Reconnecting with the Past, Training the Future
Throughout our lives, people come and go. Sometimes we stay in touch; more often, especially if both parties are not avid social media users, we lose track of all but our closest friends. A chance meeting in a new city with someone from an earlier stage of life can renew a friendship, but it’s meant more than that for Anirban Jana and Mark Kimber. Reconnecting in Pittsburgh has led them to a professional collaboration and a grant of nearly $900,000 from the DOE’s Nuclear Energy University Programs (NEUP).
Jana, a Sr. Scientific Specialist at the PSC, came to Pittsburgh in the spring of 2008. Some months later, he was browsing through the University of Pittsburgh mechanical engineering department web site when he noticed a Mark Kimber, an assistant professor in the Department of Mechanical Engineering and Materials Science, on the list. He wondered if it could be the same Mark Kimber he shared an office with at Purdue when he was a graduate student in mechanical engineering. “It’s not like that is a very common name,” says Jana. He sent Kimber an email; it was his old friend. The two began planning projects that they could work on together.
“He is an experimentalist, and I am a computational person, so that was a good fit,” says Jana. Both skill sets will be called on in the work funded by the NEUP. Along with John Brigham, Assistant Professor in the Department of Civil and Environmental Engineering at Pitt and Milorad Dzodzo, PhD, of Westinghouse Electric Company, they will computationally model the turbulent mixing in the lower plenum of Very High Temperature Reactors (VHTR) and validate their results experimentally.
The VHTR is one of the Generation IV nuclear energy systems being studied by the Generation IV International Forum(GIF), a collaboration of the world’s leading nuclear technology nations. GIF has defined eight technology goals for generation IV systems in the areas of sustainability, economics, safety and reliability, and “proliferation resistance” – which means that the fuel used should be undesirable for nuclear weapons. Eight of the GIF signatories have agreed to participate in the development of one or more of the generation IV systems; the United States will study the VHTR.
One benefit of the VHTR design is its ability to supply “process heat” to other industries. Other industries — the chemical industry in general, for example, says Jana — require heat for their processes to proceed. Previous reactor designs operated at lower temperatures, and were unable to provide sufficient heat for these purposes.
In the VHTR, helium absorbs heat from the nuclear reaction, is expelled into part of the reactor vessel called the lower plenum, and then passes into a heat exchanger where it gives up that heat to be used as process heat. Helium spews into the lower plenum at speeds of up to 100 meters per second, and at temperatures approaching 1000° C. The temperature can vary by as much as 100°C among individual helium jets. The speed of the gas and the temperature differences cause the turbulent mixing that Jana, Kimber and their co-PIs will study.
The project will also train future nuclear engineering experts. Students involved in the research will have the opportunity to intern at Westinghouse under Dzodzo. There is an age gap in nuclear expertise in the U.S., says Jana, and one of the goals of NEUP is to train the next generation of leaders in the U.S. nuclear industry. This training extends to the project team, according to Jana. “Three of us, me and Mark and John from Pitt, we are just starting out. But Dr. Dzodzo, from Westinghouse, he is an established expert, so we have both new and old blood in the team.”
OpenFOAM, an open source Computational Fluid Dynamics (CFD) code, will be used for the initial simulations. The team has also proposed to use FLUENT and STAR-CCM, commercial CFD packages. “We may need to verify something that we did on OpenFOAM: is it right or not?” says Jana, and one way to verify computational results is to run the simulation with different software and see if the results match. Because Fluent and STAR-CCM are available at Westinghouse, “That is another point of collaboration between Westinghouse and us,” says Jana. “Students can go to Westinghouse in the summer and run those commercial codes on their machines.” Once a computational model is built, it will be experimentally verified.
The thermal mixing simulation will be restricted to just a portion of the lower plenum, including some of its support structure. Simulating mixing in the entire lower plenum is too complicated for this initial study, says Jana. For now, they will also ignore stresses on the plenum structure caused by the temperature differences.
“If you heat up one side of a rod, and the other side is cold, it will bend. That means there are stresses being generated,” Jana says. So similarly, if you have temperature fluctuations in a structure, that means you have fluctuating stresses.”
Knowing how the lower plenum is being stressed can help to predict its useful lifetime, but those calculations are beyond the scope of this project.
Jana says,“Later on, we’ll feed [the results of the thermal mixing study] into a stress computation model. We haven’t proposed to simulate the whole lower plenum right now, because that’s too big. We have no idea, actually, how much computational power would be required to simulate the whole lower plenum in all its glorious detail. Full lower plenum simulations as well as stresses, those are ideas for the future.”