Material Insights · Understanding the Material World

Nuclear fuel transport: How it works

Drums, cylinders and 125-tonne casks: matching package to hazard

What this tab covers How the energy actually moves, step by step: the science that makes it work and the engineering that makes it practical.

Nuclear fuel packs so much energy into so little mass that a few lorries can carry a large reactor's fuel for a year. The engineering challenge is not bulk but safety: containers must stay intact through severe accidents and keep radiation outside them very low.

Step by step

  1. Ship uranium concentrateMined uranium oxide (yellowcake) travels in ordinary industrial drums, because its radioactivity is low; Australia, for example, sends about 50 shipments of 500 containers a year by road and rail to its ports.
  2. Move UF6 to and from enrichmentUranium is converted to uranium hexafluoride (UF6), a solid at room temperature, and carried in thick steel cylinders: the 48Y holds about 12.5 tonnes of UF6 and the 30B about 2.27 tonnes of enriched UF6.
  3. Deliver fresh fuel assembliesFinished fuel rods are shipped in Type A packages, mostly by truck in Western Europe, Asia and the US and mostly by rail in Russia and Eastern Europe. A 1,000 MWe reactor's yearly fuel (about 24 tonnes of enriched uranium) fits in 4 or 5 trucks.
  4. Cool, then load spent fuelUsed fuel is very radioactive and still gives off heat, so it is moved in Type B casks weighing about 80 to 125 tonnes, each holding about 6 to 20 tonnes of fuel.
  5. Haul by rail or dedicated shipCasks are too heavy for normal lorries, so they go by rail (the US Atlas railcar carries up to 218 tonnes) or on purpose-built ships such as PNTL's 104 m vessels, which carry 20 to 24 casks.

The science

Fresh uranium fuel is only weakly radioactive, so its packages need little shielding; the main risk is criticality (an accidental chain reaction), which is prevented by the geometry of the package and by limits on how many go in one shipment. After use, fuel contains fission products that emit intense gamma rays and neutrons and generate decay heat, so casks need thick steel, lead or other shielding and must shed heat through their walls. UF6 is chemically toxic when released, so for UF6 packages the main accident hazard is chemical rather than radiological.

The engineering

Packages are graded by contents: excepted, industrial, Type A, Type B and Type C (for air transport of high-activity material such as plutonium). Type B casks must pass a test sequence: a 9 m (30 ft) drop onto an unyielding surface, a 1 m drop onto a 15 cm steel bar, a 30-minute fully engulfing fire at about 800 C (1,475 F), then immersion under 15 m of water. Sea shipments follow the IMO INF Code (in force since 2001), and the ships are designed to survive a side-on collision with a large tanker.

Key numbers

Radioactive packages shipped worldwide About 15 million a year (WNA also cites about 20 million consignments); about 5% for nuclear power1 48Y UF6 cylinder 122 cm diameter, about 12.5 t UF6 (8.4 t uranium)1 Spent-fuel cask mass About 80 to 125 tonnes, holding 6 to 20 t of fuel1 Type B fire test 800 C (1,475 F) for 30 minutes29 Atlas railcar capacity Up to 218 tonnes (480,000 lb)3 Typical LWR fresh-fuel truckload About 6 tonnes1

Sources

  1. Transport of Radioactive Materials (updated August 2026) World Nuclear Association, 2026
  2. 10 CFR 71.73 Hypothetical accident conditions US Code of Federal Regulations (via Cornell Legal Information Institute), 2026
  3. DOE-designed railcar cleared for use World Nuclear News, 2024
  4. Backgrounder on Transportation of Spent Fuel and Radioactive Materials (updated September 2026) US Nuclear Regulatory Commission, 2026