Materials selection for advanced high temperature gas cooled reactors

High temperature gas cooled reactors such as the pebble bed modular reactor expose materials to extreme operating conditions. The selection and qualification of the materials to be used is of prime importance as available materials, in some cases, limit the performance of the design. Current high temperature gas cooled reactor designs are limited to a reactor outlet temperature of ∼900°C, largely owing to the use of qualified metallic materials for structural components. The advent of the advanced high temperature reactor concept, also referred to as the very high temperature reactor (VHTR), to be used as an energy source for both hydrogen production and electricity generation has shown the importance of achieving higher gas outlet temperatures in order to improve cycle efficiency. The reactor outlet temperature for the VHTR could be 1000°C and above. This paper presents an overview of the material selection and qualification actions required for the pebble bed modular reactor demonstration power plant as well as identifying those components for which metallic materials would need to be upgraded or be substituted with non-metallics for VHTR applications.