Assessing regulatory requirements and guidelines for the Single Failure Criterion (Research Project R557.1)

1.0	Background

The safety analysis of a nuclear power reactor is a complex undertaking. Within this analysis, a criterion (or requirement) is applied to a safety system such that the system must be capable of performing its task in the presence of any single failure; this requirement is commonly referred to as the Single Failure Criterion (SFC).

The capability of a system to perform its design function in the presence of a single failure could be threatened by a common cause failure such as a fire, flood, or human intervention. In a postulated design-basis initiating event, the SFC requires that each safety system performs all safety functions as designed, and mitigates all of the following:
1.	All failures caused by a single failure. 
2.	All identifiable but non-detectable failures, including those in the non-tested components. 
3.	All failures and spurious system actions that cause (or are caused by) the postulated event. 
Requirements for SFC are currently addressed in CNSC regulatory documents REGDOC-2.5.2, Design of Reactor Facilities: Nuclear Power Plants, and RD-367, Design of Small Reactor Facilities.

2.0	Objectives

The objective of this project is to recommend regulatory design requirements for new reactors that shall address Single Failure Criterion best-practice, particularly as it relates to in-service testing, maintenance, repair, inspection and monitoring of systems, structures and components important to safety.