control systems). Appendix A provides guidance for implementing the Evaluation
Guideline to classify SSCs as safety-class SSCs.
Safety-significant structures, systems, and components. This category of SSCs is
provided to ensure that important SSCs will be given adequate attention in the DSA and
facility operations programs. Safety-significant SSCs are those of particular importance
to defense in depth or worker safety as determined in hazard analysis. Control of such
SSCs does not require meeting the level of stringency associated with safety-class
The Evaluation Guideline is not used for designating safety-significant SSCs.
Safety-class SSCs are designated to address public risk, which makes a dose
guideline at the site boundary a useful tool. Safety-significant SSCs address risk
for all individuals within the site boundary as well as additional defense in depth
for the public, making a dose guideline at any one point an artificial distinction
distorting the process of systematically evaluating SSCs.
TSRs covering SSCs ensuring defense in depth should generally correlate with
safety-significant SSC designation for defense in depth, but exact one -to-one
correlation is not required.
Specific administrative controls . This category of ACs is provided to ensure
that controls important to safety that are needed to prevent or mitigate an
accident scenario will be given equivalent attention in the safety basis
documents had that safety function been provided by a safety-class or safety-
significant SSC. Safety analyses shall establish the identification and functions
of SACs and the significances to safety of the functions of the SAC. The
established hierarchy of hazard controls requires that engineering controls with
an emphasis on safety-related SSCs be preferable to ACs or SACs due to the
inherent uncertainty of human performance. SACs may be used to help clarify
and implement an AC.
HA Z A R D AN A L Y S I S
The initial analytical effort for all facilities is a hazard analysis that systematically
identifies facility hazards and accident potentials through hazard identification and
hazard eva luation. The focus of the hazard analysis is on thoroughness and requires
evaluation of the complete spectrum of hazards and accidents. This largely qualitative
effort forms the basis for the entire safety analysis effort, including specifically
addressing defense in depth and protection of workers and the environment. Basic
industrial methods for hazard analysis, its interface with more structured quantitative
evaluations, and the basis for both have been described in references such as the
American Institute of Chemical Engineers Guidelines for Hazard Evaluation
Procedures (1992). OSHA has accepted these guidelines as the standard for
analytical adequacy in characterizing commercial chemical processes that perform the
same type of unit operations conducted at DOE nonreactor nuclear facilities.
Appropriately applied, they help fulfill the requirements of DSAs for Hazard Category
2 and 3 facilities as specified in 10CFR830.