The special packages in which PNTL transports nuclear material are called “flasks” or “casks”. They are typically made from 25 cm thick forged steel and weigh around 100 tonnes. They can hold up to five tonnes of nuclear material.
The casks facilitate the movement of nuclear material by different modes of transport, protect workers from radiation, dissipate heat efficiently and are designed to withstand severe accidents.
Casks are monitored for radiation prior to loading onto PNTL ships and during transportation. They are thoroughly cleaned and inspected in maintenance facilities after each shipment.
Cask lids can only be attached and removed using specialist equipment at nuclear facilities.
The casks transported by PNTL belong to customers. Each cask design has to meet safety requirements established by the International Atomic Energy Agency (IAEA) in order to be licensed by national regulatory bodies.
The IAEA has set standards for packages based on the characteristics of different types of nuclear material. PNTL’s cargoes of used fuel, vitrified waste and MOX fuel must be moved in “Type B” packages. These special packages must be able to withstand a series of challenging tests that demonstrate resistance to severe impact, fire and immersion.
IAEA tests
Each cask design must be able to withstand the following tests, which are performed one after the other.
- Two drop tests, one onto a reinforced concrete and steel spike and the second onto an unyielding surface from a height of nine metres. The unyielding surface simulates real impacts from far greater heights onto rock or soil.
- An all-engulfing fire of 800 degrees Celsius for 30 minutes. The all-engulfing test is far more destructive than real fires that may reach higher temperatures.
- Immersion in 15-200 metres of water, depending on the type of material the cask is designed to transport. In fact, casks carried by PNTL are able to survive in several thousands of metres of water.
After these tests have been performed in sequence, the cask design must maintain its integrity to be approved for use.