Chernobyl Nuclear Accident Congressional Hearings Transcript

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accessible from remote terminals at each nuclear plant and at
each corporate headquarters by INPO members and participants.
This massive data base is now beginning to be used for the
improvement of component and system reliability and enhancement
of nuclear plant performance.
Two examples of using NPRDS information to improve component
performance are as follows:
o Two plants operated by a utility experienced several
essential electrical system inverter failures over a nine
year period, some of which caused plant scrams and
challenged safety systems. After searching the NPRDS data
base and reviewing inverter failure information, the
following key items were identified:
— Many other plants had inverter failures but most did not
result in a plant scram, pointing to a potential design
problem.
— The inverter failures due to heat-related component
degradation were significantly higher than at other
plants, pointing to a potential environmental or
application problem.
The utility initiated immediate and long-term corrective
actions related to the design and environmental issues. No
plant scrams from inverter failures have occurred in the
year after these corrective actions were initiated.
o A plant experienced frequent failures of the isolation
valves for the pressurizer power -opera ted relief valves,
resulting in unscheduled repair outages and the increased
potential for adverse impacts on plant operation. A search ,
of the NPRDS data revealed the following key items:
The isolation valves had a unique design for body to
bonnet closure, pointing to a potential design
problem.
Other plants were not experiencing similar failure modes
for the isolation valves.
The utility initiated several corrective actions covering
valve modifications, maintenance procedures, and training of
personnel involved in valve maintenance. The valves have
exhibited a significant improvement in reliability since
implementation of these actions, resulting in an estimated
annual increase of 0.3 percent in plant availability (cost
benefit of approximately $900,000).
Human Performance
In recent years, the utilities and INPO have begun the
development and expansion of another important operational event
data base and corrective action system. This system, called the
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