Formulation of SACs - Continued

DOE-STD-1186-2004

Diverse: To avoid the increased likelihood of failure due to common-cause effects, diverse

controls should be employed to the extent practicable. In this context, diversity refers to

separate controls of a dissimilar nature (as distinguished from merely redundant controls).

The application of these principles acknowledges that an SAC may be included as a portion of

the ensemble of hazard controls that satisfies the Order's requirements for providing multiple

layers of protection to confine and mitigate radioactivity associated with the potential for

accidents with significant public radiological impact. When SACs are used in this capacity, they

should be formulated, implemented, and maintained following the guidance given in this

Standard for improving the dependability of these controls and enhancing their availability to

perform specific safety functions when needed.

The application of these principles also acknowledges that an SAC should not be designated as

the only control provided to confine and mitigate radioactivity associated with the potential for

accidents with significant public radiological impact, to ensure that exposure to a high

consequence accident does not come about due to failure of a single barrier.

DOE O 420.1A, Facility Safety, Section 4.1.1.2 also requires that "Safety SSCs identified in

accordance with this section shall, commensurate with the importance of the safety functions

performed, be designed: (1) so that they can perform their safety functions when called upon to

operate, and (2) under a quality assurance program that satisfies 10 CFR 830.120." These

criteria also apply to SACs.

SACs should be formulated to reliably perform their safety function under those conditions and

events for which their safety function is intended, with an appropriate margin of safety. The

formulation should incorporate, commensurate with the importance of the safety function,

multiple levels of protection against normal, anticipated, and accident conditions.

The DSA required by 10 CFR 830.204 furnishes the technical basis for hazard controls. DOE

STD-3009 provides guidance to identify and document SC and SS SSCs as required in

Chapter 4 of a DSA. Where SACs are used, similar identification and documentation should be

provided in the DSA. For example, the reason for designating the control as an SAC and its

preventative or mitigative safety function should be discussed. A description of how the SAC is