Probabilistic analysis of fires in nuclear plants Page: 3 of 22
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The measures of risk include
" public risk, such as CDF, containment failure,
large releases, etc, and
" economic risk, such as extended outage time, clean-
up, regulatory requirements, occupational. hazard
costs, etc.
The events involved include most major relevant
initiating events which can lead to public or economic
risk such as
" accident initiators,
" safety equipment failures,
" failure of BOP to provide safety functions,
" operator failures, etc.
The level of detail varies depending on the data
and models available and on plant specific peculiari-
ties and may involve
" systems and subsystems,
" macrocomponents (i.e., sets of components ch
react, and may be treated as a unit for the pur-
poses of this modeling), and
" component and operator behavior.
This model is available in automated (i.e., com-
puterized) form, and thus rests heavily on plant
specific models and data derived from the (internal)
systems PRA. It may need to be augmented by (plant
specific) fire induced initiators and other perturba-
tions, if called for. (See Sections 2.2 and 2.3
below)
2.2 Relational Data Base
This is an organizational data structure which
stores a variety of information about plant elements
and functions, their locations, and their connectivi-
ties. It enables the comprehensive evaluation of the
effect of events in one location on equipment and
functions in that location and in other places in the
plant that may be coupled to it by fire related or
fire induced phenomena. It embraces locational cou-
pling, direct interactions (e.g., equipment depen-
dences) and secondary interactions (e.g., non-fire
perturbations induced by fire).
Particular emphasis is placed on:
" (general) risk significant equipment,
" support and interactive equipment,
" locational characteristics,
- barriers and their levels of effectiveness, and
" combustible loads, whether they are directly con-
nected with plant operations (e.g. cable insula-
tion, transformer oil, etc) or ancillary (stored
oil, rags, procedural documents, etc).
Sources for constructing such a data base include2.3 Fire Phenomenology and Data
The third important element in this approach is
the proper consideration of fire initiation, propaga-
tion, damage and suppression. It is clearly neither
feasible nor appropriate to deal with these topics
extensively in the present context. Instead it is
proper here to list in tabular form the major consid-
erations and characteristics which must be addressed,
accompanied by some qualitative discussion.
There are four major categories of information
involved here. These are
" experimental fire data,
" fire initiation characteristics
" fire propagation considerations, and
" target damage modes and criteria.
2.3.1 Experimental fire data. This category
includes plant specific and industry-wide fire initia-
ting experience, underwriting data, and review of
reportable events at nuclear plants, together with the
examination of non-nuclear plant incidence data as an
adjunct.
It also involves the frequencies, locations, and
magnitudes of fires in the specific plant, and if such
information is lacking or scanty, relevant generic
data of this type. Finally such data should embrace a
comprehensive list of variables and parameters needed
to characterize the fires, particularly the initiator:
these may include combustible classes, loading, loca-
tion, ignition susceptibility and activity levels
under appropriate conditions.
2.3.2 Fire initiation characteristics. This
class of.information includes the details of potential
initiating fires such as the types, amounts, and
geometry of the combustibles, in particular the physi-
cal, chemical and pyrolytic properties. It also
describes the location of this material in relation to
the room geometry, barriers, other combustibles, tar-
gets and potentially damaging connective paths.
2.3.3 Fire propagation considerations. In the
first instance the major fire propagation considera-
tions are the following:
" the fire scenario and configuration (i.e., the
enclosure, initiating fire and target[s)),
" the fire dynamics models (including the fire growth
and target damageability models), and
" the physical and combustion data for the burning
material.
Some of these have already been dealt with
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Unione, A. & Teichmann, T. Probabilistic analysis of fires in nuclear plants, article, January 1, 1985; United States. (https://digital.library.unt.edu/ark:/67531/metadc1059468/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.