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4.3 METHODOLOGY
4.3.1 Overview of the Hazards and Accident Analysis Process
The Safety Analysis presented in NSTR-011-98 used a Preliminary Hazard Analysis
@“A) technique to identify and evaluate the hazards and postulated accident scenarios
associated with the Building 991 Complex. This technique began by identifying existing or
potential hazards (eg., radioactive sources, radioactive wastes, chemicals, or non-material
hazards (e.g., thermal energy sources, pressure sources, electrical energy sources)) in terns of
quantity, form, packaging, location, affected or afTecting activities, and recognized preventive
and/or mitigative features (SSCs or elements of administrative programs) associated with the
hazard.
Based on the infomation developed by the PHA and presented in the hazards description
table, determinations were made on whether further evaluation of specific haziirds were
necessary. In general, no further evaluation was performed on those hazards: (1) which could
be characterized as Standard Industrial Hazards and (2) which had limited impact on postulated
accident initiation frequency, accident mitigation, and accident consequences. Industrial hazards
that could only lead to occupational injuries or illnesses were considered addressed by the
Industrial Hygiene and Safety program, as discussed in Chapter3, Safety Management
Programs.
For those hazards determined to require further evaluation, a hazards evaluation matrix
was developed relating identified Building 99 1 Complex activities with mrresponding hazards in
order to derive postulated accident scenarios. For each postulated accident scenario, the hazards
evaluation matrix presented: (1) scenario descriptive information including the corresponding
activity and hazard leading to the scenario; (2) a categorization of the accident type; and (3) a
qualitative assessment of scenario frequency, consequences, and risk class assuming identified,
inherent preventive and mitigative fixitures were in place. Based on the information presented in
the hazards evaluation matrix, postulated accident scenarios of higher risk were selected as
candidate, bounding accident scenarios for Mer, detailed evaluation. Bounding accident
scenarios were identified for each of those postulated accident scenarios that were not canied
forward for further analysis. Any inherent preventive andor mitigative features associated with
the bounded scenarios that rdted in the scenario being low risk were assigned to the bounding
scenarios in order to carry forward all credited preventive and mitigative features.
In some cases, a bounding accident scenario qualitative frequency assessment may have
been further refined using event tree methodology displaying accident progression and impact of
identified preventive and/or mitigative features. In all cases, the bounding accident scenario
qualitative consequence assessment was refined using Site consequence evaluation tools
Quantitative estimates of scenario initial [respirable] source terms (ISTs) were determined based
on: (1) estimated damage ratios @Rs) associated with the postulated accident scenario;
(2) bounding material-at-risk (MAR) estimates associated’ with analyzed activities and expected
radioactive or chemical Containers; and (3) airborne respirable release fractions (ARRFs) taken
from Airborne Release Fractiondbtes and Respirable Fractions for Nonreactor Nuclear
Revision L
4-3 Building 99 1 Complex FSAR
Sentember 1999 I