Hazards analysis benefits/limitations

The material in this chapter up to this point has assumed that hazards analysis is inherently worthwhile yet it is useful to examine some of the benefits and limitations of such analyses, if only to provide a sense of proportion as to what might be achieved by them. 

The extent of accommodation and characterization of uncertainty in exposure assessment must necessarily be balanced against similar considerations with respect to hazard, since the outcome of any risk assessment is a function of comparison of the two. If, for example, there is limited information to inform quantitatively on hazard and, as a result, a need to rely on defaults, there is limited benefit to be gained in developing the exposure analysis such that any increase in certainty is cancelled by uncertainties of greater magnitude associated with quantification of critical hazard, as a basis for a complete risk assessment. 

The benefits associated with hazards analyses have been described in the previous pages. Some of the limitations and concerns to do with such analyses, and with risk analysis in general, are listed below. 

Structures, systems, and components (SSCs) that are important to safety and that are identified as Safety SSCs are based on criteria contained in DOE-STD-3009 (p. xix) and the results of safety analyses, which determine the safety contributions of specific SSCs. The degree of consequence mitigation is the basis for identification of Safety SSCs and associated Safety Functions". These Safety Functions are the essential performance requirements that are imposed on Safety SSC s which maintain the consequences of accident scenarios within bounds that are described in the SAR accident analysis. The use of the term Safety Function will be limited to these essential performance requirements in this SAR. While many SSCs provide a material safety benefit and could be considered to perform a safety function, SSCs that are not relied upon to effect an acceptable outcome will not have an associated Safety Function as the term is used in this S/VR. Safety SSCs and associated Safety Functions are based on the results of hazard evaluation and accident analysis described in Chapter 3, and are specifically identified in Section 3.3.2.3. The specific safety functions important to safety are described in Chapter 4, and form the basis of the derivation of Technical Safety Requirements presented in Chapter 5. 

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