Safety during transport is of paramount importance. The four safety functions that a flask must provide are:
| Safety Function | Requirement |
|---|---|
| Containment | Protection against impacts, drops, or other external threats --- the radioactive contents must not be released |
| Shielding | Transport workers and members of the public must not be exposed to excessive gamma radiation |
| Criticality safety | The fuel must not achieve a critical configuration under any credible circumstances |
| Heat removal | The flask design must permit adequate removal of decay heat to prevent overheating |