Fuel element failure

A fuel element failure is a rupture in a nuclear reactor that allows the nuclear fuel or fission products to enter the reactor coolant or storage water.

Because the radioactive metals (such as uranium and plutonium) used in the most common types of nuclear reactors (such as pressurized water reactors and boiling water reactors) are not structurally strong and are susceptible to corrosion, they are formed into fuel elements by shaping them into rods or pellets, then cladding them with a corrosion resistant alloy (such as Zircalloy). Those elements are then assembled into channels for the coolant to flow through. As the fuel fissions, the radioactive fission products are also contained by the cladding, and the entire fuel element can then be disposed of as nuclear waste when the reactor is refueled.

If, however, the cladding is damaged, the fuel and fission products can enter the reactor coolant or storage water and be carried out of the core, into the rest of the reactor plant, drastically increasing radiation and contamination levels.