Literature Review of Preliminary Initiating Events for a Gas-Cooled Fast Reactor Conceptual Design

One of the few gas-cooled fast reactor (GFR) concepts being investigated within the United States is the General Atomics Electromagnetic Systems’ fast modular reactor (FMR). As a first step in developing the safety case for the FMR, a comprehensive range of potential accident initiators should be identified. To characterize the breadth of the initiators that could occur in GFRs, a literature review was performed to identify preliminary initiating events (PIEs) relevant to GFRs, with an emphasis on those initiators relevant to the FMR design.

For the review, PIEs were defined as deviations from normal operating conditions that could lead to undesired plant states and represent the beginning of potential accident sequences. The literature review included events meeting the definition of PIEs that had previously been identified and analyzed for GFRs, high-temperature gas-cooled reactors, very high–temperature reactors, and commercial gas-cooled reactors.

A total of 124 references were evaluated and 549 unique PIEs were identified. The most frequently assessed PIEs in the literature were categorized as loss-of-coolant accidents (LOCAs) and flow-related transients. Repeated treatment of these accident types, especially LOCAs, within the literature emphasizes the importance, and due analysis, of potential depressurization events in a GFR’s safety case, since such events can have potentially important downstream effects in some designs. Less emphasis was observed on initiating events associated with helium purification systems and external events, which also have the potential to challenge plant safety, and therefore may require further evaluation to support safety case development for GFRs, and the FMR specifically.