Phenomena Identification and Ranking Tables (PIRTs) for 4S. Loss of offsite power, failure of a cavity can, and sodium leakage from intermediate piping scenarios

The 4S (Super-Safe, Small and Simple) is a small liquid-metal-cooled fast reactor, which, in combination with power generation equipment, is designed as a power source for remote locations and is intended to operate for 30 years without refueling. The 4S project plans to apply for Design Approval (DA) to the U.S. Nuclear Regulatory Commission (USNRC). The purpose of this work is to develop Phenomena Identification and Ranking Tables (PIRTs) that explain importance and state of knowledge of phenomena relevant to the 4S, and that help develop and guide the priority and scope of programs for further investigation that will be required for the 4S DA process. Such programs include testing and theoretical evaluations, including analyses using Computational Fluid Dynamics (CFD) codes. Such investigation will be performed to confirm and improve the state of knowledge of important safety-related phenomena. These PIRTs are reviewed by independent experts to help ensure their quality. This work has been developed using typical industry PIRT procedures as have evolved from previous work. It addresses the following three events selected from representative ones for the 4S that capture a large spectrum of initiating events and accident sequences: 'Loss of Offsite Power,' 'Failure of a Cavity Can' and 'Sodium Leakage of Intermediate Piping.' These PIRTs also define and justify the choice of cladding temperature as a key Figure of Merit. Then, they identify plausible phenomena for each event, and rank the relative importance and state of knowledge for each phenomenon. In this ranking step, sensitivity studies are performed to refine the results. These results will be used to establish the priority for further investigation after being classified into five groups in accordance with a combination of the relative importance and state of knowledge rankings of the phenomena. Ultimately, 16 phenomena with highest priority are selected as objects of further investigation. (author)