ML20043D666
| ML20043D666 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 06/05/1990 |
| From: | Lanik G NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Novak T NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| Shared Package | |
| ML20043D667 | List: |
| References | |
| NUDOCS 9006110044 | |
| Download: ML20043D666 (3) | |
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MLHORANDUM FOR:
T..M. Novak, Director Division of Safety Programs Office for Analysis and Evaluation l
of Operational Data THRU:
Peter Lam, Acting Chief i
Reactor Operations Analysis Branch Division of Safety Programs.
j Office for Analysis and Evaluation of Operational Data
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t-FROM:
G. F. Lanik, Chief Reactor Systems Section GE & CE I
Reactor Operations Analysis Branch Division of Safety Programs Office for Analysis and Evaluation of Operational Data
SUBJECT:
HUMAN FACTORS TEAM REPORT - CATAWBA UNIT 1(3/20/90)
]
atabout9:45am,(CatawbaStationUnit1operatorsRCS)fillandventoper On March 20, 1900, performing a reactor coolant system increasing level in the pressurizer relief tank. A leaking pressurizer Iower operatedreliefvalve(PORV)wasfirstsuspected. About 25 minutes later, the residual heat removal (RHR) pump discharge pressure wts noted to be abnormally high, while the wide range RCS pressure instruments, which the operators had been monitoring, remained at zero indicated pressure. These RCS pressure instruments were.found to be isolated; the RCS and the RHR system had been pressurized; and the leakage to the pressurizer relief _ tank was from the RHR suction relief valve which had opened due to the high pressure.
7 As part of the AEOD program to investigate the human factors aspects of operational events, a human factors study team visited the site. The team leader was George Lanik of AE0D; other team mc:bers were Ann Ramey-Smith of l
RES and Orville Meyer and Dr. Jerry Harbour from the Idaho National Engineering l
Laboratory. The team was at the site for one day and gathered data from discussions, plant logs, and extensive interviews of plant operators. The site report prepared by the contractor is enclosed.-
l-l Specific aspects of the event relevant to human aerformance were identified and are addressed in this memorandum.
Factors w11ch contributed to the error in scheduling and those which contributed to the failure of the operators to recognize the condition are grouped separately. The first group relates to i
E the unavailability of the pressure instrumentation. The second group relates I
to the ability of the operating crew to prevent the over-pressurization regardless of the availability of the specific instruments. Operator action is important io coping with events, especially when equi;uent or instrument failures have occurred, n
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To: Thomas M. Novak Scheduling issues:
Planning and Scheduling During Refueling Outages Because of the large number of activities during refueling outages, a functional unit called " Integrated Scheduling" has primary responsibility
'for plant configuration control.
Integrated Scheduling had issued a Work Request to replace tubing fittings with socket welds on the pressure sensing lines of the primary system pressure instruments during the refueling outage. A functional test with the RCS pressurized was scheduled prior to Mode 4.
The need for these pressure instruments to be operable after fill and vent and prior to initial pressurization of the RCS was overlooked by both Integrated Scheduling and the IAE (instrumen-tation and electronics) planners. Modifications to the planning and scheduling procedures to account for changes in plant operational conditions not directly connected with mode changes (such as fill and vent)couldhelpprovideadefenseagainsttheseerrors.
Tagging of Control Room Instruments The IAE maintenance group is responsible for the pressure instrumentation-and for most control room instruments.
For activities performed by IAE, there is no procedure for tagging of inoperable instruments in the control room or for e permanently maintained log in the control room of such instruments. During outages, integrated scheduling is responsible for configuration control; during normal operations the number of activities is small.and the control room crew tracks IAE activities with informal notes. A formal procedure for tagging of inoperable instruments by the control room operators could have provided a defense h epth against human error.
Operator response issues:
Operational-Surveillance I
Other operable instruments (letdown pressure and RHR pump discharge pressure) which responded to the pressure increase were not monitored during this event. Since the initial pressure was expected to remain near zero for some time, the inoperable condition of the instruments which were being monitored did not become apparent; the operators believed that sufficient. redundancy was available from the three redundant RCS pressure instruments and did not broaden their surveillance to includo.the letdown pressure and RHR pump discharge pressure instruments.
The isolation of
,the three redundant RCS pressure instruments had created a cognitive trap
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for the operators. Deliberate actions to verify validity of instrumen-tation by periodic operational surveillance of all redundant indications can be effective in alerting the operators to unexpected failures.
To: Thomas M. Novak Operator Initial Diagnosis Upon detection of increasing level in the pressurizer relief tank, the operators' initial diagnosis was that a reactor coolant system leak had reveloped which should be found and isolated.
This diagnosis determined their actions until e systems engineer noted the elevated RHR discharge pressure indication; this new input caused the operators to consider other scenarios and eventually discover the over-pressure condition. The operators' initial diagnosis was plausible given the available indications and standard trouble-shooting by the operators would probably have led to correct diagnosis of the over-pressure condition.
Procedure Variation The reactor vessel head vent was open longer than normal, prior to initiation of pressurization. Thus, more air and other gasses escaped the reactor coolant system. The operators did not consider the effect
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of this change on the time required to reach the intended pressure after the vent paths were isolated.
Operators were expecting four to six hours but the edditional venting resulted in pressurization in less than three hours.
Odg!rmisigned by George F. Lanik, Chief Reactor Systems Section CE and GE Reactor Operations Analysis Branch Division of Safety Programs Office for Analysis and Evaluation of Operational Data
Enclosure:
As stated Distribution:
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Clanik GZech-PBaranowsky, NRR W0rders, RII SRubin JAbbo, RII ROAB:
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