This subsection identifies requirements that are specifically needed to fulfill
safety functions. Such functional requirements are specified for both the
safetysignificant SSC and any needed support safety-significant SSCs.
Limit functional requirement designation to those requirements necessary for
the safety function. Functional requirements are provided for safety-
significant SSCs for the specific accident(s) or general rationales for which the
SSC is needed (e.g., if that accident is not initiated by an earthquake, the
functional requirement does not involve seismic parameters).
Functional requirements specifically address the pertinent response parameters
or nonambient environmental stresses related to an accident for which the
safety function is being relied upon. In the hydrogen detector example, one
obvious parameter would be maintaining hydrogen concentration below the
explosive limit. If the offgas temperature was significantly above ambient
temperatures, operatio n at that temperature would be a functional requirement
This subsection provides performance criteria imposed on the safety-
significant SSC so it can meet functional requirement(s) and thereby satisfy its
safety function. Performance criteria characterize the specific operational
responses and capabilities necessary to meet functional requirements.
Safety-significant SSCs, are not required to consider performance criteria
traditionally associated with safety-class SSCs or traditional nuclear standards
in general. Performance criteria for a safety-significant SSC should be
representative of the general rigor associated with non-nuclear power reactor
industrial and OSHA practices. Performance criteria for safety-significant
SSCs are developed by DSA preparers using engineering judgment based on
the expected functions for which it was designated a safety-significant SSC
and its overall importance to safety.
Evaluate the capabilities of the SSC to meet performance criteria. The
evaluation should be as simple as possible, and rely on engineering judgment,
calculations, or performance tests as opposed to formal design reconstitution.
would exceed its interlock trip point. Such a test would typically bound the
needed equipment performance as response time is not a highly sensitive
This subsection identifies those assumptions requiring TSRs to ensure
performance of the safety function.