FIRST NEUTRONIC EVALUATION OF A HIGH TEMPERATURE SODIUM COOLED REACTOR

The focus of this work is to perform an initial neutronic assessment of a Sodium- Cooled High-Temperature Reactor (HTR-Na cooled). This involves the development of a deterministic calculation schemes, followed by a detailed physical analysis and the formulation of some design proposals. The concept of the HTR-Na cooled draws inspiration from the Japanese High Temperature Test Reactor (HTTR), a High-Temperature Gas Reactors (HTGRs). The key objective is to downsize the reactor by employing liquid sodium as a coolant to replace the helium, while simultaneously arising the power core to collecting thermal energy for industrial application as the hydrogen generation. The work is divided into three main parts: first the construction of the assembly calculation scheme, then a comprehensive physical analysis at lattice level and finally the core calculation scheme. The evaluations are carried out using the CEA’s deterministic codes APOLLO2® and APOLLO3®. The assembly calculation scheme includes the static and the depletion calculations. Through the use of Method of Characteristics (MOC), the transport equation is solved allowing a detailed analysis of the reactor behaviour. Various neutronic parameters are studied, including reactivity, temperature coefficients for fuel, moderator and coolant both at beginning and end of fuel life and the cycle length. Different assembly designs are considered, assessing their behavior at the lattice level by altering geometrical parameters and properties. The analysis highlights significant aspects, particularly the impact of packing fraction, which represents the ratio between the volume occupied by the TRi-stuctural ISOtropic (TRISO) particles and the graphite matrix. Results indicate how this geometrical parameter influences the overall behavior of the fuel assembly. Additionally, other findings provide insights into the general reactor behavior at the assembly level. Next, core calculations are performed and compared with the preliminary core analysis performed from the assembly calculation to predict core behaviour.