Radiation protection studies regarding the transportability of secondary source assemblies with a TN13/2 shipping cask.

As part of the startup of the PALUEL-2 PWR, a transport of active SSAs (secondary source assemblies) was recently carried out with a TN13/2 shipping cask (designed and operated by ORANO TN), commonly used to transport depleted fuel assemblies.Due to the extended shutdown of the PALUEL 2 PWR, its SSAs were expected not to be active enough to ensure appropriate neutron counting during the startup. This lead EDF to organize a project to transport active SSAs from other power plants towards PALUEL-2.As part of this project, radiation-protection studies regarding the transport and exploitation of a TN13/2 loaded with two SSAs were carried out.Best-estimate shipping cask models based on those previously developed by the research department PERICLES for depleted fuel transportation were adapted by describing the SSAs and the additive shielding elements needed for the transport (dummy fuel assemblies loaded with lead and Al-B4C shielding bars). Simulations were carried out using the radiation propagation Monte Carlo code TRIPOLI-4®, developed by the French atomic commission (CEA). Dose rates were computed around the shipping cask using different hypotheses on the additive shielding elements and a wide range of cooling time of the SSAs.Results show that the transport of 2 SSAs respects the transport dose-rate limitations without any additive shielding element if the SSAs are cooled at least 120 days after core shutdown. In the case which warmer SSAs need to be transported, we demonstrate that using dummy fuel assemblies loaded with lead and Al-B4C shielding bars allow to transport 20-day cooled SSAs with comfortable margins regarding the dose-rate limitations.Simulation of an exploitation configuration also show that dose rates around the shipping cask are lower than those computed for a standard depleted fuel evacuation in a close configuration.Finally, dose rate measurements carried out during the transport of 2 SSAs towards PALUEL-2 present a good agreement with the simulation, which validates the quality of these studies. By consolidating the safety demonstration and helping evaluate the operators’ dosimetry, this work contributed to successfully plan and carry out the project.