Texas A&M University

Nuclear by the Numbers By Gene Charleton

Computational science — like the calculations and simulations Marvin Adams performs — will be the key to designing the next generation of electric power-generating nuclear reactors.

Marvin Adams
Marvin Adams, a professor in the Department of Nuclear Engineering and director of the Center for Large Scale Scientific Simulation, says understanding more about what happens inside nuclear reactors will lead to better reactors in the future.

That’s the cue for nuclear engineer Marvin Adams and his colleagues.

Adams is an expert in the numbers of nuclear engineering, especially the numbers that engineers and physicists use to understand in detail the processes happening in a nuclear reactor. Fission — the splitting of atomic nuclei — is the process that releases energy inside nuclear reactors, ultimately heating the steam that spins the turbines that turn the generators that give us the electricity that flashes along the wires to our homes.

He knows more than most people about crunching the numbers that describe these processes, and he sees a lot of room for improvement over today’s computational approaches.

“Today, when we do reactor analysis, most of the time we calculate separately the different things that are going on simultaneously,” Adams says. “We do our calculations of neutron behavior with very limited knowledge of the heat transfer and fluid flow that’s going on — and with no knowledge of what’s going on in the materials. Are they changing under irradiation? Do they vibrate because of fluid flow?”

More than algebra

Solving the equations that describe each of these processes is difficult. Combining these already complex equations and solving them together has been impossible until recently.

“Right now, we use PCs to solve these problems,” says Adams, a professor in the nuclear engineering department and director of the Center for Large- Scale Scientific Simulation. “That’s all right, as far as it goes, but we can’t get the sort of resolution — detail  — we need to understand what’s going on to the level needed to gain confidence in new designs.”

Development of what computer experts call massively parallel computers, machines with 10,000 or more processors running at the same time, is bringing solutions to these problems within reach. But we have to work out the most efficient ways to use them, Adams says.

Adams is most interested in understanding how to solve neutron transport problems, but the same equations can be used to describe other complex situations — the behavior of radiation used to treat cancer tumors or of electrons as they cross a computer chip.

This is where Adams and his colleagues in Texas A&M’s departments of nuclear engineering, computer science and mathematics come in. They’re working out the most efficient ways to use the so-called ASC Purple computer at Lawrence Livermore National Laboratory and other ultra-high-speed computers to solve neutron transport and other problems.

“Our vision for the future is to have a really high-fidelity simulation,” Adams says, “one where we’re explicitly taking into account the fact that the neutrons are causing heat generation and altering materials, heat is being transferred by various processes, fluids are flowing, and all of these processes affect each other and in particular affect how the neutrons behave. “It’s all a really big coupled system.”

A virtual reactor

If nuclear scientists can solve neutron transport equations accurately, they can tell nuclear engineers the locations of all the neutrons in an operating nuclear reactor and what they are doing at any given moment. Having this kind of information is crucial for nuclear engineers to design the next generation of nuclear reactors, Generation IV reactors. Adams says the new class of reactors will be both safer and more efficient than the current generation of reactors — Generation III and III+ — which have been producing electricity since the 1960s.

Generation IV reactors and advanced fuel cycles also will allow recycling of spent fuel for further use instead of sending it off to controversial waste storage sites like the one at Yucca Mountain, Nev. This process will drastically reduce the amount of storage needed for spent fuel.

reactor The next generation of power-generation reactors will be more efficient and safer than current reactors, thanks to computations like Adams’.

“Right now, there are 104 power generation reactors operating in the United States,” Adams says. “If we operate them for another 60 years, we’ll need the equivalent of five Yucca Mountain storage sites to deal with the waste they’ll produce.

“With Generation IV reactors and advanced fuel recycling, on the other hand, we should be able to operate 1,000 reactors for hundreds of years, and one Yucca Mountain — three square miles — would hold all the waste they produce. Importantly, this reduced waste decays away in hundreds of years, not tens of thousands.”

Adams is most interested in understanding how to solve neutron transport problems, but the same equations can be used to describe other complex situations — the behavior of radiation used to treat cancer tumors or of electrons as they cross a computer chip, for example. Yet others describe the behavior of light particles, or photons, in the atmosphere, or how thermal energy is transferred during a nuclear explosion or in the heart of a star.

Another Texas A&M engineering researcher, mechanical engineer Kalyan Annamalai, is considering using the center’s computational resources to model the behavior of gases inside steam-generating boilers. (See related story)

“These problems involve some sort of transport — particle transport or radiation transport — coupled with fluid flow,” Adams says. “Once you know how to do that, you can apply it to a lot of different kinds of problems.” end of story