1 Introduction

The supercritical water-cooled reactor (SCWR) is one of the six innovative reactor concepts selected by the Generation IV International Forum for collaborative development. This chapter introduces the SCWR concept, providing historical context for the materials and water chemistry challenges that must be resolved to take the concept from the feasibility stage to a prototype. The various synergies that exist between the SCWR and other engineering processes that use supercritical water, namely supercritical fossil power plants and supercritical water oxidation, are discussed, as are the differences in conditions between these systems and the SCWR. Materials requirements are presented, and candidate alloys for use in an SCWR core are introduced.