As the life of many nuclear power plants are being extended with license renewals, researchers and industry groups are investigating a new cladding material for nuclear fuel rods that seems to offer several benefits over the currently used material.
Specifically, the new material has the potential to last longer, burn more of the fuel in a rod, reduce the amount of radioactive waste that must be stored, and enhance safety margins in certain situations.
The cladding is a ceramic composite material based on silicon carbide. It is intended to replace the zirconium-based metal (called zircaloy) cladding that has been used since the 1950s. And while the zircaloy cladding has had a very good track record of safe use in nuclear reactors, the material becomes susceptible to failure over long times. As a result, fuel rods are often taken out of service even though they may have a substantial amount of fuel remaining to produce energy.
With the new material, silicon carbide fibers would be wound into a composite tube that is the same size and shape as traditional zircaloy cladding. The advantage to using the new material is that silicon carbide has several characteristics that make it well suited to the reactor core environment. It has excellent strength at high temperatures, an order of magnitude less chemical reactivity with water or steam, very low neutron absorption, and resistance to radiation damage, according to researchers at MIT.
As a result, silicon carbide cladding potentially can last longer in a reactor core environment. If this proves to be the case, this would allow more of the fuel in a rod to be burned. And this in turn would reduce the amount of radioactive waste that would need to be managed and stored.
The new cladding is also being eyed to provide an extra margin of safety. In extreme situations, such as happens with there is a loss of reactor coolant or a major seismic event, the current metal cladding can melt or burst. The silicon carbide cladding is potentially more resilient. The material should not burst as the fibers in the ceramic composite are expected to hold together.
There also might be an economic advantage to using the new material. The ability to burn more of the fuel and to have less material to store would naturally factor into any economic justifications for replacing the tried and true zircaloy-cladded rods used today.
There is a great deal of work that must still be done for the new cladding to be used in commercial reactors. Current thought is that evaluation of silicon carbide-cladded fuel rods in commercial reactors could begin as early as 2015. Commercial adoption would be years later.
Investigative and development work into the new cladding is being done by researchers from the Department of Energy, the Energy Power Research Institute, Massachusetts Institute of Technology, Idaho National Laboratory, Oak Ridge National Laboratory, Westinghouse, and other organizations.
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