Silicon carbide was hot-pressed to uniform densities of the order of 98% of the theoretical density, with slight additions of aluminum and iron aiding in this densification. Other elements having some effect were lithium, calcium, chromium, zirconium, and boron. This dense silicon carbide had very high strength at high temperatures ; for example, it had a modulus of rupture of 70,000 lb. per sq. in. at 2500°F.

This paper was prepared for the 1991 Kroll Award. A review is presented of the development of barrier fuel. It includes the recognition of the pellet-cladding interaction (PCI) fuel failure mode and of a coordinated program to develop understanding, mitigating strategies, and a fuel that is resistant to this failure mode. The efforts to understand PCI led to the conclusion that the dominant mechanism is stress-corrosion cracking of the Zircaloy. The invention and development of zirconium-barrier fuel was intended to provide a materials solution to this fuel failure mode. This review includes the work to understand the failure mechanism as well as the program to develop PCI-resistant fuel designs. Ultimately, the zirconium-barrier fuel was tested in power ramps to ascertain and to quantify the resistance to PCI under expected service conditions in commercial boiling water reactors (BWRs). The program that led to a large-scale demonstration in a commercial power plant (Quad Cities-2) is described briefly. Subsequent to that, program work continued with in-reactor load following and experiments in a test reactor on power cycling of barrier fuel. Finally, the performance of failed fuel is discussed briefly.