When describing the SAC, provide a basic summation of the physical
information known about the SAC, including tables or drawings showing
relevant information, such as instrumentation and other SSCs, physical
boundaries, approved storage areas, and operator routes or locations.
This subsection identifies requirements that a re specifically needed to fulfill
safety functions. Such functional requirements are specified for both the SAC
and any needed support SSCs.
Limit functional requirement designation to those requirements necessary for
the SAC safety function. Functional requirements are provided for SACs for
the specific accident(s) or general rationales for which the SAC is needed.
For SACs, functional requirements may involve unimpeded access to specific
rooms or areas, use of certain instrumentation, written procedures or checklists,
and special tooling. The description of the functional requirement must fully
address all aspects important for ensuring the SAC can be accomplished.
This subsection provides performance criteria imposed on the SAC so it can
meet functional requirements(s) and thereby satisfy its safety function.
Performance criteria characterize the specific operational responses and
capabilities necessary to meet functional requirements.
The formulation of SACs should include a pro cess that validates that plant
operators can perform the task(s) called for in a SAC within the timeframes
assumed in the safety basis. If SACs require operator action and perform a
function similar to a safety SSC, assurance should be provided that the
operators can adequately perform their required tasks by analyzing the
following human performance factors at a minimum.
Adequacy of the description of the task in facility procedures
Level of difficulty of the task
Design of the equipment and feedback, e.g. indicators and alarms
Time available to do the task or recover from an error
Stress levels induced by the external environment, e.g., noise, heat,
light and protective clothing worn.
Formal engineering calculations may be necessary to ensure that plant
operators have the appropriate time and resources to carry out the required
tasks. For example, if it is assumed that operators will take action to detect and
isolate a leak, flow rate calculations will need to be performed to substantiate
the available time interval necessary to accomplish the task. Consequences of
incorrect implementation of the control should be evaluated and measures to
prevent control failure should be factored into the control formulation.