10-4     2.9 a 10-3  1.6 a 10-2    lisrdinre f ailures    0.2.8 14 y,                                     54                                                                            In all SI puiaps:

o .aean = 1.14 a 10 3 Yes - 24, 34, 1.00 a 10-2 6.48 a 10-4 7.9 a 10 2.9 a 10-3 1.6 a 10-2 liardware failures 0.2.9 45 6A in all $1 puivs: g mean.* 7.14 a 10-3 Tes - 54, 6A 8.13 a 10-3 6.45 a 10-4 1.0 a 10-4 8. 7 a 10-4 1.4 a 10-2 liardware failures 0.2.10 16 in all SI puiys; mean = 7.14 a 10-3 4 s . k 12014040081/1 2,_

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O en m

                       .e.d. on                   .g          m.m             o        e        o                               e   C 9" E                        *          -            af      *T        er             af        af     *C     O C O                       .,T,e       at           N       N         sn            en        w       N      x Ob t.# h e   k ,*

• 53 i

1 . l t

e TABLE 5 PCWER SUPPLIES FOR THE RECIRCULATION SYSTEM CCMPONENTS Motor-Operated Valve Power Supplies Valve Designator MCC Bus Yalve Designator CC Bus . 638 36B 856F 36B 640 36A 833 36B 744 36A 885A 36A 74.5A 36B 885B 36B 745B 36A 888A 36A 746 36A 8888 36B 747 36A 889A 36A - 822A 36A 889B 36B 822B 368 899A 36B 856A 36A 899B 36B 856B 36B 1802A 36A 856C 36A 18028 36B 8560 36B 1869A 36A . 856E 36A 1869B 368 Pump Power Supplies Pump AC Bus DC Bus RHR 31 3A $3 RHR 32 6A 32 SI 31 SA 31 SI 32 2A 33

               -           SI 33                                     6A     32 Recirculation 31                          SA     31 Recirculation 32                          6A     32 Auxiliary Component Cooling 31           36A      -

Auxiliary Component Cooling 32 368 - Auxiliary Component Cooling 33 36A - Auxiliary Component Cooling 34 36B - - 1281 A 4 i 54 .- 1281 A032081

                                          ~.

TABLE 6 TEST REOUIREFENTS FOR ihE RECIRCL'LATION SYSTEM COMPONENTS Valve Action e Fr ecuency, . MOVs 744 verify open (Control Roem) monthly stroke test refueling verify open cold S/D 745 A,B stroke test (Control Room) cuarterly verify open monthly verify open . cold S/D , 746 stroke. refueling verify cpen cold S/D monthly ~ 747 ~ stroke refueling. ' verify open cold S/D

                                                '                        monthly 822 A,B        stroke test                  refueling verify operable              cold S/D e

856 A,C,0,E verify open (CCR) mentnly

                  .          F,H,J,K        verify open                  cuarterly stroke test                  unscheculed refueling 856 B,G        verify closed (CCR)          monthly stroke test and              cold S/D-interlock test stroke test                  refueling l                              883           verify closed                monthly 885 A,B       verify closed                monthly strcke test and              Quarterly direct observation 888 A,B        verify closed               monthly stroke test and             cuarterly direct observation                             '

stroke refuelino stroke refueling

                              ~                                                                        .

55 - 1281A040881/1 J

                                                                                                    ~~

TABLE 6 (continvec) TEST RECUIREMENTS FOR THE' RECIRCULATION SYSTEM COMPCNENTS Valve Action Frecuency 889 A,8 ' verify closed monthly stroke test cuarterly stroke test refueling 899 A,B verify open monthly 1802 A,B verify'open _ cold S/D. verify closed- monthly stroke test cuarterly verify closed refueling 1805 stroke test refueling-verify cpen 1869 A,B ' monthly 638 stroke test' ouarterly verify open . cold S/D 640- stroke test cuarterly . verify open cold S/0 Manual Valves , t' 735 A,B verify open renthly 739 A,8 verify cpen contnly 751 A,B verify open montnly 752 A,8 verify open~ mcnthly 753 A,B,C,...,H verify open montnly 818 A,B - - 820 A,B - - 846 verify open monthly 1863' - - Check Valves 738 A,8 open on demand monthly 741 refueling 755 A,B cpen on demand monthly refueling ._ - ( .* , Dl 56 , 1281A040881/1 -

                                    -                                                                     1

       ,  ,,                                  TABLE 6 (continued)'

TEST REQUIREMENTS FOR THE RECIRCULATION SYSTEf1 CCl1PONENTS Valve Action Frecuency , 857'A,B,...,W 1eakage test refueling 895 A,B,C,D leakage test unscheduled 897 A,B,C,D leakage test unscheduled 838 A,B,C,D- leakage test unscheduled-open on demand refueling Level Indicators The level indicators for containment and . recirculation sumps are tested for operability at every refueling (PT-R1, PT-R2). , c. Pumps Pucp Action Frecuency Test Name RHR 31, 32 Run for 15 to 30 monthly PT-M18 minutes

                                          - Run for long period      cold S/D SI 31, 32, 33               Run for 15 to 30          monthly           PT-M16 ninutes Recirculation               Run for 15 to 30          refueling _       PT-R13 31 , 3 2                      minutes Auxiliary Com-              Run for 15 to 30        ,

monthly ponent Cooling minutes 31, 32, 33, 34 e L ,' ' 1281 A042081/1 57

                                                                                                                  ]
                                    ,-v                    --   y-    ,-          w     -             -,9.--  -   ,

e

                                                                                                                                                 ~

i IABLE'7 ' ., FAILURE N00E OF COMP 0llEllTS AND TilEIR CODES USED IN Tile FAULT TREES Data.

                              '                                                                                                  "r e Component                Failure Mode                                         Mean            Variance                    2-2
                                                .             In kault free                                               To e (item)

Check Valves 886(A,B) Stuck closed ECY886(A,B)C 6.9) x 10-5 1,03 x 10-8 3 755(A,B) - UCY755( A,B)C 4 741 ECV-741C 738(A,B) ECV738( A,B)C 897( A,0,C,0) ECV897( A,B ,C,0)C 838(A,B,C,0) ECVB3B( A,B,C,0)C , 857( A,B,F,M) ilCV857( A,B ,F ,M)C

 $                                Leakage                     ECV895( A,B,C,0)L        6.91 x 10-7       4.87 x 10-13             4 895( A,B ,C,0)

Manual Valve 820( A,0) Inadvertently closed UXV820( A,B)C 9.15 x 10-0 1.01 x 10-14 1 818(A,B,C,0) UXV818(A,B,C,0)C 751( A,B) UXY751( A,B)C 752( A,0) UXV752( A,B)C 753( A,B ,. . . .ll) UXV753( A,B ,. .. ll) 739( A,B) EXV739( A,B)C 735(A,B) EXV735(A,B)C 846 Not closed by the i EXV-8463 (see text) .

1863 operator during EXV18630 (see text) -

accident s 1201 A040881/1

 '**   .                                                                 p

o FABLE 7 (continued) FAILURE H0DE OF COMPONENTS AND TiiEIR CODES USED IN Tile FAULT TREES Data Component Failure Mode "*3" ##I*"C' Tab 2-2

                      ,                             In     ul t ree

( i tem) HOVs 856(A,C,D,E) Does not close due liMV856( A,C,0,E )X 1.51 x 10-3 2.64 x.10-6 6 to mechanical failure 888(A,B) Does not open due to llMV808(A,B)Q 1.51 x 10-3 2.64 x 10-6 6 889(A,B) mechanical f ailure CMV889( A,B)Q 822( A,B) UMV822( A,B)Q 885(A,0) EMV885(A,0)Q ' 856(0,F) It4V856(B ,F)Q 802( A,B) EHV802( A,B)Q 883 Transfers open due EMV-8830 9.87 x'10-8 4,33 x 10-12 -7 5 to mechanical failure 745( A,B) Transfers closed due EMV745(A,B)C 9.15 x .10-8 1.01 x 10-14 1 744 to mechanical failure EHV744-C 630 EMV-638C 640 . EMV-640C 746 EltV-746C 747 EHV-747C 899( A,B) EMV-899(A,B)C 1869( A,B) EHV-869( A,B)C Pumps . RilR( 31,32) Fails when running.or EPitRil(31,32)S . 1.50 x 10-4/ile 1.74 x 10-8/hr2 14 RECIRC(31,32) fails to restart, EPHRC(31,32)S 1.96 x 10-5/hr 1.70 x 10-7/hr2- 18 S1(31,32,33) includes motor and EPMSl(31,32,33)5 1.79 x 10-3/hr 4.77 x 10-5/hr2 13 Auxiliary Component all other related EPMCC(31,32,33,34)5 1.65 x 10-5/hr 2.22 x 10-8/hr2 16 Cooling (31,32,33,34) components that are

                        .      at pump location 1281A040881/1 m _

o TABLE 7 (continued)- y

                 .            FAILURE H0DE OF COPP0NENTS AND TilElit CODES USED IN Tile FAULT TREES Data f

Component Failure Mode in altiree Mean Variance T 222

                                                                                                          ,      (item)

Pump Mators RilR(31,32) Falls when running EMORil(31,32)S 1.36 x 10-3 1.22 x 10-6 11 RECIRC(31,32) or fails to restart, EMORC(31,32)S S1(31,32,33) includes all com- EMOSI(31,32,33)S Aux 11iary Component ponents'that are not EMOCC(31,32,33,34)S ~ Cooling (31,32,33,34) at pump location Pipes g No. 60 Plugged or breached ilPPLN60E 8.60 x 10-10/hr WASit-1400 No. 361 IIPPL361E 8.60 x 10-10/hr WASil-1400 Noncomponent Events Containment Sump Blockage of gratings ECNISUFP 5.00 x 10-5 C.3 of this section Recirculation Sump Blockage of gratings ERECSUFP, 5.00 x 10-5 C.3 of this section Component Cooling System System failure UCCWFAll llouse Event Interlock Circuitry ' 856(0,G) Interlock fails to ll856(0,G)ILC (see text)

                              .give permissive sig-                              .

nal to open 856-valves 1281A032681

l

• e TABLE 7 (continued)

FAILURE MODE OF COMPONENTS AND TilEIR CODES USED IN TiiE FAULT TREES-Data Component Failure Mode $ce Mean Variance- Ta$eU$2-2 in F ul

                                                                                                                                           .              (item)

Control Circuitry for Pumps RilR(31,32) Falls to provide. ECNTRil(31,32)S has been RECIRC(31,32) start signal or ECNTRC(31,32)S included as c2 S1(31,32,33) gives inadvertent ECNTS!(31,32,33)5 part of the pump Auxiliary Component stop signal ECNICC(31,32,33,34)S Cooling (31;32,33,34) Control Circuitry for Valves 856(k,C,D,E) Falls to provide llCilT856( A,C,0,E) has been . close signal Included as part of the MOV 883 Inadvertently opans ECNT-883 , the valve 808(A,B) Fails to provide llCNT888(A,B) 889(A,B) open signal CCNIU89(A,B) - 822(A,B) UCNI822(A,B) 885(A,B) ECitTU85( A,B) -

                                '856(B F)                                                        llCNf856(B,F)     -                                                 -

802(A,B) ECHI802(A,B)

                                      ..                                                                 m.

e TABLE 7 (continued) FAILURE MODE OF COMPONENTS AND TilEIR CODES USED .IN TiiE FAULT TREES Data

                                                              $                                 ariance Component               Failure Mode                                    can       .

Tab e 1 2-2 In F ult ree (item) 745(A,8)* Inadvertently closes ECNT-745(A,B) 744 the valve ECHT-744 746 ECNT-746 747 ECNT-747 638 ECHT-630 640 ECHT-640 ai 899(A,B) ECNT-899(A,B) 1869(A,B) ECNT-869(A,B) s Electric Power . Dus 2A Insufficient power JBS-32AD llouse E, vent Bus 3A J05-33AD Dus SA JBS-35AD Bus 6A J05-36AD DC Power Panel 31 4BS-321D DC Power Panel 32 4115-322D DC Power Panel 33 4115-323D DC Power Panel 34 405-324D

• e MCC 36A JUS 336AD
• MCC 360 JUS 336110 1281A 6

e

i TAULE 8 . SYSTEM EFFECTS OF PIPE FAILURE

                                                                                                                 "       Connents Pipe Section    Djamete       System Failure     0 11    Syst in    fnftitL Failure 10       Partial, RilR pumps         Jh) .           No     Would be detected No 293 (down-                                                                     during refueling stream of recir-               can be used.

outage only. i culation pumps). Partial; if it is Yes, LPIS No Would be detected No. 9 (crosstic 10 within one week, ' between the RilR isolated by.745 heat exchangers, - valves, then one it can also be iso-m the connecting heat exchanger will lated. T*

• pipes to low be inef fective.

s pressure pumps). Partial failure Yes, llPIS No Would be detected No. 60 (connect- 8 within one week. ing line between of hi-head SI pumps and RilR recirculation,

                               , heat exchangers).               if the break                                                                                     ,

is downsteam of ' 888 valves. No. 359 (cross- 10 Partial failure of Yes, LPIS No Would be detected tie between the low pressure within one week. lo-head discharge recirculation, SI

• lines). pumps can be used.

l }281A ( $ 4

                                                                                                                                                                      ~

TABLE 8.(continued) SYSTEM EFFECTS OF PIPE FAILURE Potential For I System Failure Other System Pipe Section fj'nh Failure Event LOCA No.10, 57 (suction 18 Partial, rectr- Yes, LPIS No Would be detected to RilR). culation pumps within one week. can be used. No. 351, 352, 353, 10 Partial. No Yes, large LOCA 350 (cold leg discharge,lo-head). 37 No.16,16A, 753, 2 Partial, can be No Yes, small LOCA 754 (cold leg dis- isolated. charge, hi-head). No. 56, 843 '(hot leg 2 Partial, can be No Yes, small LOCA

                                             ' discharge).                                    isolated.

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                                              ^

e TABLE 10 , CAUSES AND FREQUENCY OF FAILURE OF lli-ilEA0 RECIRCULATION WITil FAN COOLERS i UNAVAILABLE; C0lfGIETIT C001 GCAlTiTALL ELECTRICAL BUSES AVAILABLE Effects Cause Mean Initiating Component System Other Systems Event Operator Error Failure to initiate 3.46 x 10-4 All Falls No effect No effect switchover. Switch No. 6 is 4.72 x 10-5 SI pumps stop Falls No effect No effect ' turned to "on" post- . o, tion and no recovery actions are taken. 6 liardware Single element cutsets. Pige No. 60 rupture 1.44 x 10-7 Pipe No. 60 Falls No effect No effect

            ~

l (5 ). Multiple failures. Mechanical failure in 1.56 x 10-6 Reci rculation Fail s No effect No ef fect

                                                            pumps 31 and both recirculation

• pumps and operator 32 and all crror in switching to RilR subsystems RilR pumps. ,

1 9 1281 A040881/1 . L

• e

TABLE 10 (continued) CAUSES Ad0 FREQUENCY OF FAILURE OF lil-ilEAD RECIRCULATI0tl WITil FAN COOLERS UdAVAILABLE; C0ftPOMENT C001 IIIG AND ALL ELECTRICAL BUSES AVAILA3LE Effects Cause Mean

                                                                                                                -Ini tiating Component       System        Other Systems  ' Event All three SI pumps fall. 3.11 x 10-3        51 pumps 31,        Fall s          No effect     No effect 32, and 33 HOVs 888A and 8883         4.88 x 10-C      H0Vs 888A           Falls           No effect     No effect do not open.                                and 8880 MOVs 822A and 8220         4.88 x 10-6      tiOVs 822A          Falls           No effect     No effect g;           do not open.                                and 8228 Testing                             NR'*           NR*          No effect           NR*         No effect Maintenance and liardware Maintenahce on one SI      1.74 x 10-5      All three 51        Falls           No effect     No effect pump and mechanical                         pumps unavail-failure of the other                        able two.                                                -

Other Causes See Section 0.2.1.5 5.50 x 10-4 SI pumps or Falls 7 7 for details. M0Ys 808. Total frequency of 4.10 x 10-3 system failure. ,

                   *Not Relevant 1281 A040881/1
      ~    .

                                                          'e' -

TABLE 11 , CAUSES AND FREQUENCY OF FAILURE OF lli-ilEAD RECIRCULATI0il WITil FAN COOLERS AND ELECTRIC BUS SA UITAVAIEABLE; C014P0ilEilT COOLING AND ELECTRICAL Blf5E G A, 3A and 6A AVAILABLE Effects Cause Mean Initiating Component System Other Systems - ' Event Operator Error Failure to initiate 3.46 x 10-4 NR* Falls Containnent No effect switchover. spray-recirculation cn Switch No. 6 is 4.72 x 10-5 SI pumps stop Fails No effect No effect turned to "on" post-tion and no recovery. liardware Single element cutsets. Loss of power in 2.00 x 10-6 tiovs 022A Falls No effect No effect electric bus 360. and 747-Pige no. 60 rupture 1.44 x 10-7 Fail s No effect No effect (5 ). . I40V 18020 falls to 1.50 x 10-3 tiOV 1802B Fails No ef fect- No effect open. .

                                                                   'tianual valves 753A, F             5.40 x 10-7      Valves 753A, F     Falls     .No effect          No effect
                                                       .             G , 11, J , o r 'K cl o sed                        G II, J, or X                                                  .
                                                                 "i40t Relevant 1281 A040881/1                                    -

e TABLE 11 (continued) .. CAUSES AND FREQUENCY OF FAILURE OF lil-llEAD RECIRCULATION WITH FAN CCOLERS AND ELECTRIC BUS 5FIDIAVAEAllEETEOFWOREHTTSOETE ARD ELEGIRICAL BlTSES lADA and 6A AVATEKillE Effects Cause fican Initiating Component System Other Systems Event fiOV 8220 falls to ' 1. 51 x 10-3 lt0V 8220 Falls No effect No effect open No power at DC 3.00 x 10-8 DC Dus 32 Fail s No effect No effect ,, bus 32 g tiultiple Failures SI pumps 32 and 33 7.14 x 10-3 SI pumps 32 Falls No effect No ef fect fall to run. and 33 Recirc. pump 31 2.29 x 10-4 Recirculation Falls No effect No effect fails to run and oper- pump 31 ators fall to align RllR. It0V 8800 falls te open 1.88 x 10-4 It0V 8800 Falls No effect No effect and operators fall to open it manually. ,. , Testing NR* NR* No effect NR* No effect liaintenance See Section D.2.2.4 6.13 x 10-5 51 pump 32 Fall s No effect No effect for details or 33

• flot Relevant ,

1281A040881/1 .

TABLE 11 (continued) _; CAUSES Ad0 FREQUENCY OF Fall'URE OF lil-llEAD RECIRCULATIO!1 WITil FAN COOLERS AND ELECTRIC BUS 7A CllAVATEABCdiiF0ilETIT CDOLING AND ELLCIRICAL BUSES 24~ 3A and 6A~AVAILABLE Effects Cause Mean Ini tiating Component System Other Systems -Event Other Causes See Section D.2.2.5 5.28 x 10-4 Si pump 32 or Fails  ?  ? for details 33,140V 8888 or - recirc pump 32 or M0Y.022A M Total frequency of 1.15 x 10-2 system failure s . s , , 1281A040881/1

TABLE 12- ,

                                                                                                                              ~

CAUSES Arlo FREQUEllCY OF FAILURE OF lil-iiEAD RECIRCULATIO:1~ WITil FAN COOLERS AND ELECTRTC lilISEGA and 3A UITAVATEKQLE; COMP 0tiEt4T COOLING AND AU EEECTRTC 0USES SA and 6A'AVAILABLE Effects Cause Pean Initiating Component System Other Systems Event Operator Error

               ' Failure to initiate         3.46 x 10-4           All            Fails        Containment      No effect swl tchover.                                                                  spray recirculation
  ;;f           Sultch No. 6 is turned       4.72 x 10-5     SI pumps stop        Fall s       No effect        No effect to "on" position and no recovery action.

liardware Single eleme.nt cutsets. Pige No. 60 rupture 1.44 x 10-7 . Fall s Part of con- No 'e f fec t (5 ). tainment spray recirculation Multiple Failures Hechanical failure in 1.56 x 10-6 Recirculation Fails No effect No effect both recirculation pumps 31. and . pumps and operator 32 and all RilR error in swltching . subsystems. to RllR pumps. . 1281A040881/1

                                                                                                                                 ~
         - .Q    .,

FABLE 12 (continued) CAUSES Atl0 FREQUENCY OF FAILURE OF lli-ilEAD RECIRCULAfl0!1 NITil FAtt COOLERS AYD ELECTRIC lilTSES 2A and 3A UllAVATEABLE;_ C0 lip 0tlENT C00 LING AilDlLL ELECTAIC BUSES bA and 6A~ AVAILABLE E f fects Cause liean int tiatin.) Canponent System Other Systems Event SI pumps 31 and 7.14 x 10-3 51 pumps 31 Falls No effect No effect 33 fall. and 33 liOVs 888A and 8883 4.88 x 10-6 liOVs-888A and Falls No effect No ef fcct do not open. 3888 y w liOVs 822A and 8228 4.88 x 10-6 liOVs 822A and Falls No effect tio effect do not open. 8228 No effect NR* No effect festin) . NR* NR*

               . 14aintenance and liardware liaintenance on one SI        6.13 x 10-5       Doth SI pumps      Fails         No effect    No effect pump and mechanical                             31 and 33                             '

failure of the other. unavailable Other Causes See Section D.2.1.5 5.50 x 10-4 SI pump or Falls  ?  ? for detalls 110Vs nua . Total frequency of 8.18 x .10-3 . system failure ,

• Not Relevant .

O e ()

a. TABLE 13 . CAUSES ARID FREQUENCY OF FAILURE OF llI-ilEAD RECIRCULATION WITil FAN COOLERS C0t@DilERTC6DEDIG AHifALL EEECTRIC BUSES AVAILABLE Effects Cause Mean " Initiating Component System Other Systems Event Operator Error Failure to initiate 3.46 x 10-4 All Falls No effect No effect switchover. Switch No. 6 is turned 4.72 x 10-5 S1 pumps stop Fall s No effect No effect to "on" position li and no recovery actions are taken. 6 liardware Single element cutsets. 1.70 x 10-8 Falls No effect No effect Pip'e No. 60 rupture (5 ).

               !(ultiple Failures Hechanical failure in         1.56 x 10-6    Recirculation       Falls           No effect    No ,ef fect both recirculation                          pumps 31 and                                           .

pumps and operator 32 and all RilR error in switching subsystens. - to RilR pumps. All three Si pumps 3.11 x 10-3 SI pumps 31, Falls No effect No ef fect fall. 32, and 33 1281 A040801/1 . .-c .

e. .

TABLE 13 (continued) , CAUSES AND FREQUENCY OF FAILURE OF lli-ilEAD RECIRCULATION WITil FAN COOLERS C0ftPDNENT C50ETWAFAEC EEECTRIC DU5ES AVATD@LE

                                        .                                            Effects Cause                     Mean                                                          Initiating Component        System     Other Systems         Event
           'MOVs 888A and 8888         . 5.86 x 10-7       MOVs 888A and'      Falls        No effect       No effect do not open.                                   88Bil Testing                               NR*                 NR        No effect          NR          No effect   ,

Maintenance and liardware Maintenance on one 1.74 x 10-5 All three St Falls No effect No effect pumps 6 SI pump and mechanical failure of the other two. Other Causes Falls See Section D.2.7.5 5.30 x 10-4 SI pump or  ? ,? for details MOVs,888 Total frequency of 4.05,, x 10-3

• system failure. ,
• Not Relevant .

9 * . 1281 A040881/1 .

 . .                                                           . z,

o

                                                                                     .c                                                                                                            :
                                                                                                                                                                                                            ~

fAllLE 14 - - CAUSES AND FREQUENCY OF FAILURE OF llI-iiEAD RECIRCULATION WITil ELECTRIC BUS 6A UNAVAEAlilIiTAN COOLERS COMPGlENT COOLING Al30ELECTRICBUSES2A,3AandSANVATEAilLE Effects , Cause Mean Initiating Component Systen Other Systems Event Operator Error y failure to initiate 3.46 x 10-4 NR Fall s No effect No effect swi tchover. Switch No. 6 is turned 4.72 x 10-5 SI pumps stop Fall s No effect No effect to "on" post tion and no recovery. liardware Single element cutsets. , Loss of power in 2.00 x 10-6 It0lls 880A Fail s No effect No effect electric bus 36A. anil ll102A Pige No. 60 rupture 1.44 x 10-7 Falls No effect No effect (5 ). tiOY 1802A falls to 1.50 x 10-3 i40V 1802A Fall s' No effect No ef fect open. 1281A040881/1

            *C.,                                              .

TABLE 14 (continued) _ CAUSES AND FREQUENCY OF FAILURE OF lil-llEAD RECIRCULATION WITil ELECTRIC BUS 6A UNAVAILAllLE; FAN C00LERS C0tiP0 u DENT COOLING ' AND ELECTRIC DU5E5 2K, 3A and 5A AVAILABLE 4' Effects , Cause Mean Initiating Component System Other Systems Event s 5.40 x 10-7 Valves 752A, Fails No effect No effect Manual valves 75?A, F , G , 11, J , or K f all 3, G or 11 closed. 3 No effect 3.00 x 10-8 DC Bus 22 Falls No effect No power at DC Bus 32. Hultiple Failures 51 pumps 31 Fails No effect No effect Si pum'ps 31 and 32 1.00 x 10-2 f ail to run. and 32 2.29 x 10-4 Reqirc pump 31 Fails No effect .No effect Recirc pump 31 falls to run and operators fall l to align RilR. , I ~ 17A1A040RR1/1 a

o TABLE 14 (continued) - CAUSES AND FREQUENCY OF FAILURE OF lil-llEAD RECIRCULATION WITil' ELECTRIC OCA URAVATEATilT. i FAMT)LERS, C0tiPONENT COOLING AND ELECTRIC EUSE D A D A and 5A AVAILABLE Effects - Cause Mean Initiating Component System Other Systems Event MOV 880A falls to open 1.88 x 10-4 NOV 8883 Fall s No effect No effect 4 and operators fall to open it manually. E$ Testing NR NR- No effect NR No effect Maintenance One Si pump under 6.13 x 10-5 Si pump 31 Fall s ' No effect No effect maintenance, the other falls due to hardware. Other Causes See Section D.2.2.S 5.28 x 10-4 51 pump 31 and Fails  ? ~? for details. 32 .,r HOV 8800

                                            ..      or recirc pump                                      .

31 or liOV 822A - Total frequency of 1.00 x 10-2 system failure.

                        .                                                                            .s N

1281 A040881/1 '. . +

o TABLE 15 CAUSES AND FREQUENCY OF FAILURE OF ill-llEAD RECIRCULATION WITil ELECTRIC DUS SA UNAVAILAllLE; FAN COOLERS, COWONENT COOLING AND ELECTRIC lluSES 2A, 3A and 6A AVAILABLE Effects Cause Mean Initiating Component System Other Systems Event Operator Error Failure to initiate 3.46 x 10-4 NR Fails Containment No effect switchover, spray , recirculation U$ Switch No. 6 is 4.72 x 10-5 51 pumps stop Falls No effect No effect

turned.to "on" post- -

l tion and no recovery. Ilardware Single element cutsets.

Loss of power in 2.00 x 10-6 FK)Vs 822A Falls No effect No effect electric bus 263. and 747 Pipe No. 60 rupture 1.44 x 10-7 Falls No effect No effect j

(5"). t . HOV 18028 fails to open. 1.50 x 10-3 t0V 18028 Falls No effect No effect Manual valves 753A, F 5.40 x 10-7 Valve 753A, 8 Falls No effect No effect G,11, J, or K f ails closed. No power.at DC Bus 31. 3.0 x 10-8 DC Bus 22 Falls No effect No effect 1281A032681 .

 '  *

• 4

e TABLE 15 (continued)' . CAUSES AND FREQUENCY OF FAILURE OF llI-llEAD RECIRCULATION WITil ELECTRIC BUS SA77TAVATEAnLE; FATT~CDOLERSuC0!4P0hENT COOLING AHD ELECTRI CBIfSES 2A, 3A and 6A AVATEAnLE

                                         .                                         Effects Cause                   Mean                                             .

Initiating Component System Other Systems ' Event Multiple Failures SI pumps 33 and 7.14 x 10-3 SI. pumps 33 Falls No effect No effect 32 fall to run. and.32 Recirc pump 32 fails to 2.29 x 10-4 'Recirc pump'32 Fa:Is No ef fect No effect oo run and operators fall to align RilR. MOV 8883 falls to open 1.88. x 10-4 MOV 8883 Falls No effect No effect and operators fall to open it manually.

        , Testing                             NR              NR             No effect         NR      No effect
          !!aintenance See Section D.2.2.4         6.13 x 10-5     SI pumps 33          Falls        No ef fect  No effect for details.                                and 32 Otner Causes See Section 0.2.2.5          5.28 x 10-4    Si pumps 33 and     Falls              ?           ?-

for details 32 or 110V 8883 or recirc pump 32 or MOV B22A Total freglency of 1.00 x 10-2 system failure.

              ~e' TABLE -16 CAUSES AND FREQUENCY OF FAILURE OF llI-ItEA0 RECIRCULATION WITil C0!4P0tlEtlT COOLING ELECTRIC buses 2A and 3A uiTAVATEAKETTATC00LERS,hlE
                                                   . AllD ELECliiTC61TSES 5A and 6CAVATEA Effects Cause                  Hean                                                        Initiating Component    System       Other Systems      Event 1

Operator Error Failure to initiate 3.46 x 10-4 All Fails Contai nment No effect swi tchover. spray recirculation Switch No. 6 is turned 4.72 x 10-5 Si pumps stop Fails No effect No effect to "on" position and no recovery action. liardware Single element cutsets. Pige No. 60 rupture 1.70 x 10-8 ~tt0Vs 822A Fails Part of 'No effect (5 ), and 747 containment spray recirculation , , Multiple Failures Mechanical failure in 1.56 x 10-6 Recirculation Fall s Containnent No effect both recirculation pumps 31 and spray pumps and operator 32 and all recirculation

            .          error in switching to                        RilR pumps .                                                 -

RilR pumps. 1281 A040881/1 o -

                                                                                                                                               ~

C ,, TABLE 16 (continued) -

                                                                                                                                                 ~
                                                                                                                                            ^

CAUSES AHD FREQUENCY OF FAILURE OF ll!-IIEAD RECIRCULATION WITil CDiiP0tlENT C00 lit 4G ELECTRIC BUSES 2A and 3A'lflAVKIEABLE; FATCOOLERS,hLE AND ELECTRIC $USES SA and 6A AVAILA i , Effects Cause Nean Initiating Other Systems Component System Event SI Pumps 31 and 7.14 x 10-3 SI pumps 31 Falls No effect No effect 33 fall. and 33 HOVs 888A and 8888 do 5.86 x.10-7 MOVs 88BA Fall s No effect- No effect not open. and 8883 E3 Testing NR* NR No effect NR No effect liaintenance and lla.Jware Haintenance on one SI 6.13 x 10-5 All three SI Falls No effect No ef fect pump and mechanical pumps failure of the other. unavailable Other Causes See Section D.2.1.5 5.50 x 10-4 SI Pump or Falls  ?  ? for details MOVs 888 Total frequency of 8.13 x 10-3 system failure.

• Not Relevant -

1281 A040881/1

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              .                                                 TABLE 18 CAUSES AND FREQUENCY OF FAILURE OF LO-ilEAD RECIRCULATION WITil FAN CU0EERS UllAVA'IEAllLE; C0liPDITEilT C55 LING MD AlI ELTCTTCACDUSES AVATEXQLE Effects Cause                 Mean                                                           Ini tiating Canponent          System        Other Systems      Event Operator Error              -

Failure to initiate 4.75 x 10-3 All Fails Containment No effect switchover. spray recircu-lation fails U$ Switch No. 5 is turned 5.26 x 10-4 MOVs 746 and Fails No effect No effect to "on" position and 747 close no recovery actions are taken. liardware.

           . Single element cutsets.                       There are no          Partial      No effect       No effect singic element        Failure cutsets Multiple Failures liardware failure in       2.65 x 10-5     Recirculation         Fails        No effect       koeffect both recirculation                         Pumps 31 and pumps and operator-                        32 and all error in switching to                      RilR subsystems RilR Pumps.

e 1281 A040881/1

 \ *  .                                                          _

I O

                                                                                                                                ~

e . TAllLE 18 (continued) - CAUSES AND FREQUENCY OF FAILURE OF LO-ilEAD RECIRCULATION WITil ~ FAN COOLER 5 UMAVATEAllIT. i CT4WONENT C60 LING AND ALL ELECTRTC~ ANES AVAILAllEE Effects Cause Mean Ini tiating Component System Other Systems Event liardware failure in 1.27 x 10-6 MOVs 1802A Falls Containment No effect both MOVs 1802A and B and 1802B Spray and operator error in and RilR Reci rculation switching to RilR pumps. subsystem Falls g MOVs 8223 and 822A 4.88 x 10-6 MOVs 8220 Fail s Containment No effect fail to open. and 822A Spray Recirculation Fails Testing NR Nil No ef fect No effect No ef fect 1281A

• e 4

TAllLE la (continued) , ,. CAUSES AND FREQUENCY OF' FAllllRE OF LO-ilEAD RECIRCULATION WITil FAN COOLERS UNAVAILAULE; COM'ONENT COOLING AND ALL ELECIRICAL BUSES AVAILAllLE Effects Cause Mean . Initiating Component System Other Systems Event Maintenance and liardware' Maintenance on one Si << 10-8 See Section fails No effect No effect pump (See E.2.1.4 for , Section E.2.1.4 details o, for details), u Other Causes , See Section E.2.1.5 3.30 x 10-5 See Falls Containment No effect for details Section E.2.1.5 Spray for details Recirculation Fails Total frequency of 5.32 x 10-3 system failure. e 1281A032681 s O n

e TABLE 19 [, CAUSES AND FREQUENCY OF FAILURE OF LO-ilEAD RECIRCULATION WITil' FAN COOLERS UNAVAILAULE; COWONENT COOLING AND ALL EllTTRICAL BUSES AVAILABLE Effects , Cause Mean Initiating Component System Other Systems Event Operator Error 4.75 x 10-3 All Falls Containment No effect. ' Failure to initiate spray switchover. recirculation EE falls Switch No. 5 is- 5.26 x.10-4 F0Vs 746 and falls No effect No effect turned to "On" post- /47 close ion and no recovery actions are taken. liardware Single element cutsets. Ther'e are no Partial No effect No effect single elenent cutsets ., Phltiple Failures liardware failure in 3.74 x 10-5 . Recirculation Falls No effect No effect

                 .both recirculation                         Pumps 31 and pungs and operator                        32 and all error-in switching to                     RllR subsystems Rillt Puups.

s '. . 1281A032681 2

                                                                 .( ,

TABLE 19 (continued) CAUSES AND FREQUENCY OF FAILURE OF LO-llEAD RECIRCULATION WITil FAITTODEER5 UflAVATEABOMF0HERTTODLING ATID AEET1T. CTRICAElU5E57VATEABLE Effects Cause Mean Ini tiating Component System Other Systems Event liardware failure in 1.27 x 10-6' MOVs 1802A Fails Containment No effect both MOVs 1802A and B and 18020 Spray and operator error in and RilR Reci rculation g switching to BilR pumps. falls Testing NR NR No effect No effect No effect Maintenance and liardware Fails No effect

                                                                             ~

Maintenance on one SI 2.24 x 10-9 See Section No ef fect pump .(See Section E.2.1.4 E.2.1.4 for decalls). for details Other Causes (See Section E.2.1.5 3.30 x 1045 See Fails Containment No ef fect for detafis). Section E.215 Spray ' for details Recirculation Falls Total frequency of 5.32 x 10-3 ' system failure. , ,

                                                                                                                                                                                         ^

1281 A

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a TABLE 21 l CAUSES AND FREQUENCIES 0F FAILURE OF CONTAINMENT SPRAY RECIRCULATION WilEN LARGE LOCA IIAS OfCUMED ARD ALL EEECTRIC BUSES ARE AVAILAB T Effects Cause Mean Initiating Component System Other Systems Event Operator Error - Operators fail to open 1.5 x 10-3 MOVs 889A Falls No effect' No effect isolation valves. , liardware e Single events - There are no Partial No effect No effect sinle element failure 6 cutsets Multiple events

          .        Doth MOVs 889 fall         4.88 x 10-6   MOVs 889A      Falls        No effect          No effect to open                                  and 8890 Testing                            -             -

No effect - - Maintenance ,

                                                    -            -        No effect         -

Other Causes (see Section F.2.1.5 2.1 x 10-5 (see Section Falls No ef fect . No effect for details) F.2.1.5) 1.5 x 10-3 Total . frequency of system failure. , . 1281A .

m

           -C ,                                                                                                                  .

TABLE 22 . CAUSES AND FREQUENCIES OF FAILURE 0F CONTAINMENT SPRAY RECIRCULATION WilEN LARGE LOCA IIAS OCCURREU XHD ELECTRIC' DOS 5A 15 UNAVAIL ABLE Effects Cause initiating Mean Component System Other Systems - Event ! Operator Error Operator fails to open 1.5 x 10-3 MOVs 889A Fails No e f fect No ef fec t isolation valves. and 8893

        .       liardware eu Single events.
                   'JV 889B falls              1.5 x 10-3     MOV 889B        Fall s          No effect       No e f fec t to open Testing                             -             -

No effect - - Maintenance -

                                                                 ,-            No ef fect          -               -

Other Causes l (See Section F.2.2.5 - (See Section Fall s No effect , No e f fec t for detatis) F.2.1.5) Total frequency of ' 3.0 x 10-3 - system failure. 1201A

a i

                                                                                                                        ~

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