Examining the Inherent Safety of Prism, Safr, and the Mhtgr

Three advanced design concepts, including two liquid-metal-cooled reactors (LMRs), the Power Reactor Inherently Safe Module (PRISM) and the Sodium Advanced Fast Reactor (SAFR), and a high-temperature gas-cooled reactor (HTGR) are discussed and compared. Each provides inherent or passive safety to improve system safety. The focus is on two primary objectives: reactor shutdown and shutdown heat removal. The LMR and HTGR concepts rely on inherent reactivity feedback to provide an inherent reactor response under a failure-to-scram condition; SAFR also provides a passive shutdown system using Curie point magnets (the self-actuated scram system). For shutdown heat removal, the LMR and HTGR designs rely on passive air cooling of the reactor vessel as the ultimate safety-grade system.