U.S. Reactor Containment Technology: a Compilation of Current Practice in Analysis, Design, Construction, Test, and Operation, Volume 1 Page: 1-05
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Table 1.1. Estimated Degrees of Conservatism
in Exposure Calculationsa
Calculation or Assumption Conservatism
Removal of iodine from containment vessel 3-10
atmosphere by various physical phenomena
such as adsorption, adherence, and settling
Removal of iodine by protective safeguards 10-1000
such as cooling spray and filtration of
Vessel leakage rate calculated at constant 5-10
Wind direction shift during extended period 2-50
Wind meandering from centerline direction N3
Atmospheric dispersion under other than 5-1000
Particulate fallout from radioactive cloud 2-5
Direct gamma dose neglecting shielding from 2-1000
structures and topography
aFrom DiNunno et al., ref. 4.
126.96.36.199 Mechanical Design
The term safety factor in its strictest sense means the ratio of the
magnitude of a parameter at failure to the magnitude of the same parameter
used for design purposes. The parameter may be stress, force, pressure,
repetitive cycles of loading, etc. Unfortunately, the situation is not
clear-cut, since a definition of failure is also involved. Yielding, ex-
cessive deformation, brittle fracture, leakage, and the formation of fa-
tigue cracks all may constitute modes of failure in certain circumstances.
The permissible design stresses in the ASME Codes5 are based on a
fraction of the smallest of several values: the minimum specified or
expected ultimate tensile strength, yield strength, creep rate, and stress-
rupture. For most ferritic materials of construction operating at tem-
peratures below their creep range, the specified fraction of the ultimate
tensile strength governs the permissible design stress. This fraction is
1/4 in Section VIII of the ASME Boiler and Pressure Vessel Code and 1/3
in Section III. Generally, the membrane stresses are thus limited to 1/4
or 1/3 of the ultimate tensile strength of the material; however, stresses
due to structural discontinuities, thermal gradients, etc., are allowed to
exceed these values. In neither case is the term safety factor used in
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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/m1/33/: accessed March 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.