Risk Assessment

DOE-STD-6003-96

mandatory for establishing the design basis. Each of these topics associated with the SAR

process is discussed in the following subsections.

5.5.1 Risk Assessment

The level of detail of the risk assessment performed for a fusion facility is dependent on

the potential risk that is associated with the facility. For facilities with large-consequence off-

normal conditions, a more detailed quantitative risk assessment [e.g., a probabilistic risk assess-

ment (PRA)] should be required. However, a complete and accurate risk assessment, for

example, a PRA, in which the true risk is very close to the analysis may be difficult to perform

because of the lack of failure data for some unique components and because relatively few

PRAs have been performed to date for these types of facilities. When failure rate data are not

available, conservative estimates of failure rates should be assumed and used in the evaluation.

Also, conservative estimates should be made regarding the operability of safety systems. Risk

assessment performed on the facilities with low hazards should include, as a minimum, the

probability of occurrence and predicted consequences of hazards expressed in qualitative

terms. Quantitative results should be used unless no data or information are readily available.

For a facility categorization, the minimum requirement is to provide a general qualitative

approach to categorize facility risk. An example of the minimum approach that could be used is

presented in DOE-STD-3009-94 (DOE 1994).

The required quantification of risk is determined from a knowledge of the probability of

the event and of its potential consequences. If potential consequences could have a significant

effect on the public or the environment, a quantitative evaluation of the risk would be required.

For lesser consequences, the risk could be evaluated on a qualitative basis. The level of quan-

tification of the risk is directly proportional to the potential magnitude of the consequences. The

risk quantification will assist in identifying the critical components in the design and the SSCs

that would be the most beneficial in mitigating off-normal condition consequences. The worker

risk should be evaluated in a qualitative manner in accordance with guidelines of DOE-STD-

3009 (DOE 1994).

The following guidelines are provided for the risk assessment required for fusion facilities

having the indicated hazard categories:

a. Hazard Category 1--Perform a detailed risk analysis (e.g., PRA type analysis) using

available data and conservative extrapolations of similar data sources. The results

should be quantitative in nature and identify the significant contributions to the overall

risks. They may also include sensitivity studies to show uncertainties in data and other

parameters in the analysis if the required data are available. The risk analysis should

be quantitative in nature and identify the significant contributions to the overall risks.

b. Hazard Category 2--Ensure that the risks associated with the on-site workers are

adequately identified. The risk could be established, as a minimum, in a qualitative

manner.