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being SSCs required to implement safety. In addition, the safety analysis would verify the ade-
quacy of safety-significant SSCs in addressing the potential safety concerns. Worker protection
and potential safety concerns associated with the public safety function are identified in
Descriptions of each SSC that is providing safety functions are required in the SAR. A basic
descriptive model of the facility and its equipment must be provided in which the required SSCs
are addressed in detail commensurate with their preventive or mitigative role in meeting off-
normal condition evaluation guidelines. For example, consider a facility that cannot meet
evaluation guidelines, as discussed in DOE-STD-6002, unless credit is taken for system A.
Besides being noted in the general facility description, system A together with associated codes
and standards would be described in the section on safety-class SSCs. This system would typi-
cally be associated with a specific TSR (discussed in Section 5.7) and would be described in
detail commensurate with its importance to the safety basis. However, only the characteristics of
the SSC that are necessary to perform the safety function are classified as part of the safety
system. For example, if a valve in a system is only required to provide an external pressure
boundary, then only the pressure boundary function would be classified as a safety system
characteristic and all other functions, such as the valve operability, response time, etc. would
not be included in the safety system definition.
Conversely, if the consequences of all hazardous releases or off-normal conditions exam-
ined meet the evaluation guidelines without relying on the safety-class function of process
system B, then system B would not be considered to be a safety system performing a safety
function. Detailed identification of its functional basis and construction is not necessary because
it is not a significant contributor to the overall facility safety basis. There would also be no need
to discuss administrative provisions (e.g., initial testing, maintenance) required to ensure the
operability of system B, nor would there be a need for a specific TSR (e.g., Safety Limit, Limiting
Condition For Operation, etc.) covering system B. If a system is designated as safety-significant,
industry recognized codes and standards are to be applied and minimal, if any, TSRs are to be
specified for the operation of the system components (see Section 5.7).
A risk-based prioritization approach can be used to develop requirements for the safety-
class and safety-significant SSCs. One of the dominant factors governing risk-based prioritiza-
tion is the severity of the off-normal condition consequences associated with the facility and the
number and type of the SSCs needed to prevent evaluation guidelines from being exceeded. If,
for example, the defense-in-depth principles are satisfied by providing other SSCs to mitigate
the consequences, then added inspections and other quality pedigree requirements of the first
system would not be as important as if the original SSCs were the only means of accomplishing
the safety function. If the consequences of the off-normal condition exceed the evaluation guide-
lines by a large margin and there is no other system that will mitigate or prevent the release for
the off-normal condition, then special precautions should be taken in the design and in develop-
ing the inspection program to ensure that the system will be available to function when called
upon. This may involve special inspections, alternate design approaches, or other actions that
would significantly enhance system reliability. The rigor of compliance with the design and
inspection requirements could be relaxed for systems that have multiple backups for preventing
off-normal conditions or mitigating the off-normal condition consequences.

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