Irradiated fuel assemblies—essentially bundles of fuel rods with zirconium alloy cladding sheathing uranium dioxide fuel pellets—that have been removed from a nuclear reactor (spent fuel) generate a great deal of heat from the radioactive decay of the nuclear fuel’s unstable fission products. This heat source is termed decay heat. Spent fuel is so thermally hot and radioactive that it must be submerged in circulating water and cooled in a storage pool (spent fuel pool) for several years before it can be moved to dry storage.

The dangers of reactor meltdowns are well known. But spent fuel can also overheat and burn in a storage pool if its coolant water is lost, thereby potentially releasing large amounts of radioactive material into the air. This type of accident is known as a spent fuel pool fire or zirconium fire, named after the fuel cladding. All commercial nuclear power plants in the United States—and nearly all in the world—have at least one spent fuel pool on site. A fire at an overloaded pool […]