4.07.1 Introduction

Silicon carbide (SiC) has been studied and utilized in nuclear systems for decades. Its primary use was, and still is, as the micro pressure vessel for high — temperature gas-cooled reactor fuels. For these so-called TRI-ISOtropic (TRISO) fuels, the SiC is deposited via a gas-phase decomposition process over two layers of pyrolytic graphite surrounding the fuel kernel. In addition to being strong enough to with­stand the pressure buildup from the fission product gas liberated, this SiC layer must also withstand chemical attack from metallic fission products such as palladium and the mechanical loads derived from irradiation-induced dimensional changes occurring in the pyrolytic graphite. More recent nuclear appli­cations of SiC include its use as structural composites

(i. e., SiC/SiC) for high-temperature gas-cooled reac­tors and for fusion power systems. The possibility of using composite and monolithic SiC thermal insula­tors for both fusion and fission systems is also being investigated. Moreover, both monolithic and compos­ite forms of SiC are being investigated for use in advanced sodium fast, advanced liquid salt-cooled, and advanced light water reactors.

In this chapter, the effects of neutron irradiation on relatively pure, radiation resistant forms of SiC are discussed. This chapter has been limited to the effects of irradiation on the microstructure, and the mechanical and thermal properties of SiC, although it is recognized that environment aspects such as oxida­tion and corrosion will also be factors in eventual nuclear application. These areas are not discussed here.