An unusual twist in the multibillion-dollar battle between the federal government and utility companies over spent nuclear fuel threatens to send more than 50 breach-of-contract lawsuits back to square one after a decade of litigation.

This week, the full U.S. Court of Appeals for the Federal Circuit will hear arguments on whether the government, for the first time, can argue “unavoidable delay” to excuse its failure to pick up and dispose of the industry’s nuclear waste.