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Supercomputer’s ‘Virtual Reactor’ Models Reactor Start-Up Process

Sept. 3, 2013—A supercomputer that can keep track of several billion computational elements at the same time and can virtually mimic the workings of a nuclear reactor core is aiding researchers in studying reactor operations and performance.

Scientific computing platforms, from high-end desktop systems to supercomputers, are some of the unsung superstars of science, helping researchers model complicated phenomena in a virtual environment before new practices are tested in the real world.

Nuclear scientists and engineers also use these machines to test new ideas in much the same way that the aerospace industry tests the performance of new wing designs in virtual wind tunnels or medical researchers insert new molecules into drugs to learn how their properties might change. The biggest and fastest supercomputers are given the toughest tasks: running simulations of complex systems such as cellular membranes, the inside of diesel engines and the earth’s global climate.

One of the world’s fastest, Oak Ridge National Laboratory’s Titan supercomputer, addresses all these challenges. Perhaps its biggest test is a project to simulate the complex physical environment inside a nuclear reactor’s core.

A team at Oak Ridge’s Consortium for Advanced Simulation of Light Water Reactors (CASL) is using the supercomputer to design a “virtual reactor” called VERA (Virtual Environment for Reactor Applications) to model the inner workings of a typical pressurized water reactor similar to Tennessee Valley Authority’s Watts Bar reactor 1 in Spring City, Tenn., 60 miles from Oak Ridge.

One of the project’s recent tasks involved comparing the Watts Bar reactor data with simulation data obtained using the VERA model.

“Our simulation technology must be capable of resolving sub-millimeter phenomena over the whole reactor core,” said CASL Director Douglas Kothe. “[In a reactor such as Watts Bar 1] you have 51,000 fuel rods in 193 different fuel assemblies. Each fuel assembly has intricate grids that hold the rods in position and direct the fluid to extract heat from the rods.”

Kothe explained that VERA‘s software components implement advanced mathematical models replicating the physical processes in play inside the reactor core.

“Some of these are neutron transport, thermal hydraulics, nuclear fuel performance, corrosion and surface chemistry,” said Kothe. The interactions among these processes must also be modeled accurately.

Titan’s massive computational power allows researchers to forego some of the approximations in current industry models of the reactor core.

“A full core simulation in which the core volume is partitioned into several billion small computational elements is now possible,” Kothe said.  

VERA recently passed an important milestone, recreating the start-up test (also known as a zero-power physics test) of Watts Bar 1. Kothe said that VERA accurately replicated the measurements taken during that test. 

John Turner of Oak Ridge National Laboratory (left) and Sandia National Lab’s Roger Pawlowski analyze the Watts Bar reactor simulation using the CASL Virtual Environment for Reactor Applications. Image courtesy of ORNL.

“We took VERA for a test drive and the simulation’s predictions [were] fantastic,” Kothe said. “It was an important first step, but it also showed us where we need to do more work.”

He said the vision for VERA is to predict how a reactor and its components would behave in various operating environments.

“One of our goals is to evolve VERA to the point where we can follow an operating reactor through multiple fuel cycles,” Kothe said. “We’re not there yet.”

A more predictive virtual reactor would allow the industry to address challenges such as reducing waste, boosting power output and increasing plant longevity. For example, VERA could be used to predict the in-reactor behavior of advanced nuclear fuel cladding materials.

Kothe said that if CASL is funded for another five years, the VERA simulations also could model boiling water reactors and other advanced designs such as light water small modular reactors.