LER screening algorithm for identification of potential accident sequence precursor events Page: 1 of 6
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LER SCREENING ALGORITHM FOR IDENTIFICATION
OF POTENTIAL ACCIDENT SEQUENCE PRECURSOR EVENTS*
W. P. Poore, III
Lockheed Martin Energy Research Corp.
P. O. Box 2009, Bldg. 9201-3, MS-8065
Oak Ridge, TN 37831-8065
A computer algorithm has been developed and
implemented to search the Sequence Coding and Search
System (SCSS) Licensee Event Report (LER) database for
failures or conditions common to Accident Sequence Precursor
(ASP) events. The use of the algorithm has greatly improved
the efficiency and timeliness in identifying potential ASP
events and, by focusing attention on the most likely precursor
events, has reduced the likelihood that these events will be
overlooked in manual screening.
I. GENERIC ASP EVENT DESCRIPTION
Operational events are selected as precursors if they are
core damage initiators or if they impact systems or functions
which provide protection against core damage given an
initiator. These initiators (or transients) and adverse plant
conditions of interest are described in more detail in
Precursors to Potential Core Damage Accidents: 1994, A
Status Report, NUREG/CR-4674, Vols. 21 and 22.1
Operational events are designated potential precursors if
1. a core damage sequence initiator such as a loss of offsite
power (LOOP), a steam line break, or a loss of coolant
accident (LOCA); or
2. a failure of a system (or multiple trains of a multitrain
*Research sponsored by the Office of Analysis and Evaluation of
Operational Data, U.S. Nuclear Regulatory Commission under Interagency
Agreement 1886-8913-4A with the U.S. Department of Energy under contract
DE-ACO5-960R22464 with Lockheed Martin Energy Research Corp.
The submitted manuscript has been authored by a contractor of the U.S.
Government under contreact No. DE-AC05-960R22464. Accordingly, the
U.S. Government retains a nonexclusive, royalty-free license to publish or
reproduce the published form of the contribution, or allow others to do so,
for U.S. Government purposes.
3. failures or degradations in more than one system; or
4. a transient concurrent with a failed or degraded system,
5. the conditional probability of subsequent core damage is
greater than or equal to a cutoff value of 1.0 x 10'.
II. SEQUENCE CODING AND SEARCH SYSTEM
The Sequence Coding and Search System' was developed
by the Nuclear Regulatory Commission's (NRC's) Office for
Analysis and Evaluation of Operational Data (AEOD) and the
Oak Ridge National Laboratory (ORNL) to capture detailed
analyses of event sequences reported in LERs in a database
available to NRC staff and contractors.2 The analyses of the
events reduce the LER descriptive text to coded, searchable
sequences. The steps in the sequences describing the
information reported in the LER fall into four basic types.
1. Equipment Failures. The type and number of
component failures (e.g., two flow control valves); the system
to which the components belong (e.g., feedwater system); the
cause and failure mode (e.g., erosion resulting in a failure to
open); vendor and model number data, if stated; and links to
later steps describing system failures or unit effects.
2. Personnel Errors. The personnel activity under way
(e.g., maintenance, design, etc.), the type of personnel
involved (e.g., licensed operator), and the cause and effect of
the error are all noted in steps in the event sequence.
aAccess to the SCSS database is available on-line to NRC staff and NRC
contractors, or the SCSS staff at ORNL can perform searches and send the
results directly to the user. Searches are performed on a cost-recovery basis
for non-NRC users.
Disra~moN OF THIS DOCUMENT IS u
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Poore, W. P., III. LER screening algorithm for identification of potential accident sequence precursor events, article, September 1996; Tennessee. (digital.library.unt.edu/ark:/67531/metadc672960/m1/1/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.