Dr. Conca reports that the wrong kitty litter was probably used to treat some of the nuclear waste recently disposed at the WIPP site near Carlsbad in New Mexico in the only deep underground nuclear waste repository in the world, other than in Sweden.
Cat litter has been used for decades in radiochemistry labs and nuclear facilities to stabilize certain radioactive wastes, like liquid scintillation solutions, evaporator bottoms, and other materials that have nitrate salts in solution.