Casks are used for transport and storage at all stages of the nuclear fuel cycle : fresh and spent fuel assemblies and processed waste are typical cask contents. Casks are also used to transport radioisotopes and radioactive ores and waste liquors.

 

Casks are subject to IAEA regulations for the safe transport of radioactive material. Various aspects of the cask must be considered, including the effectiveness of the cask shielding such that specified maximum external dose-rates are not exceeded, the reactivity of the cask and its contents asuch that the cask is safely subcritical and heat transfer. The cask must meet the criteria laid down both for normal conditions and for accident conditions, which include, amongst others, a drop test and a fire test. Thus comprehensive shielding, criticality and heat transfer assessments are required. Serco Assurance have the expertise and tools to carry out such assessments.

 

Shielding and criticality assessments are performed using the Monte Carlo codes MCBEND and MONK. These allow accurate representation of the cask geometry and use nuclear data in a very fine energy group scheme, thus providing calculations without the geometry and energy approximations inherent in other methods. Shielding and criticality assessments have been carried out for a number of casks, including the TN12 cask and the TK6 cask.