ML20012C629
| ML20012C629 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/20/1990 |
| From: | TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20012C626 | List: |
| References | |
| SQN-SQS2-0097, SQN-SQS2-97, NUDOCS 9003220300 | |
| Download: ML20012C629 (99) | |
Text
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DNF CALCut ATIONS QA Record : l1itle Probabilistic Analysis Showing the Effects of Deleting the l_ l Plant / Unit Residual Heat Removal (RHR) Autoclosure Interlock (ACI) l 50N/ Units 1 and 2 lPreparingOrganl24 tion l KEY NOUN 5 (Consult RIMS Descriptors List) l_NF/RP5 l Probability. RHR. ACI ltranch/ProjectIdentifiers l lEachtimethesecalculationsareissued,preparersmustensurethatthe l original (RO) PIMS accession nunber is filled in. lSQN5Q52-0097 l_Rev (for RIM 5' use) l RIMS ACCESSION NUMBER l l l 1 ! l_ l R0 l 991006D0012 l 881 890929 004 ja,,ncabie Doign Docume""" [R,891207C 0004(S 304 90 1205 302 ["'^ I Rz ! lB04'90 0221 l5AR5ection(s) l UNID System (s) l_5,5.7.7.6.2 l l l 3nn l 74 lR l l
- l. Revision 0 i R1 i R2 l R3 15afety-related? Yes (X) No ( )
ECN (orIndicateNotAppilcable)l l l 5tatement of Problorn l Prepared l_OloriaJ.Over lI lM -Al W l $l l Perfonn a probabilistic analysis on SQN l Checked _# I lunitsIand2that: (1) shows the effects l_ Fredrick K. Hoyos l8KJ*(l$ M l lofdeletingtheRHRACIfunctioninorderto l)(, b - l Y. % m I lreducethelikellhoodofalossofRHR l Reviewed l Marv B. Townsend % i l I l l lcoolingaccidentand(2)demonstratesthe l; L lAppr.:ved ladequacyoftheACIdeletionfromboth4 ), l l l l Richard J. McMahon /) lcoresafetystandpointandaRHRsystem lDate I _#_Ib l .V (h h loverpressurl2ationstandpoint. l. l 1 5eotenber 29, 1999 [l/2[y~b I JYf o!9.ll l 1: lUSE FORM l List all pages added l l l l l: lTWA10534lbythisrevision i l < l: l l lIFMORE l List all pages deleted l lbythisrevision l l l l l' l$ PACE l l: l l l REQUIRED lListallpageschanged l l l l l ' l-l lAB5 TRACT lby this_ revision I All l S tl 3 1 1 l- [These calculations contalh an unverified assunption(s) that must be verified later. l1 l Yes ( ) No(X)]l l for SQN units 1 and 2,l This calculation provides a probabilistic detennination of the l I lt l; l This calculation compares the RHR systems of SQN units I and 2 and Salem 1 (the l' lWCAP11736)andreviewstheWCAP11736analysesasapplicabletoSQNforRHRoverp lRHRsystemunavailability. l, I ~l l-l No significant differences were found that would invalidate the Salemo WCA lSQN. l The deletion of the SQN RHR lremovalandRHRoverpressurizationevents. - autoclosure interlock was shown to have a eat net ben l l I l l I l I l l 9003220300 900313 I PDR l P ADOCK 05000327 l PDC l I I l I l(X)MicrofilmandstorecalculationsinRIMSServiceCenter l l_( ) Microflim and return calculations to: Microfilm and destroy. () l cc:- RIMS, ET SLE 26P-K Address: ,_ l HPK1 RPS - 1273L
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REVISION-4 OG i 1
***'Probabilisti'c' Analysis shouing th'e' Effects of Deleting *
title : the Residual Heat Removal (RHR) Autoclosure Interlock (ACI) SQNSQS2-0097
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DESCRIPTION OF REVISION N o. 4 ,,,...a
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Initial issue. 9/29/89 1 Major rewrite Expanded the calculation to include the comparison 12/4/89 of the Sequoyah"RHR system vith-Salem RHR- system and -a-review of - -- - _ the probabilistic analysis used to determine the effect of '
. dMM-'of ~ the RHR sutoclosure--interlock. ---- --- --- - - -- - - . - . . - -
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m. regarding power .16cEout"of 46i: tion'~ iso 11t' ion valves and added - -- '
, _ _ , references 13 and 14.
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" ~ ~ " CAf.CUI.ATION-DESIGN VERIFICATION (INDEPENDENT REVIEW). FORM.,.r ,.n . m =
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Calculation No. Revision Method of design verification (independent review) used (check method used):
- 1. Design Review V
- 2. Alternste Calculation
- 3. Qualification Test Justification (explain below):
Method 3: In the design review method, justify the technical adequacy of the calculation and explain how the adequacy was verified (calculation is similar to another, based on accepted handbook methods, appropriate sensitivity studies included for confidence, etc.). Method */: In the alternate calculation method, identify the pages where the alternate calculation has been included in the calculation package j and esplain why this method is adequate.. Method 3: In the qualification test method, identify the QA documented
, source (s) where testing adequately demonstrates the adequacy of this calculation and esplain.
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Page 1 of 2 CALCULATTON ClaSSIFTC ATTON t CATEGOREATION
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- 1. Design Review X
- 2. Alternate Calculation '
- 3. Qaalification Test Justification (explain below):
Method 3: In the design review method, justify the technical adequacy of the
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Method 3: In the qualification test method, Identify the QA documented source (s) where testing adequately demonstrates the adequacy of this calculation and explain, d) Ybi GNskh // Wilts A fr*hlnYNic IV4Aa6b of tb hheval of b
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! i SQN-SQS2-0097 R1 I Table of Centants 1.0 Purpose........................................................... 1 2.0 Background ....................................................... 1 l
3.0 Methodology ...................................................... 2 j 4.0 Residual Heat Removal n2nctional Descri
- 4.1 Normal Function . . . . . . . . . . . . . . . . . . ............................
. . . .ption . . . . . . . . . . . . . .2. . . . . .' . 2 4.1.1 Cooldown ....................................................... 2 '
4 .1. 2 Refueling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4 .1. 3 Reactor Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 , 4.2 Safety Function .................................................. 4
- 4. 2.1 Eii-v cf Core Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
- 4. 2. 2 RHR Containment Spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 ,
- 4. 3 RHR Overpressurization Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
- 4. 3.1 RHR Autoclosure Interlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .
4.3.2 Proposed Changes to the RHR Autoclosure Interlock . . . . . . . . . . . . .. 5 l 5.0 0:mparison Between the Sequoyah and Salem RHR Systems . . . . . . . . . . . . 6 5.1 System Configuration and Mechanical C+wte . . . . . . . . . . . . . . . . . . . 6 5.2 Autoclosure Interlock logic and Control circuitry . . . . . . . . . . . . . . . . 6 6.0 Analyses ......................................................... 7 6.1 Event V Analysis ................................................. 7 6.2 Iow Tw.rature Overpressurization Events . . . . . . . . . . . . . . . . . . . . . . . . 9
'6.2.1 Heat Inputs Transients ......................................... 9 6.2.1.1 Premature Opening of the RHR Suction Isolation Valves. . . . . . . . . 9 6.2.1.2 Inadvertent Control Rod Withdrawal During Shutdown ........... 10 6.2.1.3 Failure to Isolate RHR System During Startup . . . . . . . . . . . . . . . . . 10 6.2.1.4 Inadvertent Pressurizar Heater Actuation . . . . . . . . . . . . . . . . . . . . . 10 6.2.1.5 Startup of an Inactive Reactor Coolant Pun 6.2.1. 6 Ioss of RHR Cooling Train . . . . . . . . . . . . . . . .g...........,........ . . . . . . . . . . . . . . . . . 11 . 11 6.2.1.7 Heat Input Transient Analysis ...................... 1 ........ 11 6.2.2 Mass Input Transients .......................................... 12 6.2.2.1 Opening of A-lator Discharge Isolation Valve . . . . . . . . . . . . . 12 .
6.2.2.2 1stdown Isolation ............................................ 12 6.2.2.3 Charging / Safety Inj ection Pung Actuation . . . . . . . . . . . . . . . . . . . . . 13 6.2.2.4 Mass Input Transient Analysis ................................ 13
. 6.2.2. 4.1 Istdown Isolation-RHR Operablo Analysis . . . . . . . . . . . . . . . . . . . 13 6.2.2.4.2 1stdown Isolation-RHR Isolated Analysis . . . . . . . . . . . . . . . . . . . 14 6.2.2.4.3 ChartJing/ Safety Injection Punp Actuation Analysis . . . . .' . . . . . 14 6.2.3 Summary of Overpressurization Transients Analysis .............. 14 6.3 RHR Unavailability Analysis .......................,.............. 15
- 6. 3.1 Failure to Initiate RHR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
- 6. 3. 2 Failure of Short Term Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
- 6. 3. 3 Failure of Iong %rm Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 7 . 0 conclus ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 8,0 References ....................................................... 17 i
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y L g u . . SQN-SQS2-0097 R1 Page 1 of }7
' Prepared f5 c Date u 6 o/F9 checked E W Date 11A/t')
l 1.0 Purpose
. This calculation is being prepared in response to programmed !
enhancement recommendation 3a and 5 of Generic Istter 88-17 as requested by Sequoyah Engineering Project in QIR SQPSQN89330 (reference 1) to provide a probabil4*4n determination of the effect of deleting the RHR autoclosure interlock (ACI) on the.Sequoyah Nuclear Plant (SQN). This analysis will evaluate the combined ' effects of ACI deletion on the RRR - decay heat removal function and RHR system overpr-W= tion protection. I 2.0. BACKGROUND
- The Nuclear Regulatory Cor*4==4nn issued Generic Istter 88-17 " Loss of Decay Heat Removal" (reference 2) as a result of increasing concern over the loss of decay heat removal during nonpower operation and the '
consequences of such a loss. Generic Letter 88-17 requires a response which is to include: l 1) A description of the actions taken to implement each of eight recommended avp=44*4ms actions identified in the attachment to the letter. l-(2) A description of enhancements, specific plans, and a schedule for implementing each of the six programmed enhancement recommendations identified in the attachment to the letter. I
- l. Two of these programmed enhancement recommendationa specifically
' mention the RHR autoclosure interlock.
- 1) Programmed enhancement recommendation No. 3a is,
" Assure that adequate operating, operable, and/or available equipment of high reliability :is provided for cooling the RCS, l (reactor cooling system), and for avoiding a loss of RCS L cooling."
Generic Letter 88-17 goes further in the discussion of this recommendation by noting, _.
" Loss of DHR [ decay heat remov0.] due to unplanned activation of the autoclosure interlock f netion is not consistent with provision of reliable equipment. You should investigate this ' feature if ineallai in your plant and should consider changes to obtain a reliable heat removal system consistant with other requirements." -
l
- 2) Programmed enhancement recommendation 5 is,
" Technical spe4finitions (TSs) that restrict or limit the safety benefit of the actions identi.f ted in this letter should be identified and appropriate changes should be submitted."
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- SQN-SQS2-0097 R1 Page 2 of 17 !
, Prepared :rst Date H N /rt ,
Checked 9;## Data fL4 /r 9 i The discussion of this recommendation notes,
. . " Typical potential impacts include TSs that control ... the !
autoclosure interlock; ... .% a: .:.This. calculation . is . a . response to programmed enhancement 1
- recommendations 3a and 5 and will evaluate whether the proposed changes associated with the deletion of the SQN autoclosure interlock will enhance the r=14=h414+y of the decay heat removal system consistent with other
- Tequirementar such as overpressurization protection. * *
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i 3.0 MET!!ODOLOGY This analysis presents a " comparison and bounding" study between SQN and the referanos plant modeled in WCAP 11736, " RESIDUAL HEAT REMOVAL SYSTEM AUIOCI.OSURE INTERI.OCK REMOVAL REPORP FOR THE WESTINGHOUSE OWNERS i GROUP" (reference 3). Four reference Westinghouse plants were anal based on =4=41=" RHR system configurations and design charar+=%cs.yzed The reference plant with a similar RHR configuation to Sequoyah is Salem 1. WCAP 11736 presented a thorough probabilistic evain*4m of the effects of i- deleting the RHR ACI and adding overpressur4**4^n alarms in the control room. The methodology used in the WCAP study was to model sequences l involving RHR overpressurization and loss of RHR decay heat removal j i fund:icn both with and without the proposed RHR changes. The models were quantified and evaluated to determine the combined effect of the RHR l changes on minimum core cooling. I' This calculation notes the similarities and differences of the RHR
' system configuration, logic, control circuitry, and proposed changes associated with the deletion of the ACI between Sequoyah Nuclear Plant unita 1 & 2 and Salem 1. These factors are evaluated to determine whether the Salem 1 analysis and conclusions are valid for Sequoyah 1 & 2. The analyses used in WCAP 11736 are then reviewed with applicable Sequoyah j l' information included.
l i L 4.0. . RESIDUAL HEAT REMOVAL SYSTEM FUNCTIONAL DESCRIPTION
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The primary purpose of the RHR system is to remove decay heat energy from the reactor core and Reactor Coolant System (RCS) during plant cooldown and refueling operations. (references 4 & 5) . 4.1. NORMAL FUNCTION 1-L d.1.1. COOLDO WN
'The initial phase of reactor cooldown is acomplished by transferring 1 heat from the RCS to the Main Steam system through the use of the steam generators. When the reactor coolant temperature and pressure are reduced 2
to approximately 350'F and 380 lb/in g respectively, approximately four hours after reactor shutdown, the second phase of cooldown starts with the RHR system being placed into operation. 4 :.
-. .. 4 ;
6 i SQN-SQS2-0097 R1 Page 3 of 17 Prepared 75t Date H b /F9 Checked FX# Date a A AM During.this phase of operation reactor coolant is withdrawn from RCS
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hot leg 4 through RHR.: suction-_4d*irvi valves FCV-74-1 and FCV-74-2 to 1 the RHR pumps..The reactor coolant is pumped through the RHR heat exchangers where the heat is transferred to the Component Cooling Water l System.and.the reactor coolant is..rcturned to the RCS through the cold legs. The rate of. oooldown is controlled by regulating the reactor coolant , flow through the RHR hast exchangers. As cooldown continues, the steam bubble..in the pressurizer is . collapsed and the RCS is operated in the i water solid. condition. At this stage,- pressure control is accomplished by - regulating the charging flow rate and the rate of letdown from the RHR system to the Chemical and Volume Control System (CVCS). After the reactor coolant pressure is reduced to atmospheric pressure, the temperature is 140'F or lower, the reactor coolant reactivity level is reduced to an acceptable level, and the reactor coolant has been degassed, the RCS may be opened for refueling or maintenance. 4.1.2. REFUELING The refueling cavity is flooded by closing RHR inlet isolation valves, , FCV-74-1 and FCV-74-2, and opening the refueling water storage tank (RWST) l id*% valve FCV-63-1. The water from the RWST is then pumped into the i reactor vessel through the normal RHR system return lines and into 1.he refueling cavity through the open reactor vessel. After the water level reaches normal refueling level, the RHR inlet. isolation valves are opened, the refueling water storage tank supply valva (FCV-63-1) is closed, and
- j. normal RHR from the RCS hot leg is resumed.
s , l Following refueling, the RHR pump (s) are used to drain the refueling cavity to the top of the reactor vessel flange by pumping water from the l RCS hot leg 4 to the RWST. t 4.1.3. REACTOR STARTUP At iniH*% of plant startup, the RCS is in a water solid condition with the pressurizar heaters energized. The RHR system is operating in its normal decay heat removal configuration and is connected to the CVCS via , the low pressure letdown line to control reactor pressure. As heatup ' I commences, the RHR system operates in conjunction with the RCS to control temperature and pressure. At approximately 350*F, the RHR system is isolated from the RCS system by closing valves FCV-74-1 and FCV-74-2. The RCS pressure is then controlled by normal Ic.tdown and the pressurizer spray and pressurizer heaters. 1 l n t- t <-e- - m - _____ __ ____. . _ _ _ ___._ ____ _.__e
4 SQN-SQS2-0097 R1 Page 4 of 77 Prepared rs e- Date et/s./n Checked GK#. _Date M A # 9 c.:. . . . . _. . . . n _ . ~; . c . . . . ;. . . . . . . 4.2.. S AFF.TY:. FUNCTION:-.. = .r.:. c *w
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. - During' normal, power operation and' hot standby; the RHR system is .
aligned"for standby operatica.as part of ECCS (Reference 6). Following ECCS actuation in tha injection. mode,.the residual heat removal pumps take suction from'the RWST and deliver borated vatar to the RCS.' These pumps - begin'to. deliver. water to the RCS only after the pressure has fallen below . the pump shutoff head. When a low Isvel signal is received- from the RWST in conjunction with a "S" (safety injection) signal and a high containment sump level signal, the recirculation mode is entered with the RHR pump , suction automatically realigned from the RWST to the containment sump. The ' RHR block valves (FCV-74-3 and FCV-74-21) are automatically closed coincident with the opening of the sump isolation valves (FCV-63-72 and ' FCV-63-73). In the recirculation mode the water from the sump is passed thrtugh the RHR heat exchangers and returned to the reactor vessel through the cold leg injection path. The RHR system can be aligned to provide suction to the high head centrifugal charging pumps of the CVCS or the safety injection pumps of the Safety Injection System (SIS) during the recirculation phase. 4.2.2. RHR CONTAINMENT SPRAY SYSTEM The RHR system can be aligned as a containment spray system following a lOCA if conditions require it (reference 7). These conditions are: the
*oontainment pressure must exceed 9.5 paig; at least one hour has ela';. sed since the beginning of the accident; RHR suction is aligned to the containment sump; and at Inast one component cooling water pump and one cafety injection pump are running. In this configuration, water is drawn from the containment sump by the' RHR pumps, cooled by the RHR heat exchangers, sprayed through the RHR spray headers and drains back to the containment sump.
l
- l. 4.3. RHR OVERPRESSURIZ ATION PROTECTION .
The RHR system is designed as a low pressure (600 psig) system that is isolated from the high pressuIn RCS by two high pressure motor operated isolation valves in series on the inlet line (FCV-74-1 and FCV-74-2) and two series check valves on each of the discharge lines into the RCS (reference 4). ' The inlet line to the RHR system lLs equipped with a pressure relief valve (74-505) sized to relieve the combined flow of the charging pumps at the relief valve set pressure (reference 5). The discharge lines to the RCS are equipped with a pressure relief valve (63-627, 63-628, 63-637) to relieve the maximum possible back-leakage through the valves separating the RHR system from the RCS. These relief valves are part of the ECCS.
^
b_' { l
. ( SQN-SQS2-0097 R1 Page 5 of 17 !
Prepare U *'- Date u 4./v., l Checked E YM Date u A/M '
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The ~ inlet 4=^1*4nn valves, FCV-74-1 and FCV-74-2, are normally closed and are only opened for residual heat removal after reactor coolant system
- pressure is.reduosd to approximately 380 psig and the RWST suction valve (FCV-63-1) and containment sump isolation valve (FCV-63-72) are fully closed **"~. --
r- '~ u -- *- - ~' s :'.
- s :..~ : ;rr . -
. " Z.' : . . . .; . ;.T. ' ! . . . . . . . . .. . .
4'i3;1r RHR Autoolosure Interlock:/- *: ' ': - t
- - ~.
- . : ..: " '::. . . . . . .. u- : :- . . . .
The RER. autoclosure interlock (ACI) was installed to prevent
- overpressurization of the RER system which could lead to reactor coolant being discharged outside containment tlamgh a break in the low pressure system. The ACI will auM=*1 cal 1y close the RHR inlet isolation valves on RCS pressure greater than 700 psig. The RHR system is vulnerable to this type of overpressurization dur;.ng startup or during cooldown while the reactor vessel is closed. A demilari description of the overpressurization transients is presented in Section 6.2 'Iow Temperature overpressurization Events.'
While the RHR ACI is designed to protect the RHR system, it is also a centributor to the unavailability of the RHR system due to the probability cf its spurious actuation which would isolate the RHR system and could lead to a loss of decay heat removal transient. A detailed description of s this contribution is presented in Section 6.3 'RHR Unavailability ' Analysis. ' L '4.3.2. Proposed Changes to the RHR Autoclosure Interlock 1 . The proposed change described in the WCAP 11736 analysis and in SQ-DCR-3365 (refe:ence 9) removes the auMela="re interlock feature from ! the RHR suction i=^1*4nn valves, Fr:V-74-1 and FCV-74-2. With removal of the autoclosure interlock feature, these valves will not automatically close on increnaing pressure greater than 700 psig. However as stated in l the DCR-3365 and in WCAP 11736 Section 6.1, an alarm will be added, for each suction 4=^1*4aq valve, that actuates in.the main control room given a " VALVE NOT NLLY CLOSED" signal in conjunction with a "RCS PRESSURE .,, HIGH" signal. The intent of the alarms is to alert the operator that one or both of the suction isolation valves is not closed with RCS pressure greater than 700 psig. The alarm must meet the same design criteria as other safety-related function control room annunciation. Valve position indication to the alarm must be provided from the valve stem mounted limit switches and power must not be affected by power lockout to the valve. The proposed changes only affect the autoclosure interlock feature; and the " valve open permissive circuit will not be affected.
'In addition to changing the valves' interlock circuitry, the sequoyah ;
plant operating procedures governing reactor cooldown and startup must be modified to reflect the appropriate recognition and response to the new l l l l <j l ' '
i
- s. .
I SQN-SQS2-0097 R1 Page 6 of 17 ' Prepared rs ed$9-Date 8' N/n_ ! Checked Gw # Dateia M r'l added alarms. The procedures should be revised to direct the operator to taka.the necessary ac* ion to 'close the open suction.. isolation valve (s) following alarm actuation, or.if this is not possible, to take appropriate > action.to prevent RHR. overpressurization.
. u :. = . . : . ... .. . .
' 1 The removal of the ACI will require changes in TVA's documentation of Sequoyah Nuclear Plant. A partial list of documents which will need ;
revising includes the: Design Criteria, Final Safety Analysis Report, ; Technical Specifications, Surveillance Instructions, Maintenance - Instructions, TVA Drawings and othar sources. The design change process l will identify the specific documents to be revised.
.:::.;. ~ .
5.0. CbPARISONiBETWEEN THE SEQUOYAH AND SALEM RHR S 5.1. System Configuration and Mechanical Components Both Salem 1 and Sequoyah have similar vintage RHR systems consisting
. of two separata RHR trains of equal capacity, each independently capable of meeting the safety analysis design basis. Each train consists of one heat exchanger, one motor driven pump and associated piping, valves and instramentation nanamma7 for operational control. The inist line to each train of the RHRS is connected to a common letdown line from the hot leg of reactor cooling loop (loop 4 for SQN and loop 1 for Salem), while
- return lines are connected to the cold legs of all four reactor cooling loops via the SIS accumulator discharge lines downstream of the cross-connect (for SQN-train A discharges to loops 2 and 3, train B discharges to loops 1 and 4. For Salem, train A discharges to loops 1 and
'3, train B discharges to loops 2 and 4).
'Ihe RHR system for Salem 1 and Sequoyah are normally isolated from the RCS by two, series, MOVs, suction isolation valves in the single letdown <
l line connecting the low pressure RHRS to tho high pressure RCS. The RHRS t discharge lines are 4=^1**4 from the RCS by two check valves in series for each line. The RHRS suction 4=^1* inn . valves, the inlet line pressure i relief valve, the return lines to the RCS cold legs downstream of the appropriate valves and the hot leg injection lines are located inside conta:.nment while the remainder of the system is located outside _ containment. Based on this evaluation, there are no significant differences between the system configuration and mechanical components of Salem 1 and Sequoyah. O L 5.2 Autoclosure Interlock Logic and Control Circuitry Salem.1 and Sequoyah use similar designs to protect the RHR systam from overpressurization. The first protective' feature is the decreasing ' low pressure permissive interlock for opening the valves; (below 380 psig); the second feature is the passive relief valve located on the RHR inlet piping within the containment which maintains the system pressure _ below the design pressure of the RHRS for most overpressure events, and E
i SQN-=QS2-0097 R1 Page 7.of 17 i Prepared r sMate nIvo/r9 I Checked EKM- Data tt/4her the third protective. feature for both plants.is the RHR autoclosura l interlock..which : closes .both inlet isolation valves by. the appropriate train ( A for train'.A valve and B.for train B valve) instrumentation that is. set above the RHR design' pressure. This control logic and control ! circuitry is typical for both SQN and Salem. In addition to the above scheme, the SQN inlet iso 3ation valves ! (FCV-74-1.and FCV-74-2) have the powar administratively removed once the valves are cloned (breaker locked in trip position). Since the SQN valves - have backup ocatrols, pressure switches sensing RCS pressure above 700 psig automatically close the valves in the backup nontrol mode. In additico, the SQN valves have their local control switches disconnected to , preclude inadvertent operation due to the effects of a LOCA (reference !
- 10) .
In summary, there are no significant differences between the design I and confi >
. prN%guration, features mechanical for Salem and 1 andelectrical, Sequoyah. of Therefore,the the RHR overpressure use of the WCAP analysis performed for deletion of the RHR autoclosure interlock is !
reasonable for SQN. 6.0. ANALYSES WCAP 11736 (reference 3) presents a thorough analysis of the RHR overprenssurization events and system unavailability which would be affected by the deletion of the autoclosure interlock. The analyses seccians of this calculation are a review of those analyses for Salem 1
'with app 1Nhla Sequoyah informatien included. For further information on ,
the analyses, the WCAP should be consulted. 6.1. Event V Analysis An interfacing 10CA, referred to as Event V in Wash-1400, (reference
- 11) is a breach of the high pressure RCS boundary at an interface with a low pressure system, in this case the RHR system. This event has the potential to cause a non-isolatable LOCA outside containment. It is _.
assumed to occur if the RHR suction inlet valves (FCV-74-1 and FCV-74-2) fail open when the reactor is at normal operating pressure (2250 psia). 3 Since the RHR system is designed for a lower ?ressure (600 psig), the ' result is overpressurization of the RHR ' system w;.th gross failure of the ' RHR boundary and an uncontrolled LOCA outside containment. In the analysis performed in WCAP 11736 for Salem i several failure ,
- combinations are considered which would result in both inlet isolation '
l valves being open. These failure modes are defined as : 1) rupture of the two series suction valves and 2) failure to have closed one suction valve or spurious opening of the valvo and subsequent rupture of the other valve. Failure to close both inlet valves was not considered because the candition would become apparent as the RCS increased in pressure (see section 6.2.1.3) and corrective action would be taken thus precluding system overpressurization. l
* , ., , . , - . , - - , .,.m,. - . . , , - - - ---,,,e..... - - -
t c 3 ; ? t i SQN-SQS2-0097 R1 Page 8 of 17 . Prepared n c- Date u 6 /M ' Checked 7XN- Date IUw/89
- .r. w. . .r : :.;.: :: . u.:.T... . :. :. . .. . ;
- ..;;r.::.. .rt.:.:.. :.::n r - ::. :.. :/. ..: : ; ::/. *:.- -
-- . c .
. The general equation used to calculate the frequency of an Event V
- (F(VSEQ)) with the above failure modes ist - '
- w- . . - .: . . . . .
F(VSEQ) = X [(f 2 ) Q(Y 1 ) + (f1 ) Q(Y2 ) + (f 2) Q(V 1R)) , where - f t.:: -3(VS E Q) /...w. the _ frequency of an Event V sociuence . X = the number of RHR suction lines (1 for Salem & Sequoyah) [ (f2) = failure rate per year of RCS valve due to rupture ! (fi) = failure rate per year of RHR valve due to rupture i Q(V1 ) = probability that tna RHR valve is open Q(V2 ) " probability that the RCS valve is open
=
Q(V1R) probability of rupture of RHR valve Fault trees were developed to determine the probability that one of , the inlet isolation valves is open at power conditions (Q(V 1) & Q(V2 )). These fault trees are shown in Appendix B of WCAP 11736 (rarerence 3 ) Two fault trees were developed to determine the probability that the , valves were open for this sequence. One with ACI in place and the second with the ACI removal changes made. The scenarios examined in tho' fault tree for the case with the ACI are: 1) the op .i.cr fails to remove power to the valve by racking out the - circuit breaker and subsequently the valve spuriously opens during power operation or 2a) the operator fails to close the valve during startup (or the operator attempts to close the valve but due to some component failure, the valve does not close) and 2b) the autoclosure interlock fails _. to perform its function and doeo not close the valve and the operator ' fails to detect that the valve is not closed during startup or power operation.- For the case with the autoclosure interlock removed, the scenarios . developed in the fault trees are: 1) the operator ft.ils to remove power to ' the valve by racking out the circuit breaker and subsequently the valve opens during power operation (note: this is identical to scenario 1 above) or 2a) the operator fails to close the valve during startup (or the ' operator attempts to open the valve but it does not close) (notes l ddentical to scenario 2a above) and 2b) the operator fails to detect that the valve is not closed and then close it when the overpressure alarm is received (or the alarm fails to operate). i ' I h
y= . SQN-SQS2-0097 R7. Page 9 f Prepared 75 t- Date t n, o ' checked G:KM Date A M ueto ' Essentially the difference between these two fault trees is scena~rio 2b where the autoclosure interlock is replaced by a control room alarm which must be detected by the operator (s) who, then, must close the inlet isolation. valves. These-fault trees are quantified and the probability of the suction valves being open during operation is 1.48 E-04 with the autoclosure interlock and 1.10 E-06 without the auwi=lre interlock. The - fault trees indicate thet the alarm circuitry with the required operator action are less likely than the au*1=2re interlock to fail to close the inlet suction valves. .
~
t These probabilities are substituted into the general cquation for : Event V and quantified for the frequency of occurrenes with and without the au*1=lre interlock. The frequencies are: 8.35 E-07/ year with ACI and 5.77 E-07/ year without ACI. The frequency of Event V decreases by approximately 31% as a result of removing the ACI. 6.2. Low Temperature Overpressurization Events A number of events have occurred during startup or shutdown (low ' temperature events) which have the potential of overpressurizing the RHR system. The effect of these transients will be altered by the removal of the autoclosure interlock. WCAP 11736 examines these tr cients and analyzes the effect of ACI removal for Salem 1. Sequoyan 1 & 2 are ex=hi to respond the same as Salem 1 due to the =4*41adty in design of the two plants. The overpressurization analysis uses event trees to model the mitigating actions (both manual and auh*M following the occurrence of low temperature overpressurization events. s Two general categories of low temperature overpressurization events I have occurred in the industry and are analyzed: 1) events that affect the the balance between mass addition and mass letdown; and 2) events that affect the heat input / removal balance. 6.2.1. Heat Input Transients 6.2.1.1 Premature Opening of the RHR Suction Isolation Valves . If the suction 4_an1*4m valves (FCV-74-1 & FCV-74-2) were opened prior to reducing the RCS pressure below the RHR design pressure, overpressurization of the. RHR system could occur. However these valves are equipped with an open permissive interlock which prevents the opening of these valves above RHR design pressure and their electrical power is procedurely locked out during plant heatup from hot shutdown to hot standby (reference 13 & 14). The power to these valves is not restored until normal cooldown when placing RHR decay heat removal in service and RCS pressure is below 380 psig (reference 12). Because of these features, i.e., the open permissive interlock and the power lockout, this type of transient is not considered likely at Sequoyah and is not analyzed. R? WCAP 11736 states that the motor operators on thw valves at Salem 1 are sized such that the valve does not have sufficient corque to open against RCS pressure. TVA believes that the SQN valves have sufficient torque to open against full RCS pressure. However, the capability of the valves to open against RCS pressure has no . impact on this analysis as the open permissive and power lockout would sufficiently preclude this . transient. '
t l 3 L SQN-SQS2-0097 R1 Page 10 of ).7 Prepared 7e e_ Date 8'ho/ H !
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Checked FY# Date R A /f al l
. :. . :?-. ;;.. : ~. . - . . .
2.m.: &.- ..m .: -W . . :- .:v: ::. .. ::....:. j6.2.172 : Inadvertent Control Rod Withdrawal .During Shutdown
~ t Pihe withdrawal of one or more banks of control rods during RHR l
- operation would result in.a power excursion in the reactor and would be '
. terminated by automatic features of the Reactor Prv#a+% System. The RHR relief valve (74-505) would help mitigate the transient and the RMR system would not pressurize above 110% of the RHR design pressure or the ACI -
setpoint. The removal of the. ACI would not have an impact on this transient, and, therefore, it was not analyzed. 6.2.1.3 Failure to Isolate RHR System During Startup . During plant startup, the RCS is water solid and the pressurizar ; l heliters are energized. The RHR suction isolation valves are open and the RHR pumps are discharging the excess reactor coolant to the CVCS. After the reactor coolant pumps are started, pressure is controlled by the RHR system until the pressurizer bubble is formed. Following bubbic formation, i the RER system is isolated from the RCS by closing the suction isolation - valves (reference 5). , If the RHR system is not isolated as directed in the procedures, as , the RCS pressure increases above 450 psig, the RER relief valve (74-505) would discharge into the pressurizar relief tank (PRT) slowing the increase in pressure and sounding an alarm on increasing tank level. This tranziant is not considered to be a credible event past this point and is not analyzed in this calculation or WCAP 11736. Note if one of the 4 suction relief valves were left open, this event would fall under the Event V analysis presented earlier. 6.2.1.4 Inadvertent Pressurizer Heater Actuation If the pressurizer heaters are inadvertently energized during shutdown while the reactor is closed and the RHR system is operating, pressure will increase in the RCS and RHR system until the RHR. relief valves open and discharge into the PRT, sounding an alarm. If the relief valves fail to open, the RHR system would overpressurize.until the heaters are automatically shut off at 10% pressurizer volume. This event would be slow developing and annunciators in the control room would alert the operator of PRT level increase and instrumentation would inform the operators of increasing reactor pressure. Due to the pace of this transient and indication in the control room, the operators should recognize this transient and mitigate it before the autoclosure interlock setpoint is reached. This transient has not happened at a Westinghouse plant and is not analyzed in this calculation or WCAP 11736.
.y .... - . - - - .
.o . SQN-SQS2-0097 R1 7 Prepared rrc- Page11ofp19 Date a e /*
- Checked GXM- DataI M AM 6.2.1.5 Startup of an Inactive Reactor Coolant Pump During the cooldown of the reactor,3.he reactor coolant pumps are stopped when the reactor coolant temperature is.below 160'F and the RHR heat exchangers are used to continue lowering the coolant temperature.
Since the flow through the steam generators st@s when the reactor coolant pumps are stopped,.the. reactor coolant in.the steam generators may remain at.a temperature greater than the RCS temperature since there is little
- circulation through the steam generators. If a reactor coolant pump is started, the sudden heat input into the reactor coolant from the steam generators would cause a rapid increase in reactor coolant temperature.
Another transient caused by the startup of the reactor coolant pump would occur if a reactor coolant pump was stopped during heatup while the RHR system was in geration, but the charging and seal injection water continued in servios. This water would collect in the vertical pipe loop below the reactor coolant pumps. Phan the inactive reactor coolant pump was started this water would be injected into the reactor, expand as the density decreased and cause a pressure increase in the RCS and RHR systems. Depending on initial RCS pressure, this increase could overpressurize the RHR system. The startup of an inactive reactor coolant pump transients are considered in Section 6.2.1.7 " Heat Input Transient n Analysis." 6.2.1.6 Loss of RHR Cooling Train An increase in temperature and pressure would result due to loss of one of the two RHR cooling trains during the early stages of plant ' cooldewn, when heat generation from the reactor core exceeds the heat removal capacity of the remaining train of the RHR system. During this
- phase of cooldown, the operators are closely monitoring the RCS parameters
, and would mitigate this transient before the RHR system exceeded design pressure. This transient is not analyzed further in this calculation or '
WCAP 11736. 6.2.1.7 Heat Input Transient Analysis The heat input transient with tu potential for the greatest overpressurization of the RHR system is tne startup of an inactive reactor coolant pump with higher temperature coolant residing in the steam generator. WCAP 11736 ruferences another Westinghouse analysis, WCAP 10529, which indicates that following startup of a reactor coolant pump, the peak pressure change of approximately 1500 psi would occur in roughly 90 seconds without relief valve actuation. Because the RHR suction inlet valves have a two minute closing time, the RHR system would be subjected to high pressure before the valves could close which could lead to an interfacing IDCA. The low temperature overpressurization system (LTOPS) is
Na
. . j i
SQN-SQS2-0097 R1 Page 12 of A7 Prepared vcc- Date " N /M ) Checked Ww- Date u A M - designed to prevent this type of RCS pressure surge by opening the l pressurizer PORV. .Both the.RHR relief valve and the low temperature overpressurization system would have to fail in order for this event to occur and the probability of both> these systems failing is small.
- ... ':. .;a r=r=: ::u .:. ~:. a.- ::=... .. . . . i The next most severe hast input transients are loss of an RHR train, reactor coolant punp startup with injection of cold seal water, or actuation of the pressurizer heaters. These transients evolve quickly but would not raise the*RCS pressure above. 450 psig. The low temperature '
overpressurization system and RHR relief valve would' be used to mitigate these transients. Since the RHR autoclosure interlock setpoint would not ; be reached, the ACI would not be involved in1 mitigating these transients. ' Therefore, the removal of the RHR auM=lra interlock will not have an effect on these heat input transients. In the case of the reactor coolant pump startup, the low temperature overpressu*Fim system works to limit the pressure surge or RHR system overpressurizes before the ACI has time to function. For the other heat input transients the RHR relief valve prevents the RHR pressure from reaching the ACI setpoint. 6.2.2. Mass Input Transients I 6.2.2.1 Opening Of Accumulator Discharge Isolation Valve ' t Plant procedures require that the accumulator discharge valves be closed and de-energized during plant cooldown. If these valves were to open, water would be forced into the reactor coolant system causing a
' pressure transient in the RHR system The peak pressure reached during this transient would be between the initial RCS pressure and the accumulator pressure (700 psig). An event tree was not constructed for ,
this transient because the peak pressure would be below the ACI setpoint. 6.2.2.2 Letdown Isolation During cold shutdown, a letdown path is established through the RHR system to control pressure in the RCS. If this letdown path is lost _. throught 1) closure of the letdown control valve, 2) isolation of the RHR/CVCS crossover, or 3) closure of the RHR inlet isolation valves, pressure control is lost and the pressure transient must be controlled by the RHR relief valve or the low temperature overpressurization system. If the inlet isolation valves close, the use of the RHR relief valve is lost. This transient is analyzed in Sections 6.2.2.4.1 and 6.2.2.4.2 d
,e '. P SQN-SQS2-0097 R1 Page 13 of 17 i Prepared -7 5 c- Date u/b/r9 checked GX4- Date u /w/t9 > 6.2.2.'3 Charging / Safety Injection- Pump Actuation - r: .When the reactor-vessel. is water solid during cold shutdown, the safety injection signal is blocked to prevent high pressure injection by ; the _high. head safety injection pumps or the charging pumps. The inadvertent actuation of one of these pumps when the RCS is water solid without an increase in letdown would result in a pressure transient. This transientnis analyzed-in Section 6.2.2.4'.3 6.2.2.4 Mass Input . Transient . Analysis Event trees were constructed in the WCAP analysis to determine the wequences of these mass input transients. The safety functions which wc:.e questioned for transient mitigation, i.e. the top events were: 1) cass input initiating event, 2) RHR isolated, 3) RHR relief valves lift,
- 4) low temperature overpressurization system works, Sa) RHR inlet isolation valves automatically close (present design), 5b) oparator closes RHR inlet isolation valves (proposed ACI deletion changes), 6) operator 4 stops safety injection or charging pump 7) operator opens a PORV, 8) RHR relief valve ressats, 9) pressurizar PORV ressats. The success criteria
- for each of these top events was determined and the failure probability was e*1m1*=d. Consequence categories were determined for the initiating events, given that top event failure (s) did not prevent overpressurization.
of the' RHR system.
'6.2.2.4.1 Letdown Isolation Analysis--Loss of CVCS Letdown -
For this event, it was assumed that one charging pump was cphat.ing at ; its mavim"m flow rate and only one RHR relief valve or one PORV must operate to mitigate this transient. The initiating event was loss of latdown by 1) closuru of the letdown wLwl valve or 2) isolation of the ' RHR/CVCS crossover path. Two event trees were constructed, with and without the prw ACI deletion changes, and the trees quantified. The ; results showed that with the proposed ACI changes there was a slight ! decrease in the "MSCI" consequence category and that there is an increase ! in the "HOW' category from 5.66E-15/ shutdown year to 1.49E-11/ shutdown 1 year. l The "MSCI" category is Le1*4m of the RHR system with the running I charging pump not stopped; pressure control is performed by the low I temperature overpressurization system having opened a PORV. There is a l loss of coolant and the operator must take action to stop the running pump ; and then check that the PORV reseated completely. l I
~ The "HOW' consequence category is a high overpressure with the RHR system open to the RCS. The running charging pump is not stopped and no relief valves have actuated. The RHR system integrity is lost and an interfacing IOCA has occurred. The operator must attempt to isolate the RHR system.
.e .o SQN-SQS2-0097 R1 Page 14 of 17 Prepared TG c- Dateide/M Checked 9 KH- Date n A /fi
. .. The "HOPV" is a severe consequence accident with reactor coolant being released outside containment, however the frequency of 1.49E-ll/ shutdown year is very remote and thus the overall increase in the frequency of an !
interfacing @CA for.this in4*4ating event as a result of making the ACI 1 deletion changes is not significant. J p.. ...,......g .. ,
;_.: .. . _ m . t. . .. _ .. : . .. .
6;2.2.4;2 Letdown Isolation-- RHR Isolated Analysis
- The ir4*4=t4ng event for this transient is the inadvertent closure of I
.the RHR inlet isolation valve (s). In this case, if the autoclosure interlock were removed, the initiator frequency would be reduced. WCAP l 11736 assumes the frequency would be reduced by one half. The result of t reducing the in4*4*4ng event frequency decreases the challenges to the mitigating safety systems and reduces the frequencies of all the adverse consequence categories by a total of 5.89E-02/ shutdown year which is a significant reduction.
j l 6.2.2.4.3 Charging / Safety Injection Pump Actuation Analysis 1 In this event, it is assumed that one charging pump and one safety
- injection pump are started. The success criteria was determined to be two L
PORVs or one PORV and one RHR relief valve. The event tree was constructed ) and quantified for an RHR system with and without the ACI changes. There !- was a total increase in the frequencies of the adverse consequences for l this event of 2.4E-10/ shutdown year as a result of the ACI deletion l ' changes. This increase, even though it includes the most severe . consequence of an interfacing IcCA outside containment, does not represent i a significant increase due to its low (2.4E-10/ shutdown year) frequency. 6.2.3. Summary of overpressurization Transients Analysis The overpressu**im analysis considered the Event V sequence where the RHR inlet isolation valves fall open during power operation which allows high pressure reactor coolant to overpressurize the RHR system _ leading to an interfacing LOCA. The results of the Event V analysis indicate that making the ACI deletion change reduces the frequency of this event. l- 'Ihe overpressurization analysis also considered transients that occur } l, during reactor cooldown and startup. These were divided into heat input and mass input transients. The deletion of the ACI was not considered to , impace the heat input transients because they either happen so fast that the inlet valves can not close fast enough to mitigate the transient even if the ACI were installed, or the transient did not increase RCS pressure to the ACI setpoint. r
=D - ,s > w. y + - - .-+e_e v -s-ew v.-= e.--.-_ _ __ ---_ _ _ . _ _ _ _ _ _ _ _ , , _ , , _ _ _ _
t- 'O l
.e t
=
SQN-SQS2-0097 R1 Page 15 of J7 Prepared -f5c- Date " /wM Checked GKN- Date It A/[1_ The mass input transients were analyzed by constructing event trees to ' determine the _ change cin frequency. of:the consequence categories for
.several mass input -initiating events. There was a slight increase in some adverse consequence sategories as;a. result of making the ACI deletion
' shangen but.this increase.wam.pr*b414*4m11y insignificant compared to
.the decrease caused by reducing the initiating event frequency of the spurious actuation of the RHR inlet isolation valves. ;
6.3 RHR navailab'i1kty Ana5ysis . The RHR system was analyzed to determine its unava41ah411+y due to the ; spurious closure of the inlet isolation valves (FCV-74-1 & FCV-74-2) .
. Separate fault trees were developed in WCAP 11736 to determine the system unavailability for startup of the RHR system, for short term cooling (72 >
hours), and long term cooling (6 weeks). The short term and long term oooling fault trees were constructed both with and without the autoclosure of the inlet isolation valves to show the change in system unavailability due to removal of the autoclosure interlock. 6.3.1 Failure to Initiate RHR A single fault tree was developed for this phase of RHR operation to l identify those faults that oculd impact the startup and first two hours of j operation of the RHR system. The autoclosure interlock does not play a , E role in RER startup, rather the inlet valves' open permissive prevents the valve opening until RCS pressure is below 380 psig and this feature is not l 'being modified- by the proposed ACI changes. The fault tree for Salem was developed from the Salem operating procedures. The Sequcyah procedures for RHR startup, SQN SOI-74.1, Section A (reference 12), are functionally similar to the Salem procedure described in the WCAP analysis and the fault trees are therefore - applicable. The dominant contributors to RHR startup were operator errors of failure to energize control boards for valves which had been de-energized . for power operation and failure to open other valves required for RHR operation. '
~
6.3.2 Failure of Short Term Cooling " Both pump trains of RHR are required for short term cooling due to the decay heat generation immediately following shutdown. Failure to supply cooling flow from two RHR pump trains into three of four RCS cold legs constitutes RHR system failure. Two fault trees were developed to determine the impact of the removal of the ACI.
3 SQN-SQ32-0097 R1 Page 16 of 17 Prepared Trc. Date<</n/rt Checked W WW Date ILMt9 : The dominant. failure. contributor. for loss of.short term cooling for both: fault trees .(with and without ACI) was the failure of one of the two i
'RHR pumps to runtfor.72 hours. For the Salem plant, the failure '
probability .for short term. cooling was reduced 13 percent with the deletion. ofc..the..ACI. The . reduction..in RHR short term cooling' unavailability _ for.Sequoyah .would be:similar following deletion of the ACI.. 6.3.3 Failure of Long Term Cooling ~ ' Icng term cooling requires cooling flow injection into any two RCS cold legs from two of four RHR trains. for 6 weeks. This fault tree primarily features spurious closing of various valves over the six week period and failure of the first pump with failure of the second pump to ' start and run. The dominant failure contributor for Salem during long term cooling was RHR pump failure. For the fault tree with ACI present, the other top contributors involve the single failure of a component associated with the
. ACI such as the power supply, signal comparator or pressure transmitter which causes spurious closure of one of the RHR inlet isolation valves.
The deletion of the ACI resulted in a 67 percent reduction in system unavailability for Salem. The Sequoyah long term cooling unavailability would be reduced by a similar amount following removal of the ACI. C 7.0. CONCLUSION This c*1mlation examined the impact of the removal of the autoclosure interlock (ACI) feature on the inlet isolation valves (FCV-74-1 & FCV-74-2) of the RHR system for Sequoyah 1 & 2. This calculation rufstanced WCAP 11736 " Residual Heat Removal System AuP1wre InW1~'k Removal Report for the Westinghouse: Owners Group" and is a review of that report and a comparison between the reference plant, Salem 1, and Sequoyah. The two plants have very similar RHR system configuration, control logic, and design for the autoclosure interlock feature. By virtue of this similarity, the analysis for Salem is considered valid for Sequoyah. . The overpressurization transients which have the potential for an uncontrolled loss of coolant outside containment were examined to determine the effect of ACI deletion. The Event V sequence, heat input and mass input events were analyzed. A reduction in event frequency (a net positive result) was the result of removing the ACI for these transients. The RHR system unavailability to remove decay heat from the react >r core was calmlated with fault trees constructed both with and without ACI. The analysis showed that the removal of the ACI resulted in an improvement in RHR availability. 1
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SQN-SQS2-0097 d R"A Page 17 pf }7 Prepared T5 t- Date -t / h, /+d ' Checked G W Date >_A U9 D' C-Therefore, it is;the conclusion.of this. calculation that making the j design, Technical SpWN%, and procedure changes associated with the remwal of the autoclosure interlock as outlined in this calculation and ' WCAP'11736 will reduos the frequency of an RHR overpressurization event a'nd increase the RHR system availability at Sequoyah. - -
8.0 REFERENCES
- 1. Quality Information Request, QIR SQPSQN89330 RO, RIMS NO. .
B25'890828002. .
. a
- 2. NRC Generic Letter No.88-17, " Loss of Decay Heat Removal",
October 17,1988.
- 3. WCAP 11736, " Residual Heat Removal System Autoclosure Interlock Removal Report For The Westinghouse owners Group", Volumes I & II, Rims No. B26 '88 0714 364 & B26 '88 0714 365.
- 4. Sequoyah Design Criteria, SQN-DC-V-27.6 R3, " Residual Heat Removal System".
- 5. Sequoyah FSAR Section 5.5.7 R6, " Residual Heat Removal System".
- 6. Sequoyah FSAR Section 6.3 R6, " Emergency Core Cooling System".
, 7. Sequoyah Emergency Instruction E-1 R7, " Loss of Reactor or
- Secondary coolant, page 12. .
- 8. Sequoyah FSAR Section 7.6.2 R6, " Residual Heat Removal Isolation I Valves".
- 9. Sequoyah Design Change Request, SQ-DCR-3365.
- 10. TVA Sequoyah Drawings, 45N779-11 RV, 2-47W611-74-1 RO, 1,2-43N765-13 RO, 45W657-32 RG, 45N779-12 RY,1-47W611-74-1 RO, 47W 610-74-1 RN, 1,2-47W810-1 R6. _
- 11. WASH 1400, NUREG 75/014, " Reactor Safety Study, An Assessment Of Accident Risks In U.S. Commercial Nuclear Power Plants", October 1975.
- 12. Sequoyah System Operating Instruction, SOI-74.1 R 51, " Residual Heat Removal System".
- 13. Sequoyah General Operating Instruction, GOI-1 Rev 85, " Plant Startup From Cold Shutdown to Hot Standby" g-
- 14. Sequoyah System Operating Instruction, SOI 63.1 Rev 59, " Safety Injection System" 9
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l- TENNESSEE VALLEY AUTHORITY' m F' + -SEQUOYAH NUCLEAR PLANT UNITS 3 AND'2 ta - t- , >
. EVALUATION OF REMOVAL OF' RESIDUAL HEAT I:: 4 u , ,
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. REMOVAL AUTOCLOSURE INTERLOCK ~
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.QA Record -
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825 '90 0310 010 Westinghouse Enere Systems Ba ass Electric Corporation Pinsburgh Pennsylvania 15230 0355 Mr. P.-G. Trudel TVA-90-653 Project Engineer March 8, 1990
-Tennessee Valley Authority PO Box 2000 Soddy Daisy, TN 37379 Conkfu) h
$5P62.-465930 Tennessee Valley Authority Sequoyah Nuclear Plant Unit 1 Residual Heat Removal Autoclosure Interlock Removal Report
Dear Mr. Trudel:
Attached for your information and use is the suiject report. An advance
' copy was hand carried on 3/8/90.
Please call us if there are questions. Very truly yours, WESTINGHOUSE ELECTRIC CORPORATION r j B. J. Garry,, Manager
/ TVA-Sequoyah Project Custmr Project:: Department
\
cc: P. G. Davic D. M. LaFever RIMS, ET SLE 26P K w/at*-%ata I O i , < a 4
g A ; r. M i -- , f 4
, TENNESSEE VALLEY AUTHORITY I
SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 h EVALUATION OF REMOVAL OF RESIDUAL HEAT REMOYAL AUT0 CLOSURE INTERLOCK
'i
,1 u -?
.. March 1990
+
.. Prepared by:
.. A.L
,/ .N B. C19sl y ,
RiskManagdmr.ntandOpe{ajionsImprovement-t; Approved by: l ff JVPK.J. Vavrek Risk Management and Operations Impiovement Westinghouse Electric Corporation l, l' .
,{
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d TENNESSEE VALLEY AUTHORITY m .- SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 I EVALUATION OF REMOVAL-0F RESIDUAL HEAT REMOVAL AUT0 CLOSURE INTERLOCK L& o y-
SUMMARY
, L The purpose of this report is to document the qualitative evaluation of the
' deletion of the. Residual Heat Removal System suction valves' autoclosure
-interlock (ACI) and the implementation of a control room alarm for the Tennessee Valley Authority (TVA) Sequoyah Nuclear Plant Units 1 and 2. The ,
evaluation provides a comparison of the Sequoyah configuration with that in
+ WCAP-Il736-A, " Residual Heat Removal System Autoclosure Interlock Removal
- Report.for the Westinghouse Owners Group,' for Salem (the reference plant for Sequoyah).
.f WCAP-11736-A provides the analyses which justify deletion of the autoclosure' L: interlock associated ' ith w the Residual Heat Removal System (RHRS):
u -- suction / isolation valves. A probabilistic analyses was used to demonstrate L= that deletion of the autoclosure interlock and the addition of a control room (' -alarm results in a net safety benefit. The safety evaluation examined the l effect of ACI removal on interfacing systems LOCA potential, RHRS availability, and low temperature overpressurization protection. , L The estimated results for Sequoyah based on a comparison to Salem are shown , L .below: l With Without Percen ACI Afd Chanae) ! Interfacino System LOCA
-F(VSEQ) 9.49E-07/ year 5.77E-07/ year -39 RHRS Unavailability RHR Initiation 3.20E-02 3.20E-02 0 Short Term Cooling 1.63E-02 1.40E-02 , -14 l Long Term Cooling ~ 4.00E-02 1.20E-02 -70 L
Overpressurization **
~
'* (-) - Reduction
=
(+) - Increase
** - Reduction in some categories and a small increase in other categories .
Based on the comparative evaluation between Salem and Sequoynh with regard to the deletion of the sutoclosure interlock, the three different areas examined i
^ ~# ,
indicate that the results and conclusions for Salem 'in WCAP-11735-A are not-invalidated by the proposed change for Ses uoyah. The deletion of the ACI and the inclusion of a control room alarm to wan the operator that one saries suction / isolation valve is not fully closed or RHR pressure is above the alarm setpoint is acceptable for Sequoyah. 1 o-I w - + , e
( 1 fl;n? 4
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TENNESSEE VALLEY AUTHORITY ( . .:. g.
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SEQUOYAH NUCLEAR FLANT UNITS 1 AND 2 , EVALUATION OF REMOVAL OF RESIDUAL HEAT REMOYAL AUT0 CLOSURE INTERLOCK i k-i
- 2. -
Section Page ,
.n
SUMMARY
. 1 4
1.0 INTRODUCTION
AND PURPOSE I a b 1
"[:
2.0 COMPARISON BETWEEN SEQUOYAH AND SALEM 2 y. l~ 2.1' RHR' System Configuration 2 , 2.2 Present' Autoclosure Interlock Circuitry ~ 2 2.3_ Sequoyah Proposed Circuitry Change 9 l 4 3.0- IMPACT'ON PROBABILISTIC ANALYSES 19 3.1 Interfacing System LOCA 19 3.2 RHR Availability 28 3.3: Low Temperature Overpressurization 41
4.0 CONCLUSION
S 46 f ..
~5.0 REFEREllCES. -/ ~
47 APPENDIX A INFORMATION RECEIVED FROM SEQUOYAH FOR ANALYSES 48 i. t 2: h -: 1_
I
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..o- .-
TENNESSEE VALLEY AUTHORITY 4
-SEQUOYAH UNITS 1 AND 2 e
' EVALUATION OF REMOVAL Of RESIDUAL HEAT REMOVAL AUT0 CLOSURE INTERLOCK
,t
1.0 INTRODUCTION
AND PURPOSE
.The purpose of this report is to document the qualitative evaluation of the deletion of the Residual Heat Removal System suction valves' autoclosure s interlock (ACI) and the implementation of a control room alarm for the
; Tennessee Valley Authority (TVA) Sequoyah Nuclear Plant Units I and 2. The
'l evaluation provides a comparison of the Sequoyah configuration with that
{ ' proposed in WCAP-11736-A, " Residual Heat Removal System Autoclosure Interlock
. Removal Report for' the Westinghouse Owners Group," (Reference 1).
, WCAP-11736-A provides the analyses which justify deletion of the autoclosure-interlock associated with the Residual Heat Removal System (RHRS) suction / isolation valves for four reference plants (Salem Unit 1, Callaway Unit 1, North Anna Unit I and Shearon Harris). A probabilistic analyses was used to demonstrate that deletion of the autoclosure interlock and the
= addition of a control room alarm to alert the operator if an RHRS suction / isolation valve is not fully closed when RCS pressure is above the alarm setpoint results in a net safety benefit. The probabilistic analysis examined the proposed. change based on a safety evaluation of the effect of ACI removal on-interfacing systems LOCA. potential, RHRS availability, and low temperature overpressurization protection.WCAP-Il736-A was submitted to the '
l , NRC and a safety evaluation.and an acceptance, for referencing the WCAV in i g plant specific submittals.was provided in 1989 (Reference 1). The NRC acceptance statn that "the licensee should do sufficient PEA and safety analyses to ensure that its plant will not show results that invalidate the ,, conclusions of WCAP-Il736-A." This report provides an evaluation of the Sequoyah plant and TVA's proposed implementation of ACI deletion and installation of the alarm. The intent is
.to compare tha Sequoyah proposed change to that in WCAP-ll736-A and to determine if the change invalidates the conclusions in hCAP-ll736-A. The l
determination is based on a qualitative comparison of the probabilistic analyses in WCAP-11736-A and a Sequoyah analyses. 3/5/90- 1
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':2.0 COMPARISON BETWEEN SEQUOYAH AND SALEM *
- s. . ,,
- The Westinghouse Owners, Group (WOG) plants participating in WCAP-11736-A were categorized into one of four groups based on similar RHR System _,
configurations and design characteristics in order to minimize the work to be perfonned by other WOG. plants. Sequoyah Units 1 and 2 were categorized in
#k Group l'in which- thel reference plant ~ for the group was Salem Unit 1. Thus the-Sequoyah plant RHR system configuration and autoclosure interlock circuit i are' compared to the Salem plant to determine what portions of the 1 probabilistic analyses would be impacted.
2.1' RHR System Configuration t The Salem RHR system configuration is shown in Figure 1. The RHR system takes a suction from the RCS through two motor-operated valves in series. The suction line then splits into two trains of RHR, each containing'a pump i and heat exchanger. The t' rains each inject into two cold legs through a series of check valves. The Sequoyah'RHR system configuration is shown in Figure 2. The system configuration is essentially identical to the Salem configuration. There are no ' component differences between the Sequoyah and Saler RHR system
. designs. Because the RHR system designs are identical, the RHR availability analysis which models the RHR system would require only component h ,
identification numbers (tag ids) to be changed. ,
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2.2 Present Autoclosure Interlock Circuitry
-The Salem original autoclosure interlock circuitry and motor operated valve >m control circuitry are shown in Figure 3 logically and Figure 4 physically.
When a-RHR suction valve is open and RCS pressure is greater than the
.setpoint-(measured by presnire transmitter PT-403 located in the RCS), tho
. RHR suction valve would automatically close through relay 63Y/RCP.
.c The sequoyah present motor operated valve circuitry is .shown lii Figure 5 logically and Figure 6 physically. When a RHR suction valve is open and RLS
. pressure is greater than the setpoint (measured by pressure transmitter PT-405 located in the RCS), the RHR suction valve would automatically close '
through relay PB405B. The same principal applies to the other suction valve J with pressure transmitter PT-403. (, i
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SEQUDYAH RHR SUCTION CONTROL CIRCUITRY VCV 14 1 AUb VC V-14. 2. 4 3/4/90 9
3 .,"
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i,. :,:In crder to compare the autoclosure interlock circuitry and the motor operated valve control: circuitry, the two plants are compared in Table 1.- In
'the analysis of the motor. operated valves in the interfacing system LOCA evaluation, the RHRS availability evaluation and the low temperature everpressurization analysis, the components with an "NA" in Table 1 under Sequoyah would be deleted from the Salem analysis and those with an "NA" under Salen would be added to the Salem analysis to model the Sequoyah valve l circuitry.. For example, the I/V Input Modules would be deleted from the Salem fault trees because Sequoyah's circuitry does not have these modules.
The' Salem analysis would also have to be modified to include the shunt trip circuitry used in the Sequoyah design. 2.3 Sequoyah Proposed Circuitry Change The elimination of the autoclosure interlock requires the addition of a control room alarm to alert the operator in the event that one of the RHR suction / isolation valves is open and RCS pressure is greater than a given setpoint. This'is to ensure that a double isolation barrier exists between l the high pressure RCS and the lower pressure RHR system during power oper. tion. WCAP-11736-A proposed that the deletion of the ACI and the alarm circuit be added using the logic shown in Figure 7 (shown for Salem) and implemented L along the lines shown in Figure 8. l The Sequoyah proposed change is shown in F.igure 9 logically and in Figure 10 (. mechanically. This change uses an "0R" logic rather than an "AND" logic as L proposed in WCAP-11736-A. The Sequoyah change would provide a control room alarm-if one suction valve was open and the other suction valve was closed or o the? alarm would annunciate when the RHR pressure measured above a given setpoint.by either of two pressure switches. The Sequoyah proposed change l serves'the same function as the change proposed in WCAP-11736-A, i.e., to alert the operator of an improparly positioned RHR suction / isolation valve. l 3/4/90' 10 ;
, ~ - - - _ . . . .
m,- , C, .s' r *~ _ TABLE 1
' " ' c
'. COMPARISON OF SALEM AND SEQUOYAH SUCTION VALVE CIRCUITRY
.c ,
+f' COMPONENT DESCRIPTION
, SALEM 10 SE000YAH ID
.p 8702 (1RHI)
V Pressure Interlock Circuitry- 8702-(rW-74-1)
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. Pressure Transmitter PT-403 PT-405 Toggle Switch ICT-403 XS-68-68'(PS405) m . Loop _ Power Supply IPQ-403 PX-68-68 (PQ405)
'l Test Point 1-TP-403-1 PP405 11/V Inp Mod h ;
1/V Inp Mod Signal Comrrrator Dual Circuit IPC-403/R IPN-403R . NA NA
IPC-403A-B PB-405 Bistable Switch (Close) IBS-403B PS-405A Bistable Switch (0 pen)- IBS-403A. PS-405B Motor Ooerated Valve Control Circuitry
{ Common Comoonents i Circuit Breaker from MCC Bus 8 w Circuit Breaker Power Transformer 230/118V 480/120V Control: Circuit Fuses 2 15 AMP 2-Three: Phase Close Contacts. 9/C C Phase A,B & C '
- Three Phase Open Contacts 9/0 0 Phase A,B & C e Three Phase Fuses T1,T2,T3 Phase A,B & C s
. Thermal Overload Contact- 49 Power Supply. Contacts NA OL (2 in Series)
XS-74-1/NOR1,2 &7
. Blown Fuse Trip Contacts NA Note 4 (3 in Series) ~7 Close Circuitry Comoonents Pressure Transmitter Contacts (Close) 63Y/RCP PB405BX-Closing Torque Switch 33/CVC NA.
Limit Switch. Limit Switch (Torque Bypass) 33/CVO NA 33/0VC , 33/ac Interlock Contact (Close Circuit) 9/0- 42b/o Interlock Contact (9X/C Circuit) 9/C -
' :NA ' <
Handswitch Contact 5/CSV2 Handswitch Relay Coil HS 74-1A/CLOSE
- l. 5/CSV2 NA Control Room Switch Contact (Close) 1/CLOSE NA Diode-in Handswitch Circuit D5 NA Lockin Relay Coil Contacts (Close) 9X/C Lockin'Re1ay Coil (Clo w) 42a/c 9X/C NA Peaar Supply Contacts NA XS-74-1/NOR 3 g
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- NA - not used in circuitry for that plant
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TABLE 1 (cont ). < k ( ,
. COMPARISON OF SALEM AND SEQUOYAH SUCTION VALVE CIRCUITRY t-
.p COMPONENT-DESCRIPTION SALEM ID SE000YAH ID' E :, /00en Circuitry Components
$; Pressure Transmitter Contacts (0 pen) 63X/RCP PB405AX Opening. Torque Switch 33/0VO NA AL Limit Switch-(Torque Bypess) 33/CVC- NA Limit Switch. 33/0VO . 33/bo i Interlock Contact' Open Circuit 9/C 42b/c I Interlock Contact 9X/0 Circuit 9/0 NA i4 H:ndswitch Contact 6/CSV2 HS 74-1A/0 PEN d', Handswitch Relay Coil 6/CSV2 NA Control Room Switch Contact--(Close) 1/0 PEN NA y : Diode in Handswitch Circuit- D6 NA- i Lockin Relay Coil contacts (0 pen) 9X/0 42a/o Lockin Relay Coil (0 pen) 9X/0- NA Power Supply Contacts NA XS-74-1/NOR 4 Status Licht Indication ,
Red Light (0 pen)- R R-i Red Light Contact 33X/CSV2 NA Red Light Relay Call 33X/CSV2 NA Red Light Relay Coll Circuit' Limit Sw 33/CVO 33/ac Green Light (Close) G G , Green Light Contact 33Y/CSV2 NA ,
= Green Light Relay Coil 33Y/CSV2 NA Green Light Relay Coil Circuit Limit Sw '33/CVC 33/bo Power Supply.. Contacts NA -XS-74-1/NOR>5 & 6 !
Additional, Components. I Shunt Trip Circuitry NA: Shunt Trip . Shunt: Trip Contact NA 52 A JTrip Handswitch- . NA i 0-HS-13-20^/ Trip- . Power Supply Contact- - NA . XS-74-1/00R8 l E
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- NA not used in circuitry for. that plant i a
i s e 4 3/4/90 12
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. - _ ._ _ _ _ _ . - _ _ ___ . . _ . . _ . - . - .._. . . - - . _ _ . - -._~. - . . . . .
FIGURE 7 l [[ ~~
. SALEM PROPOSED RHR SVCTION VALVE LOGIC DIAGRAM .
i 1 SPRING RETURN TO AUTO RCS Hot Leg VALVE . OPEN- AUTO CLOSE Pressure 8702
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Figure 6-2. Salem Proposed Interlock-MOV-8702 r 3/4/90 13
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-SALEM PROP 0SEtt RHR SUCTION VALVE WIRING' DIAGRAM
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'SEQUOYAH PROPOSED.'RHR SUCTION VALVE LOGIC DIAGRAM j;
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-SEQUOYAH PROPOSED RHR SUCTION VALVE WIRING DIAGRAM s
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O{ .] l- (, i,lThe _Sequoyah change also has.several unique characteristics' with regard to ; j , implementation.' First the pressure switches used in the alarm circuit to alert the operator of high pressure are located in the RHR system downstream , of the RHR suction valves (Figure 11). When RHR pressure is greater than 380 psig, .the alarm would sound. The WCAP proposed change used the same pressure circuitry as used in the autoclosure interlock circuit which relied upon , [ pressure transmitters located in the RCS. The use of the pressure switches on the RHR system side would provide several " benefits: 1) excessive leakage past the two suction valves would be
~ detected 2) t,he operator would be alerted to a low temperature overpressure 4 I
event- during shutdown or startup even before the RHR relief valve lifted at 450 psig and 3) the operator would be alerted that during startup, the RHR system was not isclated as required. - The impact of this change on the probabilistic analyses would be factored into the low temperature ; overpressurization analysis u thet tiie operator would be alerted and would j have more time to respond to an overpressure event, pr'oviding additional l
, - protection of the RHR system. l l
A second implementation difference between the WCAP and the.Sequoyah proposed j change is that status light indication and the alarm would be powered from a .i separate power source and utilize the same limit switch (for valve position) l as shown in Figure 10. When power is removed from the suction valve by racking out. the circuit breaker, the status lights and the alarm would still , be operational. Thus,-the operator would have continuous indication of valve position by. two different indicators (status light and alarm). This characteristic'is factored into the interfacing system LOCA analyses in that I the operator would be- able to detect the improper valve position via the alarm even if the status light indication circuit failed or power was removed from the valve. 3/4/90 18
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FIGURE 11- ,
':C-LOCATION OF PRESSURE SWITCHES FOR ALARM o
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" ,J3.0 IMPACT ON'PROBABILISTIC ANALYSES i
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. This section determines the impact of the Sequoyah configuration ar.d proposed change on the probabilistic analyses conducted for Salem in WCAP-11736-A.
The objective is to determine if the conclusions based on the Salem results k are invalid based on calculations to estimate the Sequoyah results. ) 3.1 Interfacing S/ stem LOCA g,
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WCAP-11736-A, Appendix B, performed calculations to determine the change in I frequency of an interfacing system LOCA due to removal- of the autoclosure interlock. In the analysis, several failure combinations were considered in which both suction valves would be in the "0 PEN" position. These' failure-
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modes' included: 1) rupture of the two series motor operated valves in the RHR suction line and 2) one suction valve failing open and subsequent rupture of the other-valve. The scenarios examined for the suction valve failing open with the. autoclosure interlock in place were: 1) the operator fails to remove
. power to'the valve by racking out the circuit breaker and subsequently the i valve spuriously opens during power operation or 2) the operator fails to close the valve during startup (or the operator attempts-to close the valve but due to some component failure, the valve does not close) and the autoclosure interlock fails to perform its function and does not close the valve and an operator. fails to detect that the valve is not closed during startup or power operation.-
i For the deletion of the autoclosure interlock and the addition of an alarm, ; the scenarios developed were: 1) the operator fails.to remove power to the
- j. valve by racking out the circuit breaker and subsequently the valve l' spuriously opens during power operation or 2) the operator fails to close the valve during startup_(or the operator attempts to close the valve but due to L some component failure, the valve does not close) and the operator fails to detect that the valve is not closed via the presence of an alana (or the alarm fails to operate).
L r 1 I , 3/4/90 20 ,
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y: , -- Reviewing the dominant cutsets for Salem (Table B-3'in WCAP-II736-A) shows that the dominant failure modes ~are failures which occur during startup (i.e., the operator fails to close the valve and does not detect that the valve has not closed). Table 2 shows Table B-3 recreated with the cutsets
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applicable to Sequoyah marked on the right. The cutsets'which are not
- applicable are based on the fact that the Sequoyah valve circuitry does not contain these components. _ Table 3 shows the additional cutsets that are applicable for the Sequoyah design because Sequoyah has additional components -
in its circuitry. By subtracting out the cutsets which are not applicable to Sequoyah from the Salem mean failure probability and adding the probabilities associated with the additional cutsets shown in Table 3, an estimate of the mean ' probability of failure for Sequoyah'with the ACI can be calculated by the following: Sequoyah Probability - Salem Probability - (Probabilities for Non-Applicable Cutsets) + (Additional Cutsets)
- 1.48E 5.36E-05 + 1.19E-04
- 2.13E-04 Entering this probability into the equation for interfacing systems LOCA:
-F(VSEQ) = (lambda)2 Q(VI ) + (lambda)3 Q(V2 )+ (lambda)2 Q(VIR) t where (lambda)2 - failure rate of valve closest to RCS e (lambda)3 : failure rato of valve closest to RHRS '
Q(V). - probability that valve closest to RCS is open Q(V ) - probability that valve closest to RHRS is open
-Q(V R) - probability that valve closest to RHRS ruptures. .
and utilizing the failure rates in WCAP-11736-A for (lambda)2, (lambda) and Q(V yields:IR) and the Sequoyah estimated probability 3for Q(V )2 and Q(V )* 3, F(VSEQ) - IE-07/hr * (2.13E-04) + IE-07/hr * (2.13E-04)
+ IE-07/hr * (6.57E-04)
- 2.13E-ll/hr + 2.13E-ll/hr + 6.57E-11/hr
- 1.08E-10/hr * (8760 hrs / year)
- 9.49E-07/ year 3/5/90 21
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4 -.: WESTINGHOUSE PROPRIETARY CLASS 3-
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TABLE 2._
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. TABLE B-3 i k SALEN DOMINANT CUTSETS .-
FORQ(V) y 3 7 PROBABILITY THAT NOV 1RH1 IS OPEN l WITH ACI CASE j gpl,)(,,d[E MEAN PROBABILITY OF FAILURE = 1.48E-04 - o smJ
, PROBABILITY CUTSET DESCRIPTION j # tJO 1. 3.46E-05 SECOND,0PERATOR @ S TO DETECT OPEN MOV 1RH1 ,
OPENATORFAIi."S'T0"6EiECTOPENMOV1RH1 1
*j'gr ~ 2. 3.46E-05 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 D RELAY COIL 9/C FAILS :
OPERATOR FAILS TO DETECT OPEN MOV 1RH1
-j{$ 3. 1.15E-05 OPERATOR FAILS TO DETECT OPEN MOV 1RH1 CONT MC FAILS TO TRANSFER (TO OE'C COIL)
OPERATO FAILS TO DETECT OPEN MOV 1RH1
- 4. 1.15E-05 SEg OPERATOR,FAl g TO TECT OPEN MOV 1RH1 bJO '
Mo I.4cklo b(OMf) 655i RTAiLbO DETECF6 PEN N0v 1RH1
- 5. 1.15E-05 D SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 CONTACTORFAILSTOCLOSE(9/C)PHASEC OPERATOR FAILS TO DETECT OPEN MOV 1RH1
- 6. 1.15E-05 N SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 CONTACTOR FAILS TO CLOSE (9/C) PHASE B OPERATOR FAILS TO DETECT OPEN MOV 1RH1 -
yE$ 7. 1.15E-05 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 CONTACTOR FAILS TO CLOSE (9/C) PHASE A
- , OPERATOR FAILS TO DETECT OPEN MOV 1RH1 1
- 8. 4.03E-06 SECOND OPERATOR FAILS TO DETECT DPEN MOV 1RH1 l M l
4 go /; g,0 230V/11BV TRANSFORMER FAILS OPERATOR FAILS TO DETECT OPEN MOV 1RH1 L 9. 2.30E-06 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 L h)h Sh0 SINC TOROUC--SWIER-FARS-OPEN-41-7) L' l do ~0(ove 5 w ift),) OPERATOR FAILS TO DETECT OPEN HOV 1RH1 c ( ,
- 10. 1.73E-06 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 15 AMP FUSE #2 FAILS OPERATOR FAILS TO DETECT OPEN MOV 1RH1 0303x:1D/011988 22
a WESTINGHOUSE PROPRIETARY CLASS 3 TABLE 2 (cont.). j TABLEB-3(CONT.)- N SALEM DOMINANT CUTSETS , j FORQ(V) 3 ] j g6 PROBABILITY THAT NOV 1RH1 IS OPEN I WITH ACI CASE g4 PROBABILITY CUTSET DESCRIPTION l
$ 11. 1.73E-06 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 15 AMP FUSE f 1 FAILS
.j OPERATOR. FAILS TO DETECT OPEN MOV 1RH1 ]
O-~ 12. 1.73E-06 SECOND OPERATOR. FAILS TO DETECT OPEN MOV 1RH1-gg ) - THERMAL OVERLOAD FAILS PHASE C OPERATOR FAILS TO DETECT OPEN MOV 1RH1 IJO 13. 1.73E-06 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 - J " gi THERMAL OVERLOAD FAILS PHASE B OPERATOR FAILS TO DETECT OPEN MOV 1RH1 yQ 14. 1.73E-06 SECOND OPERATOR FAILS-TO DETECT OPEN MOV 1RH1 THERMAL OVERLOAD FAILS PHASE A (M OPERATOR FAILS TO DETECT OPEN MOV 1RH1 p gg -
- 15. 1.73E-06 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 30 AMP FUSE PHASE C FAILS OPERATOR FAILS TO DETECT OPEN MOV 1RH1
- g- 16. 1.73E-06 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 30 AMP FUSE PHASE B FAILS OPERATOR FAILS TO DETECT OPEN MOV 1RHl.
- -17. 1.73E-06 SECOND OPERATOR FAILS T0' DETECT OPEN MOV 1RH1 30 AMP FUSE PHASE A FAILS u OPERATOR FAILS TO DETECT OPEN MOV 1RH1 g5 18. 2.30E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 42.b/O CONTACT 9/0 SPURIOUSLY OPENS OPERATOR FAILS TO DETECT DPEN MOV 1RH1
- 19. 2.30E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 g THERMAL OVERLOAD CONTACT FAILS OPEN (49)
OPERATOR FAILS TO DETECT OPEN MOV 1RH1 a 20, 1.38E-07 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP Y SECOND OPERATOR FAILS TO DETECT.OPEN MOV 1RH1 l MECHANICAL FAILURE OF NOV 1RH1 l OPERATOR FAILS TO DETECT OPEN MOV 1RH1
- 5. %E45- MM3W $ -
i rdoWAPPucA6LG cot 5f75 c302cio/011sse 23
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TABLE 3 ADDITIONAL SEQUOYAH CUTSETS INTERFACING SYSTEMS LOCA WITH ACI CUTSET
- COMPONENT ** i s PROBABILITY CUTSET DESCRIPTION PROBABILITY
- 1. 8.32E-05 LIMIT SWITCH 33/AC SPURIOUSLY OPENS 8.66E-05 SECOND OPERATOR FAILS TO DETECT OPEN MOV- 0.98 OPERATOR FAILS TO DETECT OPEN MOV 0.98
- 2. 3.46E SHUNT TRIP CAUSES MOTOR CB TO OPEN 3.6E-05 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN MOV 0.98
.3. 2.30E-07 XS-74-1/NOR CONTACTS SPURIOUSLY OPEN (1) 2.4E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN MOV 0.98
- 4. 2.30E-07 2.4E-07 XS-74-1/NOR CONTACTS SPURIOUSLY OPEN (7)
SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 i OPERATOR FAILS TO DETECT OPEN MOV 0.98
- 5. 2.30E-07 2.4 E-07 XS-74-1/NOR CONTACTS SPURIOUSLY OPEN~(2)
SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN MOV 0.98
- 6. 2.30E-07 2.4E-07 XS-74-1/NOR CONTACTS SPURIOUSLY OPEN (3) 0.98 SECOND OPERATOR FAILS TO DETECT OPEN MOV OPERATOR FAILS TO DETECT OPEN M0V 0.98
- 7. 1.15E-07 CB TO MOTOR SPURIOUSLY OPENS 1.2E-07 SECOND OPERATOR FAILS TO DETECT OPEN M0V
' 0.98
OPERATOR FAILS TO DETECT OPEN MOV O.98 - 1 1.19E-04 TOTAL FROM ADDITIONAL CUTSETS Cutset probability determined by multiplying component probabilities. For example: Cutset # 1 probability - 8.60E-05
- 0.98
- 0.98 - 8.32E-05
** Component failure rate obtained from Table 7-1 of WCAP-11736-A.
Component probability determined by multiplying failure rate by 12 hours. For example: Limit Switch - 7.22E-06/ hour
- 12 hours - 8.66E-05 Shunt trip coil - 3.00E-06/ hour
- 12 hours - 3.6E-05 Contacts Spurious Operation - 2.00E-08/ hour
- 12 hours - 2.40E-07 Circuit Breaker Spurious Operation - 1.00E-08/ hour
- 12 hours - 1.2E-07 .
.3/4/90 24
- ~
4: . i d
. . . . By' utilizing the same approach for the deletion of the autoclosure interlock
.4 .and the inclusion of a control room alarm, the frequency for interfacing system LOCA' is calculated. Table 4 shows Table B-4 recreated with the l cutsets applicable to Sequoyah marked on the right. Table 5 shows the additional cutsets that are applicable' for the Sequoyah design. l i l By subtracting out the cutsets which are not applicable to Sequoyah from the )
Salem mean failure probability and adding the probabilities associated with-the additional cutsets shown in Table 5, an estimate of the mean probability of failure for Sequoyah without the ACI can be calculated by th- followingr n Sequoyah Probability - Salem Probability - (Probabilities for Non-Applicable l' Cutsets) + (Additional Cutsets)
.r
- 1.10E 2.88E-07 + 1.17E-07 -
- 9.29E-07; Entering this probability into the equation for-interfacing systems LOCA:
1 F(VSEQ)'= (lambda)2 Q(Y1 ) + (lambda)3 Q(V2 )+ (lambda)2 Q(VIR) L l - IE 57/hr * (9.29E-07) + IE-07/hr * (9.29E-07)
+ 1E-07/hr * (6.57E-04)
- i. - 9.29E-14/hr + 9.29E-14/hr + 6.57E-11/hr l-
- 6.59E-11/hr * (8760 hrs / year)
[ . t ! - 5.77E-07/ year j; . l l 3/4/90 25 l
, WESTINGHOUSE PROPRIETARY CLASS 3
,, TABLE 4
- TABLE B-4 i k. SALEM DOMINANT CUTSETS .
, FOR Q(V3 )
PROBARZLITY THAT MOV 1RH1 IS OPEN ACI DELETION CASE
, MEAN PROBABILITY OF FAILURE = 1.10E-06 x PROBABILITY CUTSET DESCRIPTION y_ > 'N ! T.
g 1. 3.13E-07 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP. SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 DPERATOR FAILS TO DETECT VIA ANNUCIATOR- . 1 g 2. 1.02E-07 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP , SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 VALVEg! {TLIMITSWITCHFAILSTOOPERATE M 3. 8.18E-08 OPERATORFAILSTOCLOSEVdLVEDURINGSTARTUP SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 3 - POWER SUPPLY T0:ANNUCIATOR FAILS-
.\/3I
- 4. 8.18E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP I SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 148 t *C POWER SUPPLY @ p g g f7 5 g ly c p
.NQ 5. 8.18E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP p SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 LOOP POWER SUPPLY.1-PQ-403 FAILS IN/FC 6. 6.00E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP I' d SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1-L ANNUCIATOR FAILS TO OPERATE g 7. 4.23E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP
, ,,va +- %f. ,
SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 RELAY COIL 63Y/RCP FAILS L L p0 . 8. 4.09E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP 4 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 SIGNAL COMPARATOR DUAL CIRCUIT FAILS 1PC403AB l
.g N
- 9. 3.95E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP 4 SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 PRESSURE TRANSMITTER PT-403 FAILS t
i 2.33E-08 N5 $ OPERATOR FAILS TO CLOSE VALVE DURING STARTUP SECOND OPERATOR FAILS TO DETECT OPEN HOV 1RH1 I 1 BISTABLE SWITCH 185-403B FAILS f,uuutJC WTOR CtRLu W WM Dcf'o3ba.TT Od WWE Di. G30 c303c10/011ssa 26
,, , WESTINGHOUSE PROPRIETARY CLASS 3'
., TABLE 4 (cont.) o
(
- TABLEB-4(CONT.).
k SALEM DOMINANT CUTSETS , FORQ(V)~3 l g l{ PROBABILITY THAT MOV 1RH1 IS OPEN I
@ ACI DELETION CASE PROBABILITY CUTSET DESCRIPTION l r
- 11. 1.81E-08 28 V DC POWER SUPPLY FAILS j Nb SECOND OPERATOR FAILS TO DETECT DPEN MOV 1RH1 NO.@ M ' OPERATOR FAILS TO DETECT VIA ANNUCIATOR
- 12. 1.41E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP i SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH.1 FAILS RELAY COIL CONTACT M P""'b
% 13. 9,38E-09 RELAY COIL DXK FAILS SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 1
l 90 LBCKlMMColL OPERATOR FAILS TO DETECT VIA ANNUCIATOR l Y@ 14. ~9.38E-09 RELAY COIL 9/C FAILS SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 OPERATOR FAILS TO DETECT VIA ANNUCIATOR l t ,/dC 15. ~ 9.38E-09
~~ RELAY COIL 5/CSV2 FAILS U
SECOND-OPERATOR FAILS TO DETECT OPEN MOV 1RH1 OPERATOR FAILS TO DETECT VIA ANNUCIATOR - Q Q 16. 5.91E-09 28 V DC POWER SUPPLY FAILS i g gyg SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 VALVE STEM-NO RT LIMIT SWITCH FAILS TO OPERATE l
.17. 4.75E-09 28 V DC POWER SUFPLY FAILS
- QQ SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 .
})O 1TVDC. -POWER SUPPLY TO ANNUCIATOR FAILS l
@ 18. 4.75E-09 28 V DC POWER SUPPLY FAILS SECOND OPERATOR FAILS TO DETECT OPEN NOV 1RH1
-I 1
il0 Lt00C- 118 V AC POWER SUPPLY FAILS I
- 19. 4.75E-09 28 V DC POWER SUPPLY FAILS l
gggg% SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 LOOP POWER SUPPLY 1-PQ-403 FAILS
@ 20, 3.48E-09 28 V DC POWER SUPPLY FAILS N6 y@c SECOND OPERATOR FAILS TO DETECT OPEN MOV 1RH1 ANNUNCIATOR FAILS TO OPERATE TOTAL ' pro 6A61 LlW OF L( B.UE47 @J AffuuGLE COMT3 -
t c303c10/011ses 27
,:o .
. ' i
?"E -'
TABLE 5 ADDITIONAL SEQUOYAH CUTSETS 7 INTERFACING SYSTEMS LOCA l WITHOUT ACI l I CUTSET
- COMPONENT ** I PROBABILITY CUTSET DESCRIPTION PROBABILITY I r
- 1. 4.23E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP 1.20E-03 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 i
! RELAY COIL ICR FAILS TO OPERATE 3.60E-05 l i- 2. 4.23E-08 OPERATOR FAILS TO CLOSE VALVE DURING STARTUP 1.20E-03 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 l RELAY COIL 3CR FAILS TO OPERATE 3.60E-05 !
- 3. 2.26E-08 LIMIT SWITCH 33/AC SPURIOUSLY OPENS 8.66E-05 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN VIA ANNUNCIAT 2.66E-04
, 4. 9.38E-09 SHUNT TRIP CAUSES MOTOR CB TO OPEN 3.6E-05 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN VIA ANNUNCIAT 2.66E-04
- 5. 6.26E-Il XS-74-1/NOR CONTACTS SPURIOUSLY OPEN (1) 2.4E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN VIA ANNUNCIAT 2.66E-04
- 6. 6.26E-11 XS-74-1/NOR CONTACTS SPURIOUSLY OPEN (7) 2.4E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN VIA ANNUNCIAT 2.66E-04
- 7. 6.26E-11 XS-74-1/NOR CONTACTS SPURIOUSLY OPEN (2) 2.4E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV- 0.98 OPERATOR FAILS TO DETECT OPEN VIA ANNUNCIAT 2.66E-04
- 8. 6.26E-11 '.
XS-74-1/NOR CONTACTS SPURIOUSLY OPEN (3) 2.4E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 OPERATOR FAILS TO DETECT OPEN VIA ANNUNCIAT 2.66E-04
- 9. 3.13E-Il CB TO MOTOR SPURIOUSLY OPENS 1.2E-07 SECOND OPERATOR FAILS TO DETECT OPEN MOV 0.98 l_
OPERATOR FAILS TO DETECT OPEN VIA ANNUNCIAT 2.66E-04 1.17E-07 TOTAL FROM ADDITIONAL CUTSETS Cutset probability determined by multiplying component probabilities. For example: Cutset # 1 probability - 1.20E-03
- 0.98
- 3.60E 4.23E-08 Component failure rates obtained from Table 7-1 of WCAP-11736-A and Salem L
analysis in Appendix B. Component probability determined by multiplying failure rate by 12 hours. 3/5/90 28
T When comparing'the results with and without the autoclosure interlock, as shown below:
~
With Without
- Autoclosure Interlog.k Autoclosure Interlock ,
1
' F(VSEQ); 9.49E-07/ year 5.77E-07/ year 1 l
the frequency of an interfacing system LOCA decreases by approximately 39 percent. The main contributor to the frequencies in each case is a double rupture of the suction valves (frequency of 5.75E-07/ year in both cases). 1- The deletion of-the ACI has no impact on the rupture of a suction valve. 3.2 RHR Availability- - The availability of the RHR system to remove decay heat during cold shutdown was considered in three phases in the WOG analyses. First the RHR system must be placed in service and go through a warm-up period in order to minimize the thermal shock to the system. Secondly, during the initial phase of. cool'down, the decay heat load is high. For this phase, two trains of RHR (two pumps and two heat exchangers) are assumed to be required for 72 hours. The final phase of cooldown is long term decay heat removal. The decay heat load is low and only one train of RHR (one pump and one heat exchanger) is assumed to be required to be in' operation. Six weeks was assumed to be the time period for this phase. , Each of these phases is evaluated for the Sequoyah plant. Failure to Initiate RHR This phase models the operator actions and component operation required to initiate the RHR system before aligning the system to RCS cooling and the
' actions required to align the system to the RCS to provide decay heat removal. The Salem model developed in Appendix C of WCAP-11736-A details the steps of the procedure for initiating RHR operation. It is assumed that the Sequoyah RHR initiation procedure is similar in the steps for aligning the RHR system.
3/5/90 29
p Because the deletion of the autoclosure interlock has no impac,t on the failure probability for RHR initiation (because the autoclosure interlock has no function with regard;to-valve opening) the failure probability for-Sequoyah would not be impacted and thus does not require an evaluation. Failure of Short Term Coolina
.'This phase models a cooldown in which both RHR trains are required to be in J
operation to provide adequate cooling. -The short term cooling phase
'primarily features spurious closing of various valves and failure of the RHR H pumps to run for 72 hours. Spurious closure of the RHR suction valves due to j failures in the 'autoclosure interlock circuitry are explicitly modeled.
Reviewing the dominant cutsets for Salem (Table C-5 in WCAP-11736-A) shows
- that the dominant failure modes for the short term cooling phase with the autoclosure' interlock. Table 6 shows Table C-5 recreated with the cutsets 1 applicable to Sequoyah marked on the right. Table 7 ihows the additional cutsets that are applicable for the Sequoyah design. -l l
By subtracting out the cutsets which are not applicable to Sequoyah from the 1 Salem mean failure probability (Table 6) and adding the probabilities associated with the additional cutsets shown in Table 7, an estimate of the I
.mean probability of failure for Sequoyah with the ACI can be calculated by ,
the following: I A Sequoyah Probability - Salem Probability - (Probabilities for Non-Applicable ! Cutsets) + (Additional Cutsets) j
- 1.60E 5.76E-05 + 3.46E-04
- 1.63E-02 '
By utilizing the same approach for the deletion of the autoclosure interlock l and the inclusion of a control room alarm, the failure probability for short term cooling is calculated. Table 8 shows Table C-6 recreated with the cutsets applicable to Sequoyah marked on the right. There are_no additional cutsets that are applicable for the Sequoyah design (the Sequoyah RHR system configuration is identical to Salem and there are no additional control circuitry failures in Sequoyah that are not modeled in Salem).
'3/4/90 30
Oc: o. WESTINGHOUSE PROPRIETARY CLASS 3' . t.- { .- 3 TABLE 6 . ; l TABLE C-5 -
)
l SALEM . I DOMINANT CONTRIBUTORS LOSS OF SHORT TERM COOLING
.WITH AUTOCLOSURE INTERLOCK /hfklC80bb MEAN PROBABILITY OF FAILURE =.1.60E-02 -
__ PROBABILITY CUTSET DESCRIPTION j65 1. 7.20E-03 RHR PUMP NO. 12 FAILS TO RUN FOR 72 HOURS y@ 2. 7.20E-03 . RHR PUMP NO. 11 FAILS TO RUN FOR 72 HOURS j@ 3. 4.18E-04 LOOP POWER SUPPLY FAILS HIGH PG -4OT
- y@ 4. '4.18E-04 LOOP POWER SUPPLY FAILS HIGH ?Q-403 i i
% 5. 2.09E-04 SIGNAL COMPARATOR FAILS 'P6 -903 W5 6. 2.09E-04 SIGNAL COMPARATOR FAILS 'PS 4of 7,
76$ 2.02E-04 PRESSURE TRANSMITTER FAILS ?TM3 V65 8. 2.02E-04 PRESSURE TRANSMITTER FAILS PT-40C y I@ 9. 1.44E-05 I/V MODULE FAILS 2-PC-405R VO 10. 1.44E I/V MODULE FAILS 2-PM-405R L .VQ.'ll. 1.44E-05 I/V MODULE FAILS 1-PC-405R hh 12. 1.44E-05 I/VMODULEFAILS1-PM.4d5R M 13. 1.44E-05 PUMP DISCHARGE CHECK' VALVE IJJHT FAILS TO OPEN N'TII g- 14. 1.44E-05 PUMP SUCTION VALVE 12RH4 SPURIOUSLY CLOSES (MOV) FCV yg ~ 15. 1.44E-05 RHR HEAT EXCH. 12 FAILS TO REMOVE HEAT (CCW VALVE SPURIOUS CLOSE) YC3 16. 1.44E-05 PUMP DISCHARGE CHECK VALVE 11RH6 FAILS TO OP y $ 17. 1.44E-05 PUMP SUCTION VALVE ,pRtf4 SPURIOUSLY CLOSES (MOV) FC V-74-3 Vp
/
- 18. 1.44E-05 RHR HEAT EXCH. 11 FAILS TO REMOVE HEAT (CCW VALVE SPURIOUS CLOSE)
VES 9. 1.44E-05 CROSSTIE VALVE 11RH19 (MOV) SPURIOUSLY CLOSES PG/-N
- 20. 1.44E-05 CROSSTIE VALVE 12RH19 (MOV) SPURIOUSLY CLOSES Fct/ ~N- Bs 6.%E45 TOTAL m6A6/c nY 0F IJotJ-n onannomusa8 31
[rf'fblGA87 C()T5ET5
~~
{r 3: 44+ TABLE 7 . ADDITIONAL SEQUOYAH CUTSETS SHORT TERM COOLING WITH ACI
~
CUTSET *- COMPONENT ** PROBABILITY CUTSET DESCRIPTION PROBABILITY .f' 1. 3.73E-04 BISTABLE SWITCH PS/403B FAILS HIGH I.73E-04
' k-
- 2. 1.73E-04 BISTABLE SWITCH PS/405B FAILS HIGH - 1.73E-04 L
-3.46E-04 TOTAL FROM ADDITIONAL CUTSETS q.
Cutset probability determined by multiplying component probabilities. Component failure rates obtained from Table 7-1 of WCAP-11736-A and Salem
' analysis in Appendix C. Component probability determined by multiplying failure rate by 72 hours.
For example: Bistable Switch - 2.40E-06/ hour
- 72 hours = 1.73E-04
-e 6
3/4/90 32
.o 4 WESTINGHOUSE PROPRIETARY CLASS 3 L ,
-TABLE 8 .
TABLE C-6 k SALEM DOMINANT CONTRIBUTORS LOSS OF SHORT TERM COOLING WITHOUT AUT0 CLOSURE INTERLOCK MEAN PROBABILITY OF FAILURE = 1.40E-02 , -ro SQd '
- PROBABILITY CUTSET DESCRIPTION
% 1. 7.20E-03 RHR PUMP NO.12 FAILS TO RUN FOR 72 HOURS
- ff5 2. 7.20E-03 RHR PUMP NO.11 FAILS TO RUN FOR 72 HOURS y $ 3. 1.44E-03 PUMP DISCHARGE CHECK VALVE W 8'FA!LS TO OPEN N ~ S yp 4. 1.44E-05 PUMP SUCTION VALVE IgSPURIOUSLY CLOSES (MOV) P
--y d 5. 1.44E-05 RHR HEAT EXCH. 12 FAILS TO REMOVE HEAT (CCW VALVE SPURIOUS CLOSE)
N/g3 6. 1.44E-05 PUMP DISCHARGE CHECK VALVE 11RH87 AILS TO OPEN g 7. 1.44E-05 PUMP SUCTION VALVE IJAH4' SPUR 10USLY CLOSES (MOV) FC s
- 8. 1.44E-05
. ( yg RHR HEAT EXCH. 11 FAILS TO REMOVE HEAT (CCW VALVE SPURIOUS CLOSE)
N(5 9. 1.44E-05 CROSSTIE VALVE 11R (9 (MOV) SPURIOUSLY CLOSES FCV'7
$c510. 1.44E-05 CRhlES VALVE IJAH19'(MOV) SPURIOUSLY CLOS pg5 11. 1.44E-06 LOCKIN CIRCUITRY FAILURE CONTACT 9/C SHORTS CLOSED Y 7 A / M QD 12. 1.44E-06 CLOSE RELAY COIL CONTACT 5/CSV1 FAILS g3 13. l'.44E-06 CLOSECONTAC1IgLDSE' SHORTS d6 -7'd -//l M L45 6~
- 14. 1.44E-06 LOCKIH CIRCUITRY FAILURE CONTACTJN SHORTS CLOSED 4ZA/C, [
NE5 h)O 15. 1.44E-06 CLOSE RELAY COIL CONTACT 5/CSV1 FAILS
'1.44E-06
%'$ 16. CLOSE CONTACT If/,,Cl:0SE SHORTS d $ - Y 2- f / C l O S F
- 17. 2.07E-10 RHR DISCHARGE VALVE 126649 SPURIOUSLYCLOSES(MOV)Fo RHR DISCHARGE VALVE 11Sd49 SPURIOUSLY CLOSES g y y93 g6 18. 2.07E-10 CHECK VALVE M FAILS TO OPEN [0 3 '57o 3 RHR DISCHARGE VALVE l y SPURIOUSLY CLOSES F Ci/~lo 3 @
i . 0306x10/011988 33
i
- WESTINGHOUSE PROPRIETARY CLASS 3
' TABLE 8 (ctnt.)
r . . TABLE C-6 (Cont)- 1
'~
SALEM . DOMINANT CONTRIBUTORS LOSS OF SHORT TERM COOLING gg(( WITHOUT AUT0 CLOSURE INTERLOCK , pggd NEAN PROBABILITY OF FAILURE =.1.40E-02 PROBABILITY CUTSET DESCRIPTION 4'yt3 19. 2.07E-10 CHECK VALVE 126043 FAILS TO OPEN h3-[o2 6
= RHR DISCHARGE VALVE IJSJ49 SPURIOUSLY CLOSES FCV .
YO 20. 2.07E-10 CHECK VALVE M1 FAILS TO OPEN 63-5bo RHR DISCHARGE VALVE IJSJ49 SPURIOUSLY CLOSESpcg 3g3 g.geg4 TOTA L Peo6A61aTY OF gy-pfpuCMcF cV15ETs
\
l 1 0306x:10/D11988 34 l
y lx ..
'_ An estibate of the mean probability of failure for Sequoyah without'the ACI
' can be calculated by' the following: .
Sequeyah. Probability = Salem Probability - (Probabilities for Non-Applicable Cutsets) + (Additional Cutsets)
= 1.40E-02 2.88E-06 + 0 i
= 1.40E-02 -
Failure of Lono Term Coolina
-Only one RHR pump and one heat exchanger are required for six weeks in the long term cooling phase to provide adequate cooling. The long term cooling analysis shows spuriour closing of various valves over the six week period along with. failure of one RHR pump to continue running and upon failure of the running pump, failure of the second RHR pump to start, run or be unavailable due to test or maintenance.
.The failure of both pumps to run for six weeks is the dominant contributor to the system unavailability in the long term cooling phase. With the ACI present, the other failure modes involve the single failure of a component; '
associated with the ACI such as the power supply, signal comparator, bistable switch, or' pressure transmitter which causes spurious closure of one of the !
.RHR suction valves.
1 i
- Reviewing the dominant cutsets for Salem (Table C-7 in WCAP-Il736-A) shows that the dominant failure modes for the long term cooling phase with the autoclosure interlock. Tab'le 9 shows Table C-7 recreated with the cutsets applicable to-Sequoyah marked on the right. Table 10 shows the additional cutsets that are applicable for the Sequoyah design.
By- subtracting out the cutsets which are not applicable to Sequoyah from the Salem mean failure probability (Table 9) and adding the probabilities associated with the additional cutsets shown in Table 10, an estimate of the mean probability of failure for Seouoyah with the ACI can be calculated by the following: 3/4/90 35
= - __ _ .
1.- ,.: WESTINGHOUSE PROPRIETARY CLASS 3
.! .- TABLE 9 t -
TABLE C-7 k SALEM DOMINANT CONTRIBUTORS LOSS OF LONG TERM COOLING WITH AUTOCLOSURE INTERLOCK Ub MEAN PROBABILITY OF FAILURE'= 3.60E-02 l PROBABILITY CUTSET DESCRIPTION j~ 6 1. 1.02E-02 PUMP NO. 12 FAILS TO RUN FOR SIX WEEKS , PUMP NO.11 FAILS TO RUN FOR SIX WEEKS '
- yf5, 2. 5.85E-03 LOOP POWER SUPPLY FAILS HIGH (1RMT) FCV-79-I
- g 3, 5.85E-03 LOOP POWER SUPPLY FAILS HIGH (1RH2) FCW7 V-2.-
.% 4. 2.92E-03 SIGNAL COMPARATOR FAILS (lRH17 fCV-7Y-l
%"5 5. 2.92E-03 SIGNAL COMPARATOR FAILS (1RMf) , FC V- p 2.
. M 6. 2.82E-03 PRESSURE TRANSMITTER FAILS (lBN1) FC V ~l PI g 7. 2.82E-03 PRESSURE TRANSMITTER FAILS (IRH2) FC V- 7 4 ( % 8. 1.02E-03 PUMP NO. 12 FAILS TO START ON DEMAND PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS
% 9. 2.81E-04 PUMP NO. 12 UNAVAILABLE DUE TO TEST PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS YE510. 2.02E-04 RHR DISCHARGE VALVE IJSJ49 SPURIOUSLY CLOSES FC Y C 5 11. -2.02E-04 RHR DISCHARGE VALVE 12SJ41 SPURIOUSLY CLOSES (MOV) pc J-Q-9L[
}JO 12. 2.02E-4 I/V MODULE FAILS (IRH1) (PC) ;
L (d @ 13. 2.02E-04 I/VMODULEFAILS(IRH2)(PC)
@ 14. 2.02E-04 I/V MODULE FAILS (IRH1) (PM)
L 2.02E-04
/JD _15. I/VMODULEFAILS(IRH2)(PM) 1.59E-04 L ' % 16. PUMP NO.12 UNAVAILABLE DUE TO MAINTENANCE PUMP NO. 11 FAILS-TO RUN FOR SIX WEEKS VC517, 2.04E-05 PUMP SUCTION VALVE 12RMT SPURIOUSLY CLOSES FC W 7 y -2.)
PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS ( . 1 0306c1D/011988 36
.. , WESTINGHOUSE PROPRIETARY CLASS 3 -v.- --, TABLE 9-(c nt.). -.
i TABLEC-7(Cont)- k SALEM - DOMINANT CONTRIBUTORS l LOSS OF LONG TERM COOLING I WITH AUTOCLOSURE INTERLOCK 1 NS(,)CAS LE MEAN PROBABILITY OF FAILURE =.3.60E-02 7D SQt) PROBABILITY CUTSET DESCRIPTION
$ 18. 2.04E-05 _. PUMP DISCHARGE-CHECK VALVE 12RM8 FAILS TO O ;
t'- PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS i Y$ _ 19. 2.04E-05 HEAT EXCH.12 FAILS TO REMOVE HEAT (CCW VALVE SPURIOUS CLOSE) PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS
~ Y[$ 20. 2.04E-05 PUMP NO.12 FAILS TO RUN FOR SIX WEEKS PUMP SUCTION VALVE IJRH4 SPURIOUSLY CLOSES F C V-74-3 1
y, gg g. TDTAL TTJM6]tITY aF fd6L1 AfPLKA/AE CuTMTs ( l 1 I s 3-I l I l l
- ( .
l i 0306c1D/011988 l
i - g
- g, ;.; .,
TABLE 10 .
.. . ADDITIONAL SEQUOYAH CUTSETS LONG TERM COOLING .!i: '
WITH ACI
.; CUTSET
- COMPONENT **
. PROBABILITY CUTSET DESCRIPTION PROBABILITY
- 1. 2.42E-03 BISTABLE SWITCH PS/403B FAILS HIGH 2.42E-03
- 2. 2.42E-03 BISTABLE SWITCH PS/405B FAILS HIGH 2.42E-03 4.84E-03 TOTAL FROM ADDITIONAL CUTSETS
- Cutset probability determined by multiplying component probabilities.
** Component failure. rates obtained from Table 7-1 of WCAP-11736-A and Salem analysis in Appendix C. Component probability determined by multiplying failure rate by 1008 hours.
For example: Bistable Switch - 2.40E-06/ hour
- 1008 hours = 2.42E-03 i
1 l 0 3/4/90 38
A .- f,. ,
.Sequoyah Probability - Salem Probability - (Probabilities for'Non-Applicable
..- -4 lCutsets) + (Additional Cutsets).
- 3.60E 8.08E-04 + 4.84E-03
- 4.00E-02 ,
By utilizing the same approach for the deletion of the autoclosure interlock and the inclusion of a control room alarm, the failure probability for short ! term cooling is calculated. Table 11 shows Table C-8 recreated with the
, cutsets applicable to Sequoyah marked on the right. There are no additional cutsets that are applicable for the sequoyah design (the Sequoyah RHR system , configuration is identical to Salem and there are no additional control circuitry failures in Sequoyah that are not modeled in Salem).
An estimate of the mean probability of failure for Sequoyah without the ACI can be calculated by the following: . Sequoyah Probability - Salem Probability - (Probabilities for Non-Applicable Cutsets) + (Additional Cutsets)
= 1.20E 4.04E-05 + 0
= 1.20E-02 Results of RHR Availability L The results with and without the autoclosure interlock are shown below:
l- [ With Without Percent ACI 8.01 Chance RHR Initiation 3.20E-02 3.20E-02 0 Short Term Cooling 1.63E-02 1.40E-02 -14 Long Term Cooling 4.00E-02 1.20E-02 -70 } l l 3/4/90 39
.. ._ _ _ _ _ _ _ _ - . - - _ . . __ __ __. . . __~ _ _-____._ _.___
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', TABLE 11
- TABLE C-8 l
L SALEM DOMINANT CONTRIBUTORS > LOSS OF LONG TERM COOLING WITHOUT AUT0 CLOSURE INTERLOCK ,
.M[LIC AOLE MEAN PROBABILITY OF FAILURE = 1.20E-02 .
NN PROBABILITY CUTSET DESCRIPTION Ye3 1. 1.02E-02 PUMP NO. 12 FAILS TO RUN FOR SIX WEEKS PUMP NO.11 FAILS TO RUN FOR SIX WEEKS Ye:3 2. 1.02E-03 PUMP NO 12 FAILS TO START ON DEMAND PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS YG 3. 2.81E-04 PUMP NO. 12 UNAVAILABLE DUE TO TEST PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS Vd3 4. 2.02E-04 RHR DISCHARGE VALVE ,11Sd49 SPURIOUSLY CLOSES PC L/-b3 " f3 g 5. 2.02E-04 RHR DISCHARGE VALVE 12SMr3PUR10VSLY CL ;
- 6. 1.59E-04 M PUMP NO.12 UNAVAILABLE DUE TO MAINTENANCE PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS
( VfE 7. 2.04E-05 PUMP SUCTION VALVE 12 M t SPURIOUSLY CLOSES FVO W PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS yt3 8. 2.04E-05 PUMP DISCHARGE CHECK VALVE .12MS FAILS TO OPEN D'9 7 PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS
% 9. 2.04E-05 HEAT EXCH 12 FAILS TO REMOVE HEAT (CCW VALVE SPURIOUS CLOSE)
PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS V y 10. 2.04E-05 PUMP NO. 12 FAILS TO RUN FOR SIX WEEKS PUMP SUCTION VALVE JJM(' SPURIOUSLY CLOSES FC V-74_3 . YE511. 2.04E-05 PUMP NO 12 FAILS TO RUN FOR $1X WEEKS HEAT EXCH.11 FAILS TO REMOVE HEAT (CCW VALVE SPURIOUS CLOSE) Yf 5 12, 2.04E-05 CROSSTIEVALVE11AH175PUR10VSLYCLOSES FG V-N N PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS g 13, 2.04E-05 CROSSTIE VALVE 12RH19 SPURIOUSLY CLOSES FCV-74-3T PUMP NO. 11 FAILS TO RUN FOR SIX WEEKS
- 14. 2.04E-05 CROSSTIE VALVE 11W19 SPURIOUSLY CLOSES FC V ~74 ~$'3 PUMP NO. 12 FAILS TO RUN FOR SIX WEEKS c30scioto11ssa 40
, WESTINGHOUSE PROPRIETARY CLASS 3
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TABLEC-8(Cont)- 0 SALEN . I DOMINANT CONTRIBUTORS i LOSS OF LONG TERM COOLING ' l WITHOUT AUTOCLOSURE INTERLOCK
'$L\CA8LGg MEAN PROBABILITY OF FAILURE =.1.20E-02 i PROBABILITY CUTSET DESCRIPTION YC3 15. 2.04E-05 CROSSTIE VALVE 12AHf9 SPUR!OUSLY CLOSES F-C#74-35~ ;
PUMP NO. 12 FAILS TO RUN FOR SIX WEEKS :
$ ' 16. 2.02E-05 LOCKIN CIRCUITRY FAILURE CONTACT TS CLOSED (JRH1)('74 90 17. 2.02E-05 CLOSE RELAY COIL CONTACT 5/CSV1 FAILS (IRH1) yc3 18. 2.02E-05 CLOSECONTACT1/st05fSHORTS(1RH1 y5-74-lA/CLo W y@ 19. 2.02E-05 LOCKINCIRCUITRYFAILURECONTACTSfC bRTS CLO g(3 20. 2.02E-05 CLOSE RELAY COIL CONTACT 5/CSV1 FAILS (1RH2) ;
- h. 0L/E-05' 7brAL. Proc 4 BILITY OF l
thJ-MPLICPc6LE cuTSC 5 I I' 0306x:1D/011968
o . :
, , 3.3' Low Temp;rature Overpressurization
- l The effect of an overpressure transient at cold shutdown conditions will be altered by removal of the autoclosure interlock. With removal of the interlock, the RHRS may also be subject to overpressure. However, the RHRS
$ reiter. valve will be available to mitigate the transient. These two ' ^ , trade-offs are examined by performing an analysis to model the mitigating i actions (both automatic and manual) following the occurrence of low temperature overpressure events. These mitigating actions affect the severity of the overpressurization events and reduce the possibility of l damage to the plant.
The results of the overpressurization analysis in WCAP-11736-A showed that j removal of the ACI feature has no effect on the heat input transients examined and'results in a slight increase (on the order of IE-10) in the frequency of occurrence for some categories of the mass input transients with' a decrease in others. The results for Salem are shown in Tables 12,13 and 14 for the charging / safety injection case and the letdown isolation /RHR operable and RHR isolated cases. The event tree node that is impacted by the autoclosure interlock is the node RSV (RHR suction valves close on overpressure via autoclosure interlock) and OD (RHR suction valves close on overpressure via operator action given alarm). The Salem analysis assumed that on an overpressure event, only one of two RHR suction valves must close. The fault trees developed for these nodes examined the failure modes which would have both valves failing to close. For the case with the autoclosure interlock, the additional failure modes that would be included for Sequoyah for a suction valve failing to close (previously identified in the interfacing system LOCA analysis) involved j components located in the control circuit for the valves and not the autoclosure interlock circuit (i.e., the shunt trip circuit, the additional circuit breaker to the valve motor and the power supply contacts XS-74-1/NOR) . These components would also be included .in the valve failing to close in the case without the autoclosure interlock. Thus, the analysis for Salem would not be significantly altered for Sequoyah for this event tree node and the Salem analysis is applicable for Sequoyah. ' 3/4/90 42 l
WESTINGHOUSE PROPRIETARY CLASS 3 ;
- . . 3 ,tt 12 l TABLE D-9 i
, ik SALEM CHARGING / SAFETY INJECTION ACTUATION i RESULTS
' FREQUENCY CONSEQUENCE FREQUENCY FREQUENCY
. CATEGORY WITH ACI WITHOUT ACI CHANGE .
I SUCCESS 8.91E-02 8.91E-02 - , , LSFO 2.47E-03 2.47E-03 - LSCI 0 0 ; I LSCO O O -
~
1 LLFO 4.30E-06 4.30E-06 - LLCO 3.00E-02 3.00E-02 - LLCI 3.30E-03 3.30E-03 - i LSFI 3.95E-13 9.3BE-12 +9E-12 , LLFI 4.82E-07 4.82E-07 - MSFO 2.63E-12 8.34E-11 +8.1E-11 i MLFO O O MSFI 7.74E-05 7.74E-05 - j ( MLFI O O - MSCO 4.54E-12 1.44E-10 +1.4E-10 MSCI 5.56E-05 5.56E-05 - MLCO O O MLCI O O MOPI 1.45E-05 1.45E-05 -
.. HOPI 1.95E-05 1.95E-05 -
HOPV 5.10E-15 1.34E-11 +1.3E-11 i 1
)
TOTAL 1.25E-01 1.25E 1 l 1 f .
~ ..
0039D.1D/101189
)
1
. WESTINGHOUSE PROPRIETARY CLASS 3 k
+
'. . TABLE 13 !
. . TABLE D-10 ,
SALEN , . LETOOWN ISOLATION RHR OPERABLE ld RESULTS i CONSEQUENCE FREQUENCY FREQUENCY FREQUENCY CATEGORY WITH ACI WITHOUT ACI CHANGE , SUCCESS 8.89E-02 8.89E-02 LSFO 2.75E-03 2.75E-03 - LSCI O 0 LSCO 3.34E-02 3.34E-02
, LLFO 1.43E-09 1.43E-09 -
i-LLCO 9.89E-06 9.89E-06 - LLCI O O LSFI 4.81E-13 4.81E-13 . I LFI O O NSFO O O . NLFO O O MSFI O 0 , I NLFI O O NSCO O O NSCI 5.38E-09 5.37E-09 -1E-11 NLCO O O MLCI O O , NOPI 4.84E-09 4.84E ,09
. HOPI 3.02E-09 3.02E-09 -
HOPV' 5.66E-15 3.49E-11 +1.5E-11 TOTAL 1.25E-01 1.25E-01 i 1 0039D;1D/101189 44
t . WESTINGHOUSE PROPRIETARY CLASS 3 TABLE 14 - v !
.-- TABLE D-11 k' SALEN ,
LETOOWN ISOLATION RHR ISOLATED l! RESULTS I' . CONSEQUENCE FREQUENCY FREQUENCY FREQUENCY -
. CATEGORY WITH ACI WITHOUT ACI CHANGE -
~~
SUCCESS 3.26E-01 1.63E-01 -1.53E-01 p LSFO O O - LSCI 1.40E-03 6.99E-04 -7E-04 l'
- LSCO O O -
~
LLFO O O l
; LLCO O O F LLCI 1.17E-01 5.85E-02 -5.8E-02 C LSFI ,1.02E-07 5.07E-08 -5.1E-08 LLFI 1.70E-05 8.48E-06 -8.5E-OS
't MSF0 0 0 - MLFO O O MSFI O O ; ( MLFI O O - MSCO O O MSCI , 0 0 - MLCO O O - MLCI O O - MOPI O O . HOPI 3.73E-04 .- 1.86E-04 -1.9E-04 HOPV 0 0 - ! TOTAL 4.45E-01 2.22E-01 ( . 0039D.1D/101189 45
In addition, because the pressure switch setpoint en the alarm'to be included for Sequoyah is lower than the RHR relief valve setpoint, the operator would j
- have more time in which to diagnose an overpressure event, isolate the RHR , system before the overpressure transient caused the RHR relief valve to lift )
t or the RHR system to be overpressurized. This results in an additional l benefit for the calculation of the operator error probability used in the ] case without the autoclosure interlock. I Therefore, the results from the Salem overpressure analysis are applicable to ; Sequoyah. The conclusion to be drawn from the overpressurization analysis is i [;- that removal of the autoclosure interlock has little impact on the j consequences of low temperature overpressure events. Furthermore, it should
, l be understood that the autoclosure interlock was not installed to mitigate l
[ overpressure transients. The RHR suction valves are slow-acting and the ACI will not protect the RHR system from a fast-acting overpressure transient. ! 1 The major impact with respect to overpressure concerns.. is that removal of the-autoclosure interlock will significantly reduce the number of letdown isolation transients and the challenges to the operator. t m e f e 3/4/90 46 t
s .
,7 ;
4.0 CONCLUSION
S e i Based on the comparative evaluation between Salem and Sequoyah with regard to l the deletion of the autoclosure interlock, the three different areas examined . I indicate that the results and conclusions for Salem in WCAP-ll736-A are not ' 1,nvalidated by the proposed change for Sequoyah. The deletion of the ACI and ! { the inclusion of a control room alarm to warn the operator that a series f suction / isolation valve is not fully closed or when RCS (or RHR) pressure is above the alarm setpoint is acceptable for Sequoyah. ! The results of the different areas of evaluation for Sequoyah are shown below: 3 f' With Without Percent ,
&L1 6(1 Chance
- Interfacina System LOCA F(VSEQ) 9.49E-07/ year 5.77E-07/ year -39 RHRS Unavailability +
RHR Initiation 3.20E-02 3.20E-02 0 , Short Term Cooling 1.63E-02 1.40E-02 -14 Long Term Cooling 4.00E-02 1.20E-02 -70 , Overpressurization **- 4
* (-) - Reduction i (+) - Increase
** - Reduction in some categories and a small increase in other estegories Based on the comparative evaluation between Salem and Sequoyah with regard to the deletion of the autoclosure interlock, the three different areas examined indicate that the results and conclusions for Salem in WCAP-ll736-A are not invalidated by the proposed change for Sequoyah. The deletion of the ACI and the inclusion of a control room alarm to warn the operator that one series suction / isolation valve is not fully closed or RHR pressure is above the , ,
alarm setpoint is acceptable for Sequoyah.
~
3/5/90 47
o .-
5.0 REFERENCES
' 1. WCAP-11736-A, " Residual Heat Removal' System Autoclosure Interlock Remuval Report for the Westinghouse Owners Group " Revision 0.0, October 1989.
l 4
-.k 3/4/90 48 j
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' APPENDIX A ,
.- -, INFORMATION RECEIVED FROM SEQUDYAH FOR ANALYSES
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5 l 3/4/90 49
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,c From: 1 Cuf I Address: Db(- CZD S d AJ Telephone: d [ b' I'l3- N Nb Special instructions: -
r Sent f rom: (015) 843-5517 Verification: (015) 843-0510 NUMBER OF PAGES (including this page):
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