analyzing the scenarios and implementing risk reduction recommendations. This by no
means implies that postulated accident scenarios that have frequencies less than 1E-6/y
are acceptable risks because they lie below the boundary between risk rejection and risk
acceptance. This standard uses the screening cutoff frequency in terms of the sum of
all aircraft crash impact frequencies, which are also the initiating event frequencies. All
individual aircraft type initiating event frequencies and subsequent accident sequences
will have frequencies less than the cutoff. This criterion applies to the frequency
screening, frequency evaluation, and damage assessment stages of the process. In all
three stages, the sum of the applicable initiating event frequencies is determined and the
same 1E-6/y screening value is applied.
Structural Response Screening Guidelines. The basis for the structural response
guidelines is predominantly the industry norms that are prescribed and uniformly
accepted by structural engineering professionals through the national and consensus
For local damage to reinforced concrete structures, it was felt that some degree of
conservatism would be achieved by increasing the penetration thickness by 10 and
20 percent for scabbing and perforation, respectively. The rationale behind this increase
is to account for any uncertainty; and because these are empirical formulas, in some
cases validated by test results, a nominal increase would ensure consistency and lend
some degree of assurance that failure would be prevented if these requirements were
met. Similarly, for steel targets, an increase of 25 percent over the penetration depth
was recommended to prevent any failure.
As for excessive structural deformation/collapse and the SSCs' functionality, the national
consensus codes were recommended to be consistent with the analysis/design
evaluation for structures subjected to any other such accidental or abnormal load.
United States Department of Energy. Preparation Guide for U.S. Department of Energy
Nonreactor Nuclear Facility Safety Analysis Reports. DOE-STD-3009-94. July, 1994.