ML20151N853
| ML20151N853 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/30/1985 |
| From: | SOUTHERN CALIFORNIA EDISON CO. |
| To: | |
| Shared Package | |
| ML20151N843 | List: |
| References | |
| TAC-62848, TAC-62849, NUDOCS 8601030163 | |
| Download: ML20151N853 (38) | |
Text
r
- d REMOTE INITIATION OF SHUTDOWN COOLING TEST PERFORMED SEPTEMBER 16 - 17, 1985 AT THE SAN ON0FRE NUCLEAR GENERATING STATION UNIT 3 DOCUMENTING flNAL COMPLIANCE WITH I5 STING REQUIREMENTS OF USNRC BRANCH IECHNICAL POSITION RSB 5-1 PREPARED BY SOUTHERN CALIFORNIA EDISON NOVEMBER 1985 M SSoIS S k 2 L
r SONGS 3 RDf0TE INITIATION OF SHUTDOWN COOLING TEST 3PA-215-01 PERFORMED SEPTEMBER 16 - 17, 1985 Table Of Contents Section Page
- 1. Summary 1
- 2. History 1
- 3. Overview 3
- 4. Sequence Of Events 5
- 5. Operation Of Plant Equipment 10
- 6. Discussion of Plant Equipment 19
- 7. Discussion Of Plant Behavior - 26 Upper Reactor Vessel Thermocouples ,
- 8. Shutdown Cooling System Performance 34
- 9. Conclusions 36
[-
l f
a SONGS 3 REMOTE INITIATION OF SHUTDOWN COOLING TEST 3PA-215-01 PERFORMED SEPTEMBER 16-17, 1985 Summary The third and final test to demonstrate USNRC Reactor Systems Branch .(RSB) Branch Technical Position RSB 5-1 was performed September 16 and 17, 1985, as the San Onof re Nuclear Generating Station Unit 3 (SONGS 3) was being brought to cold shut-down for its first refueling. The test, designated 3PA-215-01, demonstrated that shutdown cooling (SDC) could be remotely initiated from the control room while the reactor was being cooled by natural circulation, and the plant could be cooled to cold shutdown (Mode 5) using the remotely-actuated SDC. The test started from shutdown cooling initiation conditions and slightly overlapped the final conditions of SONGS 2's 80% Natural Circulation Test, designated 2PA-215-01, previously reported in the SONGS 2 Initial Startup Report of August 1983 and CEN-259, "An Evaluation Of The Natural Circulation Cooldown Test Performed At The San Onofre Nuclear Generating Station", Combustion Engineering, January 1984. All test objectives were met and the test was successfully completed. A new finding was strong indication of fluid circulation in the upper reactor vessel head during natural circulation and SDC.
The test consisted of six major parts: (1) aligning and warming the shutdown cooling system; (2) tripping the reactor coolant pumps and establishing natural '
circulation; (3) remotely initiating SDC under natural circulation; (4) cooling and heating 30 F under combined natural circulation and SDC; (5) restarting two reactor coolant pumps and stabilizing; and (6) cooling to Mode 5 using SDC.
The remainder of this report consists of detailed explanations of the test anc' equipment operation. The history of SONGS 2 and 3 testing to satisfy RSB 5-1, i an overview of the test and sequence of events, operation of equipment during the test, synopsis of plant behavior, temperature behavior and inferred flow patterns in the upper reactor vessel head, and shutdown cooling heat rejection will be discussed.
History The USNRC's RSB 5-1 scenario has no specific plant transient but its generic sequence would have the plant operate at full power, experience a complete and prolonged loss of offsite power, and be cooled to cold shutdown using only one train of safety-related equipment. The scenario from power operation to shutdown cooling initiation was satisfied by two previous startup tests on SONGS 2. The final special test to complete the scenario's demonstration was planned for SONGS 3 and is now being reported.
The SONGS 3 test continued SONGS 2's test 2PA-215-01 which started with the plant at 80% power and tripped (deenergized) all four reactor coolant pumps to simulate a loss of offsite power. The plant immediately tripped and entered Mode 3, hot standby. A series of boron mixing tests was followed by a rapid cooldown and depressurization to shutdown cooling entry conditions as shown in Figure I.
Page FIGURE I: SYNOPSIS OF TESTS PERFORMED AT SONGS 2 & 3 TO SATISFY NRC RSB 5-1 SCENARIO Three tests satisfied USNRC RSB 5-1 demonstration. The SONGS 2 tests started from power, one from 80% and the other from 20%. The 80% Natural Circulation Test brought the plant from 80% power to shutdown initiation conditions, where the SONGS 3 test wa s initiated. The 20% Loss Of Offsite Power test started at 20% reactor power and was initiated by a total loss of offsite power.
OPERATING SONGS 2 & 3 TESTS ASSOCIATED WITH RSB 5-1 DEMONSTRATION MODES 80% Natural MODE 1 Circulation Test Power 2PA-215-01 Operation 80% Power 20% Loss Of Offsite Power 3PA-381-01 20% Power MODE 2 cr' Boron Mixing Demonstration, MODE 3 Natural Circulation Cooling y Hot c And Depressurization To Standby
,o Shutdown Cooling Entry
.g Conditions a- .
$5 Remote Initiation Of MODE 4
%.h Shutdown Cooling Hot 2: ') Demonstration Shutdown j [ hutdown Cooling 3PA-215-01 mg u Entry Conditions ) ,,
- t c rwRemote Entry o To Shutdown O,5 Cooling From 5
gb Natural Circulation, et) Cooldown, And Entry gg Into Mode 5 50 4 MODE 5 O Cold
.j Ns Shutdown Figure I Page _ _ _ -
When the SONGS 2 test was performed the SONGS 2 shutdown cooling system was not fully designed for remote initiation from the control room so it was agreed to continue the demonstration program at an appropriate time prior to the ~ end of the first SONGS 3 refueling. The SONGS 3 test resumed the demonstration where the SONGS 2 test ended and continued to cold shutdown. Unit 2 was modified at its first refueling and now has full remote initiation capability.
Overview Figure II shows reactor coolant system (RCS) temperature and test parts versus minutes time from the reactor coolant pump (RCP) trip which initiated natural circulation. The RCP trip was chosen as the key event because the plant entered conditions which closely ma*ched the previous SONGS 2 natural circulation test.
The test parts will be referenced throughout the report.
The plant entered Mode 4 and was cooled to 320 F in the first part. The shutdown cooling system was prepared by closing circuit breakers, aligning valves, and warming it under the direction of normal operating procedures. The shutdown cooling system alignment procedure requires triple verification so some time was required to complete Part #1.
Part #2 started when the RCPs were tripped and ended fif ty-four minutes later when shutdown cooling flow to the RCS was initiated by opening two of the four SDC isolation valves to two of the four RCS cold legs.
During Part #3 shutdown cooling was initiated and heat rejection was shifted from the steam generators to sautdown cooling. Colder water from the shutdown
~
cooling system caused a brief decrease in RCS temperatures.
A cooldown from 320*F to 291 F (cold leg temperature) and return to 320 F was undertaken in Part #4. The plant was shown to be easily controlled and cooled with shutdown cooling and natural circulation. Thermocouples in the upper reactor vessel head showed that fluid slowly circulated in the upper head, an important finding since the 4200 gpm shutdown cooling flow is less than typical natural circulation flows of 6000 gpm. This suggests that natural circulation flow rates should be sufficient to induce cooling flow in the head and avoid steam bubble formation during rapid natural circulation cooldown and depressurization.
The reactor coolant pumps were restarted to force flow through the steam generators and cool them prior to the refueling outage since shutdown cooling does not cool them. The pumps also added heat to core decay heat and provided the shutdown cooling system with a higher heat load.
Part #6, cooldown to Mode 5, was accomplished by two settings of the shutdown cooling system. The first produced a relatively slow rate; the second was a much faster rate which decreased as the temperature difference between the RCS and shutdown cooling decreased.
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Sequence Of Events Table I is a listing of the sequence of test events and lists in detail time frames and actions.
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Page p - _ _ - . . , ,
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TABLE I: SONGS 3 REMOTE SHUTDOWN COOLING DEMONSTRATION' SEQUENCE OF EVENTS .c W;3 .
TIME CLOCK ELAPSED (MIN __)_ EVENT COMMENT 9/16/85 p
0730 -747 Entered Mode 4. Preparations started for verify'ings SDC lineup. S, tart of Part. #1.
1912 -53 Secured Steam Generator Feedwater Flow. Prepared steam gendrators for. transferring 1919 -46 Secured Steam Generator Blowdown Flow. t rejection tg the shutdown cooling system, and for quantifying heat loss from generators.
1925 -40 Opened SDC Suction Valves. Completed S9C valve lineup for warming.
Prewarming is part of normal operating procedures.
~
'1927 -38 LPSI Pump Started, Warming SDC.With Approximately 100 GPM Flow, m
g 1956 -9 Shutdown Cooling System Warmed To Prewarming completed.
m Within 90*F of RCS.
5e 2000 -5 SDC Loop Discharge Valves 3HV-9325 & .SDC system warmed with fluid being recirculated 3HV-9328 Closed. by LPSI Pump P015.
2003 -2 311V-9336 (16" SDC Suction Valve Outside Test configuration for SDC achieved.
Containment) Closed.
2005 0 Operating Reactor Coolant Pumps Stopped Test Initiated. Start of Part #2.
(3P004'& 3P003).
2020 15 Natural Circulation' Declared By Operations. %7 F reactor vessel differential temperature.
2027 22 Atmospheric Dump Valves (ADVs) Were ADVs were opened to increase steaming and Opened To 465% Open Over The 22 to 42 stabilize temperatures. They had been closed Minute Period. 'to 15% when the RCPs were tripped to minimize cooldown'due to reduced RCP heat input to the RCS.
i
. , _ _ . . . . ____ _ ._, . .--. . . . . .~
TABLE-I (CONTINUED): SONGS 3 REMOTE SHUTDOWN'C00 LING DEMONSTRATION SEQUENCE OF EVENTS -l TIME CLOCK ELAPSED EVENT' COMMENT 9/16/85 2048 43 Cooldown Observed. Heat rejection through the steam 8enerators produced a definite cooldown.
. 2059 54 SDC Valves 3HV-9328 & 3HV-9325 (Train A) SDC.in operation. Start of Part #3.
4 Being Opened To Place SDC In Service. Note: Technical Specification 3.4.1.3.
(A Brief Cooldown' Was Noted As Colder . allowed only one hour with the-
. SDC Fluid Entered The RCS.) RCPs and SDC secured; SDC was i initiated within one hour. During this time no dilutions were made and saturation margin was monitored '
by noting QSPDS "CET Saturation Margin", .page 501 of the QSPDS, in'the test log.
1 i 2104 59 ADVs Being Closed (Completely Closed Preparing to transfer. heat rejection to
', By 2105). SDC.
g
!g 2113 68 3E004 (Train A) Initiated By Opening Heat rejection is transferred to SDC.
y 3HV-8150 %10% From Fully Closed.
2127 82 ADVs Opened To 10%. Cooling with both ADVs and SDC being observed.
- 2144 99 ADVs Closed. Step 8.8.1 of Test Procedure accomplished.
Heat rejection placed entirely on SDC. No further heat rejection via the steam gener-
- ators or ADVs. Increased SDC heat exchanger -
flow to increase heat load on SDC.
1 1
6
TABLE I (CONTINUED): SONGS 3 REMOTE SHUTDOWN COOLING DEMONSTRATION SQUENCE OF EVENTS .
TIME CLOCK ELAPSED EVENT COMMENT 9/16/85 2204 119 Flow Through the Shutdown Cooling Heat Part #4 (cooldown and heatup on SIX )
Exchanger Was Increased To Start Cooldown, started. The operators observed that it was easy to produce a cooldown using SDC when the plant was on natural circulation.
2214 129 SDC Heat Exchanger Flow Was Reduced. Flow was reduced to control temperature decrease.
2224 139 SDC Heat Exchanger Flow Was Reduced To The cooldown to 291 *F from 320'F was Very Low Flow Rate. completed and a heatup started to return the plant to original (320*F) temperature so a reactor coolant pump could be restarted without an increase in primary pressure.
m
$* 2247 162 Noncritical Heat Loads Completely Work on the other (Train B) heat exchanger Transferred So Only Critical Loads And had been finished, and placing only the ao LetdownHeat Exchanger Were On Component critical loads on Train A's heat exchanger Cooling Water Heat Exchanger 3E001. provided opportunity to assess its performance.
2258 173 Heatup Observed To Be %4 F Every 8 Minutes. Heatup entirely on decay heat.
2312 187 RCP 3P004 Was Started. No Observable End of Part #4, Start of Part #5. RCPs were Change In Pressurizer Pressure Was Noted. started to permit cooling the entire reactor coolant system to Mode 5. (The SDC cools the steam generators very little.)
2322 197 RCP 3P001 Was Started. One RCP in each loop was started to promote cooling both steam generators
TABLE I (CONTINUED): SONGS 3 REMOTE SHUTDOWN COOLING-DEMONSTRATION SEQUENCE OF EVENTS
~
TIME MINUTES CLOCK ELAPSED EVENT COMMENT 9/17/85 0007 242 SDC Increased To Start Cooldown To Mode 5. 3flV-8150 was opened somewhat. Start of Part #6.
0030 266 Cooldown Rate Observed To Be %48*F/hr.
0057 292 Cooldown Rate Increased To N69 F/hr. 311V-8150 was opened further, although not fully.
The opening remained fixed throughout the rest of the test. Cooldown rate decreased as the temperature difference between the RCS and SDC decreased.
0142 337 Cooldown Rate Observed %40 F/hr. Temperature difference between RCS and SDC decreased, causing cooldown rate to decrease.
0201 356 Cooldown Rate Observed %33*F/hr. Tcold %232*F.
327 442 Mode 5 (<200 F) Achieved. End of Test.
?
. _ _ _ _ _ _ _ _ . . _ . . _ .-~__- _ . . _ ._
TABLE II: OPERATION OF PLANT EQUIPMENT 80% NATURAL CIRCULATION SONGS 3 SDC EQUIPMENT TEST (SONGS 2) TEST COMMENTS j Main Steam Isolation Closed Closed Same condition in both tests. Simulates loss of Valves (MSIVs) offsite power conditions.
, Atmospheric Dump Operated Operated The.ADVs were used to reject heat throughout j Valves (ADVs) the SONGS 2 test, and prior to complete transfer of heat rejection to SDC during the SONGS 3 Test. Use of ADVs simulates loss of offsite power conditions and simplifies the test because heat losses to the main steam lines was avoided.
Steam Generator Stopped Stopped Steam generator blowdown, normally used to Blowdown control steam generator secondary chemistry, 2 was stopped so water level changes would
$ be limited to steaming and steaming heat losses i could be quantified.
E' Auxiliary Feedwater System Used Not Used Auxiliary feedwater was stopped prior to Fain Feedwater System Not Used Not Used tripping the RCPs. Main feedwater was '
isolated and not used for either test.
Charging & Letdown (CVCS) Normal Normal CVCS was in service for both tests
< & Pressurizer Level Operation Operation in keeping with the rationale for the SONGS 2 Control test and provided RCS boron data.
Pressurizer Pressure lE (Emergency) lE During Leakage through the normal spray valves caused Control Natural pressurizer pressure to slowly decrease, but l
Circulation because normal spray is driven by RCP differential And pressure, leakage was only a problem when the Shutdown RCPs were operating. The Train A 1-E (emergency)
Cooling, heaters afforded adequate control when the RCPs Train A were deenergized (during natural circulation and Only while on shutdown cooling), so use of non 1-E '
heaters during RCP operation did not compromise test philosophy or results.
1
TABLE II (CONTINUED): OPERATION OF PLANT EQUIPMENT:
80% NATURAL CIRCULATION ' SONGS'3 SDC.
EQUIPMENT TEST (SONGS 2) TEST COMMENTS
.1-Reactor Coolant Pumps Not Operating Not Operating The RCPs were not operating while entering 1 During Nat- shutdown cooling, and.for 133 minutes after i init'iating shutdown cooling while a 30*F.
~
ural Circul- .
ation And cooldown and heatup were performed. NRC RSB 5-1 !
Remote requirements were satisfied by having the plant '
) Initiation in natural circulation when entering shutdown Of SDC. cooling.
1 Operating The steam generators are not cooled by shutdown During Cool- cooling. In order to facilitate steam generator down To maintenance during the refueling outage which ;
Mode 5. immediately followed the test, two RCPs were i operated to force circulation in the generators and speed their cooling. The RCPs also provided additional heat. to the shutdown cooling system.
7 g Component Cooling Water Normal Operation Single Train Train B salt water system was out of service for !
4
, And Salt Water Cooling (Train A) modification and was returned to. service toward i
=i Systems (CCW & SWC) Was Used. the end of the SONGS 3 test. Noncritical loads were then transferred to Train B, placing only the shutdown cooling heat exchanger (3E004)
- and letdown heat exchanger (the major heat
{ sources) on Train A. CCW flow to other critical i loads such as containment coolers was also I stopped toward the end of the test, forcing t l all of the reduced flow through the shutdown .
and letdown heat exchangers.
j , During the SONGS 2 test almost all heat was i rejected through the steam generators so CCW l and SWC lineup was relatively unimportant. '
1
! Control Element Drive Operating ~ Operating CEDM cooling was operated, consistent with ,
1 1
- = , -. --
TABLE II (CONTINUED): OPERATION OF PLANT EQUIPMENT 80% NATURAL SONGS 3 CIRCULATION SDC EQUIPMENT TEST (SONGS 2) TEST COMMENTS Shutdown Not Used Remotely The shutdowr. cooling system was warmed and initiated remotely Cooling Initiated (from the control room) and operated normally using normal System From Control operating procedures as described in Figures III through VII Room below. All valves directly in the SDC flow path were remotely operated.
Four valves and their integral bypasses connecting the SDC system to refueling water storage tank and containment spray system (but not in the SDC flow path) were closed to conform with .
procedure and to prevent leakage that could have spread radio-active primary coolant and delayed the refueling outage that immediately followed the test. SONGS 3 had failed fuel and D' the potential (however remote) for spraying the containment
$ with primary coolant was to be avoided from a commercial stand-i point. Manual alignment of these valves did not affect the Ci performance of the SDC and avoided potential costly delays, By Technical Specification 3.5.2, valves in the SDC normally used for SDC and post-accident long-term cooling are disabled electrically in Modes 1 and 2, and under certain Mode 3 conditions. Technical Specification 4.5.2 lists the valves; those important to the test are noted on Figure III. The valves are electrically enabled by closing their. circuit breakers; the breakers are located inside the control building and
, above the control room in a room adjacent to the remote shutdown control panels.
I
TABLE II (CONTINUED)i OPERATION OF PLANT EQUIPMENT -
NATURAL SONGS 3 CIRCULATION SDC EQUIPMENT TEST (SONGS 2) TEST COMMENTS Shutdown Not Used Train A (Only) Train A components (see Figures III through VII) were used to Cooling Was Used simulate a loss of one train. One LPSI pump (P015, the Train System A pump) and Train A heat exchanger (3E004) and salt water (Continued) heat exchanger 3E001 were used. The smaller of two suction valves outside the containment was open (3HV-9379, a Train A valve) to simulate loss of one train and present the smallest flow area. This small flow area also limited the SDC system to operating with only one LPSI pump.
LTOP All four suction valves inside the containment, including Train Valve Was B's 3HV-9339, were open to provide maximum flow area to the LTOP Provided A (Low Temperature Overpressure Protection) valve per Technical y Full Flow Specification 3.4.8.3.1 and in case a pressure surge occured g Path while restarting a reactor coolant pump.
L y SDC Was The shutdown cooling system was warmed to within 100 F of the Warmed RCS prior to initiating the test (deenergizing the RCPs) so Prior.To the one-hcur time limit between stopping RCPs and initiating SDC Initiation shutdown cooling (per Technical Specification 3.4.1.3) could be devoted to verification of natural circulation and stabilizing the plant in preparation.for initiating shutdown cooling. Under a RSB 5-1 scenario, natural circulation would long since have been established and the SDC could be warmed, if desired, as part of placing it in service.
Warming is described in Figure IV and involved a small flow
(< 100 gpm) of cold SDC water into the RCS. After the SDC was warmed the loop discharge valves were closed and the system was recirculated to maintain its temperature.
NOTES: (1) In Figures III through VIIbelow a colored (filled-in) valve or partly colored pump is one which is closed or off, respectively. Uncolored valves or pumps are open or on, respectively.
(2) Trains are noted by "A" (Train A) or "B" (Train B) next to the component.
(3) DC valves have 480 volt AC motors powered through inverters from Train C and D batteries.
. 4 FIGURE III: VALVE LINEUP BEFORE WARMING SDC (BEFORE ALIGNING THE SDC, PART I) ,
COMPOSITE SKETCH OF SONGS 3 SHUTDOWN AND REACTOR COOLANT SYSTEMS NOTE: Shading means pump off or valve closed. PL PL A 3HV- 4 3HV-B A Rf'2 A G 8150 lHV- 3ny. 4 3gy 9339 9337 g379 k I ; HUT- k J V3
~
L 2 L J Af DOWN VM L J [ Ps ~
HETX V3 l6= V 1 V3 pog5 12" 1lLTOP PL pt DC Y 1HV- 3C j M~
3HV_ B JTE 3HV 9378 9377 y d'h ,
8Is1 B 3oy agg3 (J LJ PSI L J SHUT-FM I O" I 77 Pot 6 FT H
- V 16" 13HV6500]
! 3TE 3E003 SHUTDOEM COOLING W PL T SUrTION r3 LINE WARMUP 3HV- %
INSIDE Ol!TSIDE 0196 p
[ CONTAINMENT CONTAINMENT yi y .
o gsn g L y g y.
(lj nL 3P002 (D (2R) STEAM ' '
g);
75 GIN-
- Wri
<- Ji 3P004 (2A) 77
& TE 3F088 3ll V - A 3HV- 3HV- A T
1 j y gy 937R Rt60 PL enri PL d' I JL 2A LlJ _
HOT LFG #2 I V LOOP ttnip 34 3HV - A 2B WEAC- 9325 IN LOOP TOR , gg g ,g LU I" 1TE 3FE TE THV- B 352 306 TE 111 Y ise *>t??
If dJ Q j vm STEAM
'P y"- "1 3Hv_
out n
3I089 2B ([; NOTE: MANY LINES AND COMPONENTS 3 Pout 3Poo3
'^ IIN) Fl HAVE BEEN OMITTED FOR L
CLARITY.
"PL" signifies a Power Lockout valve, one whose control power is disabled except during The configuration shown above is the value lineup shutdown cooling system operation as specified in Technical Specification 3.5.2. Power during the first of Part I of the test, prior to the valves is locked out (removed) as specified in Technical Specification 4.5.2.
to changing valve positions. Aligning the SDC involved closing circuit breakers to the valve actuators. The circuit breakers are located in the control building above the control room near the remote shutdown panels. ,
FIGURE IV: VALVE LINEUP DURING WARMUP (During part I)
COMPOSITE SKETCH OF SONGS 3 SHUTDOWN AND REACTOR COOLANT SYSTEMS Note: Shading means pump off or valve closed.
A 3HV-g' 3HV- T9337 g
3gy, A RI'?
A A @ 3HV-RISO 9339 h SliUT- k J 937o m A , "
/ DOWN PT
/ / A m t LPSI - CCW 3 14 lLTOP 1 if DC Y in:
3HY' 9 W' db 3HV- B JIE 3HV 9378 9377 1( RI%1 E 3gy gj$}
10" ( f) H j , gp 13HV65001 j( ,
1.E 3E003 SHUTDOWN 9"3
- . ggggpp 3HV- 4 INSIDE Ot'TS I DF. 3HV- B, LINh F
[ 3POO2 (M{AIN NT CONTAjNMfNT gnq b ,
p (2R) STEAM ' "
gl2 r3 (D Rrl CEN- _ 3P004 (2A) F' I 3 18R 3HV- 0 A TE T 3ny_ g 3HV -
[I lk
, y37, JL R150 p1f1 Jb JL
, 2A b HOT t.FC jg#2 5H V ' '
LO3P IOOP 2A CraCke A Loop inop gg T 4 IA jg 3TE 3FE TE TE IHV" ggg y 9122 I4 kb s e
y sg VM '
~
STEAM R:p GEN, h 3gy, g 3pno g 3F089 2R NOTE: MANY LINES AND COMPONENTS 3
(IA) (IB) r3 II AV E BEEN OMITTED FOR l
CLARITY.
Warmup valve alignment followed r.ormal operating procedures hlarmup consisted of operating LPSI pump P015 and recirculating so 3HV-9336 (Train B) valve was open. After warmup and prior fluid throutf1 the warmup line and valve 3HV-9353, and also cracking to tripping the reactor coolant pumps, this valve was closed. Open loop isolation valves 3HV-9328 and 3HV-9325 (Train A valves)
Flow during the warmup is shown by arrows. to allow small flow ( %100 gpm) through the shutdown cooling s ystem.
.~ . .
FIGURE V: VALVE LINEUP PRIOR TO SDC INITIATION (During parts I & 2)
COMPOSITE SKETCII 0F SONGS 3 SIIUTDOWN AND REACTOR COOLANT SYSTEMS NOTE: Shading means valve closed or pump off. .
3HV- A -
3HV-al' ? A V3- 8150 JHV- T' 'A ,
9339 9337 , h/ SHUT. k J
/\ DOWN 71
- 16"
\
b ' (4 ' I 9f
- CCW HETI 3E004 D
^
lLTOP 2 If n
DC' Y 3HV- ;)C Jg 3HV-
'llh 3HV- B JTE 3HV-9378 9377 i '( Rf" 103- 81st 10" l P f 16 j3HV6500 M( 3TF 3FOO3 IHV- A 351 CCW-S H tf T DOW N *153 p wapMPP 3HV- I A
[ INSIDF OUTSIDE lH V -- R/LLINF 3pggy CONTAINMENT CON T A [ N MF NT qiso II LlJ I
(28) STEAM W FT pri Cf;N - 3P004 (2A) F' O 3HV- 3HV-1 TE 3 t oset TF 3HV. IA jg 937, g migo pig t 121Y 12 %
I JL
'I 2A dJ , j m HOT LtG #2 Y 1.00P gmP 24 3HV- 4 "325 2B EAC- gg
/k if LOOP TOR I00P 1R I^ ~3TE 3FE IHV- 352 306 TE TE )g Ill Y l i sc- 9122 U l^ Ll2 m , ,
vm - ,
Q STEAM 4
- P G N. wu )gy_ g 0111 3 Pout 3E089 2B NOTE: MANY LINES AND COMPONENTS 3Po03 L; IIAI (IB) F7 HAVF BEEN OMITTED FOR CLARITT.
During part #2 the RCS was in natural circulation, shown above.
The shutdown cooling system was recirculated after warmup and prior flow to or from the RCS. Suction value 3HV-9336 was to SDC initiation (Part #3 ) to keep it warm. Recirculation involved also closed to conform to test conditions of assuming closing the previously-throttled loop valves (3HV-9328 & 3HV-9325) one train of SDC, and circulating fluid through warmup valve 3HV-93S3 so there was no
FIGURE VI: SHUTDOWN COOLING LINEUP AFTER SDC INITIATION (Parts #3 and #4)
COMPOSITE SKLTCH OF SONGS 3 SHUTDOWN COOLING AND REACTOR COOLANT SYSTEMS NOTE: Shading means pump off or valve closed.
A 3HV- A 3 - 3HV-p Rit? g U 3- 8150 A
3HV- lH i- 3ny. A ,
9339 9III 9170 m m b SHUT- N
^ "
" V DOWN V
' th" If LTOP 3 p
- R i 'gy~
B DC JHb- 'lH V - ;)C M 3HV- B JTE 3HV-9378 9377 if
-9336 8151 I4 N)3< R151 A 7 y k
y r h/ D jb V N 10" 7T l'01 f. V\ HTEX 16" -13HV65001 3TE 3F003 I '
SHUTDOWN ' %$
COOLING Lll
' gggypp 3HV- A y
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The natural circulation portion of the test (Part #2) ended Heat rejection from the SDC was initiated by opening
@m the loop isolation valves (3HV-9328 & 3HV-9325) were 3HV-8150, shutdown cooling heat exchanger 3E004's opened and the warmup valve (3HV-9353) was closed. Part #3 discharge valve, of the test then began.
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FIGURE VII: SHUTDOWN COOLING LINEUP ALTER RCP RESTART (Parts #5 and #6)
COMPOSITE SKETCH OF SONGS 3 SHUTDOWN COOLING AND REACTOR COOLANT SYSTEMS NOTE: Shading means punp off or valve closed. ,
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SDC continued to operate after the RCPs were restarted. Flow to loop 2A was in the direction of flow from RCP 3P004 and was orposed by the pressure head developed by the operating RCP. Shutdown cooling to loop 1B was in the direction of flow which was reverse, traveling through idle RCP 3P003 and past TE-115-2, producing a lower temperature reading after 3P001 was restarted.
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e 1
DISCUSSION OF PLANT BEHAVIOR -
HOT-AND COLD LEG TEMPERATURES AND STEAM GENERATOR PRESSURES AND LEVELS I Plant ~ behavior is characterized in two sections. The first discusses hot and cold leg temperatures and steam generator pressures and levels, and is plotted The second discusses upper reactor vessel head in Figures VIII through XI.
temperatures and will be discussed using Figures XII through XIX.
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[ MINUTES FROM RCP .STOP Figure VIII covers Part #2 from natural circulation to shutdown cooling init-intion. System configuration is sketched in Figures V and VI. The two reactor coolant pumps (RCPs) were deenergized at time zero and hot and cold leg tem-peratures started to diverge. By ten minutes temperatures had stabilized to a differential characteristic of natural circulation and the operators declared the plant to be in natural circulation. Steam generator pressure, however, continued to increase so the atmospheric dump valves (ADVs) were opened until a stable pressure was obtained. Stable temperatures followed and the period Page . _ - - - - .. -_. - ,
r .
.. Figure VIII (Continued) from thirty to forty minutes was sufficiently stable to measure core decay heat. Decay heat measurement was based on changes in steam generator water levels, measur.ements of charging and letdown temperatures and flows, and estimated RCS thermal insulation heat loss. Decay heat was estimated to be approximately 0.2% of full power, or 7.1 Mw. This low value was expected considering SONGS 3's prolonged operation at 55% power at end of cycle and the several day decay time from power operation to the test.
Steam generator levels and pressures were use throughout the test as indicators of steam generator heat rejection rate and the hottest part of the secondary.
Steam generator blowdown and main and auxiliary ~ feedwater had been stopped before the test to permit pressure to reflect' saturation temperature and heat rejection.
The reactor coolant system circulated slowly, as shown by slow temperature changes and as expected during natural circulation. Temperature behavior was clearly illustrated when the ADVs were opened at thirty-eight minutes, cooling fluid in steam generator tubes. The colder fluid arrived at the cold leg tem-perature sensors at forty-one minutes and the hot leg sensors just upstream of the steam generators at forty-five minutes. Under normal flow only a few seconds would be required.
Steam generator pressures and RCS temperatures continued to decrease until fifty-four minutes when the ADVs were shut and shutdown cooling was initiated.
Shutdown cooling had two effects. First, its 4200 gpm flow of colder fluid caused a brief decrease in temperatures. Second, it tended to reduce flow and heat transfer to the steam generators as illustrated in Figures IX and X. The response of steam generator pressure to changes in primary temperature became increasingly slower until by approximately 180 minutes secondary pressure ceased to follow changes in primary temperature. This decoupling of primary and secondary temperatures was an indication that significant heat transfer to the steam generators had ceased. For convenience, saturation temperatures corresponding to steam generator pressure is noted en the graphs of steam generator pressure, i
1 4
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FIGURE IX: INITIATION OF SHUTDOWN COOLING FROM SHUTDOWN COOLING 350 350 -
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4 Figure IX, above, shows Part #3 including the initial RCS temperature decrease due to introduction of cold shutdown cooling fluid and subsequent return to 320*F in preparation for cooldown.
Page 4
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!20 130 140 150 160 th0 18 MINUTES AFTER RCP TRIP Part #4 is shown in Figure X. A controlled cooldown of almost 30*F and heatup to initial temperatures showed that the plant could be easily and rapidly natural circulation and shutdown cooling. Cold leg temperatures cooled showedusing a 1*F/ minute (60*F/ hour) cooldown rate between 115 and 145 minutes post-trip. The cooldown at existing low levels of decay heat was sufficient to demonstrate that the plant could be easily and rapidly cooled with natural circulation and shutdowr, cooling.
During this part of che test the upper head thermocouples showed temperature changes which indica'.ed that fluid in the head was circulating.
Page
,o FIGURE XI: REACTOR COOLANT PUMP RESTART AND PRE-COOLDOWN STABILITY
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1 w 180 190 200 210 220 230 240 250 MIR,TES FRCPI RCP TRIP The reactor coolant pumps were restarted in Part #5, above, and the plant was stabilized prior to cooling to Mode 5. The first pump, 3P004, was restarted at 188 minutes and mixed the RCS, as indicated by near-uniform hot and cold leg temperatures. The second RCP, 3P001, was restarted at 199 minutes. Cold-leg 1B's temperature showed an 11'F decrease shortly after 3P001 was restarted because reverse flow through the leg's idle RCP (shown in Figure VII) caused colder shutdown cooling to flow past the temperature element. The temperature differential persisted for the remainder of the test.
Page
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.s FIGURE XII: C00LDOWN TO MODE 5 350 .
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MINtfrtS FROM RCP TRIP 9 During Part #6, above, the plant was cooled at two rates. The original cooldown rate was 48'F/ hour but at 285 minutes was increased to 69'F/ hour by changing the setting of 3HV-8150. The valve position remained constant for the remainder of the test, allowing the characteristics of the cooldown to be~ observed. As plant temperature decreased, the cooldown rate also decreased considerably. Steam generator pressures, a measure of the warmest part of the steam generator secondary sides, also decreased but less than loop temperatures. The fact that pressure did decrease indicates that some cooling was occuring. Page .. .- . , . ... _ - . .
DISCUSSION OF PLANT BEHAVIOR-UPPER REACTOR VESSEL THERMOCOUPLES One string of upper head unheated thermocouples was monitored during the test 1 to determine fluid temperatures and infer flow patterns. Temperature patterns indicate that the upper portion of the reactor vessel circulates at a slow rate and the portion between the upper core support plate and top of the hot leg actively circulates. This significant new finding potentially explains why no steam bubble was drawn during the SONGS 2 80% Natural Circulation Test. 4 Eight thermocouples are located in a vertical string extending from the top of the core support plate to near the top of the reactor vessel head as shown in i Figures XIIIa and XIIIb. The lowest thermocouple (#8) is located just above the plate. The next three (#7, #6, and #5) are located at elevations corresponding to the bottom, center, and top of the hot legs, respectively. Thermocouple #4 is located below the upper guide structure (UGS) support plate and the remaining three above.
- The lower thermocouples (#8 through #5) showed rapid changes in temperature corres-
, ponding to changes in hot and cold leg temperature readings, an indication that 1 the thermocouples are in active flow paths. The uppermost thermocouples are much i slower to respond but the fact that they show increases in temperature indicates ]! a slow circulation of fluid in the upper portions of the head. i i, Six annotated Figures describe the thermocouples and temperatures and implications of fluid circulation in the head. ll i' l e Page -. - - . - - - - _ . _ - - . . _ - _ - _ - . - - - - - - _ - . . _ . . - - - -_- -- __ - .-.
s FIGURE XIII: LOCATIONS OF IIEATED & UNHEATED JUNCTION LEVEL THERM 0 COUPLES Two strings of level-detecting thermocouples are installed in SONGS 3, as shown below. One string of unheated thermocouples was monitored.
#1 Upper llead i 110T LEG % TilERM0 COUPLE STRING
% Reactor Vessel
.e UGS Support Upper llead C #3 ]
- Reactor Vessel N / -
p Z i f Flange o o 1 TC 4-- Reactor Vessel ,
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TilERM0 COUPLE Top Of Core STRING CONTROL ELEMENT INCORE INSTRU- DRIVE M ON ( t 110T LEG Note: Thermocouples are denoted by . FIGURE XIIIa: SIDE VIEW OF REACTOR VESSEL & TilERM0 COUPLES FIGURE XIIIb: TOP VIEW OF LOCATIONS
FIGURE XIV: UPPER HEAD THERMOCOUPLE TEMPERATURE BEHAVIOR DURING PART #2 The upper head thermocouples followed trends in temperature during the natural circulation portion of the test, as shown below. This graph should be compared to Figure VIII for comparison with other plant parameters such as hot and cold leg temperatures. 340 335 - - - - - - - e x
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-15 -5 0 10 MINUTES TIME FROM RCP TRIP Legend: A Upper Head Thermocouple #2 5 Upper Head Thermocouple #4 9 Upper Head Thermocouple #6 - Upper Head Thermocouple #8 The trend of increasing temperatures measured by hot an cold legs is also experienced by all upper head thermocouples startin8 at ten minutes. This increase is an indication that the upper head circulates even under strictly natural circulation conditions.
Page J
FIGURE XV: BEHAVIOR CF LOWER FOUR UPPER HEAD THERMOCOUPLES WHILE INITIATING SDC DURING PART #3 Temperatures recorded by the upper head thermocouples showed two separate patterns. The lower four followed changes indicated by hot and cold leg resistance temper-ature devices (RTDs) (see Figure IX) although the lower ones showed the greatest change. The upper ones, as shown in the next Figure, showed little change, an indication that the upper head above the lower four thermocouples circulates very slowly. 350 345 O UPPER HEAD THERMOCOUPLE B5 4 UPPER HEAD THERMOCOUPLE E
~~ A UPPER llEAD TilERM0 COUPLE #7 l UPPER HEAD THERMOCOUPLE 58 I
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300 . 8 m i 295-9 290 , , , , , , 55 60 65 70 75 80 85 90 50 MINUTES TIME FROM RCP TRIP Page FIGURE XVI: BEHAVIOR OF UPPER FOUR UPPER HEAD THERMOCOUPLES WHILE INITIATING SDC DURING PART #3 The uppermost thermocouples showed almost no response to the rapid temperature change resulting from initiation of shutdown cooling, as the Figure below 111ustr-ates. 350 A UPPDMOST THDM0 COUPLE si A UPPER HDD THERMOCOUPLE R2 345 y UPPER HDD THERMOCOUPLE B3 g UPPER HDD THERMOC0UPLE #4 340 335
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A E F 300 8 295 y 290 , , , , , , , 50 55 60 65 70 75 80 85 90 f I MtNUTES TIME FROM RCP TRIP Page FIGURE XVII: UPPER THERMOCOUPLE TEMPERATURE BEHAVIOR DURING PART #3's C00LDOWN AND HEATUP The lowest thermocouples (#8 and #6) showed the greatest change, those in the upper part (#1 aad #2) the least, a demonstration that circulation was slow. However, the upperust thermocouples did respond to both the cooldown and heatup. 350 6 UPPERMO$f IMDM0 COUPLE N1 A UPPD HDD THERMOCOUPLE B2 345 ! IIPPD HDD THERM 0 COUPLE 54
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305 K/~ 300 , , , , , , , , , 90 100 110 120 130 140 150 160 170 180 190 MINUTES TIME FROM RCP TRIP Minimum temperatures for thermocouples #6 in the reactor vessel and #1 in the upper head were approximately twenty five minutes apart, su8gesting that under the flow and temperature conditions of the test the upper head has a turnover time of approximately a half hour. . Page i FIGURE XVIII: UPPER HEAD THERMOCOUPLE TEMPERATURES DURING REACTOR COOLANT PUMP RESTARTS The first reactor coolant pump returned the reactor to essentially isothermal temperatures, including the upper head as the Figure below shows. The reactor remained essentially isothermal throughout the cooldown, shown in Figure XIX. 350 6 UFFE15to$f THDM0 COUPLE B1 A UFFD HDD THEMK00FLE 02 345 5 HFPD HDD THDM0 COUPLE H
$ UFFS HDD THEM0 COUPLE 96
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305 300 , , , , , , 180 190 200 210 220 230 240 250 MINUTES TIME FROM RCP TRIP Page a FIGURE XIX: UPPER HEAD THERMOCOUPLE READINGS DURING C00LDOWN TO MODE 5 The upper head thermocouple readings remained essentially uniform during the cooldown to Mode 5 as the Figure below illustrates. 350
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6 l l l 240 280 320 360 400 440 460 MINUTES TIME FROM RCP TRIP l Page t SHUTDOWN COOLING SYSTEM PERFORMANCE The shutdown cooling system was demonstrated to be capable of cooling the plant to cold shutdown with only one train. It easily rejected the test's combined heat loadc of decay heat, reactor coolant pump heat, and heat stored in the metal and coolant. The combined load was approximately three-quarters of maximum expected following prolonged burnup. Component cooling water flow rate through the shutdown cooling heat exchanger was also approximately three-quarters maximum, so comparable cooldown rates as experienced during the test would be realized under maximum heat loads. Figure XX plots the as-found cooling rate of 14.5*F/ hour at 200*F (cold shutdown entry conditions), the point where Mode 4 heat rejection is least due to the lowest temperature differences. The test had constant and varying heat sources. Two constant sources were decay ( N 7.1 Mw) and RCP ( N11.4 Mwe). The variable was stored heat whose maximum was 21 Mw at 270 F to a minimum of' 12 Mw at 200*F, also shown on Figure XX. Determinativa of decay heat is discussed on page 19. RCP heat input was calculated by measuring motor current and voltage, multiplying the two by the square root of three (for a three phase motor) and by the power factor and efficiency (both 0.92 from the manufacturer's test report). At Mode 5 conditions the component cooling water system removed essentially all heat loads so qualifying heat transfer at the component cooling water heat exchangers provided an accurate measurement of heat transfer at any time. Measure-ments of CCW flow and temper:iture provided data for calculating total heat load. Stored heat loads were obtained by subtractin8 the known constant and decay heat loads from total. Page 31VH KM003 Hn0H/3. 8 R S 8 8 8 8 g l _ _ .. _ _. _ N . _ . _ _ ___.4, __...__...__..._._.4,___. . . . _ .
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O CONCLUSIONS The final SONGS demonstration test of USNRC RSB 5-1 scenario was successfully completed September 16 and 17, 1985. All objectives were met and the test was successful. The test was a continuation of earlier SONGS 2 testing and continued from the endpoint of the SONGS 2 80% Natural Circulation Test, designated 2PA-215-01. The test demonstrated that the plant could successfully and remotely enter shutdown cooling from natural circulation and could be easily and rapidly cooled using shutdown cooling and natural circulation. Adequate heat rejection capability existed even at Mode 5 entry conditions. Thermocouples mounted in the upper reactor vessel head provided additional data since the SONGS 2 tests were performed before the thermocouples were installed. The data showed that under natural circulation flow rates, fluid in the upper reactor vessel head circulates, a finding that might explain why no steam bubble was drawn during the SONGS 2 cooldown. The RSB 5-1 scenario demonstration was completed by the SONGS 3 test and no further natural circulation testing is planned for the SONGS units. Page l
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