ML20043A611
| ML20043A611 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 05/16/1990 |
| From: | William Cahill, Hood D TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-90-007, TXX-90159, NUDOCS 9005220309 | |
| Download: ML20043A611 (9) | |
Text
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"~~ ~~ ' File # 10200 909.4 C C ' Ref. # 50.73.
- 1. 7UELECTRIC 50.73(a)(2)(i) .
I 50.73(a)(2)(iv) :
L 50.73(a)(2)(v)- :
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$u's$, emu, , May 16, 1990 l
.U.~ S. Nuclear Regulatory Commission Attn: Document Control Desk !
Washington, D. C. 20555
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION '
DOCKET NO.~ 50-445 .
l ENGINEERED SAFETY FEATURE ACTUATION LICENSEE EVENT, REPORT.90-007 .
Gentlemen:
Enclosed is Licensee. Event Report 90-007-00 for Comanche Peak Steam Electric Station Unit 1, " Personnel Error and Procedural' Inadequacies Leading _ to -
Inadvertent Actuation and. Subsequent Disabling of Control Room Air Conditioning. System Engineering Safety Feature."
l l Sincerely,- [
~
William J. Ca ill, Jr. ;
a L RJB/daj I Enclosure -
c - Mr. R. D. Martin, Region IV Resident Inspectors, CPSES (3) l
'l y
9005220309 900516 ADOCKOS00gj5
{DR 400 North Olive Street LB 81 ' Dallas, Texas 73201.
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L y Enclosure to TXX-90159
. '* NF;C FORM 366 U.S. NUCLE AR RF.OULATORY COMMissoN APPROVED OMB NO. 31540104 EXPIRES:4/30112
- i. ESilMATED BURDEN PER RESPONSE TO COMPT.y WITN THIS INFORMATON l-COLLECTON REQUEST: 60.0 HRS. FORWARD COMMENTS REGARDtNO WRDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT LICENSEE EVENT REPORT (LER) GRANCH (P.630), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON.
OC,205$5. AND TO THE PAPERWORK REDUCTON PROJECT (31540104).
OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC. 20603.
l l Frchy N mo (1) Docke' Nunter (2) Page (3)
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ABSTRACT On April 16,1990, an Engineered Safety Features actuation signal occurred which resulted in Train A of the Control Room Air Conditioning System shifting to the Emergency Recirculation Mode. The actuation occurred when a Control Room air intake radiation monitor was de energized for maintenance. The actuation signal was reset in accordance with plant procedures; however, the Engineered Safety Feature was inadvertently defeated, leaving the system incapable of automatically shifting to the Emergency Recirculation Mode in response to a valid actuation signal. The condition was discovered by Control Room personnel during a review for operability, and the system was immediately placed in a configuration allowed by the plant Technical Specifications. The initial actuation was caused by personnel error, and the inadvertent defeat of the Emergency Recirculation capability was caused by procedural inadequacy. Corrective actions include event review by operating crews, changes to procedures affecting the event, and a design modification to obviate the resulting system condition.
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F Enclosure to TXX-90159
- - NF:C FORM 366A . U.S. NUCLE AR REGULATORY COMWISSON APPRO D B BOW ESTIMATED BURDEN PER RESPONSE TO COMPLY wtTH THIS INFORMATION f.
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COMANCHE PEAK - UNIT 1 0l5l0101014!415 910 0l0l7 -
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- 1. DESCRIPTION OF WHAT OCCURRED A. PLANT OPERATING CONDITIONS BEFORE THE EVENT On April 16,1990, at 0028 CST Comanche Peak Steam Electric Station (CPSES)
Unit 1 was in Mode 2, Startup. The Reactor Coolant System (RCS)(Ells:(AB)) was at ~ '
a temperature of 557 degrees F and pressure of 2235 psig.
'B. REPORTABLE EVENT DESCRIPTION (INCLUDING DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES)
' Event Classification: (1) An event or condition that resulted in an automatic actuation of any Engineered Safety Feature (ESF), (2) Any operation prohibited by the Plant's Technical Specifications; and (3) Any event or condition that alone could have prevented the fulfillment of the safety function of structures, or systems that are -
needed to mitigate the consequences of an accident.
On April 15,1990, at approximately 0809 CST, the Unit .1 Reactor Operator (utility, l licensed) placed Train B of the Control Room Air Conditioning System (CRACS)
(Ells:(VI))in the Emergency Recirculation Mode because one of the two airintake radiation monitors (Ells:(MON)(IL)) associated with the Train A CRACS lost sample flow and was declared inoperable. In accordance with plant procedures, a Limiting Condition for Operation Action Requirement (LCOAR) was initiated to document the requirement of Technical Specification 3.3.3.1 for inoperable radiation monitoring.
instrumentation. Train A was left in Standby.
On April 16,1990, at approximately 0028 CST, an Auxiliary Operator (utility, non-licensed) de-energized the inoperable radiation monitor in preparation for the performance.of a work order to replace the sample pump (Ells:(P)(IL)). Upon ae- t energization, the monitor generated an ESF actuation signal causing the Train A CRACS to shift to the Emergency Recirculation Mode. An ESF actuation signal originating from any of the four radiation monitors will place both trains of CRACS in the Ernergency Recirculation Mode. At approximately 0036 CSTthe Reactor l Operator reset Train A of the CRACS and secured the Train A Emergency Filtration Unit Fans. At approximately 0106 CST the NRC was notified via the Emergency Notification System (ENS) line in accordance with 10CFR50.72.
Enclosure to TXX-90159 N..C FORM 3e6A - U.S. NUCLE AR HEOULATORY COMMISSON APPROVED OMB NO. 31E0104 ESTIMATED BURDEN PER RES S COMPLY WITH THIS INFORMATON 60 RWAC 8 AO LICENSEE EVENT REPORT (LER) QEl,'%"7',EST, , o, , , u ,
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0IO OI3 OF 018 At approximately 0258 CST the Reactor Operator reset Train B of the CRACS,-
placing the system in the Normal Operation Mode. This placed the CRACS in a !
configuration allowed by the action requirement of Technical Specification 3.3.3.1.
At this time the ESF actuation signal resulting from the out-of service radiation
- monitor was still present. The design of the system control logic is such that resetting the Control Room Emergency Recirculation Actuation while a valid actuation signal ,
exists blocks any further automatic actuation. This design feature exists to prevent 1 overexposure to Control Room personnel during a radiological accident. The feature . _
prevents reactuation of the Emergency Recirculation Mode in a Train which has !
been reset following the initial high radiation condition at a Control Room intake.
'Therefore, as of 0258 CST, both trains of CRACS were incapable of automatically shifting to the Emergency Recirculation mode.in response to a Station Blackout. ,
signal, a Safety injection signal, or a high radiation condition at any one of the three remaining operable radiation monitors.
At approximately 1655, the Shift Technical Advisor (utility, licensed) and Shift i Advisor (contractor, non-licensed) discovered that automatic actuation of the ,
Emergency Recirculation Mode had been inadvertently defeated. Technical !
Specification 3.0.3 was immediately entered; at 1701 CST both Trains of CRACS !
were manually placed in the Emergency Recirculation Mode and Technical 1 Specification 3.0.3 was exited. At approximately 1746 CST the NRC was notified via- 1 the ENS line in accordance with 10CFR50.72. The actuation signal caused by the out-of service radiation monitor was blocked by pulling the fuse (Ells:(FU)(F.Gj)in the associated Balance of Plant Auxiliary Rack (Ells:(RK)(ED)), and at approximately 1801 CSTthe Reactor Operator reset Train A of the CRACS and placed it in Standby.
C. STATUS OF STRUCTURES. SYSTEMS. OR COMPONENTS THAT WERE INOPERABLE AT THE START OF THE EVENT AND TH AT CONTRIBUTED TO THE EVENT The sample pump associated with one channel of radiation monitoring in Train A of the CRACS was inoperable prior to the event. The affected radiation monitor was de-energized coincident with the ESF actuation.
Enclosura to TXX 90159 NRO FORM 366A ' U.S. NUCLE AR REQULATORY COMMISSON APPROVED OMB NO. 31640104
- ESTIMATED BURDEN PER RES S MPLY WITH THIS INFORMATON
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1 f m4ty Name (1) LE R Nunto, (6) Pags (3) i Docket Nurrist (2)
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COMANCHE PEAK - UNIT 1 0151010IOI414l5 910 -
0l017 -
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D. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE. IF KNOWN Not applicable - there were no component failures which contributed directly to this event.
E. FAILURE MODE. MECHANISM. AND EFFECT OF EACH FAILED COMPONENT
. Not applicable - there were no component failures which contributed directly to this event.
F. FOR FAILURES OF COMPONENTS WITH MULTIPLE FUNCTIONS. LIST OF SYSTEMS OR SECONDARY FUNCTIONS THAT WERE ALSO AFFECTED
! Not applicable - there were no component failures which contributed directly to this .
event.
L l
l G. FOR FAILURES THAT RENDERED A TRAIN OF A SAFETY SYSIf,M INOPERABLE. AN ESTIMATE OF THE ELAPSED TIME FROM THE DISCOVERY OF INOPERABILITY UNTIL THE TRAIN WAS RETURNED i TO SERVICE Train A of the CRACS was incapable of shifting to the Emergency Recirculation Mode in response to an automatic actuation signal between 0036 CST and 1701 CST- a period of 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> and 25 minutes. Train B was similarly disabled between 0258 CST and 1701 CST - a period of 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> and 3 minutes. System operability was restored about 6 minutes after the condition was identified by Control Room l personnel at 1655 CST.
t H. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SY_SIEM FAILURE OR PROCEDURAL ERROR The initial event resulting from de-energization of the radiation monitor was annunciated in the Control Room. The discovery that the Emergency Recirculation Mode actuation function had been inadvertently defeated was made by Control Room personnel during a review to confirm system operability.
! 1
Enclosure to TXX-90159
. 'NRC FORM 366A U.S. NUCLE AR His GULAYOHY COICIS$10N APPROVED OMB NO. 31540104 I ESTIMATED BURCEN PER R T PLY WITH THIS INFORMATION LICENSEE EVENT REPORT (LER) QEC7%,",'M8';
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Facday Name (1) Docket Nurrber (2)
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010 015 OF 018 w ,.,e -.. - o.. . - NacFem mA.>on I. CAUSE OF THE EVENT INADVERTENT ESF ACTUATION The root cause of the event is less than adequate self-checking by the individual authorizing de-energization of the inoperable radiation monitor. The impact on the plant war., not fully assessed prior to authorizing the clearance which took the monitor out of service.
A contributing factor is cognitive error due to misunderstood communication. The
- Unit Log contained an entry stating that the subject monitor had been "taken out of- ,
service" due to the loss of sample flow occurring on April 15. This entry was _
interpreted to mean that the monitor was already de energized; however, the intent of the entry was to declare the monitor inoperable.
An additional contributing factor is the absence of a procedure for the removal from service and restoration of radiation monitors which can cause ESF actuation signals.-
INADVERTENT DEFEAT OF CRACS ESF The root cause of the condition is proceduralinadequacy - the system operating and alarm procedures did not address the conditions encountered. The system operating procedure contains a section describing the steps to be taken in transferring from emergency pressurization to normal operation; however, performance of this section resulted in the condition described. The alarm procedure for the Safety System inoperable Indication (SSil) panel did not provide adequate information for Control Room personnel to determine that the CRACS ESF function had been disabled. The alarm was received in the Control Room, and the appropriate SSil window was illuminated; however, Control Room personnel attributed the alarm to the actuation signal caused by tha out of service radiation monitor. Neither procedure warned the operator that the presence of a valid actuation signal while resetting an Emergency Recirculation would prevent subsequent automatic ESF actuations.
J. SAFETY SYSTEM RESPONSES THAT OCCURRED Upon de-energization of the affected radiation monitor the CRACS shifted to the Emergency Recirculation Mode; all associated dampers and fans responded as.
designed.
q Enclos.ure to TXX-90159 l
- NC FORM Se6A U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3160 0104 ESTIMATED BURDEN PER RES T COMPLY WITH THIS INFORMATION S * "" "*
- LICENSEE EVENT REPORT (LER) $5l,'*""E ,, T T C D A0 8 M
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' TEXT CONTINUATION OC. 20555. AND TO THE PAPERWORK REQUCTION PROJECT (31540104).
OFFICE OF MANAGEMENT AND BUDGET. WASHINGTON, DC. 20503.
Facay Nwe (1) LER ) Page (3)
Docket Nunt).r (2)
COMANCHE PEAK - UNIT 1 01510101014l'415 910 Ol0l7 -
Of0 0l6 OF 018 w m n. n . m . .n-RC e- 3eu e> v n l
K. FAILED COMPONENT INFORMATION Not applicable - there.were no component failures that contributed directly to this event, li, ASSESSMENT OF THE SAFETY CONSEQUENCES AND IMPLICATIONS OF THIS EVENT L
The CRACS provides a controlled environment for the safety of the Control Room - -
personnel and assures the operability of the equipment located in the Control Room -
Complex during all modes of operation and following design basis accidents. ' The CRACS provides radiation protection to permit access and occupancy of the Control - i Room Complex under accident conditions, without personnel. receiving radiation exposure in excess of the limits of 10CFR50, Appendix A, General Design Criteria (GDC)
- 19. The Emergency Recirculation Mode is designed for operation during a loss of offsite power,' loss of coolant accidents, or a high radiation condition at the Control Room -
outside air intake.
INADVERTENT ESF ACTUATION The inadvertent actuation occurring on April 16 was caused by an actuation signal generated as a result of de-energization of the inoperable radiation monitor. This design feature is intended to preclude unidentified loss of ESF function in the event of a loss of power to the monitor. During the system realignment all equipment functioned as designed - the operating makeup air supply fan shut down, the control room exhaust fan !
and the kitchen and toilet exhaust fans shut down, the emergency pressurization units started, the emergency filtration units started, and all associated dampers positioned as required. The successful realignment demonstrated that the' system would have 4 performed its intended function if the actuation had been in response to one of the accident conditions for which it was designed.
1 INADVERTENT DEFEAT OF CRACS ESF An analysis was performed to consider the impact on Control Room habitability of a Condition 111 radiological accident occurring with the CRACS emergency recirculation actuation function defeated. The following accidents were considered: a radioactive gas decay tank (Ells:(TK)(WE)) rupture, a radioactive liquid tank (Ells:(TK)(WD)) rupture, and a primary coolant small line break cutside containment.
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Enclosure to TXX-90159
- 'NRC FORM 366A U.S. NUCLE AR REGULATORY COMM:SSON APPROVED DM8 NO. 3150 0104 ESTIMATED BURDEN PER RE8 h COMPLY WITH THIS INFORMATON a
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OFFICE OF MANAGEMENT AND BUDGET. WASHINGTON.DC. 20603.
Fac4sy Name (1) Dock.t Nurrtier (2) LE R Nuretser (6) Pays (3)
~ w e a em COMANCHE PEAK - UNIT 1 015101010l414l5 910 u m - . ,.o.. - NRc % 3*,A .m n 0l0l7 -
0IO OI7 OF 018 The 30 day integrated doses in the Control Room due to a gas decay tank rupture accident would increase if the accident occurred while the CRACS emergency recirculation mode actuation function was disabled. The thyroid dose would increase significantly, but would remain well below the limits of GDC-19; the increases in whole body gamma would be less significant and would also remain within the limits of GDC-19.
The beta skin dose would exceed the limits of GDC-19, but would remain within the limits of NUREG 0800.
A radioactive liquid waste tank rupture would also result in a significant increase in the thyroid dose, but would again remain below the limits of GDC-19. The whole body.
gamma and beta skin doses would remain extremely small fractions of the dose limits of GDC-19.
The primary coolant small line break outside containment would result in the integrated thyroid dose to Control Room personnel exceeding the limits of GDC-19 if no credit is.
taken for filtration by the Primary Plant Ventilation System (PPVS) filters (Ells:(FLT)(VF))
(this conservatism is in accordance with the response to NRC Ouestion O212.69). If credit is taken for the non-safety grade PPVS filtration units, all doses remain within the GDC-19 limits.
Several physical and administrative features exist to offset the effects of the inadvertant defeat of the CRACS ESF function. There are two area radiation monitors installed in the Control Room complex to monitor the radiation levels at all times. An alarm condition on either of these monitors or on any of the operable air intake radiation monitors would lead Control Room personnel to check for proper realignment of the CRACS. In the event of a gas decay tank rupture, the abnormal condition procedure directs the operator to verify that CRACS Emergency Recirculation actuation has occurred. A primary coolant line break outsids containment, or a rupture of a radioactive liquid waste tank would result in numerous radiation monitor alarms in the Safeguards Building, the Auxiliary Building, or the Plant Vent Stack. . An unexpected increase in any of those radiation monitors would lead Control Room personnel to the abnormal procedure for an accidental release of radioactive gas, and that procedure directs the operator to verify that CRACS Emergency Recirculation actuation has occurred. We have good assurance that in the event of a radiological accident occurring with the CRACS ESF function inadvertently disabled, Control Room personnel would identify the system misalignment and place the system in the correct configuration in a timely manner. It is concluded that the condition would not adversely affect the safe operation of the plant or the health and safety of the public.
l,.
' Enclosure to TXX 90159
, "'NRC FORM 366A U.8. NUCLE AR REGULATORY COMMi$$ON APPROVED OMB NO 3150 0104 EXP6RE8w30912 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THS INFORMATON
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3C. 20555. AND TO THE PAPERWORK REDUCTION PROJECT (31640104).
OFFICE OF MANAGEMENT AND BUDOET. WASHINGTON.DC.20603.
Faccay Narte (1) Dochet Nunter (2) LER Nunter (6) Page (3) v- e im su m COMANCHE
%. ,oo,. - . m PEAK ,. UNIT 1 0l510101014l4l5 910 0l0l7 -
010 0l8 OF 0l8 a NRc % =A.m n Ill. CORRECTIVE ACTIONS
- 1. The Lessons Learned from this event have been reviewed by all Shift Operating crews to ensure awareness of the details of the event, the contributing factors, and the actions taken to prevent recurrence.
- 2. The system operating procedure for the CRACS has been changed to caution the operator of the characteristics of the current plant design prior to resetting the Emergency Recirculation actuation. A similar clarification will be added to
. the SSil alarm procedure.
- 3. A Design Modification has been initiated to add a hand switch to each Control Room intake radiation monitor to block the actuation signal when the detector is de-energized.
- 4. The operating procedures will be revised to include sections for removing and restoring the subject monitors when the aforementioned Design Modification is .
complete.
- 5. A Standing Order has been issued detalling the process for removing a Control Room radiation monitor (and other radiation monitors which can cause an ESF.
actuation) from service until the aforementioned Design Modification is complete.
IV. PREVIOUS SIMILAR EVENTS There have been no previous similar events reported pursuant to 10CFR50.73.
D