A basilisk is a mythical creature able to kill with a single glance. Used or “spent” nuclear fuel would have a similar effect, if you were to stand close to it without benefit of shielding: Within a matter of minutes, you would receive a lethal radiation dose. Unlike basilisks, however, spent fuel isn’t out to get you, and is handled and stored safely at every nuclear power station in the United States. In contrast, new fuel that has never been loaded into a nuclear reactor has a very low — almost negligible level of radiation — and can be touched and directly handled without incurring any significant radiation dose.

The smallest unit of nuclear reactor fuel is a fuel pellet, a cylinder of compressed uranium dioxide, enriched to about 3 – 4.5% of the U-235 isotope. Each fuel pellet is less than half an inch in diameter and less than an inch long. Fuel pellets are loaded into a slender tube (called cladding) about 12 feet long, usually made of Zircaloy (a metallic alloy); the sealed tube is called a fuel rod, which looks similar to a wooden dowel. Fuel rods are arranged in an array called a fuel assembly. A boiling water reactor (BWR) has a 7 x 7 or 8 x 8 array of fuel rods running parallel to each other, in an assembly about five and a half inches square, about 14 to 15 feet long, weighing about 600 pounds; a typical boiling water reactor core holds between 500 and 600 such assemblies.

In contrast, a pressurized water reactor (PWR) has larger fuel assemblies that contain significantly more fuel rods — between 14 and 17 per side, though hexagonal arrays also exist — and weigh 1300 lbs or more. A typical pressurized water reactor core holds fewer than 200 fuel assemblies. A few spaces in each assembly are fitted with guide tubes instead of fuel rods, to allow control rods or in-core instrumentation to be inserted.