Modelling simplifications in flask shielding

Flask shielding calculations are required to predict the dose rates external to the flask package. The flask package must endure that the radiation levels are within the regulatory limits specified for the transportation of radioactive material. Modelling the geometrical heterogeneities in the flask design, such as neutron moderators embedded in the flask wall are often simplified for rapid solution/sensitivity studies for flask shielding problems. Examples of modelling simplifications used in flask shielding studies are described. The results presented show that the simplified approach may, in certain cases, under-predict the external dose rates compared with explicit modelling. (author)