49 CFR § 173.418 - Authorized packages - pyrophoric Class 7 (radioactive) materials.
Pyrophoric Class 7 (radioactive) materials, as referenced in the § 172.101 table of this subchapter, in quantities not exceeding A2 per package must be transported in DOT Specification 7A packagings constructed of materials that will not react with, nor be decomposed by, the contents. Contents of the package must be -
(c) Free of water and contaminants that would increase the reactivity of the material; and
(d) Inerted to prevent self-ignition during transport by either -
(1) Mixing with large volumes of inerting materials, such as graphite, dry sand, or other suitable inerting material, or blended into a matrix of hardened concrete; or