Hydrogen corrosion considerations of carbide fuels for nuclear thermal propulsion applications

Abstract

At reactor operation conditions of interest for nuclear thermal propulsion (NTP), graphiteand carbidebased fuel materials have been known to exhibit a number of life-limiting phenomena. These include the formation of liquid, loss by vaporization, creep and corresponding gas flow restrictions, local corrosion, and structure degradation due to excessive mechanical and/or thermal loading. In addition, the irradiation environment can cause a substantial change in the local physical material properties, which can produce high thermal stresses and corresponding stress fracture (cracking). Time-temperature history and cyclic operation of the nuclear reactor can accelerate some of these processes. Based on results of a review of open literature, available in the U.S., a number of major competing interrelated physical mechanisms were identified that affect hydrogen corrosion of carbide fuel materials. This article identifies and discusses in detail these mechanisms associated with the corrosion of carbide-based materials when exposed to hot hydrogen flow at conditions typical of NTP reactors. From the understanding of this complex phenomena, modeling requirements are then identified and discussed.