Volcanoes aren't hot enough to melt the zirconium (melting point 3,371˚) that encases the fuel, let alone the fuel itself: The melting point of uranium oxide, the fuel used at most nuclear power plants, is 5,189˚. The liquid lava in a shield volcano pushes upward, so the rods probably wouldn't even sink very deep, Rowe says. They wouldn't sink at all in a stratovolcano, the most explosive type, exemplified by Washington's Mount St. Helens. Instead, the waste would just sit on top of the volcano's hard lava dome—at least until the pressure from upsurging magma became so great that the dome cracked and the volcano erupted. And that's the real problem.