The failure of fuel cladding in damaged reactors at Fukushima Daiichi has led to renewed research interest in ceramics as a potential replacement for the zircaloy cladding used in commercial fuel assemblies.
Under extreme accident conditions, zircaloy can react with steam in a way that produces hydrogen – the cause of multiple explosions at Fukushima. As an alternative, research published in this month's issue of Nuclear Technology, a journal of the American Nuclear Society, explored the resilience of silicon carbide and found superior performance under simulated operating and accident conditions.
According to a release from the Massachusetts Institute of Technology, "Characteristics of Composite Silicon Carbide Fuel Cladding After Irradiation Under Simulated PWR Conditions" (subscription) evaluated samples of the material irradiated in a research reactor. The samples showed low neutron absorption and good strength retention during mechanical testing. High-temperature oxidation studies showed that silicon carbide's strength remains constant at temperatures in excess of 1,500 C, according to the release. That is in contrast to zircaloy, which becomes progressively weaker when exposed to extreme heat and loses all strength at about 1,300 C.
Though the results were promising, researchers led by MIT's Mujid Kazimi emphasized that their findings are preliminary. A commercial application for silicon carbide fuel cladding would require extensive further testing of the material's response to various conditions present inside a working power reactor, as well as research into optimal cladding design.