Nuclear reactors are among the most powerful and efficient energy sources known to man, but like anything dealing with large amounts of energy, failures can be catastrophic. For decades researchers and engineers have been working to minimize the likelihood of these failures, most especially after an incident, such as the one in 2011 at the Fukushima Daiichi plant. Now a safety measure that has been considered for years is being more closely examined by researchers at MIT, to determine just how effective it may be.
Nuclear fission reactors operate by placing enough uranium close together that the natural emission of neutrons from one atom stimulates neutrons in other atoms to also be emitted. This chain reaction releases a great deal of heat, which is used to boil water into steam and turn a turbine. The uranium is actually in small pellets not much larger than a pencil eraser or two, and these pellets are stacked together in tubes of zirconium alloy, or zircalloy. While zircalloy does its job pretty well during normal operation, if systems fail and the reaction heats it too much, it will react with the water to create hydrogen gas, a potential explosive.
For some time researchers have been suggesting silicon carbide, a ceramic, be used to replace zircalloy, as it is a thousand times less reactive with water. The MIT researchers are the first to perform the necessary and extensive tests needed before the industry can adopt it. So far the results are promising, with the ceramic holding up very well at normal operating temperatures, and the more stressful conditions that would occur during an accident. Being a ceramic though, it presents two issues. First, how ceramics fail is not as well understood as how metals fail, and second, you cannot weld ceramics to place caps on the rods. Both of these issues will have to be dealt with for silicon carbide to ever be used.