ML20214L555
| ML20214L555 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 01/07/1986 |
| From: | Heltemes C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Rehm T, Roe J, Stello V NRC |
| References | |
| TAC-60462, NUDOCS 8705300054 | |
| Download: ML20214L555 (23) | |
Text
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UNITED STATES 8'
NUCLEAR r1EGW.ATORY COMMISSION g
E WASHINGTON, D. C. 20555 s
N C-9, j
9)L}r-G January 7,1986 e
p q w,.yfoA MEMORANDUM FOR:
Distribution FROM:
C. J. Heltemes, Jr., Director Office for Analysis and Evaluation of Operational Data
SUBJECT:
8&W REGULATORY RESPONSE GROUP Enclosed for your information and use in conjunction with the meeting with the B&W Regulatory Response Group on Wednesday are the following:
1.
A preliminary list of issues that the Rancho Seco IIT has identified to date associated with the December 26, 1985 overcooling event.
2.
An INP0 SER on the December 26 event which also identifies some issues and implications associated with the event.
3.
A PN prepared by the IIT which includes a preliminary sequence of events. This PN also has attached the following two diagrams:
(a)a plot of Press-Temp vs. the Tech. Spec. Cooldown Rate and (b) the RCS-Press / Temp.
In addition, a conference call will be held with the IIT at 11:00 a.m. on Wednesday, January 8.
The purpose of the call is to receive a late status report from the team and respond to questions.
If you wish to be a party to this conference call and have not been contacted, please call Carol Gallagher on X24484.
Please let me know if I can provide any assistance.
/
C.
Jr., Director (ff ce for Analysis and Evaluation f Operational Data
Enclosures:
As stated 8705300054 860107 ADOCK 0500 2
,PDR s
r Distribution for Memo Dated January 7, 1986 V. Stello J. Roe T. Rehm H. Denton D. Eisenhut F. Miraglia F. Schroeder G. Holahan J. Taylor R. Vollmer E. Jordan E. Rossi J. Martin, RV B. Faulkenberry, RV
January 6, 1986 Issues Arising From the Rancho Seco Incidnet Investigation The following is a very preliminary list of the issues that the Incident Investigation Team (IIT) has identified to date.
- A single failure in a ncn-safety system can subject this plant to a severe overcooling transient.
- The operators had no training and no procedures on how to deal with a total loss of ICS (e.g., nothing to remind them that they could have shut the ADVs and TBVs from the Remote Shutdown Panel).
- Has anyone ever analyzed how the plant would respond to a loss of ICS Power? The lack of such analysis is particularly troublesome considering the amount of operator action required to mitigate the event, and the frequency of occurrence. Was the regulatory approach to URSI A-47 and NUREG-0667 adequate in light of this event?
- Has anyone ever told the operators that the Remote Shutdown Panel can be used for incidents other than a fire in the Control Room?
- How do licensees insure that changes in the plant are incorporated in all appropriate procedures?
- The loss of ICS power caused loss of manual (i.e., hand) as well as automatic control of several components from the Control Room.
Is this acceptable?
Should the independent controls at the Remote Shutdown Panel also be available in the Control Room?
- It appears that at least some indication (e.g., MFW flow) was lost when ICS power was lost.
- What was'said, done, and approved as a result of IE Bulletin 79-27 and the 1980 Crystal River event? It appears that Rancho Seco's answer was "It can't happen here". Were the regulatory actions appropriate?
- The operators had considerable difficulty reconciling the dichotomy between avoiding the PTS region (e.g. reduce HPI flow) and regaining
. pressurizer level (e.g. increase HPI flow in accordance with the AT0G procedures). Were the trainir.g and procedures adequate to resolve these conflicting priorities?
I
- Why were the operators so reluctant to stop the AFW pumps when they could not shut the AFW valves? It appears to be a combination of the substantial emphasis placed on the importance of the AFW system and a lack of confidence in the reliability of the AFW pumps (i.e., fear that the pumps would not restart).
- FSAR analyses generally assume no operator actions for 10 to 20 m,
c
t minutes.
Is this assumption realistic? If this had been the case in this event the incident would have been significantly more severe.
With three HPI pumps running, RCS pressure continued to decrease from 1600 to 1047 psig.
Is this expected / acceptable?
Why did the operators have so much trouble shutting the various AFW valves and determining their position? The valves are located outdoors where it was dark, cold, and very foggy.
Is the maintenance and surveillance on manual valves adequate? It appears that the manual AFW valve that could not be shut had received no maintenance or surveillance since the plant was built.
- SFAS actuation and subsequent containment isolation isolated the supply to some cwponents without stopping the component. This resulted in damage to at least one radiation monitor and an associated fire hazard.
Are there sufficient training and procedures on how to recover from an SFAS actuation?
- Are the Technical Specifications minimum staffing requirements adequate? The plant had considerably more than the minimum staffing.
If they had only the minimum staffing the incident would have been more severe.
How did NRC notification requirements impact the operators?
There appears to be a difference between how the simulator responds vs how this plant responds. At the simulator, shutting the BWST outlet valve automatically opens the makeup tank outlet valve. At this plant, this is not the case. As a result the makeup pump ran for several minutes withnut flow and was severely damaged.
If the "A" HPI pump had been running, it would also have been damaged.
More care should be taken to insure that respirators, protective clothing, and survey instruments are available throughout the plant.
The security requirements interferred with the course of the recovery effort.
i
(
01M/06D 22:01 GMT INPO RTLANTA GR
'i
. IS 5/6 FLYf94 (IWO) 02-JAN-96 12:47 PT Subjects I WO SIONIFICANT EVENT REPORT (SER):
3-06 SUBJECTS LOSS OF POWER TO THE INTEORATED CONTROL SYSTEM RESULTING IN OVERCOOLING TRANSIENT UNIT (TYPE)
RANCHO SECO (PWR)
. DOC NO/LER NO:
50-312/NA EVENT DATES 12/26/85 NSSS/AEs BABCOCK Sc WILCOX/BECHTEL REFERENCE SOER 82-7
SUMMARY
WI1H THE UNIT OPERATING AT 76 PERCENT POWER. ELECTRICAL POWER WAS LOST TO THE INTEGRATED CONTROL SYSTEM (ICS). 'THIS RESULTED IN A REDUCTION OF MAIN FEEDWATER FLOW. A REACTOR TRIP ON HIGH REACTOR COOLANT SYSTEM (RCS) PRESSURE. INITIATION OF TE AUXILIARY FEEDWATER (AFW) SYSTEM. AND INITIATION OF TE HIGH PRESSURE i
INJECTION (HPI) SYSTEM.
WITHOUT ICS POWER. STEAM LOSSES THROUGH THE ATMOSPHERIC DUNP VALVE (ADVs) AND TURBIE BYPASS VALVES (TBPVs) COULD NOT BE CONTROLLED AUTOMATICALLY.' AFW AND HPI INITIATION. TOGETHER WITH THIS STEAM LOSS. PRODUCED AN EXCESSIVE RCS COOLDOWN AND DEPRESSURIZATION SUFFICIENT TO AUTOMATICALLY INITIATE THE SAFETY FEATURES ACTUATION SYSTEM (SFAS).
l DURING THE RECOVERY FROM THE EVENT. T E RUNNING REACTOR COOLANT I
SYSTEM MAKEUP PUMP SUFFERED EXTENSIVE DAMAGE DUE TO A VALVING k
ERf6fR.
SONE REACTOR COOLANT WAS RELEASED INTO THE MAKEUP PUMP ROOM AND A MINOR RADIOACTIVITY RELEASE TO THE ATMOSPHERE OCCURRED THROUGH THE AUXILIARY BUILDING VENTILATION SYSTEM.
DEGURIPTION:
THE PLANT WAS OPERATING IN A STEADY STATE CONDITION AT 76 PERCENT POWER.
AT 0413. POWER WAS LOST TO THE ICS, RESULTING IN TE FOLLOWING:
ALL ICS DEMAND SIONALS WENT TO MID-SCALE. CORRESPONDING TO o
ZERO VOLTS.
THE IPetEDIATE EFFECT WAS THAT TE STARTUP AND MAIN FEEDWATER VALVES CLOSED TO ABOUT 50 PERCENT. WHILE THE AUXILIARY FEEDWATER CONTROL VALVES. THE ADVs. AND THE TBPVs OPENED TO ABOUT THEIR MID-POSITION.
MAIN FEEDWATER Ptw SPEEDS DECREASED TO MINIMUM SPEED o
REStA. TING IN INSUFFICIENT DISCHAROE M TO FEED THE STEAN GENERATORS.
THL RAPID REDUCTION IN MAIN FEEDWATER FLOW PRnnsm INCREASES IN RCS TEWERATLAtE AND PRESSURE.
T E REACTOR TRIPPED ON HION RCS PRESSURE ABOUT 15 SECONDS AFTER THE LOSS OF ICS POWER.
AT ABOUT THE SAME TIE. AUXILIARY FEEDWATER INITIATED DUE TO LOW MAIN FEEDWATER PUMP DISCHARGE PRESSURE.
SINCE THE LOSS OF ICS POWER REPOSITIONED THE AUXILIARY FEEDWATER FLOW CONTROL VALVES. THE ADVs. AND THE TBPUs TO A PARTIALLY OPEN
01M/06D 22:00 GMT'INPO ATLANTA GA POSI TION. TE UNIT BEOAN A RAPID COOLDO6ed.
EQUIPPENT OPERATORS WERE DISPATCED TO MANUALLY CLOSE THE ADVs. TBPVs, AND AFW FLOW CONTROL VALVES.
NS TE MAKEUP TAPGC LEVEL DECREASED. TE OPERATORS OPEED TE ISUCTION VALVE FROM THE BORATED WATER' STORAGE TAfGC (BWST) TO THE RUredING MAKEW PUE.
THIS VALVE.ALSO PROVIDES WATER TO THE "A"
HIGH PRESSURE INJECTION (HPI) PUMP. WHIdi WAS NOT RUPGWING AT THE TIME.
TO PROVIDE ADDITIONAL MAKEUP TO T E RCS. TE "B" HPI PUMP WAS MANUALLY STARTED. TAKING SUCTION FROM TE BWST Tt5 TOUGH A SEPARATE SUCTION VALVE THAT IS NORMALLY OPEN.
BOTH MAIN FEEDWATER PUFFS WERE THEN MANUALLY TRIPPED.
RCS PRESSURE DECREASED BECAUSE OF T E RAPID COOLDOWN. AND THE SAFETY FEATtNtES ACTUATION SYSTEM (SFAS) INITIATED ON LOW RCS PRESSURE.
SFAS INITIATION RESULTED IN THE FOLLOWINO:
T E SUCTION VALVE FROM THE BWST TO TE MAKEUP AND "A" HPI
- x-6 o
PUMPS RECEIVED AN OPEN SIONAL (THOUGH ALREADY OPEN).
THE SUCTION VALVE FROM THE BWST TO THE "B" iPI PUMP i
o RECEIVED AN OPEN SIONAL (THOUGH NORMALLY OPEN).
.o THE "A" iPI PUMP STARTED.
THE "B" HPI PUMP RECEIVED A START SIONAL (THOUGH ALREADY o
RUP44INO).
THE WATER SUPPLY VALVE FROM THE MAKEUP TANK TO THE MAKELP o
AND "A" HPI PUMPS CLOSED.
o AFW (SFAS) FLOW CONTROL VALVES (INSTALLED IN PARALLE U ITH THE ICS-CONTROLLED VALVES) OPENED FLA.LY.
THE MOTOR-DRIVEN AFW PUMP STOPPED AND THEN RESTARTED ABOUT o
40 SECONDS LATER.
THE OPERATORS TOOK MANUAL CONTROL AND CLOSED THE AFW (SFAS) FLOW CONTROL VALVES TO REDUCE THE EXCESSIVE FEEDWATER FLOW TO THE STEAM OEERATORS.
THE INDICATED PRESSURIZER WATER LEVEL WENT OFF SCALE LOW.
STEAM OENERATOR PRESSURE DECREASED TO THE POINT WERE THE CONDENSATE PUMPS WERE FEEDING THE STEAM OENERATORS FOR A SHORT TIME.
THIS CONTINUED UNTIL MAIN FEEDWATER ISOLATED AUTOMATICALLY ON LOW MAIN STEAM LINE PRESSURE AT ABOUT 435 PSIO.
T E EQUIPMENT OPcRATORS MANUALLY CLOSED THE ADVs AND TBPVs BUT ENCOUNTERED DIFFICULTY WHEN CLOSING THE AFW (ICS) FLOW CONTROL VALVES.
AN OPERATOR PARTIALLY SHUT THE "B" AFW VALVE. BELIEVINO IT WAS FULLY CLOSED.
HE TEN SHUT THE "A" AFW VALVE.
SINCE HIGH i
RESISTANCE WAS ENCOUNTERED BEFORE THE VALVE POSITION INDICATOR SHOWED THE VALVE TO BE FULLY CLOSED. HE CONTINUED TO TURN THE VALVE OPERATOR IN TE CLOSED DIRECTION WITH A VALVE WRENCH.
THE VALVE OPERATOR FAILED AND THE VALVE REOPENED.
HE THEN TRIED TO SHUT TE MANUAL ISOLATION VALVE DO64dSTREAM OF THE CONTROL VALVE.
BUT WAS UNABLE TO MOVE THE ISOLATION VALVE OFF ITS BACKSEAT.
A SECOND OPERATOR ARRIVED AT THE "B" AFW VALVE AND. SEEING THAT THE "B" AFW VALVE HAD NOT YET BEEN FULLY CLOSED. SHUT THE VALVE
01M/06D 21iU8'GMT INPO ATLRHTR GR THE REST OF T E WAY.
6 MILE TE AFW VALVEG WERE BEINO MANUALLY CLOSED. OPERATORS IN THE I
CONTROL ROOM DISCOVERED THE POWER SUPPLY BREAKERS FOR THE ICS WERE TRIPPED AND RESTORED ICS PO E R BY RECLOSING TE BREAKERS.
THE OPERATORS HAD PFEVIOUSLY CECKED TE BREAKER STATUS AT THE
.ICS CAbIETS SEVERAL TIMES IN RESPONSE TO A LOSS OF ICS l
Af#AMCIATOR ALARM. BUT T M BREAKERS E RE NOT IDENTIFIED AS BEING OPEN.
TE INDICATOR SWITCH POSITION WAS NOT CLEARLY DISCERNIBLE i
UNTIL INSPECTED MORE CLOSELY.
TE "A" AFW VALVE WAS THEN CLOSED FROM THE CONTROL ROOK. AND THE tma mwN WAS TERMINATED.
BEFORE CONTROL OF TE AFW VALVES WAS REGAINED. THE STEAM GENERATORS WERE OVERFItiFn. AND WATER WAS INTRODUCED INTO T E STEAM LINES.
AFTER PRESSURIZER LEVEL WAS BACK ON SCALE AND INCREASING. TE " A" W I Pl#F WAS STOPPED.
THE WI/ MAKEUP PUMP RECIRCULATION VALVES l
WERE OPEN AND ALLOWED THE MAKEUP TASGC WATER LEVEL TO INCREASE.
TO prmarF TE MAKEUP TANK LEVEL. TE OPERATORS CLOSED THE BWST SUPPLY VALVE TO THE MAKEUP PUte. ASSLMING THAT THE PUMP WOULD TAKE SUCTION FROM THE MAKEUP TAS4(.
HOWEVER. THE OPERATORS FORGOT THAT THE SFAS INITIATION HAO AUTOMATICALLY CLOSED T E SUCTION VALVE FROM TE MAKEUP TAPSC.
THIS RESULTED IN THE MAKEUP PUNP i
RUNNING WITHOUT A SOURCE OF WATER.
AFTER RUNNING FOR SEVERAL MINUTES IN THIS COtFIOURATION. THE MAKEUP PUMP INCURRED EXTENSIVE DAMAGE AND WAS STOPPED.
RADIOACTIVE WATER FROM THE DAMAGED PUMP WAS RELEASED TO THE MAKEUP PUMP ROON. AND AIRBORNE RADIOACTIVITY ESCAPED TO THE ATMOSPHERE THROUGH THE AUXILIARY BUILDING VENTILATION SYSTEM.
THE "B" HPI PUMP CONTINUED TO SUPPLY MAKEUP WATER TO THE RCS.
EQUIPMENT OPERATORS WERE DISPATCHED TO THE MAKEUP PUMP ROOM AND ISOLATED THE DAMAGED PUMP SO THAT THE "A" HPI PUNP ON THE SAME SUCTION LIE COULD BE USED.
x.pc.
DURING THE COOLDOWN PERIOD THE RCS COLD LEO TEfFERATURE DROPPED FROM ABOUT E40 DEGREES FAHRENHEIT TO 386 DEOREES FAHRENHEIT IN 25 i
MINUTES.
THIS EXCEEDED THE B&W RECOMMENDED PRESSURE / TEMPERATURE LIMITS FOR PRESSURIZED THERMAL SHOCK OF THE REACTOR VESSEL.
ALTHOUGH THE NIL DUCTILITY TEMPERATURE LIMITS IN THE TECHNICAL SPECIFICATIONS WERE NOT VIOLATED.
OPERATORS LOWERED RCS PRESSURE BY SPRAYING THE PRESSURIZER AND REDUCING HPI FLOW WHEN PRESSURIZER LEVEL WAS RESTORED.
THE CAUSE OF THE LOSS OF POWER TO THE ICS IS NOT YET KNOWN.
CONMENTS 1.
THIS EVENT IS SIGNIFICANT BECAUSE IT RESULTED IN A RAPID AND EXCESSIVE COOLDOWN OF THE REACTOR COOLANT SYSTEM. EXTENSIVE DAMAGE TO THE RCS MAKEUP PUFF. AND THE RELEASE.OF REACTOR COOLANT INTO THE MAKEUP PUte ROOM.
l 2.
THE RANCHO SECO EMEROENCY PROCEDURES DID NOT ADEQUATELY ADDRESS THE ANTICIPATED TRANSIENT OF A LOSS OF ICS POWER.
THE APPLICABLE PROCEDURE FOR EXCESSIVE MAT TRANSFER DIRECTED THE CLOSING OF THE MAIN AND AUXILIARY FEEDWATER FLOW CONTROL AND ISOLATION. TURBIE BYPASS. AND ATMOSPHERIC j
DUMP VALVES TO STOP A RAPID COOLDOWN TRANSIENT.
THE PROCEDURE DID NOT IDENTIFY ACTION IN CASE SOME OR ALL OF THESE VALVES COULD NOT BE READILY CLOSED.
A RECENT CHANGE TO THE PROCEDURE ALSO CALLED FOR TRIPPING THE " APPROPRIATE
01M/06D 21I56 GMT INPO
'RTLANTA GA FEED PUHF'S TO TERMINATE FLOW" IF FEEDWATER FLOW CONTINIED.
(THIS WAS NOT DOE).
FOR AN EVENT WERE TE FEEDWATER.
ATMOSPHERIC DUPP. OR TURBIE BYPASS VALVES FAIL OPEN. SUCH AS THROUGH LOSS OF CONTROL PO E R. PROMPTLY STOPPING TE AUXILIARY FEEDWATER Pt#PS t'risa n APPRECIABLY SLOW TE COOLDOWN TRANSIENT.
IN ADDITION OVERFILLING TE STEAM GENERATORS COULD BE AVOIDED.
3.
AT RANCHO SECO, A RECENT MODIFICATION HAD BEEN MADE TO ENABLE THE TURBINE BYPASS VALVES AND THE ATMOSPERIC DUlf VALVES TO BE RAPIDLY CLOSED FROM TE REMOTE SHUTDOWN PAEL (OUTSIDE THE CONTROL ROOM). INDEPENDENT OF THE AVAILABILITY OF ICS POWER.
THIS CHANGE WAS MADE TO ACCOMMODATE T E POSTULATED APPENDIX R CONTROL ROOM FIRE SCENARIOS.
TE CONTROL ROOM FIRE PROCEDURES INCLUDED INSTRUCTIONS FOR OPERATION OF THE VALVES, AND OPERATORS WERE TRAI E D ON THE i
USE OF THE MODIFICATION.
HOWEVER. THIS RAPID CLOSLRE l
REVISION WAS ONLY MADE TO TE CONTROL ROOM FIRE PROCEDi#tES AND NOT INCORPORATED INTO OTHER PROCEDURES THAT SPECIFIED OR REQUIRED OPERATION OF THESE VALVES FROM OUTSIDE T E CONTROL ROOM.
THE OPERATORS DID NOT REEMBER THIS ALTERNATE ETHOD OF VALVE CONTROL UNTIL AFTER THE VALVES HAD BEEN MAWALLY ISOLATED.
WHEN ADDITIONAL CAPABILITIES ARE ADDED TO A PLANT, A VARIETY OF PROCEDURES OTER THAN TE PRIMARY t
APPLICATION MIGHT BENEFIT FROM THEIR USE.
THE PLANT PROCEDURES SHOULD THEREFORE BE REVIEWED TO IDENTIFY OTHER POTENTIAL APPLICATIONS.
4.
CLOSING VALVES WITH HIGH Fl.OW RATES AND LARGE DIFFERENTIAL PRESSURES CAN REQUIRE MUCH OREATER FORCE THAN IS NECESSARY WHEN THERE IS NO FLOW.
THIS CAN RESULT IN VALVE OPERATOR DAMAGE AND CAN CONTRIBUTE TO OPERATOR DIFFICULTY IN MAWALLY 3,...
CLOSING VALVES AND DETERMINING WHEN THE VALVES ARE FULLY CLOSED.
USE OF OTHER AVAILABLE INDICATORS, SUCH AS FLOW.
CAN HELP VERIFY VALVE POSITIONS.
5.
INADEQUATE INDICATION OF T E BREAKER STATUS AT TE ICS CADINETS DELAYED DIAGNOSIS AND CORRECTION OF TE LOSS OF POWER PROBLEM.
THE PLANT IS CONSIDERING ADDING PROCEDLRAL GUIDANCE ON HOW TO READ AND INTERPRET THE BREAKER POSITIONS.
6.
THE STATION HAD NO PROCEDURAL GUIDANCE FOR RESTORING T E NORMAL HPI/ MAKEUP SYSTEM ALIONMENT FOLLOWING AN SFAS INITIATION.
AN AUTOMATIC INTERLOCK WOULD HAVE PREVENTED STARTING THE PUMP WITHOUT ADEQUATE SUCTION, BUT THIS INTERLOCK IS NOT ACTIVE ONCE TE PUPF IS RUPedING AND IS BYPASSED BY AN SFAS.
PROCEDURAL OUIDANCE MIGHT HAVE PREVENTED THE FAILURE OF TE MAKEUP PUPP.
7.
THE OPERATORS MADE TEIR EMERGENCY ENTRY INTO TE MAKELF PUNP ROON WITHOUT A RADIATION SLRVEY INSTRUMENT. RESPIRATORY PROTECTION. OR ADEQUATE PROTECTIVE CLOTHING BECAUSE-THIS EQUIPMENT WAS NOT READILY AVAILABLE.
TE OPERATORS ERE CONTAMINATED AND EXPOSED TO AIRBORNE RADIOACTIVITY.
THIS EMERGENCY ENTRY INTO TE MAKELP PUPP ROOM APPEARS TO HAVE BEEN UNNECESSARY BECAUSE THE LOSS OF REACTOR COOLANT MAKEUP WAS TERMINATED BY RECLOSING THE MAKEUP TANK OUTLET VALVE.
SINCE AN ALTERNATE SOURCE OF MAKEUP WAS IN OPERATION FROM THE BWST VIA THE "B" HIGH PRESSURE INJECTION PUMP. A MORE CONTROLLED ENTRY INTO THE MAKEUP PUMP ROOM. TAKING ADEQUATE
1 01M/06D 21:54 GMT INPO RTLANTR GR i
RADIOLOGICAL PRECAUTIONS. WAS POSSIBLE.
THE PLANT IS J
EXPEDITING ITS PREVIOUS PLANS TO PROVIDE SURVEY INSTRUMENTS, 1
RESPIRATORS. AND PROTECTIVE CLOTHING FOR EEROENCY USE AT APPROPRIATE LOCATIONS.
8.
DURING THE EVENT. OVERFILLING THE STEAN OEERATORS INTRODUCED WATER INTO THE STEAM LINES.
IN SOE PLANTS.
FILLING THE STEAM LINES WITHOUT FIRST PIDWING TE SUPPORTS COULD DAMAGE THE STEAM LINE SUPPORTS.
IN SUCH CASES WHERE l
PINNING CANNOT BE PERFORMED, APPROPRIATE INSPECTION AND l
ANALYSES SHOULD BE PERFORE D BEFORE STARTLP.
9.
AN ILLUSTRATION. WHICH MAY BE HELPFUL IN UNDERSTANDING THIS SER. IS BEING TRANSMITTED BY "FAXPAK" TO.T E SEE-IN CONTACTS.
RECIPIENTS WHO DO NOT HAVE "FAXPAK" RECEPTION CAPABILITIES AT THEIR LOCATION CAN OBTAIN A COPY OF THE ILLUSTRATION FROM THEIR SEE-IN CONTACT OR JEFF WHEELOCK.
INPO. 404/951-4730.
INPO'S EVALUATION OF THIS EVENT IS CONTINUING.
LIMITED DISTRIBUTION COPYRIGHT 1986 BY THE INSTITUTE OF NUCLEAR POWER OPERATIONS.
ALL RIGHTS RESERVED.
NOT FOR SALE.
UNAUTHORIZED REPRODUCTION IS A VIOLATION OF APPLICABLE LAW.
REPRODUCTION OF NOT MORE THAN TEN COPIES BY EACH RECIPIENT FOR.
ITS INTERNAL USE OR USE BY ITS CONTRACTORS IN THE NORMAL COURSE OF BUSINESS IS PERNITTED.
THIS REPORT SHOULD NOT BE 01NERWISE TRANSFERRED OR DELIVERED TO ANY THIRD PERSON. AND ITS CONTENTS SHOULD NOT BE MADE PUBLIC. WITHOUT THE PRIOR AGREEMENT OF INPO.
Infor mation
Contact:
CAL GOSLOW. INPO. 404/953-5312 Retrieve messages >
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ke mG January 5, 1986 PRELIMINARY NOTIFICATICN OF EVENT OR UNUSUAL OCCURRENCE PF0-IIT-86-1A This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance.
FACILITY: Sacramento Municipal Utility District Licensee Emergency Classification:
Rancho Seco Notification of Unusual Event Docket No. 50-312 Alert Site Area Emergency General Emergency X Not Applicable
SUBJECT:
STATUS REPORT FROM THE NRC INCIDENT INVESTIGATION TEAM The Incident Investigation Team (IIT) remains onsite gathering and analyzing data, i
reviewing licensee action plans, and analyzing the sequence of events. A preliminary sequence of events has been developed by the IIT and is attached.
All initial interviews with the licensee staff on-shift during the 12/26/85 overcooling event have been completed. The licensee is preparing detailed action plans for the systematic troubleshooting of failed equipment on the quarantine list.
The team expects to complete the review of these plans no later than January 8, 1986.
The IIT expects to complete its initial on-site investigation and data gathering activities by mid-week. The team will then return to Bethesda, Marylart to continue i
the analysis of the data, and to begin interviews with NRC staff members who were involved with regulatory activities and issues that may have had a direct impact on 3
the course of this event. The team expects to return to the site whea the licensee completes the troubleshooting work. The actual troubleshooting work will be monitored i
by representatives from Region V.
Contact:
Frederick J. Hebdon, (209) 748-2791 DISTRIBUTION:
j H. Street MNBB Phillips.
E/W Willste MAIL:
j Chairman Palladino IIT NRR TE-NMSS XDMfDMB j
Comm. Roberts PA OIA RES D0T: Trans Only Comm. Asselstine MPA AE0D Applicable State Comm. Bernthal ELD Comm. Zech Air Rights INP0 SECY SP NSAC ACRS CA PDR Regions:
Licensee:
Rev. 2 01/05/86 INCIDENT INVESTIGATION TEAM PRELIMINARY SE0VENCE OF EVENTS INITIAL PLANT CONDITIONS
- Unit operating at steady state power of 76% [710 MW(e)].
- Reactor Coolant System (RCS) average temperature is 582 F.
- RCS pressure is 2150 psig.
- This plant does not have Main Steam Isolation Valves (MSIVs).
- The plant had started up on December 24, 1985 following an outage of 2 days.
- Integrated Control System (ICS) in full automatic.
- The Bailey computer was out of service (one of the plant's two main computer systems in the Control Room).
Consequently, the Bailey post-trip review, Bailey alarms printout, and Bailey inputs to the Interim Data Aquisition and Display System (IDADS) are not availe.ble.
IDADS inputs from sources other than the Bailey computer are available.
TIME DESCRIPTION OF EVENT DATA SOURCE Transient Initiation 04:13:47 " Loss of ICS or Fan Power" Annunciator Alarm.
IDADS Print out Loss of ICS is caused by the simultaneous de-energizing of all redundant ICS DC power supplies.
ICS demand signals go to midscale.
(The ICS works on +/- 10 volt scale, with zero volts being 50% demand).
The startup and Main Feedwater (MFW) valves close to 50% because of this decrease in demand signal. The loss of ICS power, however, causes the MFW pump speed to decrease to the minimum speed of 2500 RPM.
With the plant initially at 76% power, this reduction in MFW flow increases RCS pressure.
The loss of ICS DC power also sends demand signals to one of two sets of Auxiliary Feedwater (AFW) flow control valves, the Atmospheric Dump Valves (ADVs) and the Turbine Bypass Valves (TBVs) to open to 50% demand.
(Note: The plant has two parallel sets of AFW valves.
2 One set is controlled by the ICS and one set is controlled by the Safety Features Actuation System).
Operator / System Response to the Loss of ICS Power 04:13:7 Control room operators notice PFW flow Opera tor decreasing rapidly. Also, they notice RCS Statement pressure increasing. Operators open the pressurizer spray valve in an attempt to stop the RCS pressure increase.
Due to the rapid overheating of the RCS by the reduction in MFW flow (it appears that MFW flow actually decreased to zero), the actuation of pressurizer spray is not sufficient to reverse the RCS pressure increase.
04:14:01 The reduction in MFW pump speed causes a low IDADS MFW pump discharge pressure of less than Print 850 psig which automatically starts the out motor driven AFW pump.
04:14:03 Reactor trips on high RCS pressure. The turbine IDADS Print trip is also initiated by the reactor trip. A out Control Room operator closes the pressurizer spray valve.
04:14:04 Peak RCS pressure of 2298 psig. Several Main Steam IDADS Print Safety Valves are believed to have lifted and out x
reseated early in the event.
04:14:06 AFW dual drive (i.e. steam & electric) pump IDADS autostarts on low MFW pump discharge pressure Print (850psig).
out This AFW pump is steam-driven throughout this transient.
04:14:06 Peak RCS hot leg temperature of 606.5 F.
IDADS Print out Operator / Systems Response to the Plant Trip and Overcooling 04:14:7 Immediately upon reactor trip, many fire alarms, Operator l
The Technical Support Center (TSC) spray actuation Statement alarm, the seismic trouble alarm, and Spent Fuel Pool (SFP) temperature high alarms are received. The significance of this is still being assessed.
The operators perform the actions of the Emergency Procedure section E.01 (Reactor Trip ImmediateActions). This includes reducing RCS letdown flow.
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m
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3 Operators then proceed with Emergency Procedures section E.02 (Vital System Status Verification).
04:14:11 AFW flow begins to both Once Through Steam Generators IDADS Print (OTSGs) through the ICS-controlled AFW Flow Control out Valve.
04:14:25 Operators note pressurizer level decreasing, Operator and fully open the "A" in,iection valve for more Statement makeup flow to RCS.
IDADS Print out 04:14:30 The loss of ICS power also results in loss of Operator manual (i.e. hand) control of ICS controlled Statement valves from the Control Room. Therefore, non-licensed operators are sent to close the TBVs, ADVs, and AFW flow control valves.
(Note: The ADVs and TBVs could have been shut from the Remote Shut-down Panel. However, the operators failed to remember this fact).
The operators recognize the beginning of an overcooling transient due to the open startup and main MFW valves, the half open TBVs and ADVs, the open AFW flow control valves, along with MFW speed remaining at around 2500 RPM.
04:14:48 Makeup tank (MUT) level decreasing rapidiv. Operators Operator open the Borated Water Storage Tank (BWST) suction Statement valve on the "A" side to provide an additional source of makeup water.
04:15:04 Operators start the "B" HPI pump to increase IDADS Print makeup flow to the RCS from the BWST.
out l
04:16:02 Operators trip both MFW pumps.
IDADS Print i
out/
MFW flow indication on the Control Poom strip Operator i
charts indicates about 3.5 million pounds Statement per hour. However, this MFW flow indication passes through modules powered by the ICS and, therefore, the loss of ICS power causes this indicator fail to midscale.
The actual MFW flow rate indicated by the IDADS print out decreased to zero upon reactor trip and does not begin increasing again before the reactor operators trip the MFW pumps. The actual MFW flow rate remained at zero due to the increased pressure in both OTSGs and the low speed demand to both MFW pumps.
s.
4 AFW flow is greater than 1000 gpm to each OTSG.
IDADS Print out 04:16:?
An operator isolates pegging steam, which is used Operator to heat MFW during low power operation. The Statement operator isolates it because he believes that a MFW heater relief valve may have lifted.
04:16:57 RCS pressure has decreased to 1600 psig.
Pressur-IDADS izer level is 15 inches. The Safety Features Print Actuation System (SFAS) automatically initiates.
out A, B, C and D HPI injection valves open to pre-determined positions. Selected SFAS equipment, including the motor-driven AFW pump, automatically sheds off the vital busses and. sequence loading of SFAS equipment begins.
AFW (SFAS-controlled) valves travel full open.
"A" & "B" Low Pressure Injection / Decay Heat Removal (LPI/DHR) pumps autostart in the recirculation mode. Diesel generators autostart but do not close onto the vital busses'as there has been no loss of power to the vital busses. SFAS also actuates containment (i.e. reactor) building isolation. This actuation isolates suction to the containment building radiation monitors, which subsequently causes one of the associated sample pumps to overheat and damage its seals.
04:16:59 "A" HPI pump autostarts on SFAS signal.
IDADS Print a
out Operator / Systems Response to SFAS Initiation 04:17:10(?) Operator overrides SFAS signal to the AFW Operator (SFAS-controlled) flow control valves and closes Statement /
them.
IDADS Print out 04:17:15 A" & "B" Control Roam / Technical Support Center IDADS Print (CR/TSC) Essential Heating, Ventilation and out/
Air Conditioning (HVAC) units start on the Operator SFAS signal. This significantly increases the Statement noise level in the Control Room.
04:17:27 Motor-driven AFW pump automatically IDADS Print sequences back on its vital bus and restarts.
out The dual-drive AFW pump has been running continuously and powered by steam since it initially started.
04:18:58 RCS temperature decreases below 500 F.
IDADS Print out
I 1
.g 5
l l
i 04:19:15 Operators secure "A" CR/TSC Essential HVAC to IDADS Print reduce the noise level in the control room.
out/
Operator Statenent 04:20:00 Pressurizer level offscale low. Subcooling IDADS Print margin is 85 F and increasing.
out 04:20:+
Shift Supervisor sends a computer technician Operators to check the ICS power supply.
Statement The technician reports that all four ICS 24 VDC power supplies are de-energized. The Automatic Bus Transfer (ABT) has not transferred and is still on the "C" bus (vital bus) which is still energized.
It is later determined that the ICS "J" bus loads (non-vital bus) had earlier been connected to the "F" power bus. The "F" power bus 4
(non-vital) also supplies power to the TSC Fire System (which alarmed upon reactor trip). Also, portions of the security lighting which is powered by the 2C bus which powers the F bus was momentarily out about the time of the reactor trip.
This is the first of four individuals who indpedndently check the ICS power supply cabinets and do not note that the power supply switches (S1 and S2) are open.
04:20:20 OTSG pressures have decreased to 500 psig.
IDADS Print out At this pressure the running condensete pumps begin to supply MFW to the OT5Gs through I
the idle MFW pumps. This adds approximately 1000 gpm of flow to each OTSG.
04:21:25 Minimum RCS pressure of 1064 psig is reached.
IDADS Print 4
out 1
04:22 The plant exceeds the B&W recommended pressure /
IDADS Print temperature limits for pressurized thermal shock out (PTS) of the reactor vessel (i.e., the PTS region).
The nil ductility temperature limits in the Technical Specifications are not violated during this event.
04:22 Operator initially throttles HPI injection flow (Note: RCS pressure is beginning to increase, but pressurizer level is still off-scale low).
04:22:50 OTSG pressures have decreased to 435 psig.
IDADS Print out
,-r
6 Main Steam Line Failure Logic actuates which closes the startup and main NFW valves.
MFW flow from the condensate pumps is stopped.
1 04:23 A0V and T8V isolation valves shut locally Operator (i.e., by handwheels) by operators.
Statement 04:23:10 Non-licensed operator attempts to close "B" AFW IDADS Print (ICS-controlled) control valve using the valve out/
handwheel. The valve is partially closed by the Operator operator, however, much of the flow appears to Statement have been merely redirected to the "A" AFW valve.
The operator thought he had completely IDADS Print closed the valve et this point. AFW out flow to the "B" OTSG, however, has decreased by only about 60%.
04:25:30 Operator opens the HPI pump SFAS-controlled recircu-IDADS Print lation valves, opening the recirculation path to the out makeup tank, to prevent overheating the pumps when flow is subsequently further throttled.
However, the discharge valve from the Makeup Tank is still closed at this time.
04:26:15 CR/TSC Essential HVAC train "B" is secured to Operator further reduce noise levels in the Control Room.
Statement Operator notes that the signal to start it in the high temperature /high radiation level mode was present. The significance of this fact is still being assessed.
04:26:?
Operator attempts to close "A" AFW (ICS-IDADS Print controlled) control valve using the valve out handwheel.
04:26:22 "A" AFW valve closed.
However, much of the flow Operator appears _to have been merely redirected to the Statement partially open "B" AFW valve. Operator believes the "A" AFW valve is only 80% closed and leaves to locate a valve wrench.
04:26:47 Pressurizer level is back on scale and increasing.
IDADS Print Subcooling margin is 170 F.
Operators throttle out i
HPI injection valves to decrease the rapid increase of reactor pressure.
04:28:00 Makeun tank level offscale high. Pressure Relief IDADS Print 1
Valve opens and discharges to the Flash Tank.
out 04:28:00 Operatnrs manually stop "C" RCP per core lift IDADS Print restrictions. The procedures require that the out
7 RCP be tripped when RCS temperature decreased to 500 F at 04:18. RCS tcmperature is now 490 F.
04:28:59 Operators stop "A" HPI pump.
IDADS Print out 04:29:40 Non-licensed operator uses valve wrench on "A" Operator AFW (ICS-controlled) flow control valve. Manual Statement portion of valve operator is apparently damaged.
The valve suddenly fails to the open position.
Operator calls Control Room and is told to close the "A" AFW manual isolation valve.
04:29:40 RCS pressure peaks a second time at 1616 psig. RCS IDADS Print temperature is 422 F.
out 04:29:45 Operator closes "C" & "0" HPI in.iection valves IDADS Print to reduce the repressurization while temperature out is still decreasing.
04:30 Shift supervisor declares Unusual Event. The Operator Senior Control Room Operator notifies State Statement and County agencies.
04:30:30 Operators start depressurizing RCS, in an attempt to Operator return to condition outside PTS region, using Statement &
normal pressurizer spray.
RC Pres ure Plot 04:33:20 Another non-licensed operator arrives at the "B" AFW Operator control valve and closes it all the way. AFW Statement &
to the "B" 0TSG is now stopped; however, scme IDADS Print of this flow may have been merely diverted to out the "A" 0TSG.
04:33:40 The "A" OTS3 is full to the top of the steam IDADS Print shroud and begins to spill water into the steam out annulus and into the main steam lines. At this time the AFW flow to the "A" 0TSG is in excess of 1300 GPM.
04:35 Operators close the "A" Loop BWST suction valve Operators in an attempt to mitigate the high level in Statements the makeup tank (MUT). However, the discharge valve from the MUT is still shut.
(Note: en the simulator, shutting the BWST suction valve automat-ically opens the discharge valve from the MUT.
2 This is not the case in the plant).
This action i
isolates the suction to the makeup pump, the "A" HPI, and the "A" LPI/DHR pump, j
i 04:36 Non-licensed operator attempts to close the Operator "A" AFW manual isolation valve but it will Statement not move, even with valve wrench.
l
8 04:39:00 RCS subcooling margin reaches peak of 201 F IDADS Print and begins to decline.
(RCS temperature = 390 F, out RCS pressure = 1430 psig) This is approximately 800 psi into the PTS region.
04:40 An SR0 discovers that the switches (S1 and S2)
Operators to the ICS DC power supplies are tripped to the Statement /
off position.
ICS power is restored by closing IDADS Print switches S1 and S2 in ICS cabinet 3.
(Note:
out the ICS DC Power Supplies are located in ICS cabinet 2).
Operator / Systems Response to Pestoration of ICS Power Initially the ADVs, TBVs and AFW valves receive a demand signal to go fully open when power is restored.
However, the isolation valves for all but the "A" AFW valve had been closed. The Control Room Operators immediately switch to manual (i.e., hand) control and shut the valves.
All AFW flow to both OTSGs has ceased. RCS begins to heat up.
Lowest RCS temperature of 386 F was reached and at this time RC pressure (1413 psig) is being reduced to achieve conditions outside the PTS region. The plant has cooled down 180 F in 24 minutes.
04:41:00 Operator calls Control Room and reports Operator that the "A" AFW manual isolation valve is stuck Statement open. The operators are directed to disengage the manual handwheel on the "B" AFW flow control valve. Other operators are directed to unisolate the ADVs and TBVs.
04:41:10 "A" OTSG level decreases below steam shroud.
IDADS Print out 04:42:42 Operator stops the "B" HPI pump. The makeup pump IDADS Print is continuing to run.
out 04:42:56 Operators close the "A"
& "B" HPI injection IDADS Print valves.
out 04:43:50 Operator rates loss of RCP seal injection Operator flow.
Statement 04:43:54 Operator restarts the "B" HPI pump to re-IDADS Print establish RCP seal injection flow.
out 04:49:
Leakage (steam) from the damaged makeup Operator pump is released via the auxiliary bcilding Statement t
l
i 9
ventilation system. The release is within Technical Specification limits. The auxiliary building stack radiation monitor alanns and isolates the auxiliary building ventilation system, stopping the release.
04:50:19 Operator stops the "B" H.PI pump.
(Note:
IDADS Print Operator had re-aligned valves in the seal out injection flow path.)
04:50:30 Operator again notices loss of seal flow, and Operator restarts the "B" HPI pump.
(Note: loss of RCP Statement seal flow is due to the failure of the makeup pump. The operators are not yet aware of the failure.)
04:52 One of the four SR0s on shift (not the shift Operator supervisor) collapses in front of the control Statement panel. This SR0 had previously assisted in closing the ADV and TBV manual isolation valves.
05:00 Operator in Control Room hears a loud noise.
Operator He looks down at makeup pump ammeter and Statement notes it is reading about 1/3 of normal running current. He realizes the makeup pump has been damaged (due to lack of suction).
05:00:10 Operator trips makeup pump. Operator opens Operator makeup tank discharge valve, which allowed Statement water to spill out of the damaged makeup pump onto the pump room floor. The operator subsequently shuts the discharge valve.
Approximately 450 gallons is spilled.
05:05 RCS pressure decreases out of PTS region. A three Operator hour soak is initiated.
(RCS Pressure = 870 psig, Statement /
PCS temperature = 428 F).
IDADS Print out 05:05
% Ambulance is called for SR0 who collapsed.
Operator Statement 05:09 Poth AFW pumps are manually stopped while OTSG IDADS Print level is reduced via the OTSG drain lines out to allow re-establishment of normal MFW flow with the condensate pumps.
05:27 Operators isolate the makeup pump.
Note: Operators Operator isolate the pump by entering the pump room Statement which contains airborne radioactivity and 3 to 4 inches of contaminated water on the floor. The operators do not wear respirators because
r 10 they were not available in the area and thus become contaminated due to water on the floor.)
05:29:04 Operators stop the second ("A") RCP.
IDADS Print out 05:33 A smoke detector locks-out Rad Waste Area Operator Exhaust Fans.
It is believed that this is Statement caused by damage to the Waste Gas Compressor which was damaged due to water from the flash tank which was filled when the makeup tank overflowed.
05:40 Main Steam Line Failure Logic is " inhibited."
Operator This permits MFW flow to the OTSGs.
Statement 05:46:?
Reactor building radiation monitor fails due to shutting the suction valve when SFAS initiated and isolated the reactor butiding.
05:54 A non-licensed operator loses his security badge.
Security He is escorted to the Control Room by a Security Report /
Guard. The Control Room calls security and requests Operator that a spare security badge be brought to the Statements Control Room.
06:06:00 Operators " Bypass" SFAS.
Operator
~
Statement 06:11 Momentary " Loss of ICS or Fan Power" alarm.
Operator The S1 and S2 switches remain closed and the Statement alarm clears without operator action. No equipment response is noted.
06:14
" Loss of ICS or Fan Power" alarm.
ICS-controlled Operator valves again receive 50% demand signals.
Statement Operators immediately reset switches S1 and S2 to restore ICS power.
ICS-controlled valved again reveive 100% demand signals. Operators manually shut the valves from the control room.
06:15 Security brings a spare security badge to the Control Security Room.
Report 07:00 SR0 released from hospital.
Operator Statement 08:41 Terminated Unusual Event.
Emergency Coordinator Log l
l k
~~
- i..
u
'Rx T R M CQ V ?AR SO'N' PRESS-TEMP.to TECH ' SPEC'.CDdLDdWN CURVE
~
2.4 -
S&WdIMIT
_.Rx TRIP 2.2 -
- CROSS B&W LIMIT AT =0422:00 INTERIM BRITTLE
- RETURN TO NORMAL RANGE AT==0505:00
_ FRACTURE CURVE.
N
~
LL 1.8 -
~
Og 1.6 -
Wm 1.4 -
Et
.DE Me 1.2 -
W D W O E'E
~
1-f E
m e
O O.8 -,
NOT LIMIT
'90 MINUTES C
f TECH. SPEC. CURVE AFTER Rx' TRIP 0.'6 -
\\
E o
0.4 -
i
\\
SATURATION
{
\\ CURVE O.2 -
i y
- -3 O
t s
n -
i n
o 200 400 600 A
TEMPERATURE Te DEGRFFS F
-..- _},
y
' i:
R EAC ~O R
~~R
' D DEC. 2 6, 1985
,cs RCS PRESSURE / TEMPERATURE (Tove)
U 590 -
- e 5 5 0 -
2.2 -
m m
)
570 2.1 -
C.560 -
2-550 -
g y540-1.9 -
Cr 530 -
i o
1.8. -
W 520 -
Rx Trip
(
,8 510 - T 1.I -
y 500 o
1.6 -
a.490 -pi e i<
{ 470 -
480 E o 1.5 -
d 1,4 _
w
$ 460 y 450 -
l3~
440 -
1.2 -
430 -
420 -
l '1 -
410 -
1-
~ 4 0 0. -
O.9 --
390 -
'3 8 0 -
O.B -
c-04:00:00 10:00 20:00 30:00 40:00 50:00 05:00:00 TIME
-G-RCS PRESS B-LOOP
-G-RCS-Tove B-LOOP 4
L-------
- - - - -