10-7 per year, realistically calculated.
Unmitigated release is meant to consider material quantity, form, location, dispersability,
and interaction with available energy sources, but not to consider safety features (e.g.,
ventilation systems, fire suppression, etc.) which would prevent or mitigate a release.
Final dose estimations representing the anticipated behavior of the facility under accident
conditions should be based on the mitigated design basis accidents (DBAs), wherein full
or partial functionality of SC SSCs is assumed. In cases where the designated SC SSC are
not capable of performing their required safety function without significant upgrade (i.e.,
backfit) other compensatory measures such as material-at-risk (MAR) limits may be
implemented in the facility and incorporated into the DSA.
Comparison of the unmitigated consequences for a limited subset of potential accidents to
the EG is performed to determine if the need for designation of SC SSCs exists. If the EG
value is approached by the unmitigated consequences of a release scenario, a need for SC
SSC designation is indicated. SC SSCs are only one of many layers of hardware- and
administrative-based controls that are incorporated into a DOE operation for the protection
of the public, worker, and environment consistent with the precepts of the defense- in-depth
philosophy. The SC designation merely helps to focus a higher level of attention and
requirements on this select subset of all controls intended for the protection of the public.
If the need for SC designation is determined, all preventive and mitigative features
associated with the sequence of failures that result in a given release scenario, as well as
any features whose functionality is assumed a s part of the scenario definition itself are
candidates for SC SSC designation. The process of designating one or more safety SSCs
as SC is judgment-based and depends on many factors such as effectiveness, a general
preference of preventive over mitigative and passive over active, relative reliability, and
DOSE COMPARISON CALCULATIONS
General discussion is provided for source term calculation and dose estimation, as well as
prescriptive guidance for the latter. The intent is that calculations be based on reasonably
conservative estimates of the various input parameters.
The dose estimate is that received during a 2- hour (with the exception mentioned earlier)
exposure to plume, as discussed in section A.3.3, considering inhalation, direct shine, and
ground shine. Other slow developing release pathways, such as ingestion of contaminated
food, water supply contamination, or resuspension are not included. However, quick
release accidents involving other pathways, such as a major tank rupture, which could
release large amounts of radioactivity in liquid form to water pathways, should be
considered. In this case, real potential uptake locations should be the evaluation points.
The airborne pathway is of primary interest for nonreactor nuclear facilities. This position
is supported by NUREG-1140, "A Regulatory Analysis on Emergency Preparedness for
Fuel Cycle and Other Radioactive Material Licenses," which states that "for all materials
of greatest interest for fuel cycle and other radio active material licenses, the dose from the
inhalation pathway will dominate the (overall) dose." For some types of facilities such as
waste storage, the surface and groundwater pathways may be more important, but accident
releases usually would be expected to develop more slowly than airborne releases. More