Assessment and Determination of Key Parameters Impact on Criticality Safety of Ductile Iron Transport Cask

As economic efficiency increases and the demand for spent fuel assembly transportation becomes increasingly pressing, the R&D of spent fuel transport cask assumes vital importance in China. The transport cask is required to meet requirements for shielding safety, criticality safety, decay heat removal, containment, and structural integrity. Etc. during transportation on account of the high radioactivity of spent fuel assemblies. The spent fuel storage rack is an important structure of the transport cask, which mainly affects criticality safety. The rack pitch and 10B surface density of neutron absorber plate are the two main parameters of storage rack. In order to meet the criticality safety and weight requirements, as well as reduce costs, the rack pitch and 10B surface density of neutron absorber plate are assessed and adjusted continuously during the research and development of ductile iron transport cask for loading 21 spent fuel assemblies. The rack pitch is finally determined to adopt a mixed configuration of 268 mm and 300 mm, and the surface density of 1⁰B is 53.0 mg1⁰B/cm2. Under these determined parameters and calculated by Monte Carlo program, taking into account various deviations and uncertainties, when 21 fuel assemblies with an initial enrichment of 4.95% are loaded in the ductile iron transport cask, the \(k_{eff}\) is 0.92590 for the normal operation condition and 0.93203 for the accidental condition, both of which are less than the acceptance criterion of 0.95, and meet the critical safety requirements.