U.S. Reactor Containment Technology: a Compilation of Current Practice in Analysis, Design, Construction, Test, and Operation, Volume 1 Page: 1-04
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1.1.4 Safety Factors
Inasmuch as containment is provided principally in order to limit the
public exposure as the result of significant activity release, it is of
interest to consider the various safety factors involved in the evaluation
of exposure. These safety factors fall into two classes: first, those as-
sociated with conservative assumptions employed in the analytical repre-
sentations of fission-product transport and, second, those associated with
the designed integrity and performance of engineered safeguards, including
the containment enclosure itself.
The term "safety factor" does not necessarily imply the uniform appli-
cation of a particular integer (e.g., 3 or 5) to adjust design data in a
direction of overdesign. It does describe a philosophy - the use of values
in design that are realistic but conservative. Although both concepts
attempt to establish a margin of safety in order to compensate for un-
known or uncertain effects, the two differ primarily in their degree of
uncertainty. The term "safety factor" implies that the basic value of a
given parameter has been established through considerable experience, whereas
"degree of conservatism" implies the use of values much more pessimistic
than otherwise indicated in order to cover the lack of experience.
188.8.131.52 Exposure Calculations
Calculations of exposure to radioactivity resulting from a postulated
maximum accident are not completely confirmable in terms of amounts and
behavior of the fission products released. Thus conservative methods that
reflect the designer's judgment as to the safety of the results are uti-
lized. The accepted approach is to exercise extreme conservatism in un-
certain situations owing to the severity of possible consequences.
As data become available, values can be estimated for these uncer-
tainties that can be designated degrees of conservatism. An example of
this is given in an AEC document4 relating to siting calculations, and the
estimates are listed in Table 1.1. Great uncertainty in these calculations
and assumptions is illustrated by the wide range of estimated values.
184.108.40.206 Energy Release Calculations
The safety factors involved in energy release calculations, while
much smaller, have not been as thoroughly documented. Thus, it is fre-
quently assumed that all the energy in the primary system is released into
the containment structure with no heat losses. Practically speaking, that
would, of course, be impossible. Similarly, the energy contributions due
to chemical reactions and nuclear energy are each conservatively applied
to cover lack of knowledge of the subject.
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Cottrell, William B. & Savolainen, A. W. U.S. Reactor Containment Technology: a Compilation of Current Practice in Analysis, Design, Construction, Test, and Operation, Volume 1, report, August 1965; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc101033/m1/32/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.