Some fuel pellets are made from cermets which is ceramicmeta

Some fuel pellets are made from cermets (which is ceramic-metal composite) Explain how this might improve the pellets ability to conduct heat if the thermal conductivity of the ceramic is poor

Solution

Cermets are composites in which ceramic materials and metals join together, typically to give something with the high temperature performance or wear resistance of a ceramic and the toughness, flexibility, or electrical conductivity of a metal.

Metal fuels have the advantage of a much higher heat conductivity than oxide fuels but cannot survive equally high temperatures.

Metal fuels have the potential for the highest fissile atom density. Metal fuels are normally alloyed, but some metal fuels have been made with pure uranium metal. Uranium alloys that have been used include uranium aluminum, uranium zirconium, uranium silicon, uranium molybdenum, and uranium zirconium hydride.

Ceramic fuels other than oxides have the advantage of high heat conductivities and melting points, but they are more prone to swelling than oxide fuels and are not understood as well

Ceramics are brilliant at high temperatures and able to resist attack by chemicals and things like oxygen in the air, but their sheer inertness means they\'re just pretty boring most of the time. Brilliant for teapots and false teeth, but fairly hopeless when it comes to doing interesting things like conducting electricity or heat or bending and flexing. If you want something that can survive in really tough environments and still behave in interesting ways, you need to switch your attention to things like alloys, composites—and cermets.

\"Cermet\" is a generic name for a whole range of different composites. Sometimes the ceramic is the biggest ingredient and acts as the matrix (effectively the base or binder) to which particles of the metal are attached. Cermets used for electrical applications are typically made this way (in other words, they are examples ofceramic matrix composites or CMCs). But the metal component (typically an element such as cobalt, molybdenum, or nickel) can also be the matrix, giving what\'s called a metal matrix composite (MMC), in which hard ceramic particles are held together by a tough but ductile metal. Cermets used in things like cutting tools are made this way.

Like other composites, cermets \"work\" by producing a material with a microstructure that has certain things in common with each of its different constituents.

For example, the metal ingredient effectively allows electrons to flow through the material, enabling what would otherwise be a ceramic insulator to conduct electricity. That suggests cermets are relatively stable structures in which the metal and the ceramic are fixed in place—but that\'s not always the case. Under some conditions, cermets behave as though they have a dynamic surface layer, with metal particles constantly detaching and reattaching themselves. This effectively forms a smoother, harder, and more wear-resistant upper layer that makes a metal behave more like a ceramic.

CerMet fuel consists of ceramic fuel particles (usually uranium oxide) embedded in a metal matrix. It is hypothesized, that this type of fuel is what is used in United States Navy reactors. This fuel has high heat transport characteristics and can withstand a large amount of expansion