Functional Requirements - doe-std-3009-94_cn3

DOE-STD -3009-94

4.4.X.3

Functional Requirements

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

as well.

4.4.X.4

System Evaluation

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.

For example, the hydrogen detector could be fed a test gas composition that

would exceed its interlock trip point. Such a test would typically bound the

needed equipment performance as response time is not a highly sensitive

parameter.

4.4.X.5

Controls (TSRs)

This subsection identifies those assumptions requiring TSRs to ensure

performance of the safety function.

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