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May 9, 2011

Oak Ridge Supercomputers Modeling Nuclear Future

Nicole Hemsoth

During the annual televised “State of the Union” address at the beginning of 2011, Barak Obama sought to renew the national focus on science and technology, in part by using supercomputing capabilities to drive progress.

To highlight the role of HPC in the new generation of scientific endeavors, the President told millions of Americans about how supercomputing capabilities at Oak Ridge National Laboratory (ORNL) will lend the muscle for a Department of Energy initiative “to get a lot more power out of our nuclear facilities” via the Consortium for Advanced Simulation of Light Water Reactors (CASL).

This speech came well before the word “nuclear” was (yet again) thrown into the public perception tarpit by the Fukushima reactor disaster, otherwise it might be reasonable to assume that there would be more attention focused on the safety angle that complements the CASL’s nuclear efficiency and waste reduction goals. Outside of the safety side of the story, another, perhaps more specific element to his national address was missing — that the power of modeling and simulation — not just high performance computing — might lie at the heart of a new era for American innovation.

To arrive at an ambitious five-year plan to enact a number of design and operational improvements at nuclear facilities, CASL researchers are developing models that will simulate potential upgrades at a range of existing nuclear power plants across the United States that will seek to address a number of direct nuclear facility challenges as well as some pressing software challenges that lie at the heart of ultra-complex modeling at extreme scale.

Despite some of the simulation challenges that are ahead for CASL, the payoff for the DOE’s five-year, $122 million grant last May to support this and two other innovation hubs could be significant. According to the team behind the effort, “these upgrades could improve the energy output of America’s existing reactor fleet by as much as seven reactors’ worth at a fraction of the cost of building new reactors, while providing continued improvements in reliability and safety.”

Director of Oak Ridge National Laboratory, Thom Mason, pointed to the power of new and sophisticated modeling capabilities that “will provide improved insight into the operations of reactors, helping the industry reduce capital and operating costs, minimize nuclear waste volume, safely extend the lifetime of the current nuclear fleet and develop new materials for next-generation reactors.”

The CASL has been designed with the goal of creating a user environment to allow for advanced predictive simulation via the creation of a Virtual Reactor (VR). This virtual reactor will examine key possibilities and existing realities at power plants at both the design and operational level. CASL leaders hope to “produce a multiphysics computational environment that can be used for calculations of both normal and off-normal conditions via the development of superior physical and analytics models and multiphysics integrators.”

The CASL team further claims that once the system has matured, the VR will be able to combine “advanced neutronics, T-H, structural and fuel performance modules, linked with existing systems and safety analysis simulation tools, to model nuclear power plant performance in a high performance computational environment that enables engineers to simulate physical reactors.”

Many of the codes will employ a number of pre-validated neutronics and thermal-hydraulics (T-H) codes that have been developed by a number of partners on the project, including a number of universities (University of Michigan, MIT, North Carolina State and other) as well as national laboratories (Sandia, Los Alamos, and Idaho).

During the first year CASL will be able to achieve a number of initial core simulations using coupled tools and models — a goal that they have reached for the most part already. This involves application of 3D transport with T-H feedback and CFD with neutronics to isolate core elements of the core design and configuration. In the second year the team hopes to be able to apply a full-core CFD model to calculate 3D localized flow distributions to indentify transverse flow that could result in problems with the rods.

According to a spokesperson for ORNL, making use of the Jaguar supercomputer, CASL will allow for large-scale integrated modeling that has only been possible in the last few years.” The challenge is not simply how to use these new capabilities, but how to make sure current programming and computational paradigms can maximize its use.

A document that covers the goals of CASL in more depth sheds light on some of the computational aspects of these massive-scale simulations. The authors note that “a cross-cutting issue that will impact the entire range of computational efforts over the lifetime of CASL is the dramatic shift occurring in computer architectures, with rapid increases in the number of cores in CPUs and increasing use of specialized processing units (such as GPUs) as computational accelerators. As a result, applications must be designed for multiple levels of memory hierarchy and massive thread parallelism.”

The authors of the report go on to note that while they can expect peak performance at the desktop to be in the 10 teraflop range and the performance at the leadership platform to be in the several hundred petaflop range, during the next five years, “it will be challenging for applications to achieve a significant fraction of these peak performance numbers, particularly existing applications that have not been designed to perform well on such machines.”

Another one of CASL’s stated goals has to do with the future of modeling and simulation-focused research. The team states that they hope to “promote an enhanced scientific basis and understanding by replacing empirically based design and analysis tools with predictive capabilities.” In other words, by harnessing high performance computing to demonstrate actual circumstances versus reflect the educated hopes of even the most skilled reactor engineers, we might be one step closer to fail-proof design in an area that will allow for nothing less than perfection.

CASL could have a chance to see its models and simulations leap to life over the course of the first five years of the project. Currently the Tennessee Valley Authority operates a total of six reactors that generate close to 7,000 megawatts. The agency is currently embarking on a $2.5 billion journey to create a second pressurized water reactor at one of its existing facilities. This provides a perfect opportunity for the CASL team to put their facility modeling research to work; thus they’ve started creating simulations focused on the reactor core, internals and the reactor vessel.

CASL claims that “much of the virtual reactor to be developed will be applicable to other reactor types, including boiling water reactors.” They hope that during the subsequent set of five-year objectives they will be able to expand to include structures, systems and components that are outside of the vessel as well as consider small modular reactors.