ML19322C511

Responds to Toledo Edison 771010 Request.Forwards Description of 770924 Depressurization Event,Evaluation of Reactor Coolant Components,Evaluation of Reactor Coolant Pumps & Evaluation of Fuel

ML19322C511
Person / Time
Site:	Crane, Davis Besse
Issue date:	11/01/1977
From:	Lauer J BABCOCK & WILCOX CO.
To:	Domeck C TOLEDO EDISON CO.
References
TASK-TF, TASK-TMR BWT-1589, NUDOCS 8001170840
Download: ML19322C511 (26)

Text

{{#Wiki_filter:a O C Babcock &Wilcox ~ e-r ce .or. P.o. Box 1260, Lynch::ur;;, Va. 24505 " ""

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) November 1, 1977a BUT-1589 A File: T1.2/12B 1 N cc: J. D. Lenardson w/a J. C. Lewis ~ D. J. DeLaCroix iMr.?C. lRf Domeck: P. P. Anas/4c w/a Nuclear Project Engineer E. C. Novak/lc w/a Toledo Edison Company Power Engineering & Construction 300 liadison Avenue Toledo, Ohio 43652

Subject:

Toledo Edison Company REPORT ON DEPRESSURIZATION EVElU ? Davis-Besse Unit 1 B&W Reference NSS-14

Dear Mr. Domeck:

By telecen of October 10, you.have requested,B&W input for a report to NRC regarding the depres;urization event of _ September. 24. The NRC. exit interview notes dated 'Octoben 7 sxrnarized the necessary content of :he report.- B&W is providing write #s in the following areas in order to substantiate the conclusions of bht-1578 and BlH-1579 dated October 5 and 7: A. Description of the event B. Evaluation of the reactor coolant cor:ponents o i' w C. Evaluation of RC pumps {b, D. Evaluation of the fuel l In order to expedite submittal of your report, we are sending Sections A, C and D at this time, as agreed in our telecon of October 24. We expect to femard Section B by i November 7, and we will try to improve on this date. Section A describes the sequence.of events as reconstructed from computer alam print-out, reactimeter plots, and control roc.n recorders ( Attachment A.1), We have attached pertinent recorder charts of T RC pressure, pressurizer level (Attachments A2, A3 and A4) and reactimeter plots of R" Vin,let temoerature, RCS flow in each loop, RC pressure, pressurizer level, and water level and outlet pressure of each steam generator (Attatn-ments A5 througn A13). l l Section B will include evaluations of stresses in the pressure boundary, the depressuriza-l tion transient, boiling the SG dry, jet impingement or the SG, and effect upon fatigue life. 80011708fC 8 9 A l /

0 0 Babcock &Wilcox November 1, 1977 bht-1589 Section C explains the evaluation which was performed to verify that there was no significant damage to RC pump bearings, seals, or iroellers (attachment Cl). The transient as it affected the pumos is sunnarized in Attachment C2. Attachment C3 defines the instrumentation and operational checks applied to the pumps. The results of the operational checks are tabulated in Attachment C4. Section D evaluates the effect.upon the core to detemine (1) whether steam was produced in the core (2) the maximum internal fuel rod pressure, and (3) whether maximum lift force exceeded the limit (Attachment D.1). Reactimeter plots are attached for reference Attachments D.2 through D.6. Very truly yours, A. H. Lazar SeniorProjecy; Manager JAL/hj J A. Lauer reject Manager Attachments i l O l car 7 annopfj ".b;y3 'l sp h.

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S O O n klTfXth*1C~W (T. ,9 I o tSequence of Events "he event started at time 21:34:20 on;Septemberi24, 1977*. The plant was in Mode 1 with power ( WI) = 263. The turbine had been shutdown earlier in the evening to repair a leak in the main steam line at an instru=ent connection batween the turbine stop valves and the high pressure turbine. At this time o half trip of the Steam and Feedwater Rupture Control System (SFRCS) was initiated by an unknown cause. This trip shut the startup feedwater valve to (2 steam generator cud stopped all feedwater to this generator (because of the low power level the main faedwater block valve was already shut, isolating the main feedvater control valve). The low level alarm was reached-in #2 steam generator at 21:34:44. Before the operator could identify and correct the problem,.the low level in f 2 steam generator produced a full trip of the SFRCS. This trip shut the main steam isolation valves j cnd feedwater isolation valves in both steam generators (time 21:35:18). SFRCS i also started both auxiliary feedwater pumps. The nu=ber one pump performed as in-tcrded, however, number two auxiliary feedwater pu=p only came up to 2600 RPM, in-sufficient to feed its steam generator (#2). The loss of feedwater, first to one and then both stea= generators, caused an increase in primary water temperature, which resulted in an increase in pressurizer level and thus reactor coolant syste= pressure. At 2255 PSIG the pressurizer electro-matic relief valve received an open signal. During the next 40 seconds, it received nine different open and close signals. After one of those signals the valve stuck cpen. This provided a continuous 21s" vent path free the pressuriser to the quench tank. When pressurizer level got to 290", the operator manually tripped the reactor (time 21:36:07). Encrgy escaping from the electromatic relief valve. and three main steam relief valves caused a rapid cocidown and depressurization of the reactor coolar. cyste=. Reactor coolant system pressure dropped to 1600 PSIG (t N 21:37:17) initiating the Safety Features Actuation System (SFAS). This started high pressure injection and closed numerous containment isolation valves, including the quench tank cooling lines. With the electromatic relief valve still open and cooling water isolated to the quench tank, the quench tank rupture disc ruptured (time 22 :40) relieving water /stea= to the contain=ent building. This discharge da= aged a nearby ventilation doet, was deflected off this dutt and directed onto #2 steam generator. The steam tore off cpproxi=ately a 10' high x 20' circumferential section of insulatien from #2 steam gitnerator. The paint from the then exposed area of the steam generator was blasted away. The steam in the containment also resulted in two fire alarms (cne near RCp 2-2 and one near the pressurizer) and a single channel FJ!S trip on high reactor building i pressure (4 PSIG). When the main steam relief _ valves rescated the decrease in reactor coolant systes temperature stopped and the ihigh pressure injection pumps started. to raise pressurizer, fievelCAtitime; 2140:34?the; operator stopped the high pressure injection pumps. (The operators had been heavily involved before this time in regaining seal injection flow to the reactor coolant pumps. This flow had been s:cpped by the SFAS actuation. By 21:39:40 the appropriate SFAS signals had been overriden and nor=al flows restored to the seals of the_pu=ps). ! Reactor.' coolant system pressure continued to decrease until; Incuration pressure was. reached and steam began toLiorm.inlthe RCS (approxi= ate time ~ s 21:42). tThis causedian insurge of. water _ into-. the pressuriser and pressuriser~ level ~ 'went'off scaleihigh as'320 inches. During this level increase the operator, seeing average reactor coolant syste= te=perature and pressuricer icvel increasing, stopped one.eactor coolant pump in each loop (time 21t43:11). ji

O O /)me.y A. / 7 z e Due to decreasing pressure in 02 stea= generator, the STP.CS system gave a low pressure block per=it signal at time 21:4S:33. This alerted the opeator to the low sevel and feed condition of f2 steam generator. He blocked the low pressure trip (tine 21:49:3S), took =anual control of the speed of 02 auxiliary feedwater pump and fed f2 generator (ti=e 21:50). The operator saw the rapid addi: ion of cold feedwater dropping the reactor coolant syste= te=pera:ure and stopped the feedwater addition to this generator. ?Atlapproximaiely 21:55 the operator shut the block valve for the electromatic ,.~ralief valve on the pressurizer and stopped the venting of the reac:or coolant sys:en to the quench tank. 'At 22:05 pressurizer level ca=e back on scale. At 22:15 the operator started a second =akeup pu=p to try and stop the pressurizer level decrease. This additional cold water started the reactor coolant syste= on a slow decreasing te=perature transient. At 22:17 pressurizer level reached the low level interlock cnd cut off the pressurizer heaters.; At 22:23-the operator started a high pressure i injection pu=p to try and stop the decreasing" pressurizer level. The level and pressure in #2 steam generator again decreased to the point where the SFRCS gave a low pressure block per=it signal. The operator again blocked the trip and, through canual speed control of its auxiliary feedwater pu=p, restored 1sve.1 and pressure in #2 stea= generator (time 22:25). . ith_pressuri=ermlevel well on its way to recovering,the operator stopped the W high pressure injection pump -(time 22:27:44). At ti=e 22:31 he restored RC makeup flow to nor:sl. This stopped the slow decreasing RC te=perature transient started at ti=e 22:15. All plant parameters were now fully under control and the plant was brought to a steady state condition and a nor=al plant cooldown started. . e e e e Jwa n~~u f J75,

4 O - 3, - 3 Odi10/23/77', ':he/ STECS _again :rippedifrc: a spurious signal. The Startup ~ Feedwater 'ialve on s:ca: generator ::c. : went closed. This ulti=ately resulted in a valid S:ca: Genera:or Icv level trip input to the STRCS and :he cys:c: functionce as intended. This was the first spuricus trip received since the char: recorders had been connected to :he SFECS. All 4 '---**d-- en the chart: could be explained except fer a prcble= en STECS logic Channel 4 ccepuner alar =, P6SC. This par:icular channel en the recorder was in:cr=i::ently failing, givir.g spurious trip indica:icas. Of the %S :otal chart recorder channels, this was the only one that had failed. I&C Technicians " checked cu:" the bad recorder channel for operation. They found that the channel was sensitive to any rechanical vibration, it did respend to a given input, and that the pens were slightly tisaligned. From all of the infor:ation ga:hered it was concluded that the indication I on the bad recorder channel was an input frem the SFRCS. ,"P680" Low ( The logic point under cuestion then was the computer poin: Main S:ea Pressure Trip). Exa:ining other charts indica:ed no change in the input to STRCS lo;ic Channel 4. Thus it was concluded the problem was internal to the systen. In exa:ining the logic centrol diagra=, it was deter =ined 3 IC " chips", 2 inpu: buffers and associated wiring could have caused :he faul:. ILC personnel replaced all of the above equip =cnt, with the exception of the in:erconnecting viring. The wiring and buffer connections were visually inspected, and no faults were observed. A functional logic test was perfor:ci and the system responded satisfactorily. Power Engineering had contacted Consolidated Con rcis Corporation, the =anufacturer, and their representative was on site the =orning of 10/26/77. The manufacturer also reco== ended changing the sa:e equip =ent that TECo I&C personnel had changed. The =anufacturer perforced a response ti=c check on both input buffers in question. The response time tes: showed no defects. TECo I&C personnel continued to =enitor one of the two input buffers in a test set. Failure of one input buffer did occur on the test set, which indicates that this was the cause of the half trip. The manufacturer's representative also took a look at the logic syste with an oscillesecpe. He was looking fer any erratic, noisy points, but every:hing tested appeared to be : cuble free. The two inpu: buffers will re ain with TEco for further tes: and evaluation, while the 3 IC chips were returned to :he manufacturer for evaluation. The canufac:urer's representative on 10/27/77 cc= piled a list of addi-ticnal points they wan =eni:ored. TECo I&C personnel are assisting to connect up the recorders. t F i N /, ,d f: "C i!! ; f ~' b ' la l i ^ t jg 1 LI L 'h l l

O . (' After the 10/23/77 even:, a study was also cenducted to see if any single 120 ";.C cr 125 V DC faul: induced vel: ge dip could have caused the one-half trip en bo:h MSIV's and closed the SG-2 SU cen:r 1 valve. This s:udy revealed that no single faul: en these power supplies could caused this p chic =. The fellowing changes have been =ade to the design of the SFRCS since the Septenber 21., 1077 inciden:: 1. Annuncia:cr windows have been added where ec=puter alar =s presently exis: for: Steam Generator Level Half / Full Trip for both Channels a. 1&2 i b. Main Feedwater DP Half / Full Trip for both Channels 1 i I &2 Loss of 4 Reactor Coolant Pu=p Trip c. 2. A new annunciator and cc=puter alar = has been added for a SFRCS Full Trip. 3. The resetting of all SFRCS related alar = will be delayed long enough to allow the ec=puter to record the event. These changes viu be cade as soon as possible. 9 e [ l ~#, I I,h i i l ibllh @I, ill:fa. Rdi, \\ gC bl D lM { l t

J. O O. B. Auxiliarv Feedouro Turbine Covernor Before describing the =cdificatiens =ade to the auxiliary feedpu=p turbine (ATFT) governor. the governor action which resulted in the binding will be described. Figure 6-1 is a drawing of :he Woodward Covernor PG-PL speed setting =cchanis=, showing the governor in the bound up condition. The sequence of events creating this condition is as follows: 1. When the Bodine cotor was at a =ini=u= speed setting, :he speed setting shaft nu was fully to the left. Thc link raised the collar, contacti,ng the base speed setting nut, raising it and the "T"-bar to an idic condition. The pivot i bearing would be contac:ing the floating lever. 2. Because the governor is not rotating, the speed setting servo retains in a fixed position at idle (as shown). It cannot cove until oil pressure is available. 3. The thu=bscrew is contacting the icw speed stop pin. 4. As the Bodine speed setting cotor is rotated toward high speed, the following events occur: 4.1 The speed setting shaft nut coves towards the high speed stop pin. 4.2 The link allows the collar to cove downward. 4.3 The collar moving downward, allows the base speed setting nut and "T"-bar asse=bly io =ove downward. 4.4 The floating lever is fixed at the speed setting servo piston end. 4.5 The low speed stop pin end of the link pushes down on the thu=bscrew, which pushes down on the speed setting pilot valve until the dashpo land contacts the dashpot plug. 4.6 Because the floating lever is now fixed on both ends it stops =oving. 4.7 The "T"-bar continues downwa.d..fo.', lowing the collar. The pivot bearing leaves the floating lever. The "T"-bar continues downward until the retainer screw contacts the floating lever. 4.8 The collar separates from :he base speed setting nut and continues downward until the stop pin in the speed ~ j shaft contacts the stop pin in the speed set:ing shaf nut. I ' 11 U s i [$, @ 3 ub wN, [' ' y N -i i h ;i!U ) l

37 - 4.9 Because the Bodine cotor centinues to rotate the manual speed setting kz.cb, slipping the clutch, a torque is placed on the speed set:ing shaft nut, link and collar. This torque agains: the "T"-bar causes friction that lecks the "T"-bar in placc. 5. When the turbine is started, the speed se :ing servo piston = oves downward vi:5 increasing oil flow, increasing the speed se::ing of the, governor. When the floating level contacts the pivot bearing, the speed setting pilot valve begins to raise. 6. When the pilot valve control land covers the metering port, the speed setting servo pisten stops =oving. I 7. Because the torcue is still present on the speed setting shaft, the "T"-bar is bound up, and the governor is at 2200-2600 rpo. 8. When the Bodice speed setting coter is backed off fro = the stop, the "T"-bar falls down to its high speed stop, dropping the pivot bearing. The pilo valve coves dernvard, increasing oil flow to the speed setting servo until the high speed condition is reached. 9. Any changes in speed setting shaf t position are now nor= ally followed by the "T"-bar, pivot bearing, pilot valve, and speed setting servo piston. When the AF?T governors arrived at the Woodward Governor Co=pany factory, one of the governors was placed on the test stand. While observing the operation of the speed setting linkage, it became evident that a simple link frem the speed setting pilot valve (plunger) to the floating lever would allev re=cval of the bellows, coupling spring, low speed pin, "C" link and dashpot plug in the speed setting pilot valve sleeve (see Figure 2). This vould allov the speed set:ing pilot valve to overtravel when the motor was set in a high speed condition with the speed setting servo at the minicum position (see Figure 6-3). The required parts were manufactured, the unneeded parts re=oved and the governcrs were reasse= bled. The governors were tested at the Woodward factory and the tests confir=ed that the codifications did rc=ove all possibility of the undesired bind-ing of the governors. Surveillance testing at the station has also confir=ed that the auxiliary feedpu=p turbine governors function properly. e oum

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C. Pressurizer Pevar Relief Valve On Septe=ber' 2S,1977, the valvd was co=pletely disasse= bled. The =ain valve was found to be clean. The sea:s on the no::le a=d = sin valve disc vare 1cpped. The pilot vc1ve was found stuck in the open position and it was thought : hat the pilot ste= vas bent so the pilot s:e= vas replaced and the no::le guide area was cleaned up to rc=ove the = arks fro = the galling of the foreign =a:erial. The valve was reasse= bled and on October 12, 1977, the valve was stroked six (6) ti=es with a pressurizer pressure of approxi=stely 600 psi. During this testing the pilot valve again stuck and the isolation valve had to be closed. The valve was again disasse= bled and under closer observation t it was found that the pilot valve ste: vas moving too far (3/8" vs 1/8" desired). I: vas also found that the clearances between the pilot ste= and the no::le guide were too s=all (.0005" vs desired cini=u= of.001"). The clearances were opened up and the stroke of the pilo: vas shortened by adjust =ent of solenoid position. The valve was tested again successfully by stroking it twelve (1.".) ti=es on October 15, 1977, at a pressuri=er pressure of approxi=ately 900 psi and one ti=e at a pressure of 2200 psi. D. Relav/ Fuse /Uirine Checks Because of the missing relay in the pressurizer electro =atic relief valve control circuit, an extensive review progra= of checking all other relay cabinets was perforced. All relay i cabinets in the plant were inspected for tissing plug-in relays and fuses. A detailed review of drawings was =ade to deter =ine the service of each =issing ite= and its effect on plant operations. The one additional relay and ten fuses found =issing were replaced. There were no essential functions affected by the additional tissing relay and fuses. The =issing fuses and relcy were for generator iso phase bus control, alar = and indications; relay cabinets power supply ) and heater supply circuits; = sin feed pu=p turbine lube oil tank level indication; and reactor coolant pe=p co=ponent cooling water return valve centrol. 1 Neither the missing relay nor the fuses were controlled under the station j==per and lif ted wire centrol procedure. This indicates the fuses and relay were re=oved by unknown l persons after checkout and testing. g hh=

b, m-o o -n-E. Other Actions n-Following this incident a(training program;was developed and presented. This progrs= vas appros:icately 'eight,(S). hoarsh of instruction and discussion) covering the. events of;this incident, c M idding aldetailed, coverage of the transient and'the actions ktaken by the. operat' ors; and-a refresher' training session cover - [ing }tihe ' operation of the' steam 'and fee'dwater! rupture control ~ ~ ~' gystes'. The ttaining was presented to all in the operating shift crews, the t.anage:ent and staff level engineers and the QA/QC staff. 9 I l \\ l h DnhQU hn u. f ly ' g!_ I e

1 I O O i l 7. EXHIBITS l A. Event Chronology i B. Event Variables Plots C. SFRCS Description D. 10 CFR Part 21 Letter on Auxiliary Feedpum Turbine Governor E. Historical Log O e S l ( F ht" su'=wuu.% i \\ \\pa Ga 4

V U cx;;t317 A - 44 '7A Event Chronology 21:34:20 S:artup Feedva:c Valve to OTSO #2 vent closed on a "!5 trip" of the Steam and Feedva:er Rupture Control Syste= (SFRCS). 21:35:18 Receivedace=ple:e-SFRCStripdueto$ovlevelinOTSG02. 21:35:23 Main Stea= Isolation valves vent closed. 21:35:26-Pressuriser Power Relief Valve cycled 9 ti=es before sticking open. 49 21:36:04 Auxiliary Feed Pu=p (AFP) #1 was febding #1 Steam Generator (SG). AFP #2 did not co=e up to full speed (3600 rp=), and the discharge pressure was not sufficient :o feed #2 SG. ~ 21:36:07 operator tripped the reactor. t 21:37:17 Safe:y Features Actuation Systen Inciden: Levels 1 and 2 were initiated due to reactor coolant system pressure less than 1600 psi. 21:37:33 High Pressure Injection (EPI) Pu=p 1-2 was on and had normal flow. 21:37:49 EPI Pu=p 1-1 was on and had nor=al flow. 21:38:13 Re-established Reactor Coolan: Makeup flow. 21:40:22 Contain=ent Nor=al Su=p Pu=p came on indicating the Quench Tank Rupture Disk had blown. 21:40:36 HPI Pu=ps were shutdown. 1 21:43:16 Auxiliary Boiler Syste= vas started and at normal conditions. 21:43:41 Tripped Reae:or Coolant Pu=ps (RCP's) 1-1 and 2-2. 21:44:05 Re-established Reactor Coolant Lerdown flow. 21:49:57 Put AFP #2 in hand and ran it up to speed (3600 rp=) and then lowered the speed. 21:58:00 closed block valve tc Pressuri:er Power Relief Valve. 22:15:22 Started second Reactor Corlan: Makeup Pu=p. 22:21:57 Started #2 HPI Pu=p. 22:27:24 Brough: #2 Main Feed Pu=p back on with Aux 111ar'y Boiler s:ca=. t 2: 27:44 Shu:down #2 HPI Pu=p. 22:33:23 Shutdown #1 Reactor Coolant Makeup Pu=p. gnpi 22:43:54 Shutdown !!1 cnd #2 AFP's. ( l

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_ 49 v ExnIF.IT C C. Systen Descrietien Stea= and Feedvater Ruoture Control Systes 1. Cencral The stens and f eedwater rupture control syste= (SFRCS) is an auto =atic syste= designed to protect against the following incidents: Main stea= line rupture, either upstrea= or downstream of cain 1. stea= isolation valve (MSIV). This condition, if allowed to proceed, could rapidly blow down both stea= generators, resulting in a rapid RCS cool down and therefore a rapid reactivity insertion under certain core conditions. b. Main feedwater line rupture. If on the steam generator side of the feedwater check valve, this is approxi=ntely the sa=e accident as the steam line rupture; on the feedwater side of the feedwater check valve this results in a total loss of feedwater. I c. Loss of all feedwater. This (as well as the above incidents) could result in boiling both stea generators dry. If this happens, there would be no stea= available for running auxiliary f eedwater pu=ps to renove decay heat. d. Loss of 4 reactor coolant pe=ps (RCP). This results in loss of reactor coolant flow and therefore auxiliary feedwater is needed to establish reactor coolant natural circulation flow. The SFRCS, upon indication of conditions a, b and c above vill isolate l both steam generators (close the =ain feedwater valves and main seca= line valves and trip the turbine) and start the auxiliary feedwater Auxiliary feedwater is initiated to keep steam available for system. the auxiliary feed pu=p turbines and to re=ove decay heat from the reactor Once this is acco plished, the operator will have time to coolant system. begin a cool down in an orderly canner. 2. Desien Criteria The design criteria for the SFRCS and the auxiliary feedvater system a e as follows: The syste= =ust perfor= its safety fune:1on after a single a. active failure has occurred. This =eans that tne single failure of any power supply, pump, turbine, instru=ent or control system logic channel vill not prevent the system from removing decay heat from the reactor coolant system. A main stes= line break upstream of the MSIV or a =ain feedwater b. break downstres= of the cain feedwater isolation valve vill disable one steam generator. After this event both auxiliary feed pu=ps and turbines will be aligned to the re=sining intact This re=aining sten = generater has adequate steam generator. capacity to rc=ove the decay heat frc= the reactor coolant e U) M - -s 'NDPnr systen. n f h=;.O"b if f 1 bi f i w 2 au QL,

O o Functional Descriotion (Refer to Enclosures 1 and 2) 3. The SFRCS is divided f or redundancy, div,ersity, and testability Logic channels 1 and 3 form channel 1, into four logic channels. In one cabinet one and logic channels 2 and 4 for= channel 2. logic channel has an AC power supply, the other a DC supply: Logic Channel Cabinet _ E Power Sucolv_ Y1 (120V AC) C5762A 1 Y2 (120V AC) C5792 2 D1? (125V DC) C5762A 3 D2P (125V DC) 4 C5792 Each logic channel receives the follwing inputs which vill cause it to trip: Six pressure switches, two on each =ain stea= line set at 600 psig decreasing and one on each =ain steam line a. set at 650 psig decreasing. Two ain feedwater pressure differential switches, one from each main feedwater line (see Enclosure 1 for sensing b. 177 psid steam generator pressure higher points) set at than =ain feedwater line pressure. Two level transmitters with bistables, one on each steam 17" decreasing level on the startup c. generator set at range. contact A contact from RPS pu=p power sensing circuit; d. opens on loss of all four RCP's. The SFRCS cabinets consist basically of an AC and a DC power supply, [~' The output relays input buffers, logic modules, and output relays. They also turn de-energize to actuate their associated equipment. ~j out a light on the cabinet when in the tripped state. l' i T Each input to SFRCS has a test switch and light so that a trip i e of that input can be initiated for testing purposes. +1 O relays. The outputs from the STRCS are contacts from the output These contacts are in the control circuits for the SFRCS actuat g';fMa Most components require two SFRCS logic channels to $35 equip =ent. See Enclosure 2 for a listing of actuated (Si@ trip to actuate. equipment. b There is a bloch feature associated with the low steas pressureactuating on trip. To prevent the system fro: channel has a " block" pushbutton on C5721 and on the SFRCS cabinet. tihen stes= pressure goes below 650 psig a block persissive light is received on C5721 along with cnnunciator and cc=puter alar:s. trip on low Vnen the block button is pushed, the channel will not is actuated stean pressure and a ".W SD1 LCh' PRESS TRIP ELKD" lightOn a hcatup on C5721 as ec11 as annunciator and cor.puter alcres.wM when the steam genera

O O s1 - There is another block which is utilized on cooldown. If the decay hes: syste= suction valves frc_ "he reae:or coolant syste= (DH11 and 12) are open, this block will prevent :he opening of the s:cc= inlet valves :o the auxiliary feed pu=p turbines. This prevents the SFRCS frc= starting the auxiliary feed pu=ps when all reactor coolant pu=ps are secured on shu:devn. This " block" is down on auto =atically re=oved when :he decay heat syste= is shut startup. 4. Syste: Loric The r'esponse of the actuated co honents depends on the type a. of trip: (refer to Enclosure 2) 1. On low steam pressure on one =ain steam line, both steam generators are isolated. In addition, both auxiliary feed pu=ps are aligned to the stea= generator which is 3 above 600 psig. If both steam generators go below 600 psig, both steam generators are isolated and y1 auxiliary feedvater is J initiated. If any other trip (such as low steam generator level) acco panies a low steam pressure trip, the valves will align per low steam pressure trip logic. 2. On high feedvater pressure differential or low stea= generator level on one stea= generator, both steam generators are isolated and each auxiliary feedwater pump is aligned to feed its respective steam genera:or (1 to 1 and 2 to 2). 3. On loss of all four reactor coolant pumps, each auxiliary f eedwater pump is aligned to its respective steam generator. The steam generators are not isolated. 4. en all of the above events, the turbine is tripped by the SFRCS. b. The auxiliary feedwater pu=p governor control switch in the con:rol room bus has 3 positions: Auto-Essential (STRCS) ICS Manual In the auto-essential position, the auxiliary feedvater pump is in auto-essential level control. In the ICS position, the auxiliary f eedwater pump is on level control frc= the ICS; via the Hand-Auto station. In =anual, the auxiliary feed-water pu=p is controlled by the operator with the Raise-Lower switch. . mYj :J6 Y QS V j;@ Q D i

O O _ s2 c. The SFRCS starting of the auxiliary feedwater pu=ps will auto. carically reset once the trip condition on the input is recoved. 1;one of the valves, however, wi11' return to their original position until operated individually fro = the cortrol roo= cr a new trip condition occurs. 5. Syste= coeration In order to understand the operation of the STRCS system, it is best to follow the various system act;Lons under several accident conditions. The following cases will'be considered: a. Steam Line Rupture b. Feedwater Line Rupture. c. Loss of Feedwater Pu=ps d. Loss of Four Reactor Coolant Pu=ps Enclosures 1 and 2 should be used as an aid to understanding the l description. All discussions assume 100% FP operation at, start. Some non-SFRCS actions are considered to aid in understandihg,the transient. (1) Steam Line Ruoture - Assu=e steam line 1 shears downstream of MSIV. Steam pressure will rapidly drop. k*nen either steam generator reaches 600 psig, all four logic channels vill trip, isolating both steam generators. (See Enclosure 2 for specific valves.) The MSIV takes five seconds to shut, the main feedwater isolation valve is seconds. Both steam lines vill probably drop below 600 psig, therefore. auxiliary feedwater will not start until one stea= generator recovers to above 600 psig. Auxiliary feedwater pu=ps will align as described in Section 3 above to feed the stea: generator chat first recovers to 600 psig, with both auxiliary feed pu=ps. The STRCS will trip the turbine. The reactor will trip on low pressure. When both steam generators are above 600 psig, the trip condi-tion auto =atically clears and the atmospheric vent valves may be used for pressure control cooldown if required and provided no other trips are present. l (2) Feedwater Ruoture Line - Assu=e feedwater line 1 shears up-i stream of the feedwater line check valve. Feedwater pressure "; hen either feedwater heater drops to l vill rapidly drop. l 177 psig less than stes= generator pressure, the SFRCS will isolate both steam generators and align the auxiliary feed l pumps to their respective steam generator (1 to 1; 2 to 2). l The reactor vill trip on high pressure and the SFRCS will trip the turbine. (3) Loss of Four Reactor Coolant Pu=os ~- If all four reactor coolant pucps trip, the turbine will be tripped by tha SFRCS and the reactor protection system will trip the reactor. The SFRCS will initiate auniliary feedwater. The stes::ig;enerators vill s not be isolated. db 20-23

O O -s>- ENCLOSURE 1 .SFECS ACTUATED EQUl? MENT (F.A'3Ti.i'.,I (fDR STEAM Y!I/E5 SEI I.IXT P.G MN FFEDWATER MN FEEDWATT_R CcNTQL VALVE. ISOL VALVE FW 7f0 FVi?;e5 F W t. l Z. QM 8 O' i M.wiFEED ix g 3 x t g rnns' 5g -l lPDS2't'" A-D l T l MN FEIDWATER. SAL CcNTRc; VALTr i (L$15 Sh ks. TAN AF 3E70 AF 603 AUX FEED PUMP 1 '~ N x L3tt A SP9 5 Gre'? AF 3tl.9 AF3371 t ,u. AF 2E74 AF 591 6 A' X FEED PUMP 2 ' J y s, m h,. .N s SG-2 lFDS 2.25A-Dl MN FTFDWATER CON TROL VALVF. FW 774 FV3PGA Fw g,cg 8 MAIN FEED s, VN a .FYSP7A g B, b\\ [g{ X }} [' ' ' ; 0.ng u ', SP9A 4.rc" I ^ l % CONTPOL VALVE. '.J. t

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