Accident Precursor Analysis and Management Reducing Technological Risk Through Diligence (2004) / Chapter Skim
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6 Nuclear Accident Precursor Assessment: The Accident Sequence Precursor Program
6 Nuclear Accident Precursor Assessment: The Accident Sequence Precursor Program
Pages 89-100
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From page 89... ...
to perform m independent evaluation of WASH-1400. That committee made a number of recommendations in 1978, including that more use be made of operational data to assess the risk from nuclear power plants The Review Group's report stated, "It is import ant, in our view, that potentially sigmific tot (accident)
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From page 90... ...
In fact, ASP was pushing the state of the a t in risk assessment to the limit, md asking for more would have been impractical. Only a few risk models besides WASH-1400, such as those for the Zion and Indian Point nuclear power plmts, could have supported detailed risk assessments of operational events.
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From page 92... ...
In 1984, ASP, with the help of the I ISNRC Accident Sequence Evaluation Program, identified classes of plants based on common responses to specific initiating events (transient, loss of off-site power, and smaD LOCA) and began to develop computerized, systemic event trees for each plant class.
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From page 93... ...
In accordance with the U.S Code of Federal Regulations (IOCFR50) , commercial nuclear power plants are required to report to the USNRC all operational events that represent a deviation from the licensing basis or failure/degradation of a safety function.
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From page 94... ...
any other event that, based on the reviewer's experience, could have resulted m or sigmificanrdy affected a cham of events leading to potential severe core damage These criteria served only as guidelines, and the reviewers were heavily relied upon to exercise judgment during the screening process to ensure that no LERs were screened out that shouldn't have been md that the screening process effectively reduced the number of events requiring further evaluation. The evaluation ofthe 198(}1981 events used the same acceptmcecntena md processes.
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From page 95... ...
The 1987 precursor selection process, in addition to the typical precursors, identified events involving a loss of containment function and other events that were considered serious but were not modeled (although these were not called precursors)
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From page 96... ...
. The 1990 precursor report identified 28 precursors and 53 events that were potentially significant but impractical or lacked sufficient information to analyze (Minarick et al., 1991)
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From page 97... ...
Because of the wide-nmgmg changes m the event-selection criteria and processes, changes m modeling methods, and the mcreasulg sophistication of the nsk models, it would not be appropriate to determine overall risk trends from ASP reports. LESSONS LEARNED ASP was established fairly early m the development of probabilistic risk assessment for the commercial nuclear power industry.
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From page 98... ...
This requires that precursor categories be defined based on accident sequences determined from full-scope risk assessments for the entire range of facilities and systems. This is impo tant because accident precursors are typically small segments of one or more accident sequences, and assessing accident precursors includes mapping these events onto the risk models.
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From page 99... ...
5. Risk assessment in the industry must be mature enough to instill confdence that potential accident sequences have been identified and that the models used to assess events are sufficient md only need changes that reflect the configurations and operatmg practices of specific facilities.
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From page 100... ...
1975. ReActm Saf~ty Study: An Assessment of Accidem Risks in US Commercial Nuclear Power P ants, WASH-1400.
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