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Part 1 of 2 Parts
        Designing a new type of nuclear reactor is a very complicated undertaking. Years of development and billions of dollars are required. In addition, many different configurations have been proposed for the next generation of commercial power reactors that researchers hope will be safe, economical and efficient. Due to the high cost of actually constructing working models of all the different designs being considered, researchers are employing high performance computers to model and test reactor designs.
    Researchers at the U.S. Department of Energy’s Argonne National Laboratory are running a variety of special programs on the supercomputers that make up the Argonne Leadership Computing Facility (ALCF) which is a DoE Office of Science User Facility. Here researchers from around the world can utilized resources that are only available at a few sites. Emily Shemon is an Argonne nuclear engineer. She said, “We have a good understanding of the laws underpinning reactor physics and thermal hydraulics, so modeling and simulation tools give us the ability to analyze potential reactor designs virtually.”  
      The purpose of the nuclear modeling and simulation activities at Argonne and other such facilities in the DoE’s national laboratory complex is to overcome some of the hurdles faced by the nuclear industry as it considers the design, licensing and deployment of next-generation nuclear power reactors. Shemon says, “The purpose of the labs' modeling efforts is to fill in the knowledge gaps for industry. They may be able to use our codes and models to inform their design decisions if we can do some of the legwork.”
    One major research project at Argonne deals with the modeling of turbulent flows in sodium-cooled fast reactors (SCFRs). SCFRs have attracted researchers for decades because of their promise of greater fuel efficiency and less production of waste than the currently popular and wide-spread light water-cooled nuclear power reactors. One very promising capability of SCFRs is the built-in passive safety features which prevent meltdowns even in cases where all the operational systems of the reactor have failed.
    In SCFRs, as liquid sodium is circulated around fuel elements in the core of the reactor, heat is carried away from the fuel. Warmer sodium rises and cooler sodium sinks which results in a circulation pattern like the old lava lamps and preventing the build up of heat at any one point.
     Very powerful computers are needed to simulate the complex movement of the whorls and eddies of hot and cold liquid sodium in a nuclear reactor core. The computer models are also used to assess the effect of the three-dimensional layout of the reactor and the fuel assemblies on the movement of heat and the flow of the liquid sodium. Alexandr Obabko is an Argonne nuclear engineer. He said, “We try to model turbulence directly, as close to the needed resolution as possible, using supercomputers. We need supercomputers because there are a lot of vortices to model, and because they all contribute to the process of mixing.”
    In order to successfully model the mixing and turbulence in a nuclear reactor, Obabko and his team use a computation coding system called Nek5000 to solve problems involving computation fluid dynamics. Nek5000 is a set of general-purpose fluid mechanics computer modeling tools. It can be used to model vascular flows, aerodynamics, hydrodynamics and the behavior of air flow in internal combustion engines and, of course, liquid sodium in SCFRs.
     There are other computer algorithms which model fluid dynamics but Nek5000 has some advantages over them. Primarily, it cuts the time and cost required for such simulation. Paul Fischer is a computational scientist at Argonne who created Nek5000. He said, “By the time most other codes get to 80 percent of the solution, we're at 90 percent, and that can make a big difference in terms of computing expense.”
Please read Part 2