Graphite, Ceramics, and Ceramic Composites for High-Temperature Nuclear Power Systems

Abstract

The age of nuclear power originated with the gas-cooled, graphite-moderated reactor in the 1940s. Although this reactor design had intrinsic safety features and enjoyed initial widespread use, gas-cooled reactor technology was supplanted by higher power density water-cooled systems in the 1960s. However, the next-generation reactors seek enhanced power conversion efficiency and the ability to produce hydrogen, best accomplished with high-temperature gas-cooled systems. Thus, international interest in gas-cooled reactor systems is reemerging. Although the materials systems of these reactors are fairly simple, the reactor environment, particularly its high temperatures and intense irradiation, present extreme challenges in terms of material selection and survivability. This article provides a brief review of materials issues and recent progress related to graphite and ceramic materials for application in gas-cooled nuclear reactor environments. Of particular interest are the drastic, irradiation-induced microstructural evolution and thermophysical property changes occurring as a result of energetic neutron irradiation, which significantly impact the performance and lifetime of much of the reactor core. For “nuclear” graphite, the performance and lifetime not only are closely related to the irradiation environment but also are dramatically affected by the specifics of the particular graphite: manufacturing process, graphitization temperature, composition (amount of coke, filler, etc., depending on where it was mined), and so on. Moreover, the extreme environmental challenges set down by this next generation of fission nuclear plants have driven the development and application of ceramic composites for critical components, pushing beyond upper temperature limits set by metallic alloys used in previous generations of nuclear reactors. The composite material systems of particular interest are continuous carbon-fiber composites and newly developed radiation-resistant silicon carbide fiber composites.

An understanding of lattice strain, defects and disorder in nuclear graphite

“…A number of irradiation damage studies have shown that the initial degree of crystallinity and the crystallite size both play an important role in asymmetrical dimensional and anisotropic property changes induced by fast neutrons in graphite (altering the magnitude and configuration of internal stresses) [4,5]. Consequently, it is important to develop a comprehensive understanding of the change in microstructural behaviour and associated structural parameters that correlate with bulk material property changes under fast neutron irradiation conditions [3,6].…”

Initial assessment of environmental effects on SiC/SiC composites in helium-cooled nuclear systems

“…Their high resistance to intense irradiation condition is an inherent property of the isotropic SiC crystal, which undergoes only modest property changes (swelling, hardness, elastic modulus, strength) in the range of temperatures of interest for high-temperature reactors. 1 In contrast, carbon-fiber composites undergo densification parallel to the fiber axis and swelling on the perpendicular direction, which is caused by the growth of new basal planes from carbon atoms displaced by neutrons in interstitial positions. This difference makes nuclear grade SiC/SiC composites the preferred material over C/C composites for components designed to withstand long-time exposure to intense radiation and elevated temperatures.…”

High Temperature Polymer Nanocomposites

“…14. The applications may be extended to any other field of science and engineering such as the automotives, the ships, thermal and nuclear engineering [10,11] etc.…”

“…20. Nanocomposites such as SiC (Silicon Carbide)/Si 3 N 4 (Silicon Nitride) composites, are another material exhibiting improved strength, creep and fracture toughness [10,11,[27][28][29][30][31][32]. The material retains strength at higher temperatures [21,20] and has good resistance to creep.…”

“…6 Actual microstructure of a SiC-Si3N4 nanocomposite [31] above [33]. The usage of such materials is experimented for various functions like the Multi-functional material or as structures for extreme temperature applications (Nuclear) [10,11] or as sensors in high temperature zones. 23.…”