12.9. The first goal in reactor safety is to prevent accidents from oc­curring. This goal has two aspects. First, the reactor system needs to be designed, constructed, and operated so that the chances of a malfunction or operational error are very small. Since some equipment failures and operational mistakes are inevitable during the service lifetime of such a complex system as a nuclear power plant, the second aspect of the pre­vention goal is to provide “self-healing” features that will cope with such incidents.

12.10. The attainment of a reliable system by conservative design re­quires anticipating possible modes of failure and making provision for them, meeting demanding quality standards, and adhering to applicable regulatory requirements. Details of system design are beyond the scope of this treatment. However, we will examine some accident scenarios, the prevention of which must be demonstrated as part of the licensing pro­cedure. The need for quality assurance is also enforced as a regulatory requirement.