External dose rate analysis of the new DN30 package for the transport of UF6

The DN30 package was developed by DAHER NUCLEAR TECHNOLOGIES GmbH (DAHER NT) for the transport of enriched commercial grade and reprocessed UF6 up to an enrichment of 5 %. It consists of a standard 30B cylinder and the DN30 Protective Structural Packaging (PSP) and is licensed as a type AF, IF and B(U)F package. The design and several aspects of the license process were already presented at PATRAM 2013 and 2016. The dose rate analysis of this package is focused on UF6 contents from reprocessed uranium, where the external dose rates are dominated by the source term contribution from daughter nuclides of 232U, especially 208Tl as a hard gamma emitter. Our covering assessment of the source term takes into account the initial 232U content, the build-up and decay of uranium daughters as well as the contributions from impurities like higher actinides and fission products. For 30B cylinders containing heels, further complexity is added to the analysis: the amount of radionuclides remaining in the heels after emptying needs to be assessed as well as the impact of the position and distribution of the heels on the external dose rates. In general, dose rates to be expected at the surface of the package and in 2 m distance from the vehicle are higher for cylinders containing only heels than for full cylinders and might exceed the dose rate limits of the Regulations for some time after emptying. The paper will present an overview of our analysis methods and results for the dose rate assessment of full cylinders and cylinders containing heels. Furthermore, a short outlook on potential design optimizations to improve shielding capabilities will be presented.