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Simulated three-dimensional fission power distribution of a single 17x17 rod PWR fuel assembly. | Photo courtesy of the Consortium for Advanced Simulation of Light Water Reactors (CASL).

Simulated three-dimensional fission power distribution of a single 17x17 rod PWR fuel assembly. | Photo courtesy of the Consortium for Advanced Simulation of Light Water Reactors (CASL).

During the first two years of its five-year award, the Consortium for Advanced Simulation of Light Water Reactors (CASL), or “castle” as we call it, has been designing and developing a virtual adaptation of a nuclear reactor core. Our vision is to predict with confidence the safe, reliable, and economically competitive performance of nuclear reactors through science-based modeling and simulation technologies. These predictive technologies will be deployed and applied broadly throughout the nuclear energy enterprise.  

CASL operates as an Energy Innovation Hub that brings together teams of top scientists and engineers from academia, industry, and national laboratories to collaborate and overcome the most critical known barriers to achieving national climate and energy goals -- goals that have proven resistant to solutions via the normal research and development paradigm. 

Our focus is on challenges that originate within reactor vessels (i.e. the reactor core, the reactor vessel itself, and the in-vessel components) of pressurized water reactors (PWR), the most common type of light water reactors (LWR) here in the United States. We study the micro-scale behavior of nuclear fuel during both normal operation and transient conditions. Our research can help identify modifications needed for plant operating processes and fuel designs that will enhance nuclear safety and improve efficiency. CASL’s intent is to advance these capabilities to a level that allows a “what-if” capability, along with the ability to look into a virtually operating reactor up close.

In fact, our CASL “challenge problems” are selected to provide the nuclear power industry with tools for delivering improved performance with enhanced safety. They include a number of safety-related issues, including fuel behavior under accident conditions. Our predictive simulation capability is a key tool for designing more robust nuclear fuel that is tolerant of upset conditions. CASL’s focus on high-precision predictions of the onset and evolution of fuel damage directly supports the analysis of accidents like the one that took place at Japan’s Fukushima Daiichi reactors in 2011.

The simulation legacy at Oak Ridge National Laboratory was established during the Manhattan Project in the 1940s. Modeling and simulation is a backbone in the nuclear industry, perhaps more than in most other science and engineering fields, towards the requiring the construction of costly beta/proto-type facilities for proof of concept and initial licensing. 

Today, with access to the nation’s leading supercomputing facilities, CASL has the virtual capability to look closely at reactor core models operating with 193 fuel assemblies, nearly 51,000 fuel rods, and about 18 million fuel pellets. These elements exist in a high-temperature, high-pressure, high-radiation environment for 3 to 5 years, and our software can simulate these conditions and predict performance.

To improve our fundamental understanding of nuclear fuel behavior, we are developing advanced modeling and simulation capabilities in neutron transport, thermal hydraulics (coolant flow), materials science, structural mechanics, and the mechanism to collectively account for the interactions between them. These new modeling and simulation capabilities, which are being incorporated into our “virtual reactor,” the Virtual Environment for Reactor Applications (VERA), will make it possible to confidently predict nuclear fuel performance under a range of conditions, even with limited experimental observations. 

Where are we today? Having made great strides in only two years, we are continuing on schedule with a passionate sense of urgency. We have an open dialog with industry, and our industry partners are at the table with us executing the plan as part of our team. VERA is now a living, breathing, and promising piece of modeling and simulation technology as a result of our team’s talent and hard work.

We have established a culture and cadence within CASL that is attracting and challenging the best and brightest scientists and engineers. We truly believe we can and will make a difference. 

With CASL we have made the hub concept a reality, where “we” is a fantastic multidisciplinary team addressing critical challenges to the nuclear power industry through modeling and simulation.

What a ride it’s been so far!