The full ‘Safety in Depth’ system encompasses the material itself, canisters, assemblies, special packages called ‘casks’ or ‘flasks’ and the protection provided by the reinforced double hulls of the PNTL fleet.
Together, these provide a series of independent barriers between the radioactive material and the outside environment.
This safety system provides much greater protection than typically exists for other hazardous cargoes such as chemicals, oil and liquid gases, which are shipped far more frequently. It also removes reliance on specialist emergency assistance being available from countries adjacent to shipping routes.
Professor H.W. Lewis, a former Chairman of the United States Nuclear Regulatory Commission (NRC) Risk Assessment Review Group wrote with regard to PNTL shipments of vitrified waste that:
‘An accident of any kind is unlikely to happen… and the environmental damage done by any conceivable accident would be thousands of times less than that done by a single oil spill.’