Development of methods for optimal assembly orificing design and application to a standing-wave Breed-and-Burn reactor

This work investigates different orificing strategies in sodium fast reactors and their application to a reference standing-wave Breed-and-Burn (B&B) core. Through analytic means, the standard method of static integral orificing is shown to be infeasible in the reference core. Using simplified physical models, a novel Mixed-Integer Linear Programming (MILP) formulation is proposed to design whole-core assembly-level orificing schemes according to constraints on various operating conditions, including peak and average temperatures, mass flowrates, flow velocities, and outlet temperature profiles. After highlighting the major assumptions employed and quantifying their impacts, the MILP formulation is used to assess two alternative methods of assembly orificing, namely static grid plate and variable orificing. These two methods of orificing are found to be suitable to B&B cores, and their sensitivities to various constraints are examined. Ultimately the use of variable orificing is found to be the most desirable from the perspectives of flexibility and ability to cope with difficult constraints, although it may be the most difficult of the three methods to implement in a realistic core design.