Nuclear Thermal Propulsion ( NTP ) is under consideration for potential use in deep space exploration missions due to desirable performance properties such as a high specific impulse ( > 850 seconds ) . Tungsten ( W)-60vol%UO2 cermet fuel elements are under development , with efforts emphasizing fabrication , performance testing and process optimization to meet NTP service life requirements [ 1 ] . Fuel elements incorporate design features that provide redundant protection from crack initiation , crack propagation potentially resulting in hot hydrogen ( H2 ) reduction of UO2 kernels . Fuel erosion and fission product retention barriers include W coated UO2 fuel kernels , W clad internal flow channels and fuel element external W clad resulting in a fully encapsulated fuel element design as shown .