Development and Performance of Metal Fuel Elements for Fast Breeder Reactors

The reduction in projected sodium outlet temperatures for commercial liquid-metal fast breeder reactors has renewed the interest in metal fuels. The U-Pu-Zr or Th-Pu-U-Zr metal fuel pins, sodium bonded to stainless-steel claddings, will yield high burnup along with adequate fuel-cladding compatibility. High burnup capability is assured by designing the fuel element so that interconnected porosity and flssion-gas release occur prior to fuel-cladding contact. Interconnected porosity and fission-gas release take place at about 30% fuel-volume swelling, independent of the metal fuel composition. The U-Fs/Type 316 stainless-steel-clad driver-fuel element used in the Argonne National Laboratory Experimental Breeder Reactor II is designed to take advantage of the phenomenon of interconnected porosity, and burnups in excess of 10 at.% are typically achieved prior to cladding breach. The adequate fuel-cladding compatibility, high burnup potential, superior breeding performance, and demonstrated remote refabrication have made metal fuels an attractive alternative for fast reactor design.