• fusion reactor
• thermo-mechanical
• TBM
• pebble bed
• ITER
• Breeding Blanket

The thesis analyzes the thermo-mechanical behavior of the Breeder Unit (BU). The BU is a component of the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM). The HCPB-TBM has been historically developed for two decades in KIT as reference breeding blanket concept for the DEMO reactor (next step after ITER). The HCPB TBM will be tested in ITER with 5 other breeding blanket concepts with the aim to determinate the tritium breeding, the capability to extract heat for electricity production and the shielding capability. The breeder is made of Lithium Orthosilicate (OSI), while the Beryllium is used as neutron multiplier. Both these materials are used in form of pebble beds and are accommodated inside a box structure called Breeder Units. The structural material is a ferritic martensitic steel, namely the Reduced Activation Ferritic Martensisitc Steel EUROFER. The TBM is cooled by helium. Intense studies and changes of the BU design were performed in the last years with the goal to improve thermo-mechanical behavior. Design temperature limits of beryllium and OSI have been defined in order to assure a low Tritium Residence Time (TRT) and to avoid damage of the pebble beds. The Helium outlet temperature is a key design parameter in order to demonstrate the possibility to achieve efficient heat conversion : Helium temperature at the TBM outlet should be around 500°C. Eurofer operational temperature range is defined in order to avoid creep or embrittlement under irradiation. The thesis illustrates steady state thermal analyses of the BU performed in order to check the temperature reached in each material. Parametric and mesh sensitivity studies have been carried out in order to determinate the model behavior and to verify the design limits of the BU. Transient thermal analysis has been carried out in order to analyze the BU thermal performance considering loading conditions simulating the ITER pulses. Structural analyses have been carried out on a simplified model of the BU Cooling Plates (CPs). CPs are made of Eurofer and cooled by Helium and they have the structural function to separate OSI and Beryllium pebbles in the BU. Two different simulations have been carried out in order to evaluate primary and secondary stresses on the CPs. The results have been compared with the allowable stress limits indicated in the reference design standards RCC-MR and SDC-IC . Thermal and structural analyses carried out with the Finite Element commercial code ANSYS have been compared with theoretical approaches.