Risk-Informed, Performance-Based Regulatory Implications of Improved Emergency Diesel Generator Reliability
Name
ANP-058.pdf
Size
8.27 MB
Format
Adobe PDF
Checksum (MD5)
3e9225906fb44d986a1e71670b00878f
Author(s)
Utton, S.
Golay, M. W.
Date Issued
January 1998
Publisher
Massachusetts Institute of Technology. Center for Advanced Nuclear Energy Systems. Advanced Nuclear Power Program
Series/Report no.
MIT-ANP;TR-058
Abstract
The Nuclear Regulatory Commission's (NRC) steady progress towards risk-informed
performance-based regulation (RIPBR) prompted the practical application of this
regulatory tool in order to demonstrate its potential benefits. This practical demonstration
makes up one part of an Idaho National Engineering and Environmental Laboratory
(INEEL) sponsored project entitled Integrated Models, Data Bases and Practices Needed
for Performance-Based Safety Regulation. Project members selected the emergency
diesel generator system as a candidate for assessment because of its high risk importance
for core damage frequency (CDF) as well as for its failure to exhibit fulfillment of its
current maintenance objectives.
An analysis of current NRC maintenance and inspection requirements of the
emergency diesel generators at the Millstone 3 nuclear power plant was performed by the
project members. Maintenance and inspection items identified as unnecessary or harmful
to the EDG qualified as candidates for removal from the current surveillance schedule.
Expert testimony and comparisons with similar non-nuclear utility industries aided in the
identification of candidate items.
Calculations of the subsequent risk, reliability, safety, and economic implications
revealed several benefits of the inspection alterations. The modified inspection provided
improved backup power availability and defense in depth during the refueling outage. A
sensitivity analysis performed on the EDG basic events affected by inspection alteration
showed that a 50% reduction in these basic event failure rates would decrease the EDG
system failure probability by 13.9%. The altered inspection also shortens the plant's
refueling outage critical path therefore decreasing the risk of fuel damage and improving
the risk profile of the plant outage. Transfer of the revised inspection to performance
while the plant is operating at power resulted in identical refueling outage benefits.
Performance of the inspection at power requires an increase in the allowed outage time
(AOT) of the plant. The subsequent rise in core damage frequency due to the increased
AOT is considered negligible.
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